文档介绍：ChapterChapterChapter 666
66 RubberRubber ElasticityElasticity
橡胶弹性橡胶弹性
RubberRubber andand
RubberRubber ElasticityElasticity
橡胶及橡胶弹性橡胶及橡胶弹性
ConceptConcept ofof RubberRubber andand RubberRubber
ElasticityElasticity 橡胶与橡胶弹性的概念橡胶与橡胶弹性的概念
Rubber 橡胶
ASTM标准:20~27°C下,1min可拉伸2倍的
试样,当外力除去后1min内至少回缩到原长
,或者在使用条件下,具有
106~107的杨氏模量者
Rubber Elasticity 橡胶弹性
橡胶弹性是指以天然橡胶为代表的一类高分
子材料表现出的大幅度可逆形变的性质
Idealized structure of a
cross-linked polymer
r
Chain r0
(a) (b)
work chain segment
Crosslinks
(a) relaxed, with a random coil conformation
(b) extended, owing to an external stress
Stress-strain behavior of lightly cross-linked
natural rubber at 50℃.
7
a. Experimental
6 b. Hysteresis(滞后)
effects e
5
important at higher
c
4 b elongations
c. Reversible nature of
3 the extension up to
Tensile strength (MPa)Tensile strength (MPa) Theoretical
2 α=
a
1
⎛ 1 ⎞
0 σ= nRT⎜α− 2 ⎟
12345678 ⎝α⎠
Extension ratio, α
ChemicalChemical StructureStructure ofof RubbersRubbers
橡胶的化学结构橡胶的化学结构
¾ 分子链具有足够的柔顺性,玻璃化转变温度远
低于室温。这就要求分子链内旋转位垒较小、
无极性或弱极性、分子间作用力小。橡胶类聚
合物的内聚能密度一般在290KJ/cm3,比塑料和
纤维类聚合物的内聚能密度低的多
¾ 在使用条件下不结晶或结晶度很低
¾ 在使用条件下无分子间相对滑动,即无冷流,
因此分子链上应存在可供交联的位置,从而可
进行交联
Tg of Conventional Rubbers
玻璃化温度使用温度
名称
°C °C
顺式聚1,4-异戊二烯−73 −50~120
顺式聚1,4-丁二烯−105 −70~140
丁苯共聚物(75/25) −60 −50~140
聚异丁烯−70 −50~150
丁腈共聚物(70/30) −41 −35~175
乙丙共聚物(50/50) −60 −40~150
聚二甲基硅氧烷−120 −70~275
偏氟乙烯-全氟丙烯共聚物−55 −50~300
CharacteristicsCharacteristics ofof RubberRubber
ElasticityElasticity 橡胶弹性的特点橡胶弹性的特点
A simple rubber band may be stretched several
hundred percent, yet on being released, it snaps
back substantially to its original dimensions. By
contrast, a steel wire can be stretched reversibly
for only about a 1% extension. Above that level,
it undergoes an irreversible deformation and
then breaks. This long-range, reversible ela