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Production of alkyd Effect of catalyst on
resins and their paints: their properties
D Doulia, S Rokotas and K Georgopoulou i
Chemical Engineering Department, National Technical University
of Athens, Zografou Campus, GR157 80, Athens, Greece
Keywords ,~\i~,yd resin catalysts, film prope! tie's~ paints,
physicocherr~icai p!o.~el tiesr p! ot.ess tir'e
Summaries Production of alkyd resh~s and their paints: Effect of
catalyst on their properties
Modified aiq~d resins were produced b}, aicoholysis of soya bean
oil with pentaer?h! itol followed vdl I . lJ~ caEaiysts with
different cc, rents, by esierificatior! with penfaerythlito! and
p.htha!k: anhyd!-icie "~-;,- ~ .
including LiOq, bub4 tin oxide and dibutTi tin chiorid6 were
used for aicohoiysis anti/or esteri,ica tion reactions. [he effect
os the catal)st or, rise reduction o r the process time of alk'/ds,
and their physicochemicaJ and Film p!.pelties, wel e investigated
>.nd evaluated [he cablvtic s}~stern iiOH 00/% - dibul?i tin
chloride 02% proved to be the best catalb, st s?stern foiio~,~ed by
LiOH 0.07%. ]he coaiing fihr~ characteristics of t~,~,o paints, r
with selected a!{',~ds, were measured and compa-ed
La production des resines alkydes et de leurs peintures : elfet
d'un catalyseur sur leurs proprietes
Des r~}sines aikjdes modifi@s ont et#; produltes gr'ace 8
i'alcooiyse de l'huiie de s';,ja avec is pen tael },th! itoi suivi
de i'(S.slerification avee ie pentaer,,4hritol et i'anhvd! ide
phthaiique Piusieurs catai- ,,~seurs ayant de dif.~rents contenus,
v cor~pds LiOH, i'exyde de ;~ub;h}tain, le chlerul e de dibutyi~.-
bin, orit ~te uti!b(,s pour i'alcooi'>,se et/ou i'Oste~
iqcation, i'effet du cata!?seul sur ia dh-~in~stion du tents du
process.s des aikydes, st sur burs propri~.tes ph),'sicochimiques
et de film, a eta} etudie. Le s},,steme catai)'tique l..iOH 0,07%
ch!oru!-e de dib,[email protected] 0,2% s'est r~ontre is reel!bur s}'st@-qe
catal}s s.,ivi de iiOH 0,0/% Lea ca! acteristiques de film de
rev~tement de deux peintul es qh.~i ~.taient -u~ mul@s avec des
a!kjdes seieetionn0s ont eta} rnesu~@s et compa~ @s.
Die Produktion yon AIkydharzen [md ihrer Anstriche: Der Effekt
yon Katal[yse auf ihre Eigenscha~ten
bloclifi,,ierte s wurden hergestellt rnittels s yon 5o2s mit
Pentaer'tthritol ur]d nachblger!de~ Esterifizie! ung rail:
Pentaervth itoi und Phthalisch~.n s idt.n. ~9'iI ve~ wen@- ten
verschiedene ~f, ataiysatoren mit unterschiediichem inha!t, z.B
i_i014, Butylzinkoxid .nd Dibut),!zinkch!orid, ~Jr die Aikohoi},se
und/oder dis Esterifizielung, und studierten die Wi!-kung des
F,~ataiysators slf die b!ersteiiungseit del /-'Jkyde, ih!e
Ph'fsiochernie und Fi!rr~eigenschafien Ein .'/,~atai?satorsystem
bestehend aus LiOH 0.0/% und Dibusr163 02% stei!te >ich als das
efiektivste hera~Is, gefolgt t~on LiOH 0079.8. Die,
Filmeigelsschafien yon 7','~,ei k31 ben die mit aus- ge~,,,9.hiten
Aik)'den hergeetei it wul cien, ve!den gemessen und
vergiiche~s.
