10.1. abstract - shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/13586/18/18... · 2015. 12....
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10.1. ABSTRACT
Guargum is having poor elongation as well as transparency therefore in order to
improve these properties; Guargum was blended with polyvinyl alcohol (PVA) using
solution casting process. In this work first blends of guargum/PVA were prepared by
solution casting process and then characterization was carried out. The optimized
batches of chitosan/PVA and guargum/PVA were selected and into which different
concentrations of CNW/LNW and CNF/LNF were incorporated again by using
casting process and their performance was evaluated. It was observed that with
varying the compositions of the guargum and PVA, most of the properties (especially
mechanical, barrier and transparency) were improved significantly. All the properties
of the guargum/PVA blends composites were deteriorated as the nanocellulose (both
cellulose nanowhiskers and nanofibers) incorporated into it.
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10.2. INTRODUCTION
Polymer Blend is a mixture of at least two polymers or copolymers. Polymer blends
are becoming more important in specific sectors of polymer industry, as they can
frequently meet performance requirements that cannot be satisfied by the currently
available commodity polymers. Consequently, their attractiveness increases with the
increasing demands for this class of materials (Aiman et al, 2006). The primary
purpose of blending polymers is to create materials with combinations of properties
superior than the individual polymers (Utracki L. A. 1989 and Hara et al, 1989).
Polymers from renewable resources have attracted an increasing amount of attention
over the last two decades, predominantly due to two major reasons: firstly
environmental concerns, and secondly the realization that our petroleum resources are
finite. Many natural polymers are hydrophilic and some of them are water soluble.
Water solubility increases the speed of degradation but this limits its applications.
Therefore blending natural polymers can be good option in order to elevate its
performance properties. Blends can also aid in the development of new low cost
products with better performance. These new blends and composites are extending the
utilization of polymers from renewable resource into new value added products (Long
et al, 2006)
In the present study guargum and PVA was blended together in order to get final
properties superior to the individual polymers. Blends of various compositions of
guargum and PVA were prepared by solution casting process and the one which gave
best results with respect to mechanical properties was optimized. Cellulose
nanowhiskers (CNW/LNW) and cellulose nanofibers (CNF/LNF) were used as the
reinforcement in optimized batch to obtain guargum/PVA blend-nanocellulose
composites.
10.3. EXPERIMENTAL WORK
10.3.1. Materials and Methods
Short staple cotton fibers and cotton linters were used as the starting material were
procured from Fem Cotton Pvt. Ltd., Rajkot, India. Sodium hydroxide and hydrogen
peroxide were purchased from Thermo Fisher Scientific India Pvt. Ltd., Mumbai,
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India. Sodium silicate (meta) nonhydrate and hydrochloric acid (11.6N) were supplied
by S. D. Fine-Chem Ltd., Mumbai, India. Nonyl phenol ethylene oxide (wetting
agent) was supplied by Amrutlal Industrial products, Mumbai, India. Microcrystalline
cellulose was produced from cotton fibers and cotton linters by acid hydrolysis using
hydrochloric acid. Guargum and polyvinyl alcohol were purchased from Himedia
Laboratories Ltd. India. All chemicals were used as supplied without any
modification or further purification.
Cellulose nanowhiskers and nanofibers were produced in our laboratory using
Chemo-mechanical process and used as the reinforcement in guargum/PVA blend
composites.
Blends of guargum and PVA with varying compositions (0/100, 20/80, 40/60, 60/40,
80/20, and 100/0) were prepared by solution casting method. The optimimum
composition of guargum and PVA was selected based on the mechanical properties of
the blends. Guargum/PVA (80:20) blend gave maximum strength therefore this
composition was selected in which different concentrations of cellulose nanofibers
and nanowhiskers varied to prepare guargum/PVA blend composites.
10.3.2. Process flow diagram
Process flow diagrams for Preparation of Guargum/PVA Blends and Cellulose
Nanowhiskers and Nanofibers reinforced Guargum/PVA Blend Composites have
been depicted in figures 10.1 and 10.2 respectively.
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Figure 10.1. Process flow diagram for preparation of Guargum/PVA Blends by
Solution Casting method
Guargum PVA
Mixing in distilled water at
70°C for 60 Minutes
Solution Casting into Moulds followed by drying
@40°C for 24 Hrs
Characterization
Mechanical
Properties
Optical Properties DSC XRD Barrier Properties
Morphological
properties
Mixing in distilled water at
100°C for 60 Minutes
Blending
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Figure 10.2. Process flow diagram for Preparation of Cellulose Nanowhiskers and
Nanofibers reinforced Guargum/PVA Blend Composites
10.4. CHARACTERIZATION
10.4.1. Mechanical properties
The tensile strength and percent elongation at break of the films was determined using
Universal Testing Machine (LR-50K, LLOYD instrument, UK) using 500N load cell
in accordance to ASTM D 882.
