Rubber particles bimodal systems

Other rubber systems have been commercially successful. Styrene block copolymers yield a HIPS product with a small particle size and provide high gloss. A mixed rubber system consisting of styrene-butadiene block rubber and/or ethylene-propylene diene modified (EPDM) rubber can be blended with the polybutadiene to form bimodal rubber particle size distribution for a... 

The particle size restrictions for toughening PS depend on the mechanical properties of the rubber particle. For a HIPS rubber particle, with a Young s modulus of 333 MPa, the minimum size is 0.8 mm, while for a pure PB particle, with a Young s modulus of 47 MPa, the critical size is 0.44 mm (27). The stiffer the particle, the larger it must be. HIPS systems with bimodal particle size distributions can also be effective in toughening (28), but the bimodal particle size distribution is generally detrimental to optical clarity. 

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