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Proteins

Proteins are large biomolecules, or macromolecules, consisting of one or more long- chain amino acid residues and are a vital constituent of most living organisms. Large quantities of protein waste can be generated by the use of plants, such as rape, for biodiesel manufacture. Loughborough University researchers have investigated the use of such material for elastomer reinforcement as part of a project to improve the efficiency of the biodiesel process (www.iom3.org/fileproxy/303562). This work demonstrated that blending of gelatinized rape meal protein with carboxylated nitrile (XNBR) rubber latex resulted in a material ten times stiffer and four times stronger than the unreinforced rubber and similar to that achievable with a carbon black. Latex blending was used to ensure good dispersion in the rubber and resulted in particles of about 2 pm.

Rice Hulls

Rice hulls or husks are the outer coating on rice grains and provide protection to the seeds during the growing period. They contain large amounts of amorphous silica and lignin and are not very digestible for humans. As a result, the hulls are usually removed when rice is harvested. They are then usually burnt as a source of energy and leave behind an ash known as RHA (rice hull ash), which is largely silica.

The RHA silica is seen as a very significant waste stream, estimated at over three million tons of silica annually worldwide. Moreover it can be regarded as sustainable, due to the plant origin. As such, it has been much studied as a raw material for many applications, including as a polymer filler. These efforts have been ongoing for at least 50 years and saw the launch of commercial filler products in the USA in the 1970s, but this initiative does not seem to have made much progress since. The early work directed at a carbon black substitute is described by Haxo and Mehta (1974); more recently, the use of rice hull ash in polymers has been reviewed by D.S. Chaudhary et al. (2004). R. Srilathakutty et al. (2002) have described the successful use in microcellular shoe soles, and E.P. Aysawarya et al. (2012) have described its potential for use in HDPE. As described in ? Chap. 22, “Sustainable and Recycled Particulate Fillers,” there is also growing interest in using the ash as the raw material for producing precipitated silicas, with some of the tire majors seeing it as a useful way to produce precipitated silica for tire use.

 
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