Guargum+PVA Cellulose Nanowhiskers
(CNW/LNW and CNF/LNF)
Mixing in distilled water at
70°C for 60 Minutes
Solution Casting into Moulds followed by drying
@40°C for 24 Hrs
Characterization
Mechanical Properties
Optical Properties DSC XRD Barrier Properties
Morphological
properties
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10.4.2. Differential scanning calorimeter (DSC)
DSC was used to measure thermal transitions of the chitosan/CNW nanocomposite
films. The test was performed using Q100 DSC (TA Instruments) equipment, fitted
with an nitrogen-based cooling system. The samples were weighed in aluminium pans
whereas an empty pan was used as the reference pan. All the measurements were
performed in the temperature range from -40 to 200ºC at a heating rate of 10ºC/min.
10.4.3. X-ray diffraction (XRD) Analysis
X-ray Diffraction (XRD) patterns were obtained using a Rigaku Miniflex X-ray
diffractometer using Cu target and having X-ray wavelength of 1.54 A through 4 to
40° angle.
10.4.4. Optical properties
The light transmittance of the chitosan and chitosan/CNW films having thickness of
about 70 µm was measured using an ultraviolet–visible (UV–Vis) spectroscope (UV-
160A, Shimadzu, Japan) in a wavelength range from 200–800 nm.
10.4.5. Water vapour transmission rate (WVTR)
Water Vapour Transmission Rate (WVTR) of the films was determined
gravimetrically in accordance to ASTM E96. The composite films were cut into
circles of 90 mm diameter and then were sealed on the permeation cells, containing
calcium chloride, using paraffin wax. The permeation cells were placed in a
desiccators in which RH was maintained at 71%. The water transferred through the
film gets absorbed by the desiccant which is determined from the weight of the
permeation cell. Each permeation cell was weighed at an interval of 24 hrs. The
WVTR was expressed in g/h.m2 per day.
10.4.6. Morphological properties
The morphology of the nanocomposite films was observed under a scanning electron
microscope (SEM). SEM analysis was carried out using Philips® XL30 (Netherland)
Scanning Electron Microscope. Samples were fractured under liquid nitrogen to avoid
any disturbance to the molecular structure. The specimens were then coated with gold
and palladium using sputter coater before imaging.
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10.5. RESULTS AND DISCUSSIONS
10.5.1. Mechanical properties
Figure10.3. Effect of various compositions of Guargum and PVA on tensile strength
of Guargum/PVA blends
Figure 10.4. Effect of various compositions of Guargum and PVA on Youngs
modulus of Guargum/PVA blends
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Figure 10.5. Effect of various compositions of Guargum and PVA on elongation at
break of Guargum/PVA blends
Figures 10.3, 10.4 and 10.5 depict the mechanical properties like of the tensile
strength, Youngs modulus and percentage elongation at break of control guargum,
guargum/PVA blends and control PVA. Tensile strength and Youngs modulus
increased as the concentration of PVA increased but as it was increased above 20%
they started decreasing. Tensile strength & Youngs modulus were found to have
increased by 38 and 39% respectively, whereas, percentage elongation at break
reduced up to 80:20 (Guargum: PVA) composition and beyond which started
increasing. As the concentration of PVA increased above 20% it might have started
distributing unevenly resulting in more number of stress concentration points.
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10.5.2. Differential Scanning Calorimetry (DSC) Analysis
Figure 10.6. Effect of various compositions of Guargum and PVA on thermal
properties of Guargum/PVA blends
Figure 10.6 depicts the effect of various compositions of Guargum and PVA on
thermal properties of Guargum/PVA blends. It was observed that PVA has slightly
lower melting range as compared to control guargum and as the concentration of the
guargum was increased; melting temperature started shifting towards higher
temperature. This was probably due higher melting range of the control guargum as
compared to PVA and synergistic effect.
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10.5.3. Transparency
Figure 10.7. Effect of various compositions of Guargum and PVA on transparency of
Guargum/PVA blends
Figure 10.7 depict the effect of various compositions of guargum and PVA on the
transparency of the guargum/PVA blend. I can be clearly seen from the above figure
that control guargum had lower transparency but as the concentration of PVA
increased it started increasing and control PVA had highest value of transparency as
compared to all blend compositions. Generally addition of transparent PVA in to
slightly opaque guargum, transparency of the blend is bound to increase and this was
quite in agreement with the experimental observations.
