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Structure of Glycerol and Cellulose Fiber Modified Water-Blown Soy Polyol-Based Polyurethane Foams


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In this brief report, the effects of reinforcing agents, glycerol and refined cellulose fiber, have been studied on the foaming reactions of polyurethane based on polyol derived from soy bean oil. The presence of glycerol and cellulose fiber has been observed to have a considerable influence on the density of the foams. Changes in density of different foams have been correlated with the chemical structures generated in the presence of the components, and analyzed by fourier transform infrared (FTIR) spectroscopic study and thermogravimetric analysis (TGA). Scanning electron microscopic (SEM) observations are in line with the modifications induced by the reinforcing components.
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Structure of Glycerol and Cellulose Fiber
Modified Water-Blown Soy Polyol-Based
Polyurethane Foams
Faculty of Forestry
Centre for Biocomposites and Biomaterials Processing
33 Willcocks Street, University of Toronto
Toronto, Ontario, Canada M5S 3B3
ABSTRACT: In this brief report, the effects of reinforcing agents, glycerol and refined cellulose
fiber, have been studied on the foaming reactions of polyurethane based on polyol derived from soy
bean oil. The presence of glycerol and cellulose fiber has been observed to have a considerable
influence on the density of the foams. Changes in density of different foams have been correlated
with the chemical structures generated in the presence of the components, and analyzed by fourier
transform infrared (FTIR) spectroscopic study and thermogravimetric analysis (TGA). Scanning
electron microscopic (SEM) observations are in line with the modifications induced by the
reinforcing components.
KEY WORDS: glycerol, cellulose fiber, foaming, density, polyurethane, spectroscopy, thermal
SOY POLYOL-BASED POLYURETHANE foams are gradually gaining industrial importance
owing to both economic and environmental reasons. Like the conventional
polyurethanes, soy oil-based ones are produced via the reaction of soy polyol with an
isocyanate. For water-blown polyurethanes, foaming basically involves two basic reactions
where the isocyanate reacts with (1) polyol to generate the urethane linkage leading to
curing and (2) with water to form urea and carbon dioxide, the latter expanding the matrix
polymer i.e.:
In polyurethane foaming controlling, the above two reactions are critical to obtain the
target morphology and the final physical properties. It is well known that ingredients in
foam formulation, like the catalyst and blowing agent, significantly affect the reactions
*Author to whom correspondence should be addressed. Email:
Figure 2(a–c) appear in color online:
Journal of REINFORCED PLASTICS AND COMPOSITES,Vol. 27, No. 16–17/2008 1745
0731-6844/08/16–17 1745–14 $10.00/0 DOI: 10.1177/0731684407081442
ßSAGE Publications 2008
Los Angeles, London, New Delhi and Singapore
leading to curing and blowing, and affect the final properties. Materials like glycerol
have been reported to reinforce foam, improving the strength [1]. Its role on foam modi-
fication is understood to be as a crosslinker, enhancing the rigidity of the foam system [2].
Though its effect on foam properties is reported, little is known about the relative effect
glycerol exerts on the reactions leading to foaming and curing, particularly involving
soy polyols of different isocyanate (NCO) indices, where an index denotes ratio of
the equivalents of isocyanate to polyol. In this brief communication, an attempt has
been made to identify the effect of glycerol on the foaming behavior of polyurethane
foams based on soy polyol. In addition, some preliminary studies involving an interesting
effect of cellulose fiber, obtained through mechanical refining, on soy polyurethane
foaming have been reported. Chemical structures generated in various foams have
been analyzed by FTIR measurements and complemented by TGA and SEM
Trifunctional soy polyol R3-170, has been obtained from Urethane Soy Systems, Volga,
SD. The hydroxyl number of the polyol is reported to be 170. The silicone surfactant,
DABCO-DC 5357, and tin and amine catalysts, DABCO T-12 and Dabco 33-LV
respectively, have been supplied by Air Products and Chemicals Inc., USA. The aromatic
diisocyanate, PAPI-27, has been procured from Woodbridge Foam Corporation, Ontario,
Canada. It has a functionality of 2.7 and an equivalent weight of 134 g/eqiv.
A typical formulation, as shown in Table 1, has been used to make a brief comparative
study of the effect of glycerol and cellulose fiber on foaming reactions. The concentration
of ingredients is expressed in parts per hundred parts polyol, php. As known, the silicone
surfactant aids in the dispersion of hydrophilic blowing agent, water, into the hydrophobic
soy polyol system. Tin catalyst mainly accelerates the curing reaction leading to urethane
formation, whereas amine functionality catalyzes both the gelling and the blowing
reaction. To justify the effect of cellulose fiber, it has been added as an aqueous suspension
to the soy polyol system. In order to understand the effect of glycerol on foaming, it has
been incorporated at levels of 0, 10 and 25 php, as distinct changes in foaming have been
noted at these levels.
