纳米银改性聚丙烯的非等温结晶动力学研究

采用共混造粒法制备了含0.5％纳米银的聚丙烯抗菌切片,利用差示扫描量热(DSC)法研究了聚丙烯及纳米银改性聚丙烯的非等温结晶行为及其动力学.结果表明,纳米银的加入使聚丙烯非等温结晶过程的成核自由能降低.Avrami方程能正确地描述聚丙烯及纳米银改性聚丙烯的非等温结晶过程.加入纳米银以后,材料的成核机理和晶体生长几何基本没有变化.聚丙烯和纳米银改性聚丙烯的Avrami指数的平均值分别为4.01和4.28,表明二者在非等温结晶时均以三维球晶方式生长.     

取代芳基杂环磷酸盐类成核剂改性聚丙烯的等温结晶研究

采用差示扫描量热法(DSC)对取代芳基杂环磷酸盐类成核剂改性聚丙烯的等温结晶过程及结晶动力学进行了研究.结果表明取代芳基杂环磷酸的一价金属盐成核剂的加入可大幅度缩短聚丙烯的半结晶时间t1/2,加快聚丙烯的结晶速度,而二价和三价的金属盐对聚丙烯结晶速度的改善不明显.对于iPP及成核iPP,其Avrami指数基本都在3左右,表明在等温条件下成核剂的加入对聚丙烯的结晶方式影响不大.同时采用Hoffman理论计算了聚丙烯和成核聚丙烯球晶生长的单位面积折叠表面自由能σe,结果表明取代芳基杂环磷酸一价金属盐的加入可显著降低聚丙烯的σe,而二价和三价的金属盐对σe的影响不明显.     

纳米碳酸钙改性聚丙烯共聚物的非等温结晶动力学

用DSC手段考察了反应釜内原位共聚制备的含有成核剂及纳米碳酸钙的聚丙烯(PP)共聚物的非等温结晶行为。结果表明，成核剂使PP共聚物的结晶温度升高，结晶度降低，结晶速率略有提高。而纳米碳酸钙则大幅提高了PP共聚物的结晶温度和结晶速率，结晶度也增加了约10％。并采用Ozawa法和Caze法描述了非等温结晶动力学。     

木粉聚丙烯复合材料的等温结晶动力学

应用差示扫描量热法(DSC)研究了有无相容剂(m-TMI-PP)的木粉聚丙烯复合体系的等温结晶行为,采用Avrami方程处理等温结晶过程,计算结晶动力学参数。结果表明,随着结晶温度的升高,各体系的结晶速率下降,结晶速率常数K、n降低,半结晶时间t1/2增大。在同一结晶温度下,木粉起到成核剂的作用,提高了基体的结晶速率;m-TMI-PP的加入,使基体的结晶速率下降。纯PP的等温结晶过程具有异相成核与均相成核的机理,复合材料的等温结晶过程属于异相成核机理。     

聚（1，3-己二酸丙二醇酯）功能化羟基多壁碳纳米管的非等温结晶

以羟基多壁碳纳米管、1,3-丙二醇、己二酸为原料,采用原位聚合法合成聚（1,3-己二酸丙二醇酯）功能化羟基多壁碳纳米管。采用差热扫描量热法测定产物的结晶和熔融行为。羟基多壁碳纳米管的添加量和冷却速率对聚（1,3-己二酸丙二醇酯）功能化羟基多壁碳纳米管的非等温结晶行为有一定的影响。在一定范围内,随着羟基多壁碳纳米管含量的增加,产物结晶温度增加。冷却速率增加,产物的结晶温度降低。羟基多壁碳纳米管起到异相成核的作用并促进结晶生长。少量羟基多壁碳纳米管对促进聚合产物结晶更加有效。Jeziorny方法描述聚合产物的非等温结晶行为出现偏离,Avrami-Ozawa方法可以更有效地描述其非等温结晶行为。     

