NEW PERSPECTIVES OF POLYOLEFIN PROCESSING STABILIZATION

摘要

Processing of polyolefins in the melt can be regarded as a severe threat to the matrix causing different kind of chemical reactions which lead to major changes in the polymer structure and properties. The overall reactions depend on the number of weak sites (branching points, unsaturated functions and oxidized groups) in the polymer chain and on the processing conditions. Rates and direction of the reactions can be modified by processing stabilizers, for which mainly a combination of hindered phenols and phosphorous based secondary antioxidants is used. While the reaction mechanisms of the hindered phenols are widely investigated, less attention is paid to those of the phosphorous based compounds. The reactions of different trivalent organophosphorous derivatives (phosphites and phosphonites) are described by the same schemes, which define the hydroperoxide decomposition and reactions of peroxy- and alkoxy-radicals together with the oxidation of the additive to the corresponding pentavalent phosphorus compound. Phosphorous antioxidants of various chemical structures, however, show different thermal and color stabilizing efficiency, probably originating from different reaction mechanisms. In the present work the effect of a new type of a phosphine based processing stabilizer, 1,3-diphenyl-phosphino-2,2-dimethyl-propane (MM 6549/072), is described in detail and compared with derivatives of conventional phosphorous stabilizers (sterically hindered organophosphites and the organophosphonite Sandostab~® P-EPQ~®) on the processing of polyolefins.