To prepare foams, polyol and all other ingredients have been mixed in the required
proportions, under ambient conditions, in a formable mold for 5 min, and then the
isocyanate has been added and mixed for an additional minute. To see the effect of
cellulosic fiber on foaming, the blowing agent water was substituted by a dilute aqueous
Table 1. Formulation used in the foaming
of polyurethane.
Ingredients Concentration, php
Soy polyol 100.0
Water 2.0
Dabco-DC 5357 1.0
Dabco-T 12 0.4
Dabco-33 LV 0.4
Glycerol 0, 10, 25
NCO index vary
suspension of the mechanically disintegrated fiber by the same amount (2 php).
The concentration of the refined fiber used has been extremely low (0.1%), and the
fibers have been obtained through a combination of high shear and impact [2]. The reason
for using such a low concentration of fiber has been to attempt to reduce the possible
agglomeration of the same at higher concentrations [3]. The dimensions of the fiber were
measured and reported to be minute (few microns). The time of stirring has been observed
to be very important in affecting the changes in foam properties, and varied from 5 to
20 min. Sample designation of the fiber-filled foam samples are listed in Table 2. Identical
preparation conditions have been followed for each system and at least four foams were
replicated for each experiment. Foams have been characterized by density, FTIR and SEM
measurements. In some cases, rise height and fiber time has been used to monitor the
foaming reactions. Rise height indicates the ease of foaming, whereas fiber time denotes
the time to gelling and is counted from the moment when isocyanate is added to the
mixture of polyol with other ingredients, and allowed to stir. In polyurethane foaming,
both urethane and urea reactions, as stated above, contribute to blowing.
Apparent densities of all the foam samples have been measured according to the ASTM
D 1621-94 method. At least three samples have been considered for density measurements.
The error in the measurement has been 5%. FTIR spectra of the foam samples have been
recorded on KBR pellets using a Brucker infrared spectrometer. The resolution of the
spectra is 4 cm
and 64 scans have been recorded for signal averaging. Comparison of the
spectral absorbances have been obtained by constructing a base line and normalizing the
absorbance of interest by dividing each absorbance by the phenyl absorbtion at 1602 cm
[4]. The concentration of the functional groups was expressed as the abosorbance ratio
(AR). Morphology of the samples have been recorded with a Hitachi S-2500 scanning
electron microscope. The samples have been fractured in liquid nitrogen and then coated
with an alloy of gold and platinum using a sputter coater. TGA analysis has been carried
out using TGA analyzer Q 500, TA Instruments, at a heating rate of 108C/min in a
nitrogen atmosphere. Decomposition temperature of the foam samples at a certain weight
loss has been reported to correlate with the structures generated in the foaming process [4].
Figure 1(a,b) shows the variation of the rise height and density of the foam systems,
based on trifunctional polyol with the level of glycerol at NCO indices of 150 and 200.
It is observed that for each foam system there is a decrease in rise height, with
a concomitant increase in the density of the foam indicating a reduction in the ease of
foaming with increase in level of glycerol. However, as the NCO index is raised, there
is an increase in rise height, accompanied by a decrease in the density of the foam at any
level of glycerol. This indicates enhanced foaming at higher NCO index.
Table 2. Designation of different cellulose fiber-filled foam samples.
Blowing agent System
(2 php of water þ5 min stirring) S1
(2 php of aqueous suspension of microfiber þ5 min stirring) S2
(2 php of water þ20 min stirring) S3
(2 php of aqueous suspension of microfiber þ20 min stirring) S4
Structure of Glycerol and Cellulose Fiber 1747
To verify the observed facts, FTIR observations have been made on the above foam
systems both in presence and absence of glycerol. Figure 1(c) shows the IR spectra of a
typical polyurethane foam based on trifunctional soy polyol. The peak assignments are
reported elsewhere [4–6]. Foams show the presence of N-H bending absorption at
1542 cm
[6] and urethane and urea carbonyl absorptions at 1743 [5] and 1664 cm
respectively. For simplicity, curing tendency has mainly been monitored by changes in IR
peak related to the urethane carbonyl functionality at 1743 cm
, while that corresponding
to blowing by the urea carbonyl group at 1664
. Figure 1(d) depicts the variation of
peaks corresponding to urethane and urea functions for glycerol modified PU foam at an
isocyanate (NCO) index of 150. It is observed that the concentration of the urethane
functionalities increases, while that due to urea group is decreased with rise in level of
glycerol. This supports enhanced networking reactions leading to urethane formation at
increasing levels of glycerol. Presence of glycerol increases the hydroxyl functionality of a
polyurethane system [2]. As the glycerol level is increased, an enhanced isocyanate-glycerol
reaction leads to urethane formation, which results in reduced foaming. To check how the
foaming behavior varies with NCO index, IR features have been compared at two NCO
indices. Figure 1(e–f) represents the comparative variation of the urethane and urea
functionalities at isocyanate indices of 150 and 200. It is observed that with increase in the
0 5 10 15 20 25 30
Rise height (cm)
NCO index: 150
NCO index: 200
Figure 1. (a) Rise height of glycerol modified soy polyurethane foams at different isocyanate (NCO) indices.
(b) Density of various soy polyurethane foams at different levels of glycerol and NCO indices. (c) Typical IR
spectra of a polyurethane foam based on soybean oil. (d) Variation of absorbance ratio due to urethane and
urea functional groups of various soy polyurethane foams modified with different levels of glycerol at a fixed
NCO index of 150. (e) Variation of AR due to urethane carbonyl group of various soy polyurethane foams with
levels of glycerol and at different NCO indices. (f) Plot depicting change in AR due to urea carbonyl group of
soy polyurethane foams at different levels of glycerol and NCO indices. (g) Fiber time of different glycerol
modified soy polyurethane foams at various isocyanate indices. (h) SEM photograph of a soy polyurethane
foam mixed without glycerol at an NCO index of 150. (i) SEM micrograph of soy polyurethane foam modified
with glycerol at a level of 10 php and NCO index of 150. (j) SEM photograph of soy polyurethane foam mixed
with glycerol at a dosage of 25 php and an NCO index of 150. (k) SEM photograph of soy polyurethane foam
modified with glycerol at level of 25 php and an NCO index of 200. (l) TGA thermograms of glycerol modified
soy polyurethane foams.
isocyanate index there is a decrease in AR of the urethane group, with a concomitant
increase in the concentration of the urea group. This indicates that blowing reactions
involving the urea group predominate over urethane formation with an increased NCO
index. The reason is not clearly understood at this point. As urea reactions are enhanced,
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
Absorbance units
1800 1750 1700 1650 1600 1550 1500 1450 1400
Wavenumber (cm1)
Figure 1. Continued.
Glycerol (php)
0 5 10 15 20 25 30
Density (kg/m3)
NCO index: 150
NCO index: 200
Structure of Glycerol and Cellulose Fiber 1749
increased matrix expansion favors reduction in density of the foam at a higher NCO index.
To justify the increased matrix expansion at a higher NCO index, fiber times have been
noted. Figure 1(k) depicts the fiber time of glycerol modified PU foams at two different
NCO indices. It is observed that the fiber time of the glycerol modified foams at a higher
NCO index is lower than the corresponding foam samples at a lower NCO index. This
indirectly supports an enhanced blowing tendency at a higher NCO index. In this case,
gelling is understood to be promoted through urea reaction. Urea formation also
contributes to the gelling process in polyurethane foaming [2, 6].
To justify the foaming behavior of various glycerol modified foam samples, SEM
observations have been carried out on different foam systems. Figure 1(h–j) represents
SEM pictures at different levels of glycerol at a fixed NCO index. It is observed that for the
system without glycerol, void structures are generated in random; but as glycerol content is
progressively increased, formation of cellular structures are much restricted. This is
consistent with the IR observation that in presence of glycerol, urethane structures are
generated in amounts higher than the urea groups and a restricted blowing causes a
hindrance to matrix expansion. To compare the microstructure of the foam at a higher
NCO index, microscopic observation is made at a particular level of glycerol. Figure 1(k)
shows the SEM picture of a foam modified with glycerol at a level of 25 php. Comparison
with a similar foam system at a lower index, as shown in Figure 1(j), shows that cellular
structure in the former are more open, indicating an increased tendency towards expansion
of the foam matrix.
In order test the various structures formed, TGA measurements have been conducted.
Figure 1(l) shows the representative thermograms of foam samples, in this case glycerol
modified polyurethane foams. Decomposition characteristics of the foams are listed in
Table 3. The polyurethane foam degradation is reported to be a multi-step process, with
the first stage representing the decomposition of urethane at about 2608C [1]. Based on
Glycerol (php)
0 5 10 15 20 25 3
Figure 1. Continued.
