聚丙烯/累托石纳米复合材料的非等温结晶动力学研究

在双螺杆挤出机上熔融共混制备了聚丙烯 (PP) 有机累托石 (OREC)纳米复合材料 ,采用广角X 射线衍射 (WAXD)定性地分析了PP OREC纳米复合材料及纯PP的结晶形态 ,由半峰宽定性地判断了对应晶面法向的晶粒的大小 .结果表明有机累托石没有改变聚丙烯的结晶晶型 (纳米复合材料主要还是α晶型 ) ,但是细化了晶粒的尺寸 .采用差示扫描量热法 (DSC)定量地研究了复合材料的非等温熔融结晶动力学 ,对所得数据分别用Jeziorny法的Mo法进行了处理 ,表明非等温结晶动力学参数Zc 及Avrami指数n随冷却速率的增加而增加 ,复合材料的Avrami指数n大于纯PP的n ;对相同配比的纳米复合材料 ,随着结晶度的增加 ,单位结晶时间里达到一定结晶度所需要的降温速率F(T)增大 ,对同一个设定的结晶度 ,纳米复合材料的F(T)比纯PP的小 ,说明需要的降温速率减小 .所有这些均说明有机累托石可作为聚丙烯的结晶成核剂 .     

GMA/苯乙烯多组分单体接枝聚丙烯结晶行为研究

使用差示扫描量热计 (DSC)研究了甲基丙烯酸缩水甘油酯 苯乙烯 (GMA St)多单体熔融接枝聚丙烯[PP g (GMA co St) ]的等温和非等温结晶行为 ,用偏光显微镜观察了结晶的形态 ,并利用Avrami方程对其结晶动力学进行了分析 .研究发现接枝聚丙烯的结晶模式与PP相似 ,属于异相成核控制的球晶三维生长 ;但接枝聚丙烯的结晶温度 (Tc)显著提高 ,幅度高达 16～ 19℃ ,总结晶速率与纯PP相比明显加快 .接枝聚丙烯上GMA co St支链的存在 ,降低了成核界面自由能 ,促进了聚丙烯结晶的异相成核 .在接枝率不太高的情况下 ,随着接枝率的提高 ,接枝聚丙烯的结晶温度升高 ,总结晶速率加快 .在高接枝率范围内 ,随着接枝率的提高 ,接枝PP的Tc 不再升高 ,且由于接枝链的增长严重阻碍了球晶生长 ,导致接枝PP的总结晶速率反而随接枝率的升高而下降     

多壁碳纳米管/聚丙烯复合材料的晶型及非等温结晶动力学

采用熔融共混法制备了多壁碳纳米管/聚丙烯(MWNT/PP)复合材料,利用X射线衍射法(XRD)、差示扫描量热法(DSC)分别研究了纯聚丙烯(PP)及MWNT/PP复合材料的晶型和非等温结晶动力学行为,并运用Mo法研究了纯PP及MWNT/PP复合材料的非等温结晶动力学行为。结果表明,多壁碳纳米管(MWNT)的加入使PP发生了由β晶型向α晶型的转变。MWNT在结晶过程中具有异相成核效应,提高了PP的结晶温度和结晶速率。MWNT/PP复合材料的结晶活化能均明显高于纯PP。MWNT的加入使PP在单位时间内达到一定结晶度所需的降温速率减小。     

流场作用对聚丙烯结晶成核过程和晶体生长过程动力学的影响

通过改进基于构象张量构建的流动诱导结晶理论模型,考虑了流场对结晶生长的影响,对比研究了流场作用对聚丙烯(PP)结晶过程中成核与晶体生长两阶段速率的不同影响程度.理论研究表明,虽然相比成核过程,流场诱导作用对PP晶体生长速率的加速程度有限,但要更为精确地描述流动引起的整个结晶动力学过程,特别是在剪切速率较高且熔体结晶温度较低的情况下,考虑流场对结晶生长速率的影响是十分必要的.研究结果还显示,由于分子链的松弛作用,PP在较低温度下的晶体生长速率受剪切流场的影响要大于较高温度下的影响.本文理论预测结果与实验现象和实验数据的很好吻合亦说明模型改进的合理性和可行性.     

