Determination of The Crosslink Parameters of a Vulcanised Natural Rubber
This experiment has two parts PART A Stress-Strain Method
A special feature of natural rubber (NR) is elasticity. Materials such as metal and glass can only be deformed elastically to a small degree, normally less than 1%, while NR can be extended to 700% or more. Elastic deformation means a material will recover to its original shape and dimension when released after being deformed.
The basis of elasticity in NR is that polymer chains without any external application of strain, will have the most appropriate configuration, statistically. ie randomly coiled. When strain is applied, the chain will be effectively extended to a longer, less appropriate configuration, followed by a decrease in entropy. If the strain is released, the chain will return to the most probable configuration and maximum entropy in accordance to the Boltzman expression: