Crosslinked polyethylene/organic montmorillonite(XLPE/OMMT)nanocomposite dielectrics were prepared by melt blending method to investigate the effects of organic montmorillonite types on the micromorphology and water-trees aging properties of the nanocomposite dielectrics.The specimens were tested by mechanical properties.It is found that the comprehensive mechanical properties reach the best when the mass fraction of OMMT is 0.5%.The micromorphology of the specimens was investigated by differential scanning calorimetry and scanning electron microscope.The organic montmorillonite(OMMT3)organically modified with dioctadecyl benzyl quaternary ammonium salt and refined,plays an obvious role of heterogeneous nucleation,leading to a more perfect crystal with a crystallinity up to 25.3%,and the average size of the crystals is only 16.67 μm.Accelerated water-tree aging tests were performed on each specimen by water needle electrode method.The stripping of the dispersed OMMT3 layer forms a more tortuous labyrinth path,and its barrier effect on water molecules and the restraint of XLPE crosslinked network structure on the movement of molecular chains,the combined effect of the two effectively inhibits the growth of water trees in XLPE/OMMT3 specimen,and the initiation probability is reduced to 23.4%.The chemical structure of the water trees before and after aging was characterized by Fourier transform infrared spectroscopy.The test results indicate that the increase of carbonyl index and vibration peak of hydroxyl in the water-tree region of nanocomposite dielectrics indicate that water-tree aging is due to electrochemical degradation,while the chain breakage of XLPE/OMMT3 is less in the process of water-trees growth,showing excellent thermal and oxygen aging resistance.
将D-胱氨酸(CYS)与甲醇进行甲酯化反应,制备出一种新型含有双硫键的扩链剂胱氨酸二甲酯(CDE),再将其对端异氰酸酯基(—NCO)二聚体(IPDI-PTMG)和端异氰酸酯基三聚体(IPDI-TEA)进行扩链,制备了含有动态双硫键的自修复交联聚氨酯脲(SH-PUU)材料.采用傅里叶变换红外光谱对SH-PUU结构进行表征,通过电子万能试验机、差示扫描量热仪、热重分析仪和光学显微镜等研究了不同配比制备的SH-PUU的力学性能、热稳定性和修复性能.结果表明,当扩链系数(CDE中—NH2与体系中—NCO的摩尔比)为0.9,IPDI-TEA的质量分数为10%时,SH-PUU材料具有较好的力学性能和最佳的修复性能,其拉伸强度为5.22 MPa、修复效率为93.9%.此外,该材料拥有多次自修复性能和一定的室温自修复能力,3次自修复后的修复率仍可达65.0%,室温修复24h后自修复率为30.0%.
生物纤维素,也称细菌纤维素,是一种由微生物在发酵过程中合成的高分子纤维素.它具有许多独特的性质,如高吸水保湿性、有效的细菌屏障、超细纳米纤维空间结构、高弹性模量以及良好的透明度和生物相容性等.这些性质使得生物纤维素能够被制备成新型敷料应用于临床医学.文中对生物纤维素的结构和性能、制备方法及在慢性创面敷料、骨修复材料、眼科材料、心血管外科材料中的应用进行了综述,并展望了生物纤维素敷料未来的发展趋势,为其在医学及其他领域的研究和开发提供参考.
文中采用熔融缩聚法合成了聚(乳酸-富马酸丁二酯)共聚物(P(LA-BF)).进一步,将P(LA-BF)与PLLA共混制备了不同组分比的PLLA/P(LA-BF)薄膜.通过核磁共振和红外光谱分析了P(LA-BF)的聚合情况.研究表明,合成了处于无定形态的P(LA-BF)共聚物.采用广角X射线衍射仪、差示扫描量热仪和拉伸试验机评估了PLLA/P(LA-BF)薄膜的结晶性能、热学性能和力学性能.结果表明,P(LA-BF)的加入未改变PLLA的结晶能力,薄膜仍处于无定形态.同时,PLLA和P(LA-BF)具有很好的相容性,P(LA-BF)的加入提高了PLLA分子链的运动性和柔顺性,薄膜表现出高柔韧特点.随着P(LA-BF)含量的增加,断裂伸长率最高增加至PLLA/P(LA-BF)60的352.5%,约为纯PLLA的104倍;当P(LA-BF)的含量为80%时,薄膜断裂前的塑性变形变得更加明显,呈现出伴有韧窝的丝束状拉丝形貌.此外,流变性能表明,PLLA/P(LA-BF)40,PLLA/P(LA-BF)60和PLLA/P(LA-BF)80均表现出牛顿流体的特征,有效提高了PLLA熔体加工时的流动性.
采用熔融共混法制备了球状聚四氟乙烯(PTFE)和原位PTFE微纤增强聚丙烯(PP)复合材料,利用自主研发的间歇式发泡系统制备了纯PP,PP/S-PTFE(球状PTFE增强PP)和PP/F-PTFE(原位PTFE微纤增强PP)发泡件.扫描电镜和光热诱导红外显微镜揭示了PTFE一步法成纤的关键因素是PTFE的伸长链晶体结构和表面处理工艺;X射线衍射分析显示PP,PP/S-PTFE和PP/F-PTFE都呈现α晶体结构.在确定的发泡压力下,发泡倍率随着发泡温度的升高先增加后减小,而发泡压力从5 MPa提高为15 MPa,发泡温度区间向低温段扩展了10℃.原位PTFE微纤对复合材料的最大发泡倍率有一定的抑制作用,但相同发泡倍率下,PP/F-PTFE泡沫件的泡孔直径最小,泡孔密度最大,泡孔尺寸均匀性最优,其泡沫件的压缩强度比相同发泡倍率PP泡沫件压缩强度提高了123%.
