【作者】 尹波；

【导师】 杨鸣波；

【作者基本信息】 四川大学 ， 材料加工工程， 2007， 博士

【摘要】 以聚乙烯(PE)和聚丙烯(PP)为主的通用塑料高性能化是当前及以后高分子材料科学与工程领域的研究热点和重点，聚烯烃与工程塑料(如聚碳酸酯等)共混是提高聚烯烃性能的一个重要途径。本论文将聚碳酸酯(PC)与聚乙烯共混，并通过形态设计与控制实现聚乙烯性能的改善。在实现PC/PE共混物形态设计与控制及其性能提高的过程中主要存在两个问题需要解决，一为共混物相形态的控制，二为聚乙烯与聚碳酸酯两相间界面作用的提高。共混物形态是影响材料性能的关键因素之一，为获得高性能的聚乙烯共混物材料，必须对PC/PE共混物在混合和成型过程中的形态演变规律进行研究，并能达到对形态的控制和预测。对于PC/PE极不相容体系，界面作用弱，界面往往是材料发生破坏的薄弱点，因此必须对PC/PE体系进行增容，以获得良好的界面作用，同时增容作用也有利于共混物形态的控制。本论文通过双螺杆挤出混合和注射成型获得共混物试样，研究了PC/PE共混物在混合和成型过程中的形态演变与控制，以及外场作用和反应增容等因素共混物形态、结构和性能的影响。主要研究内容和结果如下：1)PC/PE共混物在双螺杆挤出过程中的形态演变规律研究了PC/PE共混物在双螺杆挤出过程中沿螺杆轴向不同位置的分散相形态，建立了PC/PE共混物在混合过程初期的形态演变模型。结果表明，PC分散相在从毫米尺度的颗粒演变为微米尺度的多样化形态的过程中，经历片层状、纤维状和粒子状结构的发展过程。PC分散相的软化变形是混合初期分散相尺寸降低和形态改变的主要原因，在混合初期，PC分散相的破碎过程占主导，可忽略聚集作用的影响。研究了混合温度、两相粘度比、螺杆转速和螺杆组合等因素对分散相形态演变的影响规律。发现在PC临界流动温度以上进行了混合，PC分散相经过初期的软化变形阶段后，在混合的中后期以液滴的形式继续变形破碎，同时发生聚集；而在PC临界流动温度以下进行混合，PC分散相始终以软化变形的机理进行形态的演变，特别是在混合中后期，分散相尺寸不再下降，且形态不规则。分散相粘度越低，越接近于基体粘度，其由毫米尺度转化为微米尺度的过程越快，尺寸下降也较高粘度分散相明显；但在混合的中后期，低粘度分散相易变形、易聚集，导致分散相产生了一定取向的有序结构，同时聚集作用会导致混合后期分散相尺寸增加。螺杆转速提高，剪切作用将增强，因此分散相由毫米尺度转化为微米尺度的过程加快，最终得到的共混物分散相尺寸降低。混合初期的捏合区构造对分散相形态和尺寸的影响较大，在这一区域主要以分散相破碎为主，故加强剪切作用，可改善混合效果；在混合的中期，加强剪切作用，可改变分散相由毫米尺度转化为微米尺度的机制，获得特殊的有序结构，同时降低分散相尺寸；在混合后期，捏合区的调控可加强或减弱聚集作用的发生，从而平衡分散相的破碎和聚集过程。2)PC与EAA的大分子反应及其对PC/PE共混物形态和性能的影响通过核磁共振氢谱表征了PC/EAA共混物在催化作用下的反应产物。结果表明，PC与EAA在熔体混合过程中发生了酸-酯交换反应，生成了PC-g-EAA共聚物。DBTO是该反应的有效催化剂。该反应受共混物组成、催化剂用量和混合时间的影响。PC-g-EAA的生成提高了PC/EAA体系的粘度。DSC分析发现，在PC/EAA两相体系中，PC与EAA的反应提高了PC分子链与EAA分子链的相互作用，限制了EAA分子链的运动能力，从而导致EAA结晶度的降低。在PC/PE/EAA体系中，通过EAA的反应增容，相间的相互作用提高，PE的结晶过程受到阻碍，降低了PE相的结晶度。动态机械分析的结果也证明了PE结晶度和晶体完善程度的下降，导致α松弛温度向低温方向偏移。EAA的加入和反应生成的PC-g-EAA共聚物降低了共混体系的表面张力，导致PC分散相粒子的尺寸降低。通过动态流变分析发现EAA反应增容PC/PE体系的粘弹行为发生了改变，由于PC-g-EAA接枝共聚物的生成，增强了PC相与PE相的相互作用，导致催化体系的动态弹性模量、粘性模量和复数粘度上升。结果表明PC与EAA间的反应产物PC-g-EAA共聚物有助于改善两相界面作用，相界面的改善对在成型过程中获得分散相的形态控制有重要意义。3)PC/PE/EAA共混物在混合和成型过程中的形态控制对PC/PE/EAA共混物在双螺杆混合和注射成型过程中的形态进行了研究，并利用混合过程中的剪切与停留作用及其注塑过程中的剪切变化实现了对PC/PE/EAA共混物的形态控制。结果表明，在双螺杆挤出过程中，增加螺杆转速，将加强了剪切作用，同时也降低了停留作用，因此螺杆转速对分散相形态的影响是上述两种作用相互竞争的结果，在中等转速(120rpm)下，两种作用达到平衡，获得分散相尺寸最小和分布最窄的共混物。而螺杆组合对分散相形态的影响是剪切和停留作用相互协同的结果。通过改变螺杆组合得到的共混物分散相尺寸最低达到0.50μm(D_n)和1.24μm(D_v)。利用Palieme模型计算得到了不同条件下的PC/PE/EAA共混物的界面张力。EAA的反应增容极大地降低了共混物的界面张力，由PC/PE体系的19.3mN/m降低到PC/PE/EAA体系的7.3mN/m。由于界面张力主要受大分子反应生成的接枝产物量的影响，因此停留时间对界面张力的影响更明显。随停留时间的增加，PC/PE/EAA的界面张力逐渐下降。本工作获得的PC/PE/EAA共混物的界面张力最低可达2.5mN/m，说明通过混合过程中的调控，共混物的相界面得到显著改善。在高速注塑过程中，增容体系的PC分散相在增强的界面作用下更易获得变形，在流动过程中从剪切层到芯部均形成了较大长径比的纤维结构。在冻结过程中，由于过渡区和芯部的冷却时间较长，纤维状分散相逐渐松弛产生颈缩，并最终破碎成为有序排列的椭球状粒子。在低速注塑过程中，分散相受剪切作用较弱，形成的取向纤维的长径比较高速条件小，在冷却过程中，长径比较小的纤维分散相松弛作用较弱，两相界面能够维持其形态，从而不发生颈缩和破碎。由此获得了具有多层次纤维分散相的特殊皮芯结构，这种皮芯结构中的纤维分散相的直径随距表层距离增加而变大。4)PC/PE/EAA共混物注塑试样的形态与冲击性能关系本论文研究了PC/PE和PC/PE/EAA共混物在不同注射速率下成型试样的冲击性能。与PC/PE体系相比，PC/PE/EAA反应增容体系的缺口冲击强度明显提高。当注射速率为3.6cm~3/sec时，PC/PE/EAA共混物的缺口冲击强度达到最大值，其近浇口处为52.1kJ/m~2，远浇口处为24.5kJ/m~2，分别比未增容体系提高了3.5倍和1.9倍。说明EAA大分子反应原位增容能明显改善PC/PE共混物的冲击性能。PC/PE共混物的远近浇口冲击性能差异较小，且不随注射速率变化而发生改变。但PC/PE/EAA体系的近浇口的缺口冲击强度高于远浇口，在不同注射速率下均相差近一倍。同时增容体系的冲击性能依赖于注射速率的变化，注射速率升高，冲击性能下降。由于增容体系特别是低速注塑试样的分散相形态与未增容体系存在明显差异，因而增容前后分散相抵抗裂纹生长的能力不同，导致了冲击性能的变化。注射速率差异导致的分散相纤维的尺寸变化对冲击性能产生了较大的影响，长径比较小、直径较大的纤维在抵抗裂纹发展的过程中吸收了大量能量，因而增容体系低速注塑试样的冲击性能远高于未增容体系。界面作用和压应力也是影响PC/PE/EAA共混物冲击性能的重要因素，同时也是造成增容体系样品远近浇口性能差异的原因。在注射速率为3.6cm~3/sec的PC/PE/EAA共混物试样近浇口的断面中发现，芯部的大直径短纤维分散相在破坏过程中不发生断裂，而且在增容作用和压应力的影响下，基体与分散相结合较好，分散相纤维不能从基体中拔出，导致试样芯部的分散相与基体发生整体拔出破坏，这种破坏形式吸收了较多的能量，提高了材料的冲击性能。而远浇口的压应力较弱，分散相纤维与基体的摩擦作用降低，导致纤维从基体中拔出，未与基体结合发生变形。芯部区域纤维结构的破坏形式的差异是导致低速增容样品冲击性能变化的主要因素。在高速注塑试样中，也存在基体与分散相粘结和分散相变形等现象，但高速注塑试样的冲击性能受过渡区分散相纤维变形的影响较大。更多还原

