动态保压成型下中等分子量聚乙烯串晶形成的影响

采用自制的动态保压注射成型(DPIM)装置,向中等分子量的HDPE中添加高、低分子量聚乙烯(HMWPE、LMWPE)双重诱导成型自增强串晶的组织与性能影响进行研究。实验表明,在双重诱导和采用DPIM装置下,试样产生了大量的串晶结构,在160℃动态保压注射试样的拉伸强度为111.6 MPa,是其HDPE纯料静态试样拉伸强度24.5 MPa的4.56倍,提高了355.5%;通过WAXD、DSC和SEM测试可知,在DPIM下,试样产生互锁紧密的串晶结构;高分子量聚乙烯的加入有利于串晶脊纤维晶体的生成,低分子量聚乙烯的加入有利于片晶生长增厚,从而使得串晶结构更完善。     

聚丙烯在单向拉伸力场中形成双向自增强片材及其结构与性能的研究

采用普通挤出设备，在机头内，于单向拉伸应力场中实现了聚丙烯片材的双向自增强，纵向拉伸强度提高了6.33倍，横向拉伸强度提高了近1倍，同时纵横向拉伸强度表现出同步增长的趋势，其值随机头收敛角的不同而变化。运用SEM、DSC等测试手段对微观结构进行表征，揭示出试样内形成了串晶啮合结构，阐述了该结构与性能之间的关系。     

等规聚丙烯顺序共注射制件的结构与性能EI北大核心CSCD

采用顺序共注射成型和传统注射成型对等规聚丙烯进行成型,分别利用偏光显微镜、二维广角X射线衍射以及万能试验机测试制件的结晶形态和力学性能。结果表明,顺序共注射成型过程中表芯熔体之间的强烈剪切使得表芯材料界面处出现柱晶,并且随着延迟时间的延长,柱晶数目增多;顺序共注射成型过程中,表层熔体受到两次剪切以及芯层熔体流动时熔体内部强烈的剪切使得顺序共注射制件内部分子链取向度高,提高了制件的弹性模量和拉伸强度,实现了制件的自增强;顺序共注射制件在拉伸过程中裂纹容易在不同晶体层界面处产生并迅速扩展,从而导致制件断裂,故顺序共注射制件断裂伸长率较传统注射制件有所降低;制件成型过程中剪切形成的β晶能够提高制件的冲击韧性。     

等规聚丙烯顺序共注射制件的结构与性能

采用顺序共注射成型和传统注射成型对等规聚丙烯进行成型,分别利用偏光显微镜、二维广角X射线衍射以及万能试验机测试制件的结晶形态和力学性能。结果表明,顺序共注射成型过程中表芯熔体之间的强烈剪切使得表芯材料界面处出现柱晶,并且随着延迟时间的延长,柱晶数目增多;顺序共注射成型过程中,表层熔体受到两次剪切以及芯层熔体流动时熔体内部强烈的剪切使得顺序共注射制件内部分子链取向度高,提高了制件的弹性模量和拉伸强度,实现了制件的自增强;顺序共注射制件在拉伸过程中裂纹容易在不同晶体层界面处产生并迅速扩展,从而导致制件断裂,故顺序共注射制件断裂伸长率较传统注射制件有所降低;制件成型过程中剪切形成的β晶能够提高制件的冲击韧性。     

注塑成型二亚苄基山梨糖醇/茂金属等规聚丙烯的结晶结构及力学性能

利用普通注塑(CIM)和振动剪切注塑(OSIM)方法制备了二亚苄基山梨糖醇(DBS)不同质量含量的茂金属等规聚丙烯(m-iPP)试样,并研究了制品的结晶结构和性能。对试样的X射线衍射和差示扫描量热分析表明,DBS的加入使γ晶相对含量(fγ)减少,这是由于DBS生成网络结构增强了成型过程中α和γ晶的取向生成,进而抑制了试样中的γ晶含量。对试样的力学性能研究发现,添加0.5%DBS且经过OSIM成型的m-iPP试样具有最高的拉伸强度为45.2 MPa。     

低频振动注射自增强HDPE实验研究

利用自行研制的低频振动注射实验装置,研究振动注射成型工艺对HDPE哑铃试样的力学性能的影响。与常规注射相比,低频振动注射能明显改善试样的拉伸强度,实现注射试样的自增强。在0 Hz~0.93 Hz之间增加振动频率能明显提高试样的强度,断裂伸长率下降;当大于0.93 Hz,频率增加对拉伸强度的改变不大,断裂伸长率有明显的回升。压力振幅的增加可以明显地改善注射试样的屈服强度,HDPE 6100M试样屈服强度由39.8 MPa增加到60.6 MPa,增加的百分数为52.3%,断裂伸长率同时有所下降。SEM显示振动注射有利于片晶顺着流动方向行式排列,并具有明显的串晶结构。     

自增强高密度聚乙烯/超高分子量聚乙烯复合材料制备与表征

用自制模具制备出自增强高密度聚乙烯(HDPE)/超高分子量聚乙烯(UHMWPE)棒材.通过SEM观察、X射线分析、DSC分析以及力学性能测试,研究了挤出自增强HDPE/UHMWPE棒材微观结构和力学性能.研究结果表明,在HDPE和UHMWPE最佳配比为8:2的情况下,自增强试样的拉伸强度、抗弯强度和弹性模量分别为168.5、164.8MPa和4.9GPa,比未增强试样分别提高了534.9%、261.2%和408.3%.与普通模压试样相比,自增强试样内部有大量的微纤结构和串晶互锁结构,结晶度获得提高,(110)面和(200)面的峰值均获得提高,并且熔点向高温区发生漂移.     

剪切场下少量碳纳米管对HDPE结晶结构和性能的影响

通过动态保压注塑成型装置研究剪切场下少量多壁碳纳米管(MWCNTs)对高密度聚乙烯(HDPE)的结晶结构和性能的影响。拉伸测试结果表明,普通注塑成型下MWCNTs含量为1.8%的HDPE/MWCNTs与纯HDPE相比,拉伸强度从28MPa增加到30MPa,冲击强度由22 kJ/m2提高至29 kJ/m2;而剪切场下成型的HDPE和HDPE/MWCNTs样品,其拉伸强度分别达到49MPa和63MPa,同时冲击强度分别为54kJ/m2和69kJ/m2。微观扫描分析显示,普通成型下的HDPE和HDPE/MWCNTs制品内部均呈现出无序的结晶结构,而剪切场下成型的制品内部结晶排列规整,均有串晶状的结晶结构产生。尤其在HDPE/MWCNTs制品中,发现了片晶附生于MWCNTs表面而形成杂化的串晶结构。以上的结果表明,在剪切场下MWCNTs可以明显影响HDPE的结晶和力学性能。     

剪切场下聚合物结晶形态学研究进展

聚合物熔体被引入剪切场后，会发生与静态下不同的结晶现象。微观上可以得到伸直链晶体、片晶及串晶；宏观上除了静态下典型的球晶外，还能观察到球晶的变形和柱晶等。另外，剪切还可以使晶体发生晶型转变。本文对聚合物熔体在剪切场下结晶形态学的研究进展进行了介绍。     

工艺参数对自增强HDPE棒材的力学性能和微观结构的影响

通过口模挤出工艺获得了自增强HDPE棒材,通过SEM观察、X射线分析、DSC分析以及力学性能测试,研究了工艺参数对挤出自增强HDPE棒材微观结构和力学性能的影响.研究结果表明,与普通模压试样相比,自增强试样内部有大量的微纤结构和串晶互锁结构,结晶度获得提高.挤出温度对材料性能影响最大,挤压比次之,口模温度对材料性能影响最小.当挤出温度为130℃,口模温度为0℃,挤压比为15时,自增强HDPE棒材的力学性能最佳,其拉伸强度和弯曲强度分别为220.6和152.9MPa.     

