热拉伸对尼龙6薄膜微观结构与力学性能的影响

本工作研究了尼龙6(PA6)薄膜的热拉伸工艺对其微观结构和力学性能的影响规律.在玻璃化转变温度(Tg)到熔点(Tm)之间的加工温度范围内对PA6薄膜进行了不同程度的单向热拉伸,并对其微观结构与力学性能进行表征测试.结果表明:随着拉伸温度和拉伸比的提高,PA6中的β晶型向α晶型的转变程度增大,促进了PA6中分子链沿拉伸方向的结晶和取向,从而显著提高了PA6的结晶度,并发现其无定形区减少,玻璃化转变温度(Tg)提高.拉伸温度的提高有利于PA6中α(002)晶面的生长,高温下拉伸形成的α晶体更完整;随着拉伸比的提高,形成的α晶体完整程度先升高后降低.热拉伸后的PA6薄膜的拉伸强度和储能模量增加,断裂伸长率降低;与未拉伸的PA6薄膜相比,拉伸温度为160℃、拉伸比为3的PA6薄膜拉伸强度增加371％,断裂伸长率降低235％.     

氧化石墨烯增强水泥基复合材料的力学性能及微观结构

本文采用改进的Hummers法制备了氧化石墨烯（Graphene oxide,GO）悬浮液,通过FTIR、XRD和AFM等测试技术对GO晶体结构和尺寸形态进行了表征,考察了GO掺量和水灰比的变化对GO增强水泥基复合材料力学性能和微观结构的影响。结果表明：GO增强水泥基复合材料抗折抗压强度随GO掺量增加而先提高后降低,且对于抗折强度增强效果远超过抗压强度,当GO掺量为0.03%时,抗折强度达到最大值13.72 MPa;高水灰比条件下掺入GO对水泥胶砂强度的提高更显著;通过SEM对GO增强水泥基复合材料微观结构进行表征,发现GO能够优化水泥水化产物的微观结构形态,细化晶体尺寸,形成更加致密均匀的网络结构,从而改善水泥基复合材料的宏观性能。     

聚碳酸酯/尼龙6共混体系力学性能的研究

探讨了不同增容剂对PC／PA共混体系的影响，研究结果表明：苯乙烯－马来酸酐共聚物（SMA）对PC／PA共混体系有一定增容作用，加入少量SMA后，共混物的力学性能有所提高；自制增容剂B与SMA协同使用对PC／PA共混体系有较好增容作用，协同增容后共混物的冲击强度大幅度提高，同时共混物仍保持较高的拉伸强度和弯曲强度。     

尼龙6共混改性研究进展

本文综述了近几年国内外PE、PP、ABS、PBT、EPDM、EPR、TLCP、LCP等对尼龙6(PA6)共混改性的研究现状,重点介绍了增容效果以及改性后PA6的力学性能,最后对PA6的共混改性研究方向做出了展望。     

成膜溶剂对磺化聚醚醚酮力学性能及微观结构的影响

通过浓硫酸(95%~98%)和聚醚醚酮(PEEK)制备了磺化度为84%的磺化聚醚醚酮(SPEEK)。以去离子水、N,N-二甲基甲酰胺(DMF)和N-甲基吡咯烷酮(NMP)为溶剂,分别制备了SPEEK-H2O、SPEEK-DMF以及SPEEK-NMP三种薄膜。采用万能材料试验机和扫描电镜(SEM)对比分析了成膜溶剂对SPEEK薄膜力学性能以及拉伸断面微观结构的影响。结果表明,成膜溶剂对薄膜力学性能和拉伸断面微观结构有明显影响。相同条件下,SPEEK-NMP薄膜具有最高的拉伸强度和弹性模量,拉伸断面凸凹程度最大。     

短碳纤维增强注塑聚醚醚酮复合材料微观结构与力学性能研究

实验结果表明:短碳纤维增强注塑聚醚醚酮(CF/PEEK)注塑板材中存在"皮-芯"次层微结构,用金相显微镜可以表征CF取向度不同的皮层和芯层的厚度,整板材料的力学性能可以根据皮层及芯层的厚度及其强度按"混合规则"计算。DSC法及热烘箱法研究表明,碳纤维取向结构和PEEK在皮层和芯层中的结晶度差异导致了板材内存在较大的内应力。     

PA6／PP共混复合材料的压力诱导流动成型的微观结构和力学性能研究

本文研究了压力诱导流动成型对用普通方法注塑的PA6＼PP共混复合材料的微观结构和力学性能的影响。SEM结果表明压力诱导流动可以使PA6＼PP共混复合材料形成微观片层结构,该结构由较软的无定形区相联的交互层叠片层构成,类似于自然界贝壳结构。力学性能测试表明该结构可以大幅度提高PA6＼PP共混复合材料的力学性能,特别是缺口冲击强度由4．33KJm。提高到压力诱导流动成型后的40．51KJ／m^2,而且有应力一应变曲线可以明显的看出材料出现了二次屈服。DMA测试表明,经过PIF成型的样品在扫描范围内的任何温度下,都表现出比成型前样品更高的储能模量。     

