**5. Reactive processing**

The reactive processing (RP) of POSTC-PET for the extension of the macromolecular chains, takes place in the equipment generally used for primary polymer melt processing, at temperatures ranging between the polymer melting temperature and the degradation those, under particular working conditions to each pair POSTC-PET – chain extender (Akkapeddi, 1988;). The reaction is also used for obtaining those melt properties which make possible the PET melt processing by extrusion –blowing and thermoformation (Lacoste et al., 2005).

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

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

Solid state polymerization (SSP) is a coupling reaction between POSTC-PET and extender that takes place in steel reactors, under high vacuum, at temperature above glass transition (Tg) and under melting temperature (Tm), in the catalysts presence (Karayannidis et al., 1991, 2003; Baldi et al., 2006; Flieger et al., 2003; Mano et el., 2004; Cangli et al., 2008; Bikiaris et al., 2003; Gantillon at al,1990, 2004; Rosu et al, 1999; Karayanidis at al., 1991; 1993, 2003). Usually the reaction occurs at temperatures ranging between 200 – 240 °C. These temperatures favour the SSP chain extension in detriment of the degrading ones. In SSP, the temperature control is essential because if the temperature is too low the extension lasts too long, and if the temperature is too high then the POSTC-PET flakes agglomerate and the extension can no longer happen evenly (Lee & Lichtenhan, 1999). In SSP the reaction time is too long (hours) because the reaction speed is controlled by the diffusion of the reaction byproduct and the diffusion of the end–groups into the reaction mass (Gantillon et al., 2004; Apoorva, 2002; Yong et al., 2008). A convenient growth of molecular weight is obtained after 8 hours at 230 0C (Karayannidis et all, 2003). The reactions speed can be increased by the presence of nanomaterials probably because of their nucleation effect (Huimin et al., 2004; Tannenbaum et al., 2002;) The volatiles are constantly removed from the reactor that must

manufacture products with high technical and economic added value.

operate under vacuum or under an inert gas blanket (Awaja & Pavel, 2005).

to prepare POSTC-PET nanocomposites (Bikiaris et al,2006; Apoorva, 2002).

To eliminate the negative influence of the residual impurities there exists an alternative solution according to which the POSTC-PET is dissolved first in a selected solvent, then the polymer is recovered by precipitation with methanol and finally the polymer is chain extended according to SSP methods (Karayannidis et al. 2003). SSP can be a proper method

Although, apparently SSP can be considered a good "bottle to bottle" recycling method, due to the longer reaction time and the high cost of the equipments and of the control devices, the procedure is considered unsuitable for industrial level (Martinez et al., 2008; Cavalcanti

The reactive processing (RP) of POSTC-PET for the extension of the macromolecular chains, takes place in the equipment generally used for primary polymer melt processing, at temperatures ranging between the polymer melting temperature and the degradation those, under particular working conditions to each pair POSTC-PET – chain extender (Akkapeddi, 1988;). The reaction is also used for obtaining those melt properties which make possible the

PET melt processing by extrusion –blowing and thermoformation (Lacoste et al., 2005).

processing (RP).

**4. Solid State Polymerization (SSP)** 

et al., 2007; Awaja & Pavel, 2005).

**5. Reactive processing** 

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

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., 2007; Xanthos et al.,2001).

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


Table 1. Values of PET intrinsic viscosity, specific for different applications.

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

#### **5.1 Chain extenders / reticulants**

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

Overview on Mechanical Recycling

al., 2007; Inata et al.1986).

known chain extenders.

& Turcu, 2005).

PET for increasing the melt strength (Inata et al., 1985).

by Chain Extension of POSTC-PET Bottles 97

The chain extenders can be classified considering the POSTC-PET end functional group with which react to extend the macromolecular chains. It is known that there are chain extenders which react with carboxyl end groups and chain extenders which react with hydroxyl end groups. The chain extenders which react to *carboxyl* end groups yield chain extension reactions in a higher proportion than the branching reactions. The chain extenders which react with POSTC-PET hydroxyl end groups are more efficient in the case of PET with low molecular weight, and the hydroxyl content is higher than the carboxyl one (Cavalcante et

In the following it is presenting a few chain extension mechanisms proper to the most

**Pyromellitic Dianhydride (PMDA**) is a tetra functional chain extender (fn = 4), available on the market, thermally stable, which does not lead to secondary products. It is efficient in proportion of 0.2 – 0.3 % and grows the intrinsic viscosity based on the reaction with the POSTC-PET *hydroxide end groups* (fig.8 –(Xantos et al., 2000; Awaja & Turcu, 2005). Depending on the PMDA concentration and the way the reaction is conducted, extremely branched or even reticulated structures can result. PMDA has been used also for primary

Fig. 8. POSTC-PET chain extension with pyromellitic dianhydride (Xantos et al., 2000; Awaja

**Tri-phenyl phosphit (TPP).** The increasing of the intrinsic viscosity is a result of the reaction between the non-participating electrons from phosphorus with the end *carboxyl and hydroxyl* groups of the POSTC-PET (figs 9, 10 Cavalcanti et.al, 2007). The good results are obtained with 1-3%, preferably 1% TPP, at 260 oC. (Cavalcanti et.al, 2005). The main reactions is


Table 2. The possible chain extender for POSTC-PET reactive processing.

Each extender, depending by its own chemical structure, yields typical extention reactions. It seems that di-functional chain extenders like bisepoxy compounds or bis (cyclic carboxylic anhydride or diisocyanate), do not form by-products and lead to strong reticulated POSTC-PET. Polyfunctional extenders having in their molecule at least three functional groups (fn˃3) involving a combination of at least one group selected from those presented in table 1 (Arif et al., 2007;) are extremely efficient in case of highly deteriorated macromolecules or when a high level of intrinsic viscosity is targeted. These type of extenders are used in order to avoid combinations among extenders (i.e. pyromellitic dianhydride and pentaerytriol (Forsythe et.al, 2006)). The chain extenders with a higher than 3 functionality (fn), leads to branched molecules. As a rule, the average functionality of the chain extenders is fn › 4.

Epoxy Diepoxides (Haralabakopoulos, 1999;), Epoxy/styrene

Anhydride Maleic anhydride, Phtalic anhydride (Shivalingappa et al.,

Oxazoline 2,2 – (1, 4 phenilen) bis 2 oxazoline ( Hongyang et al., 2002;

phosphazene Ciclo-phosphazene , bis-5,6-dihydro-4h-1,3-oxazolines,

Hydroxy -acid Citric acid, Tartric acid, Trihydroxyglutaric acid. (Tang &

lactame Polyacyllactams (Bureau et al., 2002; Isocyanate Isocyanate triglycidil ( Knite et al., 2002) 0,9 %

Alcohol / polyol Polyol having 3 -6 hydroxyl groups: Glycerol,

Each extender, depending by its own chemical structure, yields typical extention reactions. It seems that di-functional chain extenders like bisepoxy compounds or bis (cyclic carboxylic anhydride or diisocyanate), do not form by-products and lead to strong reticulated POSTC-PET. Polyfunctional extenders having in their molecule at least three functional groups (fn˃3) involving a combination of at least one group selected from those presented in table 1 (Arif et al., 2007;) are extremely efficient in case of highly deteriorated macromolecules or when a high level of intrinsic viscosity is targeted. These type of extenders are used in order to avoid combinations among extenders (i.e. pyromellitic dianhydride and pentaerytriol (Forsythe et.al, 2006)). The chain extenders with a higher than 3 functionality (fn), leads to branched molecules. As a rule, the average functionality of the chain extenders is fn › 4.

Table 2. The possible chain extender for POSTC-PET reactive processing.

