1. General Purpose
General purpose elastomers are hydrocarbon polymers. They include styrene-butadiene rubber (SBR), butadiene rubber (BR), and polyisoprene rubber - both natural (NR) and synthetic (IR). These "diene" rubbers contain substantial chemical unsaturation in their backbones, causing them to be rather susceptible to attack by oxygen, and especially by ozone. Additionally, they are readily swollen by hydrocarbon fluids. The primary application of these elastomers is in automobile and truck tires.
1.1 Styrene-Butadiene Rubber (SBR)
SBR polymers are widely produced by both emulsion and solution Polymerization with a Tg of approximately -55 °C. Emulsion polymerization is carried out either hot(the polymer formed is highly branched), at about 50°C, or cold (the polymer formed with less branching, and giving stronger vulcanizates), at about 5°C, depending upon the initiating system. SBR made in emulsion usually contains about 23% styrene randomly dispersed with butadiene in the polymer chains. SBR made in solution contains about the same amount of styrene, but both random and block copolymers can be made. Block styrene is thermoplastic and at processing temperatures helps to soften and smooth out the elastomer. SBR was originally produced by the hot emulsion method, and was characterized as more difficult to mill, mix, or calender than natural rubber, and having relatively poor inherent physical properties.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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