Vibration-dependent Crystal Form of Isotactic Polypropylene under Nonisothermal Crystallization

A study concerning the effect of vibration on the crystal structure and morphology for isotactic polypropylene(iPP) was conducted. The crystallite size, crystal structure and crystallinity of iPP under or without vibration treatment were investigated by means of differential scanning calorimetry(DSC) and wide-angle X-ray diffraction(WAXD). The results reveal that the crystallinity of the vibrated samples decreases at a high cooling rate, but it remains constant at a low cooling rate because of the chain relaxation of iPP. It has been found that vibration obviously increases the content of β-form of crystal phase and the amount of β-crystal mainly depends on the vibration amplitude.

EFFECT OF FINAL HEATING TEMPERATURE ON CRYSTALLIZATION OF ISOTACTIC POLYPROPYLENE NUCLEATED WITH AN ARYL AMIDE DERIVATIVE AS β-FORM NUCLEATING AGENT

An aryl dicarboxylic acid amide compound TMB-5 is an efficient β-form nucleating agent for isotactic polypropylene （iPP）. Because of the solubility of TMB-5, superstructure and morphology of iPP crystals changed with melting conditions. Effects of final heating temperature （Tf） on heterogeneous nucleation of iPP/TMB-5 were investigated. It was discovered that the crystallization temperature increased with decreasing Tf value. The optical microscopic images indicated that when TMB-5 partially dissolved in iPP melt, the remaining （non-dissolved） TMB-5 facilitated the recrystallization of dissolved nucleating agent from the melt, which promoted crystallization. Complete solubility of nucleating agent caused the decreasing efficiency. TMB-5 recrystallized in the form of tiny needles, whose aggregates induced dendritic iPP crystals.

Mechanistic Insights into the Shear Effects on Isotactic Polypropylene Crystallization Containingβ-Nucleating Agent

The crystalline structures and crystallization behaviors of iPP containing β nucleation agent TMB-5 （iPP/TMB-5） were investigated by synchrotron radiation wide angel X-ray diffraction （SR-WAXD）, differential scanning calorimeter （DSC） and polarized light microscope （PLM）. It was found that α-crystallization lagged behind β-crystallization at normal temperatures, but the discrepancy reduced with increasing temperature. TMB-5 could not induce β-iPP when the nucleation agent is wrapped up with α-crystal that crystallized at high temperatures. The polymorphic composition of iPP/TMB-5 was susceptible to the introductory moment of shear. New crystallization process of β-nucleated iPP was proposed to understand the experimental phenomena which could not be explained by those reported in the literature. It was supposed that polymer crystallization initiated from mesophase, and the formations of iPP crystals involved the organization of helical conformation ordering within rnesophase. It was proposed that the iPP melt contained mesophases with stereocomplex-type ordering of right-handed and left-handed helical chains which could be disturbed by shear or TMB-5, leading to different polymorphic structures.

Different influences of nucleating agents on crystallization behavior of polyethylene and polypropylene

The crystallization behavior of polyethylene (PE) and polypropylene (PP), including the neat ones and the ones nucleated with the same nucleating agent (NA), was studied by DSC. It was found that the nucleating agent decelerated the PE nonisothermal crystallization process. NA did enhance the nucleating rates for both PE and PP, but the linear growth rate dominated the volumetric growth rate for PE, and the volumetric growth rate dominated the overall crystallization rate. That is why PE nucleated with NA had a slower overall crystallization rate than the neat one.

Morphology, Crystallization Behavior and Tensile Properties of β-Nucleated Isotactic Polypropylene Fibrous Membranes Prepared by Melt Electrospinning

β-nucleated isotactic polypropylene （iPP） fibers with diameters less than 5 Hm were prepared through melt electrospinning. The effects of electrospiuning process and rare earth β-nucleating agent （WBG） on the crystal structure of iPP fibers were investigated. The results indicate that the addition of WBG can improve the fluidity of iPP melt remarkably and help the formation of fine fibers with thinner diameter, while the electrostatic force applied on the iPP melt is not favorable for the formation of β-crystal in iPP fibers. In addition, the morphology and crystalline structure of WBG/iPP electrospun fibers depended on the content of WBG. Both the crystallinity and the percentage of β-crystal form of WBG/iPP electrospun fibers increase with the rise of the content of nucleating agent, which endows the prepared electrospun fibers excellent mechanical properties. The β-nucleated iPP electrospun fibrous membranes prepared in this study can be used for protective clothing material, filtration media, reinforcement for composites and tissue engineering scaffolds.

稀土β晶成核剂对聚丙烯结晶与发泡性能研究

为探讨成核剂WBG-Ⅱ在长链支化聚丙烯(LCBPP)/等规聚丙烯(iPP)共混物中的β晶诱导效果及其对PP材料力学性能和泡沫结构的影响,通过在LCBPP中引入不同成核剂,利用X射线衍射、差示扫描量热仪和旋转流变仪对样品进行表征,筛选出高效诱导β晶的成核剂WBG-Ⅱ。结果表明,当加入5份(质量份,下同) WBG-Ⅱ时,LCBPP的冲击强度提升了128%,而拉伸强度下降幅度控制在20%以内;同时,成核剂的加入对LCBPP的熔体强度无显著负面影响。利用差示扫描量热议进一步观察发现,成核剂WBG-Ⅱ对iPP具有强效的诱导β晶取向作用;在LCBPP基体中掺入iPP显著提高了混合物中β晶的结晶度;与纯LCBPP相比,LCBPP/iPP配比1∶1的样品结晶度提高了190%;此外,加入iPP还增强了PP混合物在高频下的储能模量和复数黏度。

一种高效酰胺类透明成核剂对聚丙烯性能的影响

研究了一种新型酰胺类成核剂,1,3,5-苯三甲酸三(新戊胺),对等规聚丙烯(iPP)性能的影响。首先,对iPP光学和力学性能进行表征。结果表明,该成核剂在较低的浓度下就展现了较高的成核效果,当添加量为0.3‰(质量分数,下同)时,iPP雾度降低了60.2%,弯曲弹性模量和拉伸强度分别提高了19.7%和13.7%,这说明该成核剂是一种高效的iPP透明成核剂。其次,应用偏光显微镜和差示扫描量热仪分别对iPP晶体形貌和结晶行为进行了表征。结果表明,纯iPP在30 min还未完成结晶过程,结晶速率较慢。加入成核剂后,成核iPP在4 min左右就基本完成了结晶过程,结晶速率大大提高,同时球晶尺寸明显减小。另外,成核剂使iPP结晶温度从121.1℃提高至130.0℃,熔融温度从164.1℃提高至165.8℃。这进一步说明了该成核剂的高效。最后,对纯iPP和成核iPP的等温结晶动力学进行研究,结果表明,该成核剂降低了iPP的Avrami指数n,说明其能够促进iPP的异相成核,从而加快结晶速率。

山梨醇类成核剂改性聚丙烯及其共聚物的结晶行为与性能

基于聚丙烯(PP)均聚物和不同乙烯含量的PP共聚物,系统地研究了山梨醇类成核剂含量和乙烯单元含量对PP的结晶动力学、结晶结构、结晶形貌、透明性和力学性能的影响,并通过流变行为分析了成核剂在降温过程中的自组装行为。结果表明,PP的结晶、透明性和力学性能依赖于成核剂含量和乙烯单元含量。当成核剂含量增加到0.1%(质量分数)时,显著加快PP均聚物和共聚物的结晶速率,提高结晶度,提高材料的刚性。然而,乙烯单元含量的增加使PP的结晶速率减慢,降低结晶度,降低材料的刚性。乙烯单元和成核剂的加入都促进PPγ晶的形成,而且γ晶的相对含量随乙烯单元和成核剂含量的增加而增加。增加乙烯单元和成核剂含量也提高PP的透明性。