马来酸酐接枝热塑性弹性体在PP/PA6共混物中的作用

研究了马来酸酐接枝热塑性弹性体 (TPEg )作为增容剂对聚丙烯 (PP) 尼龙 6 (PA6 )共混体系的相容性、相态以及物理力学性能的影响 .研究结果表明TPEg的加入大大改善了PP PA6共混体系的相容性 ,且随TPEg含量的增大分散相粒径明显降低 ,共混物的韧性以及延展性大大提高 ,同时拉伸强度及模量仍保持较好的水平 .TPEg增容的PP PA6共混物的非等温结晶行为的研究表明 ,共混物中PP和PA6的结晶行为不同于各自纯的聚合物 ,PA6作为成核剂使PP的结晶温度提高 ;而PA6由于TPEg的加入 ,出现分级结晶现象 ,一级结晶温度略低于纯PA6的结晶温度 ,且随TPEg含量增大结晶受阻 ,二级结晶温度与PP的接近 .由于PP、PA 6以及TPEg之间存在较强的相互作用 ,三元共混物中PP及PA6的玻璃化转变温度分别较其纯聚合物升高 .基于上述结果 ,提出了本共混体系的结构模型     

水溶性聚合物和两亲聚合物 21.丙烯酸/乙酸乙烯酯共聚物对碳酸钙结晶的影响

研究了晶种存在下丙烯酸／乙酸乙烯酯无规共聚物对碳酸钙从过饱和水溶液中结晶的影响。发现我们的实验条件下碳酸钙结晶包括溶液本体成核结晶和晶种上晶体生长两种不同过程，丙烯酸／乙酸乙烯酯共聚物同时具有明显抑制溶液成核结晶和抑制晶种上晶体生长的双重作用，而且这两种抑制碳酸钙结晶的作用均随共聚物中乙酸乙烯酯含量的增加而加强。     

预辐射聚丙烯反应挤出接枝丙烯酸的研究

利用电子束(EB)预辐照方法和反应挤出技术制备了聚丙烯接枝丙烯酸共聚物PP-g-AA. 采用化学滴定、红外光谱、偏光显微镜(PLM)、DSC和广角X射线衍射(WAXD)对接枝产物进行了表征. 研究结果表明, 接枝率随辐照剂量增加而增大并逐渐达到平台值, 但随单体浓度增大而表现为线性增加, 接枝链能起到异相成核作用, 从而提高了结晶速率并细化了球晶. 同时, 熔体流动速率(MFR)和力学性能测试结果表明, 预辐射和挤出过程造成了PP严重降解, 据此可认为接枝反应主要发生在聚丙烯断裂分子链的末端.     

硅氧烷液晶共聚物作为β晶成核剂对等规聚丙烯结晶结构与形态的影响

采用广角X射线衍射(WAXD)与偏光显微镜(POM)等手段研究了硅氧烷液晶共聚物(LCP-O2)作为新型成核剂对聚丙烯(PP)共混样品结晶结构与形态的影响.结果表明,低浓度的LCP-O2在PP共混体系中起到异相成核的作用,使PP的晶核数目增多,球晶细化,并提高了结晶速度,同时也诱导出了β晶的形成.LCP-O2的成核效果主要依赖于其在PP中的相对含量、液晶的分子结构与结晶的热处理过程,且随着结晶温度或成核剂含量的增加,对应PP试样的β晶含量(Kβ)呈现先增加,后降低的趋势.当LCP-O2质量分数为1.0%,在130℃等温结晶1h,对应PP试样的Kβ最大,为58%.此外,属于单斜晶的α球晶呈现黑白颜色,晶束呈放射状生长,边界清晰;而属于三方晶的β球晶亮度要高于α球晶,其颜色艳丽多彩,束状晶片聚集体呈支化生长,内部排列比α晶疏散,边界相对模糊,且β晶与α晶的形态分别在157和171℃完全消失.     

苯乙烯-丙烯嵌段共聚物等温结晶动力学的研究

用DSC法研究苯乙烯-丙烯嵌段共聚物(iPS-b-iPP)的等温结晶动力学。结果表明,在所选择的结晶温度(127～132℃)范围内,共聚物很好地符合Avrami动力学方程;共聚物结晶温度、结晶速率、结晶成核和生长方式都与共聚物结构和组成比有关,随着嵌段共聚物中iPS段含量的增加,结晶速率和Avranu指数(n)明显降低。     