Carboxyl / polycarboxylic acids

Phosphites/phosphates Triphenyl phosphate(Cavalcanti et al. 2007;), Lactamyl

Oligomers which can be used as master – batch (Zammarano et al., 2006) , Epoxy functionalized compounds (Ren at al., 2003; (Dhavalikar, 2002); Polyepoxides (Dhavalikar, 2002;) Di and tri epoxy, glycidil reactive (Dhalikar & Xanthos, 2001; Hambir et al., 2002;Shanti et al.,2002;), Glycidil multifunctional compounds (Bras et al., 2001 ); Bis(glycidil ester(pyrolellitimides) (Bikiaris et al.,1995;)

2005;), Pyromellitic dianhydride (Kamal et al., 2002; Giusca et al., 2002; Shah et al., 2002; Shanti et al., 2002; Denisyuk et al., 2003; Lacoste et al., 2005;)

phosphite (Pham Hoai nam et al., 2002; Bikiaris et al., 2006; Aromatic phosphates (Aharoni, 1986)

Karim et al., 2002; Shyalingappa et al., 2005; Warburton et al., 1990;)

Hexamethylene diisocyanate (Teh et al., 2004;)

Trimethylolpropane, Pentaerytritol, Sorbital ; Polyfunctional Alcohol, 0.1 – 2 % pentaerythritol (Denysiuk et al., 2003;)

Menachem, 2007)

Trimellitic or Himimellitic acid, Pyromellitic acid (Tang & Menachem, 2007)

Extender functional group Main representatives, reference

The chain extenders can be classified considering the POSTC-PET end functional group with which react to extend the macromolecular chains. It is known that there are chain extenders which react with carboxyl end groups and chain extenders which react with hydroxyl end groups. The chain extenders which react to *carboxyl* end groups yield chain extension reactions in a higher proportion than the branching reactions. The chain extenders which react with POSTC-PET hydroxyl end groups are more efficient in the case of PET with low molecular weight, and the hydroxyl content is higher than the carboxyl one (Cavalcante et al., 2007; Inata et al.1986).

In the following it is presenting a few chain extension mechanisms proper to the most known chain extenders.

**Pyromellitic Dianhydride (PMDA**) is a tetra functional chain extender (fn = 4), available on the market, thermally stable, which does not lead to secondary products. It is efficient in proportion of 0.2 – 0.3 % and grows the intrinsic viscosity based on the reaction with the POSTC-PET *hydroxide end groups* (fig.8 –(Xantos et al., 2000; Awaja & Turcu, 2005). Depending on the PMDA concentration and the way the reaction is conducted, extremely branched or even reticulated structures can result. PMDA has been used also for primary PET for increasing the melt strength (Inata et al., 1985).

Fig. 8. POSTC-PET chain extension with pyromellitic dianhydride (Xantos et al., 2000; Awaja & Turcu, 2005).

**Tri-phenyl phosphit (TPP).** The increasing of the intrinsic viscosity is a result of the reaction between the non-participating electrons from phosphorus with the end *carboxyl and hydroxyl* groups of the POSTC-PET (figs 9, 10 Cavalcanti et.al, 2007). The good results are obtained with 1-3%, preferably 1% TPP, at 260 oC. (Cavalcanti et.al, 2005). The main reactions is

Overview on Mechanical Recycling

et.al, 2007).

(Cavalcanti et al.,2005).

structures (Bikiaris et al., 1995).

by Chain Extension of POSTC-PET Bottles 99

Fig. 10. Extension of PET with TPP. Reaction of phosphite with hydroxyl group ( Cavalcanti

Fig. 11. By-products formation during the chain extension of PET with TPP (Cavalcanti, 2007).

The by-products are dangerous for the reason that, during storage, they act as degrading agent diminishing in this way the stability of "repaired" POSTC-PET. It is demonstrated that if these by-products are extracted with acetone, the degrading during storage is avoided

**Epoxy compounds** give the esterification of end carboxyl groups (fig.12, (Xanthos et.al, 2000)) and etherification of the end hydroxyl groups (fig.13, (Xanthos et.al, 2000)) from the POSTC-PET macromolecules. In both cases, secondary hydroxyls are formed that can react later with the carboxyl or epoxy groups leading to the formation of branched or reticulate

**Oxazoline compounds** such as 2,2'-bis(2-oxazoline) give, with POSTC-PET, the following 3 types of interactions: *blocking reactions* ( the molecule of chain extender reacts with the end carboxyl group from a POSTC-PET chain), *coupling reactions* ( an extender molecule reacts with 2 polymer chains) and the *absence of any reactions* ( Inata, 1987;). *(B*O) yields secondary

accompanied by the by – products development. The competition between the chain extension and the formation of by-products is obvious at temperatures ranging from 280 - to 300 0C.

