【作者】 沈岳新；

【导师】 谢邦互；

【作者基本信息】 四川大学 ， 材料加工工程， 2007， 硕士

【摘要】 本文主要运用基本断裂功(EWF)方法研究了平面应力状态下聚丙烯(PP)／弹性体共混材料在低拉伸速率下断裂破坏行为，并对材料的形态结构与断裂行为参数的关系进行了比较和分析。讨论了聚烯烃弹性体(POE)含量对均聚PP／POE共混体系的裂纹扩展过程、断面形态演变等的影响，结果表明：随着POE含量的增加，PP／POE体系比总功和比屈服后断裂功增加，而比屈服功的变化不大；屈服点的位移变化不大，而体系的断裂位移逐渐增加；发散的外部塑性区高度和聚集的外部塑性区高度都呈现逐渐上升的趋势。PP／POE共混体系DENT拉伸试样断面出现明显的分区现象，即呈现韧性断裂特征的裂纹稳定扩展区和呈现脆性断裂特征的裂纹不稳定扩展的断裂区(a)；随着POE含量的增加，材料的韧性提高，裂纹扩展区长度(b+c)逐渐增加，(b+c)或(b+c)／α值的大小可以大致反映材料韧性的差异。注射和压制成型的共聚PP／POE共混体系在EWF测试中表现出典型的延性断裂行为，每组试样的载荷-位移曲线具有很好的自相似性。随POE含量增加，共混材料的断裂方式没有发生改变，比基本断裂功(w_e)有所增加而比非基本断裂功(βw_p)变化不大，说明POE对PP的断裂韧性有提高的作用。纯PP和PP／POE共混物，屈服后的比基本断裂功和比非基本断裂功的数值大于屈服前两项的数值，表明共混物的断裂韧性和塑性变形情况主要受屈服后的变化影响，临界裂纹张开位移(COD)法预测比基本断裂功w_e与真实值较为接近。由于成型时取向和熔体压力等的差异，相同配方下注射成型试样的w_e和βw_p都大于压制成型试样。三元乙丙橡胶(EPDM)与过氧化物(DCP)在单螺杆中低温混合后，再与PP在双螺杆中高温反应挤出，通过改变EPDM的用量来控制EPDM分散相的交联程度基本不变而含量不同，研究其对材料流动性能、微观结构和断裂行为等的影响及其相互间的关系，结果表明：随着EPDM用量的增加，材料的熔体流动速率(MFR)有所提高，但趋势明显减缓，说明采用这种加工方法可以明显减少PP的降解；材料的冲击强度提高，而拉伸强度略有降低；材料的耐热性能比较稳定；扫描电镜(SEM)结果表明共混物中EPDM粒子数量明显增加，分散更加均匀；差示扫描量热(DSC)结果证实了PP／EPDM接枝共交联结构的存在；各组不同韧带长度的DENT试样的载荷-位移曲线都具有较好的自相似性；用基本断裂功方法评价材料的断裂行为表明，共混物的比基本断裂功we和比塑性功wp都呈上升趋势；在EPDM和DCP的一定用量范围内，材料的we和比非基本断裂功βwp可同时被提高；COD法预测比基本断裂功w_e与真实值较为接近。更多还原

【Abstract】 This work is an attempt to study the effect of elastomer content on the plane-stress fracture performance of polypropylene （PP）/elastomer blends, using the essential work of fracture （EWF） method.For PP/polyolefin elastomer （POE） blends, the influence of POE content on the fracture behavior and fracture surface of PP/POE blends was evaluated. With increasing POE content, specific total work （w_f） and specific work for necking and subsequent fracture （w_n） was increased. The yield stress （σ_n） of the blends was decreased and the extension at failture （e_b） Was increased. The height of DOPZ and that of IOPZ were both increased. For the fracture surface, the length of the crack stable growth region was increased and the length of the brittle fracture region was decreased.For injection molded samples and compression molded samples of PP/POE blends, the validity of EWF evaluation was verified at first. The crack propagation and the character, size and development of the plastic deformation zone ahead of the crack tip were observed and illustrated on line. The influence of POE content on the essential work of fracture, plastic deformation work, crack opening displacement, etc., was analyzed. The distribution of fracture energy in different stages was discussed through a rational method for energy partition. The critical crack opening displacement （COD）_C method was employed to predict the specific essential work of fracture. It was found that the plane-stress EWF approach worked well for the PP/POE blends, which all behaved in a typical ductile tearing manner as full yielding of ligament and stable propagation of crack. The specific essential work of fracture （w_e） was increased with increasing POE content. The dominant factor which affected w_e was the necking and subsequent fracture term (w_e,n). The specific non-essential work of fracture （βw_p） was increased slightly with increasing POE content. Finally, it was shown that w_e could be predicted reasonably well via crack opening displacement （COD） values. For the different of orientation and melt pressure of injection molded and compression molded, w_e andβw_p of injection molded were both larger than that of compression molded.For dynamically vulcanzized PP/Ethylene-propylene-diene terpolymer （EPDM） blends, PP and EPDM were dynamically vulcanized with dicumyl peroxide （DCP） added, using a two-step method of even dispersion for DCP in EPDM at first and then crosslinking at elevated temperature. The results showed that though both chain scission and crosslinking occurred, the crosslinking reaction predominated in this process and the number of EPDM particles was increased, accompanying with the reduction in particle size and uniform dispersion. Differential scanning calorimetry （DSC） results indicated the existence of PP/EPDM graft copolymer. The EWF results showed that both w_e and w_p increased with increasing EPDM content, the fracture toughness and plastic energy consumption could be improved simultaneously and the ratio of them could be controlled by adjusting EPDM and DCP content.更多还原