Thermoplastic starch applications

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. 

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. 

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... 

Table 2 highlights companies producing thermoplastic starch, the types of polymers used, the types of applications and the contact details for more information. 

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. 

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

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. 

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. 

Natural polymers such as starch and protein are potential alternatives to petroleum-based polymers for a number of applications. Unfortunately, their high solubility in water limit their use for water sensitive applications. To solve this problem thermoplastic starches have been laminated using water-resistant, biodegradable polymers. For example, polylactic acid and P(3HB-co-3HV) were utilised as the outer layers of the stratified polyester/PWS (plasticized wheat starch)/polyester film strucmre in order to improve the mechanical properties and water resistance of PWS which made it useful for food packaging and disposable articles [65]. Moreover, improved physic-chemical interactions between P(3HB-CO-3HV) and wheat straw fibres were achieved with high temperature treatment. It resulted in increased P(3HB-co-3HV) crystallization, increased Young s moduli and lowered values of stress and strain to break than the neat matrix of P(3HB-co-3HV). There was no difference in the biodegradation rate of the polymer [66]. 

The characteristics of the developed material demonstrate that pure potato starch can be used for the production of foams without the need of modified starches or blends with other additives or polymers. This will make new applications for thermoplastic starch based foams possible. 

The products based on thermoplastic starch and EVOH show mechanical properties suitable to meet the needs of specific industrial applications [99]. Their mouldability in traditional processing technologies is comparable with that of traditional plastics such as PS, ABS and LDPE [95]. The main limitation of these materials is the high sensitivity to low humidity, with consequent embrittlement. 

This chapter reviews the general context of starch as a material. After a survey of the major sources of starch and their characteristic compositions in terms of amylase and amylopectin, the morphology of the granules and the techniques applied to disrupt them are critically examined. The use of starch for the production of polymeric materials covers the bulk of the chapter, including the major aspect of starch plasticization, the preparation and assessment of blends, the processing of thermoplastic starch (TPS), the problems associated with its degradation and the preparation of TPS composites and nanocomposites. The present and perspective applications of these biodegradable materials and the problems associated with their moisture sensitivity conclude this manuscript. 

In order to adjust the properties of these starch-based materials to the desired application, it is necessary to combine starch with other polymers, as frequently done in the plastic industry. The need for tuneable properties may also require starch modifications, such as esterification or etherification, grafting and reactive or melting extrusion of thermoplastic starch (TPS). The main forms of starch utilization as a polymer are (i) starch grafted with vinyl monomers, (ii) starch as a filler of other polymers and (iii) plasticized starch (PLS), commonly known as TPS. 

Poly(butylene adipate-co-terephthalate) (PBAT) Some of its main applications are films (mulch, containers, bags), filaments, thermoformed and injection moulded products, and blown bottles. Two products in the market are Ecoflex (BASF, 14,000 t per year) and MaterBi (former EasterBio/Eastman, now Novamont, 15,0001 per year). For some applications, PBAT has a very low stiffness, and may be mixed with PITB or PEA, for example. It may also be mixed with thermoplastic starch [69, 71]. 

If starch is heated above the glass-transition and melting temperatures in presence of plasticizers, the endothermic transition can be replaced by an exothermic transition. Destructurized starch, in simple terms, is a form of thermoplastic starch suitable for applications in the sector of plastics, with minimized defects tied to the granular structure of native starch (17,94,98). 

Polylactide has high potential in agricultural applications such as mulch films either in pure form or blended with other polymers such as thermoplastic starch. In addition, polylactide is used in compostable yard bags and dog poop bags. Lactic acid based hot-melt adhesives have also been developed (90). Foamed PLA could be used as structural protective foams, loose-fill packaging and insulation material as an alternative for expanded polystyrene (EPS). While packaging is currently the high volume application... 

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