【Abstract】 Performance enhancement of general-purpose plastics (mainly polyethylene (PE) and polypropylene (PP)) is one of the most important topics in the field of polymer materials science and engineering at present and in the future. Blending modification with engineering plastics is a major route to enhance the performance of general-purpose plastics. Polycarbonate (PC) was used to modify the high density polyethylene in this thesis. Controlling of phase morphology and compatibilization are both the important problems that should be settled to realize the performance enhancement of polyethylene blend. Phase morphology of PC/PE blend is an important factor to influence the properties of the blend. Therefore, the morphology development of PC/PE during the twin-screw extrusion and injection molding was investigated in this thesis. The interface interaction is weak in PC/PE blend, which induced the decreasing of the mechanical properties. In this thesis, the macromolecular reaction between PC and ethylene-acrylic acid (EAA) was used to in-situ compatibilize the PC/PE blend. Morphology of PC/PE blend was controlled by adjusting the technical parameter of blending, injection molding and the reactive compatibilization. A novel skin-core structure was obtained in the processing, which could be the reason that the enhancement of the impact property of PC/PE blend. The main results are: 1) Morphology development of PC/PE blend during compounding in a twin-screw extruderThe morphology of PC/PE blends at different positions along the screw axis was studied and the model of morphology development of the dispersed phase in the initial stage during twin-screw extrusion was proposed. The polycarbonate pellets partially deformed to sheets and ribbons during the melt softening step. Due to the effect of interfacial tension and flow characteristics, those sheets or ribbons became unstable and holes were formed. The holes rapidly grew in size and in concentration until the ribbons were changed to fibers.The effects of blending temperature, viscosity ratio (the ratio of the viscosity of the dispersed phase to that of the matrix), screw speed and the screw configuration on the morphology of the PC/PE blend during the extrusion were discussed in detail. It was found that the morphology of the dispersed particles and the interfacial adhesion between the dispersed phase and matrix were both influenced by the extrusion temperature. The dispersed phase exhibits a spheroidal shape and a small size during high temperature processing, and an irregular shape and a large size when it was processed at low temperature. The PC phase with a lower viscosity was easier to. disperse and also to coalesce. Therefore, the deformation of the low-viscosity dispersed phase during the processing was more intense than that of the high-viscosity dispersed phase. It was found that both of the shape and size of the dispersed phase in the uncompatibilized PC/PE blend are influenced by the screw speed. The evolution of dispersed phase morphology can be affected by increasing screw speed, and the dispersed particle size decreases with the increasing of the screw speed. By comparing the effect of the screw configuration on the morphology development of the PC/PE blend, it was found that the melting and breaking up of the dispersed phase were mainly affected in the initial blending stages by the number of the kneading blocks. When a kneading block with a 90 degree staggering angle was used, the size of the dispersed particles decreased and the long fibers were shortened, the large particles were drawn by the additional kneading zone. Finally, all of these structures were completely changed to the short fibers. 