Starch plastics

Figure 1. Possible routes for biological and chemical degradation of starch-plastic composites. Note that direct biological degradation of petrochemical-based polymers does not occur. Rather, these polymers must first undergo chemical degradation to form as yet uncharacterized, lower molecular weight intermediates.

Starch-plastic composites contain a mixture of two very different types of materials (/) hydrophobic, petrochemical-derived polymers (PE, EAA) known to be highly resistant to degradation by living organisms, and (i7) a hydrophilic, natural polymer (starch) that is easily broken down by a wide array of organisms. In the process developed by Otey (3), these fundamentally incompatible materials are forced into an intimate mixture during production of the plastic film. Since... 

At this point little is known about the interrelationships between composition, structure, starch-degradation and physical disintegration properties of starch-plastic composites. Continued work towards development of a laboratory assay for biodegradability will eventually result in the establishment of a sufficient database to elucidate these relationships, allowing development of a host of starch-containing plastic products for both existing and new markets. 

According to filler theory, connectivity can be achieved at lower values when the filler form is plates rather than spheres. Depending on the proportions of the plates and whether or not an inactive phase is included in the blend, connectivity can be achieved at 8 to 16% (v/v) filler (4). The starch-plastic blends developed by Otey (2) have a laminate structure when the starch content is under 30% by volume (Figure 1) and the threshold for microbial attack on these materials is under 13% starch by volume (Figure 2). This low threshold value can be explained by considering the LDPE as a non-conductive (enzyme-impermeable) phase combined with a conductive phase of starch-EAA complex. 

Non-invasive Microbial Growth on Starch-plastic Blends... 

Figure 3. Postulated mechanism for microbial decay of starch-plastic blends.

Oxygen Availability in Degrading Films. A major difference between natural materials and starch-plastic or cellulose-plastic blends is that the hydrophilic and relatively permeable matrix of materials like wood and hydrated polysaccharide films allows diffusion of O2 and release of nutrients from sites at a distance from the invasion site. As colonization proceeds, pore enlargement occurs when the pore walls are degraded (8) or as the polymer matrix of amylose or PVA films is hydrolyzed (10.12). In contrast, the LDPE matrix supplies no nutrients, hinders diffusion of water and O2, and the pore diameter cannot be increased. The consequence of impermeability is that the sole means of obtaining O2 and nutrients is by diffusion through water-filled pores. 

Figure 4. A. Water relationships and diffusion paths for starch-plastic film in a moist environment. Lightly shaded area indicates thin water layer on surface arrows show diffusion paths for enzymes produced by microbes on film surface. B. Same as 4 A., except that film is inunersed in water.

Figure 5. Influence of subunit size on diffusion paths in starch-plastic laminates containing equal volumes of starch and plastic (not to scale). A and C intact film B and D after starch removal. Arrows indicate constrictions that would control diffusion processes.

For starch-Bionolle compound production process, we obtain data of product yield and mixing ratios of Bionolle, starch, plasticizer, and water from actual site data provided by Showa Denko. Data of electric power consumption for kneading process are taken from actual site data from Showa Denko. 

The starch plasticization is obtained by gelatinization of the grains in low moisture conditions leading to the melting of the starch grains. This is the key phenomenon in the transformation of the whole corn plant. The plasticized starch forms a continuous matrix in which the defibrated fibers are embedded, as showed schematically in Figure 5.22. 

Figure 8.7 Flexural modulus of gelatinized com starch plasticized by glycerol as a function ofwater content.284...

Breslin, V. T. Swanson, R. L. (1993). Deterioration of starch-plastic composites in the... 

Stain removers Starch preparations, laundry Starches, plastics Sweeping compounds, oil and water absorbent, clay or sawdust... 

Biodegradable plates, knives, forks, and leaf bags can be made by molding or extrusion of starch plasticized with 10% water.66 After use, the materials could be composted. A mixture of benzylated wood and polystyrene can be extruded easily.67 The properties of the product are comparable with those of poly(styrene). 

Waxy corn (WCN30G30W) materials are amorphous after moulding at a temperature above 120°C. Potato starch materials (PN30G30W) show B-type crystallinity. The relative crystallinity (compared to native potato starch) decreases from 68% (at 110°C) to 36% (at 140°C). Above 140°C the relative crystallinity increases to a value of 70% at 190°C. These values are in agreement with values previously reported.14 It has been shown that the total B-type crystallinity of potato starch plasticized with glycerol and water can be considered as a summation of residual amylopectin crystallinity and recrystallization of both amylose and amylopectin depending on processing conditions. 

J. J. G. van Soest, Starch Plastics Structure-Property Relationships, PhD Dissertation, Utrecht University, ISBN 90-393-1072-6, P L Press, Wageningen, 1995, pp. 1. 

Other effective plasticizers for starch for imparting melt processibility include a variety of low molecular weight compounds, such as glycerol and diethylene glycol, and also polymers such as poly(ethylene-co-vinyl alcohol) [55]. Furthermore, starch plasticized in that manner can be melt blended with minor amounts of hydrophobic thermoplastics, such as polyethylene and poly( methyl methacrylate), to obtain biodisintegratable molded articles with good mechanical properties. 

Spence, K.E. A.L. Allen S. Wang J.L. Jane. Soil and Marine. Biodegradation of Protein-Starch Plastics. In R. M. Ottenbrite, S. J. Huang and K. Park., editors Hydrogels and biodegradable polymers for bioapplications. ACS symposium series 627 American Chemical Society Washington DC, 1996 pp. 149-158 (Chapter 12). 

Table 9.4. Biodegradable blends based on starch, plasticized or otherwise, commercialized in 2012, and their corresponding suppliers...

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