TGA results, it is observed that the decomposition temperature at 5% weight loss,
appears to agree more closely with the thermal degradation of polyurethane. From the
table, it is observed that with increase in glycerol, at a certain isocyanate index, temp-
eratures at both 5 and 75% weight loss, T
and T
respectively, decrease with increase in
glycerol level. However, with an increased NCO index, the former is enhanced though the
later remains somewhat unaffected. Also, from the result, it appears that the influence of
NCO index and glycerol is larger on T
than the higher decomposition temperature T
As indicated by IR measurements, at a certain NCO index, glycerol addition promotes the
Glycerol (php)
0 5 10 15 20 25 30
AR-1743, NCO index=150
AR-1743, NCO Index=200
Glycerol (php)
0 5 10 15 20 25 30
AR-1664, NCO Index=150
AR-1664, NCO Index=200
Figure 1. Continued.
Structure of Glycerol and Cellulose Fiber 1751
urethane structures, and urethanes have low thermal stability [7]. Hence, decrease of T
and T
at higher glycerol levels may be attributed to the increased formation of unstable
urethane functionalities in the foam matrix. However, as the NCO index is enhanced, T
raised. This is most probably associated with the formation of thermally stable urea
structures in the foam at a higher NCO index. Urea formation has been reported to
increase the thermal stability of the polymer [8].
The effect of refined fibers has also been studied on soy polyurethane foaming.
Figure 2(a) depicts the density of the fiber modified soy polyurethane foams at an NCO
index of 120. It is observed that there is a large increase in density of the system, S4, made
with higher time of stirring (20 min). At intermediate time of mixing, such a change in
foam density has not been noted. To demonstrate and verify, if the observed changes are
due to effects of an altered mixing time, a system (S3) has been made without
incorporating suspension of the refined fiber. It is noted that there is an effect of mixing
time on the density of the resultant foam, but the observed values are much lower that the
foam incorporated with fiber. This indicates that there is an influence of mixing time on
the dispersion of the fiber. At low and intermediate time of mixing, there seems to be lack
of proper dispersion of the hydrophilic fiber suspension in the hydrophobic soy polyol
To understand the effect of refined fiber on foaming, FTIR measurements have been
carried out. Figure 2(b,c) depicts the variation of peaks at 1743 and 1664 cm
observed that, for the system S4, there is an increase in the absorbance ratio of
urethane carbonyl followed by a decrease in the urea carbonyl peak compared to the
systems, S1 and S3, without any fiber. This indicates that curing reactions leading to
urethane formation predominates over blowing with the addition of fiber, especially at
higher mixing times. The results are surprising, and the exact reason is not clearly
understood at this point and needs more detailed investigation. But it appears that
fibers act to supply the hydroxyl functionality necessary to promote urethane formation
0 5 10 15 20 25 30
Fiber time (s)
NCO Index: 150
NCO Index: 200
Figure 1. Continued.
with the isocyanate [1]. Cellulosic materials have been reported to act as a source of
hydroxyl functionality, modifying the properties of the foam and stiffening the
polyurethane foam [9]. The refined fibers are extremely small in dimension and are
characterized by high surface area [2,10] having large number of hydroxyl functions.
Hence, a reduced fiber size is expected to cause lower chain entanglement and increase
the mobility of the fiber during processing, thus enhancing the possibility of reaction of
(h) (i)
(j) (
Figure 1. Continued.
Structure of Glycerol and Cellulose Fiber 1753
more hydroxyl groups on the fiber surface. Refined fibers at a higher concentration
have been observed to loose activity through hydroxyl functionality owing to
agglomeration [3]. More detailed studies would be carried out later to ascertain this
observed fact, using fibers disintegrated for different periods of time. In order to justify
enhanced urethane formation in presence of disintegrated fiber, thermal degradation
studies have carried out to complement the IR observations. Table 4 lists the thermal
decomposition feature of two foam samples in presence and absence of fiber. It is
observed that, in comparison to the sample S1, T
is reduced for the fiber-filled foam,
S4. This seems to justify the formation of relatively more, thermally unstable, urethane
groups in the latter.
Weight (%)
0 100 200 300 400 500 600 70
Temperature (°C)
NCO index150-Glycerol-0 php
NCO index150-Glycerol-25 php
NCO index200-Glycerol-25 php
Figure 1. Continued.
Table 3. Weight loss temperatures of various polyurethane samples.
Foam system
Temperature at 5%
weight loss (T
), 8C
Temperature at 75%
weight loss (T
), 8C
NCO index:150/Glycerol:0 php 267 474
NCO index: 150/Glycerol: 10 php 253 469
NCO index: 150/Glycerol: 25 php 167 466
NCO index: 200/Glycerol: 0 php 284 474
NCO index: 200/Glycerol: 10 php 267 469
NC index: 200/Glycerol: 25 php 216 469
To justify the structure of the micro-fiber modified foams, SEM observations have been
made on two selected systems, S1 and S4, as distinct changes have been noted on these
systems. Figure 2(d,e) denotes the micrographs of two foams corresponding to S1 and S4,
respectively. It is observed that the foam mixed without refined fiber is characterized by
voids much larger in size than one incorporated with micro-fiber. Also, the generation of
void structures are relatively more hindered in presence of micro-fiber. This is due to the
expected preponderance of curing reaction involving urethane formation in presence of
fiber where the matrix is expanded less.
Effect of cellulose fiber and glycerol has been studied on the foaming reactions of
polyurethane based on polyol derived from soy bean oil. For refined cellulose fiber
modified samples, density of the foam is enhanced significantly, particularly at higher
mixing times. Infrared spectroscopic studies and thermal analysis indicate a possible
reduced foaming in presence of fiber. The effect appears to be related to enhanced
urethane formation in presence of refined cellulose fibers. In case of glycerol mixed foams,
S1 S2 S3 S4
PU foams
Density (kg per cubic meter)
Figure 2. (a) Plot showing the density of different soy polyurethane foams in presence and absence of refined
cellulose fibers. (b) Variation of AR due to urethane functional group of various soy polyurethane foam
modified without and with refined fiber. (c) Plot depicting the variation of AR due to urea functional group of
different soy polyurethane foams mixed in presence and absence of refined cellulose fiber. (d) SEM
photograph of soy polyurethane foam mixed without refined fiber. (f) SEM micrograph of a soy polyurethane
foam modified with refined cellulose fiber.
Structure of Glycerol and Cellulose Fiber 1755
S1 S3 S4
PU foams
S1 S2 S3
PU foams
Figure 2. Continued.
urethane formation has been observed to lead to an increase in the foam density with
increasing levels of glycerol at a particular isocyanate (NCO) index, and the density
decreased, due to formation of urea groups, as the index increased. IR and TGA
measurements justify the chemical groups formed in presence of glycerol. Structures of
different foams as verified using scanning electron microscopic (SEM) observations seem
to be consistent with the IR and TGA observations.
The authors acknowledge the financial support received from NSERC-CRD for
carrying out the work.
1. Guo, A., Javni, I. and Petrovic, Z. (2000). Rigid Polyurethane Foams Based on Soybean Oil, J. Appl. Polym.
Sci., 77: 467–473.
2. Chakraborty, A., Sain, M. and Kortschot, M. (2005). Cellulose Microfibrils: A Novel method of Preparing
using High Shear Refining and Cryocrushing, Holzforschung,59: 102–107.
3. Chakroborty, A., Sain, M. and Kortschot, M. (2006). Reinforcing Potential of Wood-Pulp Derived
Microfibers in a PVA Matrix, Holzforschung,60: 53–58.
Figure 2. Continued.
Table 4. Weight loss temperature of different fiber-filled samples.
Foam system
Temperature at 5%
weight loss (T
), 8C
Temperature at 75%
weight loss (T
), 8C
S1 276 464
S4 266 463
Structure of Glycerol and Cellulose Fiber 1757
4. Falke, P., Kudoke, C., Rotermund, I. and Zaschke, B. (1999). Some Aspects of Matrix Formation of
Flexible Polyurethane Foams, J. Cell. Plast., 35: 43–68.
5. Ning, L., Ning, W. D. and Kang, Y. S. (1997). Hydrogen Bonding Properties of Segmented Polyether
Poly(urethane-urea)Copolymer, Macromolecules,30: 4405–4409.
6. Modesti, L., Zanella, A., Lorenzetti, R. Bertani, R. and Gleria, M. (2005). Thermally Stable Hybrid Foams
Based on Cyclophosphazenes and Polyurethanes, Polym. Degrad. Stab., 87: 287–292.
7. Gaboriaud, F. and Vantelon, J. P. (1982). Mechanism of Thermal Degradation of Polyurethane Based on
MDI and Propoxylated Trimethylol Propan, J. Polym. Sci. Part A,20: 2063–2071.
8. Oprea, S. (2000). Effect of Structure on the Thermal Stability of Polyester Urethane Urea Acrylates, Polym.
Degrad. Stab., 75: 9–15.
9. Rivera Armanta, J. L., Heinze, T. and Martinez, A. M. M. (2004). New Polyurethane Foams Modified
with Cellulose Derivatives, Eur. Polym. J., 40: 2803–2812.
