Rubber modification

The different methods employed for rubber modification are reviewed below. 

An overview of sPS as a matrix is given in a book edited by Gausepohl [14]. One of the points reviewed is its impact modification. 

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I ew Rubber-Modified Styrene Copolymers. Rubber modification of styrene copolymers other than HIPS and ABS has been useful for specialty purposes. Transparency has been achieved with the use of methyl methacrylate as a comonomer styrene—methyl methacrylate copolymers have been successfully modified with mbber. Improved weatherability is achieved by modifying SAN copolymers with saturated, aging-resistant elastomers (88). 

The primary use of Nd-BR is in tires. This application of Nd-BR accounts for only 15% of the total amount of BR used in this field. Minor amounts of Nd-BR are used in technical rubber goods and in golf ball cores. To date, only special Nd-BR grades meet the viscosity requirements for rubber modification of HIPS. Mainly due to high solution viscosities Nd-BR is not yet used as the rubber component in ABS. 

The Role of Rubber Modification in Improving High Rate Impact Resistance... 

First, the role of rubber modification in high rate impact is to suppress spallation by inducing the material to yield in the presence of dynamic tensile stresses arising from impact. Second, this yield-spall transition occurs at different strain rates for different rubber contents and may be predictable using quasistatic, low temperature tests of this type. These tests can also provide information concerning the basic nature of the yield process in these materials through the activation parameters which are obtained. Third, the Bauwens-Crowet equation seems to be a good model for the rate and temperature sensitive behavior of the American Cyanamid materials and is therefore a likely candidate for a yield criterion to use in the analytical code work on these materials which we hope to perform as a continuation of this work. 

In this Section, an experimental approach for constructing isothermal TTT cure diagrams has been described, TTT diagrams of representative epoxy systems including high Tg and rubber-modified epoxy resins have been discussed, and perturbations to the TTT cure diagram due to thermal degradation and rubber modification have been illustrated. 

Failure of unoriented SAN copolymers is dominated by crazing behavior. The total energy absorbed by the polymer during failure has been increased by optimizing both failure modes. Yielding can be enhanced by orienting the polymer [105], and crazing can be optimized by rubber modification. 

Dow and Monsanto, among others, have investigated the manufacture of SMA resins both with and without rubber modification. Moore at Dow Chemical Company described a method of producing SMA copolymers via a recirculated coil reactor [74]. 

In the case of sPS, the problem of its brittleness can be even more acute since it has to compete with engineering plastics which possess an inherent toughness superior to that of sPS. For this reason, a good impact modification of this product is of paramount importance and may even be essential for its survival as a commercial thermoplastic. For this reason a chapter of this book has been dedicated to the impact modification of sPS using elastomers. Since rubber modification plays such an important role for styrene polymers, whether atactic or sydiotactic, we will first look at the methods of energy dissipation in these homopolymers on impact. 

The use of glass fibres to enhance energy dissipation, which only functions if the fibres are oriented perpendicular to the crack propagation, is important for applications of sPS. However, since this chapter is concerned primarily with the rubber modification of sPS, it will not be considered in detail here. 

For many applications, the toughness of sPS is insufficient, which has thus led to many attempts in the past to increase its toughness significantly compared with HIPS by blending with rubbers. In the stress field of softer or harder particles than the sPS matrix, typical deformation processes inherent to the matrix are initiated. For rubber modification it is important that the application or test temperature is above the glass transition temperature of the rubber, otherwise the stiffnesses of the two components hardly differ from each other and local stress fields around the rubber particles are not formed. The formation of numerous deformation zones round the rubber particles is generally the basis of impact modification [10]. 

RUBBER MODIFICATION OF SYNDIOTACTIC POLYSTYRENE Table 19.1 Impact modification of sPS as described in EP 318 793 [15]... 

Figure 19.10 TEM images of rubber-modified sPS with craze tips along imaginary lines (---), presumably lamellae. Rubber modification 35 % S-EB-S block copolymer...

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