【作者】 佟翠艳；

【导师】 张景萍； 杨德才；

【作者基本信息】 东北师范大学 ， 物理化学， 2008， 博士

【摘要】 聚丙烯和聚乙烯以其优良的综合性能和高性价比成为产量最多的通用大品种塑料之首。并且目前已有众多大型国际石化公司放弃十年前所奉行的“以生命科学为21世纪石化行业发展的主导,传统聚烯烃行业已过时”的理念,重新转向PP, PE等传统高分子体系的研究,尤其是对高性能新型聚烯烃(即PP, PE)结构的研究,为其进一步高性能化提供理论依据。高抗冲共聚聚丙烯(hiPP)的合成基于反应器颗粒技术的开发及应用,使PP与增韧组分直接在聚合釜内实现亚微观程度的混合,从而有效改善PP的抗冲性能并降低生产成本。hiPP的合成一般采用序列聚合工艺:第一步先合成高立构规整度,高孔隙率的丙烯均聚物颗粒(iPP);第二步在iPP粒子内合成橡胶相(乙-丙共聚物EPR)。最终产品具有良好刚性和韧性平衡。压力管材专用聚乙烯树脂是由乙烯和不同的烯烃共聚得到的产品,此产品性能优良,具有普通聚烯烃不能比拟的性能。本论文采用13C-NMR、DSC、TEM、PLM、SEM、AFM等多种研究手段,同时结合样品分级和不同级分选择性重新共混等方法对不同hiPP和PE共聚物的组成,分子链结构,结晶行为和相结构进行了系统研究,以探讨该体系分子链结构-聚集态结构-性能间的构效关系,取得一些创新性结果。1.观察到在均聚阶段得到的iPP原始粒子的三级结构形态:最小的构筑单元-初级粒子(直径约100 nm),由初级粒子聚集而成的次级粒子(直径在几个至上百微米),以及由次级粒子聚集成的宏观iPP粒子(直径约0.6 mm);首次发现由第一阶段液相聚合生成的iPP粒子中含有大量的被低等规度聚丙烯半填充的微孔。在这些微孔中存在着的填充物阻碍乙烯/丙烯共单体向iPP粒子中扩散。正是这种传质阻碍作用使得乙烯/丙烯共单体在iPP粒子内的扩散速度小于聚合速度,从而导致了EPR相在iPP粒子中的形成过程是由外向内发展。在聚合的早期,EPR相仅在iPP粒子的外层形成,随着聚合的不断进行,EPR相逐渐向内层发展,最终形成内外均一的分散相;EPR相在半填充微孔壁和初级粒子之间的间隙的内表面催化剂活性中心上直接生成,随着反应的进行,这些间隙中生成的EPR膨胀进入微孔中。该结果不仅有助于对催化体系聚合工艺和反应动力学的调控,同时加深了对EPR形成机理的理解。2.发现hiPP的分散相呈现多层核-壳结构,即内芯由聚乙烯和短序列的乙-丙多嵌段共聚物组成,中间层为EPR,外壳为长序列的乙-丙嵌段共聚物,从而证明短序列乙-丙多嵌段共聚物和长序列乙-丙嵌段共聚物的作用是完全不同的。EPR为增韧相,内芯聚乙烯结晶相对EPR有增刚作用,而外壳长序列乙-丙嵌段共聚物结晶相一方面可增加分散相的刚性,另一方面可视为“增容层”,强化聚丙烯基质与分散相的结合。正是这种内芯和外壳为硬相,中间层为软相的多重结构分散相成为决定材料力学性能的关键因素,在对聚丙烯增韧的同时,还保持其高的刚性,达到刚韧平衡;通过比较几种高抗冲聚丙烯样品的相形态及其与材料性能的关系,进一步证明hiPP中分散相的多层核-壳结构是决定材料力学性能的关键因素。AW191样品分散相的多层核-壳结构最完整,因此力学性能(韧性)最好,SP179样品分散相的外壳相对不明显,故性能较差,而7033N样品的分散相无第三层外壳,故性能最差。该结果一方面深化了对hiPP链结构和多重相形态的认识,另一方面为该材料的高性能化提供了理论依据。3.通过对压力管材专用聚乙烯共聚物熔体拉伸薄膜的微结构研究发现,熔体拉伸薄膜除高取向片晶外,还含有较多的纤维晶,纤维晶平行于拉伸方向,穿过几个片晶区,平均直径约为12纳米,其形态特征为晶区和非晶区交替排列的晶桥结构。纤维晶的生成源于聚乙烯共聚物中的超高分子量组分,该组分在压力管材制品中起到缠结和系带分子的增强作用。该结果不仅有助于深入理解和认识聚合物取向结晶机理,同时也为该材料的性能优化提供了实验数据。更多还原

