Heat stabilizers, additive

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. 

The structure shown in Figure 1 is the parent compound of the phthalocyanine pigments. The unsubstituted (no halogen atoms) ring system yields a blue pigment which is available in two crystal forms, alpha (red shade) and beta (green shade). The commercial pigments usually have some Cl substitution, which provide additional heat stability. 

Compounds of adipates, palmitates. sebacates. and stearates are used as lubricants and plasticizers for many types of plastics, including PVC and engineering plastics. Cetyl palmitate can be used in place of natural wax and can act as a lubricant for engineering plastics. Octyl and iso-octyl palmitate are clear oily liquids with anti-blocking properties and additional heat stability that are also used as plasticizers for PVC and as a viscosity modifier for plastisols. The stearates are used, broadly, as viscosity stabilizers in PVC and lubricant/flow promoters in PS and ABS, particularly where low-temperature properties are required. Cetyl stearate is used as a lubricant for engineering plastics. 

Description Cetyl palmitate heavy, rich, non-greasy used in place of natural wax lubricant for engineering plastics. Octyl palmitate, iso-octyl palmitate clear oily liquid, virtually insoluble in water but readily soluble in vegetable and mineral oils plasticizer for PVC with anti-blocking properties and additional heat stability viscosity modifier for plastisols ... 

Pigment Blue 15 1 is a stabilized or noncrystalUzing alpha or red shade. Because of differing types and qnahties of additives, heat stability can range from 275 to 300°C. Red shade bines are stabilized by additives or by the... 

Pationic 902 is a distilled (95% minimum, monoester) glycerol monostearate derived from fully hydrogenated animal fat and produced to polymer additive heat stability requirements. 

Chemical name polyamide Generic name nylon Common name nylon Type 6/6 homopolymer Reinforcement 30% glass fiber Required additives heat stabilizer Permissible additives internal lubricant Color natural color (no colorant)... 

The investigations were performed with different non-reinforced engineering thermoplastics PA66 (Ultra-mid A3), additionally heat-stabilized PA66 (Ultramid A3H2) and PA6 (Ultramid B3). The materials were modi-... 

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). 

The discussion centers on heat stabilizers for PVC because this polymer is the most important class of halogenated polymers requiring these chemical additives. PVC of ideal chemical stmcture (1) should be a relatively stable compound as predicted from model studies using 2,4,6-trichloroheptane [13049-21-3] (2) (1). 

Cost bilizers. In most cases the alkyl tin stabilizets ate particularly efficient heat stabilizers for PVC without the addition of costabilizers. Many of the traditional coadditives, such as antioxidants, epoxy compounds, and phosphites, used with the mixed metal stabilizer systems, afford only minimal benefits when used with the alkyl tin mercaptides. Mercaptans are quite effective costabilizets for some of the alkyl tin mercaptides, particularly those based on mercaptoethyl ester technology (23). Combinations of mercaptan and alkyl tin mercaptide ate currendy the most efficient stabilizers for PVC extmsion processes. The level of tin metal in the stabilizer composition can be reduced by up to 50% while maintaining equivalent performance. Figure 2 shows the two-roU mill performance of some methyl tin stabilizers in a PVC pipe formulation as a function of the tin content and the mercaptide groups at 200°C. 

The metal coordination complexes of both sahcylaldehyde phenyhiydrazone (91) and sahcylaldoxime provide antioxidant (92) protection and uv stabihty to polyolefins (see Antioxidants). In addition, the imines resulting from the reaction of sahcylaldehyde and aromatic amines, eg, p- am in oph en o1 or a-naphthylamine, can be used at very low levels as heat stabiLizers (qv) in polyolefins (93). 

Nickel dialkyldithiocarbamates stabili2e vulcani2ates of epichlorhydrinethylene oxide against heat aging (178). Nickel dibutyldithiocarbamate [56377-13-0] is used as an oxidation inhibitor in synthetic elastomers. Nickel chelates of substituted acetylacetonates are flame retardants for epoxy resins (179). Nickel dicycloalkyldithiophosphinates have been proposed as flame-retardant additives for polystyrene (180—182) (see Flame retardants Heat stabilizers). 

The phosphonate esters, HP(=0(OR)2, of alkylated phenols are used extensively as lubricating-oil additives to control bearing corrosion and oxidation, and to impart antimst properties as stabilizers, as antioxidants (qv) and flame retardants in plastics, as specialty solvents, and as intermediates (see Corrosion AND corrosion control Heat stabilizers). 

Organophosphoms compounds, primarily phosphonic acids, are used as sequestrants, scale inhibitors, deflocculants, or ion-control agents in oil wells, cooling-tower waters, and boiler-feed waters. Organophosphates are also used as plasticizers and flame retardants in plastics and elastomers, which accounted for 22% of PCl consumed. Phosphites, in conjunction with Hquid mixed metals, such as calcium—zinc and barium—cadmium heat stabilizers, function as antioxidants and stabilizer adjutants. In 1992, such phosphoms-based chemicals amounted to slightly more than 6% of all such plastic additives and represented 8500 t of phosphoms. Because PVC production is expected to increase, the use of phosphoms additive should increase 3% aimually through 1999. 

Since acetal resins are degraded by ultra violet light, additives may be included to improve the resistance of the polymer. Carbon black is effective but as in the case of polyethylene it must be well dispersed in the polymer. The finer the particle size the better the ultra violet stability of the polymer but the poorer the heat stability. About 1.5% is generally recommended. For white compounds and those with pastel colours titanium dioxide is as good in polyacetals as most transparent ultraviolet absorbers, such as the benzophenone derivatives and other materials discussed in Chapter 7. Such ultraviolet absorbers may be used for compounds that are neither black, white nor pastel shade in colour. 

The laminates are employed mainly where an intermediate degree of heat stability is required which does not Justify the use of the more expensive silicone and other laminates considered in Chapter 29. They have additional advantages over the silicones in their ease of forming by wet lay-up techniques and the greater strength of the laminates. 

The early 1980s saw considerable interest in a new form of silicone materials, namely the liquid silicone mbbers. These may be considered as a development from the addition-cured RTV silicone rubbers but with a better pot life and improved physical properties, including heat stability similar to that of conventional peroxide-cured elastomers. The ability to process such liquid raw materials leads to a number of economic benefits such as lower production costs, increased ouput and reduced capital investment compared with more conventional rubbers. Liquid silicone rubbers are low-viscosity materials which range from a flow consistency to a paste consistency. They are usually supplied as a two-pack system which requires simple blending before use. The materials cure rapidly above 110°C and when injection moulded at high temperatures (200-250°C) cure times as low as a few seconds are possible for small parts. Because of the rapid mould filling, scorch is rarely a problem and, furthermore, post-curing is usually unnecessary. 

PVC on its own is extremely heat- and shear-sensitive and cannot be processed into finished goods, as it starts degrading at temperatures considerably lower than those required to process it. The processing of PVC requires a number of additives. These include heat stabilizers, impact modifiers, processing aids, and lubricants. 

Many additives are used with PVC polymers such as plasticizers, antioxidants, and impact modifiers. Heat stabilizers, which are particularly important with PVC resins, extend the useful life of the finished product. Plastic additives have been reviewed by Ainsworth. 

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