TOXIC ADDITIVES CHALLENGE MECHANICAL AND CHEMICAL RECYCLING

Numerous institutional, economic, and policy challenges for recycling have already been mentioned in this report, but there are also technical challenges related to the complexity of post-consumer polymeric materials, and their separation and processing. Thermodegradation of polymers in the recycling process due to heat and mechanical sheer is a significant problem . Before reaching the recycling facility the waste plastic may have undergone other forms of degradation such as heat, light, oxygen, and moisture exposure , which can also degrade the output recyclate product.

A second challenge is the immiscibility of the main high-volume polymers in the remelting phase, leading to subsequent degradation of the final recyclate product. Recyclers attempt to segregate mono-streams as much as is practical in order to minimize the degradation of the end product. No mechanical recycling process has been able to achieve 100% contamination free mono-streams, but very low cross-polymer contamination levels are frequently achieved .

The third major technical challenge is the management of additives. As described in section 1, the widespread use of chemical additives in plastics to impart specific characteristics leads to significant problems in chemical and mechanical recycling. For most forms of mechanical recycling, toxic chemical additives, their degradation products, and even ‘side products’ are carried through the recycling chain and into the plastic recyclate destined for inclusion in new plastic products.

Side products can include contaminants entrained in the additive during its manufacturing process. An example is highly toxic brominated dioxins that are formed during the manufacture of BFRs which then ‘follow’ the BFRs into polymers when BFRs are added to final plastic products (Watson et al., 2010). The brominated dioxins can then be detected not only in the final BFR-added product, but also as it moves along with the shredded plastic in the mechanical recycling phase, and then into new products using plastic recyclate , and even into the environment following disposal.

Mechanical recycling workers are particularly vulnerable during shredding and extrusion phases of polymers. The temperature for extrusion of plastic lies within the dioxin formation and release range . Other toxic substances and endocrine disrupting chemicals (EDCs) can be released at this point leading to exposure including metals, volatile organic compounds (VOCs), phthalates, polycyclic aromatic hydrocarbons (PAHs), PBDEs (polybrominated diphenyl ether), polyamide-epichlorohydrin (PAE), polybrominated dibenzo-p-dioxins, and furans (PBDD/F).

Chemical recycling workers may also be subject to exposures from volatile gases and fugitive particulate from toxic additives during the processing phase whether using solvents, heating in pyrolysis plants, pre-treating plastic waste for processing, or handling the toxic residues from chemical recycling.

Mechanical recycling represents a useful contribution to the overall objective of a circular economy but in the face of exponential increases in very cheap, virgin plastic production does not represent a solution to the current plastic pollution paradigm. Virgin plastic producers unload the cost of externalities associated with their products onto the mechanical recycling sector. The addition of toxic and incompatible additives to polymers at production stage represents costly challenges to downstream mechanical recyclers that reduces their economic viability.

Holding virgin plastic producers accountable for their additives (toxic or otherwise) and unrecyclable products (complex laminates etc.) by regulation, taxes, or other policy and market instruments is necessary for mechanical recycling to adopt a meaningful position in the circular economy. These measures would also have considerable human health and environmental benefits from exposure reduction. Such measures can be implemented immediately but are still not enough. Ultimately freezing or reducing current production levels for plastics, while mandating recycled polymer content, is the essential pre-requisite to move to a circular economy for plastics.