橡胶相具有交联结构的新型抗冲聚丙烯合金

利用具有"颗粒反应器技术(RGT)"特征的Ziegler-Natta催化剂进行丙烯多相共聚(丙烯均聚+乙烯/丙烯无规共聚),通过在乙丙共聚阶段引入双烯烃单体1,9-癸二烯,使乙丙共聚物在聚合的同时实现交联,制备了新型抗冲聚丙烯合金.聚合反应结果表明,1,9-癸二烯可参与乙丙共聚,同时对聚合反应速率和共聚物组成影响较小;1,9-癸二烯使乙丙共聚物发生支化/部分交联,合金聚合物的熔体流动速率在引入1,9-癸二烯后显著降低,且凝胶含量随1,9-癸二烯用量的增加而增大.形态研究结果表明,乙丙共聚物的交联显著降低了其在聚丙烯基体中的分散尺度,提高了分散均匀性,分散相粒径随支化/交联程度提高而减小.力学性能测试结果表明,乙丙共聚物的交联使合金聚合物在保持较高韧性的同时显著提升了刚性,有利于实现抗冲聚丙烯合金的刚韧平衡.     

等规聚丙烯/二元乙丙橡胶合金相分离对结晶动力学的影响

用小角激光光散射(SALLS)、相差显微镜(PCM)、示差扫描量热仪(DSC)和偏光显微镜(POM)研究了聚丙烯/二元乙丙橡胶(iPP/EPR)共混体系的相分离行为和等温结晶行为.发现iPP/EPR(50/50,W/W)发生的液-液相分离遵循spinodal机理.通过Cahn-Hilliard方程求得了不同实验温度下iPP/EPR的表观扩散系数(Dapp)以及spinodal温度(Ts).考察了不同相分离程度的iPP/EPR体系结晶动力学,发现延长相分离时间(tps)或提高相分离温度(Tps)均会导致半结晶时间(t1/2)增大,即结晶速率降低.这被归于EPR成核作用的降低.动力学分析结果表明Avrami模型适用于描述该体系的等温结晶过程,其结晶机理基本不受相分离程度的影响,结晶均以瞬时成核和三维生长为主.     

Non-isothermal crystallization kinetics of β-nucleated isotactic polypropylene

Isotactic polypropylenes (iPP) samples were incorporated with two β-nucleating agents (NT-A and NT-C), respectively, and their non-isothermal crystallization and subsequent melt behaviors were investigated by means of differential scanning calorimeter. Jeziorny, Ozawa, and Mo methods were used to analyze non-isothermal crystallization kinetics of pure iPP and β-nucleated iPP samples. The activation energies (ΔE) of non-isothermal crystallization were calculated by Kissinger method. And the nucleation activities were calculated according to the Dobreva method. It is found that the crystallization temperature decreases and the crystallization rate increases with increasing cooling rate. The crystallization temperature and crystallization rate of nucleated iPP are higher than those of pure iPP. The order of ΔE is NT-A/iPP > pure iPP > NT-C/iPP. NT-C is more efficient than NT-A as a β-nucleating agent. But the non-isothermal crystallization kinetics of α- and β-phases cannot be determined separately. The present results should be considered with caution.     

Nonisothermal crystallization kinetics of isotactic polypropylene nucleated with a novel supported β-nucleating agent

The introduction of β-nucleating agent into isotactic polypropylene (iPP) is the most effective method to prepare β-iPP. In this paper, iPP nucleated with a novel highly efficient supported β-nucleating agent (NA100), calcium pimelate (CaHA) supported on the surface of nano-CaCO₃, was prepared and its nonisothermal crystallization kinetic, melting characteristic, and crystallization activation energy are investigated and compared with those of pure iPP, nano-CaCO₃ filled iPP, and β-nucleating agent CaHA nucleated iPP. The results indicate that addition of nano-CaCO₃ increases the crystallization temperature of iPP and has no influence on the crystal form of iPP. iPP and nano-CaCO₃ filled iPP mainly crystallize in the form of α-crystal. Although NA100 and CaHA induce iPP to mainly form β-crystal, NA100 nucleated iPP shows higher crystallization temperature, melting temperature, and β-phase content than that nucleated with CaHA without supports. Nonisothermal crystallization kinetic is well described by the equations of Avrami and Mo, and the crystallization activation energy was calculated from Kissinger’s method. It was found that the decreased crystallization activation energy is favorable to increase the crystallization rate and the content of β-crystal. Although the content of CaHA in 5 wt% NA100 nucleated iPP was less than that in 0.1 wt% CaHA nucleated iPP, the former formed more β-iPP than the latter, indicating that the β-nucleating agent CaHA supported on the surface of nano-CaCO₃ exhibits higher efficiency for preparation of β-iPP than pure CaHA powder.     

