Mechanical recycling techniques

Among different recycling techniques, chemical recycling and mechanical recycling techniques are the most widely used [4], Figure 1.2 summarises the chemical recycling of polylactic acid (PLA)/polyethylene (PE) and PLA/polyhutylene succinate (PBS) blends. 

The problem of carpet recycling is considered and the different methods being proposed or commercially utilised are discussed. The main component of the carpet waste is fibres of nylon-6 and nylon-66. The review of the literature includes a limited amount of journal publications, which focus primarily on fundamental aspects, and a large number of patents, which describe the available technologies. The most promising recycling techniques (depolymerisation, extraction, melt blending and mechanical separation) are described. 48 refs. 

Post-consumer plastic waste recycling is discussed with special reference to feedstock recycling, the advantages it has over mechanical recycling, and the techniques involved. Chemolysis and thermolysis are explained, and... 

The recycling of PET is an important environmental topic as well as a commercial opportunity due to its widespread use, abundance and availability in bottles, packaging and fibres. While mechanical recycling of PET is now well established, newer chemical recycling techniques rely on depolymerization routes which cleave the polymer chains into new monomer building blocks (see Chapter 16). 

Spanish initiatives in PVC recycling are examined with particular reference to mechanical recycling, and developments in chemical recycling techniques are also reviewed. Statistics are presented for sources of PVC waste and forms and applications of the recycled materials, and a map shows the geographical distribution of PVC recyclers in Spain. 

The liquefaction of waste plastics is not an entirely new technique, but the challenge to operate commercial plants has been tried in Germany by pyrolysis and hydrogenation. However, the former, operated by BASF was stopped in 1996, and the latter by Veba Oel GmbH in 1999 [1]. It is well known that the reason is not a technical problem, but an economic one the cost is higher than those of competitive techniques, such as mechanical recycling or blast furnace application. 

These recycling techniques aside, it is also possible to extend the lifetime of plastics dnring their nsage. It has been shown by certain studies that wood flour/poly(ethyIene) composites used to build public benches could have a more favorable balance than wood itself, which is because of the non-biodegradabihty of PE [HOL 04]. Other authors have observed that the introduction of a certain quantity of wood flour into poly(propylene) helped increase its durabihty and improve its mechanical properties [LAM 08]. 

This process is used to recycle fabrics made from natural fibres such as cotton and wool as well as synthetic fibres including polyesters, nylons and blended fibres. Hawley (2006) describes the mechanical processing technique used in facilities in Prato, Italy, where acrylic textiles are shredded down to fibre. In hw example, acrylic garments were sorted and cut up, mechanically shredded to fibre, and then re-spun into acrylic yam for weaving into blanketing (Hawley, 2006). 

Thermoset composite materials can be recycled through mechanical comminution techniques, to reduce the size of the scrap to produce lecyclates, using thermal processes to break the scrap down into materials and energy (Pickering, 2006). 

The Vinyloop process was developed by Solvay as a response to a challenge from one of its customers, Ferrari Textiles Techniques (France), who produces architectural tarpaulin and canvas in PVC/polyester compound. This is a rather difficult formulation for recycling, since the PVC is mixed with a matrix. At the same time, Ferrari felt it was important that their material would be recyclable. The first Vinyloop installation is now operational. It is a form of mechanical rather than feedstock or chemical recycling, since the PVC matrix is not changed in the process. 

A pyrolysis technique was investigated as a method for the chemical recycling of glass fibre-reinforced unsaturated polyester SMC composites. The proeess yielded liquid products and gases and also a solid residue formed in the pyrolysis of glass fibres and fillers. The solid residue was used as a reinforeement/filler in unsaturated polyester BMC composites, and the influenee on mechanical properties was studied in comparison with BMC prepared entirely from virgin materials. 

Processes for the mechanical and chemical recycling of PETP bottles and other containers are described, and waste separation techniques are also examined. 9 refs. ASSORIMAP PETCORE REPLASTIC REKO BV PURE TECH INTERNATIONAL INC. DOW CHEMICAL CO. 

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