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Fiber Reinforced Soy-Based Polyurethane Spray Foam Insulation. Part 1: Cell Morphologies

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Environmentally friendly polyurethane (PU) spray foam insulation was prepared by substituting petrochemical polyol with soy-based polyol. The effects of adding wood fiber and water on the cell morphologies were studied. Cell size increased with the presence of wood fiber, but it decreased with an increase of water (H2O). Still, shorter fiber decreased in foam density but increased in cell size and open cell content.
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FIBER REINFORCED SOY-BASED POLYURETHANE SPRAY
FOAM INSULATION. PART 1: CELL MORPHOLOGIES
Mustafa Khazabi, Ruijun Gu, and Mohini Sain*
Environmentally friendly polyurethane (PU) spray foam insulation was
prepared by substituting petrochemical polyol with soy-based polyol. The
effects of adding wood fiber and water on the cell morphologies were
studied. Cell size increased with the presence of wood fiber, but it
decreased with an increase of water (H2O). Still, shorter fiber decreased
in foam density but increased in cell size and open cell content.
Keywords: Biofoam, Insulation; Polyurethane; Spray foam; Soybean oil; Wood fiber
Contact information: Faculty of Forestry, University of Toronto, Toronto, ON, M5S 3B3 CANADA
* Corresponding author email: m.sain@utoronto.ca
INTRODUCTION
Most sprayed polyurethane (PU) foams are used in the construction/building area
(Bomberg and Kumaran 1999). PU spray foam insulation prevents air leakage and retains
effective energy (Moore and Ference 1998). Compared to traditional insulation, sprayed-
in-place PU foam quickly expands up to 100 times its original liquid size in seconds to
create an airtight environment by sealing and filling each cavity, crevasse, void, and cap,
which overcomes some of the causes of energy loss in a building. This also improves
indoor air quality by blocking harmful outside irritants and eliminates the particles that
are emitted and develop from fibrous and dusty insulations. It provides a healthier indoor
environment. This sealed envelope can also improve sound abatement because airborne
noise can no longer seep through the walls (Falke et al. 2001). In addition, PU spray foam
also has high R-value compared to common insulation materials (Anon, Honeywell
technical document), which will lower heating cost in cooler regions of Canada (Anon,
Dow technical documents). Still, PU insulation adheres well to almost any material,
especially wood and steel studs (Lohman 2005).
Biodegradable foams lower society’s dependence on fossil fuels and have drawn
attention in construction building industry to develop more environmentally friendly
practices (Pollack 2004). Biofoam is a new, entirely sustainable and biologically
degradable polymer made from renewable bio-sources (Meyer 2011). Bio-based polyol
has been prepared from biobased epoxidized vegetable oils (Tan and Chow 2010). Still,
biomass consumes less energy associated with the energy required for the fabrication
process (Anon, Omni Tech International 2010) and reduces the carbon footprint by
absorbing greenhouse gas during the plant lifecycle (Sleeckx 2006). The large output of
soybean oil in North America is motivating the use of soy-based polyol (Soyol) (USDA
2011; Allen 2009).
Soy-based PU spray foam is popular due to its good quality, superior adhesion,
and fast dry-time. Soyol is derived from soybean oils. Soy oils come from soybeans. The
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soy has achieved a higher yield due to advances in its biotechnology. According to the
U.S Department of Agriculture (USDA) figures for 2010, 93% of all of soybeans
produced in USA are genetically engineered for herbicide tolerance (USDA 2010), and
70% of the global productions are biotechnical soybeans (James 2008). The vast majority
of genetically modified soybean oils are used for affordable soyol production by adding
hydroxyl groups at the unsaturated sites (Monteavaro et al. 2005; Petrović et al. 2005).
Soyol, since its invention, has been used in various PU foam applications due to
its renewability (Sherman 2007). Natural fibers, which also are rich in hydroxyl groups,
can be introduced for reinforcement (Silva et al. 2010; Gu et al. 2010; Bledzki et al.
2001) to give a better biodegradation (Silva et al. 2010). Therefore, it would be
interesting to study the cell morphologies of PU spray foam in presence of wood fiber.
EXPERIMENTAL
Materials and Methods
Soy-based Polyol (Soyol)
Soyol, which is rich in triglycerides structures, was prepared from soybean oil by
adding hydroxyls at the unsaturated sites. Low odor Soyol® 2102 was donated by
Urethane Soy Systems (Volga, South Dakota, USA). It is the 5th generation of polyol
made using soybean oil. Its bio-renewable content is as high as 98%, as reported by
ASTM D 6866. Its hydroxyl number was 63 mg KOH/g according to ASTM D4274-99
with the viscosity of 2181 cps at 25ºC.
Isocyanate
Polymeric diphenylmethane-diisocyanate (PMDI) having 31.5% NCO content
was donated by Huntsman and used to produce sprayed foams. Its functionality was 2.7,
as provided by the supplier.
