Evaluation of Coconut (Cocos nucifera) Husk Fibre as a Potential Reinforcing Material for Bioplastic Production

Abstract

In this study the potential use of coconut husk (Cocos nucifera) husk fibre for the reinforcement of bio-plastic produced with cassava (Manihot utilissima) starch was investigated. Five compositions of the bioplastics were formulated containing 0% (control), 5%. 10%, 15% and 20% of coconut husk fibre. The tensile strength, modulus of elasticity, impact energy, water absorption, and biodegradability of the fibre-reinforced bioplastic samples were then determined in accordance with standard methods. Results obtained showed that the tensile strength values ranged from 0.36 to 0.68MPa; while the modulus of elasticity ranged from 2.7 x10 to 4.9 x10 N/m. The impact energy range was 1.73 3.7 J. Analysis of variance showed that coconut husk fibre content had a significant effect on the tensile strength. The impact energy increased with an increase in fibre content up to 15%. Also, water absorption (27.3 42.9%) increased with an increase in fibre content. The bioplastics were biodegraded within one month of grave yard test. The optimum fibre reinforcement level was found to be 10%. This may, however, be increased to 15% for impact resistance improvement. Introduction Plastic is a material consisting of a wide range of synthetic or semi-synthetic organics that are malleable and can be moulded into solid objects of diverse shapes. Plastics are used in an enormous and expanding range of products due to their long life and attractive properties including relatively low cost, ease of manufacture, versatility, and imperviousness to water. The world’s annual consumption of plastic materials has increased from around 5 million tons in the 1950s to nearly 100 million tons; thus, 20 times more plastic is produced today than 50 years ago [1]. This implies that on one hand, more resources are being used to meet the increased demand for plastics, and on the other hand, more plastic waste is being generated. Most of the plastic waste is neither collected properly nor disposed of in appropriate manner to avoid its negative impacts on the environment and public health in many African countries. Due to extremely long periods required for their natural decomposition, waste plastic is often the most visible component in waste dumps and open landfills. The increased use of synthetic plastics in developing countries is a particular concern as their waste management infrastructure are seldom able to deal effectively with the increasing levels of plastic waste [2,3]. In spite of this daunting challenge, however, the use of plastics has significantly replaced leaves, glasses and metals as a cheaper and more efficient means of packaging in many African societies, except in Kenya and few other countries that have recently banned the use plastic bags in shops and supermarkets. A group of more environmental friendly alternative materials worthy of consideration in Africa is collectively known as bio-plastics, i.e., plastics derived from renewable biomass By-Products of Palm Trees and Their Applications Materials Research Forum LLC Materials Research Proceedings 11 (2019) 195-200 doi: https://doi.org/10.21741/9781644900178-14 196 sources, such as vegetable fats and oils, corn starch, straw, woodchips, food waste, etc. Bioplastics have been used in a variety of consumer products, such as food containers, grocery bags, biodegradable utensils, and food packaging. These are called commodity plastics. Bioplastics can, however, also be used for engineering grade applications, such as electrical and electronic housings and enclosures. The greatest advantages of bioplastics are a smaller carbon footprint and a less polluted ecosystem. The problem of overflowing landfills and floating islands of trash in Africa may be addressed through increased use of bioplastics. Starch and cellulose are two of the most common renewable feedstocks used to create bioplastics and these typically come from corn and sugarcane. In Nigeria, cassava starch is of interest as a candidate for producing bioplastics, given the fact that Nigeria is the largest producer of cassava (tapioca) in the world, accounting for up to 20 % of the global, about 34% of Africa’s and about 46 % of West Africa’s cassava production. Annual production in 2017 was conservatively put at 50,000 metric tonnes [4]. It has been shown that reinforcement of bioplastics with a natural fibre may enhance the tensile strength [5]. The typical biofibre sources for bioplastics include cotton, flax or hemp, recycled wood, waste paper, crop processing byproducts, etc. However, a major potential reinforcement material in Nigeria is coconut (Cocus nucifera) husk fibre which has relatively high tensile strength, is available in abundant quantities, but largely treated as a waste material [6,7]. Nigeria produces about 267,500 metric tonnes of coconuts annually and the country occupied the 18 position on the world coconut production index as at 2017 [8]. There are two types of coconut fibres, i.e., brown fibre extracted from matured coconuts and white fibres extracted from immature coconuts. Brown fibres are thick, strong and have high abrasion resistance, while white fibres are smoother and finer but weaker. There are many general advantages of brown coconut husk fibres, the object of this study: they are moth-proof, resistant to fungi and rot, provide excellent insulation against heat and sound, not easily combustible, flame-retardant, unaffected by moisture and dampness, tough and durable, resilient, springs back to shape even after constant use, totally static free, and easy to clean [8]. The aim of this study was to investigate the effects of coconut fibre reinforcement on selected properties of a cassava starch-based bioplastic. Methodology Bioplastic specimens (a sample is shown in Figure 1) were produced with cassava starch and varied coconut husk fibre contents of 0, 5, 10, 15 and 20% (by weight). The fibres were cut into 2 mm length followed by chemical treatment to reduce lignin and hemi-celluloses contents involving soaking in 1 molar solution of NaOH at 50C for 4 hours. The fibres were then washed, dried at 80°C in an oven and mixed with cassava starch, water, glycerin and acetic acid in predetermined proportions in a container. The blended mixture was then transferred to a mould, heated up to 65C for 4 h and air cooled at room temperature. Tensile test was performed using 3 mm thick dog-bone shaped specimens. Three replicate samples were tested for each composition at a fixed crosshead speed of 5 mm/ min in accordance with ASTM D638 standard test methods for plastic properties in tension. By-Products of Palm Trees and Their Applications Materials Research Forum LLC Materials Research Proceedings 11 (2019) 195-200 doi: https://doi.org/10.21741/9781644900178-14 197 Fig. 1: A sample of the coconut husk fibre-reinforced bioplastic Impact resistance tests were performed on 60 x 60 x 2 mm specimens using an adaptation of ISO 6603-1. A known weight of 0.616kg was raised to a known height and allowed to fall on each specimen. The height travelled by the ball when the first visible crack had developed on the face was recorded. The total energy of fracture was determined using equation 1: