聚乙烯球晶在单向拉伸下的形变Ⅱ

用电子显微镜研究了聚乙烯球晶在单向拉伸下由球晶结构转变到纤维结构的全部过程,电子显微图象及大小角电子衍射表明,纤维是由一束“细纤维”所组成,细纤维则是由垂直于细纤维轴的折迭链块沿纤维轴的方向平行排列而组成的。     

论文选摘

合成纤维的形态近年来,关于结晶高聚物结构的概念已有很大的改变。研究表明,高聚物晶体是层状的,由长链分子折迭而成。然而这种新概念对拉伸纤维来说是否适用还研究得很少。本文作者用70—85℃的硝酸腐蚀拉伸聚乙烯小     

含少量共聚组分聚乙烯熔体拉伸薄膜的形态结构

利用透射电子显微学(TEM)和示差扫描量热学(DSC)等方法研究了含少量丁烯-1组分(摩尔分数为0.64%)的聚乙烯共聚物(PE100)熔体拉伸高取向薄膜的形态结构. 结果表明, 在PE100熔体拉伸薄膜中, 除存在高取向片晶结构外, 还含有大量的纤维晶, 纤维晶平行于拉伸方向, 穿过几个片晶区, 平均直径约为12 nm. 模拟实验结果表明, 纤维晶的生成源于聚乙烯共聚物中的超高分子量组分, 但不同于传统意义上的伸直链纤维晶, 其形态特征应为晶桥结构. 由此提出了晶桥结构纤维晶模型, 该模型不但有助于深入理解和认识聚合物取向结晶机理, 同时也为该材料的高性能化提供了理论依据.     

异戊橡胶微观序列结构与结晶性能研究

天然橡胶特有的应变诱导结晶能力赋予其优异的力学性能.异戊橡胶作为唯一能够替代天然橡胶的合成橡胶品种,其应变诱导结晶能力受到关注.本文对3种异戊橡胶的微观序列结构进行了分析,并研究了其结晶性能.核磁分析结果表明:3种异戊橡胶的顺-1,4-结构含量差别不大;从1,4-结构单元的键接方式(序列结构)看,SKI-5和YS-IR分子链中顺-1,4-结构单元均以头-尾相接的方式沿分子链排列,不存在头-头键和尾-尾键接方式;SKI-3中约有0.4%~0.5%的1,4-单元采取头-头键接方式,约有0.3%~0.6%的1,4-单元采取尾-尾键接方式;根据定量计算结果,从分子链上1,4-结构单元的序列分布来看,SKI-3的规整性与SKI-5、YS-IR相近或略高.XRD研究结果表明:炭黑填充的天然橡胶硫化胶拉伸至400%以上时发生取向结晶;而炭黑填充的异戊橡胶硫化胶需拉伸至500%以上时才发生取向结晶.基本物理机械性能研究表明:3种异戊橡胶的性能相当,拉伸强度和撕裂强度明显低于天然橡胶;由于结构和组成上的差异,异戊橡胶的结晶能力较天然橡胶差.     

自增强高性能聚合物的成型工艺同力学性能间相关性研究——1.超高分子量聚乙烯的应力诱导结晶理论和其自增强作用

本文发展了一种高分子量聚合物熔融体的应力诱导结晶结构形态模型,它是由微晶聚集体(以下简称微区)-高分子链组网和缠结网的网络结构组成。基于上述模型,把二种网中的单个链组作为独立的统计单元和形变单元,计算了二种网中单个链组的末端距分布函数,进一步计算了二种网和总网的形变自由能。在此基础上,讨论了诱导结晶结晶机理和自增强聚合物网络自由能的依赖性,并着重地研究了超拉伸高聚物的起始熔点拉伸比间的关系。用超高分子量聚乙烯膜和超取向高密度聚乙烯纤维的起始熔点和拉伸比的实验数据进行处理,得到理论予期的近似直线关系,初步验证了聚合物网应力诱导结晶理论。     

聚乙烯球晶在单向拉伸下的形变Ⅲ

用偏光显微镜研究了处于两个形变阶段的聚乙烯球晶在退火前后的形态,发现形变的第一阶段是可逆的,属弹性形变;第二阶段是不可逆的,属塑性形变。还发现聚乙烯纤维在单向拉伸下的断裂是通过细纤维或细纤维束的相互滑移而实现的。     

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．     

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。     

天然橡胶/聚乙烯共混体相容性的研究

本工作首先对橡胶/聚乙烯共混体系的相容性进行了计算,推测聚乙烯的非晶部分和橡胶间有一定的互容性,提出了橡胶和聚乙烯相互作用模型。然后用动态力学方法、有效网链密度测定、密度测定和广角X-射线衍射方法对天然橡胶分别未交联和交联的天然橡胶(NR)/低密度聚乙烯(LDPE)共混体系的相容性进行了验证。实验结果表明,LDPE非晶部分和NR之间存在一定的相互渗透。     

聚(2-甲氧基-5-乙氧基苯)撑纳米阵列的形态和光学特性

在阳极氧化铝(AAO)模板的纳米孑L内通过1—甲氧基—4—乙氧基苯(MEB)的氧化偶合聚合组装聚(2—甲氧基—5—乙氧基苯)撑(MEO—PPP)纳米纤维阵列，通过对纳米线的分子结构，AAO模板和聚(2—甲氧基—5—乙氧基苯)撑纳米纤维阵列的形态和形貌表征表明，AAO模板的纳米孔均匀有序且相互平行，定向生长的聚(2—甲氧基—5—乙氧基苯)撑纳米纤维的分子链与AAO纳米孔的轴线平行，聚合物分子链的定向排列能够显著提高电导率，MEO—PPP分子链的聚对苯撑(PPP)骨架有良好的π-π^*共轭体系，引起吸收带向长波方向移动，MEO—PPP纳米纤维阵列比其无序纳米纤维有5nm的发射蓝移。     

Visualization of cellulase interactions with cellulose microfibril by transmission electron microscopy

In this study, we developed a method to observe interactions between cellulase and cellulose microfibril by transmission electron microscopy. Although negative staining and low-angle metal shadowing increase image contrast, neither method is sufficient to view enzyme interactions with microfibril. However, we found that the combination of negative staining and low-angle metal shadowing provided better contrast for enzyme-like particles on the microfibril. The lengths of the particles interacting with microfibrils were 7.03 and 5.05 nm, parallel and perpendicular to the fiber direction, respectively. Accounting for the additional thickness owing to metal shadowing, the particle sizes were consistent with that of CBH I from Trichoderma reesei based on a crystalline structural analysis. The combination of these electron staining techniques successfully visualized morphological changes in microfibril as well as enzymes adsorbed on it, thus demonstrating cellulase in action. These results indicate that appropriate staining techniques can be applied to extend the applications of transmission electron microscopy, which may be particularly beneficial for studies on enzymatic behavior.     

Microfibril orientation of the secondary cell wall in parenchyma cells of Phyllostachys edulis culms

The secondary cell wall of bamboo parenchyma cells is microfibril-based. However, understanding of the microfibril orientation of secondary cell walls in bamboo parenchyma cells is lacking. This study characterized the microfibril orientation of the sub-layers of the secondary cell wall in the parenchyma cells by field-emission environmental scanning electron microscopy and the microfibril angle of the ground parenchyma cell wall with X-ray diffraction. The microfibril orientation of tight-loose alternating layers of the secondary cell wall was in the opposite direction along the longitudinal axis. Near the parenchyma cells’ pit aperture, the microfibril orientation generally bypassed the pits and continued in a flow-like pattern. The mean microfibril angle of ground parenchyma cells was 63.3°. The average microfibril angle of adjacent sub-layers of the secondary cell wall was 60° and???65° in ground parenchyma cells, and 54° and???52° in vascular parenchyma cells. A structure model of microfibril orientation of parenchyma cell wall in moso bamboo was firstly constructed. The study provides insight into the anatomical structure of the parenchyma cell wall in the bamboo plant. Moreover, it provides a structural basis for further analysis of the mechanical properties of parenchyma cells.

     

Scanning electron microscopy methods for studying interfacial interaction in polymer blends

The scanning electron microscopy method in combination with the selective etching technique for polymer blends have been used to evaluate interfacial interaction in natural rubber and low density polyethylene blends. The morphology of the polymer blends, studied under externally applied strain, has been investigated to understand the role of interface adhesion between natural rubber and polyethylene phases, for two separate crosslinking systems, i.e. sulphur and peroxide.

Externally induced strain which facilitates phase separation in sulphur cured blends by initiating cracks at the interface; peroxide curing prevents separating out of the polyethylene phase from the natural rubber matrix. In the latter case, induced stress is distributed predominantly by developing fine flaw paths in the rubber matrix.

The method which has been developed for natural rubber and polyethylene blend systems may be used to evaluate the degree of interfacial adhesion between the dispersed phase and the dispersion medium for other kinds of polymer-polymer, polymer-filler as well as polymer-fibre composites.     

Piled-lamellae structure in polyethylene film and its deformation

The fine structure of polyethylene film has been investigated by using a high-resolution scanning electron microscope equipped with a field emission source. The original film surface of a-axis-oriented blown polyethylene film and the surface of a necked region formed by drawing the film in the machine direction were observed. High magnification electron micrographs indicate that the basic unit of internal texture of this film consists of piled-lamellae units, each pile containing three to ten lamellar crystal sheets. The piled-lamellae unit acts as one body and does not separate into single lamellae during deformation. Many tie fibrils are formed between adjacent piled-lamellae units, when the film is drawn in the machine direction. Although little attention has been given to this mechanism, it is important in deformation. This fact seems to be reflected in different shapes of the stress-strain curves of films drawn the machine direction and perpendicular to it.     

HDPE,LLDPE或LDPE高取向薄膜微结构的电子显微学研究

木工作用透射电子显微术及电子衍射技术研究3种PE(HDPE,LLDPE或LDPE)均聚物高取向薄膜的微结构。定量测定了它们的结晶尺寸。通过倾斜样品电子显微学研究确定了不同种PE纤维结构的对称性。     

二烯丙基双酚A醚接枝聚乙烯增容聚碳酸酯/聚乙烯合金中的纤维化增韧现象

采用二烯丙基双酚A醚 (DBAE)接枝聚乙烯 (DBAE g PE)作为聚碳酸酯 (PC) /聚乙烯 (PE)合金的增容剂 ,通过测试合金的冲击强度和裂纹扩展功 (G1C)发现 ,PC含量约为 15份时 ,被增容的合金出现超常的增韧现象 .对合金的断裂表面形态用扫描电子显微镜 (SEM )观察发现 ,未增容的合金呈典型的脆性断裂 ,增容的合金在PC为 15份时 ,PC出现明显的塑性变形 ,形成纤维 .本文就此提出纤维化增韧机制 ,并结合结构模型用纤维化增韧机制初步解释了PC/PE合金的超常增韧现象 .     

Relaxation processes and structure of ultradrawn polyethylene

Solid-state extruded polyethylene fibers have been prepared, with a wide range of draw ratios and constant processing temperature. The draw ratios vary from 4 up to 30, and the processing temperature was always 398 K. The extruded material behaves anisotropically, owing to the high degree of chain orientation in the drawing direction. The modulus and linear expansion coefficients in the fiber axis direction have been measured, over a wide temperature range, from 140 K up to 320 K. These two properties are closely related to the degree of structural continuity of the fibers. A fibrous structure model is proposed to explain the temperature effects and the values obtained for the modulus and expansion coefficients, in terms of crystallinity and volumetric fraction of extended-chains structure. At least three relaxation processes can be identified which cause the structural continuity of the fibers to change with temperature.