Styrenics heat stabilizers

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). 

Acid-treated clay catalyst Engelhard F-24 was found to be very effective for the alkylation of diphenylamine (DPA) with an olefin such as a-methyl styrene (AMS) to obtain a mixture of mono and dialkylated diphenylamines (Chitnis and Sharma, 1995). For example, alkylation of DPA with AMS produced a mixture of 4-(a,a-dimethyl benzyl) diphenylamine, i.e. monocumyl-diphenylamine (MCDPA) and 4,4 -bis(a,a-dimethylbenzyl) diphenylamine, i.e. dicumyldiphenylamine (DCDPA) (Eqn.(l 1)). The dialkylated diphenylamine, i.e. DCDPA, is indu.strially important as an antioxidant and heat stabilizer. DCDPA is reported to be an ideal antioxidant for many materials like polyethylene, polypropylene, polyether polyol, polyacetals, nylon 6, synthetic lubricants, hot melt adhesives, etc. 

Further evidence of the heat stability of the PTHF blends with PVC and CPVC was obtained in an oven aging test at 350°F. Samples were removed from the oven at 10-minute intervals and compared with similarly treated blends containing the impact modifier, a styrene/acrylonitrile/butadiene terpolymer. The blends containing PTHF were outstanding in their resistance to discoloration at elevated temperature. The blends containing the terpolymer showed some darkening at 90 minutes and were brown at 370 minutes. The PTHF blends did not discolor at all until 190 minutes, and 920 minutes were required for the... 

The major general purpose rubbers are natural rubber, styrene-butadiene rubber, butadiene rubber, isoprene rubber, and ethylene-propylene rubber. These rubbers are used in tires, mechanical goods, and similar applications. Specialty elastomers provide unique properties such as oil resistance or extreme heat stability. Although this differentiation is rather arbitrary, it tends also to classify the polymers according to volumes used. Styrene-butadiene rubber, butadiene rubber, and ethylene-propylene rubber account for 78 percent of all synthetic rubber consumed. 

It is important in this or any other heat stability test to mold the natural resin as a control. Some resins, especially acrylonitrile butadiene styrene (ABS), darken considerably when heated above a particular threshold temperature. In the case of ABS, the butadiene rubber component may begin to go yellow and dark over 450°F. Although the customer may set its machines below 450°F barrel temperatures, shear heating or heating in the hot runner manifold could yield local melt temperatures in excess of 500°F and burn the natural resin. 

Ethanox 376 is a stabilizer that provides heat stability by preventing thermo-oxidative degradation during processing and service life. It provides compatibility with resins and extraction resistance. It can be applied in polyolefins, such as polyethylene, polypropylene, polybutene-1 and other polymers such as engineering plastics, styrenes, polyurethanes, saturated and unsaturated elastomers, styrenics, rubber modified styrenics, segmented block copolymers, and PVC. 

Non-discoloring, sulfur containing phenolic antioxidant and stabilizer that provides long-term heat stability by preventing thermo-oxidative degradation. Used for the process stabilization of polyethylene wire and cable resins for polyethylene during extruder compounding. Can also be applied in styrenic polymers, polypropylene, elastomers such as EPDM and SBR and for carboxylated SBR latex, polybutadiene rubber and polyisopropene rubber. 

Figure 2. Effect of the amount of methacrylic olygomer on the properties of polysulphone-styrene composite materials (a) tensile strength, (b) heat stability (VST).

Antioxidants. Certain components of heat stabilizers (polyols, phosphites) also serve as antioxidants. The protection against oxidative attack is not as great in PVC as it is in certain ethylenically unsaturated materials. However, PVC compounds may require protection in the high-temperature service as in electrical wire insulation bisphenol A is often incorporated into the plasticizer for this purpose. Impact modifiers containing unsaturation such as acrylonitrile-butadiene-styrene polymers often require antioxidant protection. Hindered phenols such as butylated hydroxytoluene are often used for this purpose, especially when outdoor applications are involved. 

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. 

Chem. Descrip. Ethyl-2-cyano-3,3-diphenylacrylate CAS 5232-99-5 EINECS/ELINCS 226-029-0 Uses UV stabilizer for plastics (PS, styrene, copolymers, polycarbonate, PVC), acrylic coatings, varnishes, nitrocellulose and other lacquers, PUs, polyester gelcoats, inks, acrylic and vinyl adhesives Features Good heat stability... 

ABS resins are composed mainly of styrene (over 50 %) and varying amounts of acrylonitrile comonomer in the SAN polymer backbone and polybutadiene as a chemically grafted rubber dispersion. While the styrene units provide the rigidity and ease of processability, the acrylonitrile units contribute to the chemical resistance and heat stability. The polybutadiene rubber particles in ABS provide the toughness and impact strength. StmcturaUy, ABS itself is a two-phase polymer blend system with the dispersed polybutadiene rubber phase (0.1-1 pm) embedded in a continuous matrix of SAN copolymer. Thus, the composition of ABS resins can vary widely, allowing the production of several grades tailored for different end-use applications. 

FDA sanctioned heat stabilizer and antioxidant used in styrene-butadiene copolymers. 

Methacrylate butadiene styrene MBS) impact modifiers represent the highest volume of styrenic-type impact modifiers. The modifier is used in transparent packaging applications because of its clarity. MBS modifiers have FDA clearance and deliver impact efficiency and low temperature impact, with slight improvements over acrylonitrile butadiene styrene (ABS) impact modifiers in color, heat stability, clarity and weatherability. 

Recent developments include systems with better colour fidelity and handling properties. Dover s Doverphos HiPure 4 and 4-HR are high-purity tris-nonylphenyl phosphite (TNPP) processing and heat stabilizers, claimed to reduce overall costs. With 0.1% residual nonyl phenol, they are FDA-approved for food-contact applications and also used in medicals, colour-critical polyolefins, and styrenic block copolymers. They are effective also in acrylics, elastomers, nylon, polycarbonate, polyurethanes, polystyrene. PVC. ABS, and PET. 

Dexco (Exxon/Dow) has developed styrenic block copolymers as compatibilizers. to improve impact strength. Vector SBS (not containing halide salts) gives better heat stability than conventional block copolymers due to absence of residual halides, which can lead to property degradation. It can boost ultimate elongation and impact strength of PS waste. 

Pigment Red 53 1 (4) - Red Lake C is almost identical in shade to Barium 2B. Its slightly better heat stability of 288°C allows its use in ABS (aciylonitrile-butadiene-styrene) where lightfastness is not important. Caution should be used in plasticized PVC since migration can occur. 

PSAN is probably the most important copolymer of styrene because of its improved chemical resistance, improved mechanical properties, and better heat stability. The disadvantage is that a higher portion of acrylonitrile often yields yellow products [129,130]. 

Cationic and anioiuc antistatic agents perform best in polar polymers, but their interaction with PVC heat stabilizers must be considered. Fatty acid based amines can react with the chlorine in PVC. Nonionic antistats are deployed in polyolefins, ABS and styrene polymers. 

The general structure of a t5 ical azo dye is shown in Figure 1. All azo dyes contain the bond -N=N-. One of the largest families of dyes, the azo dyes have found their way into many polymer applications. This is mainly due to their extreme brightness and low cost. Many of these dyes are staples of the color palette, especially for styrene, acrylics, some polyesters and minor ABS applications. Heat stability needs to be monitored but the light stability is acceptable for many low end applications. 

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