热历史对尼龙1212熔融行为的影响

EFFECT OF THERMAL HISTORY ON THE MELTING BEHAVIOR OF NYLON 1212

利用DSC方法研究了不同热历史条件对尼龙1212熔融行为的影响.不同的热历史条件下,在DSC曲线上,观察到尼龙1212产生2个或3个熔融峰,依据聚合物结晶理论,对各峰的来源进行了分析.在160℃下不同温度退火120 min的尼龙1212样品DSC曲线上,低温结晶熔融峰主要由低温结晶形成的一些微晶体或者片晶熔融产生,其晶体完善程度较差,熔融峰值较低,峰面积较小;主熔融峰是由样品在淬火过程中形成的晶体和升温过程中低温结晶形成的晶体的熔融重结晶形成较为完善的晶体熔融所产生,熔融峰值较高,峰面积较大.在不同的升温速率条件下,熔融峰温度有所移动,表明不同升温速率条件下产生的熔融峰的结晶晶型是相同的.在不同结晶时间下结晶,延长结晶时间对较高完善程度晶体的生长有利.在不同温度下依次退火处理的样品,熔融产生两个附加峰,这两个附加峰的峰温都比它们相应的退火温度高,而峰高和峰面积随退火温度降低而减小.根据等温结晶结果,由Hoffman方法确定了尼龙1212的平衡熔融温度为202.8℃.

The effect of thermal history on the melting behavior of nylon 1212 has been studied by differential scanning calorimetry（DSC）.Two or three melting peaks were observed on DSC curves at different thermal history.The mechanism of melting peaks of nylon 1212 was analyzed according to the theory of polymer crystallization.Lower temperature melting peaks（PⅠ） in DSC curves were mainly attributed to melting of minicrystal or lamellar crystal which developed from nylon 1212 annealed for 120 min at different temperatures.The peak temperature of these peaks is low,and their area is small.The main melting peak（PⅢ） is the melting of perfect crystals which are formed in a recrystallization process of the polymer after PⅠ and PⅡ.The value of main peak temperature is much higher and the area is much larger.The melting peak（PⅡ） might be developed from melting of crystals which formed during quenched process of nylon 1212.The position of melting peak changed slightly with different heating rate,which indicates that these crystals have similar form.Increasing crystallization time is favorable for perfect crystals formation.The sample annealed at two different temperatures exhibits two additional melting peaks.Temperatures of these additional melting peaks are higher than annealing temperatures.Moreover,the position and area of additional peak reduced with the annealing temperature decreasing.The equilibrium melting temperature of nylon 1212 was determined as 202.8℃ by Hoffman＇s method according to results of isothermal crystallization.