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10.5.4. Effect of Cellulose nanowhiskers and nanofibers on Water Vapour
Permeability of the Guargum/PVA blend Composites
Figure 10.8. Effect of CNW concentrations on water vapour transmission of the
Guargum/PVA blend
Figure 10.8 depicts the WVTR of control Guargum/PVA blend and Guargum/PVA
blend composites reinforced with CNW, LNW, CNF and LNF. It was observed that
addition of PVA into guargum reduced WVTR drastically to 72.66% as compared to
control guargum but as the concentrations of PVA in to Guargum/PVA blends were
increased, WVTR increased continuously up to 12%. Addition of PVA in Guargum
might have resulted uneven distribution as well as poor compatibility with the
guargum.
10.5.5. Effect of Cellulose nanowhiskers and nanofibers on mechanical
properties of the Guargum/PVA blend Composites
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Figure 10.9. Effect of concentration of Nanowhiskers and Nanofibers on tensile
strength of Guargum/PVA blend composites
Figure 10.9 depicts the effect of concentration of cellulose nanowhiskers (CNW and
LNW) and nanofibers (CNF and LNF) on tensile strength of Guargum/PVA blend
composites. It was observed control guargum/PVA blend had higher tensile strength
but as the concentrations of cellulose nanowhiskers (CNW and LNW) and nanofibers
(CNF and LNF) into the guargum/PVA blend increased, the blend composites
resulted with decreasing the tensile strength. This may due to higher concentrations of
nanocellulose induced more stress concentration points. The decrease in tensile
strength may also be attributed to poor interaction between the nanocellulose and
guargum/PVA blend matrix.
Figure 10.10. Effect of concentration of CNW and LNW on Youngs modulus of
Guargum/PVA blend Composites
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Figure 10.10 depicts the effect of concentration of cellulose nanowhiskers (CNW and
LNW) and nanofibers (CNF and LNF) on Youngs modulus of Guargum/PVA blend
composites. It was observed control guargum/PVA blend had higher Youngs modulus
but as the concentrations of cellulose nanowhiskers (CNW and LNW) and nanofibers
(CNF and LNF) into the guargum/PVA blend increased, the blend composites
resulted with decreasing the Youngs modulus. Youngs modulus values for control
guargum/PVA blend was 1803 MPa but reduced to 830, 966, 968 and 1169 MPa after
incorporation of CNW, LNW, CNF and LNF respectively. This may due to higher
concentrations of nanocellulose induced more stress concentration points. The
decrease in Youngs modulus may also be attributed to poor interaction between the
nanocellulose and guargum/PVA blend matrix.
Figure 10.11. Effect of concentration of CNW and LNW on elongation at break of
Guargum/PVA blend composites
Figure 10.11 depict the effect of concentration of CNW and LNW on elongation at
break of Guargum/PVA blend composites. As observed from the above figures, %
elongation at break decreased drastically with increase in concentrations of CNW,
LNW, CNF and LNF. This may due to higher concentrations of nanocellulose
induced more stress concentration points which further increases the rigidity of the
blend composite. The decrease in % elongation at break may also be attributed to poor
interaction between the nanocellulose and guargum/PVA blend matrix.
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10.5.6. Effect of Cellulose nanowhiskers and nanofibers on X-ray diffraction
pattern of the Guargum/PVA blend Composites
Figure 10.12. X-ray crystallographs of the CNW reinforced guargum/PVA blend
composites
Figure 10.13. X-ray crystallographs of the LNW reinforced guargum/PVA blend
composites
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Figure 10.14. X-ray crystallographs of the CNF reinforced guargum/PVA blend
composites
Figure 10.15. X-ray crystallographs of the LNF reinforced guargum/PVA blend
composites
Figures 10.12, 10.13, 10.14 and 10.15 indicates the X-ray crystallographs of the
control cellulose (CNW, LNW, CNF and LNF), control guargum, control PVA and
guargum/PVA blend reinforced with cellulose nanowhiskers (CNW and LNW) and
nanofibers (CNF and LNF). It was observed that as the concentration of the CNW,
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LNW, CNF and LNF increased, the crystallinity of the nanocomposite also increased.
Crystallinity of the control guargum/PVA blend was less but increased after
incorporation of nanocellulose but increase in crystallinity was not significant.