Fig. 9. Chain extension of PET with TPP. Chemical reaction between phosphate and hydroxyl group (Cavalcanti et.al, 2007).

accompanied by the by – products development. The competition between the chain extension and the formation of by-products is obvious at temperatures ranging from 280 - to

Fig. 9. Chain extension of PET with TPP. Chemical reaction between phosphate and

hydroxyl group (Cavalcanti et.al, 2007).

300 0C.

Fig. 10. Extension of PET with TPP. Reaction of phosphite with hydroxyl group ( Cavalcanti et.al, 2007).

Fig. 11. By-products formation during the chain extension of PET with TPP (Cavalcanti, 2007).

The by-products are dangerous for the reason that, during storage, they act as degrading agent diminishing in this way the stability of "repaired" POSTC-PET. It is demonstrated that if these by-products are extracted with acetone, the degrading during storage is avoided (Cavalcanti et al.,2005).

**Epoxy compounds** give the esterification of end carboxyl groups (fig.12, (Xanthos et.al, 2000)) and etherification of the end hydroxyl groups (fig.13, (Xanthos et.al, 2000)) from the POSTC-PET macromolecules. In both cases, secondary hydroxyls are formed that can react later with the carboxyl or epoxy groups leading to the formation of branched or reticulate structures (Bikiaris et al., 1995).

**Oxazoline compounds** such as 2,2'-bis(2-oxazoline) give, with POSTC-PET, the following 3 types of interactions: *blocking reactions* ( the molecule of chain extender reacts with the end carboxyl group from a POSTC-PET chain), *coupling reactions* ( an extender molecule reacts with 2 polymer chains) and the *absence of any reactions* ( Inata, 1987;). *(B*O) yields secondary

Overview on Mechanical Recycling

by Chain Extension of POSTC-PET Bottles 101

which the reactions occur. *The extender concentration is* calculated in relation with the stoichiometry of the extension reaction, considering the *measured* content of hydroxyl and carboxyl end groups (Nair at al., 2002;) In theory, a larger quantity than that resulted from stoichiometry leads to strongly reticulated structures, that means a high gel content. *Reaction time can be* up to 10 min. The measuring of the stationary time in the equipment is important because it controls the development of the chemical reactions (Janssen, 1998). Usually the

In the case of a Brabender plastometer, the extension is monitored based on the dependence between the motor torque and reaction temperature and time, while in the case of a capillary rheometer, it is recorded the correlation between the nozzle pressure and the swelling extrudate or on the relationship between the melt flow index and the melt strength (Nair et al., 2002;) In modern industrial systems the monitoring of the intrinsic viscosity is automatic. Obviously, the evolution of the chain extension reaction is rounded up with gel measurements and other properties that characterize the "repaired" POSTC-PET in the melt and solid state.

POSTC-PET has always a residual content of humidity. It was underlined that the chain extension reaction is favoured, and the thermal and hydrolytic degradation is diminished if the humidity content and the reaction time are reduced (Haralabakopoulos et al., 1999). If the chain extending reactions take place under vacuum or a nitrogen blanket then the thermal and hydrolytic degradation can be very much diminished or even eliminated. For these reasons the extruders must be equipped with high vacuum degassing areas for volatiles removal. Also the Brabender plastometers must work under a nitrogen blanket. This condition near the procedure price limit the industrial applicability of chain extension on elderly equipments. It is difficult to have industrial devices that work under such conditions (Paci & La Mantia, 1998). Nevertheless the modern POSTC-PET extrusion

