**1. Introduction**

84 Material Recycling – Trends and Perspectives

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The post consumer poly(ethylene therephtalate) bottles (POSTC-PET) can be recycled by chemical or / and mechanical processes. The POSTC-PET chemical recycling is widespread in Europe and is based on depolycondensation of secondary polymers and usage of the resulted products for the purposes of the fibre and unwoven material industry. The POST - PC mechanical recycling requires a phase transformation (melting) and can be attained without or with polymer up-gradation (Mancini, 1999; Akovali, 1988; Belletti, 1997; Ehrig, 1992; Erema, 2002; Firas, 2005; Sandro & Mari, 1999; Scheirs, 1998; Awaja, 2005).

The well-known worldwide POSTC-PET mechanical and chemical recycling ways are:


 *1Research and Development national Institute for Chemistry and Petrochemistry –ICECHIM, Spl.Independentei, sector 6, Bucharest, Romania* 

*<sup>2&</sup>quot;IC Murgulescu" Institute, Spl.Independentei, sector 6, Bucharest, Romania 3"Politehnica"University, Clea Victoriei, Bucharest, Romania*

Overview on Mechanical Recycling

(Knit, 2002; David, 2001; Novis, 2003; ).

thermo-hydrolitic degradation are exposed.

ester end group (Awaja & Pavel, 2005).

**2.2 PET degradability** 

et al., 2002; Raki et al., 2004).

by Chain Extension of POSTC-PET Bottles 87

2004). The following limits of the POSTC-PET impurity residual content have been accepted for recycling as food packaging: 20 ppm or less metal, 10 ppm or less paper and 30 ppm or less polyolefins (Di Lorentzo et al., 2002; Hong JuZhou et al., 2007; Hong Jun Zhou et al., 2007 ). The framing into these limits depends on the technicality of the applied conditioning solution (sorting - washing etc), and by the legislative effort necessary for: the increasing of the population cooperation, the setting up of the infrastructure to analyze the impurity content down to the parts per million (ppm) level, the inspection on the law observance

During POSTC-PET conditioning and melt processing, the polymer is degraded by mechanical and thermal agents that act in the presence of water and oxygen. If during the first life the POSTC-PET is exposed to UV radiations rather than to thermo-mechanical and hydrolytic degradation, the photo-oxidation must be considered too (Cioffi et al., 2002; Chen

The degradation occurs at the weakest thermodynamic links namely at the ester those between the terephthalic acid and diethylene glycol of POSTC-PET macromolecules (Sandi et al., 2005; Vasiliu et al., 2002). In figs. 1 – 5, the main reactions that characterize the PET

By thermal-oxidative degradation (fig.1, - Awaja & Pavel, 2005 ), the macromolecular chains break resulting in the formation of volatile products (i.e. acetaldehyde – fig. 5 Alexandru & Bosica, 1966 ) , 1.8 – 3 % cyclic and linear oligomers (fig.4 - Awaja & Pavel, 2005) and shorter chains with acid carboxylic and vinyl ester end groups. In hydrolytic degradation (fig.2 - (Awaja & Pavel, 2005), the mechanism is similar, with the difference that the end groups of the short macromolecules resulted from degradation are carboxylic acid and hydroxyl ester.

Fig. 1. PET thermal degradation mechanism with the formation of carboxyl acid and vinyl

mechanically recycled into performing products, it is compounded at melt processing. However the results are not spectacular.

5. **Chemical recycling** is related to the recovery of the chemical compounds based on following depolycondensation particular reactions glycolysis, methanolysis, hydrolysis, acidolysis, amynolysis,etc. (Carta, 2001; Karayannidis, 2003; Minoru, 2003;);

In spite of long lasting efforts, because of the low cost and low performance applications of the recycled material, at present, the widely accepted opinion is that the POSTC-PET mechanical recycling without a structural up – gradation is not an efficient procedure.

The chapter presents an overview on the structural up-grading of POSTC-PET by macromolecular chain extension during mechanical recycling (reactive processing), a procedure considered efficient for the enhancement of its properties.