等规聚丙烯自成核的等温结晶动力学

近年来 ,有关等规聚丙烯 (i PP)的自成核研究已引起了人们的关注 [1 ] ,但有关其结晶动力学的报道并不多见 .Carfagna等 [2 ]用膨胀计法研究了 i PP在未完全熔融重结晶情况下的等温结晶动力学 ,得到的 Avrami指数远远小于 3 .张新远等[3 ] 研究了 i PP未完全熔融情况下的非等温结晶动力学 .到目前为止 ,i PP自成核的熔体降温等温结晶动力学尚未见报道 .本文在 i PP自成核研究的基础上 [4] ,用 DSC方法研究了 i PP自成核在较高温度下的等温结晶动力学 ,讨论了结晶机理 .结果表明 ,在本实验的自成核条件下 ,i PP依然是三维球晶生长 ,…     

稀土氧化物对聚丙烯等温结晶动力学的影响

本文用差示扫描量热法测定了3种稀土氧化物对聚丙烯等温结晶行为的影响。结果表明,Avrami方程指数n、成核机理、晶体生长方式以及结晶晶型基本上不受稀土氧化物的影响。少量稀土氧化物可使结晶晶格垂直于分子链方向单位面积的界面自由能降低,结晶速率加大,其中Y_2O_3的效果最为显著,La_2O_3效果最低,混合稀土的作用效果与Y_2O_3相似。填加1wt%的Y_2O_3可使聚丙烯的结晶速度常数增大一个数量级。     

镧配合物对等规聚丙烯等温结晶性能的影响

利用Avrami方程和Lauritzen-Hoffman结晶动力学理论研究了一种镧配合物LaC对等规聚丙烯(iPP) 等温结晶行为的影响. 差示扫描量热法(DSC)和X射线衍射技术(XRD)研究表明, LaC的加入并未改变iPP的结晶形态, 但LaC的存在能提高体系的结晶度并显著加速iPP的结晶过程. 在130 ℃进行等温结晶时, 含0.5%LaC(质量分数)的iPP与纯iPP相比, Avrami指数n值无显著差异, 但前者总的结晶速率常数k值比后者提高约4倍,而半结晶时间t1/2值减少到后者的62%, Avrami方程分析结果表明LaC的存在主要起到增加晶核的作用. 利用Lauritzen-Hoffman结晶动力学理论, 通过对iPP在121 ℃、124 ℃、127 ℃和130 ℃下等温结晶的数据进行分析可知, 加入0.5%的LaC后, 体系的成核常数kg从纯PP的3.3×105 K2增加到PP/LaC的3.8×105 K2, 而结晶生长时大分子在垂直于分子链方向折叠的界面自由能σe从纯PP的0.223 J·m-2降低到PP/LaC的0.154 J·m-2, 表明LaC在iPP结晶过程中不仅起到增加晶核的作用, 同时使大分子链更易排入晶格, 即起到促进结晶成长的作用.     

Effect of Clay/Diamond and Clay/Carbon Nanosystems on Structure-Properties Relationships of iPP

The effect of the addition of two combined fillers, smectite clay and diamond and smectite clay and carbon nanoparticles, on structure, morphology, isothermal and non isothermal crystallization behaviour, tensile and thermal properties of isotactic polypropylene (iPP) has been investigated by using several techniques: wide angle X-ray diffraction, optical and scanning electron microscopy, thermogravimetry, differential scanning calorimetry and tensile techniques. It was found that nanoparticles of diamond and carbon favour the nucleation of the β-form of iPP crystal, whereas the clay nanolayers do not have any influence on the crystal structure of iPP. The thermal stability of iPP/(clay+diamond) and iPP/(clay+carbon) is improved with respect to neat iPP, whereas no influence is detected when only clay is added to iPP. At the given crystallization conditions, the overall crystallization peak of iPP/(clay+diamond) almost exactly overlaps the crystallization peak of neat iPP, whereas in the case of iPP/clay and iPP/(clay+carbon) the maximum of the crystallization peaks is shifted to higher temperature. The spherulite growth rate, G values do not differ from one another. The iPP/(clay+carbon) system shows ductile behavior. The other systems show brittle behavior with failure before necking. These results were related with the very high percentage of beta phase present in the samples of iPP/(clay+carbon).     

