Aliphatic polyesters thermoplastic starch

In the context of this chapter, the use of thermoplastic starch in blends with thermoplastic resins is of the main interest. As shown in Table 16.11, several blends have been developed, e.g., with vinyl alcohol copolymers (EVAl), polyolefins, aliphatic polyesters such as poly-e-caprolactone (PCL) and its copolymers, or polymers of glycols (e.g., 1,4-butanediol) with succinic, sebacic, adipic, azelaic, decanoic or brassihc acids, PCL + PVC. Compatibilization is possible by amylose/EVAl V-type complexes, starch grafted polyesters, chain extenders like diisocyanates, epoxies, etc. [Bastioli et al., 1992, 1993]. 

Mater-Bi (Novamont, Environmental Packaging, L. P.) Thermoplastic, compatibiUzed blends of starch with aliphatic polyesters, EVAl, PVAl,... 

It is an aliphatic polyester derived from renewable resources, such as com starch, tapioca roots, chips or starch, or sugarcane. Polylactic acid or polylactide (PLA) can withstand temperatures up to 110 °C [69]. PLA is soluble in chlorinated solvents, hot benzene, tetrahydrofuran, and dioxane [70]. It can be processed like other thermoplastics into fiber (for example, using conventional melt spinning processes) and film. Due to the chiral nature of lactic acid, several distinct forms of polylactide exist ... 

Other biodegradables include aliphatic polyesters, polycaprolactones, and thermoplastic starch [61]. 

It is difficult to process aliphatic polyesters having low melting points by conventional techniques for thermoplastic materials, such as film blowing and blow moulding. It has been found that the blending of starch with aliphatic polyesters allows their processability and biodegradability to be improved. 

Synthesis PL A is a thermoplastic aliphatic polyester which is formed by condensation polymerization of lactic acid, as mentioned in the preceding. Lactic acid is isolated from tapioca, corn and other plant root starches, sugarcanes, or other resources. Bacterial fermentation is normally used to produce lactic acid... 

Starch can also be destructured in the presence of more hydrophobic polymers such as aliphatic polyesters (141). It is known that aliphatic polyesters with low melting points are difficult to process by conventional techniques for thermoplastic materials, such as film blowing and blow molding. With reference particularly to poly(e-caprolactone) and its copolymers, films produced thereby are tacky as extruded, and rigid, and have low melt strength over 130°C moreover, because of the slow crystallization rate of such polymers, the crystallization process proceeds for a long time after production of the finished articles with an imdesirable change of properties with time. 

Ratto XA. Stenhouse EX, Auerbach M., Mitchell X, FarreU Processing, performance and biodegradability of a thermoplastic aliphatic polyester/starch system, Po/y ier 40 (1999) 6777. 

In the biodegradable plastics market, aliphatic polyesters (in the main PLA, the present main competitor of starch thermoplastics) sell for 1.5-2.5 per kilo. Starch itself is very cheap ( 0.33 per kilo), but starch-based biopolymers such as Mater-Bi (from Novamont) are more expensive ( 2.40-3.4 per kilo) [6]. 

PLA is an aliphatic polyester. It is a biodegradable thermoplastic and can be processed to become composites. Its monomer, lactic acid, is derived from renewable plant sources, such as starch and sugar. PLA can be degraded into carbon dioxide and water by an action of suitable fimgi. This means that biodegradable PLA fibers are environment fiiendly material even if the fiber is left in the natural environment. The demand for PLA fibers as a substitute for the present synthetic fibers has been growing greatly in recent years. 

Polylactic acid or polylactide (PLA) is a thermoplastic aliphatic polyester that can be derived from renewable resources, such as corn starch or sugarcanes. Although PLA has been known for more than a century, it has become of great commercial interest in recent years because of its renewability and degradability to natural metabolites. In addition, the properties of PLA can be varied over a wide range which makes it suitable to be used as a substitute to many petroleum based commodity plastics, such as polyolefins,... 

The composition of Thermoplastic Starch (TSP) is starch, aliphatic polyester, glycerol, and water. Linear aliphatic polyesters that are... 

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. 

FIGURE 19 Representative composting time (in months) of biopolymers (TPS - Thermoplastic starch, PC - Polycaprolactone, mc-PHA - medium chain length PHA, Al-co-PEs -Ahphatic co-polyester, PEA - Polyester amides, Ah/arocoPEs - Aliphatic/aromatic copolyester, and CDAc - Cellulose diacetate). 

Products are available based on thermoplastic starch in combination with polymers or copolymers of vinyl alcohol and with aliphatic polyesters and copolyesters. Their biodegradation kinetics, mechanical properties and reduced sensitivity to humidity make these materials suitable for industrial development beginning with film and foam applications. 

Swelling the thermoplastic starch and aliphatic polyester with additional plasticiser and water in the first stage of an extruder. 

Ratto, J.A., Stenhouse, P.J., Auerbach, M., Mitchell, J. and Farrell, R. (1999) Processing Performance and Biodegradability of a Thermoplastic Aliphatic Polyester/Starch System, Polymer, 40, 6777-6788. 

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