Polyolefin Rubbers

In addition to the somewhat sophisticated triblock thermoplastic elastomers described above, mention should be made of another group of thermoplastic diene rubbers. These are physical blends of polypropylene with a diene rubber such as natural rubber. These may be considered as being an extension to the concept of thermoplastic polyolefin rubbers discussed in Section 11.9.1 and although extensive experimental work has been carried out with these materials they do not yet appear to have established themselves commercially. 

These rubbers are now also being blended on a large scale with polyolefin plastics, particularly polypropylene, to produce a range of materials which at one extreme are tough plastics and at the other the so-called thermoplastic polyolefin rubbers (TPORs) (.see Section 11.9.1). 

Subsequently, much improved thermoplastic polyolefin rubbers were obtained by invoking a technique known as dynamic vulcanisation. This process has been defined (Coran, 1987) as the process of vulcanizing elastomer during its intimate melt-mixing with a non-vulcanizing thermoplastic polymer. Small elastomer droplets are vulcanized to give a particulate... 

A somewhat different approach to the production of thermoplastic polyolefin rubbers has been adopted by Allied Chemical with their ET polymers. With these materials butyl rubber is grafted on to polyethylene chains using a phenolic material such as brominated hydroxymethyl phenol. The initial grades of these polymers, which were introduced commercially towards the end of the 1970s, had polyethylene butyl rubber ratios of 50 50 and 75 25. Both low-density and high-density polyethylene-based varieties were produced. 

The minimum service temperature is determined primarily by the Tg of the soft phase component. Thus the SBS materials ctm be used down towards the Tg of the polybutadiene phase, approaching -100°C. Where polyethers have been used as the soft phase in polyurethane, polyamide or polyester, the soft phase Tg is about -60°C, whilst the polyester polyurethanes will typically be limited to a minimum temperature of about 0°C. The thermoplastic polyolefin rubbers, using ethylene-propylene materials for the soft phase, have similar minimum temperatures to the polyether-based polymers. Such minimum temperatures can also be affected by the presence of plasticisers, including mineral oils, and by resins if these become incorporated into the soft phase. It should, perhaps, be added that if the polymer component of the soft phase was crystallisable, then the higher would also affect the minimum service temperature, this depending on the level of crystallinity. 

A manufacturer considering using a thermoplastic elastomer would probably first consider one of the thermoplastic polyolefin rubbers or TPOs, since these tend to have the lowest raw polymer price. These are mainly based on blends of polypropylene and an ethylene-propylene rubber (either EPM or EPDM) although some of the polypropylene may be replaeed by polyethylene. A wide range of blends are possible which may also contain some filler, oil and flame retardant in addition to the polymers. The blends are usually subject to dynamic vulcanisation as described in Section 11.9.1. 

Thermoplastic polyolefin rubbers are usually blends based on polypropylene and ethylene-propylene rubbers. They are not resistant to hydrocarbons. 

There are two general types of polymers based on ethylene and propylene ethylene-propylene rubber (EPM) and ethylene-propylene terpolymer (EPDM). EPM accounts for approximately 20 percent of the polyolefin rubber produced. Comprising a totally saturated polymer, these materials require free-radical sources to cross-link. EPDM was developed to overcome this cure... 

Ozone (Oj) plays a significant role in oxidation and degradation of several pglyg rg s h gs polyolefins, rubber, polystyrene and polyamides . Ozone may abstract hydrogen... 

These polyolefin rubbers are produced in two main types the saturated co-polymers, ethylene propylene rubber (EPM), and the unsaturated ethylene-propylene diene terpolymer (EPDM). The monomers are co-polymerised in ziegler natta type catalysts. The EPDM types are capable of sulfur vulcanisation as they contain, in addition to olefins, a non coagulated diene as the third monomer. 

Super Nevtac 99. Seville] Pdyterpene resins tackifying resin for polyolefins, rubber, solvent and hot melt-based adbesdives. 

During the past three decades a few groups of materials have been developed that could be considered as being in this category. Designated as thermoplastic elastomers, they include (1) styrene-diene-styrene triblock copolymers (2) thermoplastic polyester elastomers and thermoplastic polyurethane elastomers and (3) thermoplastic polyolefin rubbers (polyolefin blends). 

CAS 130942-8 EINECS/ELINCS 215-17(F3 Uses Rame retardant, smoke suppressant for various thermoplastics ind. PVC and polyolefins, rubber, high-temp, adhesives and coatings Properties Wh. free-flowing powd. 10-15 mean particle size 0.4% on 325 mesh sp.gr. 2.4 bulk dens. 43 Ib/ft brightness 88+... 

Properties Lt. yel. cryst. solid insol. in water and 10% NaOH sol. in org. soivs. m.w. 263.4 m.p. 93.9 C b.p. 172 C (30 mm) flash pt. (OC) 280 F Toxicology LD50 (oral, rat) 1030 mg/kg mod. toxic by ing. irritant TSCA listed Precaution Combustible Hazardous Decomp. Prods. Heated to decomp., emits toxic vapors of NOx Uses Antioxidant in lubricants, gasoline and oils including jet engine oils, polyolefins, rubbers... 

Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of NOx and SOx Uses UV stabilizer, antioxidant for polyolefins, rubber... 

Empirical C24H41NO2 Formula HO(C6H4)NHCOCH2(CH2)isCH3 Properties Wh. to off-wh. powd. sol. in polar org. soivs. (esp. when hot), alcohol, dioxane, acetone, dimethylformamide insol. in water m.w. 375.60 m.p. 131-134 C Toxicology Irritant Precaution Combustible Uses Antioxidant and processing aid in thermoplastics, polyolefins, rubbers Manuf./Distrib. Aldrich http.V/www.sigma-aldrich.com, ChemService http //www.chemservice.com, Zeeland http //www. rutherfordchemicals. com Trade Name Synonyms Suconox-18 [Zeeland http //www. rutherfordchemicals. com. Seal Sands Chems. Ltd... 

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