聚乙烯醇纤维轴向压缩变形结构研究

研究了具有不同分子链形态PVA纤维的轴向压缩变形结构 .结果表明 ,在具有带状结构的PVA纤维中 ,带状结构对纤维的轴向压缩变形行为有很大影响 .压缩变形后纤维中的带状结构仍然存在 ,但带状结构内的分子链与纤维轴发生倾斜 ,随压缩变形程度增大 ,在有利剪切应力发展的方向形成褶皱变形带 ,最后导致纤维中所有带状结构破坏 .X光衍射实验结果表明 ,对于具有带状结构的PVA纤维 ,( 1 0 1 ) [0 1 0 ]晶面系的滑移对其压缩变形过程有重要影响     

超高分子量聚乙烯冻胶纺丝-拉伸纤维结构的研究

以煤油为溶剂,汽油为萃取剂,采用冻胶纺丝 拉伸技术纺制了超高分子量聚乙烯（ＵＨＭＷ ＰＥ）纤维．利用广角Ｘ 射线衍射（ＷＡＸＤ）试验、偏光显微镜（ＰＯＭ）观察等方法研究了拉伸过程中纤维结构的变化．结果表明,在拉伸过程中,纤维大分子折叠链向伸直链转变的同时,斜方结晶的堆砌密度增大,微晶尺寸分布变窄并趋于均匀,拉伸４０倍纤维的晶胞参数为ａ＝０７３２ｎｍ,ｂ＝０４９１ｎｍ,ｃ＝０２５４ｎｍ．在拉伸４０倍左右的纤维中还能观察到因大分子结晶晶面滑移而产生的折皱带结构．在作者研究条件下,观察不到折皱带结构对纤维整体的取向态和结晶态结构的影响．     

通过轴向配位反应实现4-乙烯基吡啶聚合物的卟啉功能化

通过轴向配位反应,将四苯基卟啉锌(ZnTPP)键合在4-乙烯基吡啶(4VP)与苯乙烯(St)共聚物P(4VP-co-St)的侧链,制得了卟啉功能化的大分子ZnTPP-P(4VP-co-St).通过FTIR与1H-NMR对其化学结构进行了表征,重点研究了时间、温度对轴配过程的影响,以及大分子轴配化合物ZnTPP-P(4VP-co-St)的谱学性能,对其光物理行为进行了较为深入的分析.研究结果表明,以共聚物P(4VP-co-St)的吡啶侧基为配体,通过轴向配位反应可顺利地制备卟啉功能化的大分子ZnTPP-P(4VP-co-St),且温度越低,键合量越大.该大分子具有类似于ZnTPP的特征电子吸收光谱与荧光发射光谱,同时也显示出轴向配位的特征.与小分子ZnTPP相比,ZnTPP-P(4VP-co-St)的吸收光谱和发射光谱都发生了明显的红移.大分子轴配化合物ZnTPP-P(4VP-co-St)的光物理行为也呈现出一定程度的高分子效应,随着大分子链中ZnTPP键合量的增大,相近的ZnTPP侧链单元之间会发生能量转移,使荧光发射强度有所减弱.     

一维取向聚酯材料的研究进展

回顾了近年来在一维取向聚对苯二甲酸乙二酯材料的形态结构，特别是其非晶区结构和力学变形机理方面的研究进展。着重对制备高取向纤维的几种新技术及所得材料的力学性能进行了介绍。     

EPDM/PP热塑性弹性体在循环应力下的老化行为研究

本文研究了动态硫化EPDM/PP热塑性弹性体的动态疲劳老化行为,考察了其力学性能的变化,并分析了产生力学性能下降的原因。实验结果表明,随着疲劳时间的延长、疲劳振幅的增大,材料的断裂强度降低,并认为疲劳过程中完全硫化的EPDM橡胶粒子和热塑性塑料PP界面处的分子链断裂、滑移导致了断裂强度的降低;紫外光的加入,加速了材料在疲劳过程的分子链断裂、滑移速率,使材料的断裂强度有更大程度的降低;在机械疲劳老化单独作用下,材料体系几乎没有发生氧化反应,而紫外光的加入,促使了机械疲劳老化过程中氧化反应的发生。     