10. Bhatnagar, A. and Sain, M. (2005). Processing of Cellulose-Nanofiber Reinforced Composites, J. Reinf.
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... Therefore, a substantial effort has been directed towards developing high performance rigid PU foams. Glycerol and cellulose fiber modified water-blown soy polyol-based PU foams were reported to have increased density and rigidity [17,18]. Rigid PU foams reinforced with spherical TiO 2 , platelet nanoclay, rod-shaped carbon nanofibers [19], and pristine and organically-modified layered silicates [14,20] have been investigated and shown to provide a significant enhancement of thermal and mechanical properties. ...
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A novel nanocomposite of rigid polyurethane foam was prepared by the polymerization of a sucrose-based polyol, a glycerol-based polyol and polymeric methylene diphenyl diisocyanate in the presence of cellulose whiskers. The cell morphology of the resulting foams was examined by scanning electron microscopy which showed both the pure foam and the nanocomposite foam had homogeneous cell dispersion and uniform cell size of approximately 200 mu m. Analysis of the foams by Fourier transform infrared (FT-IR) spectroscopy indicated that both samples exhibited signals attributed to the polyurethane including the NH stretching and bending vibrations at 3320 cm(-1) and 1530 cm(-1), the OC=O vibration at 1730 cm(-1) and the CO-NH vibration at 1600 cm(-1). FT-IR analysis of the nanocomposite indicated that cellulose whiskers were crosslinked with the polyurethane matrix as the signal intensity of the OH stretch at 3500 cm(-1) was significantly reduced in comparison to the spectral data acquired for a control sample prepared from the pure polyurethane foam mixed with cellulose whiskers. According to ASTM standard testing procedures, the tensile modulus, tensile strength and yield strength of the nanocomposite foam were found to be improved by 36.8%, 13.8% and 15.2%, and the compressive modulus and strength were enhanced by 179.9% and 143.4%, respectively. Dynamic mechanical analysis results testified the improvements of mechanical properties and showed a better thermal stability of the nanocomposite foam.
... Production of soy-based polyol is possible via the introduction of functional groups (hydroxyl groups) into unsaturated sites in triglyceride molecules which are present in the oil. The C C double bonds of the triglyceride molecules are transformed into hydroxyl groups which are capable of reacting with isocyanates (Banik and Sain, 2008a;Banik and Sain, 2010;Kiatsimkul et al., 2007). Several techniques have already been proposed for the production of polyol from vegetable oils such as hydroformylation-hydrogenation, epoxidation-oxirane opening, ozonolysis-hydrogenation, and microbial conversion . ...
This work was dedicated to the investigation of the strengthening effects of soy-based rigid polyurethane (PU) foam cores, neat and composite foams containing wood fiber, on the performance of small-scale wooden wall panels under monotonic and static cyclic shear loads. Adding wood fiber resulted in a reduction in the density (23%) and compressive strength (63%) of the foam while specific tensile modulus, ratio of tensile modulus to density of foam, increased about 39%. Both monotonic and static cyclic shear tests showed that inclusion of the composite foam core increased the maximum strength of panels significantly. Panels containing composite foam cores had an average shear strength of 12.0 kN compared to 10.7 kN and 8.0 kN for panels with neat foam and empty panels, respectively. The results of this research demonstrated for the first time that, in addition to their thermal insulation capabilities, soy-based rigid PU foams significantly contribute to the shear strength of wooden wall panels. This characteristic is important especially in the construction of residential and low-rise commercial buildings.
Thermosets from renewable sources have been the research focus of last few decades. Biobased thermoset resins are considered important candidates for sustainable development since they present the potential to reduce both CO2 footprint and the dependency on petroleum. In order to reduce the ecological impact of plastic without compromising mechanical and thermal behavior, in some cases, partially biobased raw materials are accepted. High biocontent resins based on low toxicity raw materials are the goal for the future biobased thermoset polymers. Free-formaldehyde biobased phenol resins and free-bisphenol-A epoxy resins are some examples of this green chemistry concept. The importance of the conversion of biomass into sustainable biobased polymers will be discussed. Chemical pathways developed to make monomers for thermoset polymers from vegetable oils, carbohydrates, lignocelluloses, algae, and even plastic waste will be reviewed. Application and commercialized production of the biobased thermoset polymers will also be highlighted.
Using various micron-sized fillers with cylindirical, plate-like and spherical geometries in PU rigid foams enhances their closed-cellular morphology, mechanical properties, thermal insulation and stability, and flame retardant behavior. For cylindrical micron-sized fillers, synthetic and bio-based fibers can be given as the mostly used filler examples in PU rigid microcomposite foams (PURMCFs). Among plate-like micron-sized fillers, talc and expandable graphite can be given as the most popular additives that have been used in the fabrication of PURMCFs. For spherical micron-sized fillers, silica, calcium carbonate aluminum powder, glass powder, microspheres and carbon black can be given as examples that have been used as fillers in PURMCFs. This chapter systematically reviews important PURMCF works in detail by highlighting subtopics such as morphology, mechanical, thermal and thermomechanical properties, thermal degradation and flammability and recycling and recovery behavior. In addition, potential applications of PURMCFs containing various micron-sized fillers are discussed, and the main problems that are still not resolved and the future work about this important topic are addressed.
