Effect of replacing polyol by organosolv and kraft lignin on the property and structure of rigid polyurethane foam.

1.6 MB·English

by  Pan, Xuejun

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RESEARCH Open Access
Effect of replacing polyol by organosolv and kraft
lignin on the property and structure of rigid
polyurethane foam
Xuejun Pan1* and Jack N Saddler2
Abstract
Background: Lignin is one ofthe three major componentsinplant cell walls, and it can be isolated (dissolved)
from the cell wall inpretreatment or chemical pulping. However, thereis a lackof high-value applications for lignin,
and the commonest proposal for lignin is power and steam generationthrough combustion. Organosolv ethanol
process is one of the effective pretreatment methodsfor woody biomass for cellulosic ethanol production, and
kraft process is a dominant chemical pulping method inpaper industry. In the present research, the lignins from
organosolv pretreatment and kraft pulping were evaluatedto replace polyol for producing rigid polyurethane
foams (RPFs).
Results: Petroleum-based polyol was replaced with hardwood ethanol organosolv lignin (HEL) or hardwoodkraft
lignin (HKL) from 25%to 70% (molar percentage) inpreparingrigid polyurethane foam.The prepared foams
contained 12-36% (w/w) HEL or 9-28% (w/w) HKL. The density, compressive strength,and cellularstructure ofthe
prepared foams were investigated and compared.Chainextenders were used to improve thepropertiesof the
RPFs.
Conclusions: It was found thatlignin was chemically crosslinked not just physically trapped in therigid
polyurethane foams. The lignin-containing foams had comparable structure and strength up to 25-30% (w/w) HEL
or 19-23% (w/w) HKL addition. The results indicated that HEL performed much better in RPFsand could replace
more polyol atthe same strength thanHKL because theformerhad a better miscibilitywith the polyol than the
latter. Chain extender such as butanediol could improve thestrength oflignin-containing RPFs.
Keywords: Kraft lignin, Lignin utilization, Organosolv lignin, Polyurethane, Rigid foam
Background elastomers, rigid foams for packing and insulation, to
Polyurethane is one of the most important synthetic flexible foaminmattressandcarseats[1].
polymers, and it is synthesized through a polyaddition Lignin is one of the three major components in plant
reaction between a polyisocyanate (a polymeric molecule cell walls and the most abundant aromatic polymer in
with two or more isocyanate groups, such as toluene dii- the nature [2]. Structurally, lignin is a 3-D networked
socyanate (TDI) and methylene diphenyl diisocyanate polymer biosynthesized in plants from three mono-
(MDI)) and a polyol (a polymer with two or more react- lignols, p-coumaryl alcohol, coniferyl alcohol, and sina-
ive hydroxyl groups, such as polyethylene adipate and pyl alcohol, through radical coupling processes [3].
poly(tetramethylene ether)glycol). Both the polyisocya- Lignin plays avital function inthe plant’sdefense system
nates and the polyols are currently derived from petrol- against degrading enzymes and diseases. The lignin also
eum oil. Polyurethane has varied applications in binds fibers together to form a strong and tough matrix
different areas from liquid coatings and paints, tough of plants and provides mechanical support to the plant
vessels for the transportation of water and nutrients [4].
*Correspondence:[email protected] However, the physical and chemical nature and func-
1DepartmentofBiologicalSystemsEngineering,UniversityofWisconsin–
tions oflignin make it troublesome inthe utilization and
Madison,460HenryMall,MadisonWI53706,USA
Fulllistofauthorinformationisavailableattheendofthearticle conversion of lignocellulosic biomass. For example,
©2013PanandSaddler;licenseeBioMedCentralLtd.ThisisanOpenAccessarticledistributedunderthetermsofthe
CreativeCommonsAttributionLicense(http://creativecommons.org/licenses/by/2.0),whichpermitsunrestricteduse,
distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.
