Degradability of composites, prepared from ethylene–propylene copolymer and jute fiber under accelerated aging and biotic environments

https://doi.org/10.1016/j.matchemphys.2005.01.027Get rights and content

Abstract

The utilization of natural fiber as reinforcement for the thermoplastic composites is growing not only for ecological concern but also for wide range of applications. In the present article, three types of composites were prepared by melt mixing of ethylene–propylene (EP) copolymer and (i) 3% NaOH treated jute fiber, (ii) 17.5% NaOH treated jute fiber and (iii) commercial microcrystalline cellulose powder using maleated EP copolymer as compatibilizer. The obtained composites were characterized by Fourier transform infrared spectroscopy (FTIR), Thermal gravimetric analysis (TGA) and microscopic measurements. The durability of the composites was evaluated under polychromatic irradiation (λ  290 nm) and composting condition for different time intervals. It was found that the treatments on the natural fiber have influenced the service life of the end product. Composites made from microcrystalline cellulose showed better mechanical properties as well as photo-resistance. The specimen containing 3% NaOH treated fiber exhibited relatively lowest photo-resistance and biosusceptibility. It was found that the composites were less durable under both abiotic and biotic conditions in comparison of the neat polymer matrix.

Introduction

In recent years, the consumption of natural fiber-reinforced composites has been skyrocketed not only for environmental concerns but also for yielding a unique combination of high performance, great versatility and processing advantages at favorable cost. They exhibit many advantages including low density, little damage during processing, little requirements on processing equipment, high stiffness and relatively low price [1], [2], [3]. In these materials, to evade the major problem that is incompatibility between the hydrophilic (polar) polysaccharides and hydrophobic (non polar) polymer matrix, many efforts have been focused to optimize/influence the quality of the fiber–matrix interface by some physical methods and chemical methods such as change of the surface energy, impregnation, coatings, coupling agents and graft copolymerization [4]. Among many other additives used for this purpose, MAH-PP has been found to be very efficient in improving the filler dispersion and the compatibility in polypropylene-cellulose composites [5], [6], [7], [8], [9].

There are many reports [4], [5], [6], [7], [8], [9], [10] which have been documented on the processing conditions, mechanical property variations and fiber modifications. Now-a-days it is a tendency nowadays to use the mercerization of natural fibers in the industries which is one of the cheapest and old methods and its effectiveness has been found to depend on the concentration of the alkaline solution, its temperature, time of treatment, tension of the material as well as on the additives present [11], [12]. According to Lai and Sarkanen's estimation [13], the peeling process which is degradation at the reducing ends of cellulose chains, is relatively rapid at 150–190 °C and Gentile et al. [14] also detected that the decrease in concentration of alkaline solution and temperature had reduced the peeling factor by hydrolysis of amorphous cellulose. On the other hand, it is well evident from the results of theoretical calculations of fibers [15], that the quality of fibers in terms of mechanical properties, depend on the degree of polymerization, crystallinity, orientation of chains (spiral angle) and fiber diameter. According Hermans [16] and Roy et al. [17], [18], the alkali treatment will also affect the fiber orientation by swelling, stretching and reorientation. Thus, it will be worthwhile to study the effect of concentration of alkaline solution on the mechanical properties of fiber-reinforced composites. In the present investigation, we have focused to study the effect of size and treatment of the natural fibers on the mechanical properties, thermal stability and durability of their composites in biotic and accelerated aging conditions.

There is a vast array of potential of long and short fibers for composite production. One of the stem/bast fibers is jute fiber which is renewable, versatile, non-abrasive, porous, hydroscopic, viscoelastic, combustible and biodegradable [19]. Table 1 shows the technical informations on jute fibers [20], [21]. These jute fibers were treated with low and higher concentrations of alkali to differentiate lignin content in the fibers. The ethylene–propylene copolymers have a wide range of applications by varying in composition of monomers from soft elastomers to rigid thermoplastics. For the first time, one of the ethylene–propylene copolymers is used as matrix with treated jute fibers. For comparison, composites were also prepared by using commercially available microcrystalline powder.

Section snippets

Materials

The ethylene–propylene copolymer [ethylene 15.1% mole] with melt-flow index about 3.5 g/10 min and density about 0.9 g cm−3 was obtained from M/s. Montell Ferrara, Italy. Maleic anhydride, benzoyl peroxide, sodium hydroxide and xylene were obtained from M/s. SD. Fine Chemicals Ltd., India. The jute fiber was purchased from local market and mercerized using alkaline solution. The first fiber, which was treated with 3% NaOH aqueous solution for 3 h at 80–90 °C, washed with de-ionized water upto the pH

Preparation

Fig. 1 shows the optical micrograph of microcrystalline cellulose powder. The mercerized fibers using 3% and 17.5% aqueous solution of NaOH can be seen in Fig. 2. The average values of their dimensions are presented in Table 3 where the MC was observed to be smaller in size and the aspect ratio of J2 fiber was observed to be higher than others. Fig. 3a shows the FTIR spectra of maleated EP copolymer where the peaks at 1780 cm−1 for cyclic anhydride and 1714 cm−1 for carboxylic acid groups are

Conclusion

The material properties such as mechanical and thermal properties and durability/degradability of the natural fiber-reinforced composites depend on their chemical constituents and preparation methods. The quality of fiber was generally influenced by the kinds of treatments. From the present investigation, we find that the variations in treatments on the natural fibers have influenced the performance and durability of their composites. The composites prepared from the jute fiber which was

Acknowledgement

The authors are grateful to Dr. S. Sivaram, Director, National Chemical Laboratory, for his fruitful discussions and encouragement.

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