Starch, thermoplastic

Starch gelatinization is a difficult term to define clearly and it was used in the past to describe loss of crystallinity of starch granules, notwithstanding the process conditions applied [18] namely, extrusion cooking, spray drying or heating of diluted starch slurries. 

As observed by Donovan [69] and Colonna [70], at low water volume fractions (Vi 0.45) loss of crystallinity occurred by two (pea and high amylose maize) or three (standard maize) crystalline melting steps, according to the Flory equation (Fig. 6.4)  

In the patent literature the term destructurized starch has been used [71-85] to refer to a form of thermoplastic starch described as molecularly dispersed in water [86]. Other patents [17, 87-91] use the term destructured starch to describe a thermoplastic starch which is treated by extrusion cooking to distinguish it from gelatinized starch, processed in presence of high amounts of water. Furthermore a recent USDA s paper [92] on this subject concludes that destructurized starch is not a new or novel entity but is merely another term used to describe the well-known disordering of starch chains and the melting of crystallites that take place when starch is heated in the presence of limited amounts of water . Henceforth extrusion-cooked starch will be reported as thermoplastic starch. 

Thermoplastic starch alone can be processed as a traditional plastic [67, 86, 93] its sensitivity to humidity, however, makes it unsuitable for most of the 

Otey has studied EAA (ethylene-acrylic acid copolymer)/ thermoplastic starch composites since 1977 [95-106] and has demonstrated that the addition of ammonium hydroxide to EAA makes it compatible with starch. Urea, in these formulations, enhances the film tear propagation resistance and reduces ageing phenomena due to segmental motions in amorphous starch [107,108]. The films obtained with a content of plasticized starch of about 50% showed good tensile properties (Table 6.1) [101]. The sensitivity to environmental 

LHu the fusion enthalpy per repeating unit (anhydroglucose), VuA j the ratio of the molar volume of the repeating unit to the molar volume of the diluent (water), 

At high water volume fractions, melting of crystallites and swelling are co-operative 

On the contrary, according to Colonna, during extrusion cooking and mainly under the conditions described by Mercier (water volume fraction 0.28) [73] starch undergoes a 

If starch is heated above the Tg and T in the presence of plasticisers the endothermic transition can be replaced by an exothermic transition. Destructurised starch, in simple 

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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). 

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 ... 

Granular starch is destmcturized to thermoplastic starch using temperature, pressure and plasticizer (e.g., water, glycerol)... 

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... 

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 ...

Test Standard PE-LD carrier bags (mean) Ecoflex Ecoflex + granular starch compound Ecoflex + thermoplastic starch compound... 

Russo M, O Sullivan C et al (2009) The anaerobic degradability of thermoplastic starch Polyvinyl alcohol blends Potential biodegradable food packaging materials. Bioresour Technol 100 1705-1710... 

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

Figure 15.2 (A) XRD patterns of Cloisite Na (a). Thermoplastic starch TPS (b), and the TPS/Cloisite Na" hybrid (c). (Source Park et al., 2002). (B) TEM images of TPS/clay hybrids of different kinds of clay, (a) TPS95/Cloisite Na, (b) TPS95/Cloisite 6A, (c) TPS95/Cloisite 10A, (d) TPS95/Cloisite SOB. (Reproduced with kind permission from Park et al., 2002, Wiley-VCH Verlag GmbH Co. KGaA).

Chen, B., Evans, J. R. G. (2005). Thermoplastic starch-clay nanocomposites and their characteristics. Carbohydrate PolymerSs 61 s 455 63. 

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. 

Stepto, R. F. T. (1997). Thermoplastic starch and drug delivery capsules. Poly. Inter, 43, 155-158. 

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. 

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... 

Biodegradable Materials Made from Thermoplastic Starch and Polylactic Acid... 

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. 

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. 

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. 

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. 

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