Blends, thermoplastic starch polymers

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... 

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. 

Novamont www.novamont.com/ Materbi Thermoplastic starch polymer blends biodegradable mulch films and bags, thermoformed products, injection molded items, and packaging foam... 

R.B. Maliger, P.J. Halley, Reactive extrusion for thermoplastic starch-polymer blends (book chapter), in Starch Polymers From Genetic Engineering to Green Apphcations, 2014, pp. 291-317. 

P. Sarazin, G. Li, W.J. Orts, B.D. Favis, Binary and ternary blends of polylactide, poly-caprolactone and thermoplastic starch. Polymer 49 (2) (2008) 599-609. 

Hietala M, Mathew AP, Oksman K (2013) Bionanocomposites of thermoplastic starch and cellulose nanofibers manufactured using twin-screw extrusion. Eur Polym J 49 950-956 Hoover R, Hughes T, Chung HJ, Liu Q (2010) Composition, molecular structure, properties and modification of pulse starches a review. Food Res Int 43 399-413 Hotza D (1997) Colagem de Folhas Ceramicas. Tape Casting Ceramica 159-166 Huneault MA, Li H (2012) Preparation and properties of extruded thermoplastic starch/polymer blends. J Appl Polym Sci 126 96-108... 

In summary this section has demonstrated that thermoplastic starch polymers and their blends provide an exciting foimdation for developing low-cost biodegradable polymers. The next section will examine an extension of this research into modified thermoplastic starch polymers. 

Some commercial thermoplastic starch polymer based products were highlighted in Table 6.1, and some of them can be examined in more detail in this section. Probably one of the first starch based products developed was the National Starch expanded starch foam packaging material ECO-FOAM . ECO-FOAM materials are derived from maize or tapioca starch and include modified starches. This relatively short-term, protected-environment packaging use is ideal for thermoplastic starch polymers. National starch now has additional thermoplastic starch materials, blends and speciality hydrophobic thermoplastic starches for a range of apphcations including injection moulded toys, extruded sheet and blown film apphcations. [http //www.eco-foam.com/ loosefill.asp]. 

Simmons S, Thomas EL (1995) Structural characteristics of biodegradable thermoplastic starch/poly(ethylene-vinyl alcohol) blends. J Appl Polym Sci 58 2259-2285... 

George, E. R., Sullivan, T. M., Park, E. H. (1994). Thermoplastic starch blends with a poly(ethylene-co-vinyl alcohol) Processability and physical properties. Polymer Engineering and Science, 34, 17-23. 

The blends of starch and a synthetic polymer (usually polyethylene) are products of commercial importance. Two families of blends are obtained those using dehydrated starch pellets and those using gelatinised or thermoplastic starch. In both cases, the mixture with the synthetic polymer is done by extrusion. Further processing by moulding or blowing is still possible, depending on the kind of starch used. 

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... 

Addition of starch has a nucleating effect, which increases the rate of crystallisation. The rheology of starch/PCL blends depends on the extent of starch granule destruction and the formation of thermoplastic starch during extrusion. Increasing the heat and shear intensities can reduce the melt viscosity, but enhance the extrudate-swell properties of the polymer. 

Nodax can be blended with other biodegradable polymers such as polylactic acid and thermoplastic starch for improved processing performance. 

Mano JE, Koniarova D, Reis RL. Thermal properties of thermoplastic starch/synthetic polymer blends with potential biomedical apphcabihty. J. Mater. Sci. Mater. Med. 2003 14 127-135. 

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]. 

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