Effect of chain architecture on biaxial orientation and oxygen permeability of polypropylene film

Films of two isotactic propylene homopolymers prepared with different catalysts and a propylene/ethylene copolymer were biaxially oriented under conditions of temperature and strain rate that were similar to those encountered in a commercial film process. The draw temperature was varied in the range between the onset of melting and the peak melting temperature. It was found that the stress response during stretching depended on the residual crystallinity in the same way for all three polymers. Biaxial orientation reduced the oxygen permeability of the oriented films, however, the reduction did not correlate with the amount of orientation as measured by birefringence, with the fraction of amorphous phase as determined by density, or with free volume hole size as determined by PALS. 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 polymers used in the study. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of talc orientation and non-isothermal crystallization rate on crystal orientation of polypropylene in injection-molded polypropylene/ethylene-propylene rubber/talc blends

The effects of talc orientation and non-isothermal crystallization rate on the crystal orientation of polypropylene in the injection-molded PP/EPR/Talc blends were studied by using AFM, DSC, SEM and XRD. Polypropylene was transcrystallized on the talc surface and the polypropylene crystal was oriented perpendicular to the talc surface. Therefore, the crystal orientation was affected by the talc orientation. At the surface of injection-molded specimens, the crystal orientation increased with decreasing the molecular weight of EPRs and increasing the talc content. Because talc particles were nearly oriented parallel to the flow direction in the skin layer of the specimens, the crystal orientation was amplified by the increased crystallization rate. The non-isothermal crystallization behavior of PP/EPR/Talc blends was investigated in terms of the molecular weight of EPRs and the talc content. Non-isothermal crystallization rate increased with decreasing the molecular weight of EPRs due to the plasticizing effect of EPRs and increasing the content of talc which acts as nucleating agent.     

Transient biaxial orientation of flexible polymer chains in a wide range of deformation conditions

Transient distribution function of chain ends in non-linear polymer fluids subjected to a constant biaxial flow deformation is approximated by an affine evolution of initial Gaussian distribution function. A non-linear elastic dumbbell potential is used in the evolution equation for the distribution function, with the Peterlin and Padè approximations of inverse Langevin function. With the approximations, the evolution equation reduces to a system of ordinary first order differential equations for axial components of affine molecular deformation tensor.Numerical and a self-consistent analytical method of solving the system of evolution equations are proposed. Example computations are performed for uniaxial, incompressible elongational flow.The non-linear model covers entire range of deformation rates, and predicts molecular deformation tangential to macroscopic deformation at the beginning of the process, and asymptotically converging to the equilibrium chain deformation in the limit of infinite time. The model describes time evolution of the chain distribution function between the macroscopic affine limit at the beginning of the process and the equilibrium asymptote. The evolution deviates from the asymptotes the more, the lower is the deformation rate. For slow processes, linear Gaussian model is valid, and for very fast ones, solid-like behavior takes place with minor deviation between the molecular and macroscopic deformations, up to the level of full chain extension.     

Mobility and solubility of antioxidants and oxygen in glassy polymers. III. Influence of deformation and orientation on oxygen permeability

The mobility of small molecules in a glassy polymer is largely determined by the amount of free volume present in the material. The amount of free volume can be altered by changing the physical state of the polymer. Plastic deformation under compression reduces this amount, whereas the application of a tensile stress increases it. Furthermore, orientation of a polymer introduces an anisotropy in the free volume. The change in free volume was monitored by oxygen permeation experiments. A clear correlation was found between the draw ratio, plastic deformation and stress on the one hand and oxygen permeability on the other. Since the mobility of oxygen is an important parameter for the stabilisation of a polymer against oxidation, the physical state of the polymer can have a significant influence on the service life of the product.     

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     

Determination of permeability and diffusivity of oxygen in polymers by polarographic method with inert gas

A modified polarographic method with inert gas for determination of the oxygen permeability in polymers immersed in liquids is described. Owing to the stream of an inert gas towards polymer from the cathode side, lateral oxygen diffusion (edge effects) is minimized. Unlike the standard Fatt method, the method with inert gas is suitable also for thick samples and, therefore, for high-permeable materials. The method was tested for prediction of oxygen permeability in poly(1-vinyl 2-pyrrolidone) (PVP) and poly(2-hydroxyethyl methacrylate) (PHEMA). As an electrolyte, solution of potassium chloride was used. The effect of additional resistances and small lateral diffusion was taken into account. Unexpectedly, oxygen permeability in both polymers was greater for 0.1 M KCl than for 0.5 M KCl. The experimental setup was also used for diffusivity estimation in thick samples of PHEMA and PVP. Here, the oxygen flux response at one sample surface to the stepwise change in oxygen concentration at the other surface is measured and evaluated. The effect of the additional boundary layer on the oxygen transport is taken into account. A simple procedure for the diffusivity determination from the characteristic time of response as a function of the sample thickness is given. Solubility of oxygen in polymer is calculated from the obtained permeability and diffusivity.     

