Post on 03-Jan-2017
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)