To what extent is UF resin really cured in medium density fiberboard?

To what extent is UF resin really cured

in medium density fiberboard? Warren Grigsby, James Carpenter, Armin Thumm,

Rosie Sargent and Nancy Hati

Wood Adhesives 2013 Toronto, October 9-11th, 2013

warren.grigsby@scionresearch.com

Outline

• Background

• Panel properties

• Water Extractables

resin component extraction

• Chemical Analysis

panel extractables

• Summary

Background

• UF resin is susceptible to moisture studies focus on hydrolysis and panel emissions

• MDF : differences surface and core layers resin & temperature effects

EMC, contact angle, panel bonding & swell, extractables

high nitrogen contents removed 60% !!! (urea?)

• Suggest resin cure differences within panels may confer differences in panel properties

- emissions, water soak, fibre

Grigsby, W.J., Thumm, A., Carpenter, J.E.P, “Fundamentals of MDF panel dimensional stability: Analysis of

high density layers”, Journal of Wood Chemistry and Technology 32(2) 2012 pp. 149-164.

Consider this?

Resin

Content ?

Methodology

UF resin

+

Fibre

Hot-press

Fibre

Water

Soak

20C, 24 h Analyze

Residues

%N loss,

chemistry

Acid Cure

Resin

100C

Panel

Properties

Nitrogen Mass Balance Resin Loss

Finding

• Account for 93-98% of panel nitrogen

MDF Panel

water

Residue

88.2% mass Extract

1.0 g 4.2% mass +

E0 Panel (13.3% resin loading)

grind up

freeze dried oven dried

5.41 % N 51 % N 2.68 % N

%N

content

54.1 mg N 27.2 mg N 23.6 mg N 6%

difference

(3.4 mg) +

50% Grigsby, W.J., Carpenter, J.E.P, Sargent, R., Investigating the Extent of Urea Formaldehyde Resin Cure in

Medium Density Fibreboard: Resin Extractability and Fibre Effects Journal of Wood Chemistry and

Technology, accepted, 2013

Panel Properties

• Laboratory and commercial MDF panels

Mechanical- & blowline-blending

Panel Resin

(%)

IB

(MPa)

Formaldehyde

Emissions

(mg/L)

Lab 8mm MDF

Control E0 9.1 0.53 -

Control E1 8.5 0.72 0.70

Commercial E0 3mm MDF

Comm 5 4.8 1.29 0.27

Comm 12 12.9 2.04 0.13

Comm 14 13.3 2.12 0.12

Hot-press

Fibre

Panel

Properties

Cured UF Resin Extraction

• Cure E1 resin with acid

acetic or hydrochloric acids

<2% mass loss

106% N% enrichment of nitrogen

Water

Extraction

20C, 24 hAnalyze

Residues

%N loss,

chemistry

Acid Cure

Resin

100C

• E1 resin, 100C, 30 mins (without acid)

48% mass loss

107% N%

Curing UF resin distinguishes mass loss

MDF Panel Water Extractions

• Some 50-70% nitrogen removed on soaking

0%

20%

40%

60%

Comm 5 Comm 12 Comm 14

Extr

acte

d N

itro

gen

(%

)

Water

Extraction

20C, 24 h

Analyze

Residues

%N loss,

chemistry

MDF

panel

Resin Loading

Water Extractives v Emissions

• Resin loading influences emissions

Extracted %N correlates with formaldehyde emissions

0.00

0.20

0.40

0.60

Comm5 Comm12 Comm14

Extr

acte

d N

itro

gen

(%

) 0.6

0.4

0.2

0.0

Fo

rmald

eh

yd

e (

mg

/L)

60

40

20

0

Resin Loading

Extraction Time

Q. Is the %N removed dependent on extraction time?

Finding

Resin components readily solubilised from fibre

Resin hydrolysis not cause of high %N losses

0%

20%

40%

60%

2h 6h 24h

Ex

tra

cte

d N

itro

ge

n (

%)

Water

Extraction

20C, 24 h

Analyze

Residues

%N loss,

chemistry

MDF

panel

Extraction at 2, 6 & 24 h similar values

Type of Resin Cure

• Uncured fibre v oven curing v hot-pressing

similar %N removed

No differences in %N extracted due to cure

10% E0 resin loading

0%

20%

40%

60%

Uncured Fibre Cured Fibre Panel

Ex

tra

cte

d N

itro

ge

n (

%)

Water

Extraction

20C, 24 h

Analyze

Residues

%N loss,

chemistry

MDF

panel

-5

5

15

25

35

45

1000 1200 1400 1600 1800 2000 2200 2400

RI D

ec

tor

Re

sp

on

se

Elution Time (sec)

Extractable material

Fibre only

E1 resin

Chemical Characterisation – is it just urea?

• GPC used to get MW profile of panel extractables

Water

Extraction

20C, 24 h

Analyze

Residues

%N loss,

chemistry

-10

0

10

20

30

40

50

60

70

80

90

-10

10

30

50

2.5 3 3.5 4 4.5 5

de

tec

tor

res

po

ns

e

log MW

fibre extract

Comm 14

E0

Chemical Characterisation – is it just urea?

• MW profile of extractables

Low MW oligomers

UF components

Grigsby, W.J., Carpenter, J.E.P, Thumm, A., Hati, N., Investigating the Extent of Urea Formaldehyde Resin Cure

in Medium Density Fibreboard: Characterisation of Extractable Resin Compounds, International Journal of

Adhesion and Adhesives, submitted 2013

-10

0

10

20

30

40

50

60

70

80

90

-10

10

30

50

2.5 3 3.5 4 4.5 5

de

tec

tor

res

po

ns

e

log MW

fibre extract

Lab 8

Lab 14

Comm 14

E0

Chemical Characterisation – is it just urea?

• MW profile of extractables

minor differences across extracts

Chemical Characterisation

• NMR confirmed chemistry of extracts -NH, -NH2 and N-CH2-N/O consistent with small oligomers

9 8 7 6 5 4 3 2 ppm

Pure UF resin

UF resin

(freeze dried, D2O)

UF resin

(freeze dried, DMSO)

Panel extract

(DMSO)

X

X

9 8 7 6 5 4 3 2 ppm

X

X -NH- -NH2

>N-CH2-N< >N-CH2-O-

-O-CH2-O-

Chemical Characterisation – UF oligomers?

Fibre (only) extractives (DMSO)

9 8 7 6 5 4 3 2 ppm

E0 UF resin (H2O/D2O)

Lab 14 extract (DMSO)

Comm 14 extract (DMSO)

X

X

X

• Extractables UF resin components & fibre extractives

Discussion

• Rapid loss of labile UF resin species

unlikely due to UF resin degradation and hydrolysis

• Extractables are UF oligomers

• Quantity of Extractables?

no difference once applied to fibre

relationships with resin loading, formaldehyde emissions

Hypothesize?

• Apply resin components separate within fibre matrix

a chromatography effect

• Components available only to partially couple oligomers

cannot fully crosslink

more resin greater opportunity to couple crosslink

Outcome

Incomplete cure compared to pure UF resin

Does it matter?

• Panel properties are fine, more resin better performance

• UF oligomers responsible for panel emissions?

Summary

• MDF panels contain labile resin components

High proportions, readily extractable into water

• Chemistry low MW UF oligomers

GPC, NMR confirm methylene-urea components

• UF resin may not achieve full cure within MDF/

panelboards

• UF oligomers contribute to emissions ?

Acknowledgements

• New Zealand Composite Panels Research Group

• Matched funding from New Zealand Ministry of

Business, Innovation and Employment (formerly Foundation of Research, Science and Technology)