In this study, recovery processes of isotactic polypropylene （iPP） melted spherulites at 135 ℃ after melting at higher temperatures （170 ℃-176 ℃） were investigated with polarized optical microscopy and Fourier ...In this study, recovery processes of isotactic polypropylene （iPP） melted spherulites at 135 ℃ after melting at higher temperatures （170 ℃-176 ℃） were investigated with polarized optical microscopy and Fourier transform infrared spectroscopy. The recovery temperature was fixed to exclude the interference from heterogeneous nuclei. After melting at temperatures between 170 ℃ and 174 ℃, the melted spherulite could recover back to the origin spberulite at low temperatures. Interestingly, a distinct infrared spectrum from iPP melt and crystal was observed in the early stage of recovery process after melting at low temperatures, where only IR bands resulting from short helices with 12 monomers or less can be seen, which indicates that the presence of crystal residues is not the necessary condition for the polymer memory effect. Avrami analysis further indicated that crystallization mainly took place in melted lamellae. After melting at higher temperatures, melted spherulite cannot recover. Based on above findings, it is proposed that the memory effect can be mainly ascribed to melted lamellae, during which crystalline order is lost but conformational order still exists. These conformational ordered segments formed aggregates, which can play as nucleation precursors at low temperatures.展开更多
基金financially supported by the China Postdoctoral Science Foundation(No.2012M521233)the Fundamental Research Funds for the Central Universities(WK2310000031)+3 种基金the National Natural Science Foundation of China(Nos.51033004,51227801,51303166)National Natural Science Funds for Distinguished Young Scholars(No.51325301)the 973 program of MOST(2010CB934504)supported by the Opening Project of Soochow University Biomedical Polymers Laboratory and the Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application(Soochow University)
文摘In this study, recovery processes of isotactic polypropylene （iPP） melted spherulites at 135 ℃ after melting at higher temperatures （170 ℃-176 ℃） were investigated with polarized optical microscopy and Fourier transform infrared spectroscopy. The recovery temperature was fixed to exclude the interference from heterogeneous nuclei. After melting at temperatures between 170 ℃ and 174 ℃, the melted spherulite could recover back to the origin spberulite at low temperatures. Interestingly, a distinct infrared spectrum from iPP melt and crystal was observed in the early stage of recovery process after melting at low temperatures, where only IR bands resulting from short helices with 12 monomers or less can be seen, which indicates that the presence of crystal residues is not the necessary condition for the polymer memory effect. Avrami analysis further indicated that crystallization mainly took place in melted lamellae. After melting at higher temperatures, melted spherulite cannot recover. Based on above findings, it is proposed that the memory effect can be mainly ascribed to melted lamellae, during which crystalline order is lost but conformational order still exists. These conformational ordered segments formed aggregates, which can play as nucleation precursors at low temperatures.
