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> But the issue there is that keeping the plastics completely out of the environment is expensive. I find it hard to believe that somehow we are able to manufa

> But the issue there is that keeping the plastics completely out of the environment is expensive. I find it hard to believe that somehow we are able to manufacture plastic out of raw materials very cheaply, but converting it back to raw materials is so expensive. Maybe simply more research needs to be done in the area?

eesmith 5y ago
There's a lot of research in the area, because there's a LOT of money to be made if the problem is solved. Here's one paper from 12 years ago, titled "Plastics recycling: challenges and opportunities" - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2873020/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2873020/ I'll provide a few quotes, with key parts in italics > It is possible in theory to closed-loop recycle most thermoplastics, however, plastic packaging frequently uses a wide variety of different polymers and other materials such as metals, paper, pigments, inks and adhesives that increases the difficulty. Closed-loop recycling is most practical when the polymer constituent can be (i) effectively separated from sources of contamination and (ii) stabilized against degradation during reprocessing and subsequent use. Ideally, the plastic waste stream for reprocessing would also consist of a narrow range of polymer grades to reduce the difficulty of replacing virgin resin directly. .... > Chemical or feedstock recycling has the advantage of recovering the petrochemical constituents of the polymer, which can then be used to re-manufacture plastic or to make other synthetic chemicals. However, while technically feasible it has generally been found to be uneconomic without significant subsidies because of the low price of petrochemical feedstock compared with the plant and process costs incurred to produce monomers from waste plastic (Patel et al. 2000). This is not surprising as it is effectively reversing the energy-intensive polymerization previously carried out during plastic manufacture. ... > Thermosetting polymers such as unsaturated polyester or epoxy resin cannot be mechanically recycled, except to be potentially re-used as filler materials once they have been size-reduced or pulverized to fine particles or powders (Rebeiz & Craft 1995). This is because thermoset plastics are permanently cross-linked in manufacture, and therefore cannot be re-melted and re-formed. ... > A major challenge for producing recycled resins from plastic wastes is that most different plastic types are not compatible with each other because of inherent immiscibility at the molecular level, and differences in processing requirements at a macro-scale. For example, a small amount of PVC contaminant present in a PET recycle stream will degrade the recycled PET resin owing to evolution of hydrochloric acid gas from the PVC at a higher temperature required to melt and reprocess PET. Conversely, PET in a PVC recycle stream will form solid lumps of undispersed crystalline PET, which significantly reduces the value of the recycled material.

eesmith 5y ago

There's a lot of research in the area, because there's a LOT of money to be made if the problem is solved. Here's one paper from 12 years ago, titled "Plastics recycling: challenges and opportunities" - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2873020/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2873020/ I'll provide a few quotes, with key parts in italics > It is possible in theory to closed-loop recycle most thermoplastics, however, plastic packaging frequently uses a wide variety of different polymers and other materials such as metals, paper, pigments, inks and adhesives that increases the difficulty. Closed-loop recycling is most practical when the polymer constituent can be (i) effectively separated from sources of contamination and (ii) stabilized against degradation during reprocessing and subsequent use. Ideally, the plastic waste stream for reprocessing would also consist of a narrow range of polymer grades to reduce the difficulty of replacing virgin resin directly. .... > Chemical or feedstock recycling has the advantage of recovering the petrochemical constituents of the polymer, which can then be used to re-manufacture plastic or to make other synthetic chemicals. However, while technically feasible it has generally been found to be uneconomic without significant subsidies because of the low price of petrochemical feedstock compared with the plant and process costs incurred to produce monomers from waste plastic (Patel et al. 2000). This is not surprising as it is effectively reversing the energy-intensive polymerization previously carried out during plastic manufacture. ... > Thermosetting polymers such as unsaturated polyester or epoxy resin cannot be mechanically recycled, except to be potentially re-used as filler materials once they have been size-reduced or pulverized to fine particles or powders (Rebeiz & Craft 1995). This is because thermoset plastics are permanently cross-linked in manufacture, and therefore cannot be re-melted and re-formed. ... > A major challenge for producing recycled resins from plastic wastes is that most different plastic types are not compatible with each other because of inherent immiscibility at the molecular level, and differences in processing requirements at a macro-scale. For example, a small amount of PVC contaminant present in a PET recycle stream will degrade the recycled PET resin owing to evolution of hydrochloric acid gas from the PVC at a higher temperature required to melt and reprocess PET. Conversely, PET in a PVC recycle stream will form solid lumps of undispersed crystalline PET, which significantly reduces the value of the recycled material.