有机玻璃定向拉伸的影响因素

介绍了定向拉伸的原理,从生产工艺方面分析了定向拉伸的影响因素,提出了解决方法。     

大型商用飞机客舱舷窗有机玻璃应用进展

定向拉伸的有机玻璃具有良好的光学性能、可靠的力学强度、较强的耐候性、良好的耐紫外光照射和耐化学介质作用,它质量轻、抗冲击、使用寿命长,目前,已广泛应用于各种大型商用飞机的客舱舷窗。经过30多年的不懈努力,国内定向拉伸有机玻璃已经有了长足的发展,已应用于各种航空器上。定向拉伸有机玻璃材料的性能符合美国MIL—PRF-25690B标准要求。     

双轴定向聚苯乙烯发展概况及生产过程

膜或片材的双轴定向(Biaxial Orientation)又称双向拉伸。这种聚合物加工方法已经有50多年的历史,但大规模工业化生产却在60年代以后。1968年开发了绝缘用双向拉伸聚丙烯(BOPP)薄膜生产技术。1965年日本研制第一台双向拉伸聚苯乙烯(BOPS)片材设备样机。1970年第一条BOPS生产线投入使用。在这之后,日本、美国、西欧等设备制造厂家纷纷设计、制造定向拉伸片膜生产线。在定向拉伸材料生产和使用方面,BOPS是继BOPP和BOPET之后发     

双轴定向对PVC塑料结构与性能的影响

双轴定向技术广泛应用于提高PVC塑料的机械性能。本文阐述双轴定向对PVC塑料结构与性能的影响,指出拉伸作用可使uPVC与PPVC形成有序结构以及使分子链定向,从而提高PVC塑料的拉伸强度。对PPVC塑料,为保持分子链定向,应作退火处理。     

玻璃中卤化银纳米棒定向排布制备

围绕含AgCl钠硼硅酸盐玻璃的熔融制备、析晶热处理、高温拉伸及高压还原工艺，对于玻璃中卤化银纳米棒的形成、定向排布以及对于偏光性能的影响规律进行了研究，发现卤化银晶粒更易于在富钠硼相中析出，较佳的热处理制度是析晶温度615℃、保温时间12 h。玻璃中卤化银纳米棒的形成及定向是玻璃拉伸温度、拉伸应力与拉伸速度三者的有机结合。在拉伸温度570℃、拉力735 N、拉伸速度120 mm/min条件下，玻璃样品中Ag Cl纳米棒的平均直径98 nm、平均长度558 nm、纳米棒的平均长径比1.0:5.6，并沿玻璃拉伸方向定向排布。通过高压还原后玻璃的偏光性能研究，拉伸后玻璃表层单位面积内AgCl纳米棒的数量越多，还原处理后玻璃的消光比越高。     

高压聚乙烯定向拉伸时温度对应力形变状态的影响

在工程技术装备中广泛采用以高压聚乙烯为基础的热收缩材料。以前已研究过吸收辐射剂量等级对以后定向拉伸和收缩的热处理过程中高压聚乙烯内部结构变化机理的影响,但是,还缺乏温度时间条件对定向过程的动力学和渗透深度影响的数据,也缺乏当定向拉伸到一定程度时松驰过程作用的数据。     

硅烷交联的高强度单向拉伸定向的聚合物丝带CN1388154

本发明提供了一种硅烷交联的高强度单向拉伸定向的聚合物丝带。本聚合物丝带是由硅烷可交联聚合物丝带经过单向拉伸定向后在湿热条件下再经水解缩合交联反应而成。耐热性、耐热老化性、耐水解老化性、性、耐汽油和芳烃性、用寿命长。耐环境应力开裂性、龟裂抗蠕变性能大大提高，使     

模头拉伸工艺制超强管

模头拉伸工艺制超强管郭秀春编译本模头拉伸工艺（即定向工艺）是由英国利兹（Ｌｅｅｄｓ）大学教授ＩａｎＷａｒｄ开发的，１９８９年获美国专利。在模头拉伸工艺中，已冷却和真空定向的管材，由重型履带式牵引装置拉拽通过二次加热室（内装有一个锥形芯模或模头），室内...     