Wood pulp fiber
Steam explosion pulp of trembling aspen (high energy, 8 bar pressure) was
received from Forintek Canada Corp (Point-Claire, Quebec, Canada). This air-dried
industrial aspen Chemical Thermal Mechanical Pulp (CTMP) was cut and screened into
20-35, 35-70, 70-100, 100-140, 140-200, and 200-325 mesh size ranges, respectively. Six
select fibers were introduced into PU spray foams as natural filler. This unbleached
CTMP fiber imparts PU biofoam a dark-brown color.
Catalysts
Diamine was used as a foaming catalyst, which was received from Sigma
Chemical Company. Tertiary amine donated by Air Products and Chemicals, Inc.
(Allentown, Pennsylvania, USA) was used as a gelling catalyst.
Surfactant
Polysiloxane family based surfactant was used to achieve superior cell structures;
these were donated by Air Products and Chemicals, Inc.
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Blowing agent
Distilled water was used as a blowing agent to generate foams; this was prepared
in our lab.
Foam Preparation and Evaluation
PU spray foams were prepared by a free-rise method with the formulations shown
in Table 1. The amount of pulp fiber used was in terms of 100 parts of soyol. The soyol
was manually mixed with the additives (catalysts, surfactant and H2O) for 5 mins under
ambient temperature, and then PMDI was added and mixed for another 20 seconds. The
resultant mixture was quickly transferred into a mold for foaming to get neat PU spray
foams. For the reinforced PU spray foams, wood fiber was pre-mixed with soyol for 20
min to wet completely. The process was the same as the preparation of neat foam.
Finally, all the PU spray foams were kept at the room temperature and well post-cured
overnight.
Obviously, the amount of H2O can be expected to have significant influences on
the cell performances. In this study, the amount of H2O was set in the range of 4.7 to
8.0php (parts per 100 parts) of soyol. When a lower amount (less than 4.7php) of H2O
was used, neat PU foams were shrinkable. Oppositely, neat PU foams would collapse
when the amount of H2O was over 8.0php. From Fig. 1a-c, more H2O helped create a
smooth, plump appearance. With the addition of wood fiber, the foam shrank even
further, as can be seen by comparing with Fig. 1b (no fiber) to Fig. 1d (20php fiber) with
the same 4.7php H2O content. Therefore, the amount of H2O was adjusted to 6.7php in
order to get acceptable fiber reinforced foams as shown in Fig. 1e. Meanwhile, the
foaming and gelling time was extended from 20 seconds up to several minutes when
wood fiber was introduced, according to our observations. In addition, longer curing time
was required as more fiber was added. It demonstrated that wood fiber in particular for
CTMP fiber had a delaying effect on urethane reaction.
Table 1. Formulations for PU Spray Foam Insulation
Materials Parts by weight, php
Neat PU spray foam PU-Fiber spray foam
Soyol Soyol® 2102 100 100
Catalyst Diamine 1.33 1.33
Tertiary amine 2.0 2.0
Surfactant Polysiloxane 0.67 0.67
Blowing agent H2O 4.7; 5.3; 6.7; 8.0 6.7
PMDI NCO index 120 120
Wood fiber 35-70 mesh --- 10; 20†; 30; 40; 50; 60
† Six select fibers were formulated
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Fig. 1. Evaluations of PU spray foams
Fiber Quality Analysis (FQA)
The length of fiber particles and their distribution were measured by Fiber Quality
Analyzer (OpTest equipment Inc. Hawkesburg, Canada). The fiber count was over 5000.
Morphologies of PU Spray Foam
All the foams were conditioned at 23oC and 45% relative humidity, and then the
foam slabs were extracted by cutting with a saw, followed by polishing with a belt sander
(Model 31-710, Rockwell international, Pittsburgh, USA). The size of grit was 120. The
length, width, and thickness were measured after polishing. The thickness is along the
foam rise direction.
Open cell content measurement and foam density
10 small specimens (3cm×3cm×3cm) were used to get the foam densities
according to ASTM D1622-09, and then the open cell percentage was determined by a
Quantachrome Instruments Ultrapychometer 1000 (Boynton Beach, FL) according to
ASTM D6226-05 under 23oC and 45% relative humidity.
Scanning electron microscope (SEM) investigation
Sample stub with thin foam slab was surface metalized by a sputter coating (BOT
341F) with evaporated gold (in 4nm thickness), and then was carried out by SEM
(Hitachi S-2500, Hitachi High Technologies Inc., Tokyo, Japan) at an acceleration
voltage of 15kV.
The cell morphologies were statistically analyzed by ImageJ including feret
diameter, feret distribution, and the regularity of cell (round).
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RESULTS AND DISCUSSIONS
FQA
It has been reported that natural fiber can influence the performances of PU
microfoams (Bledzki et al. 2001). However, PU spray foam is different from the reported
PU foams due to its quick expansion and fast dry-time. In this study the effects of fiber
concentration and fiber size in particular for fiber length on the sprayed foams were
investigated. The length distributions of 6 classified fibers are shown in Fig. 2. The 6
select fibers had roughly the same width by cutting the same original fiber source.
However, the select fibers had distinguished length distributions and exhibited different
average fiber sizes. Fibers in high mesh had short length and narrow distribution, such
that they were more like particles rather than fibers. All these selected fibers were
introduced into sprayed PU foam reaction system after pre-wetting by soyol according to
their fabrication process. The resultant foams were examined to reveal the changes in the
cell morphological structures and performances.
Fig. 2. Average fiber length and distribution of select fibers
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Morphological Structures of PU Spray Foams
Effect of H2O content on cell structures
In general the amount of H2O dominated the cell structures of water-blown PU
foams because the CO2 gas was released from the reaction between water and –NCO
groups of PMDI. But the influence of gas expansion should be neglected if the foam
comprised mostly open cells and avoided “exoterm” problems, such as foam core-
burning. In addition, the effect of the moisture of polyol could also be neglected due to its
very low amount reported by its supplier (max 0.01%).
The effects of H2O on foam density and cell structures are demonstrated in Fig. 3.
In this study, the densities for the neat PU foams varied depending on the amount of
water as blowing agent. Figure 3 shows the variation in density and open cell content of
the neat PU foams with 4.7-8.0php H2O, which was based on the weight of soyol. With
the increase of H2O from 4.7 to 8.0php, the densities of the neat PU foams decreased
from 40.9 to 24.5 kg/m3. This finding corresponded to the results of H2O-blown foams
based on polyester polyol (Thirumal et al. 2008; Li et al. 2006). However, there was
some deviation in cell structures as the open cell content decreased from 90.6% of 4.7php
H2O presented to 87.3% as 6.7php H2O was introduced. After that the open cell content
rebounded to 90.2% again. This change was caused by the un-uniform distribution of
H2O molecules through the whole foam. In any case, the neat PU spray foam can achieve
maximum closed cells in the presence of 6.7php H2O.
Fig. 3. Effect of H2O on foam density and open cell content
Figure 4 shows the cell size distributions of the neat PU foams with different H2O
concentration. The distribution of cell size was narrowed on the downward side as more
H2O was introduced. The decreased mean values of cells sizes have a linear relationship
with an increase in H2O amount, as computed in Fig. 5. The cell feret diameter decreased
from 401 µm to 287 µm when the amount of H2O increased from 4.7php to 8.0php. The
decrease of cell size in biofoam with an increase of H2O content is opposite to the result
of petrochemical PU foam reported by Li et al. (2006). The relationship of cell size to
H2O content can be observed from the SEM images in Fig. 6. The cells became smaller
and nonuniform as more H2O was introduced. This finding was corresponding to the
decrease of cell irregularity as shown in Fig. 5.
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Fig. 4. Effect of H2O on cell size distribution
Fig. 5. Effect of H2O on cell structures
Effect of wood fiber on cell structures
Due to the fact that polyols contain a high content of hydroxyls groups and natural
fiber are well wetted by polyols, the foam matrix was compatible with wood fiber, as
shown in Figs. 7-1a and 8b. When 20php fibers were introduced into the foams, most
fibers were framed in cell walls, as observed in Fig. 8 (a, c and d) due to the good
compatibility between the fibers and polyols. Natural fibers were compatible with
isocyanate. They may react to form units of urethane; the existence of secondary
interactions of the fiber with polymer polyurethane may also be possible. Therefore, the
surface of the fibers was well covered with the polymeric matrix. Only fewer long fibers
were isolated and located in the pores, as shown in Fig. 7. Wood fiber had the most
significant impact on the cell structures, typically to cell supports and cell windows. In
addition, a woody color of pulp fibers was imparted to the fiber-reinforced PU spray
foams with brownish-yellow color. This agglomeration of pulp fibers was clearly seen at
the foam skin, as shown in Fig. 1e.
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Fig. 6. SEM images of neat PU spray foam (50×)
Fig. 7. Long fiber isolation in the cells
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PU has a good adhesion to wood (Wake 1978; Phanopoulos et al. 1999; Somani et
al. 2003; Frihart 2005), especially at high hydroxyl content (Desai et al. 2003). Naturally,
the fiber reinforced PU spray foam is also expected to have a good compatibility between
the introduced fibers and the foam matrix to improve house insulation (Lohman 2005).
Fig. 8. Fiber framed in cell struts
Effect of fiber concentration on cell structures
The overall density of the foams increased steadily following an increase of wood
fiber, as indicated in Fig. 10. The density of the fiber-reinforced foam achieved an
increase of 3.8 times from 28kg/m3 of neat PU spray foam up to 136kg/m3 as 60php fiber
was incorporated. A similar result was also obtained in polyester polyol foam (Silva et al.
