Natural fibre-starch composites

Starch is a high molecular-weight polymer of anhydroglueose units linked by a-D-glycosidic bonds. The two main constituents of stareh are amylose and amylopectin (Fig. 8.6). Amylose is a linear molecule with an extended helieal twist and generally has a moleeular weight of 1.0 to 1.5 million. Amylopeetin is 

6 Structure of the polysaccharide components of starch, amylose (a) and amylopectin (b). 

1 Mechanical properties of natural fibre-starch composites 

The mechanical properties and water absorption behaviour of composites made from a starch-based thermoplastic matrix in combination with alkali-treated sisal fibres were studied by Alvarez et al. (2003). The variables in their experiments were fibre percentage, temperature and process time. The selected matrix was Mater-Bi -Y (Novamont), a blend based on cellulose derivatives, starch and additives (Cyras et al, 2001). Composites were prepared by blending Mater-Bi -Y with fibres in a high-intensity mixer and then compression moulding the compounded material into panels. Mechanical tests showed that the tensile modulus more than doubled from 0.95 GPa to 2.2 GPa when the fibre content was increased from 0 to 15%. Fibre treatment with sodium hydroxide solution had no statistically significant effect on tensile modulus. Similarly, the flexural modulus increased from roughly 1.4 GPa to 2.8 GPa when Mater-Bi -Y was reinforced with 15% w/w sisal fibre but was not significantly increased when alkali-treated fibres were used. 

Funke et al. (1998) used extrusion processing to examine the effect of different starch types, fibres, plasticisers and other compounding additives on thermoplastic processing. Raw starch materials from com were plasticised by 

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The water absorption characteristics of natural fibre-starch composites have been investigated by Funke et al (1998) and Alvarez et al (2003). In the former study, it was found that the water uptake on exposure to 45% relative humidity... 

Table 8.4 Mechanical properties of natural fibre-starch composites... 

In recent years starch, the polysaccharide of cereals, legumes and tubers, has acquired relevance as a biodegradable polymer and is becoming increasingly important as an industrial material (Fritz Aichholzer, 1995). Starch is a thermoplastic polymer and it can therefore be extruded or injection moulded (Balta Calleja et al, 1999). It can also be processed by application of pressure and heat. Starch has been used successfully as a matrix in composites of natural fibres (flax, jute, etc.). The use of starch in these composites could be of value in applications such as automobile interiors. An advantage of this biopolymer is that its preparation as well as its destruction do not act negatively upon the environment. A further advantage of starch is its low price as compared with conventional synthetic thermoplastics (PE, PP). 

Cellulose, Composites, Nanocomposites, Natural fibres, Lignocellulosic fibres. Cellulose whiskers, Chitin Whiskers, Starch nanocrystals... 

Most of the previous research on natural fibre composites has focused on reinforcements such as flax, hemp, sisal and jute, and thermoplastic and thermoset matrices. Some of these composites have been produced using matrices made of derivatives from cellulose, starch and lactic acid to develop fully biodegradable composites or biocomposites [52]. The emerging diversity of applications of natural fibre composites has seen the production of sandwich structures based on natural fibre composite skins (see Fig. 23.10). 

The biopolymers covered in this book chapter are Starch polymers, polyhydroxyalkanoates (PHA), polylactides (PLA), lignin-epoxy resins, epoxidised linseed oil and composites reinforced with natural fibres such as flax, hemp, and china reed (miscanthus). The first three materials are biodegradable while this is not the case for the remaining studied materials. 

Leaving PHA aside as the only exception, it can be summarised that biopolymers and natural fibres typically enable savings of around 20% (energy and CO2). Substantially higher savings up to 50% and beyond are considered feasible for certain starch polymers, printed wiring boards, certain lacquers, and natural fibre composites. 

C5 ras VP, Manfredi LB, Ton-That M-T, Vazquez A (2008) Physical and mechanical properties of thermoplastic starch/montmorillonite nanocomposite films. Carbohydr Polym 73 55-63 de Morals Teixeira E, Correa A, Manzoli A, de Lima Leite F, de Oliveira C, Mattoso L (2010) Cellulose nanofibers from white and naturally colored cotton fibers. Cellulose 17 595-606 de Moura MR, Aouada FA, Avena-Bustillos RJ, McHugh TH, Krochta JM, Mattoso LHC (2009) Improved barrier and mechanical properties of novel hydrox5q)ropyl methylcellulose edible films with chitosan/tripolyphosphate nanoparticles. J Food Eng 92 448—453 Dean K, Yu L, Wu DY (2007) Preparation and characterization of melt-extruded thermoplastic starch/clay nanocomposites. Compos Sci Technol 67 413 21 Duanmu J, Gamstedt EK, Rosling A (2007) Hygromechanical properties of composites of crosslinked allylglycidyl-ether modified starch reinforced by wood fibres. Compos Sci Technol 67 3090-3097... 

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