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lignin has to be removed (dissolved) during chemical had attractive properties such as high purity, low mo-
pulping of wood to release/produce intact, strong, and lecular weight and narrow distribution, and more func-
bleachable fibers (pulp) for making paper. In bioconver- tional groups and the lignin was expected to have great
sion of lignocellulosic biomass to fuel ethanol, lignin is potential in developing high-value lignin products
one of the major recalcitrance sources of the cellulosic [18,22].However,the productsandmarketoforganosolv
substrates to cellulases. Furthermore, the lignin isolated lignin have not been sufficiently developed. It is believed
from either chemicalpulpingorbiorefininghasnotbeen that the successful commercialization of organosolv pre-
utilized in a value-added way, and the most common treatment is greatly dependent on whether the organo-
lignin utilization is still steam and power production solv lignin can be utilized efficiently and in value-added
throughcombustion. ways, which is expected to offset the high cost of the
Extensive efforts have been made to explore high- organosolv process.
value applications of lignin, in particular in polymeric In the present research, hardwood ethanol organosolv
materials, such phenolic and epoxy resins [5]. Consider- lignin (HEL) was evaluated to replace synthesized polyol
ing the fact that lignin is a polymer with a fair amount to prepare rigid polyurethane foam and compared with
of hydroxyl (phenolic and aliphatic) and carboxylic hardwood kraft lignin (HKL). The effect of lignin
groups that own reactive hydrogen, lignin has the poten- addition on foam preparation (viscosity of polyols) and
tial to replace polyols in polyurethane production. For foam properties (density, compressive strength, and cel-
example, polyurethane film was prepared from organo- lular structure) was investigated. Chain extenders (gly-
solv lignin with polyethylene glycol as co-polyol and soft cerol and butanediol) were examined for improving the
segments [6] with or without catalyst [7]. Polyurethane propertiesofthelignin-basedpolyurethanefoams.
foam was prepared from kraft lignin using polyethylene
glycol as solvent [8]. Water-soluble lignosulfonate from Results and discussion
sulfite pulping was used to prepare rigid polyurethane Effectofreplacementofpolyolbyligninonthe
foams in glycols [9]. Lignin from straw steam explosion preparationofrigidpolyurethanefoam
was also investigated for polyurethane preparation [10]. The content of functional groups and molecular weight
A polyurethane elastomer (film) was prepared from flax of the HEL and HKL lignins are summarized in Table 1.
soda ligninwith polyethylene adipate andethyleneglycol HKL had more phenolic and aliphatic hydroxyl groups
as co-polyol and soft segment, but the resultant polyur- than HEL, suggesting that HKL should be more reactive
ethane film was heterogeneous and did not have ad- as a polyol than HEL in polyurethane foam preparation.
equate mechanical strength for any application when In addition, HKL had lower molecular weight than HEL.
lignin content was over 10% (wt.) [11]. Because of the Therefore, it was expected that HKL might perform bet-
solid state and less accessible hydroxyl groups of lignin, ter in preparing polyurethane foams because of more
chemical modification such as oxypropylation with alky- functional groups (more crosslinking points) and low
lene oxide was proposed to improve the accessibility of molecular weight (highmobilityandlowviscosity).
the hydroxyl groups, which could convert lignin into li- Viscosity of polyol is critical to the preparation of
quid polyol with extended chain and exposed hydroxyl polyurethane foam and cellular structure of resultant
groups [5,12]. As a follow-up, recently, liquid polyol foam. High viscosity could cause problems when mixing
from oxypropylatedpinekraftligninwasusedtoprepare the foam ingredients and affect the generation and dis-
rigid polyurethane foam [13]. The same group also tribution of the bubbles/cells formed by the CO from
2
investigated the reinforcement of rigid polyurethane the reaction between blowing agent (water in this study)
foam from oxypropylated ethanol organosolv lignin with and polydiisocyanate. The effect of blending the lignins
cellulose nanowhiskers[14]. in polyether polyol (Voranol 270) on viscosity is shown
Organosolv ethanol process uses aqueous ethanol to in Figure 1. In general, blending the lignins in Voranol
extract lignin from lignocelluloses in the presence of
small amount of inorganic acid as catalyst. It was devel-
Table1Functionalgroupsandmolecularweightofthe
opedin1970sandcommercialized in1980satpilot scale
ligninsamples
for producing pulp from hardwood for papermaking
Lignin Ph-OH Al-OH MeO M M M /
[15-17]. Recently, we reevaluated the organosolv process w n w
M
mmol/g mmol/g mmol/g n
as a pretreatment method of woody biomass for cellu-
HEL 2.76 2.88 6.16 2600 1600 1.62
lose ethanol production. It was found that the organo-
solv process was an effective pretreatment for both HKL 4.29 4.12 5.81 2400 1330 1.80
hardwood and softwood and the resultant cellulosic sub- Note:HEL,hardwoodethanolorganosolvlignin;HKL,hardwoodkraftlignin;
Ph-OH,phenolichydroxylgroup;Al-OH,aliphatichydroxylgroup;MeO,
strates had a ready digestibility with cellulases [18-21].
methoxylgroup;M ,weightaveragemolecularweight;M,numberaverage
w n
The isolated organosolv lignin during the pretreatment molecularweight.
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0.4
NCO/OH = 1.1 : 1
NCO/OH = 1.3 : 1
s
a 0.3
P
m
y,
sit
co 0.2
s
Vi
0.1
0
Density, g/cm3 Compressive strength, MPa
Lignin content, % (w/w)
Figure2EffectofNCO/OHratioonthepropertiesoflignin-
Figure1Effectofligninadditionontheviscosityofpolyether
basedrigidpolyurethanefoam.Foamformula:HELlignin,50%
polyol(Voranol270).HKL,hardwoodkraftlignin;HEL,hardwood
HELand50%Voranol270(molarpercentage).
ethanolorganosolvlignin.
270 increased the viscosity of the polyol. When lignin compressive strength decreased significantly when the ratio
addition was less than 28% (w/w in the polyol), the vis- ofNCO/OHincreasedfrom1.1:1to1.3:1.
cosity increased slowly. For example, 28% lignin elevated Representative pictures of polyurethane foams con-
the viscosity from approximately 400 mPa·s of pureVor- taining HEL or HKL lignin are shown in Figure 3. The
anol 270 to 1,600-1,800 mPa·s of the mixture of lignin foams appeared the brown color of lignin, and the HEL-
and the polyol. However, the viscosity jumped sharply containing foam had a lighter color than the HKL-
when lignin addition was more than 28% (w/w), in par- containing one because HEL was lighter than HKL in
ticular when HKL was added. For example, 40% lignin color. Both foams haduniformcellularstructure, butthe
resulted in a viscosity of 6,000 or 16,700 mPa·s for HEL HEL-containing foam felt tougher and stronger than the
or HKL, respectively. As shown in Figure 1, HKL caused HKL-containing one, which was in agreement with the
a much higher viscosity increase than HEL did, although resultsofcompressivestrengthinFigure4.
the former had lower molecular weight than the latter To verify whether the lignin was chemically crosslinked
(Table 1). This could be attributed to the better solubil- or just physically trapped in the polyurethane foam, the
ity/miscibility of HEL in polyol. HEL isolated from etha- foam prepared with 25% (w/w) HEL was extracted with
nol organosolv process was fairly soluble in ethanol and 90% dioxane (dioxane/water, v/v), a good solvent of HEL
thereby had good miscibility and dispensability in the lignin. In the experiment, the foam was cut into small
polyol (polyalcohol), while HKL produced from kraft pieces of approximately 5 × 5 mm and extracted withthe
pulping was insoluble in alcohols and was just sus- dioxane in a Soxhlet extractor for 24 hours to see the
pendedinthepolyol, which resultedinahighviscosity. weight loss of the foam. Pure polyurethane foam without
One of the most important parameters in polyurethane lignin was used as reference. It was found that the pure
foampreparationisthemolarratioofisocyanatetohydroxyl polyurethane foam lost approximately 3% of its original
groups(NCO/OH).AsuggestedNCO/OHratiois1.1:1for weight during the extraction, while the HEL-containing
rigid foam [1], and the excessive isocyanate is for reacting foam lost 7%. The results indicated that although more
with blowing agent (water) to generate CO and form bub- material was extracted from the lignin-containing foam,
2
blesandcellularstructureofthepolyurethanefoam.Toin- the majority of the lignin was not extractable, suggesting
vestigate the effect of NCO/OH ratio on lignin-based that the lignin be chemically cross-linked not physically
polyurethane foam, lignin-containing foams were prepared trappedinthefoam.
