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In a foregoing article, a new method based on dynamic mechanical thermal analysis(DMTA)for determining the degrees of crystallinity of the natural rubber (NR) and the eucommia ulmoides ( EU ) gum, with different crosslink densities, has been established. In order to verify the effectiveness of this method, in the present paper, the degrees of crystallinity of NR and EU gum with different crosslink densities will be determined by differential scanning calorimetry (DSC). The results indicate that the degrees of crystallinity determined by DMTA are much higher than those of DSC. This is because the degree of crystallinity determined by DMTA involves not only the ratio of the crystalline zone, but also the ratio of the mesomorphic zone, while the degree of crystallinity tested by DSC includes only the ratio of the crystalline zone. So, the degree of crystallinity, the degree of mesomorphic zone and the degree of amorphous zone of NR and EU gums with different crosslink densities can be quantitatively determined by the combination of DMTA and DSC. The results show that the degree of crystallinity, the degree of mesomorphic zone and the degree of amorphous zone of NR (crystallized at −25 °C for 12 h) and EU gum are 33%, 53%, 14% and 34%, 54%, 13%, respectively. For NR, increasing the crosslink density or decreasing the induced time will decrease the degree of crystallinity and the degree of mesomorphic zone simultaneously, but will increase the degree of amorphous zones. For EU gum, increasing the crosslink density will decrease the degree of crystallinity and increase the degree of amorphous zone, but keep the degree of mesomorphic zone invariably consistent within the critical crystallization point, which is approximately 55%. At the end of the paper, the impact of crystallization on the mechanical properties of EU gum and NR is discussed as well. [ABSTRACT FROM AUTHOR]

According 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 of Eucommia 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 −5 mol/cm −3 for vulcanized NR induced to crystallize at −25 °C for 4 h. However, it is very hard for EU gum to prevent the crystallization by crosslinking. Because, with increasing of the crosslink density, the EU gum will firstly show a percolation threshold, which is 53.34 × 10 −5 mol/cm −3 , and the degree of crystallinity is 71.04%. Then, like NR, the degree of crystallinity of EU gum will decrease rapidly to zero by increasing the crosslink density to the critical crystallization point, which is 68.89 × 10 −5 mol/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. [ABSTRACT FROM AUTHOR]

Considering the rapidity and lesser sample amount required, the Fourier Transform Infrared Spectra (FTIR) was often used to quantitatively determine the rubber content of Russian dandelion, guayule, etc. This is because their chemical structure are cis -1,4-polyisoprene (CPI) which has a unique and isolate skeleton stretching vibration peak at 835 cm −1 band, and is convenient for determining the rubber content. However, this method is not suitable for Eucommia Ulmoides (EU) gum which will crystallize easily at room temperature due to the regular chemical structure of trans -1,4-polyisoprene (TPI), that will restrict the skeleton stretching vibration of TPI greatly. As a result, its FTIR spectrum only shows a very small peak at 845 cm −1 band hiding among a number of crystalline peaks around nearby, thus it cannot be used to determine the rubber content of Eucommia ulmoides oliv ( E. ulmoids ) directly. Actually, these crystalline peaks could be eliminated easily by elevating the temperature over 60 °C, and a unique and isolate skeleton stretching vibration characteristic band at 845 cm −1 was left alone in the TPI's FTIR spectrum which can be used expediently to determine the content of EU gum. At the present paper, the Variable Temperature Fourier Transform Infrared Spectroscopy (VTFTIR) was used to determine the rubber content of E. ulmoides . The results indicate that the rubber content of E. ulmoides samples (1–40, 5–35, 22–11) provided by Northwest Agriculture and Forestry University (NAFU) are 4.66%, 4.04%, 4.32% respectively, and the errors of average value were less than 5% compared with Soxhlet Extraction. [ABSTRACT FROM AUTHOR]