2) Macromolecular reaction between PC and EAA and the effect of reactive compatibilization on the morphology and properties of PC/PE blend A grafted copolymer PC-graft-ethylene-co-acrylic acid (PC-g-EAA) was generated as a compatibilizer in situ during processing operation by ester and acid reaction between PC and EAA in the presence of the catalyst of dibutyl tin oxide (DBTO). The effects of the blend composition, catalyst content and mixing time on the reaction between PC and EAA were discussed. The influence of this copolymer formation at the interface between PC and EAA on the rheological properties and crystallization behavior for EAA/PC binary blends were studied. The equilibrium torque increased with the DBTO content increasing in EAA/PC blends on Haake torque rheometer, indicating the in situ formation of the graft copolymer, which enhanced the viscosity of PC/EAA blend.DSC studies suggested that the heat of fusion of the EAA phase in PC/EAA blends with or without DBTO reduced with the formation of copolymer compared with pure EAA. This indicated that the generation of PC-g-EAA enhanced the interaction between PC and EAA molecule, which decreases the mobility of EAA chain. Therefore, the crystallization of EAA chain was hindered and the degree of crystallinity of EAA phase decreased. Study on the crystallization of PC/PE/EAA blend indicated that PE phase crystallized still at its bulk crystallization temperature. The degree of crystallinity of PE phase in PC/PE/EAA blends was also reduced with the addition of EAA and DBTO compared to the uncompatibilized PC/PE blend, indicating that the graft copolymer PC-graft-EAA improves the interaction between PC and PE phase and hindered the movement of PE chain and arrangement into the lattices. It was found by dynamic mechanical analysis that the temperature of relaxationαandγof PE both shifted to the lower temperature due to the decreasing of the crystallinity of PE phase.Then morphology of the uncompatibilized and compatibilized blends of PC/PE was studied with different contents of EAA and DBTO. Morphological observations in PC/PE blends also revealed that the number of microvoids was reduced and the interface was imprived by increasing EAA content or adding catalyst DBTO as compared to the uncompatibilized PC/PE blends. This implied the interface tension of compatibilized PC/PE blend became lower owing to the addition of EAA and the generation of PC-g-EAA copolymer. It was found by dynamic rheological analysis that the elastic modulus, viscous modulus and complex viscosity were all increased along with the generation of PC-g-EAA copolymer, which indicated that the reactive compatibilizaion with EAA could improve the interface interaction of PC/PE blend.3) Morphology control of PC/PE/EAA blend during blending and injection molding The morphology of dispersed phase was tailored by optimizing of the combination of the share rate and the resident time during twin-screw extrusion. It was found that the increasing of screw speed provided higher shear rate and hence resulted in the less resident time. At a medium speed, the morphology of dispersed phase was modified, and the size of dispersed particles decreased and the diameter distribution narrowed. The size of dispersed phase was controlled by changing the screw configuration, and the number average diameter of PC particles was reduced to 0.50 um and the volume average diameter was 1.24 um.The interface tension of the different PC/PE/EAA blends was calculated using Palierne model. The interface tension of PC/PE blend