**6. Conclusions**

104 Material Recycling – Trends and Perspectives

The foaming of the thermoplastic semi-crystalline materials is efficient if at a certain working temperature their melt has high elongation viscosity, elevated strength and enhanced elasticity. The melt of the polymer with low molecular weight and narrow molecular distribution has low viscosity, small strength and reduced elasticity and because of these, the formation and stabilization of the cells cannot be controlled. The increase in molecular weight and polydispersity of POSTC-PET by reactive processing is a way to obtain high property foamed products (Quintans et al.,2004; Forshythe et al.,2006; Fujimoto,

It was found that the "repaired" recycled RPOSC-PET can be foamed if its apparent viscosity is 0.9 dl g-1 (Nair et al., 2002) that was realised by means of extenders with a molecular weight of 50 – 5000 and a functionality of 3 – 6. (Tang & Menachem,2007). In this way, it is possible to produce structures with closed pores which have the right density, pore size, pore distribution, mechanical and thermal properties proper for insulating panels or microcellular foams (Kiatkamjornwong et al., 2001; Xanthos et al., 2004; Chem &Curliss, 2003; Carotenuto et al., 2000). The "repaired" POST-PET can be modified in order to make of

**5.4.3 Compounds, composites and nanocomposites realised by physical modification**  In order to improve the melt processability and the utilization properties to POSTC-PET qualify for the desired application, the polymer can be physically modified with: *melt processing agents, agents for improving the mechanical, barrier and optical properties, toughening agents, crystallization and coefficient of friction modifying agent, thermo-oxidative antioxidants and ultraviolet stabilizers* (Smiidt et al., 1999; Salgueiro et al., 2004; Kalpana et al, 2006; debashis et al., 2006; Unnikrishnan & Sabu, 1998;zammarano et al., 2006; Zhang et al., 2001; Zhong et al.,

Several examples of such modifiers are: *primary* PET ( Utraki & Kamal, 2002;), glass fiber (Unnikrishnan & Sabu, 1998; longzhen et al., 2006; Aghlan, 2003; Gersappe, 2002), maleic anhydride grafted styrene – ethylene/butylene – styrene triblock copolymer (SEBS – g-MA) (Javaid, 2006), poly (ε – caprolactone) ( Guo, 2002), copolymer having at least one block comprising a vinyl aromatic polymer and at least one block comprising a conjugated diene polymer ( Kiatkamjornwong et al., 2002; Shanti, 2002;), polyolefins, recycled polyolefins with proper compatibilization agents (Tortora, 2002; Chen et al., 2002; Chabert et al., 2004; Leszezynsksa et al.,2007; Glasel et al., 1999; Chrissopouloe et al, 2005; Qing-ming et al., 2006; Hadal et al., 2004; Conde et al.,2003; Place et al., 2003; Fujimoti et al., 2003;). Clear blends must be tailored based on branched slow crystallizing PET and faster crystallizing PET ( Shriroth et al., 2006; Swoboda et al., 2008; Aghlara,2003). To improve the brittleness, "repaired" PET is modified with an epoxy group containing styrene thermoplastic elastomer and polycaprolactone (Sikdar et al., 2006). To obtain the side material for cooling towers, "repaired" PET is modified with styrenic thermoplastic elastomer ( Arif et al., 2007; Zilg et al., 1998;). Nanocomposites ca be achieved with nonmodified natural montmorillonite or with ion-exchanged clay modified with quaternary ammonium salt (Pegoretti et al.,2004; Lee & Lichtenhan, 1999; Sharma, 1999; Schmidt et al., 1999; Carotenuto et al., 2000; Aravind, 2007; Bandosz,1996; Bartholome, 2005; Buxton, 2002; Chrissopoulou, 2005; Feng, 2002; Utraki & Kamal, 2002). Nanocomposites can be

2003; Japon et al., 2004; Kumar et.al, 2001; Place et al., 2003; Warburton et al., 1992).

cheap composites for expanded panels (Deng at al., 1996).

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