Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 239

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.

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 240

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,

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 241

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.

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 242

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

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 243

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

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 244

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.

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 245

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

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 246

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.

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 247

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.

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 248

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.

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 249

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

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 250

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

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 251

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.

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 252

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

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 253

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,

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 254

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

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 255

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

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 256

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.

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 257

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

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 258

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.

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 259

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)

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 260

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.

Polymer Composites Based on Cellulosics Nanomaterials Chapter 10

Vilas Karande 261

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.