Biodegradation of thermoplastic starch

G. li, P. Sarazin, W.J. Orts, S.H. Imam, B.D. Favis, Biodegradation of thermoplastic starch and its blends with poly(lactic acid) and polyethylene Influence of morphology. Macromol. Chem. Phys. 212, 1147-1154 (2011)... 

Yu, L, Christov, V., Christie, G., Gray, J., Dutt, U., Harvey, T., Halley, P., Coombs, S., Jayasekara, R. and Lonegan, G. (1999) Effect of additives on gelatinization, rheological properties and biodegradability of thermoplastic starch. Macromolecular Symposia, 144, 371. 

Russo M, O Sullivan C et al (2009) The anaerobic degradability of thermoplastic starch Polyvinyl alcohol blends Potential biodegradable food packaging materials. Bioresour Technol 100 1705-1710... 

During the same period, commercialization of thermoplastic starch polymer blends was pursued by Novamont, a division of the Ferruzzi Group of Italy.162-172 Their products, marketed under the trade name Mater-Bi, are typically comprised of at least 60% starch or natural additive and hydrophilic, biodegradable synthetic polymers.64,165 It is stated that these blends form interpenetrated or semi-interpenetrated structures at the molecular level. Properties of typical commercial formulations have properties similar to those in the range of low- and high-density PE. Blends of Mater-Bi products with biodegradable polyesters have been claimed for use as water impervious films.173... 

A wide range of thermoplastic starch compounds have been claimed in recent years. Formulations of thermoplastic starch with linear, biodegradable polyesters, including polycaprolactone and PHBV,174 176 and with polyamides175 have been reported. Laminated structures have been claimed using thermoplastic starch or starch blends as one or more of the layers.175,177,178 The use of polymers latexes as components of thermoplastic starch blends has also been claimed.179 181 Blends with natural polymers are also claimed, including cellulose esters182,183 and pectin.184 A crosslinked thermoplastic material of dialdehyde starch and protein has been reported.185... 

This article provides a review of thermoplastic starch polymers [unlike polymers with added granular starch] including an introduction to biodegradable polymers and thermoplastic starch polymers a review of thermoplastic starch polymer development a review of reactive modification of thermoplastic starch, examining the structure-property relationships of thermoplastic starch and a review of commercial thermoplastic starch polymer applications. 

The presence of starch improves the biodegradation rates of these synthetic polymers, where a fundamental role is also played by size and distribution of ethylene blocks. Attempts to speed up the biodegradation rate by modification of EVOH copolymers with carboxyl groups have been pursued but the degradation rate of thermoplastic starch and EVOH composites is too slow to consider them compostable according to international test standards. 

This chapter reviews the general context of starch as a material. After a survey of the major sources of starch and their characteristic compositions in terms of amylase and amylopectin, the morphology of the granules and the techniques applied to disrupt them are critically examined. The use of starch for the production of polymeric materials covers the bulk of the chapter, including the major aspect of starch plasticization, the preparation and assessment of blends, the processing of thermoplastic starch (TPS), the problems associated with its degradation and the preparation of TPS composites and nanocomposites. The present and perspective applications of these biodegradable materials and the problems associated with their moisture sensitivity conclude this manuscript. 

This paper revises the wide variety of properties, structures and biodegradation behavior of thermoplastic starch in combination with polymers of vinyl alcohol and with poly-s-caprolactone and of some aliphatic polyesters like poly-hydroxybutyrate-valerate, poly-lactic acid, poly-s-caprolactone and polybutylene succinate. 

The results obtained in the field of thermoplastic starch in combination with polymers or copolymers of vinyl alcohol with aliphatic polyesters and copolyesters in terms of biodegradation kinetics, mechanical properties and reduced sensitivity to humidity make these materials ready for a real industrial development starting from film and foam applications. The present global market is around 12000 tons/year. Main producers are Novamont with Mater-Bi trade-mark, ENPAC and National Starch. The tensile properties of films made of two Novamont s Mater-Bi grades are reported in Table 3, in comparison to these of low density polyethylene (LDPE). Figs. 6-7 show applications of Mater-Bi starch-based materials now on the market. 

