Thermoplastic starch processing

Geometrical similarity is often used for its simpUcity, but it is not a strong requirement. Especially in processing thermoplastic starches, in which temperature and temperature homogeneity are very important, the principle of geometric similarity of small- and large-scale equipment caimot always be retained. Geometric similarity means that aU dimensions scale in the same way, or ... 

Granular starch can be converted into thermoplastic starch by applying high shear force, heat, and/or plasticizers (e.g., moisture, glycerol) in a separate compounding step. Compounding of starch in Ecoflex can be efficiently performed in a four-stage process ... 

Ecoflex is an essential component for the processing of renewable raw materials like starch and for producing high quality biodegradable and bio-based plastic films out of them. Ecoflex /thermoplastic starch compounds are used... 

The biodegradable polymer available in the market today in largest amounts is PEA. PEA is a melt-processible thermoplastic polymer based completely on renewable resources. The manufacture of PEA includes one fermentation step followed by several chemical transformations. The typical annually renewable raw material source is com starch, which is broken down to unrefined dextrose. This sugar is then subjected to a fermentative transformation to lactic acid (LA). Direct polycondensation of LA is possible, but usually LA is first chemically converted to lactide, a cyclic dimer of LA, via a PLA prepolymer. Finally, after purification, lactide is subjected to a ring-opening polymerization to yield PLA [13-17]. 

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. 

Cooked but unexpanded thermoplastic starches (TPS) have wider applications, because of the fact that approx. 8% of water can be removed after the cooking process by devolatilization at 300 mbar, corresponding to a cooling by approx. 70 °C down to 100°C. That means that the exiting strand does not expand but yields a glassy, plastic-like pellet that can be dried in a fluidized-bed dryer. 

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. 

In nature, starch is based on crystalline beads of about 15-100 microns in diameter. Crystalline starch beads in plastics can be used as fillers or can be transformed into thermoplastic starch, which can either be processed alone or in combination with specific synthetic polymers. To make starch thermoplastic, its crystalline structure has to be destroyed by pressure, heat, mechanical work or use of plasticisers. Three main families of starch polymer can be used pure starch, modified starch and fermented starch polymers. 

Biotec s product portfolio includes thermoplastic starch, which can be substituted for petrochemical based plastic packaging. Stanelco s radio frequency sealing technology can be used to process starch polymers without the degradation caused by other methods such as thermal processing. The purchase of Biotec will help the company develop alternatives to petroleum-based packaging. 

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

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. 

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. 

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... 

Thermoplastic starch can be processed as a plastic material, but it is sensitivity to humidity, what makes it unsuitable for most applications. Thus, its principal use is in compostable foams to replace EPS. 

Poly- -caprolactone (PCL) and its copolymers polyesters of 1,4-butanediol with succinic, sebacic, adipic, azelaic, decanoic or brassihc acids. Thermoplastic starch (Mater-Bi). Blends improved processability biodegradabUity. Compatibihzation by amylose/EVAl complexes, starch grafted polyesters, chain extenders like diisocyanates, epoxies, etc. Bastioli et a/., 1992, 1993... 

Starch is the major carbohydrate reserve in higher plants and has been a material of choice since the early days of human technology. Recently starch gained new importance as a raw material in the production of plastics, in particular, for the synthesis of monomers to produce polymers such as polydactic acid) and, after chemical modification (e.g. esterification) and thermomechanical processing, to produce thermoplastic starch. This chapter gives a general overview of the most recent research on the development of materials from starch, focusing on thermoplastic starch and the perspectives for future development in this field. A brief review on reactive extrusion of thermoplastic starch is also provided. 

Some Features of the Physical Chemistry of Thermoplastic Starch Processing... 

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