D DeLliia, S Reketas and g Geergopeubu
Chemical Engineering Departrrent, ~',ationai Technical
Ur!iversi,:}, of Athens, Zoglafou Campus, GR..!57 80, Athens,
Greece
-el: +30 2! 07723122 Emaii: ddouiia@chemeng ntua.gr Fax: +30
2!0,,723163
Cepydght OCCA 206,6
i
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Introduction The polyester obtained by the esterifica tion of a
polybasic acid with a pol3&ydric alcohol is commonly referred
to as an alkyd resin. A typical member of the alkyd resin family is
made fi'om phthalic anhydride and maleic acid, and glycerol m~d/or
pentaeuthritol and/or other poly ols, The resins are hard and have
very good stability, gloss and gloss retention, weathering
resistance a~d fast--duing characteristics, Due to the low chemical
and alkali resistance, the alkyds are usu- ally modified with
monobasic acids or oils such as soya, linseed, coconut etc,
constituting the main volume of alkyds in production. ~ Their main
difference from other polyester resins is that they contain
unsaturated fatty acid side groups}
The basic reac~ons of processing alkyd resins via the
monoglycetide process are: alcoholysis of the oil by a part of the
poiyol used, and esterification by a polyacid and the remainder of
the polyol, The oil and part of the polyol are mixed and heated to
a temperature between 240 and 270'C in the pres- ence of a catalyst
which is generally alkaline (eg NaOH, KOH, LiOH, CaO and PbO), oi"
without a catalyst ff the reaction proceeds at around 270~ s,4 The
quantities of the catalyst used are around 0.01 to O.05%w/w with
respect to the oil. The mixture obtained from alcoholysts contains
monoester (more than 40%, irrespective of the reaction conditions),
as well as diester, triester and glycerol. The monoglyceride con-
tent is sufficient to homogenise the reaction medium and allow the
process to proceed to the second stage, Mono- glycerides and
diglycerides, generated during the first phase, take part in the
polymerisation by undergoing numer- ous transesterification
reactions. Esteri fication is operated either as a catalytic
process (faster and milder temperature conditions) or a
conventional high tern perature process. The selection of the
catalyst is based on its effectiveness and on economical criteria.
The catalytic esterification process yields alkyd resins with a
lower viscosity (lower average molecular weight) and better results
are obtained by preventing the resins from gelation compared with a
high--temper- ature process under the same reaction conditions/:
Various catalysts have been used for the esterification reac- tions
of polyesters for use as coating resins. In particular., alkaline
catalysts such as LiOH, Ca salts, acidic catalysts SUCh as HsPO 4,
HCI, H2SO4, and organotin catalysts, have been reported in the
relevant literature. ~-~~ Also,
organotin compounds have been used as catalysts for the
alcoholysis and esterification reactions in alkyd manu- fa.cture, n
There is, generall Z a global effort to replace the conventional
homogeneous catalysts of the above reactions with economical and
eco fiiendly heterogeneous catalysts that have similar
effecriveness and selectM ty but without the formation of by
products or wastes. The cata154ic reac tivity of zeolite<
cation--exchange resins, enz3;mes and metal compounds (hydroxides,
alkoxides, organic poly- meric salts etc), and the related mecha-
nisms of esterification and transesterifi- cation reaction, have
thus been reported in the relevant literature, !~ !6
Apart from resins, alkyd paints contain a suitable solvent
(usually mineral spirits), a set of driers and other additives
which irrorove perforlTkance/' Modified alkyd resins have been
extensively used in paints and coatings. Alkyds rn W be old
fashioned, but they are inexpensive and effective, Future trends
will be driven by economic, quality and environmen- tal pressures
along '~ith competition from other materials. Price reductions of
paint con~onents is a continuous demand. ~,!r In the last two
decades, the research effort has focused on the cost reduction of
alkyds and the dr?ing chernistry of alk3,ds mainly because of
tighter environmental legislation. 7he reduction of VOC (volatile
organic corroound 9 emissions from paints can be achieved mainly
either by the replacement of solvent borne paints with water borne
paints or by the pro duction of solvent-borne products with a lower
solvent content, .Q~other topic is the role of metal catalysts,
which may affect not only the process time of alkyds, but also the
properties of alkyd resins and the paints derived from them5 ~
Paint drying includes the sol- vent evaporation and the oxidative
dry- ing related to a lipid autoxidation process. The
polyunsaturated fatty acids of alkyd resins are prone to autoxida
tion leading to product formation of cross linked Non volatile)
species and numerous other oxygen containing compounds. ~-~
In this work, a variety of catalysts were used in the synthesis
of modified long- oil alkyd resins (~qth an oil length of 65%) by
alcoholysis and esterification, The effect of the catalyst on the
reduc- tion of the process time and the physio- ochemical and
coating film characteris tics of the resultant prepared resins were
investigated. In addition, b.~:o paints were tbmmlated containing
selected alkyd resins, and their technical coating
properties were examined and com- pared,
Experimental
Materials Technical-grade soya bean oil, pentaery- thritol,
phthalic anhydride, xylene and white spirit were used in the
preparation of alkyd resins. The catalysts used were LiOH, in
powder fo~rc~, of 99% purity (HELM AG), dibutyl tin chloride, white
powder (R 2 Sn C12: R butyl) with corn position: Sn 51 to 54% and
chlorides 2% (Atochem), butyl tin oxide (RSnOJ (Atochem). The
components of the paints, namel3; soya lecithin, titanimn dioxide,
white spirit, etc, were also of technical grade,
Synthes is o f a lkyd res ins by a lcoholys is ester i f icat
ion of' otis
The process applied for the preparation of the alkyd resin
included two stages, in the first stage, soya bean oil (600g),
together with an initial quantity of pen- taerythritol (72g) and
the selected cat& lyst were introduced into a four necked round
bottom flask connected with a water condenser, a mechanical stirrer
and a Pt 100 thermocouple. ~[he flask was placed in an electric
jacket heater. 'Ihe flask mixture was heated gradually up to 250~
under stirring. The alco iholysis reaction occurred mainly at 250~
The duration of the reaction depended on the type of the catalyst
used, The reaction progress was moni- tored, and periodically
sarr~les fl'om the reactor mixture were obtained. The alcoholysis
reaction was considered complete when one volmne of a sam ple,
mixed with three volumes of absolute alcohol, did not give an
opaque solution, but gave a clear solu tion when cooled at room
temperature. lhis test is based on the solubility of monoglycerides
in absolute alcohol, while the triglycerides were not dis solved in
this solvent,
In the second stage, the remaining mnount of pentaerythritol
(72g) was added to the alcoholysis mixture fol- lowed by phthalic
anhydride (256g), the catalyst (whenever used) and the
reflu>soivent (xylene). ~[he mixture was heated. Ihe
distillation began at about 190 to 210~ and the water, which was
lbrmed, was distilled out as an azeotrope with xylene. Both water
and xylene were condensed and collected :in the receiver, attached
to the water condenser, and separated by gravity. Later, the
temperature of the reaction rr~xture was gradually raised to
230~
q i!{)ili i!i!!ii!ii!:i!iii,i!!8 !i)! !ii!i!ili i i ii i!i!i,!ii
ili!,!i!i:ii!:ili! !i!ii{ iili!
-
!ii!ii iii i!ilii !!i ! iiiiill ! i ! i ! i ! i ! i ! i ! i ! i
! i ! i ! i ! i ! i ! i ! i ! i ! i ! i ! i !il
and maintained constant until an acid value of 15 was obtained.