Al轻掺杂对CaMnO_3晶态材料结构与电迁移性质的影响研究

通过电子平面波函数密度泛函理论的计算分析方法系统研究了Ca位Al轻掺杂钙钛矿结构CaMnO_3基晶态材料的晶体结构、电子结构和载流子迁移性质.结果表明,Al轻掺杂使得CaMnO_3基晶态材料的晶格参数增大,在b轴方向上增大程度最高,在c轴方向上增大程度最小.Ca位Al轻掺杂之后,CaMnO_3中的O—Mn—O八面体向2个O顶点方向拉长,八面体产生扭曲变形.Al轻掺杂前后的CaMnO_3基晶态材料均为间接带隙半导体,其带隙宽度分别是0.713和0.695 eV,Al掺杂属于电子型掺杂.经过Al掺杂之后CaMnO_3基晶态材料的导带有效质量大大提高.Al掺杂CaMnO_3基晶态材料费米能以下,p状态态密度最高,s状态态密度最低;在费米能以上,d状态态密度最高,s状态态密度最低.Al掺杂大大提高了CaMnO_3基晶态材料的载流子浓度.CaMnO_3中O—Mn—O八面体中底平面上的O原子电子对载流子迁移过程的贡献大于顶点处的O原子电子贡献程度.     

甲基丙烯酸正丁酯/甲基丙烯酸β羟乙酯共聚吸附功能纤维的制备及表征

以过氧化苯甲酰(BPO)为引发剂, 合成了甲基丙烯酸正丁酯/甲基丙烯酸羟乙酯(BMA/HEMA)二元共聚树脂, 采用冻胶纺丝技术制备了低分子量有机液体吸附功能纤维, 利用傅里叶变换红外光谱(FTIR)和13C核磁共振波谱(NMR)、广角X射线衍射仪(WAXD)和综合热分析仪以及环境扫描电子显微镜(SEM)研究了共聚物的交联结构、纤维的结晶性能以及纤维的表面形貌, 同时研究了共聚合阶段HEMA与BMA投料比对纤维饱和吸附量的影响. 研究结果表明, 树脂大分子间不存在化学交联结构, 大分子内和大分子间存在氢键作用, 有利于物理交联结构的形成; 纤维结晶性能随着HEMA质量分数增加而减弱, 且HEMA质量分数对纤维表面形貌有较大影响; 纤维对甲苯和三氯乙烯的饱和吸附量随着HEMA质量分数增加而增大, HEMA质量分数相同时所得纤维对三氯乙烯的吸附量明显高于对甲苯的吸附量.     

基于生物大分子的纳米药物载体

生物大分子材料由于其可再生性、无毒性以及良好的生物相容性、生物可降解性和黏膜粘附性等特点成为药物载体研究的热点,尤其是将其作为纳米药物载体材料更加受人关注。本文首先对生物大分子纳米颗粒常用的制备方法--乳化法、自组装法和离子凝聚法进行了详细的介绍。由于乳化法在一定程度上破坏了生物大分子的生物相容性,因此自组装法和离子凝聚法是比较理想的制备方法。其中自组装法是利用两亲性的生物大分子,如蛋白质、多糖衍生物等在静电作用、疏水作用、范德华力等非键合作用力下组装成纳米结构;而离子凝聚法则是利用聚电解质与带相反电荷物质之间的静电作用形成纳米结构。接着本文对通过这些方法获得的生物大分子纳米颗粒作为蛋白类药物、抗癌药物以及基因药物的载体在近年来的研究进展进行了归纳和总结,结果显示其在药物缓释体系中具有广阔的应用前景。     

共聚酯PEIT-PEG结构与性能的研究

PET与PEG共聚可改善PET的抗静电性，但PEG含量的增加，会使共聚物的结晶温度大幅度地降低，不利于纤维加工，且伴随着结晶的发生，纤维的抗静电性也受到影响。在共聚体系中添加间苯二甲酸(IPA)，不仅能破坏大分子链结构的规整性、降低共聚酯的结晶性，而且能提高共聚酯纤雏的抗静电性能。用DSC与TG对共聚酯(PEIT-PEG)的聚集态结构、热性能、结晶性能等进行了表征。     

二维大分子的构象及凝聚态调控

近年来,二维大分子蓬勃发展,已经成为继经典线形与支化拓扑大分子之后的一个重要分支.二维大分子不但补全了经典高分子科学中缺失的二维分子维度,而且成为具有广泛且重要应用前景的材料新体系,将延续高分子科学在国民经济生产生活中的重要作用.类比成熟的线形高分子系统,深入理解二维大分子的构象与凝聚态并建立精确的材料结构调控方法是其发展的基础,目前仍然处于起步阶段.本文以我们课题组的研究工作为主线,以氧化石墨烯为二维大分子理想模型,总结了二维大分子构象行为与凝聚态结构调控的研究思路与进展.简要回顾了二维大分子构象的研究历史,介绍了构象行为规律、液晶凝聚态以及固态凝聚结构调控方法的系列新进展,并对未来二维大分子构象及凝聚态研究进行了展望,为二维大分子及材料的发展提供了新思路.     

Formation of kink bands by compression of the extrudate of solid linear polyethylene

Extrudates of solid linear polyethylene prepared under proper pressure and temperature conditions have a high c axis orientation along the extrusion direction, with lamellar crystals and amorphous layers stacked alternately along the extrusion direction. Kink bands were formed by compressing the oriented extrudate at room temperature along the extrusion direction. Inspection of the kink bands by wide-angle and small-angle x-ray diffraction and electron microscopy revealed that the fiber axis was rotated from the original axis direction by 70–75° and that the lamellar crystals were inclined to the fiber axis in the kink band by 55–60° and stacked nearly parallel to the kink boundary. The superstructural change during the formation of the kink band could not be interpreted in terms of uniform c axis shear alone. In addition to such a mechanism, it was necessary to take into account intermicrofibril and/or intercrystallite slip.     

OBSERVATIONS ON DEFORMATION BEHAVIOR OF HIGH PERFORMANCE FIBERS BY POLARIZING OPTICAL MICROSCOPY

By means of polarizing optical microscopy (POM), deformation behavior of four kinds of fibers, i.e. ultra highmolecular weight polyethylene (UHMW-PE) fiber, polyvinyl alcohol (PVA) fiber, polyethylene terephthalate (PET) fiber,and wholly aromatic (p-hydroxybenzoic acid/2-hydroxy-6-naphthoic acid) copolyester [P(HBA/HNA)]/PET (ACPET blend)fiber, in axial compression, axial impacting, and bending was observed. In compression, kink bands formed at an angle of55～60° to the fiber axis in 10-times-drawn UHMW-PE fiber, 75～80° in 40-times-drawn sample, 80° in PVA fiber, and 90°in the ACPET blend fiber. In impacting and bending, band angles of UHMW-PE, PVA and PET fibers are nearly the same asthose formed in compression, indicating that slip systems do not change. For any of the four kinds of fiber, band spacingexhibits great differences in compression, in impacting, and in bending, which may be attributed to the differences in thedegrees of strain or stress concentration.     

Deformation structures in solid-state extruded polyethylene

Deformation structures resembling kink bands have previously been reported in a number of oriented semicrystalline polymers which have undergone various modes of deformation. In the present work, such structures have been observed and studied in solid-state extruded polyethylene which has been processed to give a biaxial, “single crystal” texture. Deformation of this material by bending followed by unbending has been observed to lead to shear during the bending stage and to void formation during the unbending stage. The kink bands which form during this treatment exhibit a single morphology regardless of the axis of bending so long as the direction of compression during bending is parallel to the original extrusion direction. Besides intracrystalline slip, which is known to contribute at least in part to the process of kink band formation, mechanisms involving interlamellar slip and interfibrillar slip are also considered. These mechanisms are considered in terms of three distinct experimental observations: the relationship between the kink boundary and the x-ray long period, the process of void formation during unbending, and the single characteristic morphology of the kink bands.     

超高分子量聚乙烯膜轴向压缩变形结构的研究

继刚性聚合物经溶液液晶(如芳香族聚酰胺)或熔融液晶(如芳香族聚酯)纺丝制取高性能纤维获得成功后,利用冻胶纺丝等技术制取超高分子量聚乙烯(UHMW-PE)高性能纤维的研究已取得突破性进展。这类纤维具有伸直链结构,大分子沿材料拉伸方向高度取向和结晶,显示出优异的抗张性能,具有很大的拉伸强度和模量。     

Formation of kink bands in oriented polymers

The circumstances of the formation of kink bands have been investigated with a newly designed shearing device and light and electron microscopes. Kink bands having sharp edges and reflection symmetry about the edges were formed and studied in the two crystalline polymers, high-density polyethylene and isotactic polypropylene, but could not be formed in the two glassy polymers, poly(4,4′-dioxydiphenyl-2,2-propane carbonate) and poly(2,6-dimethylphenylene oxide). The characteristics of the oriented polymer that promote kink bands seem to be easy slip along the orientation axis, and resistance of the oriented fibrils to length changes. Kink bands were found to initiate at sites of shear stress concentration, where the fibrils are first deformed into an S-shaped curve, that then tightens and finally collapses into kinks.     

