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The Crystallization Behavior Of Natural Rubber With The Molecular Weight And Vulcanization Systems

Posted on:2016-03-02Degree:MasterType:Thesis
Country:ChinaCandidate:Y J S GaoFull Text:PDF
GTID:2191330467993627Subject:Materials science
Abstract/Summary:PDF Full Text Request
In this thesis, the crystallization behavior of natural rubber(NR) was systematically explored on the influence of the different temperatures, various molecular weights, all kinds of vulcanization as well as the degree of vulcanization systems. Using Differential scanning calorimetry(DSC) and Simultaneous Thermal Analyzer(STA), the relationship between the structure of NB and crystalline was analyzed.We investigate the crystallization behavior of NR at crystallization temperature ranging among-15℃,-20℃,-25℃,-30℃and-35℃. The results show that the crystal structure are almost built up under isothermal crystallization condition for6-8hours, with two different crystal structures. The crystallization rate and degree of crystallinity reach maximum at-25℃. If adopted the heating rate of over5℃/min to melt, two peaks, one large peak intensity and one smaller peak intensity, occur clearly in the fusion curve. The equilibrium melting point of NR is achieved, via fitting of Hoffman-Weeks Equation, at18.03-62.42℃.The molecular weight of NR is classify by the way of open mill plastication. The molecular-depedent studies show that as the decrease of molecular weight, the NR exhibits a worse thermal stability, a lower glass transition temperature, a higher crystallization rate and degree of crystallinity. When the molecular weight is distributed around200,000, the process of crystallinity requires only3hours. And also the area of two peaks in the fusion curve get approaching.The NR with different degrees of vulcanization were prepared by the conventional vulcanization(CV) system and efficient vulcanization(EV). The results show that with the increasement on state of cure, the glass transition temperature are enhanced. While, the crystallization of NB is obstructed as the increase on state of vulcanization, particularly reflected in the decrease on crystallization rate and degree of crystallinity. Thus, the NR achieved by the EV system performed a much harder trend on crystallization that than from CV system, the former possessing a lower crystallization rate and degree of crystallinity. However, the NB prepared by EV contribute to a better thermal stability than the NR from CV system.The kinetic analysis showed that the values of Avrami exponent, n, are close under different temperatures, different molecular weights and different degrees of vulcanization, which indicates that the temperature, molecular weight and degrees of vulcanization, have almost no effect on the nucleation mechanism and growth of NR.
Keywords/Search Tags:natural rubber, molecular structure, DSC, melting, crystallization, crystallization kinetics
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