2010). Incorporating of the right amount of fiber, such as 10-20php, the foam shrinkage
can be prevented due to the support of stiffer fiber. Even though wood fiber was well
wetted, some fiber destroyed cell structures high levels of fiber, as shown in Fig. 9.
Fig. 9. Fiber existence in PU spray foam with high fiber loading
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From our observation, a typical effect of the addition of fiber into the foam
mixture was an increase in viscosity. Foaming delay, induced by wood fiber, was also
observed, halting the foam expansion and increasing the foam density (Silva et al. 2010).
When more fiber was introduced, a much greater degree of time-delay-induced effects
caused high foam density. This increase in density can be observed in Fig. 10. In addition
to foam density, small amounts of fiber increased the open cell content from 87.3% of
neat PU spray foam up to 91.3% for foam with 10php fiber; this was attributable to the
high perforation behavior of wood fiber (Fig. 9a). However, the open cell content
deceased to 85.5% when 60php fiber was introduced (see Fig. 10) because some cell
walls were overlapped into microvoids in a delayed foaming process (see Fig. 11c-f).
Fig. 10. Effect of fiber concentration on foam density and open cell content
The foam quality was dependent on the amount of fibers present because wood
fiber can be framed into the cell structures, as described earlier. With more fibers
employed, more cells became irregular and defective (Fig. 11) compared to the cells
without fiber present (Fig. 6) (Silva et al. 2010). Stiff fiber also perforated the cell walls,
which made it difficult to distinguish cells. It was hard to find an intact cell in the foam
block in the presence of 60php fiber, as shown in Fig. 11f. In addition, more fiber
introduced had increased the cell size (see Fig. 12). The distribution of cells also became
inhomogeneous, which is shown in Fig. 13. Therefore, the increase in fiber content led to
large irregular cells and a decrease of cell regularity (see Fig. 12) due to the gas releasing
along the fiber axis.
The contribution of cell size in the direction of foam rise increased obviously and
more cells were broken when more fiber was incorporated. With the increase of fiber
concentration, the cell size increased from 314µm of neat PU foam to 655µm of 50php
fiber reinforced foam, as shown in Fig. 12. This finding is contradictory to the finding in
polyester polyol foams (Silva et al. 2010) because of different foam matrix, foaming
technology, and the lack of auxiliary blowing agent in our case. This increase probably
came from the cell breakage, which was caused by the continuous connected fibers,
especially for high fiber loaded foam.
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Fig. 11. SEM images of the fiber reinforced PU spray foams in different fiber concentration (50×)
Fig. 12. Effect of fiber concentration on cell structures
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Fig. 13. Effect of fiber concentration on cell size distribution
Depth-of-field SEM images of the neat foam matrix (Fig. 14) clearly indicated
polyhedral structures, which exhibited polygonal cell shapes (Bandyopadhyay-Ghosh et
al. 2010) and three-dimensional cell wall structures (Fig. 14a) because of triglyceride
molecule structure (Petrović 2008). Each polygonal cell-face was covered by a thin
membranous window. The films are considerably thinner than the struts, as shown in Fig.
8a. In addition, the cell structure altered complex three-dimensional structures when fiber
was introduced (Fig. 14b). Figure 14b shows a cross-section of broken struts, which were
always formed at the junction of three windows (Dawson and Shortall 1982). The cross-
sectional profile for the struts were seen triangular and described as a hypocycloid of
three cusps (Jones and Fesman 1965). However, the nodes were always formed by four
struts from their SEM images. The three struts seen at each node in Fig. 14 were
accompanied by a strut out of the plane of the micrograph.
Fig. 14. Three-dimensional cell structures
a- neat PU spray foam; b- 20php fiber reinforced PU spray foam
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The fiber reinforced PU foams had more broken windows due to the stiffness of
wood fiber from the observations of Figs. 6, 11, and 14. Furthermore, three-dimensional
structures contributed the foams with good dimensional stability. In our case of
predominantly open-cell PU foams (over 85%), the open cells enabled the foam to
breathe, ensuring cell gas equilibration to keep dimensional stability (Brown et al. 2010;
Tylenda 1988).
Effect of fiber size on cell structures
The use of screened fibers as continuous threads in different oriented arrange-
ments provided foams with different final properties. With the decrease of fiber size, the
foam density reduced gradually from 32.7kg/m3 for 20-35 mesh fiber-reinforced foam
down to 27.4kg/m3 for those with use of 200-325 mesh fiber, as shown in Fig. 15. This
could be caused by the existence of much more smaller but numerous fiber particles.
