Thermal stabilizers polyolefins

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. 

This polymer is typical of the aliphatic polyolefins in its good electrical insulation and chemical resistance. It has a melting point and stiffness intermediate between high-density and low-density polyethylene and a thermal stability intermediate between polyethylene and polypropylene. 

Thermal stabilization of polyolefins has been first demonstrated for low-molecular models-normal structure alkanes [29]. It has been shown that metallic sodium and potassium hydroxide with absorbent birch carbon (ABC) as a carrier are efficient retardants of thermal destruction of n-heptane during a contact time of 12-15 s up to the temperature of 800°C [130]. Olefins and nitrous protoxide, previously reported as inhibitors of the hydrocarbon thermal destruction, are ineffective in this conditions. 

Polyolefins are exposed to the effects of high temperatures initially during processing and fabrication and subsequently during in-service. Thermal stabilization of po-... 

The lower thermal stability of natural fibers, up to 230°C, the thermal stability is only small, which limits the number of thermoplastics to be considered as matrix materials for natural fiber composites. Only those thermoplastics whose processing temperature does not exceed 230°C are usable for natural fiber reinforced composites. These are, most of all, polyolefines, such as polyethylene and polypropylene. Technical thermoplastics, such as poyamides, polyesters, and polycarbonates, require... 

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... 

The PET polymer structure can also be generated from the reaction of ethylene glycol and dimethyl terephthalate, with methyl alcohol as the byproduct. A few producers still use this route. The aromatic rings coupled with short aliphatic chains are responsible for a relatively stiff polymer molecule, as compared with more aliphatic structures such as polyolefin or polyamide. The lack of segment mobility in the polymer chains results in relatively high thermal stability, as will be discussed later. 

Among the spectrum of melt-spinnable fibers such as polyolefins and nylons, PET stands at the upper end in terms of crystalline melt temperature and glass transition temperature. This provides superior dimensional stability for applications where moderately elevated temperatures are encountered, e.g. in automobile tires or in home laundering and drying of garments. The high thermal stability results from the aromatic rings that hinder the mobility of the polymer chain. 

Polyolefins and PVC Improving thermal stability, uniformity, and fine structure for packaging and insulation, rubber sheeting Cross-linking with high-energy electrons... 

All polyolefins have low dielectric constants and can be used as insulators, ill particular, PMP has llie lowest dielectric constant among all synthetic resins. As a result, PMP has excellent dielectric properties and a low dielectric loss factor, surpassing those of other polyolefin resins and polytetrafluoroethylene (Teflon) These properties remain nearly constant over a wide temperature range. The dielectric characteristics of polyfvinylcyclohexane) are especially attractive its dielectric loss remains constant between-180 and 160 C, which makes it a prospective high frequency dielectric material of high thermal stability. 

Polystyrene has somewhat lower thermal stability than the polyolefins and its pyrolysis can be undertaken between 380 and 420°C without producing gases or leaving significant... 

Various polyesters derived from phosphorous or phosphoric acids were prepared. Efiicient polyphosphites were synthesised in the early 196(. Polyphosphite prepared from 152 and 4,4 -isopropylidenebis(cyclohexanol) was tested as a thermal stabilizer for PC [199] or as secondary AO for radiation sterilized EPM [200]. Built-in phosphites obtained by transesterification of triallcylphosphite with 4,4 -isopro-pylidenebisphenol or 4,4 -thiobisphenol possess antioxidant properties in polyolefins. Stabilizer containing phosphite moiety 153 was prepared from tris(2-hydroxy-ethyl)isocyanate, decyl alcohol and triphenylphosphite [201]. Various phosphites were derived firom polynuclear phenols or dihydric phenols. For example, a polycondensate prepared by reaction of phosphorus trichloride with 2,5-di-rert-butylhydroquinone was tested as heat and light stabilizer for PP [202], A linear polyester with a built-in phenolic moiety was synthesised from (2,6-di-tm-butyl-4-methylphenyl)bis(6-hydroxyhexyl)phosphite and dimethyl terephthalate [203]. 

An interesting case of halogenated polyolefin is that of halogenated poly(vinyl chloride). After-chlorination of PVC improves thermal stability of the polymer. The distribution of chlorine atoms in chlorinated PVC has been studi successfully using Py-GC [57]. 

Naugard 445 is non-discoloring aromatic amine antioxidant that works synergistically with phosphites and phenolic antioxidants as a thermal stabilizer in polyolefins, styrenics, polyols, hot melt adhesives, lubricants, and polyamides. 

Al-Malaika, S. Scott, G. Thermal stabilizers of polyolefins. In Degradation and Stabilisation of Polyolefins, Allen, N.S., Ed. Applied Science London, 1983 247-281. 

Unfortunately, because of low thermal stability a great number of these dyes found their application for dyeing polyolefines and polystyrenes and in the case of bath dyeing for PA. But despite this interest in them, and first of all from the point of view of practical use of luniinophors, does not fall. And of course their relative accessibility plays unimportant role. 

A non-woven web having antimicrobial properties is made from a melt extmdable composition, which contains a polyolefin and an antimicrobial siloxane quaternary ammonium salt, which may be a trisiloxane having a pendent quatemaiy ammonium group and a molec.wt. of from about 600 to 1,700 or an ABA-type siloxane having a polydispersity of up to about 3.0 and a weight-average molec.wt. of from about 800 to 2,000 in which a central siloxane moiety is terminated at each end by a quatemaiy ammonium salt group. The anion can be any anion, which does not adversely affect the thermal stability of the salt. 

It is generally accepted that thermal stability of polymer nanocomposites is higher than that of pristine polymers, and that this gain is explained by the presence of anisotropic clay layers hindering diffusion of volatile products through the nanocomposite material. It is important to note that the exfoliated nanocomposites, prepared and investigated in this work, had much lower gas permeability in comparison with that of pristine unfilled PE [12], Thus, the study of purely thermal degradation process of PE nanocomposite seemed to be of interest in terms of estimation of the nanoclay barrier effects on thermal stability of polyolefin/clay nanocomposites. 

Fig. 19. Effect of branching on the thermal stability of various polyolefins [39).

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