Styrenic TPEs

Functionalization hydrogenated styrenics TPEs, Shell (Shell FG)... 

In this type of styrenic TPE the polybutadiene mid-block used in the SBS types is replaced with ethylene-butylene which is saturated ... 

Seeman s Composite Resin Infusion Moulding Process Styrene Ethylene/Butylene Styrene (TPE)... 

Styrenic TPEs are the most widely used. One such material, commercialized by BASE in 1999, is a styrene-butadiene block copolymer with a styrene content of about 70%, intended for thin film for food packaging. It has high oxygen and water permeability, and excellent toughness and optical properties. Cling films with EVA layers on the outside are also available, which provide complete recovery of deformation at elongations up to 400%, and elongation at break of over 650%. 

Commercial IPNs have been developed to combine useful properties of two or more polymer systems. For example, high levels of silicone have been combined with the thermoplastic elastomer (TPE) based on Shells Kraton styrene-ethylene/butadiene-styrene TPE and Monsantos Santoprene olefin TPE. These IPN TPEs are said to provide the biocompatibility and release properties of silicone with tear and tensile strength up to five times greater than medical-grade silicone. Thermal and electronic properties and elastic recovery are also improved. 

In 1965 Shell Oil Co. introduced styrenic TPEs, under the trade name Kraton, which are polystyrene-b-polyisoprene(or polybutadiene)- -polystyrene (PS-b-PI(or PBd)- -PS linear triblock copolymers, made by anionic polymerization. Later, BASF introduced styrenic PTEs having tapered blocks (i.e., Styroflex). The typical styrene content of TPEs is between 25 and 40wt.%. When more stable TPEs, toward oxygen. 

Styrenk Block Copolymers. Styrenic TPEs are copolymers whose molecules have the S-D-S structure, where S is a hard segment of polymerized styrene or styrene derivative, and D is a soft central segment of polymerized diene or hydrogenated diene units. Polybutadiene (B), polyisoprene (I), and polyethylenebutylene (EB) are the most commonly used rubbery segments (D). Structures for these triblock copolymers are represented as follows ... 

The characteristics of these TPEs depend on the relative proportions of the polymerized styrene and diene nnits as weU as the chemical nature of the monomers. At low styrene levels, the TPEs are soft and rnbbery. With increasing styrene contenf the TPE progressively becomes stiffer at room temperature, and it becomes a glossy, hard material similar to an impact-modified polystyrene (HIPS). Removal of the mbbery-block nnsatnr-ation by hydrogenation (to give S-EB-S materials) makes the styrenic TPEs mnch more resistant to oxidation and ozone attack. Commercially available styrenic TPEs range in hardness from 20 Shore A to 60 Shore D. 

EPDM/PP TPOs compete directly with styrenic TPEs as low-cost, low-specific-gravity (0.9 to 1.0) materials with fair to good mechanical performance and environmental resistance. They range in hardness (Table 4.15) from 60 Shore A up to 65 Shore D, with the harder products being more commonly found in commercial applications. The harder TPOs are essentially impact-modified thermoplastics and not true rubbers. The softer TPOs are rubbery at room temperature, but these characteristics are rapidly lost at elevated temperatures. EPDM/PP TPOs are therefore generally useful only below 70 to 80°C. 

Styrene block copolymers are the most widely used TPEs, accoimtingfor close to 45% of total TPE consumption worldwide at the close of the twentieth century. 1 They are characterized by their molecular architecture which has a hard thermoplastic segment (block) and a soft elastomeric segment (block) (see Fig. 3.2). Styrenic TPEs are usually styrene butadiene styrene (SBS), styrene ethylene/butylene styrene (SEBS), and styrene isoprene styrene (SIS). Styrenic TPEs usually have about 30 to 40% (wt) bound styrene certain grades have a higher boimd styrene content. The polystyrene endblocks create a network of reversible physical... 

Principal styrenic TPE markets are molded shoe soles and other footwear extruded film/sheet and wire/cable covering and pressure-sensitive adhesives (PSA) and hot-melt adhesives, viscosity index (VI) improver additives in lube oils, resin modifiers, and asphalt modifiers. They are also popular as grips (bike handles), kitchen utensils, clear medical products, and personal care products. - Adhesives and sealants are the largest single market. Styrenic TPEs are useful in adhesive compositions in web coatings. ... 

Styrenic TPEs have strength properties equal to vulcanized rubber, but they do not require vulcanization. Properties are determined by polymer type and formulation. There is a wide latitude in compounding to meet a wide variety of application properties. According to application-driven formulations, Kratons are compounded with a hardness range from Shore A 28 to 95 (Shore A 95 is approximately equal to Shore D 40), sp gr from 0.90 to 1.18, tensile strengths from 150 to 5000 Ib/in (1.03 to 34.4 MPa), and flexibility down to 112°F (-80 C) (see Table 3.1).2... 

Flexprene, Styrenic TPEs, Teknor Apex International... 

Styrenic TPE are probably the most widely used thermoplastic elastomers. There are three distinctly different main types ... 

From an adhesive viewpoint, these materials will often require a primer or some other kind of surface preparation for an effective bond (Table 4.14). However, there are many different blends and additives for styrenic TPE and so trials are recommended to verify the optimum adhesive/primer combination. 

As emphasized above, the concept of nanoreinforcement is far less practiced for TPEs than for thermoplastics [1,2,4,6,8], thermosets [1,2,8,11] and even for traditional rubbers [3,12]. This remark holds especially for addition and condensation TPEs. On the contrary, considerable amount of work was done on olefinic and styrenic TPEs. What is the reason for paying little attention to the nanoreinforcement of TPEs This is likely due to the fact that the properties of addition and condensation TPEs can be tailored upon request via the related synthesis. Recall that this was also the major argument for their less explored blending with other polymers. A further analogy with blending is that markedly more reports addressed the nanoreinforcement of TPUs compared to poly(ether amide) and poly(ether ester) block copolymers (see also Chapter 15). 

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