was reduced due to the reactive compatibilization. The interface tension of uncompatibilized PC/PE blend, 19.3mN/m, was dropped to 7.3mM/m of the compatibilized blend. The resident time was variable with the varieties of the screw configuration, which influenced the generation of PC-g-EAA copolymer. Therefore, the interface tension of PC/PE/EAA blend was obviously influenced by the screw configuration. In this thesis, the PC/PE/EAA blend with a lower interface tension of 2.5mN/m was obtained by changing the screw configuration. The morphology and interface interaction were both improved by the controlling of the technical parameter during twin-screw extrusion.In the injection molding, the dispersed phase in the compatibilized PC/PE blend is easy to deform by the shear. At a high injection rate, the dispersed particles at different zone (skin, sub-skin, intermediate and core) all deformed to the fiberious structure. But in the cooling and solidification of the polymer melt, the dispersed fibers, in the intermediate and core, would relaxed and necked, and broke up to the oriented particles. On the other hand, at a low injection rate, the deformation of dispersed phase was smaller than that of high injection rate due to the decreasing of shear rate. Therefore, the dispersed fibers in the core zone with a small length/diameter ratio did not break up to particles, and the fiber structure was held, which could be a novel skin-core structure differing from the former proposed model.4) Morphology and impact strength property of PC/PE/EAA blend The impact properties of PC/PE/EAA blends injected at different injection rate were studied in this thesis. The notched impact strength of the gate side of PC/PE/EAA blend injected at an injection rate of 3.6cm~3/sec was 52.1kJ/m~2, and 24.5kJ/m~2 of the non-gate side. The notched impact strength of PC/PE blend at the same positions was 11.64 and 8.36kJ/m~2 respectively. This indicated that the reactive compatibilization improved the toughness of the blend. The impact properties of the gate side and non-gate side of uncompatibilized blend were comparative, but the difference at gate and non-gate side of compatibilized blend was obvious. The impact property of compatibilized PC/PE blend depended on the injection rate and the impact strength decreased along with the increasing of the injection rate.The novel skin-core structure in the injection bar with a low injection rate improved obviously the impact strength because the dispersed fiber with a small length/diameter ratio and a large diameter could absorb the sizeable energy during the impacting. It was found from the SEM micrograph of the impact fracture surface of the blend injected at the low injection rate that the dispersed fiber at the gate side was pulled out and the dispersed fibers stuck on the matrix. This indicated that the interface interaction in the PC/PE/EAA blend was too intense to be destroyed, which induced that the matrix was broken during the impacting, and the improved interface bonding enhanced the impact strength of the blend. At the non-gate side, the interface contact decreased, which induced the invalidation of the interface bonding during the impact experiment. Therefore, the impact strength at non-gate side of compatibilized blend was lower than that at gate side. The dispersed particles in the core zone of the blend injected at the high rate absorbed only few of the energy during the impacting, which induced that the impact property of the blend at high injection rate was much lower than that at low injection rate.更多还原