尼龙6/氯化钙复合材料受限结构研究

采用DSC，在位红外、X射线衍射分析和高压毛细管流变等方法研究了尼龙6／氯化钙复合物的结晶和流变行为，DSC和在位红外实验结果表明，随氯化钙含量增加，尼龙6的结晶度逐渐降低，结晶温度也逐渐降低，这与结晶成核剂的作用机理相反。X射线衍射实验结果显示，随氯化钙含量增加，尼龙6晶粒尺寸和晶面间距都逐渐减小。以上结果是因为钙离子和尼龙6羰基的纳合作用破坏了尼龙6原有氢键，使分子链规整排列减弱，氯离子和胺基的氢键作用缩短了分子链间距。高压毛细管流变实验结果显示，随氯化钙含量增加，尼龙6熔体粘度逐渐增加，这也和氯化钙与尼龙6产生相互作用使尼龙6熔体分子间摩擦力增大是对应的。     

四臂星型尼龙6的合成与表征

以2,2,6,6-四丙酸环己酮为四官能团核心,进行己内酰胺的水解开环聚合,合成了四种不同臂长的四臂星型尼龙6,对产物的分子量进行了测定,并对其力学性能和流变行为进行了研究。结果表明,四臂星型尼龙6的分子量随着四丙酸环己酮含量的提高而降低,与相应分子量的线型尼龙6相比,星型尼龙6的拉伸强度和弯曲强度基本保持,冲击强度保持率在75%以上,断裂伸长率最大降低了15%,相对黏度降低了近25%,熔融指数提高了近4倍,平衡转矩降低了75%,表现出了较好的加工流动性。     

尼龙6/橡胶/天然粘土纳米复合材料的制备及其力学性能

采用一种新型的超细全硫化粉末橡胶/蒙脱土复合粉末(UFPRM),可以制备出剥离型的尼龙6/橡胶/天然粘土(尼龙6/UFPRM)纳米复合材料,所用的橡胶是一种具有特殊结构的超细全硫化粉末橡胶(UFPR).微观分析表明,橡胶粒子在尼龙6基体中分散良好,同时天然粘土在橡胶粒子之间的基体中剥离.在一定份数下,复合粉末可以同时提高尼龙6的韧性、刚性及耐热性;随着复合粉末含量的增加,材料的冲击强度进一步增加.而且,复合粉末对高分子量尼龙6的增强、增韧效果好于低分子量尼龙6.进一步研究发现,在适当的剪切速率下,尼龙6/橡胶/天然粘土纳米复合材料可以获得较好的综合力学性能.     

Investigation of the nanomechanical properties of nylon 6 and nylon 6/clay nanocomposites at sub-ambient temperatures

The nanomechanical properties of nylon 6, nylon 6/exfoliated clay and nylon 6/non-exfoliated clay nanocomposites have been investigated from room temperature to ?10 °C in a controlled environment with humidity less than 1% RH. The hardness, elastic modulus and creep resistance of nylon 6 were improved in the nanocomposites across the temperature range. However, the effective reinforcement of the clay depended on the temperature due to the change between the glassy and transition states in the nylon. The exfoliated clay nanocomposite showed the greater improvements than in the non-exfoliated clay nanocomposite at all testing temperatures due to the improved constraint of the polymer chains by the clay platelets in the exfoliated structure. The surface mechanical properties of nylon 6 and the nanocomposites were also found to be highly sensitive to the moisture level during the tests; increasing the humidity in the room temperature tests resulted in a dramatic decrease in hardness and stiffness due to plasticisation by water molecules. The kinetics of the re-humidification process on nylon 6 were studied by monitoring the change in nanoindentation response. Analysis of the indentation creep revealed a significant change in the strain rate sensitivity when the humidity of the near-surface region probed by nanoindentation was in the vicinity of the glass transition.     

The effects of carbon nanotubes on mechanical and thermal properties of woven glass fibre reinforced polyamide-6 nanocomposites

This paper presents a preliminary investigation on the effects of incorporating carbon nanotubes (CNT) into polyamide-6 (PA6) on mechanical, thermal properties and fire performance of woven glass reinforced CNT/PA6 nanocomposite laminates. The samples were characterized by tensile and flexural tests, thermal gravimetric analysis (TGA), heat distortion temperature (HDT) measurements, thermal conductivity and cone calorimeter tests. Incorporation of up to 2 wt% CNT in CNT/PA6/GF laminates improved the flexural stress of the laminates up to 36%, the thermal conductivity by approximately 42% and the ignition time and peak HRR time was delayed by approximately 31% and 118%, respectively.     

Mechanical properties of E-glass fibre reinforced nylon 6/6 resin composites

The tensile strength, tensile modulus, compressive strength, interlaminar shear strength and residual tensile strength of E-glass fibre reinforced nylon 6/6 resin composite with the variation of fibre volume fraction are characterized. The results are in line with the required limits of theoretical values.     

