摘要
不同于传统注射成型,多熔体多次注塑成型(M^(3)IM)过程中存在特殊的二次流动场和温度场,导致其试样的形态结构与演变规律更加复杂.本文采用实验与模拟相结合的方法,详细探究了熔体沿流动方向上二次流动过程中剪切场和温度场的分布,及其对试样形态结构的影响.结果发现,一次注射聚偏氟乙烯(PVDF)熔体是由一次流动层和二次流动层两部分所构成,且在一次流动层末端形成熔体突破区.此外,剪切场和温度场在熔体突破区前段、中段和后段存在显著差异,导致试样微观结构沿流动方向呈多级分布,即在突破区前段PVDF形成取向结构,而在突破区段PVDF受到强的二次剪切作用,形成了大量β晶和取向结构.与此不同,在突破区后段,PVDF则主要受到二次剪切生热作用的影响,形成了具有较高熔点(~190℃)的特殊“亮带”结构.
To study the effects of second-melt penetration on the external fields(shear field and thermal field)as well as the morphological evolution along the flow direction,polyvinylidene difluoride(PVDF)and poly(methyl methacrylate)(PMMA)were applied in the multi-melt multi-injection molding(M^(3)IM)in which PVDF and PMMA were used for the first and second shots,respectively.The whole process of M^(3)IM was also simulated by Fluent software using Cross-WLF model to quantitively investigate the distributions of melt temperature and shear rate and to better understand the formation mechanism of various morphologies in M~3IM products.The results from polarized light microscopy(PLM)with hot-stage showed that two different layers were formed in PVDF part.Specifically,one is the primary flow layer and the other is the secondary flow layer.The former one was dominated by the first shot of PVDF,while the latter one was significantly affected by the second shot of PMMA.Moreover,a penetration area was clearly observed in the region close to the end of the primary flow layer.Characterizations with differential scanning calorimetry(DSC)and Fourier transform infrared spectroscopy(FTIR)revealed that the content of PVDFβphase dramatically increased in the penetration area.This is mainly caused by the secondary shearing effect of PMMA melt in M~3IM which is in good agreement with numerical simulation.Moreover,an interesting structure,“bright ribbon”,with a higher melting temperature(~190℃)was found in the domains after penetration area.This might be due to the shear heating of the secondary flow,which results in the annealing of PVDF crystals.Finally,this work provides a detailed investigation of the secondary flow behavior of polymer melt in M^(3)IM and helps us better understand the corresponding effects on the structural evolution along the flow direction.
作者
赵鑫
陈历波
刘磊
顾俊帝
张凯
杨鸣波
Xin Zhao;Li-bo Chen;Lei Liu;Jun-di Gu;Kai Zhang;Ming-bo Yang(College of Polymer Science and Engineering,State Key Laboratory of Polymer Materials Engineering,Sichuan University,Chengdu 610065)
出处
《高分子学报》
SCIE
CAS
CSCD
北大核心
2022年第8期985-994,共10页
Acta Polymerica Sinica
基金
国家自然科学基金(基金号21674069)
创新研究群体科学基金(基金号51721091)
高分子材料工程国家重点实验室自主课题经费(项目号sklpme2020-1-08,sklpme2021-4-10)资助项目。
关键词
多熔体多次注射成型
聚偏氟乙烯
Β晶
形态结构
Multi-melt multiple-injection molding
Polyvinylidene difluoride
βPhases
Morphology
