Polyethylene peroxide cross-linking

NMR Kinetic Analysis of Polyethylene-Peroxide Cross-linking Reactions... 

Properties of peroxide cross-linked polyethylene foams manufactured by a nitrogen solution process, were examined for thermal conductivity, cellular structure and matrix polymer morphology. Theoretical models were used to determine the relative contributions of each heat transfer mechanism to the total thermal conductivity. Thermal radiation was found to contribute some 22-34% of the total and this was related to the foam s mean cell structure and the presence of any carbon black filler. There was no clear trend of thermal conductivity with density, but mainly by cell size. 27 refs. 

A high-temperature cyclic peroxyketal peroxide cross-linking agent for polyethylene has been found to function as a blowing agent as well. This is another example of dual-function additives. Activated by thiodipropionate antioxidants, it evolves COj and should be useful in making crosslinked polyethylene foams. 

Smedberg, A. Hjertberg, T. Gustafsson, B. Effect of molecular structure and topology on network formation in peroxide cross-linked polyethylene. Polymer 2003, 44, 3395-3405. 

Cross-linking polyethylene enhances its heat resistance (in terms of resistance to melt flow) since the network persists even about the crystalline melting point of the uncross-linked material. Cross-Knked polyethylene thus finds application in the cable industry as a dielectric and as a sheathing material. Three main approaches used for cross-linking polyethylene are (1) radiation cross-linking, (2) peroxide cross-linking, and (3) vinyl silane cross-linking. 

Copolymers of ethylene with a small amount of vinyl acetate are often preferred for peroxide cross-linking because the latter promotes the cross-linking process. Large amounts of carbon black may be incorporated into polyethylene that is to be cross-linked. The carbon black is believed to take part in the cross-linking process, and the mechanical properties of the resulting product are superior to those of the unfilled material. 

Cross-linking is essential in the production of elastomeric materials. Peroxide cross-linking has also been used for some plastic applications of polyethylene. What are the advantages ... 

Kolesov and Radusch prepared peroxide cross-linked binary and ternary blend SMPs from high density polyethylene and two ethylene-l-octene copolymers with medium and high degrees of branching [47]. The blends were prepared by a melt mixing and subsequently are cross-linked with 2 wt% of liquid peroxide 2,5-dimethyl-2,5-di-(tertbutylperoxy)-hexane at 190°C. The blends showed multiple shape memory behavior that appeared only at consequent stepwise application of convenient programming strains and temperatures. Obviously, that is caused by multiple melting behavior of these blends with many poorly separated peaks. 

Figure 2 Expansion characteristics of peroxide-cross-linked polyethylene. (Courtesy of Society of Plastics Engineers, Inc.)...

Peroxide Cross-Linking Polyethylene PEX-A Migration of Antioxidants... 

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