Lignocellulosic fibres mechanical properties

The generally poorer mechanical properties exhibited by acetylated lignocellulosic material in composites bonded using aqueous resin systems was considered by Korai etal. (2001). Fibres of yellow cedar (Chamaecyparis nootkatensis) were acetylated to a WPG of 24.8 % and then ozonated to different extents to increase the hydrophilicity of the fibre surface. Boards were fabricated from the fibres using an aqueous MF resin. Ozonation improved IBS of boards fabricated from acetylated fibres, proportional to level of ozone charge, and resulted in IBS values comparable to those of nonacetylated controls at higher levels of ozonation. However, although ozonation also improved MOR, the values obtained for acetylated fibres were always less than those obtained with unmodified fibres. 

Pineapple leaf fibre (PALF), which is rich in cellulose, relatively inexpensive and abundantly available has the potential for polymer-reinforced composite. PALF at present is a waste product of pineapple cultivation. Hence, without any additional cost input, pineapple fibres can be obtained for industrial purposes. Among various natural fibres, PALFs exhibit excellent mechanical properties. These fibres are multicellular and lignocellulosic. They are extracted from the leaves of the plant Ananus cosomus belonging to the Bromeliaceae family by retting. The main chemical constituents of pineapple fibres are cellulose (70-82%), lignin (5-12%) and ash (1.1%). The superior mechanical properties of PALFs are associated with their high cellulose content. 

A. Baltazar-y-Jimenez, M. Bistritz, E. Schulz, and A. Bismarck, Atmospheric air pressure plasma treatment of lignocellulosic fibres Impact on mechanical properties and adhesion to cellulose acetate butyrate. Compos. Sci. Technol. 68(1), 215-227 (2008). 

As mentioned before, agro-based lignocellulosics suitable for composites stem from two main sources. Tbe first is agricultural residues, which have unknown mechanical properties and the second source is those lignocellulosics grown specifically for their fibre. Examples of the second source are cotton, jute, flax, sisal and many others. 

Keywords Polyethylene composites, sustainable materials, lignocellulosic fibres, natural fibres, surface treatment, reinforcing, mechanical properties... 

Table 5.1 Chemical composition and mechanical properties of the lignocellulosic fibres as compared with E-glass fibre (Adapted from [4, 9, 28,30-32]). 

The performance of natural fibre reinforced polymer composites depends on several factors, including fibre chemical composition, cell dimensions, microfibrillar angle, defects, structure, physical and mechanical properties, and the interaction of a fibre with the polymeric matrix [28]. The knowledge about the characteristics of the fibre is essential in order to expand the effective use of lignocellulosic materials for polyethylene composites and to improve their performance. 

The results show that the lignocellulosic content and the type of plastic used are the main parameters that control the physical properties of composites. Some of the thermoplastic materials exhibit mechanical properties comparable to those of customary wood fibre products, i.e., medium density fibreboard (MDF) [99, 175] however they show distinctly better behaviour than the MDF and natural wood after exposure to moisture [75, 99, 175]. 

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