THERMAL DEPOLYMERISATION

Thermal depolymerisation through scission of C—O bonds can occur catastrophically above 270°C and care must be taken not to exceed this temperature during processing. 

Techniques for the chemical recycling of plastics into monomers and petrochemical feedstocks are described, including chemical and thermal depolymerisation, pyrolytic liquefaction, pyrolytic gasification and partial oxidation. BRITISH PETROLEUM CO.PLC... 

This paper discusses in depth advanced technologies for recycled materials from solid waste streams. Chemical depolymerisation, thermal depolymerisation, pyrolytic liquefaction, pyrolytic gasification, partial oxidation, and feedstock compatibility are all explained. The economic feasibility of the methods are considered. 

Thermal depolymerisation of polystyrene is possible to given back the styrene monomer along with a number of low Molecular weight compounds. 

It has an excellent outdoor life period and good strength. It is amorphous because of the presence of bulky side groups in the molecules. It is resistant to many chemicals but soluble in organic solvents like ketones, chlorinated hydrocarbons and esters. It can be thermally depolymerised to give back the entire quantity of monomer. 

Bouchardat s work on natural rubber he demonstrates the thermal depolymerisation to isoprene and the reverse polymerisation of isoprene... 

It was established, that the insertion of cyclic fragments in the side chain hinders the chain transfer reactions that proceed with release of the D -type cycles during thermal depolymerisation. The conformational and hydrodynamic properties of some polymethylsiloxanes with organocyclosiloxane fragment as pendant groups have been studied. 

The most effective method of modification of linear organosilicon polymers is the insertion of various elements or groups with a different chemical nature into the structure of the macromolecular chain. As a result of the insertion in the dimethylsiloxane chain of different fragments there are changes in the physical chemical properties [5]. The insertion of the cyclic fragments in the main linear dimethylsiloxane chain hinder the chain transfer reactions, which proceed with the release of D -type (where D = Me2SiO) cycles during the thermal depolymerisation, that raises the thermal-oxidative stability of the polymers [6]. 

Thermal depolymerisation products are monomers (or co-monomers in the case of copolymer degradation), i.e., polymethacrylates and PS degrade by depolymerisation mostly - and monomeric-dimeric and trimeric nnits (methacrylates or styrenes, respectively), split off from the system. Both are snspected of cansing cancer. For PS, monomer yield of thermal depolymerisation can be as high as 40%, while PMMA can decompose to the monomers completely above 300 C [79, 80]. 

The three major thermal depolymerisation processes are pyrolytic liquefaction, gasification and hydrogenation. If heat is applied to waste plastics in the absence of air the process is called pyrolysis if done with a controlled oxygen flow it is called gasification. Hydrogenation is a modification of the refining process for petroleum. 

The thermal depolymerisation of condensation polymers through thermofracto-graphy is excellently suited to group analysis of this polymer class but definitive identification of the particular type is guaranteed in only few cases. This is due to the lack of uniformity of the thermolysis reaction and the resulting variety of thermolysis products. Further, there is no thin-layer chromatographic system which... 

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