at two NCO/OH ratios (1.1 and 1.3:1). As expected, the
foams prepared at 1.3:1 NCO/OH ratio had more bubbles Effectofreplacementofpolyolbyligninonthedensity
than the foams at 1.1:1 ratio because the excessive MDI ofpolyurethanefoam
reactedwithwaterandformedmorecarbondioxide,which As shown in Figure 5, the addition of lignin reduced the
resulted in more and larger bubbles. They did not signifi- density of the foams, which is actually desirable if the
cantly affect the density (only slightly decreased), as shown foamisusedaspackingorinsulationmaterial.Thedensity
inFigure 2. However, sincethe larger and irregularbubbles of pure polyurethane foam was about 0.116 g/cm3, and
resulted in less uniform cellular structure of the foam, the decreased by 30% when the polyol was replaced by 50%
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Figure3Rigidpolyurethane(PU)foamscontaininglignins.A:PUfoamcontaining50%hardwoodethanolorganosolvlignin(HEL);B:PU
foamcontaining50%hardwoodkraftlignin(HKL).
withlignin.This wasprobablybecausethe lignin addition Effectofreplacementofpolyolbyligninonthe
made the cellular structure of the foam less uniform and compressivestrengthofpolyurethanefoam
formed more larger cells (bubbles), as discussed above, Replacing the polyol with 25% lignin reduced the com-
which reduced the mass per unitvolume ofthe foam and pressive strength of the foam by 40%, compared to pure
thereby the density. However, further increasing lignin polyurethane foam without lignin, as shown in Figure 4,
content reversely resulted in a slightly higher density, primarilybecause(1)theligninwaslessreactive(hydroxyl
likely because too much lignin affected the uniformity of groupsinligninwaslessaccessible)thanthepolyolVora-
thecellsandpartoftheligninwasevennotwelldispersed nol 270, and therefore the crosslinking density and
inthefoamandassembledtogetherasbiggranules,which strength of lignin-containing foam was lower than those
reduced the void volume and increased density. These of the pure PU foam; (2) the lignin was not completely
wereinagreementwiththeobservationsofcellularstruc- miscible with the polyol, and thereby the lignin was not
ture of the foams shown in Figure 6. It is apparent that uniformly dispersed in the foam; and (3) the introduction
thetwotypesoflignindidnotshownsignificantdifference ofligninreducedtheuniformityofthefoamcellularstruc-
intermsoffoamdensity. ture,andthedeficiencyinthecellularstructureweakened
thestabilityandstrengthofthestructure.
a
P
M
h,
gt
n
stre 3cm
e g/
mpressiv Density,
o
C
Ratio of lignin to polyol
Figure4Effectofligninadditiononthecompressivestrength Ratio of lignin to polyol
ofrigidpolyurethanefoams.Ratiooflignintopolyol,molarratio Figure5Effectofligninadditiononthedensityofrigid
ofthehydroxylgroupsfromlignintothosefrompolyol(Voranol polyurethanefoams.Ratiooflignintopolyol,molarratioofthe
270);HEL,hardwoodethanolorganosolvlignin;HKL,hardwood hydroxylgroupsfromlignintothosefrompolyol(Voranol270);HEL,
kraftlignin. hardwoodethanolorganosolvlignin;HKL,hardwoodkraftlignin.