At that time, the total reaction time was recorded, A sample was
withdrawn periodically from the reaction system and its acid value
was determined. After the corn pletion of the reaction, the
reaction mixture was cooled to an ambient tern perature mid
dissolved in white spirit (60%~
-
!il !ii iii i!ilii !!i ! ii iiill ! i ! i ! i ! i ! i ! i ! i !
i ! i ! i ! i ! i ! i ! i ! i ! i ! i ! i ! i !il +++++i+++
:++:+;+:+: +:: +:+;:+++ ::++++ + :+:::+;++:::; +: :+ ++ ;++:+ +
::+{+ +: +;++; ;+: :p+~:a{~aii+ ;a :a+a::e+R~;+::++;+++a+; +~+ +
~+::: ~4: +: g ++t/a~:++ ++ ++el+ :+:+++++~ ++ +:; + ++;++
+++:++;{++++(+!@ +++++:;)+++++:+?i++r +;)+++:+ [++;@:+p;:@:++
+;++:+++!+ {;:+ +++:++;+:++:;++:++:+@ {++@+>;+ ++: +:@+;::++}+:+
+++:{++++i:+++:s +++++++:+::::++:+ 8++++@ @++++@++
+++;+:++++:+}:+::++:;++!:~::+:++~ ++
~:~i+++++++:+::++~+l~+i+~+:+++:+~,R:+:+:+R:++:~g++g+~+~ +:i
i::+:;++:::+:+,+ +++::;::+
m
+1
+1 |
5 -! ~ LiOH 0 .0~ Mm ar~dit~on~l mtal~t E | m LiOH 0.14% Mno
adCtional mlalyst E | j ~,, tiOH O.OW/o MLiOfi 0 .0~ [
O J, | | ~ | | | 3.17 3.33 3.67 4.25 5.00 5.17 5.75
" I 6.25 g,42 8.75 7.17 7.50 7.75 8.00
Time (+mms)
Figure 1 : Rate of the esterification reaction based on the
charNe of acid value against time in the alkyd process using as
catalyst LiOH in alcoholysis (A) and LiOH or not in esterification
(E) and in comparison with that of the conventional alb/d (LiOH in
A/no additional catalyst in E)
~5
25-
10-
5 -
~, [iOH 0.~ Mm mtal~t [ No catalyst t~/dibutyl tin ehlmide 0.2%
[ R0 m~l~st Mb~tyl tin oxide 0.2% [ LiOH 0.07% Mdi~.tyl tin ~hlodde
0.~ [
x [iOH 0.07% ~,/hutyJ tin oxide 02% [
2.42 3.0~ 3.67 a.92 4.42 4.92 5+12 S.92 7.0~ 7.S~ 8.25 925
lime (~rs)
Figure 2: Rate of the esterification reaction based on the
cha~ge of acid value against time in the alkyd process using
different organic catalysts in esterification (E) and LiOH in
alcoholysis (A) in comparison with that of the conventional alkyd
(LiOH in A/no additional catalyst in E)
10.4% to 15,6%, by using dibutyl tin chloride and butyl tin omde
respectively at 0.2% content, compared with the esterification
reaction time of the con- ventional resin. The selection of LiOH
(0.07%) as the catalyst for the alcoholysis and an organic metal
catalyst (0.2%) for the esterification resulted in a significant
reduction of esterification reaction times (37.5% and 29.3% fbr
dibutyt tin chlo ride and butyl tin oxide respectively) and of the
overall process time of the alkyd resins (32% and 25%
respectively). Con- sequently, dibu@ tin chloride was supe- rior
compared with butyl tin oxide cata- lyst with regard to decreasing
the process time. The order of the catalyst effectiveness in
decreasing the overall process time (alcoholysis - esterification)
was as follows: idOH 0.07 % dibu@ tin chloride 0.2% > LiOH 0.07%
bu@ tin oxide 0.2% > LiOH 0.07% LiOH 0.07% > LiOI-{ 0.07% (or
LiOH 0.14%)
no additional catalyst; no catalyst dibutyl tin chloride 0.2%
> no catalyst buUl tin oxide 0.2%. The change in the acid value
against time during the ester ification reaction of the selected
alkyds :produced using a different catalytic sys- tem is given in
Figures I and 2.
The physicochemical and film coating properties of the alkyd
resins investigat.- ed, namely the @ml acid value, viscosit>
hardness and duing time, are given in 'Ihble 3. It is obvious flint
the properties (viscosit> hardness and @ying time val ues) of
the alk3~d produced with LiOH 0.14%/no additional catalyst,
although similaL were inferior in comparison with those of the
conventional resin (catalyst LiOH 0,07%/no additional catalyst) and
the resin produced with a catalytic sys- tem (LiOH 0,07?4/LiOH
0,07%). Also, the d~2ing time of the resin produced with LiOH added
in both reactions was higher than that of the conventional resin,
while the values of the other prop- erties (viscosity, hardness and
production time) were the stone or very close. Therefore, the
conventional resin is preferable because the quantity of cata lyst
and therefore the cost of the catalyst is lower.
The properties of the h~o resins pre pared with the organic
metal catalysts in the esterification reaction were similar,
Comparing their properties with those of the conventional resin,
the latter proved to be better. It should also be kept in mind that
the organic catalysts are much more expensive tha~q LiOH, The two
resins produced using a combination of catalysts for the
alcoholysis and esterifi cation reactions showed excellent prop
erties and very low process times, with dibutyl tin chloride being
slightly better.
~!~+:~!~!~iifii!!:!:~!ii!i~i~i!i!!++i~i~!~i!~!~!i~l~i~!ii!~i~+~i~i!!~!~i~ii~i!~i~!~!i~J~i~i~ii~!!ii~ii:i!!!~i~ii~i:i~!i!~i~i~
~!~i!~!~i!i~i!i~i~+i~:~+i~i!~!i~i~ii~i~i~!N~;i!i~i~!~i!~N;~!~i~!N~iN!ii!!~!~i~!~!!~!~!~N~!~!~!~!~i~+}~++!:~i
~!i~!i~@~!i~+~ii!~i!~ii:~i~i~i~i~!)~!!ii~i~i}~!~!~i~!!!i;!~!~i~!:!~;!~!ii~+!~+~!!~!~!~@~iii~i!:!!~!~!
~!~i+~i!!~!i!~!~i~i:!;;!i!~i~i!~!!~iii!~:~i;!i!+@i+~i~!~!ii~!i~@)i~i~!i~i!~!i{:ii:@~i~i!~ii~!@i!@ii!~!~!i!ii~!~:!~!i~!;~!~:~!~!~i!!~!~ii!~;~i!~ii~@~i~@~!i!!~:~!!i~:~i~i@J~!i~i!gi~i!~!i~:~i!~iii~
~i~ii~@~ii~;!ii;i~iiiii+i!)!i
-
!ii!ii iii i!ilii !!i ! iiiiiii ! i ! i ! i ! i ! i ! i ! i ! i
! i ! i ! i ! i ! i ! i ! i ! i ! i ! i ! i !il i! i:::::i
Table 3: Properties of the a l~d resins produced by alcohoiysis
(A)-esterilcation (E) pr~ess with various catalytic systems
Catalyst Acid V~scosity Drying time Non volatile Hardness, % AlE
value (dPa s) (hours) matter % oscfl Konig
24h 48h /2h
I JOH 0 07!I-o l!i.. 0 2:2) 2.750 s,;~ ,sue" 19 .:>~~ ,'4
addJtioFal ~.~,yo,~'~t ......
'~" ' , .... 18 I!,vh 0.141no ~r, C !0 2.833 5880 !8 22
addilJonai cabi;,st
i.,hiteness and hardness values were very close to each other.
The selection of the best paint with regard to their properties can
be focused on their film drying time. It is obvious that the
combined paint, containing the alkyd prepared with two catalysts,
was suped or, demonstralng lower duing lines.
Conclus ions The effect of a catalytic system used in the
modified alkyd processes, which included alcoholysis and
esterification reactions, is significant with regard to the
reduction el process times as well as the improvement of the
coating properties of alkyds and the paints derived from them. The
catalytic sys- tern (LiOH/dibutyl tin chloride) proved more
effective than the com;entiona] catalyst (LiOH/no additional
catalyst).
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