Preparation and characterization of biaxially oriented polypropylene film with high molecular orientation in the machine direction by sequential biaxial stretching

Novel approach of applying the ternary polymer blend of long‐chain branched polypropylene (LCB‐PP), conventional polypropylene (PP), and hydrogenated polydicyclopentadiene (hDCPD) has been employed to tensilize biaxially oriented polypropylene (BOPP) film in the machine direction (MD) by successive sequential biaxial stretching method. It is found that the addition of LCB‐PP improves the MD stretchability of the BOPP film of PP/hDCPD blend. Depending on the content of LCB‐PP, LCB‐PP/PP/hDCPD ternary blend could be biaxially stretched up to the MD stretching ratio (MDX) of 12 without film breakage whereas that of PP (conventional BOPP film) resulted in the MDX up to 6. This excellent MD stretchability enabled to tensilize the BOPP film in the MD, where Young's modulus in the MD could be increased up to 4.9 GPa, twice higher than that of conventional BOPP film. The orientation of total molecular chains and that of crystalline molecular chains were evaluated by in‐plane distribution of refractive indices and wide‐angle X‐ray diffraction, respectively. The results are discussed from the viewpoint of deformation behavior during stretching process. Moreover, the resultant film had a dimensional stability substantially equivalent to that of conventional one, in spite of the higher stretching ratio, and an improved moisture barrier property. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

BOPP纵拉过程的应力应变行为

采用高温下挤出厚片纵拉过程的模拟反映出来的应力应变行为，对厚片高温纵拉过程的形变特征进行分析研究，结果表明，EB在加工过程中具有更大的形态能力和更宽范围拉伸速度的适应性，在实验范围内，不同温度下的拉伸屈服应力与对数应变速率均呈线性关系，同时也受到相对分子质量的影响：高温下拉伸比的变化不会改变厚片形变的基本特征，但拉伸比提高后，应力应变曲线后端的硬化现象比较明显；深入理解BOPP拉伸温区结构变化现理，对于提高挤出厚片的形变能力，降低拉伸过程中薄膜的破损，提高生产效率将起到重要作用。     

Microporous membranes of isotactic poly(4‐methyl‐1‐pentene) from a melt‐extrusion process. II. Effects of thermal annealing and stretching on porosity

A two‐part study utilizing isotactic poly(4‐methyl‐1‐pentene) (PMP) was undertaken to investigate a three‐stage process (melt‐extrusion/annealing/uniaxial stretching) (MEAUS) utilized to produce microporous films. In this report, the thermal‐annealing (second stage) and subsequent uniaxial‐stretching (third stage) results of selected PMP films from three resins, labeled A, B, and C, are discussed. From sequential analysis of the effect each stage had on the resulting microporosity, it was discovered that the melt‐extruded precursor morphology and orientation, as a consequence of the first‐stage extrusion parameters and resin characteristics, were crucial to controlling the membrane permeability. The annealing parameters were also critical, where a temperature of 205°C applied for 20 min under no tension was the optimum annealing condition for producing highly microporous PMP films upon stretching. For the conditions studied, the stretching parameters that were found to be the optimum for producing the desired characteristics in the final film were cold‐ and hot‐stretch temperatures of 70 and 180°C, respectively. The cold‐ and hot‐stretch extension levels concluded to be the best were a cold‐stretch extension of 80%, followed by hot stretching to 90%, and, thus, a total overall extension level of 170% for the processing window studied. However, these results were only with respect to resin A films, while resin B and C samples could not be produced into microporous films via the MEAUS process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1076–1100, 2002; DOI 10.1002/app.10395     

Study of crater structure formation on the surface of biaxially oriented polypropylene film

Biaxially oriented polypropylene (BOPP) film accounts for a large amount of polypropylene since it is well suited for food packaging films or industrial films, because of its high performance in terms of mechanical and optical properties. Recently machine speed has been increasing to obtain higher production rate and film thickness has become thinner to reduce the environmental load. To meet the demands, many researchers have been investigating stretchability of PP by connecting the stretching force at the yield point and crystalline structure. Many other studies have been conducted regarding the surface structure of BOPP. Although there were some cases that crater‐like film surface roughness was formed on BOPP films, the formation mechanism of craters has not been clarified. In this report, new hypothesis of the crater‐like film surface roughness formation mechanism is proposed by observing the transformation of crater from sheet to BOPP film and by investigating the relationship between the stress–strain curve and surface roughness change. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

