**3. The chain extension up-gradation of POSTC-PET**

Considering the general opinion according to which POSTC-PEC can be mechanically recycled only into low-property goods, it becomes clear the interest to find new economic solutions for the reprocessing of these materials into products with practical importance. In the last 20 years the researchers have been concerned in the up-gradation of POSTC-PET by increasing the macromolecular weight based on chain extension reactions (Cavalcanti et.al., 2007, Awaja & Pavel, 2005, Villalobos et.al, 2002, Karaianidis, 1993).

The efficiency of these reactions is controlled by many factors. Their presentation begins with emphasis the importance to eliminate humidity by drying before melt processing and to stabilize the POSTC-PET at melt processing.

#### **3.1 Drying /degassing**

Before the chain extension, the POSTC-PET is dried to remove the humidity. It was observed that drying before chain extension and degassing and /or operation under vacuum during chain extension are able to decrease the degradation of POSTC-PET during

Overview on Mechanical Recycling

properties (Yilmazer et al., 2000).

by Chain Extension of POSTC-PET Bottles 93

Fig. 6. Schematically presentation of the chain extension reaction (Villalobos et al., 2006).

Fig. 7. The dependence of the nature of the reactions in chain extension and the possible applications depending on the accomplished intrinsic viscosity (Villalobos et al., 2006).

Otherwise, in practice, the obtained results demonstrate that the chain extension can be controlled in such a way to ensure the best melt processing properties and the most convenient usage properties for up-graded recycled POSTC-PET. The process can be controlled by monitoring the value of the intrinsic viscosity (ASTM D 4603 -91) and of the carboxyl and hydroxyl end group. An increased carboxyl end group content is associated with a very degraded polymer and the decreasing of the hydroxyl end groups means in progress chain extension reactions (Changli et al., 2006; Bizzaria et al., 2007). The process can be also monitored in terms of melt flow behavior, die swell degree and viscoelastic

melt processing. The drying of POSTC – PET restrains the hydrolysis during the melt processing but it is not a simple action (Buxton at al., 2002;). The POSTC-PET drying method should be the same as the ones used for primary polymers that means 3 - 7 hours at 140 - 180 oC, in desiccators or standard drying equipments (Xanthos et al., 2000). According to other opinions, the drying at temperatures greater then 160 oC can not be done because at this temperature the polymer hydrolysis becomes active. These opinions argue that the efficient drying temperatures should range between 110 – 140 oC, and the drying time should be greater than 12 hours. The final accepted water level is no more that 50 ppm - 0,01 %. If the POSTC-PET water content is smaller than 100 ppm, then the loss in the intrinsic viscosity during reprocessing shall be less than 0,04 dl g-1 (Denisyuk et al., 2003; Awaja & Pavel, 2005).

#### **3.2 POSTC-PET stabilization**

The POST – PET stabilization has the aim to block the polymer's thermo-hydrolitic degradation, to remove the formation of acetaldehyde as a result of degradation and to reduce the influence of the residual PVC. The free radicals resulted from the splitting of the macromolecular chain during degradation and those appeared after the decomposition of hydroperoxides can be captured with phosphorous compounds. Avoiding the degradation, these stabilizers hinder the formation of acetaldehyde (Karayannidis at al., 2003; Swoboda et al., 2008). For the capture of the existing acetaldehyde, compounds such as amino-benzoic acid, diphenylamine, 4,5 dihydroxy benzoic acid are very practical. The PVC traces are inhibited by tin mercaptide, antimony mercaptide and lead phthalate. The only disadvantage in using the stabilizers is the rise in the cost of the POSTC- PET mechanic recycled (Awaja & Pavel, 2005).

