Bioplastics modifications

Above we have shown the attractiveness of the so-called green nanocomposites, although the research on these materials can still be considered to be in an embryonic phase. It can be expected that diverse nano- or micro-particles of silica, silicates, LDHs and carbonates could be used as ecological and low cost nanofillers that can be assembled with polysaccharides and other biopolymers. The controlled modification of natural polymers can alter the nature of the interactions between components, affording new formulations that could lead to bioplastics with improved mechanical and barrier properties. 

Starch is the major carbohydrate reserve in higher plants and has been one of the materials of choice since the early days of human technology. Recently, starch gained new importance as a raw material in the production of bioplastics, in particular for use in the synthesis of monomers to produce polymers such as polyflactic acid), and after chemical modification and thermomechanical processing, to produce the so-called thermoplastic starch. 

The aquatic, anaerobic biodegradation test was first published by the European Centre for Ecotoxicology and Toxicology of Chemicals Technical Report No.28 [10]. Later, more or less the same procedure was adopted as ASTM D5210 in 1992 and ISO 11734 in 1995. Within the field of bioplastics a new version with some minor modifications was published in 2005 as ISO 14853- Plastics - Determination of the ultimate anaerobic biodegradability in an aqueous system - Method by measurement of biogas production. 

On the other hand, proteins possess very interesting functional properties. Owing to their specific structure with both hydrophilic and hydrophobic properties they can stabilize interfaces and form films. By physical, enzymatic or chemical modification the subunits can be dissociated and the polypeptide chains can be unfolded which improves the interface-stabilizing properties. And last but not the least they can form networks to build bioplastics (Figure 10.1). 

Natural polymer research has included use of these alternative materials with nanoparticles [487] because of three significant properties multifunctionality, biodegradabihty, and bio-compatibihty. Breakthroughs in cost of production and property profiles for biomaterials will be needed before they become reasonable to market. Research has been conducted on melt formation of a starch-clay nanocomposite for bioplastic applications [487] however, an issue is the high water uptake and thus loss in mechanical properties requiring modification of the clay and the composite process. As with other nanocomposites, microstructural characterization is typically by TEM and AFM. 

The reason for this is that frequently all the fossil resources used during the manufacture of bioplastics are not taken into account, particularly when chemical modification of the biological raw material is involved during manufacture. Nor has the question of alternative use of agricultural land for polymer intermediates been accounted for when it competes with food production. The calorific value of hydrocarbon polymers when burned in an appropriate waste-to-energy incinerator is similar to the oil from which they were manufactured, whereas bio-based polymers are generally less useful as fuels. 

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