COMBINED EFFECT OF MODIFIED ZEOLITE 13X AND β-NUCLEATING AGENT ON IMPROVING β-CRYSTAL CONTENT AND TOUGHENING POLYPROPYLENE RANDOM COPOLYMER

Although addition of β-nucleating agent directly into homo-polypropylene （PPH） is a useful method to improve ,β-crystal content and toughen PPH, polypropylene random copolymer （PPR） makes this method powerless due to its random structure and low crystallinity. In this study, the β-nucleated PPR with high β-crystal content was prepared by a novel high effective β-nucleating system which consists of β-nucleation agent （TMB-5） and modified zeolite 13X （M13X）. It was found that M13X and TMB-5 had a synergistic influence on improving β-crystal content and toughening PPR. The content of β-crystal in PPR/M13X/TMB-5 was significantly larger than the sum of that in PPR/M13X and PPR/TMB-5. Besides, fracture behavior, phase morphology and relaxation of matrix chain segments were also investigated. The results showed that M13X and TMB-5 improved the mobility of amorphous chain segments at low temperature and contributed to much energy dissipation. This work provides a powerful method to modify PPR.

聚丙烯成核剂的开发与进展

聚丙烯(PP)是一种典型的半结晶热塑性聚合物,由于PP熔体的结晶速率较慢,易形成较大尺寸的球晶,其制品的光泽度和透明性较差,限制了PP在透明包装和日用品等领域的发展。目前,主要通过改变PP晶型的结晶行为达到改性PP的目的;而成核剂与PP共混改性在保留了PP原有特点的同时,透明性济表面光泽度均得到明显改善,为PP改性常用的方法。基于此,总结了PP结晶的机理,并且,综述了目前PP成核剂的研究现状,涉及的α成核剂种类包括无机类、枞酸类、环状羧酸盐类、山梨醇缩醛类及磷酸酯盐类成核剂;β成核剂种类包括稠环类、二元羧酸盐类、酰胺类、稀土类成核剂及复配型成核剂。

豆蔻酸盐/磷酸酯羟基铝诱导PP结晶行为影响

为了研究不同金属种类的豆蔻酸盐与双[2,2′-亚甲基-双(4,6-二叔丁基苯氧基)磷酸]羟基铝(APAl-OH)复配后对聚丙烯(PP)结晶行为的协效作用,将一价金属豆蔻酸盐(14Li,14Na,14K)和二价金属豆蔻酸盐(14Zn)分别与APAl-OH共混形成复配成核剂体系,通过熔融共混的方法添加到PP基体中制备了PP复合材料。采用差示扫描量热仪研究了复配成核剂体系对PP结晶性能的影响以及复配成核剂体系中不同金属种类的豆蔻酸盐与APAl-OH之间的协效结晶作用;采用偏光显微镜研究了复配成核剂体系细化PP球晶的能力。结果表明,当一价金属豆蔻酸盐(14Li,14Na,14K)与APAl-OH复配后,其复配成核剂体系促进PP结晶的能力随金属相对原子质量的增加而呈先上升后下降的趋势,其中14Na与APAl-OH的协效结晶作用最突出,相比于纯PP的结晶活化能(366.17 kJ/mol),PP/APAl-OH-14Na的结晶活化能下降至228.75 kJ/mol,相比于纯PP的结晶温度(110.2℃),PP/APAl-OH-14Na的结晶温度提高至126.9℃。当二价金属豆蔻酸盐(14Zn)与APAl-OH复配后,其复配成核剂体系促进PP结晶的能力不如单独添加APAl-OH,这说明14Zn与APAl-OH之间并无协效结晶的作用。

