| Polybutene-1(PB-1)is a non-toxic and odorless polymer material,which is widely used as pipes and other industrial materials because of its special properties,such as superior resistance to high temperature creep and environmental stress cracking resistance,good chemical corrosion resistance and mechanical properties,called "plastic gold".PB-1 is a semi-crystalline polymer material of α-polyolefin with various crystal forms.During melt processing in industry,PB-1 crystallize into metastable crystal form II and the spontaneous conversion of form II to stable form I usually takes several weeks to complete at room temperature.This increases the production period and severely limit and affects its properties and commercial value.In this thesis,the crystalline transformation was regulated by different nucleation methods(homogeneous nucleation and heterogeneous nucleation)in PB-1,PB-1/MMT and PB-1/PC under different static and tensile conditions,by means of differential scanning calorimeter(DSC),wide-angle X-ray diffraction(WAXD)and Fourier infrared(FTIR)and other test techniques.This thesis provides more experimental evidence to analysis possible form Ⅱ→Ⅰ mechanism and structure control of crystalline transformation.The main results are summarizaed as follows:First,a continuous melt memory process was used to control the crystallization nucleation conditions,and the effect of the pre-ordered structure(crystal form II)on the transformation of form Ⅱ→Ⅰ and the development of the crystalline structure was analyzed.The results showed that the transformation of the cyclically treated sample was approximately completed at 173 h.which was 220 h shorter than that of the non-cyclically treated samples.The transition half-cycle of cyclically treated samples was 50 h,and that of the non-cyclically treated samples was about 100 h.The pre-ordered structure of the crystal form Ⅱ under melt memory method shortened the induction period of the crystal form I.and melt memory has a significant accelerating effect on both the initial crystallization and transformation process of the crystal formⅡ→Ⅰ.For samples without of the non-cyclically treatment,the crystallinity during the initial stage of formation of crystal form I increased.which is not accompanied by a simultaneous decrease in crystal form Ⅱ content.The inconsistency of the crystal form transformation may support a new mechanism in which at least part crystal form I is not obtained form transition process which happened inside the crystal form II at the initial stage of transformation.but form directly from the amorphous phase or at the interface.Secondly,montmorillonite(MMT)was added to PB-1 as a heterogeneous nucleating agent using melting blend method.and the effects of different pretreatment temperatures on crystal form transformation and crystal structure transformation were analyzed.The experimental results showed that compared with the heterogeneous nucleating agent MMT,temperature has a more significant effect on the transformation of crystal form Ⅱ→Ⅰ.For both PB-1 and PB-1/MMT,it was found that the form Ⅱ→Ⅰ transition rate of smples pretreated at-50℃ is the fastest,which takes approximately 24 h for a complete transformation.The PB-1 and PB-1/MMT samples pretreated at 80℃ has the slowest transition rate of about 168 h.We found that pretreatment below the glass transition temperature(-50℃)is conducive to the nucleation of crystal form I,and the transformation of crystal form Ⅱ→Ⅰ can be completed quickly.For the PB-1/MMT composite,the addition of MMT reduces the mobility of the PB-1 molecular chains during crystallization process,which reduces the crystallinity of the composite material.Pretreatment temperature of-50℃ results in the predominance of homogeneous nucleation,and heterogeneous nucleation at temperature of 0℃ and 80℃ is dominant.The addition of MMT favors the transformation of crystal form Ⅱ→Ⅰ for samples of heterogeneous nucleation,while it is inconducive to the transiton process at homogeneous nucleation condition.Finally,the nucleation of PB-1 and PB-1/PC under two stretching conditions was controlled to analyze the effects of different nucleation methods on the crystal structure and crystal from conversion in PB-1.The experimental results revealed that the average time required for the completion of crystal form transformation is about 80 h for samples pretreated at 0℃ and 46 h for samples pretreated at-25℃.The low temperature pretreatment facilitated the nucleation of crystal form I and accelerated the crystal form transition process.The form Ⅱ→Ⅰ transformation for samples pretreated at 0℃ takes 78 hours and 54 hours at strain of 20%and 40%respectively,which are 26 and 50 hours less than the 0%strain condition.The stretching caused the orientation of PB-1 crystal structure,which is beneficial to the nucleation of crystal form I and accelerates the process of crystal form transformation.The formation of orientation-induced nucleation eventually increases transition degree of crystal formⅡ.Through the transformation analysis of the tensile heterogeneous nucleated PB-1/PC samples、it was found that the transformation completion takes 48 hours under both 40%and 1 00%strain conditions,which is 25 hours longer than that under 0%strain.Comparing the conversion rates of samples under two nucleation methods,it was found that the tensile heterogeneous nucleation faciliated the nucleation of crystal form I and accelerates the transformation proess.Compared with tensile homogeneous nucleation,the increase in strain did not accelerate the crystal form transformation but rather inhibited it.However,the strain favors the nucleation of the crystal form Ⅱ,increass the crystallinity and melting point of the final product.Consistent with the orientation-induced homogeneous nucleation,the heterogeneous nucleation also benefits the conversion degree of form II. |
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