Reprocessing of Thermoplastic Recyclates

Mechanical recycling is the most common method of recycling. Here plastics are physically ground back to a suitable size (regrind) and reprocessed. The end use can be the original one or something different. 

In the plastics industry it has long been common practice to reprocess waste material arising from normal production. This in-house recycling, known as primary recycling, makes economic sense as it reduces both production waste and utilisation of raw materials. For example, with injection moulding, regrind from start-up waste and production waste snch as reject parts, can be fed directly back into the production machine. 

For reclaiming used material or recyclate outside of this scenario, the situation is slightly different and greater effort may be reqnired on the part of the reprocessor. This type of mechanical recycling is termed secondary recycling (see Table 5.1). 

Primary Recycling In-house reprocessing of production waste 

Secondary Recycling Mechanical recycling of single or mixed plastic materials from external sources 

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Health and Safety Issues. Polyesterether elastomers derived from dimethyl terephthalate, butanediol, and Ptmeg are not hazardous according to the published Materials Safety Data Sheets (MSDS) for this elastomer. Polymers of a similar structure containing isophthalic acid are also not considered hazardous. For other copolymer elastomers, the MSDS put out by suppliers should be consulted by potential users before evaluation. One environmental advantage of thermoplastic elastomers of this type is that they are melt-reprocessible and thus scrap and off-specification material and even obselete parts can be easily recycled. Up to 25% by weight of recycled material can be incorporated (see Recycling, plastics). 

Thermoplastic elastomers (TPEs) combine the physical properties of vulcanized rubber with the ease and economy of conventional thermoplastic processing. They are also well suited to reprocessing and recycling and minimize toxicity issues. Many types of thermoplastic elastomers are polymer blends cranprising a thermoplastic continuous phase in combination with a discontinuous vulcanized or unvulcanized elastomeric phase, which in the latter case could also be co-continuous. 

The reinforcing fibers in composites offer unique properties but create complications in recycling. Thermoplastic composites have the potential of primary and secondary recycling since the reprocessing of waste can result in a prodnct with the same or comparable properties, whereas thermoset... 

Most of the published studies of primary recycling of thermoplastics have dealt with the effect of reprocessing on the mechanical properties. Various polymers have been... 

Reprinted from The recycling of thermoplastics prediction of the properties of mixtures of virgin and reprocessed polymers Bernardo, C. A., Cunha, A. M. and Oliveira, M. J., Polym. Eng. Sci. 36, 511-519 1996 Society of Plastics Engineers... 

Recycling of HDPE. Polyolefins, including HDPE, are the second most widely recycled thermoplastic materials after PET (110). A significant fraction of articles made from HDPE (mostly bottles, containers, and film) are collected from consumers, sorted, cleaned, and reprocessed (110—113). Processing of post-consumer HDPE includes the same operations as those used for virgin resins blow mol ding, injection molding, and extmsion. 

When a thermoplastic polyurethane elastomer is heated above the melting point of its hard blocks, the chains can flow and the polymer can be molded to a new shape. When the polymer cools, new hard blocks form, recreating the physical crosslinks. We take advantage of these properties to mold elastomeric items that do not need to be cured like conventional rubbers. Scrap moldings, sprues, etc. can be recycled directly back to the extruder, which increases the efficiency of this process. In contrast, chemically crosslinked elastomers, which are thermosetting polymers, cannot be reprocessed after they have been cured. 

Thermoplastics, which account for 87% of plastics sold, are the most recyclable form of plastics because they can be remelted and reprocessed usually with only minor changes in their properties. Five resins are commonly used in consumer packaging applications. 

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