Polystyrene thermal recycling

J. M. Arandes, J. Erena, M. J. Azkoiti, M. Olazar, and J. Bilbao, Thermal recycling of polystyrene and polystyrene - butadiene dissolved in a light cycle oil,. 1. Anal Appl Pyrol, 70, 747 (2003). 

Eoamed polystyrene sheet has exceUent strength, thermal resistance, formabUity, and shock resistance, as weU as low density. It is widely known for its use in beverage cups, food containers, building insulation panels, and shock absorbent packaging. Polystyrene products can be recycled if suitable coUection methods are estabUshed. Eoamed polystyrene sheet can also be easily therm oformed (see Styrene plastics). 

F. Vilaplana, A. Ribes-Greus, and S. Karlsson, Analytical strategies for the quality assessment of recycled high-impact polystyrene A combination of thermal analysis, vibrational spectroscopy, and chromatography, Anal Chim. Acta, 604(l) 18-28, November 2007. 

A-Alkyl-4-boronopyridinium halides such as 31 catalyze the esterification of a-hydroxycarboxylic acids <20050L5047>. When the quaternized iV-alkyl group is attached to a polystyrene resin, the supported iV-alkyl-4-boronopyridinium salt 32 serves as a catalyst in amide formation reactions. These catalysts are thermally stable and easily recovered and recycled <20050L5043>. 

Although solution blending has only been used at the lab scale at this time, compared with the in situ process, it may be more industrially friendly, particularly for the primary polymer producers who have operations, which can easily recover and recycle the solvent. High dilution is required and this may have an effect on the production of the PNs and the process is quite dependent on the individual polymer. Some polymers have many solvents from which to choose while others do not. A typical example is polystyrene, which can dissolve in a variety of solvents, so it is easy to find a solvent that is compatible with both the clay and the polymer. Polyolefins, on the other hand, require high boiling solvents and the high temperature may exert an effect of thermal degradation on the modifier. 

High-temperatnre pyrolysis and cracking of waste thermoplastic polymers, such as polyethylene, polypropylene and polystyrene is an environmentally acceptable method of recycling. These type of processes embrace both thermal pyrolysis and cracking, catalytic cracking and hydrocracking in the presence of hydrogen. Mainly polyethylene, polypropylene and polystyrene are used as the feedstock for pyrolysis since they have no heteroatom content and the liquid products are theoretically free of sulfur. 

Thermal processes are mainly used for the feedstock recycling of addition polymers whereas, as stated in Chapter 2, condensation polymers are preferably depolymerized by reaction with certain chemical agents. The present chapter will deal with the thermal decomposition of polyethylene, polypropylene, polystyrene and polyvinyl chloride, which are the main components of the plastic waste stream (see Chapter 1). Nevertheless, the thermal degradation of some condensation polymers will also be mentioned, because they can appear mixed with polyolefins and other addition polymers in the plastic waste stream. Both the thermal decomposition of individual plastics and of plastic mixtures will be discussed. Likewise, the thermal coprocessing of plastic wastes with other materials (e.g. coal and biomass) will be considered in this chapter. Finally, the thermal degradation of rubber wastes will also be reviewed because in recent years much research effort has been devoted to the recovery of valuable products by the pyrolysis of used tyres. 

PE = polyethylene PP = polypropylene PS = polystyrene ASR = automobile shredder residue VGO = vacuum gas oil LCO = light cycle oil. SA = Si02/ AI2O3 MOR = mordenite. TD/CD = thermal degradation followed by catalytic degradation COMB = mixed polymer and catalyst in a batch reactor COMS = mixed polymer and catalyst in a semibatch reactor FB = fixed bed flow reactor BIRR = Berty internal recycle reactor. 

Three commodity addition polymers, polyethylene, polypropylene and polystyrene, were the focus of this review. Although thermal decomposition of these polymers is one strategy used for tertiary recycling, it is inherently non-selective... 

Another new product is Saytex HP-7775. This is an extruded blend of brominated polyst5rene (HP-7010 from Albemarle) and Sb203 in a ratio of 77.5/22.5. It comes as dust-free, fi ee-flowing granules. It provides outstanding thermal stability and electrical performance, making it ideal for polyamides and polyesters in electrical applications. It has excellent mechanical properties, flow, non-blooming and, not least, recyclability, all similar to the basic brominated polystyrene. 

A laser flash technique has been used to determine the diffusivity of pyroelectric polymers such as polyvinylidene fluoride [83], whereas hot-wire techniques have been used to determine the thermal diffusivity of high-density polyethylene, low-density polyethylene propylene, and polystyrene [83], Dos Santos and coworkers [84] utilized the laser flash technique to study the effect of recycling on the thermal properties of selected polymers. Thermal diffusivity expresses how fast heat propagates across a bulk material, and thermal conductivity determines the woiking temperature levels of a material. Hence, it is possible to assert that those properties are important if a polymer is used as an insulator, and also if it is used in applications in which heat transfer is desirable. Five sets of virgin and recycled commercial polymers widely used in many applications (including food wrapping) were selected for this study. 

Mural and co-workers [57] also optimised the mechanical properties of an rPP and recycled high impact polystyrene (rHIPS) blend at a composition of 70/30 wt%. Consequently, this composition was mixed with a styrene-ethylene-butylene-styrene (SEES) block copolymer triblock copolymer and Cloisite 20A OMMT. Using X-ray diffraction, the samples containing 3 wt% of nanoclay were found to lack the characteristic nanoclay peak, which indicated the mixed intercalated and exfoliated clay layers where the intercalated layers were further pushed toward the interphase [76]. The incorporation of a compatibiliser and nanoclay also improved the thermal stability of the PP/HIPS blend. SEES and nanoclay performed as an interfacial compatibiliser, which led to the reduction in particle size of rHIPS and the promotion of interfacial adhesion. 

Expanded polystyrene products have widely increased the market for polystyrene resin (see the section on polystyrene foams in Chapter 1 of Plastics Fabrication and Recycling). With as light a weight as 2 Ib/ft (0.032 g/cm ), the thermal conductivity of expanded polystyrene is very low, and its cushioning value is high. It is an ideal insulation and packaging material. Common applications include ice buckets, water coolers, wall panels, and general thermal insulation applications. 

---