Unlike cell density, the open-cell content increased from 86% to 92% following the fiber
size decreasing from 1.04 mm (20-35 mesh) to 0.175 mm (200-325 mesh). The small
fibers can serve to increase cell amounts to large quantities by an enhanced
heterogeneous nucleation (Ramesh et al. 1994; Rodrigue et al. 2001), which causes cell-
cell borders overlaps, leading to a minor increase of open cell content.
Fig. 15. Effect of fiber size on foam density and open cell content
The experimental measured cell size distributions for each sample were fitted in
Fig. 16. With decreasing size of the fiber, the average cell size distribution increased.
This deviation was exhibited clearly for the foam in a presence of 0.175 mm (200-325
mesh) fiber.
Alternatively, the average cell diameter increased with decreasing fiber length,
which was observed from Fig. 17. However, the effect of fiber size was not clear on the
cell regularity.
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Fig. 16. Effect of fiber size on cell size distribution
Small fiber particles can accelerate the amount of foam cells as a nucleation agent
(Ramesh et al. 1994; Rodrigue et al. 2001). The thickness of cell wall was expected to be
thin following the decrease of the foam density. Therefore, several crowded thin cells
must crowded together to build large microcavities, as shown in Fig. 18.
Shorter fibers contributed to a larger average cell size, which was computed in
Fig. 17. The increase of cell diameter was hypothesized as coming from these overlaps.
Unlike the fiber content, the fiber size had less impact on the cell regularity. These
findings indicated that the cell regularity mostly depended on the amount of fibers, not
the fiber length.
Fig. 17. Effect of fiber size on cell structures
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Fig. 18. SEM images of the fiber reinforced PU spray foam in different fiber size (50×)
CONCLUSIONS
PU spray foams with varying density using water as a blowing agent were
prepared via a free-rise method. The amount of water affected the cell structures by
increasing cell size. It was possible to prepare sprayed PU biofoams with wood fiber
using a soy-based polyol. From their SEM images, wood fiber was compatible with the
foam matrix due to their chemical reactions and similar polarities. The amount of fiber
had significant effects on the cell structures, in particular the increase of cell size and of
foam density, which was estimated from the cell walls broken and the low foam rise.
In general, long fiber showed better comparative properties, which was related to
its high aspect ratio, contributing to complex structures that can act as a chain extender.
Short fiber showed low aspect ratio. Such particles acted as a nucleation agent to create
more cells and decreased the thickness of cell walls, since foam density decreased. The
foam cells with decreased cell walls were favored in terms of overlap effects by building
large microvoids, exhibiting an increase of cell size and open cell content.
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ACKNOWLEDGEMENTS
The authors would like to thank the NSERC-CRD and FPInnovations for the
financial support. We would also thank Air Products and Chemicals Inc., Huntsman, and
Urethane Soy Systems for their donations of materials.
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... The morphology changes at higher fiber concentrations, and the fibers present good adhesion with the matrix. The fibers can improve the crosslink reaction, promoting higher porosity with smaller cell sizes, as shown in Table 2. 42,43 No loose fibers were found in the middle of empty cells confirm the good adhesion. 40 Good adhesion at higher concentrations of fiber can be associated with the more significant number of free hydroxyls available to interact with the active isocyanate groups and the hydrophilic character of PU and fibers. ...
... 43 The formation of hydrogen bonds forms urethane units, and the fibers participate in the formation of the porous structure. 41,42 The PU composite foams' open porosity plays a crucial role in numerous applications, such as sound absorption efficiency and removal of toxic compounds of gases. 43,44 The fibers reinforced in polyurethane do not exhibit preferential orientation either; however, they were more irregular, and a defective shape of cells with many cracks was observed. ...
... 40 Additionally, the fibers restrained the cell's expansion, which promoted a significant number of small cells with a thinner cell structure, commonly observed in PU composites. 41,42 Mechanical results: Compression tests Figure 5 shows the compressive stress-strain curves for PU and its composites. The curves presented three typical stages of deformation: initially, there is a linear behavior between stress and strain; then a plateau region where the deformation increases significantly without significant changes on stress; and finally, a region where the densification of foam occurs and the stress rises quickly until the fracture point. ...
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This work prepared eco-friendly biocomposites of polyurethane (PU) and sheath palm residues, using castor oil as a polyol. PU composites filled with natural fibers were prepared at different loading rates: 0 to 20 wt.%. Results indicated that the sheath palm was hydrogen-bonded to PU chains and increased the foams' density. Pore size decreased with an increase in fiber content, from 256 to 116 µm. The fiber's addition improved the ductility of PU foams (compressive modulus from 4.74 to 0.26 MPa) and the foams' crystallinity index (from 5.4 to 15.4%). Compared to pristine PU, the composites showed high hydrophobicity (reaching 123° of contact angle for PU-15%) and thermal stability (T onset from 96 to 96.3°), and high density (from 41 to 60 kg.m ⁻³ ), making the developed composites an excellent option for environmental applications, such as oil removal and contaminant adsorption.
... Polyurethane (PUR) is a class of polymer exhibiting a wide range of applications. Therefore, many efforts have been made to investigate the applicability of bio-based polyols in polyurethane materials; these include glycerol derivatives (Mamiński et al. 2012), liquefied wood (Wei et al. 2004;Juhaida et al. 2010), soy derivatives (Khazabi et al. 2011) and oils (Desroches et al. 2012;Gava et al. 2015). The pathways for conversion of vegetable oils into polyols for rigid and flexible foams were widely discussed by Petrović (2008). ...
... The phenomenon comes from variability in the viscosity of the formulations and overall reactivity of the system that subsequently affected carbon dioxide entrapping and the foam-shape fixation conditions. The pore sizing, shown in Table 1 and Fig. 2, was comparable to those reported in other works for bio-based PUR foams, e.g., 0.28 to 0.40 mm (Khazabi et al. 2011). ...
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Lignosulfonate and lignosulfonate hydrolyzed under alkaline conditions were used as the polyol components in polyurethane foam formulations. Although the treatment increased hydroxyl group abundance, it did not improve the applicability of hydrolyzed lignosulfonate in polyurethane foam. Thus, the use of original lignosulfonate yielded foams of thermal stability and mechanical properties comparable to other types of bio-based foams (Young's moduli 0.95 to 4.42 MPa, 50% weight loss, and temperature ca. 500 °C). Lignosulfonates can be a renewable polyol component for the formulation of rigid, semi-rigid, and flexible foams.
... The authors are aware of several papers (Harikrishnan et al., 2006;Wang and Yang, 2020;Zhang et al., 2019) describing the synthesis of open-cell PUR foams with relatively high apparent densities (45-90 kg/m 3 ) for purposes other than insulation. Gu et al. (2011) and Khazabi et al. (2011) described the manufacture of a fiber-reinforced soyoil-based polyurethane foams with an apparent density >24.5 kg/m 3 and open cell content >85%. The thermal conductivity coefficient of the foams was not tested. ...
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Used cooking oil is a widely available and inexpensive waste with a high application potential as a feedstock for the bio-based polyurethane production. Usually, bio-polyols from vegetable oils have higher viscosity and lower hydroxyl values compared to commercial petrochemical polyols, which limits their usefulness. This article reports on the development of open-cell polyurethane foam systems wherein 100% of the polyol components were bio-polyols obtained from used cooking oil. What is particularly considered is the effect of bio-polyol properties (molecular weight, viscosity and hydroxyl value) on the properties of the final open-cell polyurethane systems - apparent density, thermal conductivity coefficient, content of closed cells, mechanical strength, brittleness and short-term water absorption. It was found that the key step in the synthesis of bio-polyols designed for open-cell polyurethane foams is the epoxidation reaction. The epoxy value has a significant effect on the occurrence of side reactions (mainly oligomerization) during the oxirane ring-opening process determining the properties of bio-polyols. The resulting open-cell foams were characterized by apparent densities from 12.4 to 13.3 kg/m3, thermal conductivity coefficients from 36.6 to 38.2 mW/m∙K, and closed cell contents below 10%, which makes them comparable to commercial products. The results demonstrate that used cooking oil-based polyols can provide an alternative starting material for open-cell polyurethane foam production.
... Wood fibre based materials still have a high optimisation potential (Hobballah et al. 2018). The same is true for combination of lignocellulosic fibres with foams, but there is little literature referring to the topic in combi- nation with polyurethane foams ( Khazabi et al. 2011). No literature is available which considers 100% natural fibres foams as insulation materials. ...
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X-ray tomography and densitometry (XRT and XRD) were applied to characterise wood fibre based insulation materials, which were produced by the foam forming technology. XRT is a high resolution approach with long measurement times of around 29 h, while XRD measurement needs only a few minutes. The determination of density distribution of boards in the thickness direction was the focus of this study. Both approaches visualised well the impact of raw materials and manufacturing processes on the structure of the panels. The density profiles were dependent on the pulp applied for panel production, and the processing conditions were also influential. Air flow resistance correlated with the maximum density measured inside the board. Both XRT and XRD revealed similar trends, which are useful for the characterisation of insulation materials.
... Moreover, for PUR/BSG20 and PUR/ BSG10/GTR10 samples more cells were broken comparing to PUR without fillers. Similar observations were described by Khazabi et al. (2011), which investigated the impact of wood fibers on morphology of soy-based polyurethane spray foam. On the other hand, the microstructure of PUR/GTR20 sample was similar to reference sample (average cell size for these samples: 200 μm), which indicates that application of GTR enhance formulation of smaller and more regular polyurethane cells. ...
