双向拉伸聚乙烯的微观结构及热学表征

采用红外光谱、核磁共振波谱和高温凝胶色谱对2个双向拉伸聚乙烯试样(分别记作M1,M2)的链结构进行了表征,确定了试样的共聚单体类型、支化度、相对分子质量及其分布。利用差示扫描量热法(DSC)研究了试样的熔融和结晶行为。通过连续自成核退火热分级法测定了不同共聚物中亚甲基序列长度(MSL)的分布。结果表明:M1以短链支化为主,M2则以长链支化为主;M1的总支化度略高于M2,与红外光谱测试结果一致;MSL分布随MSL的增加呈单调递增趋势,M2的MSL集中在198,其峰面积占总峰面积的52.4%;M1的MSL分布呈现2个峰值,在MSL为61处有小峰,峰面积占总峰面积的8.3%,MSL为273处的峰面积占总峰面积的35.1%,与DSC测试的双熔点相对应。     

Production and properties of biaxially oriented polyethylene tubes

A study of the production of biaxially oriented polyethylene tubes by the die-drawing process was carried out examining the effects of draw temperature, haul-off speed, and mandrel size. The effect of postmandrel cooling was also studied. A range of biaxially oriented tubes of various draw ratios and thicknesses were produced. The Young's modulus and the tensile strength of biaxially drawn samples show considerable enhancement in both directions over the isotropic material. Biaxially drawn samples show remarkable improvement in their impact strength over the isotropic material. The crystalline orientation and texture of these samples are characterized using wide-angle X-ray scattering pole figure analysis. © 1996 John Wiley & Sons, Inc.     

双轴取向聚氯乙烯管材解取向研究

将双轴取向聚氯乙烯（PVC-O）管段进行加热，使其发生2种不同程度的解取向：完全解取向、轴向解取向。通过对PVC-O成品管段、完全解取向管段、轴向解取向管段、坯管进行低温抗冲试验，另对PVC-O成品管段和轴向解取向管段进行轴向拉伸和径向拉伸试验，分析解取向前后管材的力学性能。结果表明，完全解取向管材的低温抗冲性能和轴向拉伸性能会降低；轴向解取向管材的低温抗冲性能和轴向抗拉性能降低，径向拉伸性能变化不大。     

Sorption and transport of linear and branched ketones in biaxially oriented polyethylene terephthalate

Equilibrium sorption and kinetics of acetone, methyl ethyl ketone (MEK), methyl n-propyl ketone (MnPK), and methyl i-propyl ketone (MiPK) uptake in uniform, biaxially oriented, semicrystalline polyethylene terephthalate films were determined at 35 °C and low penetrant activity. Sorption isotherms for all penetrants were well described by the dual-mode sorption model. Sorption and desorption kinetics were described either by Fickian diffusion or a two-stage model incorporating Fickian diffusion at short times and protracted polymer structural relaxation at long times. Diffusion coefficients and equilibrium solubility at fixed relative pressure decreased in the following order: acetone>MEK>MnPK>MiPK. Diffusion coefficients for each penetrant increased with increasing penetrant concentration.     

双轴取向聚氯乙烯管材最佳拉伸温度和径向拉伸比的研究

以聚氯乙烯（PVC）树脂为主要原料，通过一步法挤出加工方式，采用纯净配方，在配方和轴向拉伸比不变的情况下，将拉伸温度设置为80、85、88、90 ℃，径向拉伸比设为1.8（坯料管外径63 mm、壁厚5.2 mm）和1.9（坯料管外径为60 mm、壁厚6.0 mm）制备双轴取向聚氯乙烯（PVC⁃O）管材。通过对不同工艺生产的管材进行静液压试验、落锤冲击试验、拉伸试验、环刚度试验来表征管材的力学性能。结果表明，适合此配方和轴向拉伸比的PVC⁃O管挤出成型的最佳拉伸温度为85 ℃，最佳径向拉伸比为1.9。     

Characterization of metallized biaxially oriented polypropylene film

The effect of corona unit energy applied for retreatment of metallized biaxially oriented polypropylene film surfaces before the lamination process was studied using optical, scanning electron, and atomic force microscopies. Increased surface roughness and polarity due to oxygen groups were detected, and these changes became more evident with the increase of corona treatment intensity. The number and size of spots on the surface, possibly deriving from processing aids incorporated as additives into the polymer, increase with corona treatment. The response of specimens in accelerated aging was also studied for evaluation of the outdoor stability of these composite structures. Specimens were exposed to the combined action of UV‐radiation, humidity, and heat, and the stability of yellow, orange‐yellow, orange, green, and bordeaux colors was determined as a function of the exposure time. Minor color changes were recorded for exposure up to 100 h, which became more significant for longer exposure intervals depending on the type of color. Finally, a 40% decrease in tensile strength was observed after 216 h of ageing, accompanied with a decrease of 15% of modulus and an increase of 160% in the elongation at break, possibly because of the plasticizing effect taking place during the ageing process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Structure-properties relationships in biaxially oriented polypropylene films