Increase in the crystallinity of the sample was attributed to incorporation highly
crystalline nanocellulose.
10.5.7. Effect of Cellulose nanowhiskers and nanofibers on thermal properties of
the Guargum/PVA blend Composites
Figure 10.16. Thermal properties of the CNW reinforced Guargum/PVA blend
Composites
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Figure 10.17. Thermal properties of the LNW reinforced Guargum/PVA blend
Composites
Figure 10.18. Thermal properties of the CNF reinforced Guargum/PVA blend
Composites
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Figure 10.19. Thermal properties of the LNF reinforced Guargum/PVA blend
Composites
Figures 10.16, 10.17, 10.18 and 10.19 depicts the DSC thermograms of the control
Guargum/PVA blend and CNW, LNW, CNF and LNF reinforced Guargum/PVA
blend composites. From the above figures it can be clearly observed that with increase
in concentration of CNW, LNW, CNF and LNF, melting peaks have been shifted
towards higher temperature which indicated the presence of nanocellulose can
enhance the thermal resistance of the guargum/PVA composites. The probable reason
is that melting of nanocellulose is rather difficult as it is highly crystalline material
(the molecules are tightly bound together) therefore for melting it requires higher
energy. As the concentration of nanocellulose (CNW, LNW, CNF and LNF)
increased into Guargum/PVA blend matrix, increase in thermal resistance is bound to
happen.
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10.5.8. Effect of Cellulose nanowhiskers and nanofibers on transparency of the
Guargum/PVA blend Composites
Figure 10.20. Effect of CNW concentrations on transparency of the Guargum/PVA
blend Composites
Figure 10.21. Effect of LNW concentrations on transparency of the Guargum/PVA
blend Composites
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Figure 10.22. Effect of CNF concentrations on transparency of the Guargum/PVA
blend Composites
Figure 10.23. Effect of LNF concentrations on transparency of the Guargum/PVA
blend Composites
Figures 10.20, 10.21, 10.22 and 10.23 indicate effect of CNW, LNW, CNF and LNF
concentration on the transparency of the Guargum/PVA blend Composites. It was
observed from above figures that control Guargum/PVA blend films were more
transparent and started reducing as the concentration of increased from 1% to 5% in
case of CNW, LNW and 0.1% to 1% in case CNF and LNF. Addition of CNW,
LNW, CNF and LNF in Guargum/PVA blend increased its crystallinity providing
barrier to the transmission of light, thus increasing haziness of the composite film.
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10.5.9. Effect of Cellulose nanowhiskers and nanofibers on morphological
properties of the Guargum/PVA blend Composites
Scanning electron microscopy (SEM) analysis was done in order to understand the
correlation between the dispersion behaviour of CNW, LNW, CNF and LNF in to
Guargum/PVA blend composite films and their performance.
Figure 10.24. SEM micrographs of the optimized concentration of the nanowhiskers
and Nanowhiskers (a: 1% CNW, b: 3% CNW, c: 1% LNW and d: 3% LNW)
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Figure 10.25. SEM micrographs of the optimized concentration of the nanowhiskers
and nanofibers (a: 0.25% CNF, b: 0.5% CNF, c: 0.25% LNF and d: 0.5% LNF)
Figure 10.24 and 10.25 depicts SEM micrographs of the guargum/PVA blend
composites reinforced with CNW, LNW, CNF and LNF for a: 0.25% CNF, b: 0.5%
CNF, c: 0.25% LNF and d: 0.5% LNF loaded guargum/PVA blend. It was observed
that dispersion was not uniform through out the CNW, LNW, CNF and LNF
reinforced guargum/PVA blend composites. From these micrographs it can be clearly
observed that there was completely absence of interactions between the
nanoreinforcements and the guargum/PVA blend matrix. This can be also one of the
strong reasons that all the properties of the guargum/PVA blend composites decreased
with increase in concentration of CNW, LNW, CNF and LNF.
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10.6. CONCLUSIONS
The guargum/PVA blend composites reinforced with CNW, LNW, CNF and LNF
were successfully prepared by using solution casting method. Most of the properties
(tensile strength, Young’s modulus, and transparency and water vapour transmission)
of the guargum/PVA blend increased with increase in composition of the PVA up to
20% and beyond which reduction was observed. The optimized batch guargum/PVA
blend was taken and various concentrations CNW, LNW, CNF and LNF were used as
the reinforcement. It was observed from the experimental work that mechanical and
barrier properties were decreased drastically as compared to control guargum/PVA
blend.