Alkali-treated wood fibre-reinforced polyurethane (PU) foams were fabricated with a free-rising foaming process. The surface chemistry of alkali-treated wood fibres was characterized using in situ Fourier transform infrared spectroscopy (FTIR), and the fibre surface morphology was explored using scanning electron microscopy (SEM). X-ray computed tomography (CT) was performed to observe the cell structure of foams incorporating the treated wood fibres. Compression tests were conducted and the influence of treated fibres on the compressive strength and modulus of PU foam was investigated. The foams reinforced with treated fibres exhibited increase of 40% in strength and 64% in modulus. The high surface roughness and high aspect ratio of the treated fibres contributed to these improved mechanical properties through enhanced interfacial bond strengths.
The search for alternative polymer composites prepared by renewable resources is gaining increasing attention in the industrial sector. Here we prepared new polyurethane (PU) composite foams with high percentages of the natural vegetable fibers Spartium Junceum in conjunction with biodegradable polyethylene glycols (PEGs). The density and mechanical properties of PU foams were investigated. Further characterization of the morphology of these materials was carried out by scanning electron microscopy. Here we show that these properties can be easily tuned by changing the molecular length of PEGs, the weight ratio between the two principal monomers, and the fraction of water added to the reacting mixtures. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers
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Cellulose nanofibers are obtained from various sources such as flax bast fibers, hemp fibers, kraft pulp, and rutabaga, by chemical treatments followed by innovative mechanical techniques. The nanofibers thus obtained have diameters between 5 and 60 nm. The ultrastructure of cellulose nanofibers is investigated by atomic force microscopy and transmission electron microscopy. The cellulose nanofibers are also characterized in terms of crystallinity. Reinforced composite films comprising 90% polyvinyl alcohol and 10% nanofibers are also prepared. The comparison of the mechanical properties of these composites with those of pure PVA confirmed the superiority of the former.
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In this study, the reinforcing potential of cellulose “microfibres” obtained from bleached softwood kraft pulp was demonstrated in a matrix of polyvinyl alcohol (PVA). Microfibres are defined as fibres of cellulose of 0.1–1 μm in diameter, with a corresponding minimum length of 5–50 μm. Films cast with these microfibres in PVA showed a doubling of tensile strength and a 2.5-fold increase in stiffness with 5% microfibre loading. The theoretical stiffness of a microfibre was calculated as 69 GPa. The study also demonstrated that the strength of the composite was greater at 5% microfibre loading compared to 10% loading. Comparative studies with microcrystalline cellulose showed that the minimum aspect ratio of the reinforcing agent is more criticalthan its crystallinity in providing reinforcement in the composite.
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New polyurethane foams were elaborated with different cellulose derivatives as raw material, by the one-shot process. The foams were submitted to soxhlet extraction in order to quantify the amount of cellulose derivative incorporated in the foam by chemical bonding. The foams were characterized by means of FTIR, solid state 13C NMR spectroscopy, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy and dynamic mechanical analysis (DMA). The FTIR- and solid state 13C NMR showed characteristic peaks for cellulose derivatives and polyurethane. DMA measurements indicated that storage modulus increased with increasing content of cellulose derivatives. The highest value was obtained for foams prepared with cellulose sulphate.
FTIR was used to investigate the effects of thermal annealing on the hydrogen-bonding properties of a poly(urethane urea) copolymer. The copolymer was based on ethylene oxide-capped poly(propylene oxide) diol, 4,4‘-diphenylmethane diisocyanate (MDI), and 3,5-diethyltoluenediamine (DETDA). The result showed that thermal annealing caused the rise of the number of free urethane groups and the ordering of urea groups. The ordered urea hydrogen bonds were not destroyed below the melting point of the DETDA−MDI hard domain.
This paper describes a novel technique to produce cellulose microfibrils through mechanical methods. The technique involved a combination of severe shearing in a refiner, followed by high-impact crushing under liquid nitrogen. Fibers treated in this way were subsequently either freeze-dried or suspended in water. The fibers were characterized using SEM, TEM, AFM, and high-resolution optical microscopy. In the freeze-dried batch, 75% of the fibrils had diameters of 1 μm and below, whereas in the water dispersed batch, 89% of the fibrils had diameters in this range. The aspect ratio of the microfibrils ranged between 15 and 55 for the freeze-dried fibrils, and from 20 to 85 for the fibrils dispersed in water. These measurements suggest that the microfibrils have the potential to produce composites with high strength and stiffness for high-performance applications. The microfibrils in water were compounded with polylactic acid polymer to form a biocomposite. Laser confocal microscopy showed that the microfibrils were well dispersed in the polymer matrix.
