TPS and Its Nature

The interest in using starch as a basis for packaging material originated in the 1970s, when environmental awareness was increasing drastically. Since then a steady development of new products can be seen. The ability to compete in price with traditional materials, such as plastics, has always been indispensable for the general acceptance of these new materials. 

Griffin [1, 2] was the first to use starch as filler in synthetic plastics. Polyethylene films containing starch and other items based on this technology are available on the market. In this technology starch addition is restricted to a maximum of 10% by weight. The starch has to be dried to under 1% moisture to avoid steam formation during extrusion processes, and the starch granules are surface-treated (with silanes, for example) to increase the compatibility of the hydrophilic starch with the hydrophobic plastic matrix. 

Starch-thermoplastic polymer composites have also been prepared by graft polymerization. Chemical treatment of starch leads to the development of free radicals in the starch backbone, and these can act in the presence of various polymers (polystyrene, polyethylene, and poly(vinyl halides)) as macroinitiators to yield polymer grafts of high molecular weight [6-8]. 

Thermoplastic Starch. Edited by Leon P.B.M. Janssen and Leszek Moscicki 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32528-3 

TPS produced from starch plastified only with water becomes very brittle at room temperature. To increase the material flexibility and to improve processing, other plasticizers, such as glycerol, propylene glycol, glucose, sorbitol, and others, are also used [12, 16, 17, 19, 20, 22]. 

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As the effect of crystallization kinetics becomes unavoidable, it is important to understand its impact on Crystaf profiles. Figme 36 shows how the Crystaf peak temperatures vary as a function of CR for three ethylene/1-hexene copolymers [29]. It is clear that the CR can have a dramatic effect on Crystaf peak temperatures even at very low CRs. The Crystaf profiles are significantly shifted to higher temperatures when slower CRs are used. Empirical linear relationships can be established between the Crystaf peak temperature of each polymer sample (Tp) and the natural logarithmic of the CR, as shown in Fig. 36. 

The chemical nature of the TP affects its miscibility with the thermoset precursors and, consequently, the phase-separation process. On occasions, it can also modify the cure kinetics. 

Compression molding is an old and common method of molding thermoset (TS). It now processes TS plastics as well as other plastics such as thermoplastics (TP), elastomers (TS and TP), and natural rubbers (TS). By this method, plastic raw materials are converted into finished products by simply compressing them into the desired shapes... 

As reported in Ref. , the spread rate of a flame moving up a vertical surface of a sufficiently thick PMMA sheet increases under the effect of an external heat radiation. Depending on the heat radiation intensity and exposure time, various effects on the flame spread rate are observed. Additional heating of the polymer surface by a radiative flux results, first of all, in a decrease of the temperature dilTerence (T — Tp) and, in accordance with Eq. (2.19), in an increase of v. The experimental relationship v (T — To)" at T = 363 °C is close to that predicted by theory. According to Femandez-Pello , an increase of the initial polymer surface temperature, Tp, cause a parallel enhancement of the natural convection in the boundary heat layer and heat radiation by the surface, leading to its partial cooling. Therefore, when the intensity of the external radiative heat flux is low, the flame spread rate increases with time, but only up to a certain constant value. 

We now turn our attention to the effects of CTR As noted earlier, CTP inhibits the action of AffCase. X-ray studies of ATCase in the presence of CTP revealed (1) that the enzyme is in the T state when bound to G TP and (2) that a binding site for this nucleotide exists in each regulatory chain in a that does not interact with the catalytic subunit (Figure 10.11). active site is more than 50 A from the nearest CTP-binding site. The question naturally arises, How can CTP inhibit the catalytic activity of the enzyme when it does not interact with the catalytic chain ... 

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