Embed Size (px)
Citation preview
\STRUCTURE-PROPERTY RELATIONSHIPS OF LIGNIN-BASED
ISOCYANATE A...~D AMINE ADHESIVES FOR WOOD/
by
William Henry\l Newman,,
Thesis submitted to the Faculty of the
Virginia Polytechnic Institute and State University
in partial fulfillment of the requirements fo= the degree of
MASTER OF SCIENCE
in
Forest Products
APPROVED:
Di\. G. Jrfju t I ,, > rl > rn - 'l:X I-• --. C ' ' '<,_..,,,,
Dr. A. L. DeBonis
December, 1984
Blacksburg, Virginia
STRUCTURE-PROPERTY RELATIONSHIPS OF LIGNIN-BASED ISOCYANATE AND A.L'1INE ADHESIVES FOR WOOD
by
William Henry Newman
(ABSTRAC'l')
Hydroxyakyl lignin derivatives were reacted with
polymeric methylene di phenyl diisocyanate (PMDI} and
hexametho:{y-methyl-melamine ( HMMM) to form polyurethane and
polyether wood adhesives respectively.
Adhesive performance in shear block tests indicated:
(a) that the combination of lignin and PHDI reduced the
adhesive strength shown by neat PMDI. The HM.MM failed to
produce an acceptable wood adhesive in the absence of
lignin, requiring 50-60% lignin derivative co-substrate for
peak performance; (b) adhesive performance ·was related to
molecular weight, if an organic solvent was the carrier, or
solubility if the formulation was emusified; (c) adhesive
performance for the lignin based adhesives was better than
a urea formaldehyde reference.
Structure property relationships were determined by
correlating data obtained by the analysis of (in vivo)
cured adhesive films and (in vitro) adhesive strength data
resulting from shear block testing. The results indicated
t!1at: (a} glass transition tem.9eratures o: the in vivo
cured adhesives were inversely related to the strength of
the adhesives cured in vitro; (b) variations in infrared
analysis of the in vivo cured adhesives were used to deter-
mine the levels of products from the cross linking
reaction. In vitro adhesive strength was directly related
to the level of reaction products determined to be present
in the in vivo wood adhesives; (c) the relationships
between the analysis of in vivo and in vitro cured ad-
hesives indicated that the lignin component may act as a
soft segment blocks or domains in a more rigid polymer
matrix.
Particle board was produced with the lignin adhesives
with: (a) properties equal to those produced with com-
mercial OF resins; (b) spray application greatly reducing
the effects of carrier compatibility; (c) none of the
lignin based adhesives were water resistant.
ACKNOWLEDGEMENTS
Completing this work makes me all the more certain
that very few things are truely done by an individual. For
the times I found courage, determination and faith deep
within myself, I thank my parents. For the times I was
empty within and reached out, I thank my parents for being
there. My brother,
his generosity, special
, helped more than he knows with
surprises, and support. My
sisters, helped sustain me with their
friendship and encouragement. For all the times I needed
inspiration and love, and found both in one remarkable
person, I thank my grandmother.
I especially acknowledge the efforts, support and
determination of Dr. Glasser, without whom this work would
not have been possible. I thank for her
knowledge, skills, and friendship in the lab which were so
very important to me.
iv
TABLE OF CONTENTS
Abstract . ii
Acknowledgements iv
List of Tables . vii
List of Figures viii
Introduction a~d Objectives l
Part A: Svnthesis and Performance of Lignin Ad-hesives with Isocyanate and Melamine 9
Abstract . 9 Introduction . 10 Materials and Methods 15 Results and Discussion . 20 Conclusion . 28 References . 30 Part B: Structure-Property Relationships of Lignin-
Based Isocyanate and Amine Adhesi '!es for Wood 43
il.bstract . 43
Introduction . 45 Materials a~d Methods 47 Results ~9
Discussion . 49 Conclusion . 54 Re:erences SS
v
TABLE OF CONTENTS (Continued)
Part C: Lignin-Based Isocyanate and Amine Adhesives for Wood Composites ..•...
Abstract
Introduction . .
Materials and Methods
Results and Discussion .
Conclusion .
References .
Vi ta . . .
vi
62
62
63
69
72
78
79
89
Table
Part A
I.
II.
III.
Part B
I.
Part C
I.
II.
III.
LIST OF TABLES
Qualitative properties of possible lignin-adhesive combinations determined in pre-trials . . . . . . . . . . . . . . . .
Standard conditions used in the preparation of test samples . . . . • . . . . .
Shear strength and wood failure . .
Regression analysis results and shear strength data . . .
for IR, Tg
Standard particleboard paration parameters
mat and board pre-
Strength properties of particleboards .
Boil test results (% swelling)
vii
34
35
36
56
83
84
85
Fiqure
Part A
l
2
3
4
5
6
Part B
1
2
LIST OF FIGURES
The reaction of hydroxypropylated lignin with an amine and an isocyanate .
Effects of varying press conditions on shear strength. (Blocks had standard formulation as given in Table I.)
Effect of increasing lignin content on shear strength. (Blocks had standard formulation as given in Table 1.)
Effect of lignin type on shear strength (---- is the UF control, arrows indicate standard deviations).
The effect of lignin derivative type on shear strength (---- is the UF control, arrows indicate standard deviations)
The effect of crosslinking agent type on shear strength (---- is the UF control, arrows indicate standard deviations)
The effects of IR pecks on the cross-linking reactions of isocyanate anc amines (a:Kraft HPL, b:uncured Kraft HPL-isocyanate resin, c:cured Kraft F.PL-iso-cyanate resin)
Representative relationships between IR ratio and shear strength for the indi-vidual adhesive formulations. (Kraft HPL-isccyanate formulation, the ratio is the height of peck l. in the insert divided by the height of peck number 3)
viii
37
38
39
40
41
42
57
58
Fiqure
3
4
5
Part C
1
3
LIST OF FIGURES (Continued)
Representative relationship between Tg and shear strength for the individual adhesive formulations. (Kraft HPL-isocyanate for~ulation)
The relationship between IR ratio and shear strength for all six adhesive for-mulations (the value for each of the five samples per adhesive formulation was converted to a percent of their average values to allow interformulation comparisons)
The relationship between Tg and shear strength for all six adhesive formu-lations (the value for each of the five samples per adhesive formulation was converted to a percent 0 of their average values to allow interformulation com-parisons)
The effect of lignin type on adhesive strength properties
The effect of lignin derivative type on adhesive strength properties .
The effect of crosslinking agent type on adhesive strength properties
ix
59
60
61
86
87
88
INTRODUCTION
Lignin is a polyphenolic component of plants deposited
to provide structural support, resistance to mechanical and
biological degradation, and to create water impervious
conducting pathways for water transport systems. An enzyme
catalyzed dehydrogenative polymerization of several
cinnamyl alcohol derivatives is known to produce lig~in in
plant .;.. . ... issue. Coniferyl, sinapyl and P-OH cournaryl
alcohols are the primary derivatives involved in lignin
synthesis (Sarkanen, 1971). Phenoxy radicals, present
during lignin formation have unpaired electrons available
as sites where coupling processes occur to form the polymer
network (Glasser, 1980).
Lignins can be very diverse in their chemical struc-
tures and physical properties depending on the source cf
the lignin and the method of isolation (Glasser, et al.,
1983) . Differences in the properties of lignins can be due
to the genetic origin of the source or due io biosynthetic
differences occurring during .t: •• .:..orma t:ion. Methods of lig~in
isolation include mechanical and chemical procedures. The
effect of lignin' s chemical structure of the most ccrmr:on
industrial methods of lignin isolation have recently been
reviewed. Such properties as molecular weight distributio~
1
2
and bond distribution are highly variable between lignins
derived from different isolation procedures {Glasser, et
al., 1983).
Lignin analysis relies on the identification of
monomeric and dimeric degradation products :t"rom , . . J..lgnin
(Freudenburg, et al., 1968). Degradat.ive depolymeri-
za tions, such as permaganate oxidation (Miksche, et al.,
1969) are employed for determining lignin structure. Gel
permeation chromatography (GPC) is employed in determining
relative molecular mass and mass distributions. Lignin
molecular weights can vary widely from below 1,000 to
greater than 1,000,000 g/4mole depending on the lignin used
and the method of molecular weight determination. Lignin
dispersity can range from 2 to 20 (Glasser, et al., 1983).
The major industrial methods of lignin isolation are
the Kraft and sulfite pulping processes. Lignin comprises
from 16 to 24 percent of the total wood substance of hard-
woods, and 24 to 33 percent of softwoods. It is not
surprising that the pulp and paper industry produces a
large portion of the available 1 • . ... igni.!1. In the UniteC.
States sul.:i te pulp mills produce 2. l million tons, anC.
Kraft pulp mills, 21 million tons of lignin annually
{Goheel".., 1979).
The majority of lignin (93 percent) produced by
in~ustry is used as a in-house fuel source .:or the pulp and
3
paper industry. The utilization of the remaining lignin
includes its use as drilling muds and surfactants, asphalt
binders, chemical feed stocks and adhesives. The fuel
value of lignin (black liquor) is approximately $60/ton.
Vanillin production can raise lignins value to $400/ton.
Lignin dispersants have similar value. The use of lignin
as a component in polyurethane plastics or PF-resin ad-
hesives can raise its value to $500/ton (Glasser, 1981).
Lignins natural variability, insolubility and complex
structures have prevented a larger percentage of lignin
being utilized in the higher value applications.
The application of lignin as a wood adhesive follows
naturally from its role in woody materials. Prese::1tly,
urea-formaldehyde and phenol-formaldehyde are the two major
cornrnercial ·wood adhesives network molecules in which
phenonuclei are joined by a methylene linkage are clas-
sified as "novolacs", and are formed by condensation
reactions. Urea formaldehyde adhesives are formed by
condensation reactions forming ether linkages (Drunm,
1972} Low cost, ease of application and durability have
been the major factors in the use of P? and UF resins.
Both UF and PF resins are primarily mechanically attached
to wood and r.ot chemically bonded (Eickso~, 1972). Recent
problems with the steaCy release of formaldehyde emissions
from formaldehyde based products has caused the forest
4
products industry to seek alternative adhesives (Archibald,
1982).
Isocyanate based adhesives offer many advantages over
conventional PF and UF resins. The major difference
between them is that Isocyanates form a chemical bond with
the wood surface. Urethane bonds form between the iso-
cyanate groups and the hydroxyls of the wood surface. This
chemical bond results in urethanes which produce superior
adhesives (Rowell, 1981). Isocyanates are much more
expensive than conventional adhesives and also present some
processing problems such as low tack, low liquid volurrre,
reactivity with water, and adhere::ce to processing equip-
ment (John, 1980).
The combination of lignin and phenol formaldehyde as a
wood adhesive has been very attractive due to obvious
structural similarities. Unfortunately, lignin has been
used primaril~l as a non-::-eactive filler in past adhesive
systems (Nimz, 1983). The use of lignin as a chemically
engineered component of polymeric adhesive networks is
discussed in ?art 1 of this paper.
5
OBJECTIVES
General Objectives
The overall objectives were to investigate the feasi-
bili ty of utilizing lignins cross linked with isocyanates
and amines as wood adhesives and to determine the effects
of lignin type, 1 . . ~ignin derivative type and crosslinking
agent type on adhesive performances.
Specific Objectives
The specific objectives were:
l. To examine the effect of using a Kraft lignin as the
base for a wood adhesive vs using an organosolv
lignin.
2. To determine what chemical and physical properties of
the lignins derived fror.l different sources accounted
~or differences in performance.
3. To examine the effect of using a hydroxypropyla ted
lignin derivative in tr..e wood adhesive vs a
hydroxyethylated derivative.
4. To determine what chemical and physical properties of
the two lignin derivatives accounted for perfor:nance
differences.
5. To compare a urethane crosslinked lignin system
deriV'ed from an isocyanate crosslinking agent to an
6
ether crosslinked lignin syste8 derived from an amine
crosslinking agent.
6. To determine if the physical and chemical properties
of the adhesives cured as films were related to
adhesive performance within the glueline . ... ... ... :.::1 s c.anaarc.
shear block tests. Physical and chemical properties
of the films being determined by !R and thermal
analysis.
7. To examine the performance of the lignin-isocyana te
and lignin-amine adhesives in particleboard production
in comparison with conventional UF and isocyanate
adhesives.
REFERENCES
Archibald, Erika. 1982. Formaldehyde's Future in Ad-hesives. Adhesives Age, July, 27-30.
Drumm, M. F. and J. LeBlanc. 1972. The reactions of formaldehyde with phenols, melamine, aniline, and urea. Chapter 5 in Step Growth Polymerizations, D. H. Solomon (Ed.), Marcell Dekker, Inc., NY.
Freudenburg, K. and A. C. Neish. 1968. Constitution and Biosynthesis of Liqnin, Springer-Verlug, NY.
Glasser, W. G. 1930. In Pulp and Paper: Chemical Technology, Vol. I, Casey, Wiley-Interscience, NY, 39-99.
Chemistry and J. P.· (Ed.) I
Glasser, W. G., C. A. Barnett and Y. Sano. 1983. Classi-fication of Lignins with Different Genetic and Indus-trial Origins. Appl. Poly. Symp. No. 37, 441-460.
Glasser, W. G. 19 81. Opportunities for Nonconven tional Chemical Processes. Proceedings of the 9th Annual Hardwood s:ymposium of the Hardwood Research Council I Pipestem, WV, May 25-28, 67-71.
Goheen, D. W. 1979. Proceedings of NSF Conference, Columbus, OH, October.
Hickson, c. present,
H. 1976. and future.
Particleboard adhesives, past, Adhesives Age, Sept. 29-34.
John, W. 1980. Is there an isocyanate in your future. Proc. Wash. 177-184.
State Univ. Particleboard Symp. 14,
Miksche, G. E. and S. Larsson. 23, 917.
1969. Acta. Chem. Scand.
Nimz, N. H. 1983. Lignin-based Wcod Adhesives. In: Pizzi, A. (Ed.), Wood .Z\dhesives, Chemistry and Technology, Marcel Dekke=, Inc., NY.
Rowell, R • . M. and Ellis, W. D. 1981. Bonding of iso-cyanates to wood. Fo=est Products Laboratory Symposium Series, Las Vegas, August.
8
Sarkanen, K. V. and C. H. Ludwig, Eds. 1971. Lignins-Occurrence, Formation, sTructure and Reactions, Wiley-Interscience, NY, 916 pp.
~o
tf
0 ......
·--"'
rl
II>
Ill cl
jll r;: I IP
Ill
I'· <: Iii
Ill :.> ..
Ill
(l
.
Ill
I'·
1.fl !.i
I•·
t •i
I'·
0 l•l :1 rt·
~
11l o·
Ul " I) IO
: 1
l(l rt· : } .
1-h :j " !J4 ID
11:. ..
0 Ii
IJ .... I :1·
() r: IS
Iii
0 t1
!-j C: I·•
Ill
cl
I•·
() :1 ct
I·• ·lJ "' ~~
()
·1 il> 0 11,
("!• :1·
(() ,.J I·'·
lQ :j I-'· :1 fl.
(0
''i
I·'- ·• '• 111
d I·'· '~
(II I ()
() rs ct
111
I•· ::s I•·
: 1
•Ii
Ul
0 ·-· ..• .. ([I :1 rt
rt
:.1'
Ill :.J t-'·
~j
(j) :-1 r-: t-•
Ill
1-··
0 ::i <-: :J~
ID
I 1
(j)
IU
{J) :J io ·-·' 111 tJ I'·
I j (i> ::: Ill
l1l
~-~ rj Ill
I •1
Iii
II>
()
ct
w
I).
tY
1. .. --:
;>;'
I 1
Ill
lt1 c I"
I .,. iii l-1
~
l\l
Ul !l ..
I·'·
l(l :_}·
ill
rn cl
l·-i
U
l 0 0 I • .....
Ill
:j ll•
1"1"
Ill
Ul
'Cl Ill
11
11,
0 I j H
CD n. IS
(ii 11" d (j)
•i
I•· :J
~
Ill
Ul b'
(\)
Ill rt
0 Ii
Ill
0 1--· r: b'
t-•-
1~
I•·
cl
'"<! t•·
II\
("I !J. m
l·t, 0 •i
:-1 i.-: jJ
(ll rl
I•·
0 !J ~
Ill
Ul
ID :J ~
1~
lll
I"
111
I'·
CD I).
.... H1 Ill
: 1
0 11
l!l
IU !.1 I··
()
Ul 0 1-• " ... Ill :"J rt
....... i~i
~
i;
ll'
(J) rt·
tl'
Ill
JU g: (Ii
Ill
I'· < ID tr
Ill
Ill (!>
;>;'
11
Ill
1"11
r! I :n Id
t·•
Ii
CD
II)
ii>
11
(J) :j ()
Ill
Ill n. ~}'
([)
(ll
I·-'·
<..:
Ill
Ill
~J b. I'·
ct
~
Ill
l/)
11 ID 1-•
Ill
ct
CD
(}.
ct
()
:-1 0 1~
Ill
()
.~
I-•
Ill
1-~ ::: 1() I'-
\fl :.}·
cl
'd
I{)
l'j
I ti
()
11
q !u • j i) (0
-~ "'· Ill
Ill
P' 1-· ;i: Ill
'<
Ul t.J
(ll rt
ct·
(J)
'1 rt :l· IU
! I Ill
I~
Ii
tD
Ill , .•. 0 •1 ~j
Ill
~--'
!).