A series of biaxially oriented polypropylene films has been extensively investigated with respect to structural characterization and with regard to various end-use properties. The relationships between properties and structural characteristics such as crystallinity content and molecular orientation in crystalline and non-crystalline phases were compared with similar relationships in uniaxially oriented polypropylene films. Notable differences between uni- and biaxially oriented films, in particular with regard to non-linear mechanical behavior (tenacity, impact strength, tear strength) could be explained, at least partly, in terms of structural characteristics (molecular orientation and mobility) related to the non-crystalline phase.     

Properties of biaxially oriented Nylon 66 film

Biaxially oriented Nylon 66 film has been developed by a new tubular process. The relationship between the structure resulting from the manufacturing conditions and properties have been examined. A key technology of manufacturing is quenching of the melt, because of the high rate of polymer crystallization. The properties of biaxially oriented Nylon 66 film are found to be determined mainly by the degree of polymerization, the molecular and hydrogen bond plane structure, orientation within the film, and the degree of crystallinity. Toughness and high thermal resistance are also properties of this film. Therefore, applications for packaging have been examined, and a “retortable pouch” seems especially promising.     

Oxygen permeability of biaxially oriented polypropylene films

The effect of thermal history on the oxygen permeability of biaxially oriented polypropylene (BOPP) films was investigated. Compression‐molded sheets prepared with different cooling rates were biaxially oriented at several temperatures in the range between the onset of melting and the peak melting temperature and at a strain rate similar to that encountered in a commercial film process. The stress response during stretching was found to depend on the residual crystallinity in the same way regardless of the thermal history of the compression‐molded sheet. Biaxial orientation reduced the oxygen permeability measured at 23°C; however, the reduction did not correlate with the amount of orientation as measured by birefringence or with the fraction of amorphous phase as determined by density. Rather, the decrease in permeability was attributed to reduced mobility of amorphous tie molecules. A single one‐to‐one correlation between the oxygen permeability and the intensity of the dynamic mechanical β‐relaxation was demonstrated for all the films used in the study. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Mechanical properties,stress‐relaxation,and orientation of double bubble biaxially oriented polyethylene films

Biaxially oriented linear low density polyethylene (LLDPE) films were produced using the double bubble process with different machine direction (MD) orientation levels and the same transverse direction (TD) blow‐up ratio. Their mechanical behavior was characterized in terms of the tensile strength and tear resistance. The viscoelastic behavior of oriented films was studied using dynamic‐mechanical thermal analysis (DMTA). The microstructure and orientation were characterized using microscopy, X‐ray diffraction pole figures, and birefringence. The results indicate that MD ultimate tensile strength increases and the TD one decreases with MD stretching ratio. Tear propagation resistance, in general, remained mainly constant in TD and decreased in MD, as the draw ratio was increased. The morphology analyses exhibit a typical biaxial lamellar structure for all samples with different lamellar dimensions. Orientation of c‐axis in crystalline phase, molecular chain in amorphous phase along MD increased with draw ratio. In most crystals, a‐axis was located in the normal direction (ND) and the b‐axis in the ND–TD plane. A good correlation was observed between c‐axis orientation factor and MD mechanical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3545–3553, 2006     

Orientation distribution functions for biaxially oriented polymers

The use of the ‘most probable’ distribution function previously introduced for the prediction of orientation distribution functions for uniaxially oriented polymers is extended to biaxial polymers. Isometric projections of plots of the functions for model distributions are given, together with the application to a set of experimental data.     

Shear yielding of biaxially oriented styrene-acrylonitrile copolymer films

The shear yielding processes in the deformation of biaxially oriented styrene-acrylonitrile (SAN) copolymer films (machine oriented with draw ratio = 6.9 in the machine direction and 2.9 in the transverse direction) were studied. In the transverse direction, two sets of shear bands with an intersection angle of about 123.6 degrees (61.8 degrees with the tensile axis) were developed. When necking occurred, the bands in the necked region were thin and discontinuous with an intersection angle of about 81 degrees. In the machine direction, shear bands appeared to be short and diffused with an intersection angle of about 119.2 degrees. Only a slight necking effect was observed. The Luders strain in the transverse direction was about 0.56 and in the machine direction, about 0.16. The shearstrain-volume of activation obtained from the strain rate dependence of shear stress was about 3440 ± 400 ų in the machine direction and 2700 ± 500 ų in the transverse direction. The work hardening behavior in both directions seemed to follow a linear relationship between 1n (tensile stress) and tensile strain at large strains. From a consideration of localized shearing toward tensile axis, the fraction of deformed materials was calculated. These observations indicated that (1) a strong orientation hardening effect existed in unbalanced biaxially oriented films, resulting from the difference of the amount of deformable materials between individual directions; and (2) deformation proceeded by shear banding with the high orientation direction involved more correlated molecular segments than the low orientation direction during the activation process.     

