Polyolefins degradable

This equation seems to be a key reaction point in the antioxidant action of these amines—>N radicals in the presence of oxygen are transformed via peroxy radical intermediates into nitroxyl radicals. The nitroxyl radicals are very persistent and react efficiently with radicals produced on polyolefine degradation. Such radical interception blocks the chain in radical oxidation and therefore causes the antioxidant activity of sterically hindered amines (Brede et al. 1998). 

V. Dufaud and J. M. Basset, Catalytic Hydrogenolysis at Low Temperature and Pressure of Polyethylene and Polypropylene to Diesels or Lower Alkanes by a Zirconium Hydride Supported on Silica-Alumina a Step Toward Polyolefin Degradation by the Microscopic Reverse of Ziegler-Natta Polymerization, Angew. Chem. Int. Ed., 37, 806-810 (1998). 

Homogeneous catalysts used for polyolefin degradation have mostly been classical Lewis acids such as AICI3, metal tetrachloroaluminates melts and more recently, new catalytic systems based on organic ionic liquids. 

V. Dufaud and J.-M. Basset, Catalytic hydrogenolysis at low temperature and pressure of polyethylene and polypropylene to diesels or lower alkanes by silica-alumina a step toward polyolefin degradation by the microscopic reverse of Ziegler-Natta polymerization, Angew. Chem. Int.Ed., (1998) 37(6) 806-810. I. Nakamura and K. Fujimoto, Development of new disposable catalyst for waste plastics treatment for high quality transportation fuel. Catalysis Today, 27,175-179 (1996)... 

Polyolefin degradation comprises of initiation, propagation and termination steps 2.2.1 Initiation... 

Chemical breakdown usually involves oxidative chain reactions that cause embrittlement of semicrystalline polymers and discoloration of poly(vinyl chloride) and polymers with aromatic groups. The reactions are complicated by the presence of transient intermediates and by rates that depend on minute concentrations of molecular defects, impurities and additives. They also depend on several important piiysi-cal factors outlined in this brief overview of polyolefin degradation, two of these factors, the transfer of excitation energy and the transport of products and protectants, play a major role in stabilization processes. 

Chemical processes related to polyolefin degradation and deterioration of their properties are usually linked with either the reduction of average molar mass due to the scission of bonds in the macromolecular chain or with the increase of the molar mass due to the cross-linking while the polyolefin becomes insoluble in any solvent... 

Some traces of metal and metal ions may initiate the decomposition of hydroperoxides even at room temperature and contribute to the polyolefins degradation as well. The traces of metal ions are to a more or less extent present in any polyolefin from the catalyst residues and may affect the polymer oxidation and... 

The formation of volatile degradation products as observed by non-isothermal thermogravimetry is a complex process. The non-isothermal thermogravimetry curve that is apparently composed of several independent processes was described by the first-order scheme, i.e. — = km where t is time, m is the actual mass of the degraded sample, and k is the rate constant of polyolefin degradation to volatile products. In a non-isothermal mode,... 

Al-Malaika, S. and Scott, G. (1983) Photostabilisation of polyolefins. Degradation and Stabilisation of Polyolefins, (ed. N.S. Allen), Applied Science, London, pp. 283-336... 

Naturally Occurring Polyolefinic Degraded and/or Modified Isoprenoid Compounds... 

The oxygen uptake curve for polyolefin degradation has an S shape (similar to some curves for the evolution of products (see Figs. 3 and 4) with a pronounced induction period whose duration increases with the stability of polymer and varies with the reaction conditions [92]. The initiation by heat leads to a longer induction period than in photo-oxidation (Fig. 5) and this induction period decreases with increasing temperature [4, 92, 117]. 

Polyolefin degradation and decomposition constitutes the topic of an enormous number of publications, so that it is practically impossible to cite them all. Most of... 

As already shown, as polyolefin degradation may occur in every stage of the polymer s life, it is advisable to add some kind of stabilization as early as possible, even in the polymerization process, or to add the antioxidant before the polymer comes into contact with the air. 

While most plastics are produced, fabricated and used today with die help of additives of various t5qies, the emphasis here is on those used to enhance the usefulness of polyolefins. Thousands of publications in the past 35 years deal with various facets of polyolefin degradation and stabilization. The interested reader is urged to consult monographs and reviews in articles " to obtain a feel for this complex and fascinating area of endeavour. It... 

The action modes of polyolefin degradation in the presence of HA(L)S are still issues of discussion. This refers to the function of free hydroperoxides and intermediately formed dialkylketones in course of the initiation of photo-oxidation. 

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