CD !Y
'< I).
CD
()
0 (/) r: tJ"
(/) rt
t"i
IU rt
(0 ,J. !J
0 11 p.
(Jl
Ii
fl
0 1·1
ID
Ill
() !J'
'() ro Ill
;-..-4
•o
111
11
11,
0 'i
~1
1\1
':! 0 ((
) :i:.i g: ID
(Jl I-'. '!
ll>
fl·
:J··
([)
Ill tr
Ill
(ll :J ()
(\)
0 t•1
j-•
1•-
1.(l
~j
I'· :::s Ill :J fl,
11
ID
1L) 1: ... l"i
(l) p.
l/l
0 I (JI
0 O'~
1~
t·'·
1(l :J I·•· :J fl,
m
'1
I'· ,. 11i
ct·
I'· .. '•
11>
()
0 :::s Ii
11
P>
Ul rt
l•i
p1 I•·
1~
m
j}.
fl
0 'O
Ii
0 fl.
~:
()
(()
(ll
!.1 P•
()
()
Ill
'O
ct
111 b- 1··
ID .... () 0 n. I\> fl,
!")""
IO
UI .... <: Ill
l'- :j
Ul ,,. Ii
([) !.S
lQ
cl·
~1·
'Cl
11
()
'O
(\)
11
( t
l·'-
(1) Ul p.
!ll
Cl
(Jl Ii ,.J. 0 Ii
ill
rt
Ill
ti
Ill
'O
•--'~ n. t·.
'< ,.'-, i1i 1~
l\l
~)
t···
'j w
u· '<
1~
Ill
Ul
IJl ct Lf
111
~J
N 0 '-
.0
0"'
~
I'·
ct
:_)'"
1~
f•·
1.{l :J l'- ::i
0 0 :j rt w
::.:i cl
Ii
,.J.
(/) I-'· :·1 Ill rt
0 (J)
0 '.0
0
"'
Ill
111 rt
II>
ti
2--:
~]' ,_,, () :J·
(/) rt
Ii
(\) :::s 1.Q
cl :r I'·
~:i ,,. !J'
(Jl
()
111
(Jl
(I)
0 1·11 tu [) 1-1 tr
(..~ ct
rt·
!.l·
l\l
ct
ct :r I•
· Il
l 'i
({) n .. i::
()
ct
l'- 0 H
I'·
{J)
1-•
I-'·
Ul
~j
I-'· ::s ()
0 ~j ct
ID
~J
( .. ..J.
(J) Ii
ID
(II 'O
0 ~1
(J) t-•·
b'
1~
Ill
11,
()
Ii
rl· !J"'
Ill
11 cu fl,
i:: ()
ci·
I·'· 0 :j .......
::t l\l C: iii
(/) t·'· . .... Ill
0 11, .,. .. ti
Pl t-11
rt
Ill
~") n. 0 11
U:l
1\1
"j 0 Ul
0 I-;' .... I•
I·'·
1.f
l :1 I-'· ::s H
!J'
ID
Ii
IP
Ill ~
f-J rt
IJl
t-'· :1 o. I'·
()
Ill
ct·
ill
11
!J'
l\l ,,
.J. :::s ()
t-J
~: n. (() µ..
•J-' ~ fl,
I 1
0 x .A 'd 11
0 '(1
•<! 1~
p1
'1 b .. !J .. '< fl.
11
() x IA
'-. Ill
ct·
~->"" '<
1~
1-•
P·
Ul :1 I"
!J
p,
CD
11
I-'·
<"' < Ill
ct
I•· .:.: Ill
(I)
tJ
l\l
Ill
ill p.
Ill
!.1 r1. (ll
()
1~
<: IP ::s ct
I IJ'
Ill
UI
(Jl n.
Ul
'<
(/) rt
w
;J IJl I-] :r ll>
1-· ,.J.
•fl :j I-'· :1 o. Ill
ti
1~- <: Ill
rt· ..... ': (()
U
l
llJ El 1-1
p1 :::s n. ~) ..
(ll :>: 1\1 a ([)
r1 !Y
0 x '< I ;:3
(p
rt :x· "<!
1~
I ~1
(ii
I-•
Ill
~J
.~.
!J ID 'l' ~
~J ·"' :~ •·'· H
Ill
;J
i::
j-J
Ill
I"
0 :j I
Ill §: Ill
(/) I'· <! (()
UI
~: ... ... :1· '0
0 1~
•<' d Ill
Ii .... () ;-J !ll
rl· !J'
·<
1-J
(Jl !:1 (Jl n. I"
'd
!">'
co :J '<
t··
fl.
I·-•·
I-'·
UI
0 ()
'<
111
~j
Ill
rt
t(J
~
'< p,
Ii
0 :< •<:
l\l
1-•
;.;'
'-<! 1~
.~
IJ·
<fl r1 I-'· :.1 Cl.
(D
t1 ... <: p1 ct·
I-'·
..:: !ll
(J
l
~· ai 11
11>
t11
0 11
:j C: 1~
l\J ct
(j)
!l.
p1
(/) ~
0 0 CJ ..
;i;.
tJJ
Ul
H ~
'1~ 0 H
H tll
0 ()
'<
l\l
~J
Ill
rt
(Jl pi :1 CL
:.:::
(lJ
1~
Ill
:J
I'· !.1
ID
I ttJ
;J:.o ~
t-3
l:V
(/)
~< :::s rt· :.J·
CD
Ill I·'·
Ul
p1
•1 P. •ti
(D
I)
t-t,
0 •i ::1 Ill
:::s n Ill
0 t11 t'
1•-
1.(l
~j
I··'· r.1 ·r, G: Ill
IJ
l I··
'• <~
((
) Ill :E:
l·'· rt
!l ..
•u ., 0 '(j (lJ
q rt·
I'·
(I>
(Jj 111 :1 p,
(II
I-'·
•il :j I'· ••• I'·
()
Ill
'j
~I I·•·
• j h t)
(I) Jll
lit w
(II
I···
:.1 'C
l q fll
(I)
(/) rt·
I'·
;J
((J LJ)
.: ...
I'·
~J f 1
'(j Ii
0 ().
f;
(l
(I> rn i:: tr
CJ) cl
111
: 1
ii
I"
Ill
1-·
t)
(0 n. I~
(l ii
1~·
0 :1 IJl
I·'·
:1 fll
fl. }' ;I> lf•
I·'· <: ii>
(I) ct
I 1
Ill :J •l1
cl
~J'
·---'
I·'·
~l ... cl
(() n. ct·
0 I·'
0 ~
l•l ~: tr
CJ) cl
1 •·
ct
i..: " I-'· 0 ::i 1-J w
<' oi 1-~
IJl 1u
'j h. :.i·
1\.1
!JI lJ'
(11 w
~j
Ill
• 1 •
() ~
;l
(I
()
l/)
l-·'·
::1
•(J
1~
([) Ill fl,
().
I·•·
it
I·'· 0 :J 0 It,
~:
•j
~J 0 p. ••• II
\ I"
(lJ
p.
1-~
l-'·
•fl :1 1-~- :-.1 ct
0 'd
!J' co :·1 0 1-·
I-'·
()
1·1
Ill
(JI I-'· :-1 Ul
I'·
UI
•u I 1
Ill
11
Cl> .q ~.
I-'·
Ill
I'·
ct·
(II
11)
0 I)
llJ n :.l'
I-'· co ... " I'·
~-j
ill
:-J~
I'·
ul ::r v (.
.,)
0 ;,~
Ul r: tr LJ
) d 1-•·
(I• ~
rt
I·'· 0 :j 1-'
w
.. '• w
I··•
{l
l
~J
0 1--'
11>
() r: 1~
Ill
I) ..• <
, (I>
t-•
· •Q
!Y
ct 0 0 :1 'ti
I) :1 ID
!J ,, (Jl . ,. ~. ({I cl
~
0 11 ;.;·
I"
:·j (l
0 Ii
'Cl 0 11
(ll cl
t-'·
0 ~j
I'·
Ul
111
8 0 p.
t"
t•i
I-'· n 111
cl
I·"
()
~
0 11 El 0 1-·
tl>
()
i:~
1~
111
I 1
Iii
I)
111
()
ct •... ()
~j
JU rt ·-·· 0 ;1 I)
Cll n ~ '•
111
l·-·
0 .... , ...... () .... <,
rt
!:!'
.- (fl
'll !J'
([) :·1 0 t--··
I ti
0 11 ti
Ill
1--'
().
II> !:l"
·<
().
CD :.1 (() er :<..
0 1·1
;i..J
1)
(lJ .n r: I-'·
I)
((l Ul
(()
I '·
ct
!J' w
I{
()
~J ..
ti> D
I-'·
()
Ill , ..
I·-'
I.{)
co
1f
> H
~t
1--'·
{J) i;
()
11 ;:.;·
Ul r: ill
u~ w
(/l cl
UI ct·
~J'
Ill
cl·
1~
I·•·
•ll :1 I'· :::i ll1
I-'·
• j fl 0 t !
'(j 0 Ii
~)
cl
,._J,
0 ~1
I'·
: 1
rt
()
IJ"j
0 1-
j (,
) Ill
I 1 J ~ :::i·
11
:..1 lu 'J b I ·'
•O
-J
•.D
~·
•"'- r: 1~
1~
(II 11
()
1~
IU
Ul
(/l
(!) 11
I-'
<O
OJ
1f-:i.
;--,,:
i::
1--·
1~
<I•
11
(() rt·
111
I ,
11
CD
()
(() !.1 rl
•o ~
b'
1~
I-'·
()
Pl
(I .... 0 ~
(/l tJ
0 ......
(]) H
:';"
0 0 , ... p1
11
~·;·
IP
1-•
•O
,]
Q) tJJ
pi •··-' ~
t·-~
10
o-.
lfl
IU
~1 p.
1~ ·-·· u I-
'· ct
UI
0 1·11
(I·
tP
() :1.0
~
I-•·
()
111
l·-..1
•o
Ill
l"f
1·11
0 I { 3 Pl :J ()
(()
~· . Pl
<! ((J tr
IV
([I
~1 CL
w
Iii ..... !1 11> fl,
J-Jo
~j
'lJ
~)·
(() ~
0 ......
111
()
I!
~j
1\1
I·-' p.
(1' !.1·
'<
f),
CD
ll> fl.
•·1·
(p (Jl
I'- .. '•
((I
(J}
lJj
0 ct t.1"
.~
I'·
;J
I-'· rt
Ill 0 111
(J) c o· UI
II
I•·
cl
(~ c 1· , ... 0 :J
r• I-'·
1(~ !J •····
~1
i)
Ill :j 11
ID
'd
1~
pl
(l
iP
Ill
til r.1 i:: ()
!J'
Ill
UI
<.n
0 I -.-.] 0 'a
0, 0 1·
11
'(j
~,· iii :J 0 1-· , .. : 1
0 1·11
1~
I•·
u') ~-j I·" :j 1-•· :.J 11
Ill
(/l I-'· :::J Ul
·<
Ul !I
(() ::l
{J)
'lJ ~
(() ~
0 1~
.~
()
Pl f L ~ (!)
(/l
~ .. < w
LJ) •·'· ~-1 < I-'·
ct
m
I'· :1 < ro UI
rt
I·-'·
u1
Ill
cl·
t-•·
0 :.1 ·-·· ~j o·
0 ct
!:l' ro ~ rt
I-'·
1--
J ·-·· M Jll ( t
I-"
0 ~
:<: I-'·
( t :)· li1
0 11
:J IU
I·-' p.
(!l
~)·
'<
(l.
CD
Ill
!J n. ·-·· rt (/l
(/l rt
t{
~
(l ci· i:: 11
l\l
I·-'
Ill l·'·
;J
I·
'· ......
pl
t 1
......
c1
'<
~
I"
ii
~y
p.
ID rt
11
JU
()
rt
(J) ti,
t)
0 ~j ..... rt
(/l
~: rt
I-'· , ... I-'· rt
·<
IU
(l}
IU :j IU !} II> LJ
) I"
.. -. w , ... cl
Ill tt
II•
pi
()
fl' , .. . .. ·-·· ct· I
• .....
0 1·11
I·-'
I·'·
•0
!j
,_,. ~1
Ill
'lJ
0 1-~ ·a 11>
1-1
......
()
~-1 Ill
ct·
:t 0 Ii
~J
fl,
i::
11
I·-•·
~j
•Q
(!l
!~
cl
11
Ill
()
( ,. ·-·· 0 :J ....
.....
I-'·
(/l 0 1~
IU
it
I-'· 0 ;:1
•t
CD
()
(j) :1 ct
1~
a-..-;:: tr
<O
tP ~
11
(() -:: t--'·
(])
:::~
(() p.
tJ'
•.::: z I-'· 8 N
I-'
I.{)
ro
w
-;;'
""
- !J ...
({)
•1
(j) l•l
(/l fl.
([)
~
11
fll fl.
Ill
rt
~-··
0 :1
{J) '<
H
rt
!.f'
(() IQ
I-'·
(/l 0 1•1
1-·
I-'·
•Q :.l ... :·.1 I b'
Ill
(/l
(() iJ,
Ill n. ~1·
(I)
In
I·•·
<! ((
l (J
)
I ] !:J
•. 4
.
(/l
I I\
.~.
(() 1~
p,
!Y
111
{I}
ti)
I-'· b'
CD
1·1
(/l ct
0 1Q
<D rt
~J'
([)
11 :i ...
IJJ
{I} I"
:J < l·J.
ct·
tD p.
<: lll
11
, . .J
.
() c (J
J (()
N
'tl
r~
0 '1
IU
ct·
I-'· 0 :j (/l I-'· ~
rt·
0 ct· :·)"'
(lJ
cl· ::>'
(l>
Ii
El 0 Ill
tll
cl
rt
I-'·
~j
~
'd
0 ~
·~ (ll 11
I-'· ~
~· 0 0 n. . ~: !)"
l-'·
()
:~1·
,.~
Ill :J I·•· :1 IU
ct
(()
(/l n (() 1~
1--· ~
1~
0 (J) l·"
()
1-'] !:J
(() 11
(()
()
0 ill ::j 1-
h ci
.~.
0 ~
ct· :s· ru (I
t--;•
I-'·
\Q
!"J
I'· :1 tl1
r·
:; n rt ......
0 :j !/) 111
(J) Ill
~J
Ill ::1 0 11 ·u ::>•
0 ~
(ll
t-t
t_/ i-'j
•u b CJ
G
(}
l·-3
1-1 0 •·;
.:....
~
0
11
1983) . "!odi:ied ligri .. ins r.a~ie a: forded highe:- subs-t: ":uticn
levels without drastic loss of strength. Dole::iko a!"ld Clarke
(1978) methylolated kraft ligni:l before i:lCO!:pC:"ating .; .. .......
into an acid cu~ed phe~olic resin. Replacements of 60% of
the resin solids were achieved without drastic strength
reduction. Mu.:.. le!" et al. ( 1984) first hydroxymethylai:ed a::d
the!"l phe:::;.olatec ligni::i before replacing as rnuc.r:. as 60~~ of
the phenol in pl-:er;.olic resin with the p!"epolyme=. Bct:"l
and st:-ength pe::-f or~ance 'tie re sirni lar -co co:lt.ro l. ~~sins.
Forss and Fuhrmann ( 1979) fou:id that the high r..olecular
Vleigh-= .frac-:ior: cf kraft lig~:.:: and of lign:.:i sulfcnat:es,
• • 1.., wnic .. was obtained by ultrafiltraticn, ::1ay reol ace as rrn..:.c~
as 70% of phe!1.ol in . , pneno.:. acH:esi ves.
Al i:hough there exist numerous pa ten":s i:: this area (see
Nimz, 1983 for review), there have been very few con~ercial
applications.
The contri~ut.ion of lign:.n ~o the per-:or;na::..ce of a
ther~oset depends on i~s contri~ution to :ietwork properties,
a~d is t:"lus related to its crossli:r .. ka!:>ili ty (by covaler.t
!:londs) wi tl':. network compo~e~~s. additior:..
lig:ti!"l have also been s"":uCieC. ..
solids, by oxidati7e coupling (Ni~z, Eit=e. 1980; ?~i~!~pc7,
12
1977; Shen, Calve, 1980). Van C· ........ -· Klashoist, For:Oes a:::d
Psotta ( 1983), in an effort to find a suitable polyes"':er-
type crosslinking agent for l.1: g~l. !"1, reacted. a~yl acid
chlorides with several lignin model compounds. W!lereas the
models produced the corresponding esters in satisfac~ory
yields, l:i.gninsulfonates by cont:::-as"': gene:::-a"t:ed only small
quantities of este:::-s, a::d this ::-esul ted in high swellir.g
indicating poor :..nter:nolecular c:-cssli.r:king. A~ct~e!"
attempt to crosslink ligninsulfonates to form wood adhesives
concentrated on diazonium derivatives (Psotta, Forbes, 1983;
Forbes, Psot~a, 1983; a~c Psotta et al., 1993) . !"1"1""'~ .:... .... _ d:i.azotized lignosulfonates, in contrast to model compounds,
failed however to p:-oduce satisfa-c~o::-y resi::s c.·,'"' ..... _ to the
inability to cor:.trol tl1e cu:::-e p:::-ccess in tl1e presence cf
phenols, once diazotization of the nitrcgroups had occurred.
?clyethylene.:.::i.ine was used as a crossli:-.king age!"l.t fo:::- a
lignin based ad...i.esi ·.;e ny Osborg ( 1969) . Tr.e reaction of
ligninsulfcnates with epichlorchydr:.n (Eolsopple et al.,
1981) denc::.strated that although the phenolic hydroxy groups
of lignin. can be epoxidized successfully, tr .. e de:-i~.;a~i~1es
failed ~c ~ehave sat:.sfa~tc:::-ily dur.:.~g cu:::-e (~ubel, 1983).
ISOC'ta~ .. ates nave long been :~::lOW'!: tc ~=prese::i: ~~a.1.:..:i.ed
;:-oss~:.n~<:.ng age~.~s ::o:: l:!.gr.in ( ?-::==..t=l e~ al., l962; ::s~,
Glasse:-, :976,
poly:.sccyar.at:as
1977).
... -~ _.,.c:;i. .:i c,..~::)"'.-~..-4 - -- __ ....... 11"'~::::. --·- adve::.t cf ::7t1..l:, s i::.: a.:O le
i~~e=es~ i~ c~ossl~~k~~g :~g~~~
i3
polyol derivatives in aqueous wood-bonding systens (Lar:iliuth,
1981; Sa:i.yo-Kok'.lsaku Pu.!.p Co., 1982; Blount, 1983 ) .
Isocyanates have long been recognized to be excellent wood
adhesives by the:nselves (Johns, Wilson, l980; Rowell, Sllis,
1981) and in solve:i.t-based resins with ligni:i. (2su, Glasser,
1977; Glasser ........ -'"" al• I ~c8?) J. J - •
'T''-';::. -··- co~l3.lent u~ethane bor:ds
formed between the wood surface and the isocyanate molecule
result ir:. ,,. ; crh .... _ - adhesive s~re:i.gth (Witt:nan, 1976; Rowell,
Ell:.s, 1981). Lower resin contents, shorter press ti:nes and
absence of formaldehyde release have propelled isccyanates
i~to potent challenge~s for conventional wood bending ,...oi:::.; r. ~ -----·-(Jo i-.--"".,... a 1 1 98~.1.· ~,1,...ra,.,...·n 1 i·...., 19°0) .t.4.ti.•.;j - - - • - I • ._ -.,i ._":'• .- •.I. f - '-J • ! socyanates have
been facing two najor problens :.n t~e past, hi.gh reactivity
with water and cost. Only recently have e:::ul s:. f i a!J 1-=
i socyanates :Ceen developed w!:ose no:. stu!"e sens:. ti vi ty a::-1.d
volatility we=e greatly reduced (Adams, 1980; Sall, ::981),
a::d which have allowed ~he use of water as a carrier. The
handicap of a:i. up -co fi·v·e fold cost facto::- as ccmpa~ed ::o
conven':ior:.al weed a~...,_esi ·v·es ( ....iohns, Wi:.son, l980) !'las
e:::ccuraged _..,...Q \.._.;...,_ .investiga-c.ion l.:: ":O low cost emulsified
isocyana~e =esi~ exte~ders.
~a~u-o::i ( 1981) has e:~:pe!"i.:r~e!:~ed ~,lit.~ a ~cr:-~:.na-:::.o:: of
several . ....:~ ,:,:C::."""O,.._ _ .... _____ ...... pulp:..ng :-esidues and
diisccyanates. Seve:::-al - . . . ccr.-..o :::at.: or..s 'N'e~e
s~pe~ior ~~a~ p~er-ot f·:l:-::taldeCyC.e and u:-ea
er..u:..s:.:::a~le
Q.~ ~ - 1 -~-..-.a .. ':o or
- .. . . . : o ~:-::.a..:..c.e:!.yc.e
'(j It , .. 0 11
r1·
0 n i.-:
Ii
Ill ·-.l·
c I r1 ,. .. •·· {J
I 11
ti• ill
(J) r.: lit
'lj (ll 0 ct
II> p,
ct· : >"
Ill
rt
jll f ),
,J'
([) (/l ... ,. '
((1
0 0 ~l
'd
Ill
cl
•. J
. u· ......
I·'
I'· ,, '<
~
I'·
cl :)· 111
• 1 b. i::
~1
I'· ''• 0 ti ;J I-'· " •....
;! 0 1-1, cl :1· IP
'i
Ill
(/) , .. :1 :Cl I" >: cl
i..: I 1
(P
()
!.l'
Ill
Ii
Ill
()
rl
(\l Ii
I'·
Ill ct
I-'·
()
(/
l 0 111
1~
I•·
•.ll ;:1 I-'· :-J 111
I i
(I) Ii
((I
1-·
Ill " (II n. (I
0 Ill 0 ... r: tr
I'·
I·'
t •· cl'
•..::
I'· :i
ll•
t-•
t-•
\0
'-1
•D :<: c: <.I
1~
Ill
(/)
(/)
(ll Ii
t-•
\.()
00
,,,,
.
{j)
t·'·
•-s 0 (\
)
()
ti
0 (/1
(/) I '
t-•·
:.:s ;..,·
I-•· :·s li
l
'C:l 0 I·'
'<! 0 .~ -·· "'· •. J.
cl :1· I-'
0 i;
<Q
1~
fll
(/)
(J}
cl
Ii
Ill
~j
(/) 1-J·
ct
I'·
0 ~-i .... w
~1
'd
(D
•i
Ill cl
!~
Ii
{(I 0 ..... 111
(J) Ill ID •1
IP
cl
0 x I'· p,
f(I •a
•i
0 n. c: n IP
(J) Ill ~-'
0 ;J I t•·
0 ~I
•. J
.
()
UI 0 1~
,. ' w :1 c1
Ul
0 ,., r.: tJ'
t -•
(ll
~: :1 I'·
111 ~
, I f) " ... ()
~::s Ill
1~
I) :·s· (1
)
()
')' iD B
I···
()
Ill
t-·
•
E-1 0 n. I·"
ta,
t•·
()
p1 rt .... () ::1 0 t•i
1-·
I•·
1Q ;1 t•·
~j
<; .... rt·
::.i·
'l1
11
()
'd
•<:
1~
ID :1 ((I
Ii
ID Ill .... U
l ct
Ill
~l
()
(\) pt ~1 ().
~I'
I"
•Q :.> ..
I·-'·
~1
0 •i
If~ 01 !l
t•·
0 0 0 :1 rt
IP
~1 ct
ID Ill
'd
(j)
0 1 •·
p1 t·•
1~
•<:
0 II• i:
UI ct I·'· 0
{/} ~·
0 11
c-t- o 0 El I·'· : 1
•Q
{/} 0 11,
( t :.l· ID ·--· .... lfl !J I·•·
~J
Ill n .. !) ..
I'·
ct
I··
0 ;:1 I-'·
~i
()
1-· r.: n. (0
t-•
0 (J)
(J) 0 ti\
~I 0 I·'·
(/) cl
!~
11
(p
.... IJ) 0 ()
'-<
Ill
~s
Ill
ct
(I) Ill n. ~}I
(!)
(/) .... <.!
CD :.>'
0 ~
(j) ~
(j) 11
t-•·
(/)
() :·J iD
0 1-1,
((I
()
()
::-1 0 ;:I .... ()
IJ) ~
(\l n 0 '!~ . t·'·
II w
p.
IJ) I-'•
<Q r1 I-'·
111 ,, . ()
JU
·1
~1·
()
0 ::1 ct
11
I'· ti•
1: c 1·
I'·
0 :1 0 hi .... , ·-·· ul :j t•
· :1 (1
0 cl
~·
(Jl w
;J
~:
t-•
Ul
I"
l•I)
f .
. Ill
n.
t-•·
Ut
0 ()
•<:
Ill :J Ill ct
!P
I-'· :.1 ()
Ii
tP
II'
IJl
f •.
':1 1Q
()
Ill
11
I j ~-··
Ill
t1
()
0 ;J
'd
Ill
cl
ll• lr .... f
-~
1-·· ct
'<
I ] :] .. ll•
:J 0 Ut
ci
1--'
I-'·
<Q
~J
I•· :.s '(
j CD
Ii
1·1, 0 11
;J
Cl>
!).
II>
ll) P• :.J (ll
t 1,
Hi
(I>
Ct
<1· ,,. <: tD
((I :.i
~-:
t--·
Ill
t •·
II\
'<
I'· :1 1Q
Ill
ul
!O
!1 rt
I •i
0 Ii
! 1 •
') co
I·•·
~
t-•
(II
(/)
(/) 'd
IP :j Ill
't
I 1
Ill It , .. 0 ::i
111
'1
b~
~--'
0 Ill
(Jl l t
Ill
:i fr r: rt
~·
Ill
1~
(J) 0 t-1)
0 i::: 'j n. rt·
~)·
pt rt
t-t1 0 tj ti P>
cl
I·'· 0 ;::s 0 I I)
Ill
!J Jll P.· .1'
((I
lQ .... < (0
11,
I-'·
.~
~I
0 :1 rl :j·
(I) ~
0 0 Cl.
!II r.: lj
I I\
111
()
(I) Ii
Ill
(/l
~
I-'
rt , .... :
j ul
Ill u· (/
) 0 Ii
'd
ct·
1 •·
0 ::i u·
1..:::
-~
0 0 n. (I) r.: Ii
11\
Ill
()
(0
(/) Ill
() .. p.
~-'· It
)·-'•
0 ~j
0 111
,~
I-'·
1Q
::i
I··"
~1 , .... Fl 'd
rt
0 <' '
(IJ n. ct :f (I)
<: .... (J)
()
()
(I) I-'· ct
'<
0 tt1
'd
0 1--· I< I-'·
(/) 0 ()
'-<
Ill
H
Ill
cl m
(/) ~
tD
11
((I 11\
() r: H n. rt·
0 ()
Ill
~
(/l CD
([)
~-.: n w
(I) Ut
t •. <: (\
)
JU
1--' 0 H
C!J
t-•
IU
()
;x,~
I ] ~
tll
Ii
w
1~
Ill
rt .... <: ((
I 1~
~~
1~
0 ~
~cl 0 .~
(j) ()
,~
1~
Ill
1 j
~
([I t•·
1Q :.]·
rt
JU ~1 n .. .. ~ ()
i;
~1'
0 1--' p, .... !J
~
'(J lj
0 'Cl (I)
lj
rt ..... (D
(/) n. r.: 1 j .... ~j
1Q
;J
Ill
rt a () <: ID
~l
IP ~J ct
rt :.r llt
rt
l--'·
Ul
0 ()
'-<
Ill !J Ill c I !D
(/)
rt
Ill
() .... - f-'· H
Ill (/)
(J) 0 11,
b' , ... JU
()
;.t..--
1-~
I'·
10 r.: 0 I j
Ul
~
IU
(/)
11,
0 r.: :-i !} ..
fl
0 1~·
;J
'd
II'
lj
r1·
~j
(I)
IP
~i. tD n. Ul :Y Ill
'O w
()
0 a 'tj
Ill ct
IU
tY
I'·
t·~
I'· ct
'<
~·
(Jl
lj
())
~j
0 ct·
((I p,
~ :.>'
((I ~
t-·'
I •·
<Q
~1
t·-'· :j ~:
Pt (J) Ill
p,
fl.
m
~). H
~·
tD
: j IU
rl·
.~
11
Ill
t ...
Ul r.: ti
ti)
Ill
()
(Jl
(/) 0 1~
I-'• fl.
!II
()
0 H
()
ID
~j
rt·
Ii
IU ct
I-'· 0 H
Ill :J n. . .... 8 'CJ
11
0 <~
tD p.
()
Jll
1·-c
lj , .. (J
l 1-
j
'O
Ii
0 ()
ID
Ul
(Jl
I-'• H
U:l
•0
Ill
I j
Ill
:=.i
(() ct
([)
lj
IJ) !II c: ()
~j·
Ill
Ul
I·'·
:j ()
11
ID
ju
(I
) ti> p.
rt
Ill
() ;i;·
l·'-
~I
'd
Ii
0 <: ((J n.
1~ .... 1
(l
::.i 1•·
H I t11 Ii
((I tD .... (J)
0 ()
'<
Ill
~j
Ill
rt
(1) t·•i
()
11
;-3 r.: 1--'
Ill ct ..... 0 ~j
{/)
{/)
()) <: 1[1
Ii
Ill ,_, I'·
:;1
•{J
Ii
() < 1\1 3 Cl> :..i r1·
Ul
1-J· :1
Ii
ID
(/) .... :1 {/) I-'·
~ ct
(0
I'( :J {/
) 0 111
ll) ct
I'( m
'j
.Q <I !.l ..
'Cl ,, 0 'Cj (lJ
Ii
(I
I·•·
((I
(/)
1-J
~j
()
0 ~1 ·a pl
'i
I-'·
(/) 0 ;-1 n·
0
I-'
.)>
15
perfcrnance of lignin-isocyana~e e~ulsion-based res:.ns
be ir::p ro\red by chemical ~od::ficatio!"l of ligni::
cor..por.ent. This hypot:-iesi s is t!":.e focus c: the present
study.
work conti:-... :.4es ir..vestiga ti or. t~e
engineering of lignin based ;o:ymeric materials. :1odified
lignins are examined for t:. se as wood aC.~esi\res
crosslinking. Isocyanates a~e t.:.sed as or..e of tl"le ncssible
crosslinking agents based on previous work, and melamine is
explored as a!1. option. Melamine derivatives have :ou::d
in a vari.ety o: ad.."-;.esives and coatings a~·plica tio:ls
(fu~~e:-ican Cya:ia:nid; Blan~~~ 2.979), ar:C. they offs~ e~·:Jncmic
ad··.,.ra~ta·;es 01\.ter isocyar~at.es. T~e su.ccess a: h~·d.roxyalky:
1 . . J.ign.in derivative-exten~ed isocyar:.a""Ce nas
previously been limited to solvent-based systems wn~cn,
contained subs""Cantial an:our:ts o: a.l.:phat:ic
po!y(ox:,rpropylene) components (~su, Glasser, 1977)
sti..;.dy explores useft.:.l:::ess
ligni~ derivatives orga~ic and i.:: er..ulsion-!:::ased
wood a.C...~esive fo::-:nula~icns cor:tai~i:-.g i.soc:.tanate or mela.:r.ir:.e
as c:-~ssli~king age!1~.
,Wateriais
16
1. Lignin Compc~e~ts:
a) Kraft Lignin ( K) : Kraft lignin was obtained fron the
Westvaco Corporation, Charleston, South Carolina, under the
trade name ID.1DULIN A7 It was pu::::-ified by precipitatio:-i
f::-om aqueous alkali ,,,; .... ;.. \f'f- ._ ... :-::.ineral acid
-1 average r:iolecular weigh"': ( M ) was 1. 3 gM by gel n
(G?C) and 2.8 3 - , x 10 g~ - by vapor
pressure osmometry (VPO). its weight average mo~ec~lar
weigh;: (MW) 12 103 -1 by was x gM GPC. Its polydispersity,
M /M by GPC was 9.2. Its n w chemistry is described
elsewhere (Glasse::- e-i: al., 1983).
b) Orgonosolv Lignin ( 0) : Organosolv lignin was obtained
f rorn Biological E::e!:"gy Cor::ioration, -'-Valley ;:. o:-ge,
Pennsylvania. The lignin was prepared from aspen wood cn~ps
in a piloi: pulp digester ~sing a~~eous ethanol as solvent.
I"': !r;as recei ~1ed as a dry powde~, and its cha::-acte=-i sties
were desc~ibed i~ an ea~lier publicaticn (Glasse=, et al.,
1983) .
GPC a::i,d 1 ~ 103 gM -1 ':;)y V?O, and i<:s ~11eig~ ... t. .... .<:: x
_, gM ~ by
average mclec-.ila.r 'fHeigh~ •,;as "' 1 :< 1 ..,3 ~M-.i. r--.::; .l.v "::J. ... - ._,.
polydispersity ~y G?C was 2.8.
c) Steam Explosion Ugnin (SE): ~~--~.:....., __ ,,, ____ _
was obta~~ed ==om Iotec~ Co=p. L~mited, Ottawa, Ca~ada. . .,..
aqt1eous Nae~ ( 0 . 4:~~) . T!'le ; '": --~.,..., --~·:..-~.
17
received as a dry powder, ar:.d its characteristics were
desc=ibed in an earlie= publication (Glasser et al., 1983).
d) Acid Hydrolysis Lignin (AH): An acid hydrolysis
lignin was obtained from a pilot plant operated at New York
University.
white pine wood chips in a twin screw ex~ruder. =ne
resulting residue was extracted wi~h aqueous alkali and
precipitated with mineral acids. The characteristics of the
resulting lignin fraction was descr.:.bed in earl.:. er
publication (Glasser et al., 1983).
e) Hydroxyalkyl Lignin Derivatives: T~e ligr:.ins we=e
hyd=oxypropylated using prcpyle!'le oxide in aqueot:s 2N KOE,
at room temperature. < A solid hydroxypropyl lig:lin (~?::.)
derivative was precipitated in water containing a sillall
a~ount of HCl, and collected by centrifugation. Kraf"t ?:?!:..
(KP), organosolv SPL(OP), s~eam e:<~losicn ~?L(SE?), a::-.d acid
we?:e sc p!"epa.::-ed. Eydroxye~hyl kraft
lignin ( K::S) was prepared using 50 ::le les of ethyle:1e oxide
per 1000 g of kraft lignin in ~oluene. It was cb~ained from
an ur..ide:iti!'ied source as a pilot plant p:=och . .:.c"':.. !t :.s a
n~n-ionic, wate:=-so1u;,1a pol~;me!".
2. C=osslinking Agents
a) Isocyanate: T~e isocyanate used was a poly~eric
r:tetl:ylene C.i;r.er..yl dii socyana":e ( :?:•!D:) p!"oduced by -:.he
UpJchn Ccr;>. :t i.s .sold as a. ·"·:.scou.s, bro\.~ l:..~.:d u~c.e!'"
18
t!le trade r:.ame lCO. isocyan.ate is
emulsifiable grade.
b) Melamine: The rnelarnir:.e used was hexarnethoxy-nethyl-
melamine produced by the American Cyanamid Corp. ur:.der the
tradenarne "Cyrnel 303 !r. It was received as a clear, viscous
liq..:.id cu:::-able with an acid catalyst ("Cycat 4040").
3. Test.ing Eq:i..iipme:it
a) Strength Anc:!ysis: Strengt!'l testi!'lg was done en a
Tinius Olson .i:estir.g rnach:.::e ·-..1i t:i. a shea:- testir.g hec.d as
recornrner;.ded in ASTM standard D 905-4:9. Ea rd maple, sir:.gle
lap snear blocks with a specific gravity of 3 0. 6 g/c::i. we:::-e
used.
I!. Methods
1. Adhesive ~or~ula~ions
a) Organic Solvent Based Formulations: ligr.in.
(12g) we::e s~.~o 11 e!"l methylethyl ketone
( 7ml) . A gradual addit:.on of the MEK to the OP prepa:-ation
facilitated dissolution. T:'.::e aC.C.i tio::: cf a few d::cps of
water aided the complete dissolution of K? in MEK. A
special precau':ic=: , . .::aa
corrtbir:a tior:s where
d.:. s sol u -c:. c::..
was
of
with t~e ~P-isocya~ate
.. ·- .... Q,... .v a.·---
!socyar:ate ir: t~e small amour:t of wate~. ar:d the~ accir:g t~e
19
Once 1ign:n deri v2ti ·v-e ;..ras t:ie
crosslin%ing agent (12g) was added, a lignin
derivative content was maintained throughout.
b) Emulsified Formulations: The lignin derivative solution
was added to wate;: (29 ml) containing 1% of an e~ulsifying
agent, "Scr-ipset 700!1 (Monsanto Co. ) , anc cr-osslinking
agent { 12g). The mixtu!:'e v1as ag~ ta-:ed l:J. a hi.gh speed
blence;:, and a 6C% lignin content was ~aintained t~:=oughout.
2. Assembly and Cure
a) Assembly conditions: Standar-d achesive fo;:~ulation
"'"'a ..... a,...,"" ..... ,,,..._ (.; e ::' ... """ - I_. - - t:J - • • l~g~in ccn~e~t) were deter~i~ed by a series
of pret:-ials. All of the ad...~esive ccnb~~aticns w~re tested
on 12 x 2.5 x 0.5 ir.ch . . . ~-;,a:=a. nap.Le block.s ac::::or:iing to
standa:=d D 905-49. The r:1oi stu!"'e cont.ent of -r.b.e weed. ~,..,'as
11~·~, and eacr.. piece '~as lightly pla:--.ed be.:.ore a.d:--ies: ·ve . . ... . appl.:ca'-ion. '!!:e adhesive ( S g d:=y weight) was ap?l.ied to
one of t~e two halves of bloc:·:, using a ru~ber spa~~la.
rr• __ "le s:.des we:'.."e then closed ir:::r>.edi ate l y a::d C • .,.,,..o....i ..... __ _ in a
ho-: press.
b) Cure Conditions: a.::c.
pressi.ng
using an ~de~tical for~ulation :or eac~ of ~~e six aC.:~esive
. . . . cor..;:,:.nat::.or..s. T~e resulti::g s~ea;: s~;:e::gths of t:~ese blocks
were a~ i~dicat~on of acceptable pr~ss te~pe~a~~~es a~c
press ~i:nes.
and sho:-test p:-ess ti.me
six of t!"le possible
20
resulting ; --·· adec;ru.a ::e
l:.. g:i.i n acr.esives was
of
adopted
- 1 l c:,.;.._
as
standard. After :-emoval f:-om the press, the specimens we:-e
post-cured for 36 hours at 27° C :.n 50% relative humidity.
3. Testing
a) Shear Strength Analysis: Each block was cut into six
shear samples as defined by ASTM standard 0905-49. ci·ve of
these samples we:::e tes~ed she a~ accordi::g to
standard, ar..d the =orce requ.i~ed fer fail~re and tr~e pe::-cent.
wood failure we:::e recorded.
b) Wet Strength: The sixth shear sa~ple f:-o:n each s~ear
block was cut in half anc then subjected to 4 and 24 hour
boil tests. shear s~~er.~~~ of these sa:r.ples \/as
measured.
RESuLTS A.:.\ID DISCUSSION
I. .~eoction of Lignin Derivatives with Isocyanate and ivfelamine:
The crosslinking reaction of unifunctional hydrcxyalkyl
lignin de:-ivatives with diisocya:lates is
illust:-ated for a propoxylated lignin-like model compound
-'-. Prcpcxylated lignins have secondary hydroxy
groups as ~heir pri~ary :-eac~iva sites, whereas hyci=oxye~hyl
a:nC. ::tel a.mi ~.e
r:iay also T • .; -\.i ""'- --- .: c r::l --~ - Q--C::..i.~J.- ..... --~ I
: soc::/ar:a-:::c:s
21
homopolyrnerize crosslink ..... ; -v _;;i the format:. en
allophanate and (Wittman, 1976).
particular ffie l ami r:.e used, hexamethoxy-methyl , . me.!.amine
(RJ."1J:lf~), requires an acid catalyst for reaction with another
hydroxy-containing subs~ance.
ether in~erchange reac~~cn wi~h simultaneou3 ~elease o=
methanol (American Cyana~id, 1979; Blank, 2.979).
The reac~icn of hydroxy groups on the surface of wood
with monoisocyanates has been explored by Rowell ana Ellis
(1981). reaction of diiso~yanates with water
the ~elease of carbor- dio~~ide, and Wi":t:nan (1975)
calculated on the basis of co2 -evolution ~hat ever 50% of
the diisocyanates used in the manufacture of oarticlebcards
emulsj_::.:.ed d:.isccyanat.es for:n bonds.
Isocyanates are capable of bonding wood without any ::ur~~er
Hexa::le-':!"lc:<~l-~etb.yl rnel.am.:.r .. e, by ccr-.t~ast, ~eG'"'~ires a secor:d.
(poly~e~ic) ~yd!:"oxy-ft.::lc~ional cornpo?"".e~-:. -::o ~eac~ rt1:. t:i, a:ld
is not a qualified wood ad...'-:esi?e by i ~sel.:.
ccrr .... 111erci ally coa.-~i~gs :i::isI'.es of "laricus
(Ame~ican ~ya~amid Co., l979; 3lank, ~979)
I I. Screening of Adhesive Combinatfons:
SQ lu!J~:. i ""=!.' / ad~es:.o:t
abili--:y 9 . • • c. e-:. ::= ?:9:':" .. J...::.. ec. a ':Otal cf
22
crosslinking agents.
Table I: The .lignin hydroxypropyl
1 ; " . ( K::i ) _ ... gn..:..n .. , ( K~) I an crgancsolv
hyd::-o;-:ypropyl lignin ( O?), a steam explosion hydroxypropyl
lignin (SEP), and a.:1 acid hyd::-olysis hydro;<ypropyl lignir:.
(AE?). T~e crosslinking age~.ts we!'"e a . . po~y:ne!"i:::
methylene diphenyl diisocya:i.ate ( I ) and a
Since adhesive performance was fcund
to be affected by ernulsifiability a~c solubility, only t~ose
cornbir..a 7;:7_ ons w:.-cn satisfact:.Jry solubility
o::-gar::.c solvent (methyl ethyl and
sa~is:actory aG._'i:.esion we:::-e S -"', o---.:.,..l ---"-'--- full-scale
evaluation. These we:::-e OP
a::c. e::i.ulsi.fied fo~:nulatior:s. prepara~icn w-as
equally qualified tests, was not included in
this study due to li~ited availability.
was insufficiently soluble
satisfactory aC....~esion.
..:. .!. l. . Screening of Cure Conditions
shea= block ~=s~s fo~ each a.C.:-:es:. ve
pre:ss i:empe !"a ~l.1::e
~~e O?-baseC.
.. -~-=""-- -
•• ,-1 ar:.a. c:..- ~ot ::-rod~ce
series
. . . c::~:.::a ::.io=--......
T::e
s:-..cw 3..S
23
te~perat~res and :ewer press times tha~ those o= t~e K? and
•.'.!"-=: ""'asec· -=~....,··°'-"'-"~re-:: (-::-i· ~·.,...- ? " ;-,__ ;,.., - ~ ' - - - ';J '-'- - ':::! - r. I B, D, E). The KE-based
adhesives ( B, E), required longer press t:imes <:na:: the K?-·
based ad..~esives (t\,D), but the press te~peracures with
either of crosslink.ing age~ts very
(Fi~~re 2 A-C vs. D-:).
These screen.i:lg ~ests of cure co!1dit:io~s
. . , . , es -ca;:,~ l. sn. standard ccndit:..ons - 1 1 c. ..........
co~~i~aticns pe~fo~~ed sa~isfactorily. These i::volved press
times of 4:0 minutes at a p::::-ess terr.per-a-::u::e of 150°C. A.ll
cu.:=-e cond.it:.ons.
IV. Screening of Lignin Oerh'ative Contenc:
~esul-::s f::::-om a series of shea~ b:ock "C.ests i..ls~:i.g
adhesives formula~ad with varying lig~i~ de=iva~iv~ ccnte~~s
preser:..ted 3. The results
isocyana~e-co~tain~~g aChesi ~les s!":ow
prope?:ti~s dee ;..ir:e an a,.le~age of :I.5;~ as colnparea 1:-0 pt:. re
isocyanate, wit~ lignin con~ents rising f::::-cm 0 to 6C%. A-:
lignin de!'"i._tati'f.le
deteriora·~=d ~.ln ti l oc::ur:-ed a.-:.
approxi~a-:ely 90% lignin derivative co~tent. 3y con-::ras-:,
t.o 60~~.
24
si:ni la::- to the cbserva tions made w' .,.. . .., t:he i s::cyana te-l:ased
adhesives.
The results indicate that isocyanate, in contrast to
melamine (me .... ..,.,vl c. ... ,,.,e .... ) H i.... .... ,. - - ~.i..4 "'- I is a qualified wood acU1esive by
itself. Al~hcug~ it is likely that both tr.e a~ine a~d t~e
isocyanate have t::.e potential of reac~ing with solid wood
surface, the isocyanate p~epara~icn, by virtue its
ability to hoznopolyne!"ize and ur.dergo a variety of side
~=actions, is able to achieve a la:::-ge e::.ougn moleci.l.la::
st.::-ucture to acq-...i.i z:-e ad.."-lesi ve ability. A lig~in co-r-eagent
is necessa.::-y for the amine to fur.ction as an adhesive. The
i socya:late ::u~ctions as an ad-"-1esi "'v"'e ·t1i the tit the need for a
co-reage!:.t, a~~ ~:te aC.di tic~ of lig:i:.n dis-:.::-acts f::om its
adhesive strength. Build-up of a subs~antial macromolecular
structure seems to be necessa::::y fer. ad:.esi ve perfor:nance, !Je
it through homopol:merization as in case
isocyanates or cc po 1 :1rner i ::at:. on .. ,~ .... ..., .... - '-·· 1 ~ .-"""" ~ ,.., -- ~~""--•
prepolymers, as ir. the cas~ o~ the.ami.nes.
':'he screening reascna:::,ly
conditi.ons of f o r:r~ul a.-ci 0!'1., of c:.:re, a:ld of
cont:H1t.
derivative ar.d of c::oss l:.::ki.!"'" .. g ager.i: t:tpe
evaluated. Sta~Ca~~ co~di~io~s ~sed
---·------ C...,1""'4<;-.~ :~---,.~;:.-... - ~Cl-:..;.../:-.... ..
.:o o~
.10
'--~---:::i-.o=-----._./
U1°
. .,. ... .!. .I.
26
resulted ir.. sligl":tly t!':e
OP-based acL."1esi ves. In solvent tr.e isocya:::ate-based
adhesi ~1es performed better than the amine-based f or:nula tiori.s
of lignin type. In an aqueous emulsion t:ie ., :-..-
and the C- ad..'1.esi ve combinations ,,., . _.ac simi.!.a!""
strength, regardless of crosslinking agent type.
'!'he res"..ll ts suggest that, in solvent, t::-.e higher
molecular weight kraft lignin contributes more effectively
::o a&.es!·,te per!'or::iance "t.:ian t:--.i.e lower mo..Lecu.La!"" Y1eight
organosolv preparation. Isocyanates perform bet~er
amines probably because of their ability ~o nomopolyr:-.erize.
Emulsification was ~ore detri~ental to the isocyanate-~ased
ad...'1.esi ves, especially ..... .... r:.e fo:-:nulaticr: containi::g
high molecular weight lignin de.:?:"ivative (!.::?-I). ?:::.-oblems
with emulsifyi!"lg a high molecula:::- weigh~, water-insoluble
lignin deriv·ati~1e, a~d problems wi-:.h isocyanate reac~i~-1.,.ity
with. water beth must be held responsible fer this red1.:.ction
in st::-engt!l.
studies of Nunes al. (1982), w:::o !ound highe::
~olecula= weight pr'.'.lcuce crossl::n~...:ed
po~yme~s ~it~ fewer c~ain e~ds. Cha~~ e~Cs act as points o=
:.npe!:"fe!:"tion i.-1hich weake!"l the pol~'rne::- net;..;crk. !'1-.e neg a ti ~le
effect of e~ulsifica~icn was less cro~cunced !or ~~e lower
rnolec....ilar organcsolv derivative, pr~bably . --~,.- ='~ -~ -. ------==>- '-'-
27
Vb. Effect of Lignir. De::::-i ·;ati ?e ':v~e:
Hydroxyp::::-opyl lig::.i:: de::::-i·v·atives are compa::::-ec:. to their
hydroxyethyl analogs in Figure 5. :-esults . .. . .. l. !1.C.J. ca,_ e
that, an organic ca~rier,
produces highe:- shea= st.:-::-en.gt~.. thar... "tl":e cor:-espcn~.:.ng ~E
combi~ation with eit~e~ c~osslinki~g age~t. r::~e i socyana-:e
formula~ior1 again super:. or to am.:ne
regardless of type. Tne ad":.rantage of -",..., ,Q .__.1,_
propoxylated de::i ·v·a ti .,,,e is lost:
emul si fie a ti er:.; t.r.e K;:-r a&.esive clea::::-ly - . pe:-::crr:'.ed. best
emulsified ;'\ , 1 .n..;. - othe::- ad!'lesive f or:::tul a tior:.s we~e
...... ~r ... ese ::esults suggest t::at tl:.e
deri \Ta ti v·e, withou~ aliphatic polyethe::::- chain extensicr:.,
produces a oetter adhesive t:~an the correspor:.di::.g etl:.yl
deri .,,.a ":i ve, which was fo~nd
aliphatic polye~::.e::::- c!"lains
(Glasser et -, 0.-. 1979) .
important
ana !CZ), ar:d so l i.;.b i l i -c y
be :nore li~:e~y ccr...tain
of
solubili~y i~ water :s isocyanate adhesives,
f ·--Q.,... NC:.·---
Solubility i~ solven~ (~?
( ::::: ) obvicusl.y £a,1or
raact.:!.on o:: isocyanate groups 1 ..; ('"'!' ....... .: -
---:: .. ·-·· co- ~eage!""' .. t
,... __ lo"\~
- a.'-··- - tl-.an f,-~Q.,. Y"fd. ___ _
28
A comparison of she a!':' st~ength cf achesive
combinations crosslinked with isocyanate is . . . . . '\.. :nac.e w i i:.n t: .... o s e
crosslinked with amines in Figure 6. In an organic solvent-
based syste~, the isocyanate adhesives produced higher shear
strength values. Emulsification greatl7 reduced. the
adhesi -,;e ability of the isocyanate cor.J:>ina tions but :-;.ad
little on the ~elarr~i:ie combinatior:.s. ?::-obler:ts W.~ .... ,.., - \.-.. the solubility of the lignin derivative in water, an-::.
problems with the reac~ivity of isocyanates with water
obviously contribute to the lower strength data of the
ernulsi.f:'ied isocyar.ai:e combinations. er.:ulsion,
isocyanates ::ave essen::ially e~al ad..'.;.esive perfor:7ta:-.ce as
t:1.e me 1 a:ni r:.e .
VI. Wet Strength:
Shear of samples subjected to 4: and 24-hour
boil tests reflect:ed catast::-ophic loss of perfo~~ance in all
cases. No ligr:.in de=ivative-cor.tai~~ng
for:nul.ation, ~ega?:"dless of "t.Y1Je of c~ossl!nki:::g agent or
or t:ype J any
CONC~uSIONS
1. ca~ be wood
ac:i.'.;.esi v-ss co?:":bir.a tio:;, w_ '-••
.: o !'rr;u2. a c.:i. ons .
29
2. Where reaction of l i gni n derivat:.ves with
isocya:i.ate al;..rays results in adhesive strengt~ less ( <20~~
with lignin contents rising to 60% and drastica!ly at lignin .
contents in excess of 60%), mela~ine does not function as a
wood ad.."riesi ve by itself, and reaches optimt.:.rn pe::-formance
only in cor.~ination with S0-5C% lignin deriva~ive.
3. In e~ulsified formulations, adhesive performance is
related to component solubility and compatibility. Only
hydroxye~~yl-isocyana~e combinations perfo::-m significantly
better tcan u::-ea formalde~yde.
4. In solvent-based fcr~ulations, aehesive perfo::-~ance
is ~elated to pre-pol:nne~ (lig~i~ de=ivative) ffiOlecular
weight, a~d pe=fcr~ance decli~ed in t~e o=der o= K?, K~, a~d
OP.
5. The ability to hcmopolyrr.erize, to under·;o s:..de
~eact.ior ... s, anc to reac~ with water, favors -::;.e use cf
o:-gai:..ic sol·le!'lts in combinatio!1 w:..-:.:i ~socyana~e, \v:~ereas
amines work as well in organic solvent as in water.
6. None :::f the adhesives tested survived a 4-l':our :.:ioil
tes"t:. Ligni:i c!:ri ·v·a 'ti "'Te co::tent ?reduces :r~ois~:ire
scns:.1=.i .. ,t:.-:.y in al: a.:ni::.e ar..d isocyar.a~e-ba3ed ad-~esives.
30
LITERATURE: C!TSD
Adams, A. D. 1980. ~rnulsifiable MDI isocyanate binder for particleboard and waferboard. ?roceedings, Fourteenth Washincrton S~ate University International Svmnosium on Particleboard, T. M. Mahoney, Ed., Washington State University, Pullman, WA, 195-~05 .
. .;merican Cyanamid Co. 5/79, SK.
1979. Technical P~blication 9-21:4
Blank, W. J. 1979. Reaction mechanism of melamine resins. J. Coatings Tech. Vol. 51 (No. 656), 61-70.
Ball, G. W. 1981. New opportunities in manufact~ring
conventional particleboard using isocyanate binders. Proceedi:tgs, E"i fteenth Washincrton State Uni ve:::-si tv !nc:ernational Svmoosium on Particle!:loard, T. M. Mahoney, Ed., Wa~hingc:on Sta~e University, Pullman, WA, 255-85.
3lount, o; E. 1983. silicate pcl:y·me:-s 4:,377,674.
?olyols from lignin- o:- cellul.ose-fo=- polyu~e-+:b.anes. U .. S. Paten~ :-Jo.
Dolenko, A. J., and M. R. Cla:-ke. 1978. Resin k:-aft lignin. For. Prod. J. 28(8), 41-45.
. . . 02!'1.a.ers :: ~c ::r.
Fo:-bes, c. p • I and tc. Psotta. cross linking :-eactions. 2. lignosulphonate with diazoniu~
37(2), 201-206.
1983. The
salts.
Lignosulpt:or:ate coupling o:: Holz.:orsc:~ung
:c'orss, K. G. , a:-.c. pa:-ticleboa::-d, adhesive.. For.
P. •• Fuhr:na:in. 1979. Fi.nr..i. sh olvwood .. .... f
d -·· b . d . ' , . . . an t.:...oer oara. ma e w.:.. ~n a J...:..gn.:..n-.oase Prod. J. 29(7), 39-41.
Glasser, W. G., C. A. Ba:-nett, P. Sarkanen. ~983. ~he chemistry lignins. J. Agric. Food C~em.
C. Muller, and K. V. of several bioccnve:-3icn 31(5), 921-930.
Glasser, W. G., V.. P. Saraf, a::d ~,v. :l. Net.vma~. 19.32. Hydro:<:lP!""Opyla ted li gn:.n-:.. sccyana ~e ccrr.bi::a t:..o::s bonding agen~s :or wood and cellulosic fibe:-s.
as ,. v .
A ,. . .. c.....'1.es1on ~ '1. """..,.... ""c: -.... , .::::..:i..:i-.::::-.:J.
Glasser, W. G., ~- C.-~. Wu, and J.-~. Selin. 1973. S t 1.. • . . • . . •
~"!l J. .. es:.s, s~:-,.ic-:.:.ire, a?:c scme p~ope:::-1::.i:s ot hyd.roxyp::-opyl. lignins. :,;rood a.::.d Ag:::-i.:ul ~u::al ResiC.ues -~esea=ch on Use :or Feed, Fuel ar:d C!"'~er:tical s, =:ct .J. Soltes, Ed., Acadecic ?::ess, New ?erk, N.?., pg.
31
14:9-166.
Eolsopple, D .. B., W. W. Kurple, W. Kerple. 1981. Method of ~ahing U.S. Pat. No. 4,255,809.
:M • Ku rp le, and K . R. epoxide-lignin resins.
Hsu, 0. H. -H., and W. from carboxylated 297-307.
G. Glasser. 1975. Urethane foams lignins. .;ppl. Polym. Sym.p. 28,
Hsu, 0. H.-H., and W. G. Glasser. 1976. Polyurethane Adhesives and Coa~ings :ram Modified Lignin. Wood Sci. 9(2), 97-103.
Johns, W. E. 1980. !s there an isocyanate in your future?. Chemical Aspects. Proceedings, Four~eenth Washinaton State Universitv International Svrnnosium on Particlenoard, T. M. Mahoney, Ed., Washing~on Sta~e
University, Pi.illman, WA, 213-39.
Kratzl, K., K. Buchtela, Ettingshausen. 1962. phenol and isocyanates.
J. Gratzl, J. Zauner, and 0. The reaction of lignin with ':'appi 45(2), 113-119.
Kubel, H. compot:.nds HOUT 303,
1983. with
Reactior..s of epichloronydrin.
lignosulphonate ~cdel CSIR Special Repor~
!S3N 07988 2785 8. Na~~onal ~i::ilie~ ~esear~h Institute, Pretoria, South Africa.
Lambuth, U.S.
A. l98l. Aqueous 4279788.
pclyisccya:late lignin aC....':esi ve. Pat. No.
~!cLaughlin, A. 1980. Polymeric isccyana~e as a recons~it~"':ed weed product binder, Proceedings, Fourteenth Washincrton State Universitv International Svr:".oosium on Part:icleboard, '" M. Mahor:.ey, ~a..,
Washing~cn S~a~e Universi~y, Pullman, WA, 207-11.
s. s. Kelley, and w. G. Glasser. plas"':ics from li g!'l:..:i. V!I! ?he:lolic
Mu 11 e :::- , -:> C . , Engineering prepol:nne=-157-173.
syn':hesis and ar..alysis. J AC....'1.esion ,
Muller, P. C., S. S. ~elley, a=d W. G. Glasser. plastics from lignin. IX. Phenolic resin pe:-!'·~r::iance, .J. F-.C....~esicn 17 ( 3), 185-2C6.
Ni:riz, E. ?i.zzi, .. ~.; -:ech....,,o :.cgy.
1983. ".;'.-l _.._. • I
Lignin-based wocd Wood Ad.">;.esi ves,
Dekke:- !nc., N.Y.
a.C....".:.esi 'les. c::.e~i st::-:.:
-
3..934. re sir:. 7 (2 \
I I
.l. n.: a::c.
32
Nimz, H. E., and G. Eitze. 1980. The appli~at~on 0£ sulfite liquor as an ad:1.esive for particieboa::-ds. Chem. Technol. 14, 371-382.
spe:it Cell.
Nunes, R. W., J. R. Martin, a:-id J. F. Johnson. 1982. Influence of molecular weight and molecular weight distribution on mechanical properties of polymers. Polymer Eng. Sci., Marc~, 22(4), 205-228.
Osberg, H. 1969. Cellulosic polyethemeirnine reaction 827,630.
~aterials treated wi-:~ lign:.n-C an . ? at: . No . products.
Philippov, J. L., W. E. Johns, and ..,., Ngi..4yen. 1982. Bonding of wood by graft polymerization. The effect of hydrogen ~eroxide concentration on the bonding and proper-:.ies cf pa=ticleboa:-d. Eolz=orschung 36, l, 37-42.
Phillips, R. B., W. Brown, graft copolyrnerization Kraft softwood lignin.
and V. T. Stan~ett. 1972. The of styrene and lignin. II.
J. Appl. Poly~. Sci. 16, 1-14.
?sotta and C. ? Forces. Lignosulphcna":e cross linking reactions. 1. The reaction of lignosolphc::i.ate model compoi..4nds Holzforschung 37(2), 91-99.
with dic.zcr.ium sal~s ..
Psotta, C. P. Forbes and H. ii. Nimz. 1983. Ligncsulphor.ata cross.l.inking reaction. 4. ?he cross linking of diazotized lignosulphonate. :-:olzforscl'-.u::;,g 3 7, .l.85-188.
Rowell, R. M., and D. isocyanatas to wood.
~tl.
ACS ";:" 1 , ..; ~ _____ .;i.
,S ympo s i u::t 1981.
Series Bondi::.g o::
172, 263-284.
Santelli, '!'. R., and R .. Wallace. 1963. Organic isocyanate lignin reaction products and ?at. No. 3,072,634.
processes. U.S.
Sanyo-Ko~saku ?~lp
adhesives. .Jpn.
She!"l, ~:. C. ~o-a. - - I - •
Co., L~d. l.982. ?:ienclic ::-es.::i-.~.:..,;::.:.~
Kokai Tokkyc Koho. JP 57128764.
Modified powdered spen':. su.l.fi te as ~.i::.der 38-44.
for ax~erior waferboard. - ~ d ~ .:: c r. = -::o . ..; . l:.c;uo::-24: ( 2) /
1Si7. :or. ?~ed. J., 27(5), 32-33.
33
Shen, K. C. and L. Calve. 1980. A~mcnium-based
sulfite liquor for waf e:r:board binder-. Ad!:esi ves August 1980, 25-29.
spe::t Age,
Van der Klashoist, G. H., C. P. Forbes, and K. Psotta. 1983. Lignosulphonate reactions. 5. The reactions of lignosulphonate and lignosulphcnate model co~pounds with acid chlorides. Holzforschung 37, 276-286.
Wilson, J. B. 1980. !s ~here an isocyanate in your fut~re? Proper~y a~d cost compa~isons. P~oceedings, Four~ee~~~ Washing-con State University International Symposium o!"' .. Particleboa:-d, T. M. Mahoney, Sd., Wash. State Ur.iv., Pullman, WA, 185-194.
Witt~an, J. 1976. Wood bending wit~ isocyanates. ~ol= als Roh-und Werkstoff 34, 427-31.
Wu, L. c.-F., and w. G. plastics :rem lignin. lignin. J. Appl. Poly~.
Glasser. 1984. Engineerir..g I. Synt!:esi s of C.ydroxv-oroo•rl Sci. 29(4), 1111-1123.
34
Table ! . Qualitative properties of pcssible lignin-based adhesive cor.~inations deter~ined in pretria:s.
Adhesive Components
~p
- Isocya:i.ate - l'\mi:le
KE - Isocyanate - Amine
O? - Isocyanate - Amine
S ":''O ..... - Isocyanate
.~mine
AEP - Isocyanate - Amine
E:nulsifiability
peer poor poor
good fair good
fair poor good
fai:-poor good
poor poor poor
*NA - No adhesion
So2..ubility (MEK)
good : . .- a.l ~ : a:. r
good good good
good good good
good good good
poor poor poor
Adhesion Emulsion Solution
fair good geed good
good good good good
N"* • :i. pc or poor poor
poo:::: poor poor poor
NA* NA* NA* NA*
Note: Adhesive =or:nulations contained EC% lig:lin, 40% c::::oss-linking agent, had 50% solids by weight, and were pressed at 150° C, 1000 psi for 40 min. Test samples were 2 in. by 2 in. yellow poplar. Ad..~esicn evaluatio~ was qu.ali~a~ive, i.e. resistance to bei~g pried apa~t.
35
Table II. Standa=C c~~d~t:o~s used in ~he prepa~a~ior. of test samples.
Formulation
Lignin derivative content: (% of aC...."-lesi ve solids)
Lignin derivative (g):
Crosslinking agent (g):
Catalyst:
Snulsifying agent (ml):
Solvent:
?::-ess tine: (::-,in)
P~ess tenpe~a~ure (°C):
?ress oressure (psi):
Emulsion Solu::ion
60 60
18 18
12 12
(amine) 1% of crosslinki~g age~t as ~ecou~ended by manufacture:-
1
Water: 29 MSK: 7
40
150
lOOO
MZ.K: 7 nl
4:0
150
1000
36
Table III. Shear streng~h and wood failure.
0/ 1.1 :' 1 /::I fl • .1.. •
Kraft/ Isocyanates
KP-Isocyanate 93 KE-Isocyanate 91
Kraft/1'.mine K-o - A:nine 60 . KP - Amine 52
CP-Isocyana~e ~2
OP - ;._r:ii :-.e <S
Urea-=o~maldeh1de reference 53
Isocyanate control C'"'
J I
1 -w. ~
- • I wood fai. lt;.::-e.
Solution
c;• ~ 7' S D~ -near ;:;,.- .· .J
(KP a)
723.0 76.7 669.77 6. ' --
542.9 l3 .6 498.4: 2 .7
610.0 69.S
436.6 137. l
~37 .. 2 7.5
825.l 20. 4
2 ~ ---- _.,_ __ .,..... Sno::=:._ S. , ~--~=-... st:::-engt:'1.
3<"" '"' -- ·- ..... ....: ~. u., s~anC=-~ deviation.
Emulsion ~~+-~~~~...,,_~~-1
/~ W.F. 1 Shear S.'- S.D:, (K?a)
34 460.8 ::!.30. 2 83 655.2 43 .2
4.; 441. 5 18.2 so 501. 0 3.5
37 '1..,, -:i - J .l.. - 46.2
0 435. 7 ? • • -..L . .!.
53 437.2 7 .S
95 71:. 7 40.0
1··· CH I '
Y''• 171)
n"Y Otl
Li gr.in
+ 0 ...- CH, -.... I
Ctl I ' CH,
KOtl --~
CH, I TH' CH, I
[') ... ~ R I o-T11,
HC-Oft I CH,
+
C=ti~R-M'=C ----·-··:> II II
.. 0 0
Oi-ISOCJOtlOfP.
~H, yH, ~H,
.-0 R I
O-yH 1 t11 HC-O-C-tl-R-H=C
I . II II CH 1 0 0
llre1t1011e
P1opyltne 0<1de +
~H,
Y"• TH·
llPL
x I
Cll,- o-c11,-N-CH,-O-Cll,
Arnone
- CH,- Oil ----·-----?
Fi!Jure J. lhe react.ion of hydrnxyprnpylat.ed I ignin with an isoi:yanate ancJ an amine ( X is a me I amine).
... (11 R I
0-CH 1 X I I
HC- 0-CH,-N-cH.-o -c11, I
CH 1
~lhcr
w -...J
KflAfT 111 'L -ISOCYANATE ADHESIVE
s.1t 41' tfft(tuifH
(KP11I
·HO
,,, x <' y--.,.;_;/,.,o Y $.;;./'•"
Jo ,l-o t ......,.-' a'l ,t~
.. ..,.o , .. i."'~<;.\
.J
~ .... .t:,-.1' /' ..... ,/r-.,~
l<r!AFT llPL.-AMINE AOllESIVE
$1iflll SlHlttlllM
h<P111
~10
HO
170
.,..../'t~ (0) , .. (. ... >1··-~<_···~. ··~/ ~··· "· ' .
·~ '<' ''-....] y /.>:.-· ·"u ............... ~ ~~· \t.Q
""":r<."".r.r"o''·-....._~'>#'',·i.•>'\\.''' ...... ~ .. - J"~ .Cl ~'
• .,, .... a.-l •"'" -:''
""c,ll
KRi1FT //EL -/SOCY1WME AOtlEStVE
lttf.U; Sllrllf/••Htt
(11.Pq,I . ., 4JO
ll'
~(Bl
/\i;~~
-'o~ X ~· ""!"'...-.,. ... " '-/"" -.............., ,,.o ':,.
• .-.. ,:.: -1;'f.- -'o "'-.... ,.........-;o .,., 1 t. .... .no ,.,1. <c.'
~ ,. I
KRAFT ,lfEL -AMiNE J\OllESIVE
111(.lll 1\ft(MQfM
(k~I
(El
510 ~·.
)-41)
110
" . )i:-· ') 1 ;ljr .,, .
"'""' ,,.,.,,..,- -........, -'-:.~ ~ · ,oo '~~ /.............. .-~·,t}l
"'":1>,4' •• "'"'-.....~~ .. --/",1.Q ,t. ... , ,.. ..... : J'_,~ J.., ':;;:;~ e,O 'If.\.·~~(.\
Of1GMJOSOLV HPL-ISOC'rAMATE ADI IESIVE
)ll(lJlt !l"l'IOrH
(i..Pol . .,
"'
~u.o
ORGAMOSOLV llPL -AMIME ADHESIVE
(Fl
HO
ITO
.•...,.')
riv. 2. Effects of vJryirvJ press c:o11dilions lo shear sli·envtti. (Blocks had standard fon1111lal.io11 as given in Table I.)
w 00
Shellr Strength ( l<Po)
860
6£15
430
215
~::::_---·~"-<-:\ ·~ ·-&
: :~~'\1 (j ~~\.
@
/m --0~@
I ==== ·~----.---·t--t---
•- l<P-1 A-l<E-1 •-OP-I ~-~<P-A
O-l<E-A 0-0P-A
10 20 30 40 50 60 70 00 90 100 LIGNIN DE111VATIVE (%)
rig. 3. [ffect of increasing lignln contlrnt on shear strength. (Blocks had standard solvent based for"ITTlalions as given lnlaul1?!.)
w \0
She or S trenyth
(KPo) 645 10efij'~ fo'rno ____.. ce
0~o~ :..---neferen ,,.,.
...........
430 I ..._ ......
215
_ _,/"'
......
...... --------
..... -· / .............
_,....
~/s\o\'\ ~ \l\\J""
_...,.
fi9. 4. Effect of l l911in type on shear strength. (--- is the UF control, arro\'1s indicate standard deviations)
........ _ _,,.
_,.... ...._
+' 0
Sheor Slrenglh
Md~ .........-:1-...... (KPo) I
1de e 10 -(,c 6'15 fo'll ~e<c ~ ;..---~e urc<Y.
/"" /
/
·130f'-~
2151 1 l / ----/
....... -1. ,,.,.,.
--- / /
--- I / -......./
fi9. 5. lhe effect of liqnin del'ivative lype on shear strength. (--- is lite lJf control, arrm~s indicate standard deviations)
.f:'-1--'
Shear Sirenglh
(l<Po)
645
430
215
..,.... -....
1JellYd;_, /. forf'1° / e t!!!o; ....... fl-;;f e' er1C
-...;; .......
-...... ....... .....
~
/ / .......
/ /
......... ..... / ..,....
fig. 6. lhe effect of cross I inking agenl type on shear strength. (--- is Lile lJF control, arrows indicate standard deviations)
~ N
PART B: Structure-Property Relationship of Isocyanate and Melamine Adhesives for Wood
ABSTHACT
Wood adhesives were produced by the reaction of lignins
from several sources with isocyanate and amine crosslinking
agents to form polyu.::-ethanes and polyethers respectively.
Adhesive samples were cured in vivo within the glueline of
shear block samples. Adhesives were also cured in vitro as
films on glass plates .. The network structure of the in
vitro cured adhesives was evaluated by IR spectroscopy and
differential scanning calorimetry (DSC) .
Variations in a ratio of IR pecks produced by the in
vitro cured adhesives were used to detect crosslinking
reaction products whic!"l i:ldicated degree of cure. Glass
transition temperatures determined for the in vitro cur-ed
adhesives were taken to be related to crosslink density.
Results of IR and Tg analysis of the in vitro-cured
adhesives were correlated with shear strengths of single lap
joint wooden blocks (in vivo-cured) using identical ad-
hesives. Statistically, significant realtionships were
revealed indicating that increases with degree of cure, but
decreases with network density. These results indicate that
some degree of a lack of network incorporation of lignin,
which is tantamount to phase separation, results ~~ a
desirable toughening of network adhesives by lignin
43
44
derivative fracticns. If this toughening mechanism should
be a general requirement of network type wood adhesives, low
modulus lignin prepolymers could become useful components in
conventional resins. Lignin modulus varies with origin and
chemical modification.
45
INTRODUCTION
The previous paper in this series has presented
results on isocyanate and melamine-based wood adhesives
containing a constant 60% hydroxyalkyl lignin derivative
(Newman, Glasser).
This study concluded that the performance of these two-
component wood adhesives was limited by solvent compatibil-
ity if isocyanates were used as crosslinking agents, or by
molecular weight if solubility was not a critical issue.
It had been observed that isocyanate adhesives generally
out perform their amine counterparts, except where soli..<-<
bility became a limitation. Results showed that isocyanate
performed best by itself, without lignin derivative
addition, whereas the particular melamine used (Cymel 303
by American Cyanamide) required 50 to 60 wt % , . . ... ignin
derivative as co-reactant.
Solubility constraints in two-component adhesive
systems result in a network formation process during cure
which escapes control via formulation parameters. Such
parameters as reaction kinetics, phase separation, and
domain size and structure can be expected to vary in
relation to component solubility and cornpatability during
cure. However, network structure can be evaluated in solid
state by such methods as IR spectroscopy and differential
46
scanning calorimetry (DSC) . The objective of this paper is
to evaluate the structure of in vitro-cured adhesives by IR
spectroscopy and DSC, and to correlate this information
with adhesive performance in single lap joints of hard
maple wood (in vivo test).
47
MATERIALS 1'.ND METHODS
I. Materials
The six lignin derivative-based adhesive combinations
described previously we:::-e used (Newman, Glasser). These
were combinations of polymeric methylene diphenyl diiso-
cyanate (PMDI) and a hexamethoxy-methylmelamine (Cymel 303
with an acid catalyst, Cycat 4040) with hydroxypropyl kra~t
lignin (KPl), hydroxylpropyl organosolv lignin (OPl) and
hydroxyethyl kraft lignin 1KE1) . The adhesives were
formulated with constant lignin derivative content of 60%,
in methyl ethyl ketone as solvent.
II. Methods
Cure: In vivo-cured adhesive samples we::ce prepared
using shear lap specimens cured in a hot press at 150°C for
50 min., as described earlier (Newman, Glasser).
In vitro cure was achi-eved with solvent cast films of
each adhesive mixture cured on glass coated with a silicone
oil surfactant, in an air circulating oven at 120°C for 5
min. The shorter temperature and time was roughly calcu-
lated to compensate for thermal insulation properties of
the half-inch hard maple sample blocks with an 11% moisture 3 content and a density of 0.6g/cm .
48
Strengh analysis: The adhesive combinations were
tested as described previously, on 30 x 6.4 x 1.3 cm hard
maple blocks according to ASTH. standard D 905-49. Each
adhesive combination was tested on 5 blocks, and each block
resulted in 5 independent strength tests.
IR analvsis: Infrared analysis of in vitro-cured
adhesive samples was conducted using the KBr-pellet method.
Samples of the cured adhesive films were ground to a fine
powder and mixed with KBr (l mg adhesive powder/200 mg
KBr). Spectra were recorded on a Beckman Acculab 8 IR
spectrophotometer using an external recorder for ordinate
expansion.
DSC anal vs is: Glass transition temperatures (Tg) of
the in vitro-cured adhesive films were determined on a
Perkin Elmer System 4 DSC equipped with auto baseline and
thermal analysis data station (TADS) . The sample was
placed in an aluminum capsule and heated under dry N 2 to
160°C at a rate of 10°/rnin. The sample was then cooled to
ambient and scanned again at 10°/min to 190°C. The glass
transition temperature (Tg) was defined as one-half the
change in heat capacity that occurs over the transition of
the second scan.
49
RESULTS AND DISCUSSION
I. Methodoloav
The cure of isocyanates in an organic solvent in the
presence of a hydroxyl group containing lignin derivative
involves homo- and copolyrnerization. Cure results in the
formation of urethane, urea, allophanate, and biuret bonds
{Glasser, et al., 1983). Each of these different iso-
cyanate-derived bonds has in common a CO group which raises
. 1 . th IR .._ t , -2 0 -l a signa in . e spec 1..rum a ~ / c.:n . This is illus-
trated in Figure 1 Thus, the ~R band at 1720 cm-l of the
in vitro- cured isocyanate adhesives expresses degree of c
cure. If normalized to a non-variable lignin band in the _,
IR spectrum, a ratio of the 1720 cm - peak and the non-
varying peak can be used as a quantitative expression for
degree of cure.
The particular melamine crosslinking agent used in
this study was a methyl ether, which cures by transetheri-
fica tion with other hyd=oxy containing substances in the
prese:lce of an acid catalyst (America:i Cyanamide, Blank,
1979). ':'his melamir:e preparation does not form a horr:o-
polymer under the reaction conditions selected. The ether
resulting from the crosslinking reactior: raises a peak at _,.,
1620 cm - in the IR spectrum, Figure 1 In analogy to the
in vitro-ct:red isocyanate adhesive, the IR band at 16.SO
50
cm-l can be normalized with regard to a non-variable lignin
band, and the ratio between them can be used as a quanti-
tative expression for degree of cure. This assumes that
all ethers have undergone transetherification, and the 1650 -1 cm band represents a transetherification product.
The molecular structure of polymers is most comi~only
evaluated by DSC. The glass transition temperature of
lignin der i va ti ves cross linked with isocyana tes has been
found to be directly related to the average molecular
weight between crosslinks (Mc) , and thus to network density
(Rials, et al., 1984). Variations in Tg of in vitro-cured
adhesives can therefore be taken as quantitative expression
for network structure.
In vivo-cured adhesive performance was determined on 5
shear block specimens per adhesive type, involving 5
independent shear strength measurements per shear block.
One adhesive sample for each of the five shear blocks was
also cured in vitro on a glass plate, under conditions
simulating cure in the maple shear block specimens.
Network parameters of in vitro-cured adhesives as defined
by IP. spec~roscopy and DSC, were compa.:-ed to the shear
strength values of in vivo-cured adhesives.
51
II. Structure Property Relationship
For each of the six adhesives tested there were 5
samples producing IR, Tg and shear strength results.
Figures 2 and 3 are representative of the relationships
found between IR ratio and. Tg o:f the in vitro-cured ad-
hesives and the shear strength results of the in vivo-
cured adhesives. Figure 2 indicates that the adhesive
samples which displayed the higher shear strengths in the
five shear samples also displayed the. higher IR ratios in
their cured films. Figure 3 illustrates that the adhesive
samples displaying the higher shear strengths also had the
lower Tg for their cured films.
To illustera te these two trends for all six adhesive
combinations without the effects on shear strength of such
variables as lignin type and crosslinking agent type
overwhelming them, the data was normalized. The average IR
ratio, Tg and shear strength of each set of five samples
for each of the six adhesives was determined. That average
value was assigned a value of 100%. Each of the :five
sample values above or below that value was di·,rided by
their average and multiplied by 100 converting them to a
percentage of the average.
The relationship betwen shear strength and IR ratio is
illustrated in Figure 4 for all of the six adhesive com-
binations with their five samples, resulting in 30 points.
52
A significant correlation (R 2 = 0.88 as calculated in Table
I) is revealed indicating that shear strength increases
with IR ratio rising. This suggests that shear strength
increases with degree of cure, as expected.
Figu.:re 5 illustrates the relationship between shear
strength and glass transition temperature. A statistically ..,
significant correlation (R ... = 0. 84 as calculated in Table
I} is obtained indicating that shear strength decreases
with Tg rising. Since it is know that Tg of network
polymers increases with decreasing Mc, this observation
suggests that shear strength is network density limited,
and that reduced network density results in greater
strength.
Since shear strength is found to increase with degree
of cure, but decreases with Tg, it is plausible to suspect
that some exclusion of lignin prepolymer from the adhesive
network is beneficial for strength performance by in-
creasing adhesive toughness and reducing brittleness. This
surprising observation can be rationalized on the ground of
phase separated lignin derivative fragments, which serve as
rubbery segments in an otherwise glassy netwo=k adhesive.
Although this observation has many parallels in the
polymer literature dealing with mu~ticompo~ent polymer
blends and composites (Koenig, 1980) I this a ~. ..... :rirs._
indication for lignin derivatives to cont:ibute to proper-
53
ties of adhesives in the role of phase separated polymer
segments.
toughening
It seems logical that the role of lignin as a
agent is controlled by its overall modulus,
and that modulus is a function of both origin and chemical
modification by alkoxylation.
This topic will require further confirmation by
experimentation.
54
CONCLUSIONS
1. Shear strength properties of two-compo!1ent wood
adhesives based on isocyanate and amine crosslinked lignin
derivative prepolymers were found to be significantly
correlated with network structure parameters of in vitro-
cured adhesives. These parameters were described quanti-
tatively by use of a normalized IR ratio and the glass
trans~tion temperature.
2. The relationships indicate that shear strength
increases with degree of cure (IR ratio) and with decreases
with glass transition temperature. <
3. The results are explained with the separaticn o~
two incompatible polymer components during cure with the
consequence of lignin derivative fragments serving as low
modulus toughening agents.
55
LITERATURE CITED
American Cyanamid Co., 1979. Technical Publication 9-2114, 5/79, SK.
Blank, W. J., 1979. Reaction mechanism of melamine resins. J. Coatings Tech. Vol. 51 (No. 656), 61-70.
Glasser, W. G., C. A. Barnett, P. C. Muller, and ;<. V. Sarkanen, 1983. version lignins.
The chemistry of several biocon-J. Agric. Food Chem. 31(5), 921-930.
Koenig, J. L., 1980. Chemical chains. John Wiley & Sons,
microstructure Inc. , New York.
of polymer
Newman, W. H. and W. G. Glasser. Engineering plastics f:::-om lignin XII. Synthesis and performance of lignin adhesives with isocyanate and melamine. Holzforschung, in press.
Rials, T. G. and W. G. Glasser, 1984. Engineering Plastics From Lignin. IV. Effect of crosslink density on polyurethane film properties--variat~on in NCO: OH ratio. Holzforschung 38(4) / 191-199.
56
TABLE I. Regression analysis results for IR, Tg and shear strength data.
Exponential Linear Regression
B =intercept= 85.742 A= slope = 1.537 E-19
for % IR vs % (X)
In (Y) = In A + B {X)
r-square Pearson's r
= .887 = .942
= 2.808 E-2
Shear Strength (Y)
Standard Error of Estimate Significance of Equation: Standard Error of Slope
F = 188.06li with 1, 24 D.F. = 1.1212 E-20
Power Modle Linear Regression for % Tg vs. % (X)
B =intercept= 41447.81 A= slope = -1.303
In (Y) = In A + In B (X)
r-square Pearson's r
= .844 = -.919
= 2.4848 E-2
Shear Strength (Y)
Standard Error of Estimate Significance of Equation: Standard Error of Slope
F = 129.8772 with 1, = .1143
24 D.F.
57
Afv11NE
F~gure l. The effects on IR pecks of ~he c=csslinking reactions of isocyanate a~d amines {a:Kraft EP~, b:uncured Kraft HP~-isocyana~e =esi~, c:c~=eC Kra=t EPL-isocyana~e =es~n).
Shear Slrenglh (I< Po)
OGO
G'I~
430
215
E ---------
t----===-..
"'' "'4
--- .. -//--... f'·---..--0.3 0.8 0.9 ~j
ir~ nalio . ~
__ .,.._
~2
1112 IS
1 IL~ • '°b~ · .J<><i • ,ro
l.Utt!~g~>Hl120 cm.fl
l.Ut~:rllooyl !16!10 1:111 "II
lPtlyol (14'!1 tni•l1
Figure 2. Reprsentativo relationship between IR ratio and shear strength for the individuHl adhesive formula lions. (Kraft IJPL-isocyanate formulation, the ratio is the height of peck 1. in the insert divided by tho height of peck number 3.).
Vl 00
She or Strength (I< Po)
OGO
G·15
IJ 30
215
_! _____ _
f -------------------
r--==--'---- -------·-----
"'2
"I
"'4
-------;------~-----_,,, ____ _ 90 /00 !~ (°C)
.. ,-~'
-----.-------;-----
,, 3
F j 91He 3. nepre~H;;,11 ta tive relationship bt.~ tween 'l'g Lind shear strength for tlw individual adhes]ve formula-tions. (Kraft I!PL-isocyanate formulation).
VI \D
60
140 - 0
I 0 0 0
1201
0 0
0
IR Ratio 0 0 Q
( 0/o of avg.) 0 Q
c Q 0
3 0 0 0
100 0 2 2 0 0 i)
0
80 .l..
l 0 50 100 150 200 250 300
Shear S trenath ..;
( 0/o of avg.)
Figure 4. The :::elationship betw9en IR ra~io and shear strength =or all six adhesive fo:::mulations (the value for each of the five samples per adhesive =ormulation was converted to a percent o: their average values to all0w interforrnulation com-parisons) .
Tg (~,6 of avg.)
120 l I
110 j 1·~0 I v I 90 l I
I ,..L T
0
0
50
0
0 0
61
0 2. 3 2 0 -0
0 g 0 0 0 0 0 2 0 0 0 0
100 150 200 250 300
Sheer S trenath ..J
(0/ ~ ) lo OT avg.
~ig~re 5. The relationship betw9en Tg ~~d shear strength for all six adhesive formulations (tne val~9 for eac!": of the five samples per adhesi'J'e ::ormulation was converted to a perce~t of their average values to allow interfor~ulation ccmparisons}.
PART C: Lignin-3ased :socyanate and Amine Adl:esives for
Particleboard
ABSTRACT
Emulsion-based wood adhesives were formulated from
several types cf , . . ... 1gn1n de~i--:a.ti~./es a::= both a poly:r.eric
isocyanate and a melam:.ne crosslinking agent. :igni~
der:.vative content was a constant 60% of solids; and
particleboards were asse!':".bl.ed wi ~h a ccnsta!"' .. t 5% resi?:
content. The particleboards were tested with re.gard to dry
ar.d wet s-:rength prope:::-ties. Lign:.n deri·.:~ti~ves included
hydroxyprcpyl and hydroxyethyl deri vat:. ves cf k:::-aft ar_d
orga:iosolv lignin. Pol :r.neri c .... . , me .... :i.y ... ene d.:.p~e~yl
diisocyar:ate (?MDI) and he:i::amethoxy-r:tethylmela:nine (r-:M~1IM)
served as crosslinking agents. All forr:tula~ions were equal
to or better tha~ u~ea-formald~hyde ::-es ins, e:<cep~ a
hydroxyprcpyl k:::-aft lignin-isccyanate c·:.r:tbinatior:., •.-1hi=!"- •.,;as
significantly better. Li:niting factors we::-e mclec~lar
weigh-: and solubility in watar. ~Vet stre::gth \'4·as be\:te:-
than urea =or~aldehyde, bu~ ~ever as good as stra~g~t
~socya::ate.
62
63
INTRODUCTION
Each year 40% of the thermosetting resins consumed in
the United States are incorporated into forest products
(White, 1979). Urea for;:naldehyde and phenol formaldehyde
are the two i:taj or wood ad.'1.esi ves, and thei:= consumption
amounted to 1365 and 1537 million pour.ds per year (1979),
respectively (White, 1979). Although formaldehyde based
resins have most of the qualities requi :=ed by the forest
products ind'..lstry, they have several well-knowr. problems.
Despite improvements regarding· for;:naldehyde release from
urea resins (Udvardy, 1979), total formaldehyde control
remains elusi •Je. Because of the recognized hazards to human
physiology of formaldehyde, alternatives to 1.;.rea
f crrnaldehyde ::-es ins hav·e recent:ly been receiving
considerable attention.
!socyanates are difunctional molecules capable of
homopolymerization (in t~e presence of water), anC. of
copolymerization wit~ hydroxy-containing substances, s~ch as
wood surf ace ar.d t.'!'- +-.::. .... V'f=1. --- (Witt.man, 1976). Their per=or~ance
is characterized b~· water resistance (low swelling), l.or,.;e:::
bir.de~ =equi=ements, ==eedom of ado~ i~ se~vice, a~d shor~==
p::ess cycles ( ""9~- .. 1--.;,,,.,,. .;_ """".:,....;.,,.. .. ,, • ._.:iu_._~r:."= -•• --~-= ... e ... m.:.-- capaci ~y). Because
o: 'thei::- superior per:c::::na:ice, a::.d. de soi t.e •""'c.;.,... -.....~ .-~o.,. '-•·--- ··--:t··--price, pol:meric isoc::-·ana-:es !:ave capt:ured :!.ncus":ria.l. fores'(:
produc~s r:.a=~-.:ets :!'l Z:..i::-ope ar:ci Japan ' .. \ \J Ct:.!'lS I 1960). T::ei=
64
supe::-ior performance a.s a wood adhesive is related to the
formation of a che~ical bond (urethane linkage) between the
isocyanate groups and the hydroxy functionality of the wood
(Rowell and Ellis, 1979; Johns, 1980; Wittman, 1976).
Deppe and E::-nst (1977) first used isocyanates i:l
particleboard in 1971. MDI I 4-4 diphenylmet!lane .. . . ... ; - ~he most widely used isocyanate (in ai:!.socyana1..e -"'
aC.....'-":.esi ves) today (Adams, 1979; Rowell, and Ellis, 1979) and
this has a characteristically low vapor pres~ure, good
viscosity and is !."elatively inexpensive compa.::-ed to other
isocyanates. The S';.lpe::-io.::- p:::-ope::-ties of isccyanates over
phenol 0!." urea-::::iased wood aC...."ri.esives well
documented {McLaughlin, 1980; E"ri~k, Sachs,
1977) . Internal bond and water resistance a!."e bo~h greater,
and ove.rall conte:lt can be lower tha:i with
conventional adr..esives (McLaughlin, 1980). At 3 01 lo resin
content, isocyanate beards give the sa~e internal bond
s-tre~g-ths as phenolic boards at 7.5% :::-es.:.n content· (Deppe,
1977). No:::-~al p:::-ess time can be reducd by 30% as compared
to conventional acfr..esives (Deppe, 1977). !socyanates have a
longer 3hel£ they grea'ter e • • ,. c..::r:e::s l cr...al.
stability othe= ad..."-lesives 1980) .
!socyana':es are r:.ot ::eleased :~om and
although ~hey are a sensi':i=ing agent and very ':oxic,
or ~o ~tape:- :-:lease .::a!"l be de-=ec~ed ..; - no~:::al 9=ocessi:ng
65
procedures (McLaughlin, 1980; Frink, Sachs, 1981).
Although .isocyanates have been attractive bondi::g and
crosslinking agents !or years, mo st: applications have
remained li:mi ted to non-aqueous, organic sclve!1t-based two-
component systems. Two ~ajor proble~s commonly encountered
with i socyanates !lave been incompatibility with wate:::-, anc
ad:"l.ere:lce ~i....o -··- developrr.e!'lt cf
er..ulsi fi able i socyana::es r.as alleviated first p:::-oble:m
( McLaughli!'l, 1980; Frink, Sac:is, 1981), a:id caul !"el.ease
agents are helping other (Deppe 1977). Several
examples of emulsifiable a!'ld self releasing
isocyanates on the ~arket.
Processi::g problems st.A.ch as ca:::-rier ccmpa::ibili -:.y a:id
caul release, may scan be eli~inated, but adcpticn of
isocyanates by the forest products ind:.:.s"'i:::::-y may s"t.ill be
resisted due to thei:::- :::-elatively high cost.
The important gap-.:illing ability of a wood adl-:.esive
usually requires ready homopolymerization cf a liquid or
solvent (water) soluble p:::-epolymer. ~his is t~e case w~t~
i.:.::-ea for::ialC.ehyde, phe!'lo lie 1:'esi::.s, and i sccyana -:es a:.ike.
:-:cogni.~ion c£ pcssi~ly !"'.eec.J...ess for:naticn ar:
isocyana~e ~o~opolyr.:e= is the ~asis cf ~~e idea o: addir:q a~
ir:expensive capable bridgi::g isoc:_;ana.-:e
saa!""ch :o= --c:..i.. gap-
£illing polyme=ic
66
necessarily have to be tacky itself) drew atte'!'lticn to
lignin as a multifur.ctional, wood-derived, a~orphous netNork
polymer. As an inexpe'!'lsive and abundant by-product of pulp
and paper making, lignin appeared as the ideal wood adhesive
block compone'!'lt. The use of lignin as an extender
phenolic resins has seen exte!'l.Si7e research activities in
the past, and these have been reviewed recently by Nimz
( 1983) .
Water-solu:ile lignins, ligninsulfcnates ar:.d black
liquor solids, have been· c~osslinked ..... WJ. ._n er:lulsified
ci.iisocyar:.ates '::Jy Lambuth (1981). Unlike lig~i~sulionates,
however, k~aft lig~in and ~ost other non-ion~c lignins a """" --too intractable and ur..rr.anageable in ter:ns of solubility or
ther:noplastic flew to act as a quali.:ied e;{ter:.de::- for wood
adhesives. I::! se:-vice, however, -~c ._ __ _ wate:- solubility of
ligninsulfonates amou!'lt to a severe i:andicap. T~ ... us, .; --'"
seemed prudent to search for other, non-ionic, o:-ganic (a3h-
free) totally or partially water sol~ble and ther~oplas~ic
lig~i~-based ad..~esive extende~s. Such derivatives have
:-ecently !'.:ecorne available in the .:or::i. of alkoxylat.ed
!.ignins, ar..d t;ieir syr.t:~esi s, p:-oper~:..es, ar:d u'":il:!. t:y ~as
been desc:r!bed elsewhere ( Gl.asser at al. , 1983) .
the gap-fill.!::;.g !'t.:.:lc~!c::. cf wood bir:.ders can. be
ful.:illed l:y lign!:: blocks connec-::ed by adhesive :ioLec"-J.les,
~he:i -::-:.a ad..."-lss:.~1e assumes t::e :-ole of a crossli:ik:.r.g age:!.1:.
67
In .... . . ... ni s case, ability to hcmopolyn:erize becomes a deterrent
to the interaction with the cheaper lignin block. Thus, a
crosslinking agem: capable only cf copolywerization (with
hydroxy-containing cosubstrates) and unable to
hornopolyme:::ize, becomes the ac.hesi ve component of choice.
This is available as methyl ether cornpo=:em: of ~elamir.e
(hexarnethoxy-me-chylmelamine, E?'!MM). • 1 • . ~· e.:.a?n:.ne a cost-
advantage over isocyanate, and is used ccmmcnly i!"l the
textile industry (American Cyanamide Co. 1979).
with other hydroxy group containing components ..... -.ne
presence of an acid catalyst by ether interchange. Me t.:'1a.::.o l
is generated as by-product :.n this reac~ion (America~
Cyanamicie Co. 1979, Blank 1979).
Previcus a::.d cornpar:.ion research on lignin-based wocd
adhesives isocyanate and cor:ipor.e::;:cs as
crosslinkir.g age!"lts, when applied as spreadable ad.";,esi ·.le Or'.
single lap joints resul~ed in four conclusions (Newman,
Glasser, :.n press). (a) Useful adhesives can be .:o::::-mulated
in wa~er and organic sol vent-based resin syster:.s :::-esul ting
in stre:i.g~:i prope:::-ties superior .:o · u:::-ea fo?:":naldehyC.e. (b)
~~e replacement of up to 60% isocyanate by lignin de:::-ivative
results i:l cr:.ly app::::-o;<:imatel y 20~' ::::-eduction in s~reng~_:i.
amine c:::-csslinki::g age:i.t en ... ;.. "" '--·- ether ha:id,
pe:::-.:or:s bes~ wi~h incorporatio~ of 50-60% lignin derivative
68
co-substrate. ( c) ?erforraance l.ir:ti ta tions of the lignin-
based adhesives were reccgnized to result from either
carrier incompatabili ty or, in t•,..,,.,, case of compatabi li ty
with the carrier, the molecular weight of the lignin
starting rna~erial. (d) Low water resistance was recog~ized.
':i:'he objectives of ":his study ccr.cern the evaluation o=
the performance of an ernulsi=ied ligni~ isocyanate and
lignin amine resin as particleboard binder :n relation to
type of c:-osslin:-:ing agent, type of lignin, and type of
11.g~.- ... ;n ~,.,,_~_1··v·a~_ ... •.,e. -~~~-~ ...... •cl.ebc~~-c.· res•n co~-,.,,~- (5%) a-~ ... , .... v - - -· ......... _........ 0 ........
ligr..in content of solid binder (60%) re~ained constant.
69
MATERIALS .t.. .. ND ME'.:'20DS
I. Materials
1. T • • .._ ~ignin componen~s: The lignin components used
included hydroxypropyl a:-.d hydroxyethyl lignin derivatives
from kraft lignin and from organosolv lignin. Kra::t l:i.gnin
was obtained from the Westvaco Corporation, Charleston, SC,
under the trade name of T. • 1 , .nc.u ...... n .'A.T. Organosolv lignin was
obtained from Biological Energy Corporation, Valley Forge,
PA. Kraft lignin was obtained from pine chips, ar:.d
organcsolv lignin was isolated from aspen chips. Beth
lignins have previo~sly been characterized in ~erms of their
chemical characteristics and molecular structure (Glasser et
al., l 983) . :-:..e hydrox:,.,rpropyl lignin C.eri ?a-::i ves of :Ooth , . . .Llgn1:-.s were prepared wit:i aqueous al~ali at room
tempera tu re, as described previously. 3ydroxyethyl kra~t
lignin (KE) was obtained from an t.:.niC.ent:'..fied source as a
pi lo.t pla!'lt product as a non-ionic, water soluble po ly:t'.er.
2. Crosslinking Agents: Polymeric me~hylene diphe!'lyl
d.iisocyanate (PMD!) was a cc~ercial prcduc": obtained u:r:.der
the ~racie ~affie Isobind 100 =rcrn the Upjohn Corpora":ion. ~he
~elawine was a nexamethoxy me~~yl melamine corrnercially
available as C~'1':tel 303 by Cyanamide.
catalys~. Cycat 4040 by Cyanamicie.
........
.:.. ..... ::-eq~i:::-es ar: ac:.d
3. ?- ,...+ ~,.. i Q ._Q, ___ ._ __ - . . _ .. ,~.., ... -~ . .... ...... _ ...... - -=-- . !'l-":e a~ti.c les used. we:-: :;a" Ea=~er~~ll sou~~e~~ yellow pi~e ch~ps. :':~e:. = ::-.o i s~:.:.r~
70
content was 10~~' and the chips we::-e screened to 1/16 " to
remove the :inds.
4. Urea Formaldehyde ( UF) . Reference ?.cL"-lesi ve: For
reference purposes, a UF resin manufactured ~y Borden
Chemical ("Casco-Resin SH") was used according to the
manufacturer's instructions.
II. Methods
1. AcL.~esive Formulation: The hydroxypropyl lignin
derivative (18g) was dissolved in r.:.ethyl ethyl ketone
( 7 , ) . i . i ... h 1 . k. +- ( 12 ) rn_ ana m_xea W-~ a cross in. :.ng agenw g rnai. =~:~aini ng
a 60% lignin content. 7his solution was added to water (29
ml) contain~ng the ernulsi=ied c~~sslinki~g agent in a hig~-
speed blende:::-. The hydroxyethyl lignin was r..ixed directly
with t:':;.e emulsified crosslinking age::1t in t.he blende:::. More
procedural details for mixing the acL'li.esive for=nulati::ns a:;,d.
asserr.Dly condi ~ions are given in a cor.:.par..icn pape:::- ( New"1an,
Glasser, in press).
2. ?article Mat Asser.~ly and Cu:::-e: ':he adhesi -;e ( 3 S
ml , . . ... :.gnin solution, 29g ligr.in derivative in 7 ml of M=:K,
suspended in 29g of water) was sprayed under cressure at a
=ate of ~oughly 3 ~l pe~ ~~~ute onto ~~: fu~~ish, 540g a~~-
dried, which was being rcta~ed ~~ a c=urn to assure a~ eve~
.:,,. ..,..._..; c:::;., .... .,._ ··--·· was pre-presseC. into a
l.O" x lC, 000 lb load.
71
and 1000 psi.
3. Stre:i.gth analysis: Static bending tests W,,..,....,, ---conducted accordir..g to AST~1
... . . s ... anaara 1037-78 on a .T!nius
Olson testing machine. The recommended sar.iple length to
thick.~ess ratio was not used due to press size ccnstrai~ts;
instead o: tl':.e recommended 15" sample specimen, a 10" sample
was used. MOE and MOR were calculated according to -~Q ._ .... -procedures set forth in the standard.
Internal bond tests were conducted as recommended i~
ASTM standa::-d 1037-78. A pure polymeric !socyanate was used
as t!:.e plate ad.....,,esive.
4. Boil tests: The 4 and 24 hour boil tests were
conductec as rec9:n.-nended in .;S':'M sta~dard :Jl03 7-78a.
72
RESULTS .:U-l'D DISCUSSION
I. Aci."'-lesi ve Formula ti on and Testi:::g Method:
The adhesive formulation technique employed in
study was adopted from e ::: ... , , .:...--· -~-- work on spreadable ad..."1-iesives
using single lap joint shear block tests (Newman, Glasser,
in press). :::i ~he previous work, optimal conditions had
been . .- . .. ce::1nea. regarding ad..."'-lesive 't .,; - .- • ~ co!T'..o"'"n~ ,_10 .. s,
co~di~ions and lignin conte~t.
·Particleboard specimens were asse~~led and c~red ~nder
standard conditions, and these a ... .,,. summarized in Table I.
T!le boards we"?:"e prepared with a cor.stant acU:esive solids
content of 60~~ The solids content :::nils if i ~d resins
was 50%. Chip mois~ure content was 10%, and a ma~ moisture
con~en': of resulted after adhesive spraying. The
time was a constant 9 min. .: 1 • . , . ~o-~ow1ng a c~os~r.g time
seconds, as com.'ncnly used for s~:nilar
!:oa:::-ci.s. ?ress temperat~re was a constant 150°C.
'!'est particleboards with the dir:tensior:.s of 10 11 :< 10 11 7.
0 ~" • .:> were su!Jjected to a standard . . . oenc.i:lg test, which
dete=~i::es rl!OE anci MOR, a!"ld a s-:.anda~·:i i::ter~a.l bend testi::g
procec~..ire. 1 - additio~, all boa~~ samples we~e subjected ~o
a 4 and 24: hour
S"w'el.:.i:lg.
i~. 3oa~d P~cper~ies:
A. Stre~g~~ ?~o~erties
73
The strength prope::::-ties of the boards asser..bled with
the various adhesive combinations are given in Ta'.::>le II.
Properties were affected by lignin type, lignin derj.va~ive
type, and crosslinking agent type.
1. 2ffect of lignin type: Xraft vs. organosolv 2?L
The results of MCR, ~10E, ar;.d internal bond strength
deter~inations of adhesives derived fron kraft F...?S (~?) and
organosolv· E?L (OP) lignins cross linked with isocyanates (I)
and ar:iines (A) a=e shown in Figure 1. A reference strength
level for a urea-fcr~aldehyde (UF) sample is indicated by a
refere~ce line. Only the ie?- I ad...':ssi ve combination proved
to be significantly higher tha:::: t:::e urea control in all
categories cf s-c:-eng~n. Jl.ll c~~er ad:;.esives were
appro:--:i:nately eqt...;.al to i-, .... :ie re.:e!'"e!'lce.
In shear block tests (Newman, Glasser, in press)
er:n.:.lsification significar:tly ?:educed the k::.-aft based.
ad...'1.e s i ve per-f or:nance corr.pa::-ed to its effect on -+-" ._."le
organosolv based ad.1":.esives. Spray applica'tio:;. of ............ .:::. ....... _ emulsified ad...~esives reduced the d:t=ime~tal e=.:ect of
emulsifica~io~ or. the k=aft based ad...~esives.
