Available online at www.icemme.com

Proceedings of the

1st International Conference on Engineering Materials and Metallurgical Engineering

22- 24 December, 2016 Bangladesh Council of Scientific and Industrial Research (BCSIR)

Dhaka, Bangladesh

PREPARATION AND CHARACTERIZATION OF FIBER (COTTON AND JUTE) REINFORCED POLY(LACTIC ACID)/POLY(VINYL ALCOHOL) COMPOSITES

Md. Hafezur Rahamana*, M. A. Gafurb, Rasel Habiba, M. R. Qadirb and Md. Ariful Islama

aDept. of Applied Chemistry and Chemical Engineering, Islamic University, Kushtia-7003, Bangladesh

bPilot Plant and Process Development Center (PP & PDC), BCSIR, Dhaka,-1205, Bangladesh

Abstract Poly(L-lactic acid) (PLLA), poly(vinyl alcohol) (PVA) and fibers (jute and cotton) were dissolved in 1,4-Dioxane and mixed homogeneously. Green composites were prepared with different compositions by film stacking and compression molding processes. Physical, mechanical, thermal, and morphological analyses of these blends were carried out. Water absorption and bulk density were affected by the composition of the composites. Composites with jute fiber showed better mechanical properties than that of cotton fiber composites. Thermal stability of raw cotton fiber and jute fiber composites increase with the increase of percentage of fiber and PLA content and the incorporation of 10% (by weight) of fiber yielded the stable composites. From the analysis of XRD data it becomes evident that the crystallinity of the composite decreases with increasing fiber content. SEM analysis supports the changing morphology with different compositions. Keywords: Green composite; Poly(L-lactic acid); Poly(vinyl alcohol); Jute; Cotton; Thermal Stability.

1. INTRODUCTION

With the increasing of population all over the world, environmental pollution occurs rapidly. Every year hundreds millions of tons of plastics and non biodegradable product are produced from petroleum resources. Most of these plastics are goes in environment such as landfills, water and other places. As a result the environment posing significant health risks to people, wild animal, and the average person's lifestyle would be impractical without them [1-3]. By the using petroleum resources product, green house effect and global warming increase day by day this has bad impact effect on environment. So rapidly increasing environmental awareness growing global waste problem, geometrically increasing crude oil prices and high processing costs trigger the development concepts of sustainability and reconsideration of renewable resource [4]. This problem can be overcome by using nature fiber composites with biodegradable polymer matrix. Natural fibers composite have recently attracted the attention of researchers because of their advantages over other established materials. They are environmentally-friendly, fully biodegradable, abundantly available, non-toxic, non-abrasive, renewable, and cheap, and have low-cost [5]. Poly(lactic acid) (PLA) is one of the most popular biodegradable biocomposite and is highly investigated by researchers. PLA is using as biomaterial due to their unique properties of bioabsorability. They are also renewable and have relatively high strength and stiffness and cause no skin irritations [6-7]. However, its inherent brittleness, low-melt viscosity, moisture uptake, quality variations, and low-heat distortion temperature of PLA have restricted its applications [8]. In order to improve mechanical and thermal properties of PLA, several natural polymers were blended with PLA such as poly vinyl alcohol (PVA) [9-10] and natural fibers. Generally, these blends showed considerably higher toughness than pure PLA. Polylactide polymers are stiff and brittle materials, for these reason various percentage of poly vinyl alcohol used as plasticizers to improve the elongation and impact properties. Among various natural fibers, jute fiber is a promising reinforcement for use in composites on account of its low cost, easy availability, renewability, much lower energy requirement for processing, high specific properties and no health risk [11]. Cotton fiber is almost pure cellulose fibers which contain almost 90% cellulose and used as reinforcement materials in polymer composites of its renewability, biodegradability, easy availability, non-toxic and has low cost [12-14]. PLA has two enantiomers: Poly(L-lactic acid) (PLLA) and Poly(D-lactic acid) (PDLA) [15,16]. In this research, PLLA were blended with PVA and cotton/jute fibers to prepared ternary composites by film stacking and compression molding processes. The effects of the composition contents on the physical, mechanical, thermal, and morphological behavior were successfully studied using the various techniques.

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2. EXPERIMENTALS

2.1. MATERIALS

Poly(L-lactic acid) in pellet from was obtained from Mitsubishi Chemical Corporation, UNITIKA Plastics Division, Japan. It has a specific gravity 1.24 g/cm3 and melting point 150-160OC. Poly(vinyl alcohol) (Mw: 125,000 and degree of hydrolysis approx. 89%), density 1.19-1.31 g/cm3 , melting point 200O C was supplied by PP & PDC, BCSIR, Dhaka, Bangladesh. Jute (Corchorus capsularis) and cotton (Gossypium arboretum L) was purchased from the local market of Kushtia, Bangladesh. Fibers were subjected to a washing pretreatment to remove impurities and waxy substances covering the external surface of fiber cell walls. After washing cotton fiber was used and jute fiber was bleached with 0.7% NaClO2 at 90 OC for 1.5 h [17] and then used. The solvent used was 1, 4- dioxane secured from Merck, Germany.

2.2. METHODS COMPPOSITES PREPARATION

10 wt% solution of PLLA and PVA in 1,4- dioxane and water respectively, were prepared by stirring the solution inside the water bath at 60O C until fully dissolved. Also 10 wt% solution of fibers (jute and cotton) in 1,4- dioxane was prepared. For the preparation of Cotton/PLLA/PVA and Jute/PLA/PVA composites, calculated amounts of solution of fiber, PLLA and PVA were mixing with a magnetic stirrer until homogeneous solution were obtained and solutions were immediately cast on the clean petri dish and left solvent evaporated at ambient temperature for 72 hours. The composites obtained were then molded into sheets by hot pressing at 100O C and 80 KN pressure for 20 min, followed by slow cooling at room temperature for 90 minutes [18]. The composites were coding as in Table 1.

Table: 1 Preparation of PLLA/PVA composites with fibers

Fiber Sample Code PVA (wt%) PLLA (wt %) Fiber (wt%)

Cotton C-05 85 10 5 C-10 70 20 10 C-15 55 30 15

Jute J-05 85 10 5 J-10 70 20 10 J-15 55 30 15

2.3 CHARACTERIZATION 2.3.1 PHYSICAL PROPERTIES

Water uptake specimen was prepared according to ASTM designation: D570-81(Reapproved 1988) Standard test method for water absorption of plastic. The test specimen was 5mm length 4 mm width and 7-8mm height.

2.3.2 MECHANICAL PROPERTIES Mechanical properties of the composites were analyzed by measuring the tensile strength (TS), Percentage of Elongation and Young’s modulus (according to the standard ASTM method D 882-88 using an Instron Universal Testing Machine (Model 5565, Instron Engineering Corporation, Canton, MA, USA) equipped with a 0.5 kN load cell. Rectangular strips (2.54×15 cm) were cut from individually prepared film using a precision double blade cutter (model LB.02/A, Metrotec, S.A., San Sebastian, Spain). Initial grip separation was set at 50 mm and cross-head speed at 50 mm/min. The TS (MPa) was determined by dividing the maximum load (N) by the initial cross sectional area (m2) of the film sample, the E (%) was determined by dividing the extension at rupture of the film by the initial length of the film (50 mm) multiplied by 100, and the EM (GPa) was determined from the slope of the initial linear portion of the stress- strain curve obtained from the tensile test using a tangent method.

2.3.2. THERMAL PROPERTIES

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Thermal properties were monitored by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) of the composites were performed by using a TG/DTA EXTAR 6000 STATION, Seiko Instrument Inc., Japan.

2.3.3 X-RAY DIFFRACTION ANALYSIS (XRD) X-ray diffraction analysis of the composites film was performed at room temperature with a D-8 ADVANCE BRUKER diffractometer operating at 40 kV and 30 mA, using the radiation (λ= 0.1546 nm) . The crystalline degree of the samples was determined as the ratio of the areas of crystalline reflections to the whole area (after subtraction of background) in the 2θ range.

2.3.4 SCANNING ELECTRON MICROSCOPY (SEM) The morphology of film composites was observed by scanning electron microscopy (SEM). SEM analysis was carried out using a JSM-7610 F model at an accelerating voltage 15.0 kV. The samples were sputter coated with platinum to prevent charging. The micrographs were taken at a magnification of 200 and 500.

3. RESULTS AND DISCUSSIONS

3.1 WATER ABSORPTION PROPERTIES

The effects of immersion time on water absorption of Cotton/PLLA/PVA and Jute/PLLA/PVA composites were shown in Fig.1. Generally, all natural fibers are hydrophilic in nature and they tend to absorb water even from the air [19]. In case of PVA matrix, it will absorb more water than that of natural fiber. From the figure, it is seen that the water absorption increases with increasing absorption time and highest water absorption occurred in composites with 85% PVA content for both cases. That means with the increase of percentage of PVA content in the composites will increase the absorption of water. Water absorption of the all composites were above 100% even after 24 hours latter which support previous report for water absorption of pure PVA was 105.2% after 24 hours [20].

0 24 48 72 96 120 144

C-05 (5% Cotton+ 10% PLA+85% PVA)C-10 (10% Cotton+ 20% PLA+70% PVA)C-15 (15% Cotton+ 30% PLA+55% PVA)

100

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300

350

% W

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orbt

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J-05 (5% Jute+ 10% PLA+85% PVA)J-10 (10% Jute +20% PLA+70% PVA)J-15 (15% Jute+30% PLA+ 55% PVA)

Hours

% W

ater

abs

orbt

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(b)

FIG. 1: WATER ABSORPTION OF COTTON (A) AND JUTE (B) FIBER COMPOSITES.

3.2 TENSILE PROPERTIES

Tensile properties (tensile strength, %of elongation and Young’s modulus) are shown in Fig. 2. As can be observed from Fig. 2 (a), the Cotton/PLLA/PVA and Jute/PLLA/PVA composites with 10% jute content in the composite had the highest tensile strength (~ 11.16 Mpa) as compared to others. The higher tensile strength of the composite might be attributed to the homogeneous dispersion and specific interaction that took place between the PLLA, PVA and jute fibers. The tensile strength of cotton fiber composites is lower than jute fiber composites, this should be due to the small amount of lignin present in jute fiber act as natural adhesion promoter in the composite [21,22] . In general, the tensile strengths of the natural fibre reinforced polymer composites increase with fibre content, up to a maximum or optimum value, the value will then drop [23,24] The tensile strength of cotton composites decreases with the increasing the percentage of fibers content. The

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decrease in tensile strength was probably due to non homogeneous stress transfer from matrix to cotton fibers, which caused by less dispersion and agglomerations of cotton fibers in the matrix (PLLA and PVA).

FIG. 2: TENSILE STRENGTH (A), PERCENTAGE OF ELONGATION(B) AND YOUNG’S MODULUS (C) OF COTTON AND JUTE FIBER COMPOSITES.

It is normal, that the adding fiber which has a fragile character decrease the elongation at break. In addition the observed decrease on the elongation at break may be attributed to a reduction in deformability of the rigid interface between fibers and matrix [25]. It is clearly observed from Fig 2(b) that 10% jute fiber composite shows highest percentage of elongation as compared to the others composites. The percentage of elongation of jute fiber composites is higher than cotton fiber composites since jute fiber contain percent amount of lignin, hemicelluloses, pectin material which is also responsible for elongation increase of jute fiber composites than the cotton fiber composites. The measured young’s modulus of cotton and jute fiber composites with PLLA and PVA are shown in Fig. 2(c). The Young modulus of the composites decreases with the increase of percentage of fibers and PLLA matrix materials. Due to the brittle nature of PLLA matrix materials decreases the Young’s modulus of composites. Young’s modulus of jute fiber composites is higher than that of cotton fiber composites and 5% jute fiber composites has highest young’s modulus as compared to the other composites. Jute fiber contain percentage amount of lignin, hemicelluloses, pectin material which is also responsible for young’s modulus increase of jute fiber composite than the raw cotton fiber composite.

3.3 THERMAL PROPERTIES Thermogravimetric analysis (TGA) was performed in order to investigate the effect of cotton and jute fiber with PLLA and PVA matrix on thermal stability of ternary composites. From the TGA profiles of the cotton composites and jute composites (not shown), half degradation temperature (T 50%) and maximum decomposition temperature (T max) values are summarized in Table 2. All composites have shown similar decomposition pattern of two-step degradation process. The addition of fiber enhanced the thermal stability of composites based on the T max values with highest improvement occurring at 10% fiber loading for both cotton and jute fiber composites. The improvement in the thermal stabilities of the composites could have resulted in uniform dispersion of cotton and jute in the PLLA and PVA matrix and consistent with previous report [26]. From Table 2 it is also observed that jute fiber composites is the highest thermal stability than cotton fiber composites and 10% jute fiber composites has highest maximum degradation temperature as compared to the other composites.

Table: 2 Thermal degradation temperatures of cotton and jute fiber composites

Sample code Degradation temperature (oC)

T 50% T max C-05 317.0 328.2 C-10 323.3 347.1 C-15 318.0 321.0 J-05 325.3 327.6 J-10 348.6 356.4 J-15 317.0 321.0

Table: 3 DTA endothermic peak top of cotton and jute fiber composites

(a) (b) (c)

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Sample code 1st Peak (OC) 2nd Peak (OC) 3rd Peak (OC) 4th Peak (OC) C-05 161.9 211.0 299.9 404.4 C-10 162.2 213.3 310.1 407.6 C-15 162.5 212.2 307.3 - J-05 163.5 213.3 308.2 424.3 J-10 164.0 213.9 383.0 436.5 J-15 164.6 212.2 315.6 -

