α／β复合成核剂对等规聚丙烯结晶形态的影响及非等温结晶动力学

Crystallization morphologies and non-isothermal crystallization kinetics of isotactic polypropylene modified by α/β compounded nucleating agents

采用偏光显微镜(POM)及示差扫描量热(DSC)法考察了3种α/β复合成核剂NA40/NABW、NA40/HHPA-Ba、NA40/PA-03对成核等规聚丙烯(iPP)的结晶形态及非等温结晶动力学的影响。对成核iPP结晶形态的研究结果表明:α/β复合成核剂的加入能够减小iPP的球晶尺寸。影响α/β复合成核剂成核iPP结晶形态的主要因素是ΔTCp(ΔTCp为成核iPP结晶峰值温度与iPP结晶峰值温度的差值),即复合体系中ΔTCp较大的成核剂在iPP结晶过程中起主导作用,最终的结晶形态与单独添加这一成核剂时iPP的结晶形态相类似;当两种成核剂的ΔTCp接近相同时,两者竞争成核,成核iPP的结晶形态表现为两种成核剂共同作用的结果。因此,通过改变α/β复合成核剂的复合比例即改变两种成核剂的添加浓度,进而改变其ΔTCp,可以得到结晶形态完全不同的iPP。采用Caze法对非等温动力学进行了研究,结果表明:添加α/β复合成核剂能够提高iPP的结晶温度,缩短半结晶时间。复合成核剂成核iPP的结晶行为也同样受成核剂ΔTCp的影响,复合成核iPP的Avrami指数接近于复合体系中ΔTCp较大的成核剂单独添加时iPP的Avrami指数。

Crystallization morphologies and non-isothermal crystallization kinetics of isotactic polypropylene （iPP） modified by three α/β compounded nucleating agents （NAs） were studied by means of polarized optical microscope （POM） and differential scanning calorimeter （DSC）. The size of spherulites in nucleated iPP appeared much smaller than that in pure iPP. However, iPP nucleated by different ratios of α/β compounded NAs showed different crystallization morphologies. Crystallization morphologies of nucleated iPP depended on △Tcp （△Top refers to the difference in crystallization peak temperature between nucleated iPP and pure iPP） of a and β NAs. The one with the higher △Tcp played a leading role in the crystallization process, resulting in that the crystallization morphology of nucleated iPPappeared close to that with the NA alone. Competitive nucleation would occur when the difference of △Tcp between two NAs was not pronounced. △Tcp was related to the concentration of NA. Thus crystallization morphologies could be adjusted by changing the ratio of α/β compounded NA. The Caze method was used to deal with non-isothermal crystallization kinetics obtained by DSC. The obtained parameters showed addition of α/β compounded nucleating agents could greatly raise crystallization peak temperature of iPP and shorten the crystallization half-time. Avrami exponent of α/β compounded nucleated iPP was close to that of iPP nucleated by the NA with the higher △Tcp individually, which demonstrated that the crystallization process of iPP nucleated with α/β compounded NAs also depended on △Tcp of a and β NAs within the compounded system.