Shin BY, Lee SI, Shin YS, Balakrishnan S, Narayan R. Rheological, mechanical and biodegradation studies of blends of thermoplastic starch and polycaprolactone. Polym Eng Sci 2004 44 1429-38. 

The main use of thermoplastic starch alone is in foam applications. Starch-based foams have been found to be an effective alternative to PS foam in loose-fill protective packaging. Starch-based foams offer the advantage that they are readily biodegradable if they escape into the environment. They also offer superior antistatic properties. Starch-based foam, however, has some disadvantages it is brittle and the density is higher than PS. Foamed, starch-based articles are prepared by heating starch in an extruder in the presence of water with subsequent extrusion. 

In the last five years Asian countries, and specifically China and Korea, have performed impressively in the sector of blends of thermoplastic starch with polyolefins, in terms of intellectual property and products range offered to the market. The non compliance of these products with the international norms of biodegradability and compostability, however, did not permit a significant market growth in western countries where low environmental impact products have more market potential. 

Ratto et al. (1999) has examined poly butylenes sueeinate adipate (PBSA) terpolymer/granular starch composites for blown films and showed they could produce good film tensile properties and control biodegradation with granular starch addition. Thermoplastic starch/cellulose fibre extrudates and injection moulded products were examined by Funke et al. (1998) and they showed a reduction in water adsorption with increasing fibre content. Work by Halley et al. (2001) examined the use of thermoplastic starch-polyester blends for use in mulch film applications noting excellent field performance and biodegradability for these materials. 

Bastioli C, Biodegradable materials - Present situation and future perspectives , Macromolecular Symposia, vl35 193-204 (1998). (An excellent summary of thermoplastic starch polymers from one of Novamont s leading scientists.)... 

Agricultural polymers (polysaccharides or proteins) can be extracted and eventually purified. They can be used alone or in a mixture with a synthetic biodegradable polymer such as polycaprolactone or other synthetic biodegradable polyesters (e.g. blends of thermoplastic starch and polyesters). 

The utilization of TPS for the production of biodegradable plastics has increased and has been the object of several studies in the last decade. However, TPS has two main drawbacks namely its water affinity and its poor mechanical properties. To overcome these problems, the addition of other materials to TPS is necessary. In order to increase its water resistance, TPS has been blended with synthetic polymers and modified by cross-linking agents such as Ca and Zr salts. Substances such as waxes and lignin have also been tested to decrease the water uptake of starch-based materials. TPS s mechanical properties have usually been improved by addition of synthetic polymers, such as ethylene-acryhc acid and ethylene-vinyl alcohol copolymers. Another approach requires the use of natural fibers and mineral fillers. The inclusion of reinforcing fillers such as fibers could, however, enhance the degradation of thermoplastic starch because of the increase in the melt viscosity [79-81]. 

Averous, L., Fauconnier, N., Moro, L and Fringant, C. (2000) Blends of thermoplastic starch and polyesteramide processing and properties. Journal of Applied polymer Science, 76,1117-28. Mani, R. and Bhattacharya, M. (1998) Properties of injection moulded starch/ synthetic polymer blends. Ill Effect of amylopectin to amylose ratio in starch. European Polymer Journal, 34 (10), 1467-75. Mani, R. and Bhattacharya, M. (2001) Properties of injection moulded blends of starch and modified biodegradable polyesters. European Polymer Journal, 37, 515-26. 

Special mention must be made of poly(lactic acid), a biodegradable/bio-resorbable polyester, obtained from renewable resources through fermentation of com starch sugar. This polymer can compete with conventional thermoplastics such as PET for conventional textile fibers or engineering plastics applications. Hie first Dow-Cargill PLA manufacturing facility is scheduled to produce up to 140,000 tons of Nature Works PLA per year beginning in 200245 at an estimated price close to that of other thermoplastic resins U.S. l/kg.46 Other plants are planned to be built in the near future.45... 

Ecoflex is an essential component for the processing of renewable raw materials like starch and for producing high quality biodegradable and bio-based plastic films out of them. Ecoflex /thermoplastic starch compounds are used... 

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