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... Natural fibers might also be suitable for use in fiber reinforced polyurethane foams. Fibers can improve the mechanical strength [11,12] and potentially yield cost savings. However, mixing short fibers with the fast curing foams is a challenge that may limit the fraction of fibers in the final product. ...
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Natural fibers can be attractive reinforcing materials in thermosetting polymers due to their low density and high specific mechanical properties. Although the research effort in this area has grown substantially over the last 20 years, manufacturing technologies to make use of short natural fibers in high volume fraction composites; are still limited. Natural fibers, after retting and preprocessing, are discontinuous and easily form entangled bundles. Dispersion and mixing these short fibers with resin to manufacture high quality, high volume fraction composites presents a significant challenge. In this paper, a novel pneumatic design for dispersion of natural fibers in their original discontinuous form is described. In this design, compressed air is used to create vacuum to feed and convey fibres while breaking down fibre clumps and dispersing them in an aerosolized resin stream. Model composite materials, made using proof-of-concept prototype equipment, were imaged with both optical and X-ray tomography to evaluate fibre and resin dispersion. The images indicated that the system was capable of providing an intimate mixture of resin and detangled fibres for two different resin viscosities. The new pneumatic process could serve as the basis of a system to produce well-dispersed high-volume fraction composites containing discontinuous natural fibres drawn directly from a loosely packed source.
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Polyurethane (PU) composite foams were successfully reinforced with different concentrations (1 wt%, 2 wt%, 5 wt%) of nutmeg filler. The effect of nutmeg filler concentration on mechanical, thermal, antimicrobial and anti-aging properties of PU composite foams was investigated. PU foams were examined by rheological behavior, processing parameters, cellular structure (Scanning Electron Microscopy analysis), mechanical properties (compression test, impact test, three-point bending test, impact strength), thermal properties (Thermogravimetric Analysis), viscoelastic behavior (Dynamic Mechanical Analysis) as well as selected application properties (thermal conductivity, flammability, apparent density, dimensional stability, surface hydrophobicity, water absorption, color characteristic). In order to Disc Diffusion Method, all PU composites were tested against selected bacteria (Escherichia coli and Staphylococcus aureus). Based on the results, it can be concluded that the addition of 1 wt% of nutmeg filler leads to PU composite foams with improved compression strength (e.g. improvement by ∼19%), higher flexural strength (e.g. increase of ∼11%), improved impact strength (e.g. increase of ∼32%) and comparable thermal conductivity (0.023–0.034 W m⁻¹ K⁻¹). Moreover, the incorporation of nutmeg filler has a positive effect on the fire resistance of PU materials. For example, the results from the cone calorimeter test showed that the incorporation of 5 wt% of nutmeg filler significantly reduced the peak of heat release rate (pHRR) by ca. 60% compared with that of unmodified PU foam. It has been also proved that nutmeg filler may act as a natural anti-aging compound of PU foams. The incorporation of nutmeg filler in each amount successfully improved the stabilization of PU composite foams. Based on the antibacterial results, it has been shown that the addition of nutmeg filler significantly improved the antibacterial properties of PU composite foams against both Gram-positive and Gram-negative bacteria.
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The effects of filler loading and size of kenaf fibre on the mechanical properties of kenaf fibre-filled natural rubber latex foam (NRLF) have been studied. The NRLF was prepared by using the Dunlop method. The kenaf fibre was sieved to 97, 144 and 200 µm particle sizes and incorporated into the rubber vulcanizates at 0, 1, 3, 5 and 7 part per hundred rubber fibre contents. Increasing kenaf fibre loading in NRLF resulted in the reduction of tensile strength, elongation at break and recovery percentage but increased in modulus at 100% (M100), compression strength, compression set, hardness and foam density. At the same kenaf fibre loading, smaller size of kenaf fibre-filled NRLF showed higher tensile properties, compression strength, compression set and hardness. Scanning electron microscope demonstrated that as kenaf fibre loading and size increased, a larger pore size of NRLF was formed and this led to tensile strength, M100, compression strength and hardness.
Chapter
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Wood has played a major role throughout human history. Strong and versatile, the earliest humans used wood to make shelters, cook food, construct tools, build boats, and make weapons. Recently, scientists, politicians, and economists have renewed their interest in wood because of its unique properties, aesthetics, availability, abundance, and perhaps most important of all, its renewability. However, wood will not reach its highest use potential until we fully describe it, understand the mechanisms that control its performance properties, and, finally, are able to manipulate those properties to give us the desired performance we seek. The Handbook of Wood Chemistry and Wood Composites analyzes the chemical composition and physical properties of wood cellulose and its response to natural processes of degradation. It describes safe and effective chemical modifications to strengthen wood against biological, chemical, and mechanical degradation without using toxic, leachable, or corrosive chemicals. Expert researchers provide insightful analyses of the types of chemical modifications applied to polymer cell walls in wood. They emphasize the mechanisms of reaction involved and resulting changes in performance properties including modifications that increase water repellency, fire retardancy, and resistance to ultraviolet light, heat, moisture, mold, and other biological organisms. The text also explores modifications that increase mechanical strength, such as lumen fill, monomer polymer penetration, and plasticization. The Handbook of Wood Chemistry and Wood Composites concludes with the latest applications, such as adhesives, geotextiles, and sorbents, and future trends in the use of wood-based composites in terms of sustainable agriculture, biodegradability and recycling, and economics. Incorporating decades of teaching experience, the editor of this handbook is well-attuned to educational demands as well as industry standards and research trends.
