Plasticized starch-based blends

There are a certain number of advarrtages to blending different components. It is the easiest process to use in order to combine different polymers. It enables us to obtain materials with, ofterr, improved or new properties, for an interesting eost This approach is generally less expensive than developing new polymers with new macromolecular architectures. A key element in blend making is the compatibility between phases, which will determine the interface and interphase interaction of the final material. 

Plasticized starch has widely been studied in a mixture with other polymers [AVE 04a, AVE 00a, AVE 00b, AVE 01a, MAR 01a, MAR 01b, SCH 04]. A large nrrmber of patents have been pubUshed on this subject [AVE 04a]. These research efforts have led to the commercialization of different biodegradable blends - some of them based on plasticized starch (Table 9.4). 

Brand name Company Associated compounds Note 

Mater-Bi Novamont (Italy) PCL, PBAT Current market leader 

Bioplast Bio-Sphere (France) and Biotec(Germany) PBAT Starch-based 

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So far, various bio-based polymers have been developed, e.g., cellulose acetate, poly(alkylene succinate)s, starch-based blends, poly(3-hydroxy alkanoate)s (PHA) [1], poly(lactic acid) (PLA) [2], etc. Nowadays, some typical commodity plastics have also been S5mthesized from biomass, for example, polyethylene, polypropylene, poly(methyl methacrylate) [3], polyamide-4 [4], and polycarbonate [5]. If plastic materials are synthesized from renewable resources and circularly utilized with precise control of their depolymerization, an ideal recycling system could be constructed for plastic products, in which the resources and production energy could be minimized. Thus, the development of bio-based recyclable polymers is significant. In Scheme 9.1, t5 ical... 

Altpeter H, Bevis MJ, Gomes ME, Cunha AM, Reis RL, (2003) Shear controlled orientation in injection moulding of starch based blends intended for medical apphcations , Plastics Rubber and Composites, v32 n4 173-181. 

A particular mention goes to Mater-Bi, produced by Novamont, who have revolutionised starch-based biomaterials for two decades. The commercial success of this biodegradable and biocompostable plastic relies on two main factors the scale economy that allows the reduction of costs, and the diversity of formulations to develop different end products (plastic bags, tableware, toys, etc.). More than 210 references in Chemical Abstracts are available on this (registered) keyword, and the number of patents related to different formulations and developments is also impressive. Mater-Bi can be essentially described as a blend of starch with a small amount of other biodegradable polymers and additives. The actual compositions are still known only by a very few people. 

These discoveries provided the technology base for commercialization efforts of starch-based plastics by the Novon division of the Warner-Lambert Company.157,158 The thermoplastic compositions were based on blends of destructurized starch and various hydrophilic polymers, such as ethylene-vinyl alcohol copolymers (EVOH). Hydrophobic polymers and additives, such as plasticizers and lubricants, could also... 

L. Averous, O. Martin and L. Moro, Plasticized Wheat Starch-based Biodegradable Blends and Composites, 6th 1SBP and 9th BEPS, Honolulu-Hawaii (USA), 12-16 December 2000. 

Several companies have developed starch-based plastics. By using carefully selected starch feedstocks, and water as a plasticizer, they produce thermoplastics from nearly 100% starch, or from blends of starch with other biodegradable components. Many of these materials are water-soluble in addition to being biodegradable. The major target application has been as a replacement for polystyrene foam, including both molded cushions and loosefill. 

Generally speaking, bio-based plastics include starch-based plastics, protein (soybean protein) based plastics, and cellulose-blended plastics. They can also be blended with conventional plastics such as polyethylene (PE), polypropylene (PP), and poly(vinyl alcohol). However, such bio-based plastics are only partially biodegradable. The residual petroleum-based plastics remain as broken pieces, creating additional pollution. In addition, these plastics have intrinsic thermal and mechanical weaknesses, and they are now discouraged for applications. 

Chemical or enz5miatic agents may also be used to destructur-ize, oxidize, or derivatize the starch. Modified starches have been used to make biodegradable plastics, wherein the modified starch is blended as an additive or the minor component with petroleum-based or synthetic pol5m ers. 

Starch-Based Plastics. As can be seen in Table 8.7, a variety of starch-based plastics have been produced by several companies. Starch-based plastics are often water-soluble as well as biodegradable. Some contain almost entirely starch others contain blends of starch with other biodegradable components. 

Due to the brittleness of starch materials, plasticizers are commonly used. A frequently utilized low weight hydroxyl compoxmd is glycerol. Another effective plasticizer is water, although not the best because it evaporates easily. Still, starch-based materials readily absorb water and this may result in significant changes in the mechanical properties. Different routes have been explored in order to improve the mechanical properties and water resistance of starch materials. These are chemical modifications to the starch molecule, blends with polymers such as polycaprolactone [61], or reinforcement with different types of cellulose-based fillers, such as ramie crystaUites [62], and timicin whiskers [63], or montmorillonite clay particles [64]. 

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