Two cyclotriphosphazenes, containing OH groups, have been synthesized: hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene (PN6), with six hydroxyl groups, and 2,2-di-[p-(hydroxymethyl)phenoxy]-4,4,6,6,-bis[spiro(2′,2″-dioxy-1′,1″-biphenyl)cyclotriphosphazene (PN2) with two hydroxyl groups. They were used in the preparation of modified rigid polyurethane foams as OH containing compounds, alone or in mixtures with polyol components. The thermal stabilities of the resultant hybrid foams were analysed using thermogravimetric analysis (TGA), in inert (nitrogen) and oxidizing (air) atmosphere. The fire behaviour has been investigated by means of oxygen index (LOI) tests. The results showed that the introduction of increasing amount of cyclotriphosphazene in foams leads to a significant improvement of the thermal stability, both in nitrogen and in air. Improvement has also been observed in the fire behaviour of modified foams, particularly for the foams containing cyclotriphosphazene PN2.
A series of poly (ester-urethane-urea)s containing pendant acrylate and methacrylate functionality has been prepared in the presence of the inhibitors of double bond polymerization and without. Introducing diamine and methacrylic structural units extends the hard urethane segments. The effect of structural segments on the thermal stability of curable poly(ester urethane urea) acrylates was studied. A series of compounds, where one segment of the molecular structure was varied, was tested for thermal stability. Increasing the length of the soft segment increases the thermal stability within a given series of compounds. The thermal oxidative stability of the polyurethane acrylate curing system was measured by TGA under air atmosphere. The decomposition of polyurethane acrylates and polyurethane methacrylates has been compared. Polyol-based urethane urea acrylates were found to be more stable than their amine counterparts. It was verified that the presence of urea groups and longer soft segments promoted an increase in the thermal stability. The oligomer structure and presence or not of the inhibitor of double bond polymerization, all afect the thermal stability of the cured coatings.
The reaction of liquid raw materials like isocyanates, polyols, and water, to build a structural polymer network is a very complex sequence of different chemical reactions. We can describe some of these essential processes by the use of a dynamic measurement of the viscosity during the course of the foaming reaction, on-line FTIR-spectrometry measurements and the determination of the curing behaviour. We employed a laboratory FT-IR system, that was interfaced to an optical fibre loop. The formation of the soluble and associated urea species, the decay of isocyanate groups and the development of urethane species during the polymerization reaction were studied by FT-IR. The onset of the formation of associated urea species is influenced by the chemical composition of the reacting mixture. For the viscosity measurements we used a rotational viscosimeter. The network development was shown by the determination of the viscosity profile. By extrapolation of the course of the indentation force over time, estimated after the demould of the flexible foam, we determined the green strength of the moulding and the vitrification of the foam at a frozen morphology. We also illustrated the dependence of the mechanical properties of flexible PU foams on the chemical structures formed during the reaction.
Both HCFC-and pentane-blown rigid polyurethane foams have been prepared from polyols derived from soybean oil. The effect of formulation variables on foam properties was studied by altering the types and amounts of catalyst, surfactant, water, crosslinker, blowing agent, and isocyanate, respectively. While compressive strength of the soy foams is optimal at 2 pph of surfactant B-8404, it increases with increasing the amount of water, glycerin, and isocyanate. It also increases linearly with foam density. These foams were found to have comparable mechanical and thermoinsulating properties to foams of petrochemical origin. A comparison in the thermal and thermo-oxidative behaviors of soy-and PPO-based foams revealed that the former is more stable toward both thermal degradation and thermal oxidation. The lack of ether linkages in the soy-based rather than in PPO-based polyols is thought to be the origin of improved thermal and thermo-oxidative stabilities of soy-based foams.
A polyurethane based on diphenyl methane diisocyanate (MDI) and propoxylated trimethylol propane was thermally degraded by using the techniques of pyrolysis and thermogravimetric analysis (TGA) in an inert atmosphere. Identification of pyrolysis gaseous products at 600°C showed that the first degradation step consists of a reversal of the polycondensation process, i.e., dissociation into starting polyol and diisocyanate, followed by the polyol degradation and a probable diisocyanate polymerization. Kinetic parameters were determined using dynamic and isothermal TGA curves. It is shown that the degradation can be closely compared with a random chain scission process.