Recycling pellets

A shift in controlhng mechanism from coalescence to layering when the ratio of recycled pellets to new feed changes [Sastiy and Fuerstenau, Trans. Soc. Mining Eng., AIME, 258, 335-340 (1975)]. 

A number of studies (F3, 12, M4, V2) have shown that, provided the constituent particles are small enough, any particulate material will pelletize by systematic agitation without the use of a binder. The rate of agglomeration is greatly accelerated in the presence of relatively large-size solid particles or agglomerates. These seeds, nominally plus 200 mesh in size, are usually the recycled pellets of the powder itself. 

Hope et al. studied the effect of various contaminants (types of household industrial chemicals) on the recycling of HDPE bottles. Detergent, bleach, lubricating oil and white spirit bottles were recycled. They found that the contaminants generally were absorbed into the walls of the container and were not removed by thorough washing. The main contaminants in the recycled pellets were 1-2 wt% of white spirit, 0.7 wt% of hydrocarbon oil, and between 100-500 ppm chlorine from the bleach. Another common contaminant in post-consumer... 

The plastic pellets then can be sold as recycled pellets for plastic manufacturers of bottles, containers, caps, and plastic packaging. 

Post-industrial recycled plastics occur in most plastic products, wherein the plastics from the sprues runners, extrudate, etc. are added back into the virgin plastic at the plastic manufacturing plant. Postconsumer resin (PCR) refers to plastics that were made into products, for example, bottles, bags, film, packaging, used by a consumer, collected by a waste disposal company, processed into recycled pellets at an MRF, where the recycled plastic parts are converted into recycled plastic pellets. The plastic pellets are then sold to plastic companies. 

The economics of recycling PET are more favorable than recycling HDPE. To iacrease the recycling of HDPE, the separation of bottles made of these two plastics could be omitted and a mixture processed. Coarse, light-colored powders of the two polymers have been prepared by an experimental soHd state shear extmsion pulverization process (55). The powder has been successfully injection molded without pelletization. 

If a linear mbber is used as a feedstock for the mass process (85), the mbber becomes insoluble in the mixture of monomers and SAN polymer which is formed in the reactors, and discrete mbber particles are formed. This is referred to as phase inversion since the continuous phase shifts from mbber to SAN. Grafting of some of the SAN onto the mbber particles occurs as in the emulsion process. Typically, the mass-produced mbber particles are larger (0.5 to 5 llm) than those of emulsion-based ABS (0.1 to 1 llm) and contain much larger internal occlusions of SAN polymer. The reaction recipe can include polymerization initiators, chain-transfer agents, and other additives. Diluents are sometimes used to reduce the viscosity of the monomer and polymer mixture to faciUtate processing at high conversion. The product from the reactor system is devolatilized to remove the unreacted monomers and is then pelletized. Equipment used for devolatilization includes single- and twin-screw extmders, and flash and thin film evaporators. Unreacted monomers are recovered for recycle to the reactors to improve the process yield. 

Operabihty (ie, pellet formation and avoidance of agglomeration and adhesion) during kiln pyrolysis of urea can be improved by low heat rates and peripheral speeds (105), sufficiently high wall temperatures (105,106), radiant heating (107), multiple urea injection ports (106), use of heat transfer fluids (106), recycling 60—90% of the cmde CA to the urea feed to the kilns (105), and prior formation of urea cyanurate (108). 

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