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。     

累托石/聚丙烯插层纳米复合材料的制备与性能

采用熔融共混法制备了有机改性累托石 (OREC)粘土 均聚聚丙烯 (PP)纳米复合材料 ,以X 射线衍射分析 (XRD)及透射电子显微镜分析 (TEM)观察了复合材料的相貌结构 ,研究了复合材料的力学性能及热性能 .结果表明 ,OREC在添加份数较少时可与均聚聚丙烯熔融插层形成插层型聚丙烯纳米复合材料 ,该复合材料与纯PP相比 ,具有较高的拉伸强度、断裂伸长率及冲击强度 .在有机粘土添加 2 %时 ,复合材料的拉伸强度、断裂伸长率、冲击强度最高 ,与纯PP相比 ,2 %添加量的聚丙烯纳米复合材料拉伸强度提高 6 5 7% ,断裂伸长率提高 2 89 3% ,冲击强度提高 14 1% ,10 %失重率时对应的热分解温度提高 50K .     

聚丙烯/蒙脱土纳米复合材料的等温结晶研究

采用差示扫描量热法 (DSC)对插层聚合法制备的聚丙烯 /蒙脱土纳米复合材料 (PP MMT)的等温结晶过程进行了研究 .引入蒙脱土 (MMT)后 ,PP MMT的结晶速率大幅度提高 ,相对结晶度略有下降 .采用Avrami方程对结晶动力学进行研究 ,Avrami指数n≈ 3 .0 ,半结晶时间t1 2 大幅度降低 .采用Hoffman理论计算了PP MMT的球晶生长的单位面积表面自由能σe,结果表明σe 随MMT含量的增加逐渐降低     

聚丙烯/蒙脱土纳米复合材料非等温结晶动力学的研究

用熔融插层法制备聚丙烯 蒙脱土纳米复合材料 ,用DSC手段研究了其非等温结晶行为 ,并与聚丙烯进行了对比 .对所得数据分别用修正Avrami方程的Jeziorny法、Ozawa法和Mo法进行处理 .结果表明 ,用Jeziorny法和Mo法处理非等温结晶过程比较理想 ,而用Ozawa法处理则不太适用 .用Jeziorny法求出的参数Zc和n随冷却速率的增加而增加 ,但复合材料的Zc 和n略大于聚丙烯的Zc 和n ,用Mo法求出的参数F(T)随结晶度的增加而略有增加 ,a几乎未变 ,复合材料的F(T)略小于聚丙烯的F(T) ,复合材料的a约为 1.40略大于聚丙烯的a(其值约为 1.0 4) .按Kissinger方法计算出聚丙烯及聚丙烯 蒙脱土纳米复合材料的结晶活化能分别为 189.37kJ mol,15 5 .6 9kJ mol,说明有机蒙脱土的加入 ,降低了聚丙烯的结晶活化能 ,起到了异相成核的作用     

去氢枞酸类成核剂改性聚丙烯的非等温结晶动力学研究

对以去氢枞酸盐为成核剂的聚丙烯非等温结晶动力学进行了研究，用修正Avrami方程的Jexiorny法和莫志深法进行处理。结果表明：修正Avrami方程的Jeziorny方法和莫志深法都适用于去氢枞酸类成核剂改性的聚丙烯的非等温结晶动力学。在同样的降温速率下纯聚丙烯的t1/2比成核聚丙烯的t1／2要长，当降温速率为20K/min时，纯聚丙烯和成核聚丙烯的t1/2分别为0．78min和0．51min。同时从莫志深法得到的F(T)结果可以看出，达到相同的结晶度时纯聚丙烯所需的降温速率要大于成核聚丙烯所需的降温速率，说明成核剂的加入提高了聚丙烯的结晶速率。从Jeziorny法求出的纯聚丙烯和成核聚丙烯的Avrami指数分别为4．46和2．77，表明成核剂改变了聚丙烯的结晶成核和生长方式。     

改性高岭土对PP/高岭土纳米复合材料结晶性能的影响

通过将不同改性的高岭土与聚丙烯共混, 制备了聚丙烯插层的PP/高岭土纳米复合材料. 并通过X射线衍射分析(XRD)、透射电子显微镜(TEM)研究了复合材料的微观结构, 同时通过差示扫描(DSC)非等温结晶方法和偏光显微镜(PLM)照片, 研究了改性高岭土母粒对聚丙烯的结晶性能的影响. 采用Avrami方程式及Jeziorny修正过的Avrami的方程式对PP/高岭土的非等温结晶动力学进行了研究. 结果表明, 有机改性过的高岭土可被聚丙烯完全剥离, 在XRD谱图中, 高岭土的001峰不可见, 在TEM中可见剥离的片层. 同时随着改性高岭土的加入, 使得聚丙烯异相成核结晶增长, 且填充聚丙烯的最快结晶温度在395K. 结果也表明, 有机改性的高岭土能有效促进PP的异相成核, 提高PP的结晶速率和结晶温度, 但对结晶速率常数影响不是很大.     