A comparative study of the load transfer mechanisms of the carbon nanotube reinforced polymer composites with interfacial crystallization

With the help of shear-lag theory, load transfer analysis is performed on the carbon nanotube reinforced polymer composites with interfacial crystallization of different morphologies, including transcrystallinity layer (TCL) and nanohybrid shish-kebab (NHSK) structures. By comparison, we find that the TCL structures can ease the burden of the CNT while the NHSK structures can lead to a fluctuating distribution of the axial stress in the CNT. Both structures can improve the effective elastic modulus of the composites, though the effect of the TCL structures is more pronounced. Besides, the enhancement of the load transfer efficiency of the composites is also observed, the study of the interfacial stress on different kinds of interfaces shows that the reinforcing effect of the TCL structures is sensitive to both the CNT/crystalline polymer interface and crystalline polymer/amorphous polymer interface, while the major decisive factor for the NHSK structures is confined to be the CNT/crystalline polymer interface because of the interlocking effect. Based on these features, some suggestions are given for tailoring the high-performance carbon nanotube reinforced polymer composites.     

Synthesis,processing sand properties of thermotropic liquid-crystal polymers

Thermotropic liquid-crystal polymers for high-performance applications are typically based on wholly aromatic polyester and polyamide architectures. The linear character of the aromtic monomers produces polymer chains with stiff, extended conformations. As a result, the chains organize themselves into a nematic melt and readily orient in response to processing flow fields. The close coupling between chain orientation and flow fields produces both a rich variety of materials and a high degree of controllability of their structure and properties (such as the tensile strength, elastic modulus and coefficient of thermal expansion). In this paper, we describe synthetic efforts to develop liquid-crystal polymer structures and the relationships between chain molecular structure, processing, and properties of this class of polymers in two distinct processing situations: Injection molding and fiber formation. The special importance of the orientational flow field in developing high orientation and excellent mechanical properties will be highlighted.     

振动场作用下注射成型制件力学性能的实验研究

将聚合物熔体在振动场中进行注射成型,对制件力学性能与振动参数之间的关系进行了实验研究。实验采用自行研制的振动实验装置,分析使用结晶型材料PP,HDPE和非晶型材料PS为原料,在振动场中进行注射成型,对成型试样进行了拉伸试验,对结果进行了分析,得出了结论。     

Deformation of oriented high density polyethylene shish-kebab films

Decrystallization is defined as the mechanically induced reduction and reorganization of the crystalline phase. The decrystallization of oriented high density polyethylene (HDPE) was observed here by transmission electron microscopy (TEM). A special drawing technique was used to form thin films with an idealized, highly oriented, shish-kebab morphology. These oriented films were uniaxially elongated at room temperature along or perpendicular to the chain direction, and then viewed by TEM. The use of such a well defined initial morphology reduced the deformation of polyethylene as a whole to that of three structural elements: long shish crystals, chain folded kebabs, and the non-crystalline phase. The non-uniform deformation characteristic of spherulitic film, in which the elongation direction is parallel to lamellar normals in one region and perpendicular to them in another, was thus avoided. High strain transformed the shish-kebab morphology into filaments which were generally non-crystalline and of uniform diameter, with occasional crystalline remnants within them. Upon decrystalliz ation, internal defects were generated within crystallites, facilitating subsequent yielding. Stressed kebabs decrystallized and fed into the shish core. Defect generation also resulted in a reduction in crystal thickness along the chain direction, indicating that such a reduction can occur in the absence of thermally induced melting. Crystals underwent <001) crystal shear and chain slip, reducing crystal width, as well as martensitic transformation to the monoclinic crystalline form. No subsequent recrystallization was detected by darkfield studies. The influence of the initial shish-kebab morphology of undeformed films on the growth of crazelike structures was discussed.     

振动力场对聚合物挤出胀大的影响

为了改善聚合物材料的挤出胀大现象,将振动力场引入聚合物的挤出过程.采用动态毛细管流变仪对不同振动参数下的挤出胀大进行研究,建立了相应的物理模型和数学模型,并借鉴前人的工作成果,运用数学推导得到了挤出胀大与振动参数间关系的解析式.研究表明:随着振动频率和振幅的增加,挤出胀大呈非线性减少,并最后趋于稳定.     