The effects of Clay on fire performance and thermal mechanical properties of woven glass fibre reinforced polyamide 6 nanocomposites

The effects of small amount of organically modified Clay (Clay) in polyamide 6 (PA6) on fire performance and thermal mechanical properties of Clay/PA6/woven glass fibres (GF) laminates are investigated by cone calorimeter test, dynamic mechanical thermal analysis (DMTA), and heat distort temperature (HDT) measurement. The mechanical properties, such as tensile and flexural properties of Clay/PA6 composites and Clay/PA6/GF laminates were also measured. Up to 3 wt.% Clay in a Clay/PA6/GF laminate with fibre volume fraction of 30 vol.% delayed the ignition time and peak heat release rate (PHRR) time by 55% and 118%, respectively, even though the value of the PHRR or the HDT was not significantly affected. 2 wt.% Clay increased flexural modulus and strength of the Clay/PA6/GF laminate by 10% and 16%, respectively, but more Clay did not increase the mechanical properties accordingly. Small amount of Clay does not affect glass fibre dominated properties, such as HDT, but do affect matrix dominated properties, and significantly affect the fire performance in terms of delaying ignition time and PHRR time. Optimization of laminate making process could benefit from additions of more Clay, therefore further improve fire performance and enhance mechanical properties.     

The mechanical properties and fracture behaviour of unidirectionally reinforced Nylon 6

The tensile and shear properties of Nylon 6 polymerizedin situ around unidirectionally aligned carbon and glass fibres have been investigated and the fracture behaviour characterized by optical and scanning electron microscopy. The tensile strengths are found to lie within the limits predicted by the law of mixtures and deviations from the predicted strengths have been correlated with fibre type and surface treatment. The shear strength values follow the same trend and an important mode of fracture in bending is shown to be the compressive failure which accompanies a yield drop in the load deflection curve. Depending upon the fibre type and the properties of the matrix this compressive damage need not lead to catastrophic failure of the composite as, in certain cases, the matrix can undergo substantial deformation before failure.     

Creep properties of fatigued short carbon fibre reinforced nylon 6 plastics

The effect of low-cycle fatigue on the creep properties of a fibre-reinforced thermoplastic has been examined from the standpoint of the stress dependence and cycle ratio, which is the fraction of the mean life cycles to fracture. The time dependence of the strain and the strain rate of a virgin specimen can be described by a straight line on a logarithmic scale, therefore the deformation process seems to be ruled by a flow law. In addition the time dependence of the strain rate does not indicate the stress dependence for each stress level, which shows the same value as in the gradient of these relations. In the case of fatigued specimens, however, a knee point which divides the creep process into a primary region and a secondary one appears in the creep relation. The gradient in the primary region is less than that for the virgin material, and the magnitude and the timing of its appearance show either a stress dependence or a cycle ratio dependence. A weak stress dependence of the relation for log against logt can also be found; however, the results do not indicate a dependence on the cycle ratio. The reason for these results and the relationship of the structural changes of the materials are discussed using a McLean model.     

Synthesis and properties of waterborne polyurethane/attapulgite nanocomposites

The novel nanocomposites derived from waterborne polyurethane (WPU)/Attapulgite (AT) nanocomposites have been successfully synthesized by in situ polymerization progress. AT functionalized by chemical modification were incorporated as a crosslinker in prepolymer. The chemical structures, morphology, thermal behavior, and mechanical properties of the WPU/AT nanocomposites were investigated by Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and tensile testing respectively. The experimental results indicated that the organically modified attapulgites were homogeneously dispersed in the WPU and resulted in an improvement of thermal stability, tensile strength and elongation at break of WPU/AT nanocomposites.     

Effect of shearing on the orientation, crystallization and mechanical properties of HDPE/attapulgite nanocomposites

High density polyethylene (HDPE)/attapulgite (AT) nanocomposites, prepared by conventional injection molding (CIM) and dynamic packing injection molding (DPIM), were investigated with focus on AT-induced crystallization and orientation under shear. Infrared spectroscopy (FTIR) analysis showed there is no special chemical interaction between HDPE and AT, but shear induced significant changes on the material structure and properties. Differential scanning calorimetry (DSC) analysis showed strong nucleation effect by AT especially under shear. And more, shear will induce much better dispersion of AT in the DPIM sample vs. CIM. AT nanorods and lamellae of HDPE are more organized in the DPIM sample while there is only random distribution in the CIM sample. Most AT nanorods embed in the HDPE lamellae and form a brush-like hybrid structure due to shear. The shear-induced orientation will be enhanced with higher AT loading. The mechanical performance of the composites was significantly improved via DPIM.     

Preparation,microstructure and thermal mechanical properties of epoxy/crude clay nanocomposites

To improve the performance/cost ratio of epoxy/clay nanocomposites, epoxy resin was reinforced with crude clay with the help of a silane modifier. The epoxy/crude clay nanocomposites were produced through a recently developed “slurry compounding” approach. The microstructure of the nanocomposites was characterized with X-ray diffraction (XRD), optical microscopy and transmission electron microscopy (TEM). The thermal mechanical properties were studied with dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). It has been shown that only 5 wt% of silane modifier is required to facilitate the dispersion and exfoliation of crude clay in epoxy matrix. The storage moduli and thermal stability were improved with the addition of crude clay.