同步拉伸速率对双向拉伸聚乙烯薄膜结晶结构及性能的影响

实验采用双向拉伸聚乙烯(BOPE)原料线型低密度聚乙烯(LLDPE),用同步双向拉伸的方法制备BOPE薄膜,研究了双向拉伸过程中拉伸速率对薄膜结构和性能的影响。使用偏光显微镜(PLM)和差示扫描量热法(DSC)对未拉伸聚乙烯流延片的结晶形貌和热性能进行了研究。研究了不同拉伸速率下机器方向(MD)拉伸力的实时变化趋势,用DSC表征了不同BOPE薄膜样品的热性能。发现拉伸速率影响拉伸过程中聚乙烯晶体和分子结构及最终样品的结晶度和晶片厚度分布。实验研究了BOPE薄膜的力学和光学性能,分析了薄膜的宏观性能和分子结构之间的关系。实验结果表明,较高的拉伸速率有利于薄膜性能的提高。     

Microporous membranes of polyoxymethylene from a melt‐extrusion process: (II) Effects of thermal annealing and stretching on porosity

A two‐part study utilizing polyoxymethylene (POM) was undertaken to investigate a three‐stage process (melt‐extrusion/annealing/uniaxial‐stretching) utilized to produce microporous films. In this report, the thermal annealing (second stage) and subsequent uniaxial‐stretching (third stage) results of selected POM films from two commercial resins, labeled D & F, are discussed. Specifically, the annealing and uniaxial stretching effects on film morphology, orientation, and other pertinent film properties are addressed. Additionally, sequential analysis was performed regarding the influence each stage had on the resulting microporosity. It was found that the melt‐extruded precursor morphology and orientation, as a consequence of the first stage extrusion parameters and resin characteristics, are crucial to controlling the membrane permeability. The annealing parameters were also deemed critical, where a temperature of 145°C applied for 20 min under no tension was the optimum annealing condition for producing a highly microporous film upon stretching. For the conditions studied, the stretching parameters that were found to be optimum for producing the desired characteristics in the final film were a cold temperature of 50°C and hot stretch temperature of 100°C. The optimum extension levels were concluded to be 90% for both the cold and hot stretch steps, and thus a total overall extension level of 180%. However, these results were only with respect to resin F films. Because the resin D melt‐extruded precursors possessed twisted lamellar morphologies and relatively low crystal orientation, their samples could not be produced into microporous films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1762–1780, 2002; DOI 10.1002/app.10587     

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.     

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     

Improving the dielectric performance of poly(vinylidene fluoride)/polyaniline nanorod composites by stretch‐induced crystal transition

The introduction of conductive polyaniline (PANI) can significantly improve the dielectric constant of polymer‐based materials. However, there is a drawback of high dielectric loss. Herein, a simple and efficient stretching process was applied to improve the dielectric performance of poly(vinylidene fluoride)/PANI (PVDF/PANI) nanorod films through the stretch‐induced crystal transition from non‐polar α‐crystal to polar β‐crystal in PVDF and the oriented distribution of PANI nanorods. XRD, DSC and Fourier transform IR analyses indicate that the stretched PVDF and stretched PVDF/PANI films possess a high content of β‐crystal at the stretching temperature of 135 °C under a stretching ratio of 200%–400%. Furthermore, the stretched PVDF/PANI film with 10 wt% PANI displays a high dielectric constant of 338 at 100 Hz, which is increased by 20% compared to non‐stretched PVDF/PANI film (281). More importantly, the corresponding dielectric loss is reduced from 0.31 for the non‐stretched film to 0.17 for the stretched film. © 2018 Society of Chemical Industry     

Effect of uniaxial stretching on thermal,oxygen barrier,and mechanical properties of polyamide 6 and poly(m‐xylene adipamide) nanocomposite films

In this study, the effect of uniaxial stretching on the thermal, oxygen barrier and mechanical properties of aliphatic polyamide 6 (PA6) and aromatic Poly(m‐xylene adipamide) (MXD6) nylon films as well as their in‐situ polymerized nanocomposites with 4 wt% clay were studied. Cast films were prepared by extrusion process and rapidly cooled using an air knife. The precursor films were uniaxially stretched at 110°C with draw ratios varying from 1.5 to 5. DSC results showed that the cold crystallization temperature (T_cc) of the uniaxially stretched MXD6 and MXD6/clay films drastically shifted to the lower temperatures when draw ratio increased. The aromatic nylon films had lower oxygen permeability than those of the aliphatic films, due to more rigidity and chain packing. However, the oxygen permeability of the stretched films increased with draw ratio (DR) up to a critical value for each sample, while further stretching resulted in a reduction in the oxygen permeation. This phenomenon was related to the changes in free volume upon uniaxial stretching. The ability of different geometrical models to describe the experimental relative permeability data was investigated. The Bharadwaj model that took into account clay orientation was the most successful one to predict the oxygen barrier characteristics of the stretched nanocomposites at high draw ratios. The Young's modulus and tensile strength of the aliphatic and aromatic nylons increased with uniaxial deformation, while the flexibility and elongation at break of the former decreased with increasing DR. A larger increase in the Young's modulus of the uniaxially stretched nanocomposite films compared with the neat samples was observed and could be related to the improvement in the clay orientation as well as a better alignment of the crystalline phase due to incorporating the clay platelets in the polymer matrix. In contrast, the flexibility of the stretched MXD6 improved remarkably (ca., 25 times) compared with the precursor film (DR = 1) when the draw ratio increased to 1.5. This could be related to the effect of hot stretching on the enhancement of polymer chains relaxation and mobility at low draw ratios. POLYM. ENG. SCI., 55:1113–1127, 2015. © 2014 Society of Plastics Engineers     