聚乙烯醇发泡成型技术及其吸水性能研究进展

目的综述聚乙烯醇(PVA)发泡成型技术及其吸水性能的研究进展。方法详细介绍PVA泡沫的4种发泡方法(机械发泡、化学发泡、成孔剂发泡、物理发泡剂发泡),4种成型工艺(模压、熔融挤出、注塑、熔融沉积)以及吸水性能的研究进展,并对其在海军舰艇冷链运输中的应用进行展望。结果 PVA极性泡沫是一种新型的环保泡沫塑料,通过不同的发泡方法和成型工艺,配以不同的改性剂,可以制得不同领域需求的材料。结论 PVA泡沫具有性能优良、可生物降解、经济环保等特点,在农产品冷链运输和包装领域具有较大的发展潜力,在发泡方法和成型工艺的优化、储水储热性能等方面有较大的研究空间。     

Stress field simulation of carburized specimens with different carbon content during quenching process

This study focuses on the numerical model simulation of stress and temperature fields of carburized specimens with different carbon content during the quenching process. In the models the coupling between thermal field, phase transformation field and stress field was considered. The changes of the thermomechanical parameters of the material, as a function of carbon content and thermal field, were considered in the stress simulations. The residual stress fields of 20CrMnTi specimens with different carbon content of 0.8% and 1.0% were measured using an X-ray stress analyzer. Finite element model (FEM) was built for simulating the residual stress field after quenching. Meanwhile, the temperature and stress fields during quenching were simulated. The measured and simulated results are in good agreement.     

发动机振动对排气歧管低周疲劳寿命影响研究

发动机排气歧管在动态热负荷与整机振动载荷耦合作用的恶劣环境中工作,在热负荷单独作用时其部分区域就已经发生塑性变形,而整机振动载荷的耦合作用将使其疲劳失效问题更为严峻。为量化整机振动载荷对排气歧管低周疲劳损伤的影响,以某三缸增压发动机为研究对象,首先,基于流固耦合方法获得了排气歧管在标定工况和怠速工况下内外流场的换热边界,并联合增压器、催化器等部件温度和换热边界对两工况下排气系统的温度场进行计算。然后,根据温度场计算结果,耦合螺栓预紧力的作用,对怠速工况下的弹性应力场以及标定工况下的弹性和弹塑性应力场进行了计算,并基于标定工况下的弹塑性应力场,应用模态瞬态动力学对标定工况下的整机振动载荷作用下的动应力进行分析。最后,依据标定和怠速工况下的弹性应力场、标定工况下的动应力场结果,参照发动机低周疲劳试验标准分别建立了排气歧管常规高温低周疲劳与整机振动-热耦合低周疲劳分析模型,引入Neuber准则对两者的载荷谱进行应力-应变修正后采用主应变法进行疲劳寿命评估。结果表明：排气歧管疲劳破坏风险点主要位于高温拉应力区域,叠加振动载荷会使整体疲劳寿命下降接近25.2%,部分区域下降幅度甚至高达57%。研究结果为排气歧管整机瞬态振动-热耦合低周疲劳寿命预测提供了一定的理论依据和参考。     

聚合物基微纳米复合材料的制备及微型注塑加工研究

微型高分子功能器件具有独特优点,发展迅速,应用广泛,是当今科学技术的重要前沿,迫切需要发展高性能多功能聚合物基微纳米复合材料,实现其微型注塑加工。介绍了近年来作者课题组在聚合物基微纳米复合材料制备及其微型注塑加工方面的研究进展:通过有机/无机杂化、固相剪切碾磨、纳米复合、分子复合及熔融共混技术等制备适合于微成型加工的高性能多功能聚合物基微纳米复合材料,如尼龙11/钛酸钡压电复合材料、聚乙烯醇/羟基磷灰石生物医用纳米复合材料、聚氨酯/碳纳米管导电复合材料等。解决了微纳米填料难分散、复合体系难加工的难题,实现了聚合物基微纳米功能复合材料的微型注塑加工,研究了其流变行为和充填行为,调控和优化了微型制品的结构与性能,为制备高性能多功能的聚合物微型器件提供了新材料、新技术和新理论。     

聚乙烯亚胺为主链的液晶高分子研究进展

综述了近几年以聚乙烯亚胺(PEI)为主链的液晶高分子的研究进展.从PEI型液晶高分子的原理、结构和性能方面着手,展望了几类新型PEI液晶高分子的发展趋势.