具有各向异性结构的聚乙烯醇水凝胶的制备及性能表征

首先对聚乙烯醇（PVA）水溶液进行定向冷冻-解冻制备出具有各向异性结构的PVA水凝胶,然后采用⁶⁰Co-γ射线对其进行辐射交联以提高其热稳定性和力学性能。扫描电子显微镜（SEM）结果显示PVA水凝胶保持了各向异性的微观结构,在平行冷冻方向上具有相对规整的取向结构,在垂直冷冻方向上呈现均匀孔洞结构。热稳定性测试结果表明：辐射剂量在30~70 kGy范围内、定向冷冻次数为1次的PVA水凝胶在60℃热水浴中保持凝胶状态长达10 h以上。对辐射交联PVA水凝胶进行拉伸力学性能测试,凝胶具有各向异性的拉伸性能,且拉伸强度和弹性模量均有提高,辐射剂量为10 kGy、定向冷冻次数为3次的PVA水凝胶（DFT-RC-3-10）在垂直定向冷冻方向上的拉伸强度和弹性模量分别为0.86和0.10 MPa。     

聚酯纤维拉伸时粗疵的形成

聚对苯二甲酸乙二酯(φ)纤维,在低于它的玻璃化温度Tg时进行定向拉伸(即所谓冷拉伸),能够制取具有规定性能的定向纤维并获得广泛的应用(例如;制造高收缩纤维)。在一定条件下,“冷拉伸”导致纤维内部出现大量的孔隙。在研究形成孔隙的规律性时确认,它与在形成细颈区域里纤维的加热或与提高拉伸速度时细颈中流体静力学应力的提高有关。     

Studies on the stretching of polypropylene film. II. Polyaxial stretching

Polypropylene film was stretched polyaxially at 100–160°C., and the orientation behavior was studied by means of optical and x-ray method. The molecular chains oriented progressively to the film surface with an increase in stretching area v_A in the range 1–16, and the (040) selective uniplanar orientation developed at the extreme stretching. The plot of orientation versus v_A was less steep when the stretching was carried out at higher temperature, but the final degree of orientation was independent of the temperature, because the final v_A increased with temperature. At 160°C. premelting occured to such a degree that the high stretching and, consequently, the high orientation could not be obtained. The orientation of the amorphous chains was always behind that of the crystalline region. In the initial stage the polyaxial stretching was not as effective in attaining high biaxial orientation as the two-step biaxial stretching, but the final orientation was the same in both types of stretching because v_A reached a value of 16 in the polyaxial stretching while it was only 2 in biaxial stretching.     

Orientation of poly(vinyl alcohol) nanofiber and crystallites in non-woven electrospun nanofiber mats under uniaxial stretching

The development of macroscopic nanofiber orientation and microscopic crystallite and molecular chain orientation have been investigated during uniaxial stretching of electrospun poly(vinyl alcohol) (PVA) non-woven nanofiber mats. Scanning electron microscopy and stress-strain/small-angle X-ray scattering show that the macroscopic nanofiber orientation significantly increases during the initial stage of deformation, and approaches a plateau on the way of stretching. Detailed analyses of the stress-strain/wide-angle X-ray diffraction measurement and polarized Fourier transform infrared spectroscopy indicate that the microscopic crystallite and molecular chain orientation rapidly increase at the initial stage of stretching due to macroscopic nanofiber orientation. At higher deformation, the microscopic modes of orientation continuously develop as a result of the nanofiber stretching. The complicated deformation process of non-woven nanofiber mats is discussed in terms of macroscopic nanofiber orientation and the microscopic crystallite and molecular chain orientation.     

PAN基碳纤维连续石墨化过程中的取向性

利用XRD研究了PAN基碳纤维在连续高温石墨化和热牵伸石墨化过程中纤维内石墨微晶沿纤维轴择优取向性的变化。结果表明：碳纤维中石墨微晶的择优取向性随石墨化温度的提高和热牵伸的增大而增加。两种工艺中纤维的拉伸模量均随微晶取向性的增加而增大,但在获得相同的模量下其取向参数却不同;碳纤维的拉伸模量不仅仅取决于石墨微晶的择优取向,而且与晶体的大小有关。另外,经过3000℃的高温处理后,纤维的择优取向参数Z仅为14.71°,说明纤维中乱层石墨的层面仍没有高度取向。     

双向拉伸聚丙烯薄膜横拉过程探讨

本文通过对双向拉伸聚丙烯薄膜横拉过程薄膜厚度变化的分析，发现薄膜的横拉过程有多拉伸起始点；延伸过程具有前后交替性；拉伸速率是不断变化的等，使横拉过程各部位的拉伸、取向、受热、结晶等履历不尽相同。这是引起产品最终性能差异的重要原因之一。     

Studies on melt spinning. IV. Spinning through a ribbon die

An experimental study has been carried out to investigate effects of stretch ratio on molecular orientation in polypropylene monofilaments which are melt spun from a ribbon die into a water bath with an adjustable air gap distance between the two. By varying the air gap distance and the rate of stretching, a variety of filaments of different molecular orientations were obtained. Measurements were taken of fiber birefringence of finished filaments under a polarizing microscope with camera attachment and mercury lamp. It has been found, according to the already established relationship between the molecular orientation and birefringence, that the molecular orientation in polypropylene filaments is increased with the rate of stretching. Two other interesting observations were made. One was that the filaments form crimps whose frequency increases with the rate of stretching. The other was that the phenomenon of draw resonance was observed when the rate of stretching was increased beyond a certain critical value.     

Studies on the biaxial stretching of polypropylene film. XI. Type II orientation during [2-2FI]-type stretching and its change by subsequent thermal contraction

In order to study the deformation mechanism of type II stretching, the change in orientation during the restretching and subsequent thermal contraction was investigated by x-ray diffraction method. When a uniaxially oriented film is restretched, the lamellae which are stacked in the stretching direction by the stretching rotate as a whole toward the restretching axis. They rotate backward nearly reversibly during the thermal contraction, unless the restretching exceeds a balancing state, where the orientation in the film plane are equal in all directions. However, when the restretching degree is so high and the film orientation exceeds the balancing state, the lamellar rotation is accompanied by a complex phenomenon. It is considered from the wide-angle and small-angle x-ray diffraction patterns that the lamellar surface becomes indented because of slippage between microfibrils composing the lamellae, and the microfibrils themselves bend at the boundary between the amorphous and crystalline regions within which the tilting of c-axis also occurs. Upon contracting of the film; these changes recover, but even in the last stage of contraction the orientation approaches the symmetrical biaxial orientation but not the uniaxial orientation from which the biaxial orientation is started. These orientation and disorientation behaviors are not affected basically by a slight change in the restretching temperature and the degree of stretching.     

Preparation and characterization of biaxially oriented films from polybutylene terephthalate based thermoplastic elastomer block copolymers

Film casting and biaxial stretching of a series of polyester thermoplastic elastomers (TPEs) were studied. Biaxial orientation in the stretched films was characterized by wide‐angle X‐ray diffraction and birefringence measurements. Biaxial orientation factors were determined. The X‐ray diffraction and birefringence clearly indicated the development of planar biaxial orientation in the stretched films with biaxial stretching. The phenyl groups in the stretched PBT and TPE films gradually became more parallel to the film surfaces with increasing biaxial orientation. The lower the PBT content in the stretched TPE films, the lower the planar biaxial orientation achieved. The β form of crystalline PBT was found only in the stretched PBT films, but not in the TPE films.     

Morphology-property relationships in oriented PET films: A role of in-plane crystalline orientation distribution on the film properties

The role of in-plane crystalline, amorphous, and overall molecular orientation on various properties in the plane of the films was investigated using a variety of techniques. It is shown that for a fixed value of crystallinity the in-plane crystalline orientation and the nature of the constraint imposed by the crystallites on the molecules play an important role in obtaining isotropic in-plane expansion or shrinkage properties. Achievement of in-plane isotropic tensile strength and elongation at the break are found to depend entirely upon an isotropic distribution of the amorphous orientation; the orientation of crystallites plays no detectable role. Furthermore, the deformation mechanisms of sequential and simultaneous biaxial stretching processes have been investigated and compared. The simulteneous stretching process is considered to be a more controlled film-fabricating method compared to sequential stretching in achieving balanced, in-plane film properties. © 1993 John Wiley & Sons, Inc.     

Relationship between biaxial orientation and oxygen permeability of polypropylene film

Biaxially oriented polypropylene (BOPP) films were produced by simultaneous and sequential biaxial stretching to various balanced and unbalanced draw ratios. The BOPP films were characterized in terms of density, crystallinity, refractive index, oxygen permeability and dynamic mechanical relaxation behavior. It was found that the density and crystallinity of BOPP films decreased as the area draw ratio increased. Sequential stretching led to a slightly lower density than simultaneous stretching to the same draw ratio. Moreover, sequential stretching produced lower orientation in the first stretch direction and higher orientation in the second stretch direction compared to simultaneous stretching. The study confirmed the generality of a one-to-one correlation between the oxygen permeability of BOPP films and the mobility of amorphous tie chains as measured by the intensity of the dynamic mechanical β-relaxation. Moreover, the study established the correlation for commercially important sequentially drawn BOPP films with an unbalanced draw ratio. Finally, the chain mobility in the stretch direction was found to depend on the final stress during stretching.     

Preparation and Characterization of high‐strength poly(ether ether ketone) films

High‐strength poly(ether ether ketone) (PEEK) films were prepared through melt extrusion followed by stretching. The tensile strength, orientation, and crystallization behaviors of PEEK films were characterized by universal testing machine, thermomechanical analysis, wide‐angle X‐ray diffraction, and differential scanning calorimetry. The results indicated that the tensile strength of PEEK films mainly depended on the stretching rate (ν), stretching temperature (T), and stretching ratio (λ_L). Moreover, the tensile strength of the stretched PEEK film (333 MPa) was almost four times higher than that of the unstretched PEEK film (87 MPa) under an optimized condition. This is attributed to a synergistic effect of orientation and crystallization in the stretching process, and the influence of orientation is stronger than that of the crystallization on the improvement of the tensile strength of PEEK films. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40172.