【作者】 杨红梅；

【导师】 郑强；

【作者基本信息】 浙江大学 ， 材料加工工程， 2003， 博士

【摘要】 采用两步法熔融插层工艺，在双螺杆挤出机上制备了以乙烯—醋酸乙烯共聚物(EVA)为增容剂的低密度聚乙烯(LDPE)基蒙脱土纳米复合材料。通过X-衍射(XRD)、热重分析(TG)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)以及傅立叶变换红外光谱(FT-IR)的表征结果讨论了影响蒙脱土剥离的因素，分析了复合材料的形态结构和性能。用高级流变扩展系统(ARES)及毛细管流变仪对复合体系熔体的线性粘弹行为、稳态剪切流变行为进行了表征，并对熔体粒子网络结构的形成与演化作了较系统的研究。 研究发现，非极性聚合物LDPE很难插层于无机蒙脱土片层间，即使用烷基季铵盐类的有机插层处理剂对蒙脱土进行有机化处理后，也较难与LDPE作用而良好剥离分散于基体中。而加入EVA作为增容剂后，聚合物分子易于插层。 复合材料的制备受多种因素的影响，其中蒙脱土结构的不稳定性不容忽视。由于在高热(200℃以上)或强机械剪切作用下，蒙脱土层状堆叠结构会坍塌，导致不能与聚合物分子作用生成聚合物—层状硅酸盐纳米复合材料，因此熔融插层的温度选择显得十分重要。另一方面，EVA与LDPE的配比、添加方式等因素，均对复合材料中蒙脱土的最终分散状况造成影响。实验结果表明，LDPE／EVA=77／20是一比较理想的配比，可以兼顾插层效果和工艺的可行。在该配比下，可通过双螺杆挤出机，先将EVA与有机蒙脱土熔融挤出复合后，再与LDPE熔融挤出复合，制备具有剥离结构的LDPE基蒙脱土纳米复合材料。 TEM、FT-IR等表征发现，复合材料中蒙脱土片层可以很好地剥离分散于聚合物基体中，但片层并非完全以单片层分散状态剥离，而是以片层堆叠形成“准粒子”；同时，还存在一定量的团聚体。蒙脱土片层之间、蒙脱土片层与聚合物基体间均具有强烈的相互作用。由于片层在基体中不呈单片层分散状，故复合材浙江大学博上学位论文摘要料的拉伸模量大大低于由加加动一Tsa艺连续方程得到理论计算值。尽管如此，复氛菜馨摹氰摆默氢篡资鼎迄饭琴氰黔耀零髯的特殊性能均得益于由径厚比较大的蒙脱土片层在基体中良好的分散。 复合材料熔体呈现独特的线性粘弹行为。在蒙脱土含量低至3叭%时，体系低频率区域(末端区域)的动态模量出现近似于固体的粘弹行为尸类固(s olid-li毅的”行为)，模量对频率依赖性降低甚至无依赖性。然而当蒙脱土含量低于和脸或蒙脱土片层在基体中呈完全团聚状态，则复合材料表现出与聚合物基体类似的线性粘弹特性。实验发现，在熔体经大振幅振荡剪切后，上述“类固..行为会明显减弱。表明良好剥离分散的蒙脱土片层在聚合物基体中由于强烈相互 子网络结构是其独特粘弹行为的关键。研究结果表明仁复合体系 G‘和动态损耗模量宁的对数关系性呀G‘一109夕，_印维乖温 动态模量满足时温叠加原理，频率移动因子(aT)的对数与塌度的倒攀即种马与了一‘有良好的线性关系·一_ 面，复合体系熔体的稳态剪切流变行为具有不同于普通粒子填充聚合 性。在低剪切速率下，复合体系熔体仍存在牛顿流动区。同时可观察到填充舞合物体系特有的屈服和剪切变稀现象·与普通粒子填充聚合物体系相比，耳9辉基蒙脱土纳米复合体系在相对较低的填充量时剪切变稀即十分明显宁 黑翼器钾纂器纂粱鬓攀鬓耀馨鬓告片。粼翼踪艾需囊簇是翼暴攀黯黯纂袅作用的存在，是该体系结构一性能关系的根源。___更多还原

【Abstract】 The nanocomposites with exfoliated structure composed of low density polyethylene (LDPE), of organically modified montmorillonite and ethylene vinyl acetate copolymer (EVA) were prepared through two steps melt intercalating technique using a twin-screw extruder. The factors relevant to montmorillonite intercalation and exfoliation were analyzed through X-ray diffraction (XRD), thermogravimetry (TG), transmission electron microscope (TEM), scanning electron microscope (SEM) and Fourier transform infraredspectroscopy (FT-IR). The morphology, structure and properties for the composites were discussed. And the linear viscoelastic behavior, steady rheological behavior and the formation/evolvement of particles net structure for molten nanocomposites were studied using an advanced rheometric expansion system (ARES) and capillary rheometry.It is believed that the melt intercalation is a more efficient processing for formation of nanophase in polymer-layered silicates hybrids. LDPE intercalated into the space between the layers of organically modified montmorillonite (org-MMT), especially in the presence of compatibilizer EVA. The unstable stacking of layers of org-MMT was easily damaged under force and heat. Hence, it is very important to decide the process temperature for preparing the composites, and it was found that 200 ℃ was a upper limitation of temperature. On the other hand, the proportion of LDPE/EVA and adding of EVA were very important factors for composites preparing. The results shown that the nanocomposites with exfoliated structure could be prepared in the case of LDPE/EVA=77/20, EVA/org-MMT melted firstly and then extruded with LDPE using a twin-screw extruder.The layers of montmorillonite could disperse into polymer matrix uniformly rather than individually. Based on TEM images and FT-IR characteristics, it is found that most of layers formed as "pseudoparticles", which connected due to very stronginteraction. As a result, the tensile modulus of the composites were more tower than the corresponding values calculated by using Halpin-Tsai continuous equation, but higher than those of polymer matrix. While the steam barrier of films prepared by casting from the composites were enhanced as compared with that of the matrix film.The linear viscoelastic behavior of melts for nanocomposites with different content of montmorillonite modified by cetyltrimethylammonium bromide and octadecyltrimethylammonium bromide was studied. The results obtained through examining the dynamic storage module G’, dynamic loss module G" and stress relaxtion module G(t) of the composites revealed that the linear viscoelastic properties of composites strongly depended on the loadings of montmorillonite exfoliated into the composites. With the increasing of montmorillonite content ,thecomposites showed a trend of pseudo-solidlike at lower frequencies, The montmorillonite layers could align along the stress direction, and as a result, the dependence of dynamic modules on the frequency was quite different before and after suffering from large amplitude oscillatory shear.The results obtained through examining loss tangent tan at deferent temperature and G’ dependence on frequency ω of the composites revealed that the secondaryrelaxation asd G’ of samples depended on the loadings of montmorillonite exfoliated into the composites. With the increasing of montmorillonite loading, the peak position corresponding to secondary relaxation for composites moved to higher and the peak values appeard higher, too. Time-temperature superposition principle could bee applied to G’ dependence on CD, and the dependence of shifted factor aT on temperature demonstrated a linear relationship by a plot of In aT vs. T-1.The steady rheological measurements for nanocomposites melts were conducted.The results revealed that the melts of exfoliated nanocomposites with lower loading oforg-MMT exhibited shear-thinning even at lower shear rate as compared with polymers filled with common particles, while the melts flow depended weakl更多还原