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... 

The most relevant achievements in this sector are related to thermoplastic starch polymers resulting from the processing of native starch by chemical, thermal and mechanical means, and to its complexation to other co-polymers. The resulting materials show properties ranging from the flexibility of polyethylene to the rigidity of polystyrene, and can be soluble or insoluble in water as well as insensitive to humidity. Such properties explain the leading position of starch-based materials in the biodegradable polymer field. 

Thermoplastic starch polymers are generally used as films in shopping bags, bread bags, bait bags, over wrap, flushable sanitary product backing material, and mulch films. 

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. 

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. 

It is clear that research into modifications to thermoplastic starch based polymers is burgeoning and that property and processing improvements derived from this research will help thermoplastic starch polymers widen their application products and markets. 

Commercial Applications and Products for Thermoplastic Starch Polymers... 

The above is focused on thermoplastic starch polymers for traditional polymer markets, and thus much research and development for these materials has focused on improved water resistance and better mechanical properties for engineering and packaging applications. 

Figure 1. The effect of relative humidity (RH) on mechanical properties [stress-strain curves] of at thermoplastic starch polymer.

Table 1. Diffusivity of Water at different Temperatures in Thermoplastic Starch Polymers pre-stored at various relative Humidities...

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

Halley P. J. Thermoplastic starch polymers, in Biodegradable polymers for industrial applications R.Smith (ed), Woodhead Pub., London, UK 2005. 

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... 

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