Polyamides reprocessing

Thermoplastics are plastics which undergo a softening when heated to a particular temperature. This thermoplastic behaviour is a consequence of the absence of covalent bonds between the polymeric chains, which remain as practically independent units linked only by weak electrostatic forces (Figure 1.4(a)). Therefore, waste thermoplastics can be easily reprocessed by heating and forming into a new shape. From a commercial point of view, the most important thermoplastics are high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene tereph-thalate (PET), polyamide (PA), polymethyl methacrylate (PMMA), acrylonitrile-butadiene-styrene copolymer (ABS), and styrene-acrylonitrile copolymer (SAN). 

Reprocessing polyamides — using the molecular repair concept... 

Eriksson, P.-A., Aibertsson, A.-C. et ai. Reprocessing of Fiberglass Reinforced Polyamide 66 Influence on Short Term Properties, Polymer Composites, 17 (1996) 6, p. 823-829... 

There are recycling opportunities for other plastics beyond the few recognized by SPI RICs. The automobile industry, for instance, utilizes a series of engineering thermoplastics that have a built-in market if they can be recovered and reprocessed. These high value plastics include polyamides (Nylon 6, Nylon 6,6, etc.), polycarbonates (PC), acrylics (PMMA), styrenics (ABS), and blends (TPO, PC/PBT, PC/ ABS, etc.). Their higher value and demand allow recyclers the opportunity to practice more exotic recovery procedures and still have an economically viable product. 

DSC was used for samples 1-4 (Table 5.4) at an isothermal temperature of 260 °C. The OIT was determined to be 21.4, 17.8, 14.1 and 8.6 minutes for Samples 1 to 4, respectively. Reprocessed samples exhibit lower OIT values compared with that of the virgin reference samples. The presence of glass fibres in the polyamide matrix seems to decrease the thermo-oxidative stability. 

In the case of polyamides, this recycling technique is unfavorable (Table 3). Additionally, polyamides exhibit the excellent feature that, even after reprocessing, their properties are still relatively high, making them attractive for use as engineering plastics [18]. However, one should bear in mind that incineration is the simplest way of waste utilization, and the combustion energies of plastics are comparable to or higher than that of coal. 

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