Polymerisation Process stream

Except for the solvent process above, the cmde product obtained is a mixture of chloroprene, residual dichlorobutene, dimers, and minor by-products. Depending on the variant employed, this stream can be distiUed either before or after decantation of water to separate chloroprene from the higher boiling impurities. When the concentration of 1-chloro-1,3-butadiene [627-22-5] is in excess of that allowed for polymerisation, more efficient distillation is required siace the isomers differ by only about seven degrees ia boiling poiat. The latter step may be combiaed with repurifying monomer recovered from polymerisation. Reduced pressure is used for final purification of the monomer. All streams except final polymerisation-grade monomer are inhibited to prevent polymerisation. 

The metathesis polymerisation of dicyclopentadiene, an inexpensive monomer (commercially available cyclopentadiene dimer produced by a Diels-Alder addition reaction containing ca 95 % endo and ca 5 % exo form), leads to a polymer that may be transformed into a technically useful elastomer [144-146, 179] and thermosetting resin [180,181]. The polymerisation has characteristics that make it readily adaptable to the reaction injection moulding ( rim ) process [182], The main feature of this process comes from the fact that the polymerisation is carried out directly in the mould of the desired final product. The active metathesis catalyst is formed when two separate reactants, a precatalyst (tungsten-based) component and an activator (aluminium-based) component, are combined. Monomer streams containing one respective component are mixed directly just before entering the mould, and the polymerisation into a partly crosslinked material takes place directly in this mould (Figure 6.5) [147,168,183-186],... 

In the case of semi-crystalline polymers, reports can be found on a two-step process in which short chains are crystallised after which the polymerisation is continued in the solid state to obtain, e.g., high-molecular-weight PLLA [19]. In this process, an inert gas stream is applied to remove by-products from the surface. The coupling mainly takes place in the amorphous regions of the materials, where the reactive end groups reside. 

In suspension polymerisation, the chemical reaction takes places in droplets that are in suspension in a solvent. Suspension polymerisation is characterised by a good transfer of the reaction heat, a low dispersion viscosity and low separation costs on the one side but also by the fact that it is a discontinuous process, and there are relatively high amounts of waste water, significant reactor wall fouling and suspension agents remaining in the final product and in the waste streams. 

The chemistry of polymer production consists of three basic reaction types, polymerisation, polycondensation and polyaddition, thus the number of operations/processes used remains reasonably small. These include preparation, the reaction itself and the separation of products. In many cases cooling, heating, or the application of vacuum or pressure is necessary. The unavoidable waste streams are treated in recovery and/or abatement systems or disposed of as waste. 

At the end of their useful life, waste polymers enter waste streams as either post-consumer waste or industrial scrap. Households and the distribution industry sector are sources of the former while the latter arises from processing, filling, assembling, installing, and polymerisation. Much of the industrial waste is recycled within the process and the rest is usually sent for reprocessing by a third party. Consequently, little of this material is discarded as waste. The majority of postconsumer plastic waste, however, reaches the environment and hence the emphasis in polymer waste management is on this type of waste stream. 

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