Biocomposites in Advanced Biomedical and Electronic Systems Applications

Introduction

Newly emerging technologies and techniques have made it possible to invent and fabricate new biocomposite materials that are able to serve fundamental roles in diverse applications. Such newly invented biopolymers are being used not only for the enhancement of the performance, properties, and characteristics of the devices, but also to provide designers with new possibilities for satisfying new attractive features required by a specific application. Transparency, flexibility, and degradability are examples of such new requirements to be satisfied (AL-Oqla & El-Shekeil, 2019; AL-Oqla & Salit, 2017b; Alaaeddin et al., 2019a, c; Alaaeddin et al., 2019d).

Bio-based composites are increasingly replacing conventional composites in a wide array of applications for sustainable industries. However, enormous efforts are still required to better exploit these composites and to expand their applications to include high-tech ones in several fields such as electronics, biomedical, drugs, civil, and sports. Also, the need to improve their qualities for reliable performance is still demanding (AL-Oqla, 2017; AL-Oqla et al., 2019). To achieve these goals, establishing efficient and robust evaluation and selection techniques for the composites’ constituents is the most important step. In these techniques, the various desired fibers as well as polymer properties such as physical, mechanical, economic, environmental, and thermal have to be considered together and evaluated to discover the best type of both fibers and polymers for a certain application (AL-Oqla et al., 2014a; AL-Oqla et al., 2014b; AL-Oqla et al., 2015b; AL-Oqla et al., 2017; Aridi et al., 2016a. b, 2017; Sapuan et al., 2013; Sapuan et al., 2016). Besides, potentials of new materials with new levels of performance would be revealed, which in turn, expand the applications for the biomaterials.

Recently, new biomaterials derived from natural plants and agronomic residues called natural cellulosic fibers (NCF) have been utilized as a reinforcing filler with starch-based materials. NCF have various characteristics, such as availability, affordability, low density, biodegradability, recyclability, and secure handling (AL-Oqla & Omar, 2015; AL-Oqla & Sapuan, 2015, 2018a). Remains from agricultural fields, such as maize stover, sugar palm residues, cassava bagasse, and pineapple wastes, are generated yearly in bulk and cost less; these are the most abundant sources of natural fiber. In addition to its availability, cellulose plant fiber is characterized by flexibility, affordability, durability, high extendibility, and low density, making it an attractive study area. However, the addition of cellulosic fibers to reinforce the starch-based materials has provided significant enhancement, specifically in terms of tensile performance and thermal stability, as well as water barrier characteristics. This enhancement is associated with the high compatibility and compositional similarity between fiber and starch because both originate from biological sources. In fact, the proper selection of biomaterial constituents for a certain performance in a particular application is a multi-criteria decision-making problem where suitable fields of optimizations and decision-making (e.g., the analytical hierarchy process and TOPSIS method) were implemented to enhance the performance of biomaterials as well as others in various applications (AL-Oqla & Hayajneh. 2007; AL-Oqla & Omar, 2012; AL-Oqla & Omar, 2015; AL-Oqla & Salit, 2017a; Al-Widyan & AL-Oqla, 2011, 2014).

Biopolymer Processing and its Development

Extrusion

Extrusion is a plastic industry manufacturing process with a high-volume rate. It is practically a combination of screw conveyor and compressor with other accessories to cause raw heated plastics to melt and form under a continuous cycle as seen

Extrusion process device

FIGURE 3.1 Extrusion process device.

in Figure 3.1. A heated helical screw (either single- or twin-screw) compresses the raw plastics with other additives like chain-extenders, stabilizers, plasticizers, and/or colorants through the machine hopper to make a homogeneous melt plastic by forcing the air out of the barrel without causing damage to the molten.

Various benefits can be achieved using single-screw or twin-screw based upon the polymer being processed and the products to be fabricated. A comparison between single- and twin-screw is illustrated in Figure 3.2. The ratio of the screw length to its diameter (L/D) is responsible for homogeneous mixing and varies for various polymer types. Generally speaking, screws with large L/D ratios can give higher shear heating, as well as better blends and longer melt residence times in the extruder (AL-Oqla et al., 2015c; AL-Oqla & Sapuan, 2014a).

In polylactic acid (PLA) polymer extrusion for instance, hydrolytic degradation is the main drawback. Thus, it should be dried to 0.025% w/w moisture content before extrusion. Accordingly, to avoid reduction of molecular weight, higher working temperature (about 240°C) must maintain its moisture content below

.

0.005% w/w. However, drying of PLA resin is an exciting issue as it degrades at elevated temperatures and high moisture content environments. PLA resins are formed by means of conventional extruder with a general-purpose screw (L/D ratio = 24-30). To make sure that all PLA crystalline are melted as well as attaining an optimal melt viscosity for processing, the heater set point is usually between 200-210°C.

A PLA/sisal biocomposite has been recycled for eight times via the extrusion process, to illustrate its recyclability (Chaitanya et ah, 2019). The specimen’s performance has significantly dropped after the third recycle processing as a result of severe damage of fibers and PLA degradation. A screw speed of 60 RPM combined with temperature profile of 150-185°C have caused thermal degradation to the composite. An increase in surface roughness also appeared as a result of the hydrolytic

Comparison between single and twin screw

FIGURE 3.2 Comparison between single and twin screw.

degradation that reduced the PLA molecular weight and increased its melt flow rate, which led to improper fiber wetting as illustrated in the morphological images in Figure 3.3.

 
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