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Figure6Effectofligninadditiononcellularstructureofrigidpolyurethanefoams.HEL,hardwoodethanolorganosolvlignin;L/P,lignin/
polyol(Voranol270).
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Table2Lignincontentinrigidpolyurethanefoams column) and light microscope (images in the right col-
Ratiooflignintopolyol 25/75 50/50 60/40 70/30 umn). Pure polyurethane foam without lignin had uni-
form cell size and regular cell shape, and it looked
HKLinPUfoam,%(w/w) 9 19 23 28
semitransparent with a light yellow color. With the
HELinPUfoam,%(w/w) 12 25 30 36
introduction of HEL, the foam turned to the brown
Note:Rationoflignintopolyol,molarratioofthehydroxylgroupsfromlignin
color oflignin.In addition,theshapeofthe cells became
tothosefrompolyol(Voranol270).HKL,hardwoodkraftlignin;HEL,hardwood
ethanolorganosolvlignin;PU,polyurethane. less regular, and large cells formed as well. It seemed
that the effect of lignin on the cellular structure of the
foams was insignificant when lignin replacement was
Further increasing lignin content from 25% to 60% did less than 50%. However, when lignin ratio increased to
not result in additional drop of the strength, but when 60% in particular to 70%, the foam cells became signifi-
lignin content was more than 60%, the compressive cantly irregular and many large cells (bubbles) formed.
strength decreased again because too much lignin Furthermore, with the increased lignin content, lignin
resulted in more irregular cellular structure and wea- became poorly dispersed in the foam, and many large
kenedthe crosslinks,asshowninFigure6. lignin granules were clearly visible under light micro-
ItwasalsoseenfromFigure4thatthefoamscontaining scope. The irregular cells, large bubbles, and poorly dis-
HELhadhighercompressivestrengththanthosecontain- persed lignin were likely responsible for the low
ing HKL. Better miscibility of HEL with the polyol over compressivestrengthofthefoamsathighlignincontent,
HKLwaslikelythereason.As discussed above,poormis- as discussed above. The cellular structures of HKL
cibilityofHKLwiththepolyolresultedinpoordispersion foams (images are not provided) were similar to those of
of the lignin in the foam and therefore fewer and weaker HELfoams,but moreirregular.
chemical crosslinking between the lignin and MDI. It
should be pointed out that HKL had more hydroxyl
groups than HEL (Table 1), and therefore at the same Effectofchainextendersonpropertiesoflignin-
molarratiooflignintopolyol,thefoamwithHELactually containingpolyurethanefoam
had more lignin by weight than the foam with HKL. As The results above clearly indicated that replacing polyol
compared in Table 2, the HEL foam had approximately with the lignins negatively affected the strength and
30% more lignin than HKL foam. Considering this fact, structure of rigid polyurethane foams. This was partially
HELfoamactuallyhadmuchhighercompressivestrength due to the low hydroxyl groups content of the lignins
thanHKLfoamatthesamelignincontent. and the poor accessibility of the groups. Chain extender
is supposedly able to solve the problem and improve the
performance and properties of lignin-containing foams.
Cellularstructureoflignin-basedpolyurethanefoam Chain extenders generally have low molecular weight
As shown in Figure 6, cellular structure of the HEL- and are bifunctional compounds for enhancing the
containing rigid polyurethane foams was observed under crosslinking in polyurethane foams. Glycerol and 1,4-
scanning electron microscope (SEM, images in the left butanediol are common chain extenders in polyurethane
O=C=N MDI N=C=O O H
+ O H O H Lignin O O
HO-CH2CH2CH2CH2-OH O H
O
+ O
−
OH
HO− Polyol −OH OPolyolO OO Lignin OHOH
+
OH OH O
OH O O
Lignin Lignin O
OH OH OH OH OH
OH
Figure7Illustrationofthefunctionofchainextender(butanediol)inpolyurethanefoam.
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3m
c
g/
y,
sit
n
e
D
Chain extender addition
Figure8Effectofextendersonthedensityoflignin-containingrigidpolyurethanefoams.Foamformula:HELlignin,50%HELand50%
Voranol270(molarpercentage).
foam formulation. The function of chain extenders in However, the addition of chain extender, such as 3.5%
the preparation of lignin-containing polyurethane foam butanediol, improved the compressive strength of the
is illustrated in Figure 7. The effect of the chain exten- foam, as shown in Figure 9, because the chain extender
ders on density is shown in Figure 8. It can be seen that increasedtheaccessibilityof hydroxylgroupsinlignin.At
the density values did not significantly changed when lower loading percentages, butanediol did not have sub-
more chain extender (butanediol) was added. This sug- stantial effect on compressive strength improvement,
gested that chain extender did not substantially affect probablybecausetheextendermoleculeswerenotenough
foam structure (cell amount, size and distribution) when to improve the crosslink between MDI and lignin. Gly-
theratio ofNCO/OH waskeptconstant. cerol was not as effective as butanediol as chain extender,
Figure9Effectofextendersonthecompressivestrenghtoflignin-containingrigidpolyurethanefoams.Foamformula:HELlignin,50%
HELand50%Voranol270(molarpercentage).
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presumably because the three hydroxyl groups of glycerol
CH
consumed more MDI than butanediol, thereby reducing 3
thecrosslinkingdensitybetweenMDIandligninandcon-
CH O(CH CHO) H
sequentlythestrengthofthefoam. 2 2 x
CH
3
Conclusion
Polyolwasreplacedwithhardwoodethanolorganosolvlig- CHO(CH CHO) H
2 y
nin (HEL) or hardwood kraft lignin (HKL) from 25% to
70% (molar percentage) in preparing rigid polyurethane CH
3
foam (RPF). The prepared foams contained 12-36% (w/w)
HEL or 9-28% (w/w) HKL. The density, compressive CH O(CH CHO) H
2 2 z
strength, and cellular structure of the foams were investi-
gated and compared. It was found that themajority of the
lignin was chemically crosslinked not just physically Scheme1Structureofpolyetherpolyol(Voranol270).
trapped in the foams as filler. The foams had satisfactory
structureandstrengthupto25-30%(w/w)HELor19-23%
(w/w) HKL addition. The results indicated that HEL per- using gel permeation chromatography (GPC). In brief,
formed much better in RPFs and was able to give a better Functionalgroups(phenolichydroxyl,aliphatichydroxyl,
strengthatthesamelignincontentorreplacemorepolyol and methoxyl groups) were determined using 1H-NMR.
at the same strength than HKL presumably because the Lignin acetate (50 mg) and 5 mg of p-nitrobenzaldehyde
formerhadabettermiscibilitywiththepolyolthanthelat- (NBA, internal standard) were dissolved in 0.5 mL of
ter. Addition of chain extender such as butanediol could deuterochloroform, and 1H-NMR spectra were recorded
improvethestrengthoflignin-containingRPFs. on a Bruker AV-300 spectrometer. The functional
groups were estimated from the areas of their peaks, re-
Methods ferring to the proton peak area of NBA [25]. The num-
Materials ber average and weight average molecular weights (M
n
Hardwood organosolv ethanol lignin (HEL) was gener- and M , respectively) of HEL and HKL were estimated
w
ouslyprovidedbyLignolInnovation(Vancouver,Canada), by GPC using a Waters (Rochester, MN) HPLC system
produced from mixed hardwoods using the organosolv equipped with a Waters 717 autosampler, a Waters 2410
ethanol process [23]. Hardwood kraft lignin (HKL) was refractive index detector, and three Waters Styragel col-
generously contributed by Westvaco (Covington, VA), umns (HR5E, HR4, and HR2) in tandem. Lignin acetate
which waspreparedfrom the black liquor of mixed hard- (0.5 mg) was dissolved in 1 mL of tetrahydrofuran, and
woods kraft pulping [24]. Both lignins were spray-dried 30 μL of the solution were injected. The columns were
and had uniform and fine particle size, and HEL was calibratedwith polystyrenestandards[18].