芳基二酰胺成核剂对均聚聚丙烯应用性能及结晶行为的影响

以均聚PP-700+为基体树脂,以2,6-苯二甲酸环己酰胺(TMB-5)为β晶成核剂,采用熔融共混法制备β晶改性聚丙烯。利用偏光显微镜、差示扫描量热仪、万能试验机、数位冲击试验机以及热变形温度测定仪分析了TMB-5对均聚聚丙烯应用性能及结晶行为的影响。结果表明,添加TMB-5成核剂后,诱导α晶型逐渐转变为β晶型,随着添加量的增加,PP-700+的β晶含量,结晶温度逐渐增大,结晶速率逐渐增快。当0.2%的TMB-5添加到PP-700+基体中,β晶改性材料的β晶含量提高至84.9%,拉伸强度提高4.5%,弯曲模量与弯曲强度分别提高14.6%和13%,同时冲击强度未受到损失,悬臂梁冲击强度与简支梁冲击强度分别提高9.8%和5.9%,热变形温度提高了42.13℃。

不同金属离子复配的有机磷酸盐成核剂调控PP结晶行为和应用性能

通过添加成核剂来调控聚丙烯(PP)的结晶行为进而改善其应用性能是非常有效且可行的调控手段。采用熔融共混法分别制备了添加成核剂磷酸酯盐/硬脂酸锂(AlP/LiSt)及成核剂磷酸酯盐/硬脂酸钠(AlP/NaSt)质量分数都为0.5%的PP-Li和PP-Na复合材料,通过差式扫描量热分析仪和偏光显微镜对PP复合材料的结晶行为进行测试,结果表明,成核剂AlP/LiSt和AlP/NaSt作为有效的成核位点,可显著提高PP的结晶温度及细化PP球晶;在降温速率为5℃/min的条件下,相较于纯PP的结晶温度(113.5℃),PP-Li和PP-Na复合材料的结晶温度分别提高到127.7℃和131.3℃。力学性能测试结果表明,PP-Li和PP-Na复合材料的拉伸强度分别比纯PP提高了6.7%和14.8%,而弯曲模量分别比纯PP增加了16.6%和38.0%,说明AlP/LiSt和AlP/NaSt成核剂均可明显改善PP的拉伸强度和弯曲模量,其中AlP/NaSt成核剂的提升效果更为显著;PP-Na复合材料的冲击强度与纯PP基本持平,PP-Li复合材料的冲击强度比纯PP提高了10.3%,说明AlP/LiSt成核剂更有利于提高PP的韧性。由Kissinger法计算得到的PP复合材料的热降解反应活化能(Ed)数据表明,两种成核剂均有利于提高PP的耐热性能,PP-Li,PP-Na复合材料的Ed值较纯PP分别提高了55.4 kJ/mol和49.3 kJ/mol,表明PP-Li和PP-Na热降解所需要的温度和能量均比纯PP高。

复合成核剂对聚丙烯结晶行为的影响

以超细橡胶粒子与有机磷酸盐成核剂复配的方法制备了一种新型复合成核剂,通过示差扫描量热法(DSC)比较了复合成核剂改性PP以及有机磷酸盐成核剂改性PP的结晶温度、等温结晶行为及等温结晶动力学;利用扫描电子显微镜(SEM)的能谱附件和透射电子显微镜(TEM)研究了复合成核剂的微观形态及其在PP中的分散情况.研究结果表明,复合成核剂中超细橡胶粒子作为载体使有机磷酸盐成核剂附着在其表面,提高了成核剂在聚丙烯中的分散性,因而提高了成核剂的成核效率,当成核剂用量较小时,即可明显提高PP的结晶速率和力学性能.