Effect of flow history on poly(vinylidine fluoride) crystalline phase transformation

This study was devoted to the effect of extensional flow during film extrusion on the formation of the β‐crystalline phase and on the piezoelectric properties of the extruded poly(vinylidine fluoride) (PVDF) films after cold drawing. The PVDF films were extruded at different draw ratios with two different dies, a conventional slit die and a two‐channel die, of which the latter was capable of applying high extensional flow to the PVDF melt. The PVDF films prepared with the two‐channel die were drawn at different temperatures, strain rates, and strains. The optimum stretching conditions for the achievement of the maximum β‐phase content were determined as follows: temperature = 90°C, strain = 500%, and strain rate = 0.083 s^?1. The samples prepared from the dies were then drawn under optimum stretching conditions, and their β‐phase content and piezoelectric strain coefficient (d₃₃) values were compared at equal draw ratios. Measured by the Fourier transform infrared technique, a maximum of 82% β‐phase content was obtained for the samples prepared with the two‐channel die, which was 7% higher than that of the samples prepared by the slit die. The d₃₃ value of the two‐channel die was 35 pC/N, which was also 5 pC/N higher than that of the samples prepared with the slit die. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Production and properties of highly oriented polyoxymethylene by die‐drawing

Highly oriented monofilaments were produced by a high‐temperature die‐drawing process followed by tensile drawing. It was shown that a successful high‐speed process required high‐quality melt‐extruded rod. The mechanical properties and structure of the die‐drawn products were investigated by means of tensile and bending tests, dynamic mechanical measurements, DSC, and X‐ray diffraction. The bending modulus and the tensile strength increased with increasing draw ratio. It was also observed that at high draw ratios the γ‐dispersion peak in the dynamic mechanical tan δ curve, which is associated with main chain micro‐Brownian motion in the amorphous regions, diminishes, implying that these chains become taut. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1268–1278, 2003     

Micropore formation process during stretching of polypropylene casting precursor film

Abstract

The micropore formation process during stretching of polypropylene casting precursor film was followed by DSC, SEM, AFM, SAXS and WAXD. DSC and SAXS results prove that annealing improves the lamellae periodicity and new crystals are formed. The increase of lamellae thickness is also observed by SEM and AFM. Preferentially oriented crystalline grain is along the direction perpendicular to the MD. After cold stretching, the newly formed crystals between the lamellae disappear and the voids appear in SEM and AFM. The hot stretching makes the lamellae separated step by step and many connecting bridge crystals appear between the adjacent lamellae, at the same time pores are formed. Their crystallisation behaviour is proved by the higher temperature shoulder in DSC curves and the broadening of second order peak in SAXS curves. During stretching, the long period decreases and the lamellae become twisted. More crystal grains are preferentially oriented along the direction of (110) plane.     

Synthesis and properties of the semi‐interpenetrating polymer network–like,thermosensitive poly(N‐isopropylacrylamide) hydrogel

A new strategy was used to prepare a semi‐interpenetrating polymer network (semi‐IPN)–like poly(N‐isopropylacrylamide) (PNIPAAm) polymeric hydrogel, consisting of either low (2300) or high (33,000) molecular weight linear PNIPAAm chains and the crosslinked PNIPAAm network. The properties of the resulting PNIPAAm hydrogels were characterized by DSC and SEM as well as their swelling ratios at various temperatures, the deswelling in hot water (48°C), and the oscillating shrinking–swelling properties within small temperature cycles. It was found that the deswelling rate of these semi‐IPN–like PNIPAAm hydrogels was improved if the molecular weight and/or composition of the linear PNIPAAm chains within the semi‐IPN–like PNIPAAm hydrogels were increased. This improved deswelling rate was attributed to the fast response nature of the linear PNIPAAm chains and the increased pore number in the matrix network, which provided numerous water channels for the water to diffuse out during the deswelling process at a temperature above the lower critical solution temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1935–1941, 2003     

Melt processed microporous films from compatibilized immiscible blends with potential as membranes