聚丙烯/插层改性水滑石纳米复合材料结构与性能研究

采用离子交换法制备了十二烷基磺酸钠和衣康酸共同改性水滑石(LDHs2),FTIR、XRD分析表明,十二烷基磺酸钠和衣康酸能够同时进入水滑石片层之间,层间距有很大提高。利用改性水滑石,通过马来酸酐-苯乙烯共接枝改性聚丙烯相容剂的熔融共混和聚丙烯与水滑石溶液共混制备母粒,然后与聚丙烯分别熔融共混两种方法制备聚丙烯/水滑石纳米复合材料。TEM分析表明,马来酸酐-苯乙烯共接枝改性聚丙烯作相容剂可以使水滑石在聚丙烯基体中达到更好分散。DSC、XRD分析表明,水滑石、相容剂以及短链共聚聚丙烯对聚丙烯晶型没有影响,但对其结晶速率、结晶度以及晶粒大小有所改变,复合材料中聚丙烯的起始结晶温度、结晶峰温度、结晶速率、结晶度均比纯聚丙烯高,晶粒粒径分布也更均匀。     

聚乙交酯非等温结晶行为研究

利用差示量热扫描热分析仪(DSC)测得了不同降温速率下聚乙交酯(PGA)的非等温结晶的温度-热焓曲线。分别通过Ozawa法、Jeziorny法和莫志深法对PGA的非等温结晶机理进行了分析。Ozawa法结果表明:在给定的温度范围内,Ozawa法并不适用于描述PGA的非等温结晶行为;Jeziorny法结果表明:不同降温速率下,PGA结晶过程的Avrami指数(n)接近4,PGA非等温结晶为均相成核、晶粒三维增长的过程;莫志深法结果表明:Avrami指数与Ozawa指数的比值(a)基本无变化,动力学参数f(T)随降温速率增加逐渐增大,即在更快的降温速率下,PGA结晶更充分,可获得更高的结晶度。通过Kissinger方程计算得到的PGA结晶扩散活化能为-66.9kJ/mol。     

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     

聚丙烯/纳米蒙脱土复合材料的结晶动力学研究

采用热分析方法，研究了聚丙烯／纳米蒙脱土复合材料（PP／CLAY）的等温结晶行为，并分别用Avrami方程和赵志英方法对所得数据进行了分析，研究结果表明，纳米蒙脱土微粒对聚丙烯等温和非等温结晶行为均有不同程度的影响，可提高聚丙烯的结晶速率并改善结晶结构。     

Organically modified rectorite toughened poly(lactic acid): Nanostructures, crystallization and mechanical properties

To improve the toughness of PLA, poly(lactic acid) (PLA)/organically modified rectorite (OREC) nanocomposites were prepared via the melt-extrusion method. A partially exfoliated and partially intercalated structure was confirmed by WAXD and TEM. The crystallization behaviors of neat PLA and nanocomposite were studied by POM and DSC, and it was found that OREC had a great effect on the overall crystallization rate and spherulitic texture of PLA. The presence of OREC could toughen PLA greatly. For example, when 1 wt.% OREC was added, the elongation at break of the nanocomposite was increased to 210%. The toughening mechanism was analyzed through the observation of the inner structure of the tensile test bar using SEM.     

聚丙烯-g-聚氨酯共聚物的非等温结晶动力学研究

用DSC法研究了聚丙烯 (PP)和聚丙烯接枝聚氨酯的共聚物 (PP g PU)在不同冷却速率下的非等温结晶动力学 .用Avrami方程和莫志深改进法对DSC测定结果进行了处理 ,结果表明 ,PP g PU的动力学参数能很好的符合Avrami方程和莫志深改进方程 .PP接枝了聚氨酯支链后 ,结晶速率增大 ,球晶的生长和成核机制也相应发生改变 ,而其变化规律与接枝物的组成和结构密切相关     

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.     

Nonisothermal crystallization and morphology of poly(butylene succinate)/layered double hydroxide nanocomposites

Biodegradable poly(butylene succinate) (PBS) and layered double hydroxide (LDH) nanocomposites were prepared via melt blending in a twin-screw extruder. The morphology and dispersion of LDH nanoparticles within PBS matrix were characterized by transmission electron microscopy (TEM), which showed that LDH nanoparticles were found to be well distributed at the nanometer level. The nonisothermal crystallization behavior of nanocomposites was extensively studied using differential scanning calorimetry (DSC) technique at various cooling rates. The crystallization rate of PBS was accelerated by the addition of LDH due to its heterogeneous nucleation effect; however, the crystallization mechanism and crystal structure of PBS remained almost unchanged. In kinetics analysis of nonisothermal crystallization, the Ozawa approach failed to describe the crystallization behavior of PBS/LDH nanocomposites, whereas both the modified Avrami model and the Mo method well represented the crystallization behavior of nanocomposites. The effective activation energy was estimated as a function of the relative degree of crystallinity using the isoconversional analysis. The subsequent melting behavior of PBS and PBS/LDH nanocomposites was observed to be dependent on the cooling rate. The POM showed that the small and less perfect crystals were formed in nanocomposites.     

Effect of silver nanoparticles on the morphology,crystallization, and melting behavior of polypropylene: A study on non-isothermal crystallization kinetics

The nanocomposites were prepared using melt intercalation method and the effects of the processing conditions on silver nanoparticles dispersion were investigated by transmission electron microscopy. Non-isothermal crystallization kinetics of virgin polypropylene (PP) and its nanocomposites have been evaluated using differential scanning calorimetric technique. The non-isothermal crystallization melt data were analyzed using macro kinetics equation with the help of Avrami, Malkin, and Mo’s models. The crystallization rate increased with the increasing of cooling rates for virgin PP and nanocomposite, but the crystallization of nanocomposite was faster than that of PP at a given cooling rate. The activation energy for non-isothermal crystallization of virgin polymer and nanocomposites based on Kissinger method has been determined to be 186 and 211 kJ/mol, respectively. Transmission electron microscopy analysis reveals balanced dispersion and presence of some silver nanoparticles aggregates, which act as a heterogeneous nucleating agent during the crystallization of the nanocomposite.     

Isothermal crystallization behavior of exfoliated‐PP/IMMT nanocomposites via in situ polymerization

Highly exfoliated isotactic‐polypropylene/alkyl‐imidazolium modified montmorillonite (PP/IMMT) nanocomposites have been prepared via in situ intercalative polymerization. TEM and XRD results indicated that the obtained composites were highly exfoliated PP/IMMT nanocomposites and the average thickness of IMMT in PP matrix was less than 10 nm, and the distance between adjacent IMMT particles was in the range of 20–200 nm. The isothermal crystallization kinetics of highly exfoliated PP/IMMT nanocomposites were investigated by using differential scanning calorimeter(DSC) and polarized optical microscope (POM). The crystallization half‐time t_1/2, crystallization peak time t_max, and the Avrami crystallization rate constant K_n showed that the nanosilicate layers accelerate the overall crystallization rate greatly due to the nucleation effect, and the crystallization rate was increased with the increase in MMT content. Meanwhile, the crystallinity of PP in nanocomposites decreased with the increase in clay content which indicated the PP chains were confined by the nanosilicate layers during the crystallization process. Although the well‐dispersed silicate layers did not have much influence on spherulites growth rate, the nucleation rate and the nuclei density increased significantly. Accordingly, the spherulite size decreased with the increase in MMT content. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2215–2225, 2009     

超细CaCO_3的粒子尺寸对PP结晶行为的影响

The effects of CaCO3 on the crystallization behavior of polypropylene (PP) were studied by means of DSC and WAXD.The average sizes of the CaCO3 powders used were 0.1μm (UC) and 0.5μm (GC),respectively.The PP/CaCO3 composites at compositions of 1phr and 10 phr were investigated.The results showed that the addition of CaCO3 reduced the supercooling,the rate of nucleation and the overall rate of crystallization (except for the 10phr UC/PP sample).The crystallinity of PP was increased and the size distribution of the crystallites of α-PP was broadened.On the other hand,the crystallization rate of 10phr UC/PP is 1.5 times higher than that of neat PP.It has an overall rate of crystallization 2 times as much as that of the neat PP and has the maximum crystallinity.The sizes of crystallites and the unit cell parameters of α-PP were varied by the addition of CaCO3.β-PP was formed by addition of GC and was not detected by addition of UC.The differences of crystallization behaviors of PP might be attributed to the combined effects of the content and size of CaCO3 filled.     

Isothermal and non-isothermal crystallization kinetics of branched and partially crosslinked PET

The crystallization kinetics of branched and partially crosslinked poly(ethylene terephthalate) (PET), prepared using trimethyl trimellitate as branching agent was studied using DSC and WAXD. Crystallization rates were retarded with increasing branching agent content. Avrami equation was used in the isothermal crystallization, while for the non-isothermal process the Ozawa model was applied. Isothermal crystallization half-times increased with branching agent content and crystallization peak temperatures during cooling, decreased. WAXD showed big broadening and reduced degree of crystallinity compared to the neat polyester. Though, the crystal lattice parameters did not seem to alter, crystal size reduction was evidenced.     

EFFECT OF N,N,N’,N’-TETRAALKYL TEREPHTHALAMIDE ON NON-ISOTHERMAL CRYSTALLIZATION KINETICS OF POLYPROPYLENE

The effect of N,N,N＇,N＇-tetraalkyl terephthalamide （TATA） on the non-isothermal crystallization and melting characteristics ofpolypropylene （PP） was studied. The addition of TATA can lead to the formation ofβ-crystal PP. With the increase in TATA concentration the degree of crystallinity for β-crystal PP increased significantly, and that for a-crystal PP decreased, which indicated that TATA effectively induced the formation of β-crystal PP. WAXD also revealed the existence of β-crystal PP after the introduction of TATA into PP. PP containing TATA crystallized at a temperature range of 5-10℃ higher than that of pure PP, and the half-crystallization time （t1/2） and Avrami exponent （n） of PP at the same cooling rate were decreased by the addition of TATA, indicating that TATA influenced the crystallization rate and crystallization growth mode of PP. The rate constant of crystallization of PP containing TATA （Zc） was larger than that of pure PP, which further indicated that the crystallization of PP was accelerated by the addition of TATA.