Microstructure of biaxially drawn ultrahigh molecular weight polyethylene

The microstructure of ultrahigh molecular weight polyethylene (UHMW-PE) sheets biaxially drawn in the molten state was investigated by means of wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and electron microscopy. The crystallographic c-axis tended to be oriented in the sheet plane by the biaxial drawing in the molten state. The microstructure of the biaxially drawn UHMW-PE was shown to depend upon molecular weight of UHMW-PE. The biaxially drawn sheet of higher molecular weight (M_v = 2,700,000) showed a fibrous structure, while the lower molecular weight sample (M_v 700,000) had a lamellar structure. The result of DSC measurements suggested that a small number of nucleating extended chain crystals was produced by biaxial melt drawing of the UHMW-PE sheet with higher molecular weight.     

The relationship between microstructure and toughness of biaxially oriented semicrystalline polyester films

The relationship between microstructure and toughness of biaxially stretched semicrystalline polyester films was investigated. Optically transparent films were prepared by simultaneous biaxial stretching of melt-cast sheets near the glass transition temperature. Copolyesters of polyethylene terephthalate (PET) with different compositions of two diols: ethylene glycol (EG) and cyclohexane dimethanol (CHDM), and stoichiometrically matched terephthalic acid were used to produce films with different degrees of crystallinity. In addition, the PET films with different crystalline morphologies were produced by constrained high temperature annealing of biaxially oriented films. The toughness, degree of crystallinity and crystalline morphology/molecular ordering were studied using mechanical testing, synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD) techniques, and differential scanning calorimetry (DSC). The results indicate that the toughness of a semicrystalline polymeric film is determined by the interconnectivity of the crystalline phase within the amorphous phase and is greatly influenced by the degree of crystallinity and the underlying crystalline morphology.     

Processing and characterization of a biaxially oriented conducting polymer

Two methods have been developed for the preparation of biaxially oriented poly(phenylene vinylene) from its poly(sulfonium salt) precursor. A two-stage stretching process permits non-equibiaxial stretching over a wide range of deformation ratios and a bubble expansion technique allows equibiaxial planar extension. The resulting films were examined using X-ray diffraction prior to chemical doping with SbF₅ vapor. Biaxial orientation was shown to exert considerable influence over the attainable electrical conductivity.     

Stress‐induced crystallization of biaxially oriented polypropylene

The hot stretching of thick, extruded sheets at high temperatures is a very important process in the production of finished biaxially oriented polypropylene (BOPP) films with special inner structures. Through a simulation of hot stretching in the machine direction (MD) of the processing of BOPP films, it was found that at high temperatures, the stretching ratio greatly influenced the obtained crystalline structure, as observed by differential scanning calorimetry (DSC). Also, in MD hot stretching, the crystallinity increased by an average of 20%. Wide‐angle X‐ray diffraction patterns of extruded sheet samples with and without stretching confirmed the structural changes shown by DSC, and the results proved that β‐crystal modification did not occur during the MD hot‐stretching process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 686–690, 2003     

The effect of molecular structure of polypropylene on stretchability for biaxially oriented film

Biaxially oriented polypropylene films are widely used for food packaging and industrial films. Recently, machine speed has been increasing in order to obtain higher production rate, and film thickness has become thinner to reduce the environmental load. The customers' requirements for better production ability and thinner films have been becoming more demanding, but their demands are not always met because of lack of film stretchability in the final product. To meet the demands, research on stretchability has been conducted with the goal of finding the optimum polypropylene molecular structure for developing a new product by analyzing stretching force–strain data using a table tenter, which was thought to be the parameter of stretchability. It was found that low crystallinity and wide molecular weight distribution were effective in improving the stretchability from the table tenter test. By running the test with a sequential and biaxially oriented stretching machine, it was verified that samples produced by the above designed polymer indicated good thickness uniformity, which was considered to be the barometer of stretchability. Furthermore, it was concluded that analyzing the stretching force–strain data obtained from a table tenter is a good method to predict machine speed and film thickness. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers