Poly heat stability

Poly(vinyl chloride). To be converted into film, poly(viayl chloride) [9002-86-22] (PVC) must be modified with heat stabilizers and plasticizers, which increase costs. Plasticized PVC film is highly transparent and soft, with a very high gas-permeation rate. Water-vapor transmission rate is relatively low. At present, PVC film is produced by blown-film extmsion, although casting and calendering are employed for heavier gauges (see Vinyl POLYAffiRS). 

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometaUic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinyhdene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. Without the use of heat stabilizers, PVC could not be the widely used polymer that it is, with worldwide production of nearly 16 million metric tons in 1991 alone (see Vinyl polymers). 

Polymers. In combination with various metal salts, sorbitol is used as a stabilizer against heat and light in poly(vinyl chloride) (qv) resins and, with a phenohc antioxidant, as a stabilizer in uncured styrene—butadiene mbber (qv) compositions and in polyolefins (see Heat stabilizers Olefin POLYMERS Rubbercompounding). Heat-sealable films are prepared from a dispersion of sorbitol and starch in water (255). Incorporation of sorbitol in coUagen films gready restricts their permeabiUty to carbon dioxide (256). 

Plastics and Synthetic Products. To prevent degradation of plastics at elevated processing temperatures, it is necessary to use suitable heat stabilizers. Eor example, flexible poly(vinyl chloride) (PVC) manifests uncontroUed color development in the absence of stabilizers. Accordingly, cadmium salts of organic acids are typically used in a synergistic combination with corresponding barium salts, in about a 1 3 cadmium barium ratio, to provide a cost-competitive heat stabilizer for flexible PVC. 

Neodecanoic acid is also used as the carrier for metals in poly(vinyl chloride) heat stabilizers (qv). Metals used in this appHcation include barium, cadmium, and zinc. Tin as the neodecanoate salt has also been claimed as a heat stabilizer for maleic anhydride (97). 

In the massive form poly(vinyl chloride) is a colourless rigid material with limited heat stability and with a tendency to adhere to metallic surfaces when heated. For these, and other, reasons it is necessary to compound the polymer with other ingredients to make useful plastics materials. By such means it is possible to produce a wide range of products, including rigid piping and soft elastic cellular materials. 

Poly(N-phenyl-3,4-dimethylenepyrroline) had a higher melting point than poly(N-phenyl-3,4-dimethylenepyrrole) (171° vs 130°C). However, the oxidized polymer showed a better heat stability in the thermogravimetric analysis. This may be attributed to the aromatic pyrrole ring structures present in the oxidized polymer, because the oxidized polymer was thermodynamically more stable than the original polymer. Poly(N-phenyl-3,4-dimethylenepyrroline) behaved as a polyelectrolyte in formic acid and had an intrinsic viscosity of 0.157 (dL/g) whereas, poly(N-pheny1-3,4-dimethylenepyrrole) behaved as a polyelectrolyte in DMF and had an intrinsic viscosity of 0.099 (dL/g). No common solvent for these two polymers could be found, therefore, a comparison of the viscosities before and after the oxidation was not possible. 

P.O.72 is as well suitable for the application in polystyrene and ABS. Colorations of PS in 1/3 SD, requiring only 0.15% pigment, exhibit a heat stability of 280°C, colorations of ABS are stable up to 290°C. In these media the lightfastness equals step 8 on the Blue Scale. Pigment concentration of less than 0.1% in poly-oxymethylen (POM, polyacetales) may lead to coating of the manufacturing equipment (see plate out, Sec. 1.6.4.1). 

The ball milling of poly(vinyl chloride) and acrolein gave a product with improved heat stability and electrical properties (25). The milling was performed at 108 rpm and at room temperature for four hours using porcelain balls 1.2-2 cm in diameter. After milling with 20% of acrolein for two hours, the decomposition temperature of the polymer product increased from 150 to 160° C and the darkening temperature from 200 to 220° C. After four hours the two temperatures were, respectively, 220 and 280° C. The ball milled product, also, showed a 37-fold improvement in volumetric resistance and a 15000-fold improvement in surface electrical resistance over the original poly(vinyl chloride). 

This polymer has a crystal structure different from the normal hexagonal poly(thioformaldehyde). At 153° C it changes to the hexagonal configuration. Credali and Russo (8) state that this new form ran be heat-stabilized by acetylation of its end groups and that the acetylated polymer does not degrade at 250-260° C, a temperature range at which ordinary poly(thioformaldehyde) is very unstable. 

Ethylhexanal, the reduced aldol condensation product of -butyraldehyde, is converted into 2-ethylhexanoic acid [149-57-5], which is converted primarily into salts or metal soaps. These are used as paint driers and heat stabilizers for poly (vinyl chloride). 

Poly(vinyl chloride). PVC is one of the most important and versatile commodity polymers (Table 4). It is inherently flame retardant and chemically resistant and has found numerous and varied applications, principally because of its low price and capacity for being modified. Without modification, processibility, heat stability, impact strength, and appearance all are poor. Thermal stabilizers, lubricants, plasticizers, impact modifiers, and other additives transform PVC into a very versatile polymer (257,258). 

Bourbigot et al.85 at Lille have used poly(vinylsilsesquioxane) (POSS) in PP (110 wt%) to melt spin filaments, which were then knitted into fabrics. POSS was thermally stable and no degradation was detected in the processing conditions. They have tested the flammability of the fabrics using cone calorimetry. POSS presence had minimal effect on peak heat and total heat release values of PP fabric, but delayed the TTI. This behavior of POSS is opposite to that of layered silicates, which have minimal effect on TTI, but reduce PHRR. Authors claim that POSS does not act as a FR but only as a heat stabilizer via a decrease of the ignitability. 

The Control of Thermal Degradation Pathways in Poly(vinyl chloride) by Heat-Stabilizing Additives... 

Here we report the use of a readily prepared polymer immobilised TEMPO as a catalyst for alcohol oxidations.15 It was derived from a commercially available oligomeric, sterically hindered amine, poly[[6-[(l,l,3,3-tetramethylbutyl)amino]-l,3,5-triazine-2,4-diyl] [2,2,6,6-teramethyl-4-piperidinyl)-imino]-1,6-hexane-diyl[(2,2,6,6-tetramethyl-4-piperidinylimino]], better known as Chimassorb 944 (MW 3000 see figure 3 for structure). This compound is used as an antioxidant and a light stabiliser for plastics. It contributes significantly to the long-term heat stability of polyolefins and has broad approval for use in polyolefin food packaging.16... 

An additive system was developed for poly(vinyl chloride) for medical applications. The additives include primary stabilisers (Ca-Zn stearate and Zn stearate), secondary stabilisers (epoxides) and lubricants (ethylene bisamide and high density polyethylene), to improve melt processing and heat stability. The use of the stabilisers resulted in reduced equipment down-time, increased the level of recycled material which could be incorporated, and enhanced the product characteristics, including colour, clarity, blush, aqueous extractables and particle generation. 5 refs. 

It should be noted that the SIS block copolymer is unstable in high temperature (100-150°C) and oxygen because of the presence of a double bond in the poly-isoprene subunit. Hence, the addition of antioxidants such as butylhydroxytoluene is necessary in the hot melt coating process. In addition, heat stability is also required in manufacturing drugs. 

Recently Purac [223] has developed a PLA compound with heat stability and impact strength comparable to poly(acetonitrile butadiene styrene) (ABS) in injection moulding apphcations based on the stereocomplex technology. 

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