\STRUCTURE-PROPERTY RELATIONSHIPS OF LIGNIN-BASED ISOCYANATE 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
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A~D€¦ · a urea formaldehyde reference. ... States sul.:i te pulp mills produce 2. l million tons, anC. Kraft pulp mills, 21 million tons of lignin annually {Goheel".., 1979).
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\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
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
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.
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.
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.
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:-
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
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.
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: