Starch-Filled Plastics

Starch can be used as a natural filler in traditional plastics [20, 27-37] and particularly in polyolefins. When blended with starch beads, PE films [38] biodeteriorate on exposure to a soil environment. The microbial consumption of the starch component, in fact, leads to increased porosity, void formation, and the loss of integrity of the plastic matrix. Generally [36, 39-42], starch is added at fairly low concentrations (6-15%) the overall disintegration of these materials is achieved by the use of transition metal compounds, soluble in the thermoplastic matrix, as pro-oxidant additives which catalyse the photo-and thermo-oxidative process [43-48]. 

The temperature has to be kept below 230 °C to prevent decomposition of the starch, and exposure of the masterbatch to air had to be minimised to avoid water absorption. Direct addition of starch and autoxidant without the masterbatch step can also be used as this requires some specific equipment, it is only practical for large volumes [46]. It is claimed that under appropriate conditions, the disintegration time of a buried carrier bag, containing an Ecostar additive of up to 6% starch, will be reduced from hundreds of years to three to six years [42]. However there is no evidence of a compliance of such materials with the norms of biodegradability and compostability already in place at the 

Within the field of starch-filled materials other systems were studied, some of which a completely biodegradable such as starch/poly(E-caprolactone) (PCL) [53], others which are partially biodegradable, such as starch/polyvinylchloride/PCL and its derivatives [54] or starch/modified polyesters [55]. In all these cases starch granules are used to increase the surface area available for attack by microorganisms. 

The use of native starch as filler in traditional plastics such as polyolefins nowadays is [12-15] less popular than in the past. Nevertheless, in this paragraph a short review of such kinds of products will be disclosed. 

When blended with starch beads, PE films [16] deteriorate on exposure to a soil environment. The microbial consumption of the starch component, in fact, leads to increased porosity, void formation, and the loss of integrity of the plastic matrix. 

Generally [17] starch is added at fairly low concentrations (6-15%) the overall disintegration of these materials is achieved by the use of transition metal compounds, soluble in the thermoplastic matrix, as pro-oxidant additives that catalyse the photo and thermo-oxidative process [18-21]. 

When processing this sort of materials, temperature has to be kept below 230 °C to prevent decomposition of the starch, and exposure of the masterbatch to air had to be minimized to avoid water absorption. 

Direct addition of starch and pro-oxidant without the masterbatch step can also be used. Since this requires some specific equipment, it is only practical for large volumes [20]. 

Starch-filled PE containing prooxidants have been used in the past in agricultural mulch film, in bags and in six-pack yoke packaging. Commercial products based on this technology were first sold by Ecostar and Archer Daniels Midland Companies 

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Today, PSM (HK) Co. Ltd. (a subsidiary of Engrowth Investments Limited incorporated in BVI) is one of the few companies which still use starch-filled plastics producing raw materials for injection moulded products usually for catering purposes [26]. 

This article reviews the main results obtained in the fields of starch-filled plastics and thermoplastic starch, with particular attention to the concepts of gelatinization, destructurization, extrusion cooking, and the complexation of... 

This chapter reviews the main results obtained in the fields of starch-filled plastics and thermoplastic starch with particular attention to the concept of gelatinisation, destructurisation, extrusion cooking, and the complexation of amylose by means of polymeric complexing agents with the formation of specific supra-molecular structures. The behaviours of products now in the market are considered in terms of processability, physical-chemical and physical-mechanical properties and biodegradation rates. 

If starch is modified by partially fermenting it, or esterifying or etherification, the resulting material can be extruded by adding plasticizers. Starch-based plastics are readily biodegraded. In most cases, the polymers are also water-soluble. Several suppliers now offer thermoplastic starch. Major markets include soluble films for industrial packaging, films for bags and sacks, and loose fill. 

The largest share in terms of volume corresponds to the starch-based plastic market. The main applications are compost bags, shopping bags, loose-fill packaging and mulch films. 

Fig. 7.7 Glass-rubber transition temperatures associated with the midpoints of the transitions versus water content for glycerol plasticized waxy maize starch filled with 0 (filled circle), 3.2 (circle), 6.2 (filled square), 16.7 (square), and 25 wt% (filled diamorul) tnnicin whiskers. Solid lines serve to guide the eye (Angles and Dulresne 2000). Copyright (2000) American Chcanical...

Starch-based plastics can be classified as compostable if the additives are also biodegradable under industrial compost environment conditions. Starch can be an additive for petroleum-based plastics like polyethylene, polypropylene, polyurethane, and polyester. However, these starch-filled petroleum-based plastics are not included in this book since they would not biodegrade under industrial composting conditions and would not be recyclable with commercial mechanical recycling operations. 

Westhoff, R.P., Otey, F.H., Mehitretter, C.L., and Russell, C.R., 1974, Starch-Filled Polyvinyl Chloride Plastics. Preparation and Evaluation. Ind. Eng. Chem. Prod. Res. Develop. 13 123-125. 

This starting position makes a. one of the most important raw materials in the production of biodegradable - starch plastics as well as a component in starch-filled synthetics or in ->starch-containing plastics. In such systems, firmness, elasticity and flexibility is enhanced with rising a. content whereas the amylopeetin eomponent imparts brittleness and lower firmness. Therefore, a high a. content is demanded for most applications of starchy materials in biodegradable plastics as well as in many other applications as RR. 

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