【作者】 杨晓明；

【导师】 戴文利；

【作者基本信息】 湘潭大学 ， 高分子化学与物理， 2007， 硕士

【摘要】 本文通过熔融接枝的方法制备了双峰聚乙烯接枝马来酸酐(BMPE-g-MAH),并用红外光谱对其结构进行了表征。将BMPE-g-MAH作为增容剂加入到聚碳酸酯(PC)/双峰聚乙烯(BMPE)共混材料中,制得了PC/BMPE增容共混材料,并对其耐溶剂开裂性能和静、动态力学性能进行了测试。通过扫描电镜(SEM)对PC/BMPE共混材料的断裂面和裂纹尖端结构进行了观测,对材料的裂纹扩展过程及其机理进行了较为详细的分析。耐溶剂开裂性能测试表明,随着PC/BMPE共混材料中BMPE含量的增加,样品在二甲基甲酰胺(DMF)中的开裂和溶胀程度减小。添加增容剂BMPE-g-MAH的共混材料较未增容共混材料的开裂和溶胀程度小,说明BMPE-g-MAH的加入改善了PC/BMPE材料在有机溶剂中的耐溶剂开裂性。力学性能测试表明,随着BMPE-g-MAH含量的增加,PC/BMPE共混材料的缺口冲击强度呈上升趋势:当BMPE-g-MAH用量为10%时,比未加入相容剂的PC/BMPE共混材料的冲击强度提高了约45%。与未增容的共混材料相比,PC/BMPE增容共混材料的储能模量略低,损耗模量峰较小,在140℃附近的损耗因子峰较小,这是由于BMPE-g-MAH增强了PC/BMPE两相界面处的粘合作用,使BMPE更好地分散到PC相,从而缓解了PC相内部由于刚性PC分子取向而产生的应力。对共混材料脆断面的SEM观测表明,BMPE-g-MAH的加入改善了PC和BMPE相容性。共混材料的冲击断裂面上形成了一些微细纤维,且增容共混材料比未增容材料断裂面上的纤维状物更多。共混材料的断裂面可分为两个区:微空穴化的裂纹引发区和形成了大量纤维的裂纹扩展区。裂纹尖端的SEM照片显示,PC/BMPE共混材料的两个断裂面之间存在具有纤维连结的粘结区。粘结区的纤维可分为靠近裂纹尖端的初生纤维和距尖端稍远的细长纤维,相应地有两种不同的形成机理:表面拉伸和纤维拉伸。裂纹尖端边界处的粘结应力通过断裂准则的静力学牵引机理进行了描述。裂纹形成中存在纤维的微细颈化过程,并用细颈化理论建立了其微颈细化的理论模型。粘结纤维的形成过程中通过能量耗散阻碍了裂纹的扩展。更多还原

【Abstract】 Maleic anhydride grafted bimodal polyethylene (BMPE-g-MAH) was prepared by melt blending , and it’s structure was characterized by IR spectrum. polycarbonate (PC)/bimodal polyethylene (BMPE) compatibilized blends were prepared by introducing BMPE-g-MAH as a compatibilizer. The organic solvent resistance and static/dynamic mechanical properties of PC/BMPE blends were tested in this study. The fracture surface and crack tip structure of PC/BMPE blends were observed by scanning electron microscopy (SEM). The process and mechanism of crack evolution were studied intensively.The organic solvent resistance testing suggests that in N, N-Dimethylformamide (DMF), the crack and inflation level of PC/BMPE blends decrease as BMPE concentration increase. Compared with the uncompatibilized blends, the crack and inflation level of BMPE-g-MAH compatibilized blends is lower. The results imply that the addition of BMPE-g-MAH improved the organic solvent resistance of PC/BMPE blends.The mechanical properties testing suggests that the notch impact strength of PC/BMPE blends increases with BMPE-g-MAH concentration: when BMPE-g-MAH concentration is 5wt%, the impact strength is 45% higher than uncompatibilized PC/BMPE blends. The storage modulus, maximum of loss modulus and loss tangent at 140℃of PC/BMPE compatibilized blends are lower as compared with uncompatibilized blends. The results may due to the enhancement of cohesion at PC/BMPE interface by BMPE-g-MAH which brings better disperse of BMPE in PC, and thus relaxed the internal stress stems from orientation of rigid PC molecular chain.The SEM photographs of cryogenic fracture surfaces of the blends suggest that BMPE-g-MAH improved the compatibility of PC and BMPE. Fibrils were formed on the impact fracture surface of the blends. Compared with the uncompatibilized blends, there are more fibrils on the fracture surface of the compatibilized blends. The fracture surface can be divided into two regions: crack initiation region which has cavitation and crack propagation region which has a lot of fibrils.The SEM photograph of crack tip of PC/BMPE blends suggests that the crack structure involves a so-called‘cohesive zone’where the two surfaces of the crack are bridged by thin fibrils. These fibrils again are of two types: primitive fibrils close to the craze tip and much thinner fibrils spanning the rest of the crack. The fibril formation mechanism are of two types too: surface-drawing and fibril-stretching, respectively. The cohesive stress at the boundary of the process zone can be described by the hydrostatic traction of fracture criteria. The formation of the fibrils has a micronecking process during crack evolution, and a micronecking model was presented using necking theories. The fibrils blunt the crack through energy dissipation during the fibril formation process.更多还原