聚羟基丁酸酯的等温与非等温结晶动力学

用差示扫描量热法(DSC)研究了聚羟基丁酸酯(PHB)的等温与非等温结晶动力学。采用Avrami方程分析了等温结晶动力学,Avrami指数n≈2,表明PHB以异相成核的二维平面晶体方式生长,等温结晶活化能为82.4 kJ/min。采用Jeziorny法和莫志深法分析了PHB的非等温结晶动力学,Avrami指数n≈3,表明PHB非等温结晶过程以异相成核的三维球晶方式生长。     

稀土β成核剂含量对PPR性能与结晶行为的影响

选用新型稀土β成核剂(WBGⅡ)对无规共聚聚丙烯(PPR)进行改性。借助广角X射线衍射(WAXD)、差示扫描量热仪(DSC)及偏光显微镜(POM)研究了稀土β成核剂诱导无规共聚聚丙烯的结晶行为及晶体形态;并研究了WBGⅡ对PPR力学性能和热变形温度(HDT)的影响。结果表明,加入少量WBGⅡ后,PPR的晶型和结晶形态均发生变化;非等温结晶过程的结晶温度(Tc)从95.8℃提高到102.1℃;PPR的冲击强度提高24%,拉伸和弯曲性能却略有下降;热变形温度提高20℃。     

氧化锆对聚丙烯非等温结晶动力学的影响

以不同含量的氧化锆(ZrO2)作为成核剂对聚丙烯进行改性,通过差示扫描量热(DSC)方法研究改性聚丙烯的非等温结晶动力学,对所得数据分别用修正Avrami方程、Jeziorny法进行处理。实验结果表明:氧化锆的加入使聚丙烯在较高的温度下就可以产生结晶现象,氧化锆具有明显的成核作用;氧化锆的加入并未改变聚丙烯的成核和生长机理,但降低了聚丙烯的结晶活化能。     

白贝粉对均聚聚丙烯非等温结晶行为的影响

采用差示扫描量热仪（DSC）研究了白贝粉（SP）对均聚聚丙烯非等温结晶行为的影响,采用莫志深法对其结晶动力学进行了分析。结果表明：由生物合成的,主要成分为碳酸钙（CaCO3）的白贝粉,对聚丙烯（PP）有很强的B成核作用,且随着其填充量的增加而增强,在5wt％填充量时β晶的含量达到最大。Kissinger公式计算结果显示成核剂的加入提高了结晶活化能。     

熔融聚合耐高温聚酰胺的非等温结晶动力学研究

通过差示扫描量热仪(DSC)研究了熔融聚合耐高温聚酰胺10T以及10T/11树脂在不同降温速率下的非等温结晶行为。通过Jeziorny法、Ozawa法以及Mo法分析了PA10T和PA10T/11的非等温结晶动力学,并采用Kissinger法、Takhor法以及Vyazovkin法计算了体系的结晶活化能。结果表明,在初期结晶阶段,PA10T和PA10T/11晶体的生长方式是一维针状生长和二维片状生长并存,同时存在异相成核现象;Jeziorny法、Mo法适合研究PA10T和PA10T/11树脂的非等温结晶过程,而Ozawa法不适合研究其非等温结晶过程;随着11-氨基十一酸含量增加,非等温结晶活化能的绝对值呈现先减小后增大再减小的变化趋势,说明结晶速率呈现先增加后减少再增加的变化趋势。     

聚丙烯接枝交联物的结晶行为

以马来酸酐(MAH)和三烯丙基异氰脲酸酯(TAIC)固相法接枝等规聚丙烯(iPP)制备了高接枝率、高极性的PP接枝交联物，并研究了接枝物的流变特性、结晶与熔融行为和结晶形态。在接枝链上引入TAIC后稳定了分子结构，熔体流动速率减小。接枝物的结晶峰温、熔融峰温、结晶度及结晶速度均低于纯PP。但是较高接枝率的交联物的成核作用很强．其等温结晶行为不同于PP和MPP，成核和生长方式为瞬时成核的二维晶粒生长。     

酸刻蚀玻璃纤维增强等规聚丙烯(iPP) 复合材料的界面结晶形态

将在稀酸溶液中刻蚀不同时间的玻璃纤维(GF)添加到等规聚丙烯(iPP)基体中制得GF/iPP复合材料。通过偏光显微镜研究了刻蚀不同时间的GF对界面结晶形态的影响。结果表明, 在刻蚀4 h的GF增强iPP复合材料中, GF表面在结晶初期诱导iPP基体生成独特的环带状晶核, 并在此晶核上可以进一步诱导生成β横晶。此外, 该复合材料在142 ℃等温结晶的结果进一步说明了刻蚀4 h的GF对基体的异相成核作用具有二元性, 即同时具有β成核和α成核的能力。      

原位聚合尼龙11/石墨烯氧化物纳米复合材料的等温结晶和熔融行为

采用原位聚合法制备了尼龙11/石墨烯氧化物纳米复合材料,并利用差示扫描量热分析仪(DSC)研究了材料的等温结晶动力学和熔融行为。研究结果表明,Avrami方程能够较好地描述尼龙11及其纳米复合材料的等温结晶动力学;尼龙11结晶速率受晶体生长速率控制,而纳米复合材料的结晶速率在不同的结晶温度范围内分别受晶体生长速率或成核速率控制;与纯尼龙11相比较,复合材料具有较低的平衡熔点和表面折叠自由能。     

Nano-hybrid shish-kebab: Isotactic polypropylene epitaxial growth on electrospun polyamide 66 nanofibers via isothermal crystallization

Polyamide 66 (PA 66) nanofibers, with the mean diameter of about 140 nm, were prepared by electrospinning. Nano-hybrid shish-kebab (NHSK) structure was achieved in PA 66 nanofibers/isotactic polypropylene (iPP) composites via isothermal solution crystallization. The morphology of such NHSK was observed by scanning electron microscopy (SEM). It was found that PA 66 nanofibers act as “shish”, and iPP crystals serve as “kebabs”. Furthermore, the concentration of iPP solution remarkably affects the morphology of the NHSK, i.e., the size of iPP crystals becomes much bigger with the increasing iPP solutions' concentration. The reason for this can be explained as that the high concentration of iPP solutions contain more free chains which can participate into the process of crystallization.     

Ageing effects during isothermal crystallization of polypropylene blended with elastomers

The secondary crystallization of isotactic polypropylene in its blend with the elastomers ethylene-propylene-diene-terpolymer (EPDM) and trans-polyoctenylene (TOR), which occurs during isothermal crystallization, has been measured by time-dependent recording of X-ray wide-angle scattering. From the results, Avrami exponents were determined, which show that secondary crystallization takes place primarily within the already formed spherulites. Avrami exponents of the primary crystallization have been determined by the same method and also by observation of the spherulitic growth in the polarization microscope. It was found that both elastomers have different effects on the crystallization behaviour of the polypropylene.     

羧酸盐类β晶成核剂与α晶成核剂的复合体系对等规聚丙烯成核结晶行为的影响

采用差示扫描量热(DSC)、广角X射线衍射(WAXD)以及力学性能分析等方式考察了两种α晶成核剂和一种羧酸盐类β晶成核剂复合后对等规聚丙烯(iPP)的结晶性能、晶型结构以及力学性能的影响。结果表明,α/β复合成核剂对聚丙烯的结晶峰值温度、晶型结构以及力学性能的影响都与复合体系中结晶峰值温度较高的单一成核剂相似,说明在α/β复合成核剂体系中,两种成核剂竞争成核,结晶峰值温度较高的成核剂在结晶过程中起主导地位,而结晶峰值温度较低的成核剂成核作用较小。     

降冰片烯二羧酸盐类成核剂在等规聚丙烯中的成核效应

应用DSC考察了降冰片烯二羧酸盐对等规聚丙烯结晶和熔融行为的影响。结果表明,降冰片烯二羧酸盐的加入提高了聚丙烯的结晶温度和熔融温度。其中钠盐(BCHE11)和钙盐(BCHE20)成核效果较为显著,添加质量分数在0.2%时可使聚丙烯的结晶峰值温度提高10.8℃和9.4℃。应用Avrami方法对降冰片烯二羧酸盐成核的聚丙烯等温结晶动力学进行了研究,结果表明,成核聚丙烯半结晶时间都小于空白聚丙烯,尤其是BCHE11和BCHE20。成核聚丙烯的Avrami指数n都在3左右,这表明成核聚丙烯的结晶生长方式为异相成核的三维球晶生长方式。     

Crystallization behaviour of isotactic polypropylene blended withtrans-octenylene rubber

The crystallization behaviour of isotactic polypropylene (iPP) blended withtrans-octenylene rubber (TOR) has been investigated by optical microscopy. It is found that crystallization kinetical parameters like nucleation densities, Avrami exponents and spherulitic growth rates are strongly dependent on the TOR concentration in the blend. While at 10% TOR content the nucleation density passes through a maximum, both the Avrami exponent and the spherulitic growth rate are minimal. Due to an increased dispersion of TOR in iPP at 10% TOR concentration and the subsequent formation of interfaces, the nucleation changes from preferentially homogeneous to preferentially heterogeneous. The concentration oftrans double bonds in the TOR chain has no influence on the crystallization behaviour of the samples.     

Study of shear-induced interfacial crystallization in polymer-based composite through in situ monitoring interfacial shear stress

In order to further investigate shear-induced interfacial crystallization of polymer-based composites, an improved fiber-pulling device was designed and built. Its peculiar characteristic is that a force transducer is assembled to in situ monitor the variation of interfacial shear stress between the polymer matrix and pulling fiber. Thus, the relationship between interfacial shear stress and the subsequent crystalline morphology can be quantitatively established. In the preliminary study via this device, isotactic polypropylene (iPP)/glass fiber composite was adopted as a model system. The results indicate that interfacial crystallization kinetics is promoted by the presence of interfacial shear stress. Furthermore, there are two thresholds of interfacial shear stress for interfacial crystalline morphology. To be specific, one (0.017 MPa) is for the induction of iPP nucleation, above which α-form iPP crystals are obviously encouraged during the subsequent isothermal crystallization; the other is for the generation of β-form iPP crystals (0.042 MPa), above which β-form crystals are favored to be triggered in the transcrystalline region.     

Morphology, crystallization and melting behaviors of isotactic polypropylene/high density polyethylene blend: effect of the addition of short carbon fiber

The effect of vapor grown carbon fiber (VGCF) on the morphology, crystallization and melting behaviors of isotactic polypropylene (iPP)/high density polyethylene (HDPE) blend have been studied by means of Scanning Electron Microscopy (SEM) and Differential Scanning Calorimeter (DSC). It is found that the addition of VGCF results in a dramatic change in the morphology of iPP/HDPE blends. The crystallization peak temperature and melting point of iPP are not altered significantly by the blending. However, the degrees of crystallinity of iPP in the blends are reduced. Compared with the unfilled blends, the crystallization peak temperatures of iPP increase dramatically for the composites. The isothermal crystallization behavior of iPP is further investigated. The analysis of the crystallization half time shows that the crystallization rate of iPP is reduced by the presence of HDPE melt, and is enhanced by carbon fibers. For the unfilled blends in which iPP is the major component, the Avrami exponent closes to 3, independent of the HDPE content. However, for the composites, the Avrami exponent varies with the composition in a rather complex manner. An explanation based on heterogeneous and homogeneous nucleation is supposed. The sharp changes in the crystallization and melting behaviors for the composites containing 30–35wt% HDPE correspond to the sudden change in the morphology of the two phases. It is supported by the observation of SEM and the electrical measurement.