#### **3.3 Methods for POSTC-PET up-gradation by chain extension**

The macromolecular chain extension is a result of particular post condensation reactions between the degraded polymer and selected chain extenders. Theoretically, these coupling reactions annihilate the effect of degradation as they determine the growth of molecular weight by extension, branching, reticulation. Expertise has shown that it is very difficult to separate these reactions from the degradation that occurs in the same time. The intensity of the degradation is greater or smaller depending on the way the extension reaction is conducted. The reaction of molecular weight increase has to be performed in such a way as to diminish or avoid the degradation. As the high gel content is a disadvantage for the melt processing and for the control of reprocessed POSTC-PET usage properties, the reticulation near degradation should be avoided (Raki et al., 2004;torres et al., 2001; Yilmazer et al., 2000; Inata et al., 1987; Bikiaris & Karayannidis, 1993).

The chain extension reaction is rendered schematically in figure 6 (Villalobos et al., 2006) The most suggestive presentation of the way in which the chain extension reaction can develop depending on the reaction conditions (i.e. concentration of the extender) and how the same material can yield both chain extension and reticulation was accomplished by (Villalobos et al., 2006;) ( fig.7). The same figure shows that the chain extension can result in intrinsic viscosity values, proper for various targeted applications.

melt processing. The drying of POSTC – PET restrains the hydrolysis during the melt processing but it is not a simple action (Buxton at al., 2002;). The POSTC-PET drying method should be the same as the ones used for primary polymers that means 3 - 7 hours at 140 - 180 oC, in desiccators or standard drying equipments (Xanthos et al., 2000). According to other opinions, the drying at temperatures greater then 160 oC can not be done because at this temperature the polymer hydrolysis becomes active. These opinions argue that the efficient drying temperatures should range between 110 – 140 oC, and the drying time should be greater than 12 hours. The final accepted water level is no more that 50 ppm - 0,01 %. If the POSTC-PET water content is smaller than 100 ppm, then the loss in the intrinsic viscosity during reprocessing shall be less than 0,04 dl g-1 (Denisyuk et al., 2003; Awaja & Pavel,

The POST – PET stabilization has the aim to block the polymer's thermo-hydrolitic degradation, to remove the formation of acetaldehyde as a result of degradation and to reduce the influence of the residual PVC. The free radicals resulted from the splitting of the macromolecular chain during degradation and those appeared after the decomposition of hydroperoxides can be captured with phosphorous compounds. Avoiding the degradation, these stabilizers hinder the formation of acetaldehyde (Karayannidis at al., 2003; Swoboda et al., 2008). For the capture of the existing acetaldehyde, compounds such as amino-benzoic acid, diphenylamine, 4,5 dihydroxy benzoic acid are very practical. The PVC traces are inhibited by tin mercaptide, antimony mercaptide and lead phthalate. The only disadvantage in using the stabilizers is the rise in the cost of the POSTC- PET mechanic

The macromolecular chain extension is a result of particular post condensation reactions between the degraded polymer and selected chain extenders. Theoretically, these coupling reactions annihilate the effect of degradation as they determine the growth of molecular weight by extension, branching, reticulation. Expertise has shown that it is very difficult to separate these reactions from the degradation that occurs in the same time. The intensity of the degradation is greater or smaller depending on the way the extension reaction is conducted. The reaction of molecular weight increase has to be performed in such a way as to diminish or avoid the degradation. As the high gel content is a disadvantage for the melt processing and for the control of reprocessed POSTC-PET usage properties, the reticulation near degradation should be avoided (Raki et al., 2004;torres et al., 2001; Yilmazer et al., 2000;

The chain extension reaction is rendered schematically in figure 6 (Villalobos et al., 2006) The most suggestive presentation of the way in which the chain extension reaction can develop depending on the reaction conditions (i.e. concentration of the extender) and how the same material can yield both chain extension and reticulation was accomplished by (Villalobos et al., 2006;) ( fig.7). The same figure shows that the chain extension can result in

2005).

**3.2 POSTC-PET stabilization** 

recycled (Awaja & Pavel, 2005).

**3.3 Methods for POSTC-PET up-gradation by chain extension** 

intrinsic viscosity values, proper for various targeted applications.

Inata et al., 1987; Bikiaris & Karayannidis, 1993).

Fig. 6. Schematically presentation of the chain extension reaction (Villalobos et al., 2006).

Fig. 7. The dependence of the nature of the reactions in chain extension and the possible applications depending on the accomplished intrinsic viscosity (Villalobos et al., 2006).

Otherwise, in practice, the obtained results demonstrate that the chain extension can be controlled in such a way to ensure the best melt processing properties and the most convenient usage properties for up-graded recycled POSTC-PET. The process can be controlled by monitoring the value of the intrinsic viscosity (ASTM D 4603 -91) and of the carboxyl and hydroxyl end group. An increased carboxyl end group content is associated with a very degraded polymer and the decreasing of the hydroxyl end groups means in progress chain extension reactions (Changli et al., 2006; Bizzaria et al., 2007). The process can be also monitored in terms of melt flow behavior, die swell degree and viscoelastic properties (Yilmazer et al., 2000).

Overview on Mechanical Recycling

2007; Xanthos et al.,2001).

**5.1 Chain extenders / reticulants** 

by Chain Extension of POSTC-PET Bottles 95

Usually for RP the following equipment, that operate as reaction reactors, is used: one or twin screw extruders, Brabender plastographe, capillary rheometers, rheomixers, injection machines s.o, (Ganzeveld, 1993; Torres et al., 2000; Dhavalikar & Xanthos, 2002). In laboratory experiments or at industrial level, the twin screw extruders are preferred because of their effectiveness in achieving a better dispersion of small compounds into the polymeric

Depending on the chemical structure of the extender and the concrete reaction conditions, the chain extension is more or less accompanied by ramification and reticulation, with gel formation or / and by degradation (Paci & La Mantia, 1998). Nevertheless it is considered that the extender chemical structures can be so conceived and the operating conditions can be found in such a way that, the prevalent reaction during the POSTC-PET reactive processing to be the chain extension those. The "reconstruction" of the macromolecular chains by reactive processing is a simple procedure that takes minutes, and has been performed at industrial level by extrusion and injection (Chem et al., 2002; Cavalcanti et al.,

The obtained experimental results show that based on reactive processing, it is possible to reach an intrinsic viscosity higher than 0,6 dlg-1, the basic quality condition needed for reprocessing POSTC-PET in products for high performing applications. (table 1). It was also

> Recording tapes 0,60 Fibres 0,65 Bottles for drinks 0,73 – 0,8 Cord for industrial tyres 0,85

In most cases, by reactive processing, one can obtain mechanical and rheological performances equal or higher than those of virgin polymers. This is the reason for which the reactive processing of POSTC-PET is seen as an important possibility to add value to the post consumer condensation polymers and to create products with added technical and economical value. The "repaired" POSTC-PET can be used without physically modification in main applications as bottles and foam sheets or after physically modification as compounds,

The chain extenders ("recycling aids" (Rossi et al., 2002)) are mono, di or polyfunctional (fn) organic liquid or solid compounds, with low molecular weight (Mn < 3000) and controlled polydispersity. The typical extender functional group are hydroxyl, carboxyl, anhydride, amine, epoxy, etc (table 2) (Inata, 1985; Inata, 1986;). Oligomeric or multifunctional

Micro and nano foam for multi-layer panels 0,7 – 1,1 Fields with outstanding mechanical properties > 1 Table 1. Values of PET intrinsic viscosity, specific for different applications.

composites and nanocomposites applications that will be detailed in the following.

polymeric extenders are more and more used (Volker et al., 2008).

**Application Intrinsic Viscosity, dlg-1** 

matrix (Janssen, 1998; Akkapeddi et al., 1988; Rober et al., 2006).

reported an intrinsic viscosity higher than 1 dlg-1 (Fumio Asaba, 2002).

In most cases, chain extension leads to thermal, mechanical and rheological performances equal or even higher than the performances of the primary polymers (Bikiaris at al., 1998). It is appreciated that chain extension is an important way to add value to POSTC-PET and to manufacture products with high technical and economic added value.

The following two alternatives are known for macromolecular chain extension, which are applied to all polycondensation polymers: solid state polymerization (SSP) and reactive processing (RP).