成核剂对聚丙烯及其共聚物的结晶行为和性能的影响

研究了成核剂 1 ,3∶ 2 ,4-对二乙基苄叉山梨醇 (EDBS)对聚丙烯及其乙烯共聚物的结晶行为和结晶形态的影响 ,并对其薄膜进行了光学性能的表征 .结果表明 ,添加少量 (质量分数 0 .5 % )的成核剂 ,使聚丙烯样品的结晶温度大大提高 ,结晶度明显增加 .而对于乙烯共聚聚丙烯样品 ,添加少量 (质量分数 0 .5 % )成核剂 ,不仅使其整体结晶温度大大提高 ,结晶度增加 ,而且明显强化了低有序部分的结晶 .少量成核剂的加入 ,使聚丙烯及其共聚物的球晶尺寸明显缩小 。

山梨糖醇/稀土复合成核剂对等规聚丙烯非等温结晶行为的影响

采用差示扫描量热仪(DSC)研究了山梨糖醇/稀土复合成核剂不同组成对等规聚丙烯非等温结晶动力学及其熔融行为的影响。动力学分析结果表明莫志深方法很好地描述聚丙烯非等温结晶动力学,用Kissinger公式计算所得非等温结晶活化能表明复合成核剂的加入提高了结晶活化能。结晶形态和熔融行为均依赖于复合成核剂的组成和降温冷却速率,较低的降温速率有利于β晶型的生成,随着降温速率的增加,β晶型的相对含量减少。在较多的β成核剂含量和较低的降温速率条件下,可以获得较高含量的β晶型。

成核PP注塑样品的非等温结晶行为与熔融特性

用 DSC研究了两种成核剂成核 PP的非等温结晶行为与熔融特性。两种成核剂均使 PP的降温结晶温度提高 ,结晶峰半高宽变窄 ,结晶度与熔点略有提高 ,但结晶峰对称性变差 ,熔融峰半高宽加大 ,成核样品的结晶温度对冷却速率的依赖性较纯 PP的小。根据过冷度和成核 PP与纯 PP的结晶温度之差 ,成核剂成核作用大小顺序为 :A>D。

β成核剂对等规聚丙烯结晶性能的影响

研究硬脂酸盐作为β成核剂对聚丙烯结晶性能的影响。WAXD结果表明:硬脂酸盐能诱导聚丙烯生成β晶型,在添加量为0.3%时,β晶的相对含量达到最大为76.64%。DSC曲线表明:硬脂酸盐改性的聚丙烯在152℃出现β晶型的熔融吸热峰,其结晶起始温度和结晶峰温度均向高温移动,表明添加硬脂酸盐可诱导PP中α晶向β晶转变,具有明显的β成核作用。

一种新型β成核剂及其对聚丙烯结晶性能的影响

研究了一种稀土类新型β成核剂WBG对等规聚丙烯(iPP)结晶性能的影响。WAXD研究发现,WBG加入后可大大提高PP中β晶型的含量,当其加入量超过0 3%时,β晶型的含量可达90%;利用DSC考查了130℃时PP在加入WBG前后的等温结晶过程,发现WBG显著提高了PP的成核速率。从结构上看,WBG不同于目前常见的任何一种β成核剂,是一种高效的新型成核剂。

磷酸盐与山梨醇类成核剂成核PP样品等温结晶行为与熔融特性

用差动扫描量热计 (DSC)研究了一种有机磷酸盐类成核剂 (A)、山梨醇类成核剂 (D)成核PP和纯PP的等温结晶行为和熔融特性。结果表明成核样品缩短PP的半结晶时间 ,成核剂A比D更明显 ;纯PP样品的半结晶时间正比于结晶温度 ,而成核PP的半结晶时间与结晶温度的关系在结晶温度低时 ,依赖性较纯PP的小 ,而在高结晶温度 ,半结晶时间对结晶温度的依赖性比纯PP的大。成核剂的加入使PP结晶完善性提高 ,且熔融峰发生改变 ,熔融峰高温区出现一肩峰 ;而纯PP在低温区有一很宽的肩峰。根据半结晶时间 ,2种成核剂的成核效果为A >D 。