The POSTC-PET extending chain reactions that take place in an extruder are controlled by the reaction parameters presented in fig.14 (Awaja & Pavel, 2005). For controlling the reactions that occur in such conditions first of all the system has to be stable (Janssen, 1998;). The stability of the twin screw extruders depends on their designing concept (Bulters, 2001;

The fluctuation of the parameters presented in fig.14 is the major cause determining the *thermal, hydrodynamic and chemical instability,* and consequently the fluctuation in the operation of the reactive extruder. All these types of instability were described in detail in (Awaja & Pavel, 2005) where the bi-univocal relations between the parameters presented in

The concentration of the extender / reticulant and the stationary time within the extruder are two parameters which control the efficiency of the procedure. A longer waiting time in the extruder is the main reasons of the system instability because the longer the waiting time the bigger the thermo - mechanically degradation (Giusca et al., 2002; Hongyang et al., 2002;

fig.14 and the way in which they influence each other were explained.

reaction temperature ranges between 260 0C and 310 0C (Bras et al., 2001)

**5.2.2 Operation under vacuum or nitrogen blanket** 

systems have high vacuum lines for volatiles removal.

**5.2.3 The engineering of reactive processing** 

Potente & Flecke, 1997;Shen et al., 2005;).

reactions because the oxzoline ring is sensitive to acids. 2.2 – (1.4 – phenylene) bis(2 – oxazoline) ( PBO) is a very reactive compound considering only the carboxyl groups within the macromolecular chains. PBO can be used together with a chain extender which reacts with hydroxyl end group i.e. phtalic anhydride.

Fig. 12. Initial esterification step in PET chain extension with diepoxide (Xanthos et.al, 2000).

Fig. 13. Initial esterification in the chain extension of PET with diepoxide (Xanthos et.al, 2000).

#### **5.2 Conditions for the chain extension reactions**

#### **5.2.1 Reaction parameters - Reaction control**

In POSC-PET reactive processing, the chain extension reactions are controlled by the extender concentration, reaction temperature and time and parameters proper to the equipment in

reactions because the oxzoline ring is sensitive to acids. 2.2 – (1.4 – phenylene) bis(2 – oxazoline) ( PBO) is a very reactive compound considering only the carboxyl groups within the macromolecular chains. PBO can be used together with a chain extender which reacts

Fig. 12. Initial esterification step in PET chain extension with diepoxide (Xanthos et.al, 2000).

Fig. 13. Initial esterification in the chain extension of PET with diepoxide (Xanthos et.al, 2000).

In POSC-PET reactive processing, the chain extension reactions are controlled by the extender concentration, reaction temperature and time and parameters proper to the equipment in

**5.2 Conditions for the chain extension reactions 5.2.1 Reaction parameters - Reaction control** 

with hydroxyl end group i.e. phtalic anhydride.

which the reactions occur. *The extender concentration is* calculated in relation with the stoichiometry of the extension reaction, considering the *measured* content of hydroxyl and carboxyl end groups (Nair at al., 2002;) In theory, a larger quantity than that resulted from stoichiometry leads to strongly reticulated structures, that means a high gel content. *Reaction time can be* up to 10 min. The measuring of the stationary time in the equipment is important because it controls the development of the chemical reactions (Janssen, 1998). Usually the

In the case of a Brabender plastometer, the extension is monitored based on the dependence between the motor torque and reaction temperature and time, while in the case of a capillary rheometer, it is recorded the correlation between the nozzle pressure and the swelling extrudate or on the relationship between the melt flow index and the melt strength (Nair et al., 2002;) In modern industrial systems the monitoring of the intrinsic viscosity is automatic. Obviously, the evolution of the chain extension reaction is rounded up with gel measurements and other properties that characterize the "repaired" POSTC-PET in the melt and solid state.

reaction temperature ranges between 260 0C and 310 0C (Bras et al., 2001)

#### **5.2.2 Operation under vacuum or nitrogen blanket**

POSTC-PET has always a residual content of humidity. It was underlined that the chain extension reaction is favoured, and the thermal and hydrolytic degradation is diminished if the humidity content and the reaction time are reduced (Haralabakopoulos et al., 1999). If the chain extending reactions take place under vacuum or a nitrogen blanket then the thermal and hydrolytic degradation can be very much diminished or even eliminated. For these reasons the extruders must be equipped with high vacuum degassing areas for volatiles removal. Also the Brabender plastometers must work under a nitrogen blanket. This condition near the procedure price limit the industrial applicability of chain extension on elderly equipments. It is difficult to have industrial devices that work under such conditions (Paci & La Mantia, 1998). Nevertheless the modern POSTC-PET extrusion systems have high vacuum lines for volatiles removal.