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Vegetable oils are excellent but very heterogeneous renewable raw materials for polyols and polyurethanes. This review discusses the specific nature of vegetable oils and the effect of their structures on the structure of polyols and polyurethanes. One section is dedicated to polyols for rigid and flexible foams and methods of their preparation such as direct oxidation of oils, epoxidation followed by ring opening, hydroformylation, ozonolysis, and transesterification. The next section deals with preparation and structure‐property relationships in polyurethanes from different groups of polyols, different isocyanates, and different degrees of crosslinking. The final section covers the environmental aspects of bio‐based polyurethanes, i.e., thermal stability, hydrolytic stability, and some aspects of biodegradability.
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The contents of a report by the US Department of Agriculture on world trade in cotton released in August 1997 are summarized. World production and prices, imports, exports and stocks, and the textile industries of the USA, Colombia, France, Paraguay, Syria and Uzbekistan are discussed.
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Epoxidized vegetable oils (EVO) have drawn much attention in recent years, especially in the polymer industry as they are economical, available, environmentally friendly, non-noxious and renewable. Vegetable oils can be transformed into useful polymerizable oxygenated monomers commonly by Prileshajev-epoxidation, catalytic epoxidation using acidic ion exchange resin, chemo-enzymatic epoxidation, or metal-catalyzed epoxidation. Among those epoxidation methods, chemo-enzymatic epoxidation has achieved considerable interest nowadays since this method is safe, environmentally friendly and conversion rate of epoxidation usually exceeds 90%. Bio-based epoxidized vegetable oils from renewable natural resources are potential green materials to partially substitute and toughen petrochemical-based polymers.
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A slab stock urethane foam cell ideally resembles an elongated pentagonal dodeca hedron. The faces are bounded by ribs, and membranes stretch across the ribs during the expansion of the foam. The normal formation of the foam does not result in the rupture of all the membranes. Data are presented showing that Air Flow values for flexible polyether and polyester foams are affected profoundly by the membrane population and, to a smaller extent, by density and cell geometry. It is also shown that within a given bun Air Flow values may vary with both position and orientation. Air Flow val ues also vary considerably between different foams. Because variation in Air Flow values is related to cell structure, it can be related to certain physical properties. Examples of this are given for ball rebound, compression load deflection, flex fatigue, and color shad ing. A quantitative definition of operating range based on Air Flow values is demon strated for tin catalyst concentration in a polyether foam. As a result of these findings Air Flow is recommended as a new parame ter for describing flexible urethane foam cell structure.
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Theories of adhesion are based on adsorption and wetting, on diffusion, on donor/acceptor or electrostatic interactions and on simple mechanical interlocking of the adhesive into irregularities of its substrate. The principal contributions of recent work to these theories are outlined. Joint strength is also a matter of stress distribution and knowledge of this has been advanced both by formal mathematical methods and by the use of finite element analysis. The tack of adhesives is now better understood as involving the interaction of both bulk and surface properties with the rate of separation. Fracture mechanics has been applied to the investigation of the failure of structural adhesives in humid environments. The properties determining adhesive behaviour comprise Tg, solubility parameter, surface free energy, viscosity and the microstructure of the polymer. The latter, more recently explored, is examined in detail. The structure of the adhesives for use at high temperature and the changes in technology demanded by impending legislation conclude the review.
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Density is an important parameter that influences the properties and performances of rigid polyurethane foam (PUF). Rigid PUF with different densities were prepared by varying the amount of distilled water as blowing agent. This investigation reports the mechanical, morphological, water absorption, thermal conductivity, and thermal behavior of rigid PUF varying with the density, which controls the foam architecture. The density of the PUF decreased from 116 to 42 kg/m3 with an increase in the amount of water from 0.1 to 3.0 parts per hundred polyol by weight (phr), respectively. It was found that the mechanical properties of the PUFs changed with the foam density. The results of water absorption of the PUFs showed that water absorption increased with decrease in density, due to increase in the cell size and decrease in the cell-wall thickness. The thermal conductivity measurements showed that the thermal conductivity decreased with increase in density. It was due to the decrease in cell size. The thermal analysis of the PUFs shows that the glass transition temperature increases with the decrease in foam density, but the thermal stability decreases with the decrease in foam density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008