':~e superior:. t~l ·=>f -c:ie k~a.ft EPL de=:i.,.J'a~i~re as ::or:'~pared
to t!ie ccr:-:sponding o:-ga:tosol·"· product. ~ust be a-:-:ri~uted
-:.o mo2.ec~la!" ~11:ig~t. charac~aristics. That ~.:.g:i wolecu:.a:-
wei.gl':t li-;~i:: based adhesives ::reduce st::::-o::.ge!:" ~c~ds than
101-,; :rLo:ecula:: weig~t. lig::i.~ :!"ag::-.e~.;.-cs has :-:ee=-i ~Cse~·1ed.
74
. , . ,.,.. . t 1 (198~) previous_y oy !alx e a . ~ ~ .
The greater strength of the KPI adhesive· may also be
due to unincorporated l . . _1gn1n de!"ivative molecules (sol
fraction) serving as plasticizers in the adhesive network
structure as discussed in an earlier pape!" in this series
(Rials, Glasser, 1984a and b).
2. Effect of lignin derivative type: 2?!:. vs. :I:C:L:
The chemical modification of lignin with ethylene oxide
produces hydroxye~hylated derivatives with primary hydroxyl
groups as principal func-:ionality, some chain extension and
high degrees of substi~ution (Glasser et al., 1983). Kra.:t
EEL is wate= soluble, and this is indust=ially available as
a non-ionic industrial su:-facta~t. By contrast, 1-:=-a=t. ::?L
has essentially no chain extensior.. and lower degrees of
substitu-:ion. I-: has secondary OE groups as principal
reactive sites and is generally not soluble in water.
The results of streng-:h testing are given in =igure 2.
All acfr..esive combinations, e:-::cept the KP-A cc:n.bination which
_'las a slightly lower MOR value,
s\::rengt!l characteris'tics s~pe::::-io:-
produced ad.°'lesi ves
-:o tr.a-: o:: -~o "-·A-
W.;.;-i,... - ._.:.,
!_; !!
:-:fe~e~ce -:,.;i -:.n t~e e:-::cep~:.on of -'h"" ._.., __ O?-A 1 • ..-I'..:. c:i. was sligh";:2.y
~ower. i:::at. tl1e KP-I ad::.esi·,,re was s~!'"o~ge:- t!lan -:he KE:-I
prepara~io~ prese~ted a s~r?rise,
results ,... ... ....... sir:.gle lap . . . . J o:.n";: 3.nea:-
c: spreaC.able ad.hesi -:.tes, a ~..,._~c::.: -:·Q ~·---, _
a~d this co~t~adic~3
~lock -:.est3. I:: -=;:e
--.:. ._ .... ._
ca:se
pe:::-=orT.a~"'ce ~.vas l:.:n:. -:.ad by
75
solubility and with water-based
formulation. Sprayed adr..esives are appa:-e::.tl~l less
sensitive sclubi li ty and co:r.patibi li ty. This may be
explained with the more uniform ccrnpone~t distribution due
to s9=ay!ng wnicn tu=~s the =~~lsion into a fi~e mist. ~he
ami:::i.e-based ad::.es::.ves, by contras"':, performed ~etter if <::'.:".ey
were f or:r.ula-ced . .._. W11...."'l a kraft preparation
with kraft ::";) i ·-- w
de!"ivative. KE-A produced O!'ll V
unifcrmily miscible resi~ fo~~ulation tested.
3 . Effect of crosslinkir.g agen"t "':ype: ?MDI ·.;s.
:'he result:s of dry tests of i socya:;.a "':e a::c
amine bended particleboards a:-e illustrated in E'ig--.lre 3. r .... . .... is apparent 'cha<: the isocyanate-based binders, K?-I a::d C?-
I I produce stronger pa!'"ticle boards than co=responding
amir.e-der~ved products.
The greater reactivity of the isocyana<:e groups, thei:-
ability to homopolywerize and to bc:-.d to wood s~r.:ace
bridge wide gaps may have contri~uted to t:ie superior
s·t:-engt!: o= ~he pa~t.:.c1e:;oa::d produced ~y ~l:.a isocyana~e
cross l :!.:iked ad.:"'le s i ~le. super:. or:. t.y cf isocya~a.-ce
sys~e~ i~ an aq'~eous e~ulsicn was not precic~ed on ~~e basis
of ~~e s~ear block tests.
ad..'-: es:. ves perf or:ned ec~all ... , - - fo:."":nulated as aqu.eous
er::t:.l. Si 0:1.S. wa ::e::: :. soc;;a~a ~es
76
seen in the shear block tests was'reduced by the method of
adhesive application used in the particleboard production.
The fine mist spray procedure used to apply ad..~esives to the
wood chip furnish resulted in more intimate contact between
isocyanates a~d the wood.
B. Wet Strength Properties
Table ~II presents the results of 4 and 24 hour boil
tests of particle baords ~ade from the six di=ferent lignin
adhesive combinations. Swelling da~a. reported
percent cf the original dime~sio~s of the sawple block. The
data show that lignin introduces moisture sensitivity. The
k:ra.:t :Cased aC:.esives produced particleboard that had
superior water :resistance as ccrnpar::c. the organosolv
based ad.11.esives and t:"le UF co:.:-.trol. The E?-based adhesives
had g~eater water resistance correspor..ding
products. The samples prod~ced with the a~ine cross:inki~g
agent and the u- control all disin~eg:rated during -::he 24
hour boil test. High molecular weight, low water
solubility, and crosslinking with diisocyana~es all serve to
increase moisture resis~ance. Low r:i.ois-:ure
si:nilar to ~as been noted previously
?:esistance,
l ..; ,_...._.; --~-::··-·-
isocyanate co;n:,inations (Newrna~, Glasser, i:i press) .
appears ~hat it -::akes greater co~cent=aticns of crosslinki~g
sc1'.1ble lignins. High :::-ossl.in.~: . . . c.e::s:.. -::.es are
77
result in brittle glasses with high modulus but reduced
adhesive strength. Thus, it might be difficult to prod~ce a
wa"ter resistant ad...'1-iesive from lignin with sufficier .. -:.
toughness.
78
CONCLUSIONS
1. Emulsif iable and partially-emulsifiable
derivatives can replace as ~uch as 60% of a polymeric
isocya::ate adhesi ·.;e in part:icleboa:::-d binders (at constant 67~
resin content on wood).
2. nexar;.ethoxy-nethyl melamine, S·!MM, is an optional
water-borne crosslinking agent, less costly than isocyanates
but producing resins with slightly lower ad..."'-lesive strength.
3 . Neither cure t:empe!"'a -cu.re nor press
change as compared to standard urea formaldehyde boards.
4: • Lignin causes swelli:-.g, much more t.:ian r.1.e at
polymeric isocyanate, but gene!"ally less tl:an urea
formaldehyde.
5. Strr:?r.gt:'1. prope:-ties depend or: li.gnin type, :..ig::i:.n
de!"ivative type, and crosslinking agent type. Eowe't..rer,
sprayed ad..."-lesi ves are not as to solvent
compatibili t:.y as was observed for spreadable resins. T!':.e
effect of molec~lar weight differences re~ains the same, --~ c:::i. ........
this indica~es a superiority of the hig~er molec~lar weight
lig~i~ prepa~at~ons.
79
REFERE~ICES
Adams, A. 1980. Emulsifiable MDI isocyanate binde!' particleboard and waferboard. Proc. Particleboard. 195-204 (1980).
for 1 a. - - I
American Cyanamid Co. 1979. Cymel 303 Techr:.i ca 1 ?ublicaticn. 9-2114 5/79 SK.
American Society for Testing ar.d Mate::::-ials. 1974. ASTM 01037-72. Standard methods for evaluating the properties of wood-base fiber and pa!'~icle panel ma~erials. ASTM, Philadelphia, ?A.
Archibald, E. 1982. Formaldehyde's Future in P..cL.'1.esi "Jes. Adh. Age, July 1982, 27-30.
3all, G. W. 1981. New Opportunities in Manufactu::::-ing Conventional Particleboard Using Isocyanate Binders. Proceedings, Wash. State Univ. I!'lt. Sy,-np. en Particleboa::::-d, 15, 265-285.
3lank, W. J. 1980. Reaction Mechanism of Melamine Resins. J. Coat. ~ech., 51(656), 61-70.
Browning, 3. L. 1973. The Chemistry of Wood. P .. cber~ -Kriege!' ?ublishi!'lg Co., Eungtington, NY.
Deppe, H. J. 1977. Technical progress in using isocyanates as an ad..~esive for particleboard manufacture. ?roe. Wash. State ~niv. Symp. on Particleboard. 11, 13-31.
Faix, 0., W. Lange, and E. C. Salud. l981. use of EPLC for the determination of average molecular weights ar:.d molecular weight di s1::::-ibutior:.s of :nilled wood spri..:.ce lignins from Shorea ?olysperma. Eolz::orschu::g 35 ( 1), 3-9.
2rir:.k, J. w. I
for wood 285-309.
. ~ ana ·-· !. composi-:e
Sachs . beards.
1981. .;cs
Isccyana~e binde~s
Syrr:p. Se~ies 172,
Glasser, W. G., ~. C.-2. Wu, and J.-2. Selir:.. 1963. Syr:.thesi s, structure, and some -orot:>erties of hydroxypropyl lign.ins. Wood and Ag:::-icul tural ?.esiC.ues -Research on Use =or Feed, Fuel ar.d Che~icals. Academic ?:::-ess, New York, NY.
Glasse!', W. c. 3a.rnett, ~ C. ;(. \.7. Sa:::-kanen. 1983. T::..e cl'lem:. s t.!"y of several novel
80
bioconve:::-sion lignins. 921-929.
J. Agric. E'ood Che;.i. 31 ( 5 ) ,
Glasser, W. G., V. ?. Saraf, and J.-E'. Selin. ::..981. The utilization of lignin as a bonding agent for cellulosic fibers. Org. Coat. Plast. Chem. 45, 551-555.
Glasser, W. G., 0. H.-B. L. c.-F. Wu. polyisocyanates and 172, 311-338.
Hsu, D. L. Reed, R. C. Forte, and 1981. Lignin-derived polyols,
polyurethanes. A.C.S. Syn'.p. Ser.
Glasser, W. G., V. ?. Saraf, a:r..d W. E. Newman. 1982. Hydroxypropylated lignin-isocyanate combinations as bonding agents fo:::- wood and cellulosic fibers. J. Ad..~esion 14, 233-255.
Glasser, W. G. 1981. Potential role tomorrow's wocd utilization technologies. 31(3), 24-29.
; .... -·· of lignin For. ?rod. J.
Glasser, W. G., ad..'"-lesives and 9(2), 97-103.
and 0. H. -E. co·at:.ngs from
Esu. 1976. Polyurethane ~edified lignin. Wood Sci.
Gould, D. F. 1959. "?he::.olic Resir;.s", Reirili.old ?ubl. Co. , New York, NY.
Eickson, C prese!'lt,
H. 1976. Particleboa.:-d P..dh. Age, Sept.
adhesives, past, 1976, 16-27. and fu'ture.
Johns, W. E. 1980. Is 'there an isocya!'late in your future? Chemical Aspects, Proc. Wash. State Univ. Symp. on Pa::-ticle:Oca!"d. 14, 177-184.
Jor.ns, W. E. 1981. Isoc7J'anate 3inde:-s for ?articleboard Manufactu.:-e. Proc. Wash. State Univ. Int. Symp. on Particleboa:-d, 15, 213-39.
La~~uth, A. 1981. U.S. Pat:en-c No.
Aqueous polyisocya::.ate 4279788.
J.1. gn:..n ad.!"i.e s:. ~1-:.
Ma:-ti::., ?.. W. 1958. "The Che:-=i.is"t:-y of P::..e:::olic Res·ir.s", Eutte:-worths, London.
~l!cLaughli:l, A. Reconstitu<:ed
1980. "Polv~eric Woods ?:-odu.ct -Binder!',
Isocyanate Proc. Wash.
Univ. !~t. St~P- en ?a~ticleboard, 14, 207-11.
as a Sta~e
A. :.980. Polyr=ier:.c :. soc1·ar:.a. tes as '.NOOC
81
binders. Proc. USDA Forest Se!"vices Adh. s yrr.p • I
Madison, WI, Sept., 23-25.
Meyer, B. 1979. Urea forr:\aldehyde resins. Addison-Wesley Publishing Co., Inc., Reading, MA.
Moorer, H. H., W. K. Dougherty and F. Synthetic lignin-polyisocyanate resin. 3,519,581.
J. Ball. 1970. U.S. Patent No.
Moslerni, A. A. 1974. Particleboard, Scuthern University Press, Carbondale and Edwardsville,
-, , . . .1. J...~.:..no::.. s
IL.
Nestler, Max. 1977. based produc-cs. Report E'PL-8.
The USDA
formaldehyde oroble~s
Forest Service General ir-. wood-Technical
Newman, W. E., and lignin. XII. adhesives with submited.
W. G. Glasser. Engineering plastics from Synthesis and performance of lignin
isocyanate and ~elarnine. nclzfcrschung,
Ni::iz, E. :::. 1983. Lignin-based wood adhesives. Chapte::- in Wood AC..~esives, Chemistry and Technology, Pizz::.., A., Ed., Marcel Dekker, Inc.-, NY.
Rials, ~ G., and W. G. Glasser. l964a. ~ngineering
plastics from lignin. IV. E!"fect of cross link density variation on polyurethane film properties-Va.:::-iation in NCO:OH ratio. Eclzforschung 38(4), 191-199.
Rials, ~ G., and W. G. Glasser. 1984b. Engineering plastics f:ror:\ lignin. V. Effect of cress link density variation en polY'..Lrethane fil:n prcpe?:''ties-Variat:icn in polyol hydroxy content. ~olzforschung 38(5), 236-2~9.
?-ice, James T. E?aluation of emulsion crosslinked polymers as adhesives ?resented at the 34th Anr.ual FPRS Bosten, Mass.
D. Ellis.
based isocyanate-for wood gluing. Meeting, July 7,
l979. c: ..... emical Rowell, R. M., modifications
and W. of wood. Wood Science 12(1), 52-57.
Udvardy, 0. G. wa.:erboard.
1979. Evaluation of isocyanate .o:..::ce:.-S :_nnp.
for
Particleboa::d.
1979. ad::..esives 3.r..d
?:-cc. Wash. Sta-:e 13, 159-:.77.
Growing C.ependency of o~:i.er ~he::i.icals. =or.
tJn.: ~,. or:
N"cod !=:r:Jducts en ?:-Qd. J. 29(1:),
14-19.
Wilson, J. 1981. composition board.
82
Isocyanate adhesives as binders for Ad.~. Age, May 1981, 41-44.
Wilson, J. B. 1981. Is there an isocyanate in your future, property and cost comparisons. Proc. Wash. State Univ. Symp. on Particleboard, 14, 185-194.
Wittnan, W. 1976. Wood bonding with isocyanates. Solz als Roh und Werkstoff 34(1976), 427-31.
83
7able l. Standard particleboard mat anci board preparation parameters.
Target Density: Dimensions (c:n): Resin Content:
3 64:0 kg/rn 25. 4x25. 4:{2.. 3 ..
6% Resin Solids Content: 50%
Content: 60% Resin Lignin
~'!.C. o! chips: M.C. of Mat: M.C. of final boards:
Press time: 9 mir: Closing t~me: 45 sec Press Te~p: 1S0°c
i a.01 - -lo
6%
84
, Table II. Strength properties of particleboards- .
IB S.D. MOR S.D. MOE S.D . . ;dhesive KP a KP a KP a KP a MP a MP a
KP-I 26.l 6.2 1Q37 162 1-L!. t:) - 23
KE-I 25.5 - L!. ::i. - 1030 130 153 18
OP-I 24:.9 3.9 1014 134 159 19
KP-A 23.6 5.3 1003 129 , =:, _ _, ... 20
K::!:-A 24.6 2.6 1009 :.oo 152 9
OP-.~ 23.3 3. 4: 996 126 149 19
Urea-for~aldehyde reference (UF) 23.6 3.0 1007 120 150 14
Isocyanate control ( I) 38.6 0.8 1112 83 177 0.8
1 1\ 11 b . . d . ,.ol • ...... ,..., • • . ..... • • n oarcs procuce i~ acccr~ance w1~~ con~itions sta ... ec ~n Table I.
2 -~ I ..... . B d l.~- n ... e:::-na..:. on MOR-Modulus of Rupture MOE-Moduli..:.s of Elasticity SD-Standard Deviation
85
Table 3. Boil test results (% swelli~g)
Ad..."ri.esive 4 hr 24 :hr (%) (%)
KP-I so. 13 13
i<E-!so. 25 31
OP-I so. 35 4:5
K?-A."!tine 25 F
K~-A.'T.ine 28 F
OP-Ar.:i~e ~ F
Urea-f or.naldehyde reference 40 ·~
Isocyanate cont::-ol 0 4
-~
------·
fi9. I. The (ffec:t of L ig11in Type on Adhesive Strength Properties.
00
°'
I 13 o<ro)
fifJ. 2. The Effect of Lignin Derivative Type on Adhesive Strength Properties.
00 -...,J
..,., ..:: w
L'• .....
r.; -;
!?
,....,
<=
...,
..... ...., r;,
" .... ;
0 ;::;
...., ..,
('")
.....
0 I'
~ V>
V>
V>
~ "' <.::> > ..::
ro "' .... __, '<
"C
ro 0 = ~ r: v.
< ro
\
88
The vita has been removed from the scanned document