Microporous flat films with potential as membranes were produced via melt processing and post‐extrusion drawing from immiscible polypropylene/polystyrene blends containing a compatibilizing copolymer. The blends were first compounded in a co‐rotating twin‐screw extruder and subsequently extruded through a sheet die to obtain the precursor films. These were uniaxially drawn (100%–500%) with respect to the original dimensions to induce porosity and then post‐treated at elevated temperatures to stabilize the resultant structure, which consisted of uniform microcracks in the order of a few nanometers in width. The effects of blend composition and extrusion process parameters on surface and cross‐sectional porosity and solvent permeability of the prepared films are presented and related to specific microstructural features of the films before and after drawing. Finite element modeling of the stretching operation in the solid state yielded a successful interpretation of the blend response to uniaxial tension that resulted in microcrack formation. Comparison of some of the novel microporous structures of this work with commercial membranes prepared by solvent‐based phase inversion processes suggests comparable pore size and porosity ranges, with narrower pore size distribution.     

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。     

Orientation microstructure and properties of poly(propylene carbonate)/poly(butylene succinate) blend films

The blends of high molecular weight poly(propylene carbonate) (PPC) and poly(butylene succinate) (PBS) were melt blended using triphenylmethane triisocyanate (TTI) as a reactive coupling agent. TTI also serves as a compatibilizer for the blends of PPC and PBS. The blend containing 0.36 wt % TTI showed that the optimal mechanical properties were, therefore, calendared into films with different degrees of orientation. The calendering condition, degree of orientation, morphologies, mechanical properties, crystallization, and thermal behaviors of the films were investigated using wide‐angle X‐ray diffraction, scanning electron microscopy, tensile testing, and differential scanning calorimetry (DSC) techniques. The result showed that the as‐made films exhibited obvious orientation in machine direction (MD). Both tensile strength in MD and the tear strength in transverse direction (TD) increased with increasing the degree of orientation. The orientation of the film also increased the crystallinity and improved the thermal properties of the PPC/PBS blend films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

BOPP薄膜双向拉伸过程中拉伸力的探讨

研究了不同拉伸工艺下,双向拉伸聚丙烯(BOPP)薄膜拉伸成型过程中的拉伸力及其变化规律,并通过实验归纳出了几种典型的拉伸力曲线。结果表明:薄膜拉伸力曲线的形态与设定拉伸工艺相对应,并能够反应出薄膜的拉伸过程及薄膜性能。通过研究建立了薄膜拉伸力变化与薄膜拉伸工艺的关系,提供了一种更加直观的薄膜拉伸工艺快速评价方法。     

Morphology and texture development of uniaxially stretched poly(ethylene naphthalene‐2,6‐dicarboxylate)

The texture development of PEN films with different semicrystalline morphologies have been studied by X‐ray diffraction. These different structures have been obtained by uniaxially stretching PEN amorphous films at 100 and 160°C (below and above T_g) at different drawing ratios. Samples have also been characterized by DSC to determine the crystallinity ratios, the crystallization, and melting temperatures. To define the orientation of crystallites in the oriented samples, pole figures have been constructed, as a function of temperature and drawing ratio (DR) in the range 1.5–4. In the range from DR = 2 to 4 the orientation is clearly uniplanar‐axial. At T_draw = 100°C the crystallinity shown by DSC analysis is higher than the sample stretched at 160°C. The orientation is also higher when samples are stretched at 100°C. The naphthalene rings mainly stay in the plane of the film with a lower fraction perpendicular to the plane of the film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 395–401, 2007     

Synergistic enhancement of mechanical,crystalline and dielectric properties of polyarylene ether nitrile‐based nanocomposites by unidirectional hot stretching–quenching

Copper tetra‐amine phthalocyanine (NH₂‐CuPc) was grafted onto barium titanate (BaTiO₃) whose surface was modified by carboxylic polyarylene ether nitrile (CPEN) to afford a nano‐filler (CPEN‐f‐BaTiO₃@NH₂‐CuPc). Through a solution‐casting method combined with ultrasonic dispersion technology, the obtained CPEN‐f‐BaTiO₃@NH₂‐CuPc was successfully incorporated into biphenyl polyarylene ether nitrile (BP‐PEN) matrix to prepare nanocomposite films with various mass fractions of CPEN‐f‐BaTiO₃@NH₂‐CuPc (0, 2.0, 5.0, 10.0 and 20.0 wt%). After that, the nanocomposite films were unidirectionally stretched with various stretching ratios at 280 °C. All the nanocomposite films show excellent mechanical and thermal stability, which is provided by the BP‐PEN matrix. The crystallinity and mechanical, thermal and dielectric properties of the nanocomposite films are efficiently enhanced after the unidirectional hot‐stretching process. The results show that hot‐stretching is a useful method for improving the mechanical and crystallization behaviors as well as the thermal and dielectric properties of the nanocomposite films. © 2017 Society of Chemical Industry