Paper thermoplastics Pulp materials

As mentioned earlier, suspensions of particulate rods or fibers are almost always non-Brownian. Such fiber suspensions are important precursors to composite materials that use fiber inclusions as mechanical reinforcement agents or as modifiers of thermal, electrical, or dielectrical properties. A common example is that of glass-fiber-reinforced composites, in which the matrix is a thermoplastic or a thermosetting polymer (Darlington et al. 1977). Fiber suspensions are also important in the pulp and paper industry. These materials are often molded, cast, or coated in the liquid suspension state, and the flow properties of the suspension are therefore relevant to the final composite properties. Especially important is the distribution of fiber orientations, which controls transport properties in the composite. There have been many experimental and theoretical studies of the flow properties of fibrous suspensions, which have been reviewed by Ganani and Powell (1985) and by Zimsak et al. (1994). 

Cellulose is the most abundant polysaccharide in nature with approximately 180 billion tons produced and broken down every year (Engelhard 1995). Cellulose, which occurs as microfibrils, is the component responsible for the excellent load bearing properties of plant cell walls (for a summary for the cellulose content of the different cell wall layers, see Table 6-1). The cellulose microfibrils in wood fibers are important raw material for the pulp and paper industries, and those in cotton and hemp for the textile industries. Moreover, the renewable plant fibers have substantial potential to replace man-made fibers in fiber-reinforced thermosets and thermoplastics to produce environmentally friendly materials (Mohanty et al. 

The most common cellulose esters comprise cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB). They are thermoplastic materials produced through esterification of cellulose. Different raw materials such as cotton, recycled paper, wood cellulose, and sugarcane are used to make the cellulose ester biopolymers in powder form. Bioceta, plasticized eellulose acetate, is prepared from cotton flakes and wood pulp through an esterification process with acetic anhydride. Cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) are mixed esters produced by treating cellulose with appropriate acids and anhydrides in the presence of sulphuric acid. 

Wood-thermoplastic composites usually consist of wood flour, thermoplastic, and various additives. The wood used in WPCs mostly refers to wood flour or wood fibers. Apart from woody materials, the agricultural plant residues, such as stems, stalks, leave, and seed hairs could also be used as a filler to manufacture WPCs. Generally, wood fiber is the most abundantly used plant fiber due to their extensive use in pulp and paper industries. Commercial composite products typically contain approximately 50 % wood. In some cases, some products only contain little wood, while others contain as much as 70 %. It has been proved that material compositions is highly related to the weathering of WPCs. Therefore, it is imperative to understand the chemical constituents and physical properties of wood. 

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