第6章-橡胶弹性.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * (3) Mooney-Rivlin Equation 当橡皮发生形变时，外力所做的功储存了下来，因此储能函数W是拉伸比的函数，考虑对称性等因素，Mooney and Revlin由纯粹的数学论证推出应变储能函数表达式： C1 , C2 are constants, no physical meanings. C2 – Slope C1– Intercept Empirical law C1与弹性模量有关 C2对统计理论偏差的校正 (4) 幻象网络 Phantom network 校正因子A?, A?1 ?——交联点的功能度 Phantom II In Phantom network by P.J. Flory （5）S.F Edwards approach (1976) 高分子链间的缠结作用是高分子物理中悬而未决的难题,其实质是高分子链的拓扑限制作用的表征——Topology Mobius belt Different relationships between modulus and elongation ratio 6.5 Swelling effect 溶涨效应 溶剂小分子进入橡胶交联网络，不能将其溶解，只能使其溶涨。体系网链密度降低，平均末端距增加，进而模量下降。 溶涨 交联橡胶的溶涨包括两部分： 溶剂分子与大分子链混合，熵增，有利于溶涨 ?GM 分子链拉长，储存弹性能，熵减，不利于溶涨 ?Gel 达到溶涨平衡 化学位达平衡 即溶涨体内部溶剂的化学位和溶涨体外部的化学位相等 According to Flory-Huggins Theory 溶涨平衡时 If the volume fraction of polymer ?2 is very small If the number of segments x becomes very large 弹性自由能 ?=?1=?2=?3 理想交联网等温等压拉伸过程中内能不变，体积不变 求偏导 代入到平衡条件中 网链的平均分子量 聚合物的密度 溶剂的摩尔体积 Hunggins parameter 溶涨前后体积比 Application To obtain the Hunggins parameters To obtain the average molecular weight between cross-linked points Mc 交联度低时Mc大，Q大即溶涨后体积增加多 6.6 Thermoplastic elastomer - TPE 交联为弹性体（橡胶）具有高弹性的条件之一，如果交联点为物理交联，则形成热塑弹性体。 兼有橡胶和塑料两者的特性，在常温下显示高弹，高温下又能塑化成型。 生产方法 聚合方法，得嵌段共聚物， TPE 机械共混法，得共混物， Ethylene propylene rubber/PP Definition in English Elastomer - rubber. Hot shot scientists say a rubber or elastomer is any material that can be stretched many times its original length without breaking, and will snap back to its original size when it is released. Thermoplastic - a material that can be molded and shaped when its heated. 热固性塑料 Thermoset Thermoset - a hard and stiff crosslinked material. Thermosets are different from thermoplastics, which become moldable when heated. Thermosets are crosslinked, so they dont. Also, they are different from crosslinked elastomers. Thermosets are stiff and dont stretch the way elastomers do. MOLDED TPE POLYMER W/PVC