#### **5.2.3 The engineering of reactive processing**

The POSTC-PET extending chain reactions that take place in an extruder are controlled by the reaction parameters presented in fig.14 (Awaja & Pavel, 2005). For controlling the reactions that occur in such conditions first of all the system has to be stable (Janssen, 1998;). The stability of the twin screw extruders depends on their designing concept (Bulters, 2001; Potente & Flecke, 1997;Shen et al., 2005;).

The fluctuation of the parameters presented in fig.14 is the major cause determining the *thermal, hydrodynamic and chemical instability,* and consequently the fluctuation in the operation of the reactive extruder. All these types of instability were described in detail in (Awaja & Pavel, 2005) where the bi-univocal relations between the parameters presented in fig.14 and the way in which they influence each other were explained.

The concentration of the extender / reticulant and the stationary time within the extruder are two parameters which control the efficiency of the procedure. A longer waiting time in the extruder is the main reasons of the system instability because the longer the waiting time the bigger the thermo - mechanically degradation (Giusca et al., 2002; Hongyang et al., 2002;

Overview on Mechanical Recycling

and a minimal variation (Cavalcanti, 2007).

temperature and the flow speed are constant.

**5.3 SSP and PR comparative economical analyse** 

**5.4 POSTC-PET chain extended applications** 

obtained by physical modification.

et al., 2001; Hu et al., 2002; Lochhead, 2006;)

**5.4.2 Sheets and foamed panels** 

**5.4.1 Bottles** 

by Chain Extension of POSTC-PET Bottles 103

The counter-pressure and the pressure fluctuation are the most frequent instability described by most of the researchers (Kamal, 2002). Fluctuation can as well occur in the high vacuum degassing system. The pressure in the vacuum system also needs a severe control

It is considered that the reaction system specific to the reactive processing is constant if the defining parameters vary within a minimally accepted controllable level. Actually it is considered that the reactive processed is constant when the nozzle pressure, the cylinder

A correct approaching of comparative economical analysis for SSP and PR needs details for both procedures and the reaction devices, details about the cost of energy, nitrogen, cooling water, additives and specific labour. In [Vilabados, 2006] it is demonstrated that the chain extension with Joncryl-ADR-4368 (Epoxy/styrene oligomeric extender) by reactive processing in a single screw extruder results in a competitive PR of POSTC-PET. As the reaction uses smaller quantities of energy, water and nitrogen, the reactive processing is more cost-efficient than SSP, which needs catalysts and other special reaction conditions..

The main applications of the "repaired" mechanically recycled POSTC-PET, valuable in practice, are manufacture of: bottles, expanded sheets, multi-layer sheets and foamed panels for constructions and /or compounds composites and nanocomposites for different uses

In chap.1 it was underlined that only the colour selected POSTC-PET can be mechanically or thermally recycled into bottles. The chain extension reactions offer o new perspective on this subject. Currently "closing the loop" has become an actual possibility as the bottles and containers can be recycled back as bottles and containers. So, considering the chain extension possibilities it seems that the bottle-to-bottle recycling system is a feasible approach. These bottles can be used for packaging of non-food or food contact products. The re-use of POSTC-PET into food area depends on the potential of the reprocessed material to provide as much safety as the primary polymers do. POSTC-PET can be reprocessed also in multilayer bottles that do not require special safety measures as their inner layer, which comes into contact with the food, is made of primary polymer (Chaiko et al., 2002; kamal et al., 2002; Tannenbaum et al., 2002; Liane et al., 2002; Tjong et al., 2002; Kim

The "repaired" POST-PET can be used for obtaining sheets or multi-layer structures in which at least one layer consists of POSTC-PET (Hong et al., 2007; Yan & Zao, 1988). Sandwich panels (Banosz et al., 1996) and /or high strength uniaxially drawn tapes (Morawiec et al., 2002) can

be also attained from "repaired" POST-PET or "repaired" POST-PET foams.