【Abstract】 The composition, molecular chain structure, crystallization and phase morphology of different hiPP and PE copolymer were investigated by solvent fractionation, 13C NMR, DSC, TEM, PLM, AFM and SEM to establish the molecular chain structure-property relationships of this material. Some novel results are obtained.The production of high impact polypropylene copolymer (hiPP) is based on reactor granule technology. A sequential polymerization process is usually applied to produce hiPP. First, isotactic polypropylene (iPP) particles with porosity are prepared. These particles are transferred to the next reactor where the elastomeric phase (EPR) is produced within the iPP particles. The end-products exhibit excellent toughness-rigidity balance.The original homopolymerized iPP particle exhibits a multiple structure, i.e., the iPP particle ( ca. 0.6 mm in diameter) is an agglomerate of many subparticles (ca. several to hundred microns in diameter), while the subparticle is in turn formed by a great deal of primary particles (ca. 100 nm in diameter); It is found for the first time that ethylene-propylene copolymer (EPR) phases in polypropylene (iPP) particle produced in the first stage slurry polymerization exhibit a developing process from exterior to interior. During the early stage of ethylene-propylene copolymerization, with lower content of copolymerized ethylene (7.4 mol%), the EPR phases occur only in external layer of the particle, while at the late stage of the copolymerization with higher content of copolymerized ethylene (26.7 mol%), the elastomer phases distribute uniformly in the whole particle. This phenomenon is due to an effect of mass transfer resistance. The origin of mass transfer resistance is loosely agglomerate inclusions of low tacticity polypropylene within the semi-filled micropores inside the iPP particles. It is the inclusions inside the micropores that resist the diffusion of ethylene/propylene comonomers into the particle.It is found that the dispersed phase of hiPP in both the solution-cast films and the bulk exhibits a multilayered core-shell structure, i.e., inner core, intermediate layer and outer shell. The inner core is mainly composed of polyethylene and ethylene-propylene segmented copolymers with shorter sequence length, the intermediate layer is ethylene-propylene random copolymer (EPR), and the outer shell consists of ethylene-propylene block copolymers with longer sequence length. The outer shell could not only increase the stiffness of the dispersed phase, but also be considered a compatibilizing layer to enhance interfacial adhesion between the dispersed phase and the iPP matrix. It is the multiphase morphology that makes the material possess both the high rigidity and the high toughness.The study on morphological structure of melt-drawn films of polyethylene containing small amount of copolymerized component indicates that, in addition to highly oriented lamellae, the melt-drawn films of the polyethylene copolymers contain a large amount of fibrous crystals with average diameter about 12 nm, which are parallel to drawing direction. Simulation experiment (adding 1 wt% ultra-high molecular weight polyethylene into regular high density polyethylene) proves that the formation of the fibrous crystals originates from ultra-high molecular weight component in the polyethylene copolymers. However, this kind of fibrous crystal is different from classical extended chain fibrous crystal. Morphological characteristic of the fibrous crystal of the copolymer should be a crystal-bridged structure with an alternating alignment of crystalline and noncrystalline regions. A model of the crystal-bridged fibrous crystal has been proposed, which not only benefits understanding the mechanism of the oriented crystallization of polymers, but also provides a theory foundation for improving properties of the material.更多还原