DTA curves (not shown here) of the composites show endothermic peaks, this should be due to the thermal degradation as TGA. DTA profile comparison indicates that phase transition occurred in four endothermic reactions. The lignocellulosic (jute) and cellulosic (cotton) materials are chemically active and decompose thermochemically between 150 and 500oC: hemicellulose mainly between 150 and 350oC, cellulose between 275 and 350oC, and lignin between 250 and 500oC [27]. So, first endothermic peaks assigned to the melting point related peaks of PLLA. From Table 3, it can be seen that, with the increase of the percentage of cotton and jute content in composite materials the melting point of the PLLA were increases slightly and jute composites has little bit higher melting point than cotton composites. The second endothermic peak is due to the fiber (cellulose) decomposition temperature and 10% fiber loaded composites show the higher decomposition temperature than others. The third broad endothermic peaks of composites materials which are assigned to the decomposition temperature of composites. From the absence of exothermic peaks in DTA curves, there were no crystallization transition occurred. DTG is difference thermo-gravimetric, measuring the weight loss of the sample during the heating process with respect to TGA. Usually it decreases when exothermic reaction occurs. DTG profiles comparison shows that (Table 4) maximum degradation temperature of the jute fiber composites is higher than cotton fiber composites and 10% fiber loaded composites show highest maximum degradation temperature as compared to the other composites which is consistent with TGA and DTA results.

Table: 4 DTG maximum degradation temperatures of raw cotton and bleached jute composites

Sample Maximum Degradation Temperature (0C) Maximum Degradation Rate

(mg/min) C-05 321.8 2.36 C-10 323.1 1.52 C-15 318.8 1.87 J-05 325.8 1.51 J-10 348.6 1.95 J-15 317.7 1.03

3.4 X-RAY DIFFRACTION ANALYSIS (XRD) The XRD profiles and crystallinity of cotton and jute composites were shown in Fig. 3. Crystalline species could be observed from Fig. 3(a) and Fig. 3(b). Crystallinity were calculated from these profiles data and were shown in Fig. 3(c). From Fig. 3(a) and 6(b), it is seen that broad peak at around 2θ= 17o and 19o exibit a semicrystalline phase of PLLA in the composites which supports previous report [28]. The peak at 2θ= 22.5o showing the crystalline nature of the cellulose content of cotton and jute fiber in the composites. These peak positions are in accordance with those reported results [29,30]. Crystallinity of the composites decreases with the increase of fiber percentages in the composites. This means the crystalline structure of the PLLA has been disturbed by fibers content. This type of observation is consistent with reported results [31,32]. It is also revealed from the Figure that the crystallinity of cotton composites is higher than that of jute composites. This may be due to the small amounts of lignin, hemicellulose and pectin matter in jute fiber. .

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10 15 20 25 30

Inte

nsity

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itrar

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2)

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40

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% c

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Jute fiber composite

Cotton fiber composite

(c)

Fig. 3 XRD profiles cotton composites (a) and jute composites (b) and their crystallinity (c).

3.5 SCANNING ELECTRON MICROSCOPY (SEM) Scanning electron microscopy (SEM) provides an excellent technique for examining the surface morphology of composite. SEM images of the fractured cross-sectional surfaces of C-05 (Cotton05/PLLA10/PVA85), C-10(Cotton10/PLLA20/PVA70), J-05(Jute05/PLLA10/PVA85) and J-10(Jute10/PLLA20/PVA70) composites are presented in Fig. 4(a)-(d). As can be observed from Fig. 4(a) and 4(c) SEM image of C-05 and J-05 composite shows that there are less amount of fiber which results in less numbers of voids around the fractured cross-sectional surface. These indicate that the reinforcement by fiber is less. From Fig. 4(b) and 4(d), SEM images of composites C-10 and J-10 shows that there are more fiber content which results in large numbers of voids around the fractured cross-sectional surface. This association decreases the stress transfer efficiency from matrix to fibers [33]. There are too many slip in 4(c) as compared to 4(a) and this may be due to interfacial adhesion between cotton fiber and matrix is weaker than that of jute fiber with matrix. The morphology evaluated by this SEM indicated that there were less voids on the fracture surface, and this indicated that the fiber were well trapped by the PLLA matrix as well as the PVA matrix and consistent with reported result [34].

FIG. 4: SEM MICROGRAPH OF THE FRACTURED CROSS-SECTIONAL SURFACES OF (A) C-05, (B)

C-10, (C) J-05 AND (D) J-10 COMPOSITES

(b) (a)

(d) (c)

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4. CONCLUSIONS On the basis of the results obtained from our investigations, the following conclusion may be drawn-

Cotton/PLLA/PVA and Jute/PLLA/PVA composites were successfully prepared through film stacking and compression molding process.

Water absorption is higher for composites with higher PVA content. The tensile strength and percentage of elongation depend on fiber content and 10% fiber content

yielded higher mechanical properties. Thermal stability of the jute composites is higher than that of cotton composites. The incorporation of 10% jute yielded the most stable composite consistent with previous result.

From the analysis of XRD data it becomes evident that the crystallinity of the composite decreases with increasing fiber content and cotton fiber composites has higher cryatalline nature as compared with jute fiber composites.

From SEM micrographs of the composites it was observed that increase in the incorporation of percentage of fiber content changing the morphology of the composites.

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