Polyolefins degradation/stabilization

Spivack J D, Pastor S D, Patel A and Steihuebel L D (1985) Bis- and trisphosphites having dioxapho-sphepin and dioxaphosphocin rings as polyolefin processing stabilizers, In Polymer stabilization and degradation, Klemchuk P (Ed), ACS Symp Ser 280 247-257. 

M. Predel and W. Kaminsky Pyrolysis of Mixed Polyolefins in a Fluidised-Bed Reactor and on a Pyro-GC/MS to Yield Aliphatic Waxes. Polym. Degrad. Stabil, 70, 373 (2000). 

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. 

George, G.A., Celina, M., VassaUo, A.M., Cole-Clarke, PA. Real-time analysis of die tiiermal oxidation of polyolefins by FT-IR emission. Polym. Degrad. Stabil. 48, 199-210 (1995). doi 10.1016/0141-3910(95)00035-K... 

It has been recognized for many years that polyolefins are susceptible to oxidative degradation, and a great deal of research has been done to determine why and how, and what to do about it. The reader is encouraged to consult monographs and review articles (8-13) in order to acquire some of the details and complexities of polyolefin oxidation (see also Degradation Stabilization). In essence, oxidative degradation can be summarized as follows. 

TPE-0 generally exhibits good aging resistance. The thermal-oxidative behavior largely corresponds to that of polyolefins. Suitable stabilization protects them from thermal- oxidative degradation. Elastomer phases with unsaturated structural elements can influence thermal-oxidative degradation negatively [86]. 

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]. 

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. 

When the degradation of a polymer gives rise to free radicals, the addition of compounds that can trap and neutralize these radicals is the logical solution. For example, polyolefins are stabilized by addition of substituted phenols or polyphenols, which act as antioxidants ... 

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... 

Polyolefins are intrinsically unsuitable for outdoor durable applications since the will easily photo-oxidize in exterior conditions. However, their combination of low cost, ease of processing, and recyclability continues to promote research into effective methods of photo stabilization of polyolefins. Adequate pigment levels will afford some protection from UV radiation to the host polyolefin. UV stabilizers and antioxidants, however, need to be added to the durable in order to ensure long term performance in outdoor environments. There is usually negligible to no protection of colorants from photo degradation with these same polymer additives. 

Because of the high melt viscosity of polyolefins, normal spinning melt temperatures are 240—310°C, which is 80—150°C above the crystalline melting point. Because of the high melt temperatures used for polyolefin fiber spinning, thermal stabilizers such as substituted hindered phenols are added. In the presence of pigments, the melt temperature must be carefully controlled to prevent color degradation and to obtain uniform color dispersion. 

S. Al-Malaika and G. Scott "Thermal Stabilization of Polyolefins," iu N. S. AUen, ed.. Degradation and Stabilisation of Polyolefins, AppUed Science Pubhshers Ltd., London, 1983, pp. 247—281. 

Poly(hydrosilane)s have been successfully applied as processing stabilizers for organic polymeric materials subject to oxidative degradation. The degradation of polyolefins during processing takes place by a widely accepted... 

Thermal stabilizers combat degradation by removing the hydrogen chloride that is generated. Additionally, we treat polyvinyl chloride more gently than we do polyolefins. We use milder processing conditions (lower temperatures and lower shear rates) and add lubricants to... 

Nonwoven materials such as cellulosic fibers have never been successfully used in lithium batteries. This lack of interest is related to the hygroscopic nature of cellulosic papers and films, their tendency to degrade in contact with lithium metal, and their susceptibility to pinhole formation at thickness of less than 100 fjim. For future applications, such as electric vehicles and load leveling systems at electric power plants, cellulosic separators may find a place because of their stability at higher temperatures when compared to polyolefins. They may be laminated with polyolefin separators to provide high-temperature melt integrity. 

The material considered here allows us to understand the influence of sterically hindered amines, which act as stabilizers against the light-induced degradation of polyolefines. The sterically hindered amines easily undergo oxidation after cation-radical formation ... 

Uses. Solvent for polymers polymerization catalyst stabilizer against thermal degradation in polystyrene UV stabilizer in polyvinyl and polyolefin resins... 

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