Study on degrees of mesomorphic zone of polymer.Ⅰ.Determination of degrees of crystallinity of Eucommia ulmoides gum and natural rubber by dynamic mechanical thermal analysis

摘要

AbstractAccording to the two-phase model theories of polymer crystallization, the degree of crystallinity of natural rubber (NR) induced to crystallize at??25?°C can be directly determined by dynamic mechanical thermal analysis (DMTA) by testing its tanδ peak areas of crystalline state and 100% amorphous state respectively. The degree of crystallinity is 86% when the induction time increases to 12?h. However, due to the tanδ peak area of 100% amorphous state cannot be measured by DMTA directly, the degree of crystallinity ofEucommia Ulmoides (EU)gum can only be determined indirectly with DMTA by using the tanδ peak areas of 100% amorphous state extrapolated from the linear equation (y?=?ax?+?b) which is derived from the relationship between tanδ peak areas and crosslink densities. The degree of crystallinity is 87%, which is very close to NR. The crystallization of NR can be prevented effectively by increasing slightly the crosslink density to the critical crystallization point, which is 6.20?×?10?5mol/cm?3for vulcanized NR induced to crystallize at??25?°C for 4?h. However, it is very hard forEUgum to prevent the crystallization by crosslinking. Because, with increasing of the crosslink density, theEUgum will firstly show a percolation threshold, which is 53.34?×?10?5mol/cm?3, and the degree of crystallinity is 71.04%. Then, like NR, the degree of crystallinity ofEUgum will decrease rapidly to zero by increasing the crosslink density to the critical crystallization point, which is 68.89?×?10?5mol/cm?3. In the end of the paper, the linear relationship of the equation is verified and the influence factors on slope a and intercept b of the linear equation are discussed as well.Graphical abstractThe number of free chain segments of the amorphous zone in NR andEUgum, tested with DMTA, can be used to calculate their degrees of crystallinity. The results indicate that the degree of crystallinity of NR is 86% after crystallizing at??25?°C for 12?h, which is very similar to the degree of crystallinity ofEUgum, which is 87%. By increasing the crosslink density, unlike NR, which only shows the critical crystallization point,EUgum will firstly show the percolation threshold, and after that show the critical crystallization point.Display Omitted]]>