to what extent is uf resin really cured in medium density fiberboard?
TRANSCRIPT
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
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)