Thermoplastic elastomer, chemical modification

The properties of PHAs are dependent on their monomer composition and therefore it is of great interest that recent research has revealed that, in addition to PHB, a large variety of PHAs can be synthesized microbially. The monomer composition of PHAs depends on the nature of the carbon source and microorganism used. PHB is a typical highly crystalline thermoplastic whereas medium chain length PHAs are elastomers with low melting points and a relatively lower degree of crystallinity. By (chemical) modification of the PHAs, the ultimate properties of the materials can be adjusted even further, when necessary. 

IR spectroscopy can be used to characterise not only different rubbers, but also to understand the structural changes due to the chemical modification of the rubbers. The chemical methods normally used to modify rubbers include hydrogenation, halogenation, hydrosilylation, phosphonylation and sulfonation. The effects of oxidation, weathering and radiation on the polymer structure can be studied with the help of infrared spectroscopy. Formation of ionic polymers and ionomeric polyblends behaving as thermoplastic elastomers can be followed by this method. Infrared spectroscopy in conjunction with other techniques is an important tool to characterise polymeric materials. 

It is not possible to discuss here the special properties of all the different types of plastic materials that can occur within these three groups. The plastics industry today, by employing copolymerization or chemical modification, is capable of producing an extraordinary number of combinations of properties, making the identification of corresponding plastics more complicated. Its physical appearance and its classification as a thermoplastic, thermoset, or elastomer therefore permit us to draw conclusions about the chemical nature of the plastic only in simple cases. But they often provide a useful additional way of characterizing the material. 

The progress of chemistry, associated with the industrial revolution, created a new scope for the preparation of novel polymeric materials based on renewable resources, first through the chemical modification of natural polymers from the mid-nineteenth century, which gave rise to the first commercial thermoplastic materials, like cellulose acetate and nitrate and the first elastomers, through the vulcanization of natural rubber. Later, these processes were complemented by approaches based on the controlled polymerization of a variety of natural monomers and oligomers, including terpenes, polyphenols and rosins. A further development called upon chemical technologies which transformed renewable resources to produce novel monomeric species like furfuryl alcohol. 

Rubber vulcanization crosslinking was an early chemical modification method. Block and graft methods are also widely used in polymer modification. One of the successful examples of a block copolymer is a thermoplastic elastomer. It is a new material that can be processed like plastic and has elasticity like rubber. Among graft copolymers, the most widely used one is the acrylonitrile butadiene and styrene copolymer... 

Oyama H and Nakaishi E (2003) Thermoplastic elastomer compositions, moldings and automobile interior parts therefrom with high wear resistance and good sliding property, Jpn Kokai Tokkyo Koho JP 2003,277,519, to Sumitomo Chem Co, Ltd. Ikeda Y, Kodama K, Kajiwara K and Kohjiya S (1995) Chemical modification of butyl rubber. II. Structure and properties of poly(ethyleneoxide)-grafted butyl rubber, J Polym Sci Part B Polym Phys Ed 33 387-394. 

Poly(ether-ester) (PEE) copolymers obtained by modification of poly(ethyl-ene terephthalate) with up to 20 wt% of poly(ethylene ether) glycol was first described by Coleman [8]. Subsequently, the DuPont Co. developed poly(ether-ester) elastomers, which were commercially introduced in 1972 under the trade name Hytrel [4,9]. The polyester thermoplastic elastomers are nowadays produced by several companies. Apart from DuPont, these are DSM, The Netherlands (Arnitel ), General Electric, USA (homed ), Hoechst Celanese, USA (Retiflex ), Toyobo, Japan (Pelprene ), Elana, Poland (Elitel ) [2,10]. The synthesis, chemical structure, physical properties, and some new applications of polyester TPE are discussed in this chapter (about the development of TPE, see also Chapter 1, while details on some commercial TPE products can be found in Chapter 17). 

G. Polyetherpolyole F. polyetherpolyols P. carry hydroxylic groups to be reacted with di/tri-isocyanates for producing polyurethanes, such as thermoplasts, - coatings, elastomers and foams. Traditional starting materials for p. are glycol and the RR-based ->glycerol, - sucrose, ->dextrose, - sorbitol, - sucrose molasses, xylitol, - mannitol, and products of hydrogenolysis of sucrose (- sucrose, chemical modifications). 

The thermo-chemical properties of PHA have been shown to be strongly related to their structure. Thus, PHAscl are mainly brittle thermoplastics with high melting and glass transition temperatures, whereas PHAscl are mainly elastomers. Biocompatibility is another interesting property of PHAs. In this case, PHAmcl have been shown to be more biocompatible than PHAscl, however, they are also more hydrophobic and the hydrophobicity may be an important drawback for such types of applications. Thus, postfermentation modifications of PHAs were also applied to modify their structure. Those modifications consist either of monomeric modifications,... 

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