Thermoplastic starch properties

In the matrix of PLA/ polycaprilactone (PCL)/OMMT nano-composites, the silicate layers of the organoclay were intercalated and randomly distributed (Zhenyang et at, 2007). The PLA/PCL blend significantly improved the tensile and other mechanical properties by addition of OMMT. Thermal stability of PLA/PCL blends was also explicitly improved when the OMMT content is less than 5%wt. Preparation of PLA/thermoplastic starch/MMT nano-composites have been investigated and the products have been characterized using X-Ray diffraction, transmission electron microscopy and tensile measurements. The results show improvement in the tensile and modulus, and reduction in fracture toughness (Arroyo et ah, 2010). 

Table 6 Comparison of properties of blown films (30 pm) PE-LD, Ecoflex , compounds of granular starch and Ecoflex , compounds of thermoplastic starch and Ecoflex ...

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. 

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. 

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. 

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. 

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. 

A review of initial research on processing, rheology and properties of thermoplastic starch is provided by Lai [3] and concentrates on effects of starch... 

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. 

Understanding Thermoplastic Starch Structure-Property-Processing-Performance-Biodegradation Relationships... 

Clearly, understanding these relationships will provide the ability to understand these systems and aid in the smart design of new thermoplastic starch products. Our future work is focussing on effects of subsequent conversion processing conditions on structure-property-biodegradation relationships. 

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.

Clearly thermoplastic starch based polymers offer a very attractive base for new biodegradable polymers due to their low material cost and ability to be processed on conventional plastic processing equipment. The engineering of more advanced properties into these low cost base materials will continue to be... 

Vinyl alcohol copolymers, EVAl Starch or thermoplastic starch. Blends with a wide variety of morphologies and properties —limitation is the sensitivity to H2O and embrittlement. Biodegradation takes 2-3 years. Bastioli et a/., 1992, 1993, 1994... 

Here we will briefly discuss two major topics related to thermoplastic starch physical chemistry the starch granule destructuration or gelatinization during TPS production and the macromolecular properties of the semicrystalline plasticized starch which include indistinctly thermoplastic starch, destructurized starch and plasticized starch. 

Currently, great efforts are being made to produce thermoplastic starch with improved mechanical properties, low water sensitivity and better compatibility with other polymers, which is of fundamental importance to the production of TPS-based blends. Studies have also been carried out on multilayered systems, as an interesting way to overcome some TPS drawbacks [58]. These... 

Thermoplastic starch is also blended with other polymers to improve its properties for particular applications. For example, a bag for collection of household food waste for composting that readily dissolved when it got wet would not function very well In applications such as this, the resins used for blending are also biodegradable, so that they do not interfere with the composting operation. In other cases, starch is blended with nonbiodegradable resins such as polyolefins. 

AVEOOa] Averous L., Fauconner N., Moro L., et al, Blends of thermoplastic starch and polyesteramide processing and properties . Journal of Applied Polymer Science, vol. 76, no. 1, pp. 1117-1128,2000. 

CYR08] Cyras V.P., Manfredi L.B., Ton-That M.T., et al, Thysical and mechanical properties of thermoplastic starch/montmorillonite nanocomposite films . Carbohydrate Polymers, vol. 73, no. 1, pp. 55-63,2008. 

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