slightlylightincolor(bothbrown)thanHKL.Thelignins
were dried in a 105°C oven overnight before used in pre- Preparationofpolyurethanefoamfromlignin
paringpolyurethanefoam. Lignin, polyol (Voranol 270), blowing agent (water), surfac-
Polymeric MDI (Methyl Diphenyl Diisocyanate, PAPI tant (Tegostab BF 2370), and catalyst (Kosmos 29) were
27, isocyanate content 7.5 mmol/g) and polyether polyol weighed into a container (polystyrene foam cup) according
(Voranol 270, polyether triol, molecular weight 700, hy- to preset foam formula. The ingredients were first thor-
droxyl content 4.3 mmol/g) were generously provided by oughly mixed manually using a glass rod to disperse lignin
DOW Chemicals (Toronto, Canada). The structure of in the polyol. When the pre-determined MDI was added
Voranol 270 is shown in Scheme 1. Polyether-modified into the container, the mixture was stirred at high speed
polysiloxane (Tegostab BF 2370) as surfactant and Tin- usingakitcheneggbeaterfor20seconds,andleftinafume
(II)-isooctoate (Kosmos 29) as catalyst were generously hood at room temperature to allow the foam rising. The
provided by Goldschmidt Chemical (McDonald, PA). All prepared foam was kept at room temperature in the hood
these commercial products were used as received with- for one week for curing and aging before characterization.
out any modification or pretreatment. Other chemicals Polyurethanefoamwithoutligninwaspreparedasreference
were purchased from Sigma-Aldrich(St.Louis,MO) and following the same procedure above. All the foams were
usedasreceived. prepared in five duplicates, and the average of the results
from the five samples was reported. The amount of lignin,
Characterizationofthelignins polyol and MDI were determined according to the desired
The functional groups of HEL and HKL were estimated lignin content to add and the molar ratio of isocyanate to
using 1H NMR, and molecular weight was estimated hydroxyl (NCO/OH). The NCO/OH ratio was calculated
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usingtheequationbelow: Authordetails
1DepartmentofBiologicalSystemsEngineering,UniversityofWisconsin–
NCO W ½NCO(cid:2) Madison,460HenryMall,MadisonWI53706,USA.2DepartmentofWood
¼ MDI MDI Science,UniversityofBritishColumbia,2424MainMall,VancouverBCV6T
OH W ½OH(cid:2) þW ½OH(cid:2)
L L P P 1Z4,Canada.
Received:2October2012Accepted:21December2012
Where, W , W and W = weights (g) of MDI, lig-
MDI L P Published:28January2013
nin and polyol, respectively; [NCO] = molar content
MDI
of isocyanate groups in MDI; [OH] and [OH] = molar
L P Reference
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polyol, respectively. 1999.
2. RowellRM:HandbookofWoodChemistryandWoodComposites.BoacRaton:
Taylor&Francis;2005.
Viscosity 3. LuF,RalphJ:Lignin.InCerealStrawasaResourceforSustainable
Viscosity of the mixture of the polyether polyol (Voranol BiomaterialsandBiofuels.EditedbySunRC.Amsterdam:Elsevier;
2010:169–207.
270) and lignin (HEL and HKL) was determined using a
4. ElumalaiS,PanXJ:ChemistryandReactionsofForestBiomassin
Brookfielddialreadingrotaryviscometer(ModelLVT).The Biorefining.InSustainableProductionofFuels,Chemicals,andFibersfrom
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AmericanChemicalSociety;2011:109–144.
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Characterizationofpolyurethanefoamsfromlignin alternativetononrenewablematerials.JPolymeEnviron2002,10:39–48.
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Citethisarticleas:PanandSaddler:Effectofreplacingpolyolby
organosolvandkraftligninonthepropertyandstructureofrigid
polyurethanefoam.BiotechnologyforBiofuels20136:12.
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