Kamal et al., 2002). The system instability can result in various situations. The presence of the branched chains within the polymer structure has a great influence on the crystallization induced by shearing (Hanley, 2007; Rosu et al., 1999; Van Meerveld et al., 2002). The resulted morphology will be heterogeneous if the chemical reactions have fluctuations in their evolution (Rosu et al.1999). The orientation of the macromolecules within a shearing field is directly linked to the increase in viscosity. The orientation degree will be irregular in the case of a random viscosity increase (Soares et al., 2004).

Fig. 14. The factors influencing the stability of an extruder system used for chain extension (+ positive influence; - negative influence) (Awaja & Pavel, 2005).

Kamal et al., 2002). The system instability can result in various situations. The presence of the branched chains within the polymer structure has a great influence on the crystallization induced by shearing (Hanley, 2007; Rosu et al., 1999; Van Meerveld et al., 2002). The resulted morphology will be heterogeneous if the chemical reactions have fluctuations in their evolution (Rosu et al.1999). The orientation of the macromolecules within a shearing field is directly linked to the increase in viscosity. The orientation degree will be irregular in

Fig. 14. The factors influencing the stability of an extruder system used for chain extension

(+ positive influence; - negative influence) (Awaja & Pavel, 2005).

the case of a random viscosity increase (Soares et al., 2004).

The counter-pressure and the pressure fluctuation are the most frequent instability described by most of the researchers (Kamal, 2002). Fluctuation can as well occur in the high vacuum degassing system. The pressure in the vacuum system also needs a severe control and a minimal variation (Cavalcanti, 2007).

It is considered that the reaction system specific to the reactive processing is constant if the defining parameters vary within a minimally accepted controllable level. Actually it is considered that the reactive processed is constant when the nozzle pressure, the cylinder temperature and the flow speed are constant.

### **5.3 SSP and PR comparative economical analyse**

A correct approaching of comparative economical analysis for SSP and PR needs details for both procedures and the reaction devices, details about the cost of energy, nitrogen, cooling water, additives and specific labour. In [Vilabados, 2006] it is demonstrated that the chain extension with Joncryl-ADR-4368 (Epoxy/styrene oligomeric extender) by reactive processing in a single screw extruder results in a competitive PR of POSTC-PET. As the reaction uses smaller quantities of energy, water and nitrogen, the reactive processing is more cost-efficient than SSP, which needs catalysts and other special reaction conditions..

### **5.4 POSTC-PET chain extended applications**

The main applications of the "repaired" mechanically recycled POSTC-PET, valuable in practice, are manufacture of: bottles, expanded sheets, multi-layer sheets and foamed panels for constructions and /or compounds composites and nanocomposites for different uses obtained by physical modification.

### **5.4.1 Bottles**

In chap.1 it was underlined that only the colour selected POSTC-PET can be mechanically or thermally recycled into bottles. The chain extension reactions offer o new perspective on this subject. Currently "closing the loop" has become an actual possibility as the bottles and containers can be recycled back as bottles and containers. So, considering the chain extension possibilities it seems that the bottle-to-bottle recycling system is a feasible approach. These bottles can be used for packaging of non-food or food contact products. The re-use of POSTC-PET into food area depends on the potential of the reprocessed material to provide as much safety as the primary polymers do. POSTC-PET can be reprocessed also in multilayer bottles that do not require special safety measures as their inner layer, which comes into contact with the food, is made of primary polymer (Chaiko et al., 2002; kamal et al., 2002; Tannenbaum et al., 2002; Liane et al., 2002; Tjong et al., 2002; Kim et al., 2001; Hu et al., 2002; Lochhead, 2006;)

#### **5.4.2 Sheets and foamed panels**

The "repaired" POST-PET can be used for obtaining sheets or multi-layer structures in which at least one layer consists of POSTC-PET (Hong et al., 2007; Yan & Zao, 1988). Sandwich panels (Banosz et al., 1996) and /or high strength uniaxially drawn tapes (Morawiec et al., 2002) can be also attained from "repaired" POST-PET or "repaired" POST-PET foams.