Occurrence of rippling during the deformation of oriented polyethylene

Rippling is another mode, in addition to kink-band formation, by which oriented polyethylene can deform and results in a profuse and irregular waviness in the fibrils. For the medium-density and high-density polyethylenes investigated, rippling tended to occur only at strain rates below about 1 min^?1 at 25°C. Above this rate, kink bands tended to form. It is suggested that rippling results from easy slip between the fibrils of the oriented polymers and from the resistance of the fibrils to shortening under a compressive stress. The applied shear stress is reduced by the easy slip to a simple compression along the fibrils, and this distorts the fibril into the series of waves that constitutes rippling. Stress–strain measurements confirm that fibril slip is considerably easier under the rates at which rippling occurs than at the rates at which kink bands form.     

The growth of shear bands in polystyrene

Shear-band growth velocities have been determined as a function of stress and temperature in polystyrene. The results demonstrate that shear bands can propagate under isothermal conditions; an adiabatic temperature rise at the shear band tip is not necessary for continued localization and growth of the band. The velocity is stress activated with a shear activation volume of 4600 ų and thermally activated with an activation enthalpy of 2.8 eV. Comparison of these values of the activation parameters with those for bulk shear flow in polystyrene indicates that the shear band propagation is controlled by the plastic strain rate of the glassy polymer immediately ahead of the tip of the band. Argon's molecular kink model of the elemental deformation process is consistent with measured values of the activation parameters whereas Bowden and Raha's dislocation model is not. The shear bands grow at an angle of ca. 38° to the axis of compression, and if the direction of compression is altered, the shear bands will change direction so as to maintain the 38° angle. Current explanations can not quantitatively account for the large deviation of the shear bands from the 45° plane of maximum shear stress.     

Texture development in polyethylene. I. Uniaxial extension and uniaxial compression

Texture development of high-density polyethylene has been studied by x-ray diffraction at various strains for uniaxial extension, as achieved by uniaxial tension and extrusion, and for uniaxial compression. Pole distributions were measured for the (100), (200), (020), and (011) reflections. Textures were described by ideal single-crystal orientations with inverse pole figures. In uniaxial extension, samples were deformed up to true strains of 1.83 (reductions of up to 84%). After a strain of 0.55, the c axis oriented at 35° from the extension axis and with increasing strain approached the extension axis. This was attributed to initial (110) or (310) twinning in combination with (100) slip, followed subsequently by [001] slip. In compression, samples were deformed up to true strains of 1.83 (reductions up to 84%). The texture consisted of strong components of the compression axis near (100) and weaker components near (110). At higher strains the intensity of the near-(100) components decreased, whereas the near-(110) components became more intense. The near-(100) components are explained by slip on (100) planes. The growth of the near-(110) components at the expense of the near-(100) components can be explained by relaxation twinning of the near-(100) components.     

Plastic deformation behavior of β phase isotactic polypropylene in plane‐strain compression at elevated temperatures

Isotactic polypropylene (iPP) rich in β crystal modification was deformed by plane‐strain compression at T = 55–100 °C. The evolution of phase structure, morphology, and orientation were studied by DSC, X‐Ray, and SEM. The most important deformation mechanisms found were interlamellar slip operating in the amorphous layers, resulting in numerous fine deformation bands and the crystallographic slip systems, including the (110)[001]_β chain slip and (110)[ ]_β transverse slip. Shear within deformation bands leads to β→α solid state phase transformation in contrast to β→smectic transformation observed at room temperature. Newly formed α crystallites deform with an advancing strain by crystallographic slip mechanism, primarily the (010)[001]_α chain slip. As a result of deformation and phase transformation within deformation bands β lamellae are locally destroyed and fragmented into smaller crystals. Deformation to high strains, above e = 1, brings further heavy fragmentation of lamellae, followed by fast rotation of crystallites with chain axis towards the direction of flow FD. This process, together with still active crystallographic slip, leads to the final texture with molecular axis of both crystalline β and α phase oriented along FD. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 92–108, 2008     

Kink motion in poly(vinylidene fluoride) form I

The diffuse-streak x-ray scattering intensity from poly(vinylidene fluoride) form I, which is caused by kink bands with GT_n? (n odd) conformation contained in the crystallite, decreases with increasing temperature, while the intensity of the 001 reflection does not change. This is attributed to the disappearance of the kink bands in the crystallite, not to partial melting of crystallites containing kink bands. The disappearance of the kink bands suggests that kink motion takes place in the crystallite. Plots of the intensity of diffuse-streak scattering, estimated from the asymmetric part of the 001 reflection, against 1/T roughly give ΔH_v = ?4.6 kcal/mol. This suggests that the kink band is energetically more stable than the regular structure of form I.