Recent advances in chemistry and polymer processing

Scheme 1. Processing of secondary polymers methods.

The goal of plastic management policy, in accordance with the principles of sustainable development (development that meets the needs of the present generation without compromising the ability of future generations to meet their needs), should be not only the reuse of polymer materialsLinks to an external site., but also the production of raw materials (monomers), from which they can be reproduced, or other secondary valuable products that could be useful as raw materials for various industrial processes, downstream or as fuel for transport. In this sense, including the methods proposed for the recycling of waste polymers, the most difficult method is chemical or raw material recycling and various technologies have been successfully demonstrated and continue to be developed (Achilias and Karayannidis, 2004).

The purpose of this chapter is to provide a critical overview of the methods proposed and / or applied during the main over the last decade for the chemical processing of polymers. Thus, the introducedLinks to an external site. methods of chemical processing of a number of polymers will be presented. The polymers to be studied include commonly used plastics based on poly (ethylene terephthalate) (PET), polypropylene (PP), polystyrene (PS), low density polyethylene (LDPE), high density polyethylene (HDPE), poly (vinyl chloride) ( PVC), polycarbonate (PC), poly (methyl methacrylate) (PMMA) and nylon.

2. Chemical processing of polyester (ethylene terephthalate) PET

PET is a polyester with ester functional groups that can be cleaved with certain reagents such as water (hydrolysis), alcohols (alcoholysis), acids (acidolysis), glycols (glycolysis), and amines (aminolysis). Thus, the chemical processing processes for PET are subdivided as follows: (I) Hydrolysis, (II) glycolysis, (III) methanolysis, and (IV) other processes (Scheme 2). According to the reagent used, various products are obtained (Karayannidis and Achilias, 2007; Karayannidis et al. 2006; Karayannidis et al., 2005; Karayannidis et al. 2002; Kosmidis et al., 2001). The various process options for chemical processing of PET waste can be classified as follows: (I) regeneration of base monomers (methanolysis for dimethyl terephthalate (DMT) and hydrolysis to obtain pure terephthalic acid (TPA) and ethylene glycol (EG)); (Ii) conversion to oligomers (glycolysis or solvolysis); (Iii) use of glycolyzed waste for high value-added productsLinks to an external site.; (Iv) conversion to specialty chemicals by aminolysis or ammonolysis; (V) transformation into special intermediates for use in plastics and coatings.

Recently, PET recycling using hydrolysis, glycolysis, and microwave-assisted aminolysis has been proposed (Achilias et al., 2010; Achilias et al., 2011; Siddiqui et al., 2010). for PET recycling in a microwave reactor has been proven to be a very useful method not only in material recovery, but also in significant energy savings.

This section will not be presented in detail here as it is the subject of another chapter in this book. The interested reader can find extensive information about the methods used for the chemical processing of PET in a number of recent review articles appeared in the literature (Scheirs, 1998; Karayannidis and Achilias, 2007).