Overview on Mechanical Recycling

obtained results (Hong Jun, 2007).

with polymer up – grading.

**6. Conclusions** 

so.).

procedure.

processing.

processing (RP).

by Chain Extension of POSTC-PET Bottles 105

also obtained with CaCO3 (Di Lorenzo, 2007). Experimental models were conceived for understanding the interaction between the polymer and the ranforsant (Kalpana, 2006; lingaiah, 2005; Tortora et al., 2002). Also, researches are known about the possibility to increase the exfoliation degree of the multilayered silicate, the order degree of the resulted lamellae (Gilmer, 2004; Ren et al., 2003; Rossi, 2002;), the influence of the ranforsant, possible compatibilizer (Giselle, 2005; Hambir, 2002;Pegoretti et al., 2004;Schimidt et al., 1999; The et al., 2004;) The parameters of the reactive processing have a critical role on the

1. The chapter presents an overview on the up-gradation of POSTC-PET by increasing the macromolecular weight based on chain extension reactions, as the most efficient method for adding value to the secondary polymers and for the creation of products with added technical and economical value, for applications within the economy. 2. The post consumer poly(ethylene therephtalate) bottles (PET-PC) can be recycled by chemical or / and mechanical procedures. The PET – PC chemical recycling is based on the depolymerisation of secondary polymers and the use of the depolymerisation products within the fibre and unwoven material industry. The PET - PC mechanical recycling is based on a phase transformation (melting) and can be performed without or

3. The mechanical recycling is controlled by the impurities content and by the reprocessed polymer degradation. The mechanical recycling of PET – PC without up – gradation takes into account the melt processing of the recycled polymer into packages for non – food goods and into thermoformable sheets with a resulted shape adjusted to the transported packed products ( eggs, tomatoes, strawberries, apples,

4. In spite of the long efforts performed during the years, because of the low cost and low performance applications of the obtained products, the widely accepted opinion is that the mechanical recycling of PET – PC without up – gradation is not an efficient

5. The chain extension reaction is favoured, and the thermal and hydrolytic degradation is

6. The POSTC-PET drying is performed as in the case of primary polymers: drying for 3 -12 hours at a temperature of 120 - 180 oC in desiccators or standard drying equipments. The drying of POSTC – PET restrains the hydrolysis during melt

7. The POSTC-PET stabilization during melt processing is needed to block the polymer thermo-hydrolitical degradation, to remove the formation of acetaldehyde as a result of

8. The macromolecular chain extension is a result of particular post condensation reactions between the degraded polymer and selected chain extenders. The following two alternatives are known for POSTC-PET macromolecular chain extension, which are applied to all polycondensation polymers: solid state polymerization (SSP) and reactive

diminished if the POSTC-PET humidity content is reduced by drying.

degradation and to reduce the influence of the residual PVC.

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

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

### **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., 2004;).

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 also obtained with CaCO3 (Di Lorenzo, 2007). Experimental models were conceived for understanding the interaction between the polymer and the ranforsant (Kalpana, 2006; lingaiah, 2005; Tortora et al., 2002). Also, researches are known about the possibility to increase the exfoliation degree of the multilayered silicate, the order degree of the resulted lamellae (Gilmer, 2004; Ren et al., 2003; Rossi, 2002;), the influence of the ranforsant, possible compatibilizer (Giselle, 2005; Hambir, 2002;Pegoretti et al., 2004;Schimidt et al., 1999; The et al., 2004;) The parameters of the reactive processing have a critical role on the obtained results (Hong Jun, 2007).