Microstructure, morphology, crystallization and rheological behavior of impact polypropylene copolymer

Impact polypropylene copolymer (IPC), named polypropylene catalloy, not only possesses excellent impact property, but also presents good rigidity. Its superior performances result from the complicated composition and microstructure. In the present article, recent progress in the studies on microstructure, morphology, crystallization and rheological behavior of IPC is summarized, and findings of the authors and their collaborators are reported. In general, IPC is divided into three components, i.e., ethylene-propylene random copolymer (EPR), a series of different segment lengths ethylene-propylene copolymer (EbP) and propylene homopolymer. The reasonable macromolecular structures of EbP and a multilayered core-shell model of dispersed phase structure in IPC were proposed, in which the dispersed phase consists of an outer EbP shell, an inner EPR layer and an EbP core. It is found that the annealing at melt-state may lead to an abnormal phase inversion, and the phase inversion disappears when temperature cools down to room temperature. The cause of phase inversion is ascribed to the existence of EbP component, which results in the stronger activity of the dispersed phase. The crystalline structure and morphologic results confirm the formation of β-iPP in IPC. Furthermore, it is found that the ethylene content in IPC and cooling rate of the samples have an important influence on the formation of β-iPP. Based on the crystallization kinetics analyzed by Lauritzen-Hoffman theory, crystallization behavior of different IPC samples is discussed and it is proposed that the dilution effect of ethylene propylene copolymer has a more remarkable influence on surface nucleation than on crystal growth. In addition, annealing at high temperature can result in the changes of chain structure for IPC, and this instability is ascribed to the oxidative degradation and crosslink reaction mainly in iPP component.     

The influence of thermoelastomers on the crystallization behavior of isotactic polypropylene under shear

The crystallization behaviors of isotactic polypropylene (iPP) and its blends with thermoelastomers have been investigated with in situ X‐ray scattering and optic microscopy. At quiescent condition, the crystallization kinetics of iPP is not affected by the presence of elastomers; while determined by the viscosity, the differences are observed on sheared samples. With a fixed shear strain, the crystallization rate increases with increasing the shear rate. The fraction of oriented lamellar crystals in blends is higher than that in pure iPP sample, while the percentage of β phase is reduced by the presence of the elastomers. On the basis of experimental results, no direct correlation among the fraction of oriented lamellae, the percentage of β phase, and growth rate can be deduced. The evolution of the fraction of oriented lamellae supports that shear field promotes nucleation rather than growth process. Shear flow induces the formation of nuclei not only with preferring orientation but also with random orientation. The total density of nuclei, which determines the crystallization kinetics, does not control the ratio between nuclei with and without preferring orientation, which determines the fraction of oriented lamellae. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1188–1198, 2006     

The effect of the addition of polypropylene grafted SiO2 nanoparticle on the crystallization behavior of isotactic polypropylene

The crystallization behavior of isotactic polypropylene (iPP)/silica particle (SiO₂, 26 nm) nanocomposite has been investigated. In addition to the non surface-modified SiO₂, iPP grafted SiO₂ was synthesized and adopted to this study with an aim to understand the role of grafted polymer chain on the crystallization process. The crystallization rate of non surface-modified iPP/SiO₂ composite stays constant up to 1 vol%. It suggests the very weak nucleation ability of nano-sized silica particle. While large acceleration effect was observed for iPP-grafted SiO₂/iPP composite. The spherulite density increased with increasing SiO₂ contents, and more interestingly, the spherulite growth rate also increased. This finding leads to the conclusion that the grafted iPP chain has a plasticizing effect that reduces the chain entanglements at the interface. Further increase in SiO₂ contents, the crystallization rate, the spherulite density, and the spherulite growth rate showed the steep decreases at higher SiO₂ content range regardless of the surface modifications of SiO₂. It was attributed to the confinement of matrix chain since the inter-particle distance of adjacent SiO₂ approaches to the end-to-end distance of matrix chain, which a large molecular motion is restricted. Moreover, the average size of SiO₂ aggregation in iPP matrix was successfully evaluated by analyzing the contents dependence of the growth rate, assuming that the inter-particle distance with zero growth rate coincided with end-to-end distance of matrix iPP chain.