Polyesters thermoplastic starch

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... 

Modified processing techniques have been useful for thermoplastic starch polymers. Recent work [45, 46] has examined the use of coextruded sheet processing to produce polyester / thermoplastic wheat starch / polyester multilayer films. They found that adhesion strength between the layers and stability of the interface were crucial properties in controlling the final performance properties of the films. Work by Sousa [47] has examined use of the novel shear controlled orientation injection molding (SCORIM) process to control morpholoiges and provide tensile property increases of thermoplastic starch/synthetic blends. 

Reactive blending of thermoplastic starch/polymer blends has been examined recently and aims to increase properties and performance via control of blend morphologies. Mani [58, 59] examined different techniques for compatibilising starch-polyester blends. They examined development of maleic anhydride grafted polyester/starch blends and starch-g-polycaprolactone... 

In terms of nanocomposite reinforcement of thermoplastic starch polymers there has been many exciting new developments. Dufresne [62] and Angles [63] highlight work on the use of microcrystalline whiskers of starch and cellulose as reinforcement in thermoplastic starch polymer and synthetic polymer nanocomposites. They find excellent enhancement of properties, probably due to transcrystallisation processes at the matrix/fibre interface. McGlashan [64] examine the use of nanoscale montmorillonite into thermoplastic starch/polyester blends and find excellent improvements in film blowability and tensile properties. Perhaps surprisingly McGlashan [64] also found an improvement in the clarity of the thermoplastic starch based blown films with nanocomposite addition which was attributed to disruption of large crystals. 

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]. 

WAN 00] Wang L., Shogren R.L., Carriere C., Preparation and properties of thermoplastic starch-polyester laminate sheets by coextrusion . Polymer Engineering Science, vol. 40, no. 2, pp. 499-506,2000. 

Natural polymers such as starch and protein are potential alternatives to petroleum-based polymers for a number of applications. Unfortunately, their high solubility in water limit their use for water sensitive applications. To solve this problem thermoplastic starches have been laminated using water-resistant, biodegradable polymers. For example, polylactic acid and P(3HB-co-3HV) were utilised as the outer layers of the stratified polyester/PWS (plasticized wheat starch)/polyester film strucmre in order to improve the mechanical properties and water resistance of PWS which made it useful for food packaging and disposable articles [65]. Moreover, improved physic-chemical interactions between P(3HB-CO-3HV) and wheat straw fibres were achieved with high temperature treatment. It resulted in increased P(3HB-co-3HV) crystallization, increased Young s moduli and lowered values of stress and strain to break than the neat matrix of P(3HB-co-3HV). There was no difference in the biodegradation rate of the polymer [66]. 

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

Particularly suitable polyesters considered in the past have been poly-e-caprolactone (PCL) and its copolymers. Nevertheless, films made of thermoplastic starch and PCL are tacky as extruded, rigid, and have low melt strength at temperatures over 130 °C. Moreover, due to the slow crystallization rate of such polymers, the complete cooling process needs a long time after production of the finished articles, giving an undesirable change of properties with time. 

Starches are insoluble in water. They can be digested by hydrolysis, catalyzed by enzymes (called amylases), which can break the a/p/za-linkages. Humans and other animals have amylases, so they can digest starches. Potato, rice, wheat, and maize are major sources of starch in the human diet. Thermoplastic starch is used for niche products, because of the water solubility often in combination with other polymers, e.g. as blends with PVAL, polyesters, polyesteramids, sometimes as fillers of synthetic polymers. 

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) combines the thermo-mechanical properties of PE (strength, flexibility, ductility, toughness, elasticity) with the physical-chemical properties (compatibility) of polyesters (printability, dyeability, barrier performance). It forms blends with PLA and thermoplastic starch. 

Natural polysaccharides, such as starch derived from com, wheat, rice or potato, and cellulose and its derivatives, are the main biopolymers employed in the development of green nanocomposites. The biodegradable thermoplastic polyester PLA, starch, and epoxidized vegetable oils are other examples of polymers widely used in the development of reinforced biopolymers. 

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. 

The addition of starch has a nucleating effect which increases the crystallisation rate of the polyester [92]. The rheology of the starch/PCT blends depends on the extent of starch granule destruction and the formation of thermoplastic starch during extrusion. Increasing shear and heat intensities can reduce the melt viscosity, but enhance the extrudate swelling properties of the composite [94]. 

Bacterial cellulose has been used as a material in combination with many others to develop composites. It has been used with materials such as xmsaturated polyester [185], the conducting polymer polyaniline [158-162, 186], as well as various acrylic and phenolic resins [178, 187-189]. It has also been used with several biodegradable materials such as cellulose acetate butyrate (CAB) [146,190], PLA [167,174,191,192], PHB [193-195], PVA [196,197], and thermoplastic starch [198,199], to produce completely biodegradable composites. Though renewable and biodegradable composites are the focus of this review, techniques and resulting composites from non-renewable sources are also mentioned. 

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. 

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