Nanolayer enhancement of biaxially oriented polypropylene film for increased gas barrier

An order of magnitude improvement in the oxygen barrier of biaxially oriented polypropylene (BOPP) films was achieved using a layer-multiplying, forced assembly process. The improvement was achieved without sacrificing clarity and toughness of the films. Sheets with 33 alternating layers of polypropylene (PP) (17 layers) and poly(?-caprolactone) (PCL) (16 layers) were coextruded using layer-multiplication and two thick PP skins were added to the multilayered core as the last step in the continuous coextrusion process. The sheets were subsequently biaxially oriented to draw ratios from 4 × 4 to 6 × 6. Biaxial orientation at elevated temperature reduced the thickness of the melted PCL layers from the microscale to the nanoscale, which created 2-dimensional confinement for subsequent crystallization of the PCL layers. It was anticipated that the PCL layers would recrystallize as highly oriented, in-plane lamellae that would resemble single crystals. However, the PCL lamellae were oriented perpendicular to the film surface, which actually facilitated oxygen permeation through the PCL layers and increased the oxygen permeability of the oriented films. Crystallization as on-edge lamellae was attributed to nucleation by the polypropylene surface. However, the surface nucleation was prevented by inserting buffer polystyrene (PS) layers in between the PCL and PP layers. In this case, the PCL lamellae were oriented in-plane. With the very high aspect ratio lamellar crystals oriented perpendicular to the flux direction, the permeation pathway of oxygen became very tortuous and the oxygen barrier was significantly improved.     

Plywood-like structure of injection-moulded polypropylene

Injection-moulded products having unique structure, in which the direction of molecular orientation in the skin layer is perpendicular to that in the core layer, are developed employing isotactic polypropylene with a nucleating agent. The extraordinary three-layered structure with β trigonal crystal form in the core layer, which shows higher impact strength than the conventional α monoclinic form, leads to high level of toughness. Moreover, an injection-moulded product having five-layered structure is also demonstrated in this paper. Because of the complicated crack propagation nature due to the abrupt change of molecular orientation, which avoids fractured pieces with sharp-edge, the products with plywood-like structure will be employed in various applications to improve the safety.     

Molecular orientation and stress in biaxially deformed polymers. II. Steady potential flow

The development of biaxial segmental orientation and stress in a flexible-chain polymer fluid subjected to steady biaxial extensional flow is analyzed. Closed-formula model based on the Padè approximation of the inverse Langevin function in the non-Gaussian distribution of the chain end-to-end vectors is considered. The approach is free from the limitations related to finite chain extensibility and slow convergence of the series expansion formulations at higher chain deformations.Segmental orientation is characterized by the average orientation tensor, related axial orientation factors and global orientation anisotropy. Orientational behavior and corresponding stresses in the biaxial elongational potential flow are discussed in a wide range of elongation rates. Orientation characteristics calculated for the biaxial flow deformation are much higher than those predicted for the affine biaxial stretch deformation in polymer solids.     

Characterisation of biaxial orientation gradients in poly(ethylene terephthalate) films and bottles using polarised attenuated total reflection FTIR spectroscopy

Polarised attenuated total reflection (ATR) infrared spectroscopy has been used to quantify biaxial orientation in commercially manufactured poly(ethylene terephthalate) (PET) films and stretch-blow moulded bottles. Using a single-bounce accessory with a high refractive index element, and applying appropriate data normalisation prior to measuring band intensities, measurement of the average square direction cosines that describe the orientation is simple. Using this technique it was shown that uniaxially drawn PET films were actually biaxially oriented, and there were significant gradients in orientation through the film thickness. Bulk measurements, or methods that assume uniaxial orientation, would give incorrect results from these materials. The bottles exhibited complex orientation patterns that depended on preform and mould design, and again there were strong orientation gradients through the bottle walls. Kratky's model (pseudo-affine) was used in an attempt to predict the biaxial orientation gradients as a function of preform and bottle dimensions.     

Synthesis and stable high oxygen permeability of poly(diphenylacetylene)s with two or three trimethylsilyl groups

We synthesized two new poly(diphenylacetylene)s having two or three trimethylsilyl groups and found these membranes having extremely high oxygen permeabilities of more than 1000 barrers which are of the same order as that for poly[1-(trimethylsilyl)-1-propyne]. Whereas oxygen permeability of poly[1-(trimethylsilyl)-1-propyne] was reported to decrease largely with time, these high oxygen permeabilities were stable for several months. These membranes also showed ethanol permselectivities because of their hydrophobicity. It was found that the introduction of two or three trimethylsilyl groups to poly(diphenylacetylene) was very effective for obtaining stable high oxygen permeable and ethanol permselective membranes.     

Shear-induced orientation in the crystallization of an isotactic polypropylene nanocomposite

Isothermal crystallization of isotactic polypropylene (iPP)/organic montmorillonite (OMMT) binary composite under shear field was investigated by in situ polarized optical microscopy, rheometry and transmission electron microscopy. When shear strain was small, shear flow could enhance the crystallization of iPP, and the crystallizing entity was spherulitic in iPP/OMMT composite in which the OMMT content was below the percolation threshold. With shear strain increasing, the orientation extent became stronger and cylindrites and strings of spherulites appeared in these samples. However, for iPP/OMMT composite with OMMT content higher than the percolation threshold, when the shear strain was not big enough to destroy the fillers network in the matrix, the crystallization of iPP was similar with that of the un-sheared sample. When shear strain was large enough, the fillers network was destroyed and clay layers were aligned along the flow direction. There formed oriented crystals including cylindrites and strings of spherulites, which were much smaller in size than those formed in the previous case, because the aligned clay layers acted as heterogeneous nucleation agents to promote crystallization of iPP.     

Studies on biaxial stretching of polypropylene film. X. High-temperature x-ray and optical study of type III orientation

Change of orientation and crystalline state of uniaxially stretched polypropylene film during subsequent restretching with the film width unrestrained was studied by means of x-ray, optical, and calorimetric methods. Uniaxially stretched film immediately after 5 min of preheating at 130°C barely suffers premelting. When the preheating temperature rises above 150°C, the premelting proceeds gradually and the x-ray pattern becomes a halo around 160°C, which, however, returns nearly to the original crystalline pattern after cooling to room temperature. The fraction premelted in the preheating amounts to about ½–? under the condition yielding type III orientation at room temperature, as previously reported. The 130°C restretching brings type II orientation already at that temperature, similar to what has been observed at room temperature. When the restretching is performed above 155°C, the crystalline pattern remaining after the preheating converts to a halo during the restretching, which, however, converts again to the crystalline pattern of type III orientation when it is rapidly cooled. This suggests that the restretching at higher temperatures breaks up lamellae into smaller-sized crystallites. Upon cooling, the smaller-sized crystallites reorganize lamellae, the deformed lattice recovers its ordinary state, and the pulled-out chains crystallize into intermolecular crystallites, aligning in the direction of restretching. Concurrently, disorientation proceeds fairly rapidly at such high temperatures, hence, type III orientation cannot be observed even at room temperature unless the film is quickly cooled after restretching. It is concluded that type III orientation results from restretching when thermal motion of the chains within the crystalline phase becomes so violent that the unfolding occurs easily as compared with lamellar rotation.     

双轴取向聚氯乙烯(PVC-O)管道的发展

结合国内外管材原材料、技术和市场的需要,简述了PVC管材的现状及发展方向。认为双轴取向拉伸管材作为一种新型先进技术,在提高管材性能的同时可节约材料,具有非常好的竞争优势。详细研究分析了双轴取向聚氯乙烯管材生产技术、优越性能及良好的社会效益和经济效益。     

可热封双向拉伸聚酯薄膜简介

在聚酯生产过程中,采用第三或第四组分进行共聚改性,破坏或降低其结晶结构,便可具有可热封性能。以三层共挤结构为例,叙述了可热封双向拉伸聚酯薄膜的生产工艺,并将其主要性能与BOPP,CPP薄膜的进行对比。     

Crystallization and orientation studies in polypropylene/single wall carbon nanotube composite

Crystallization behavior of melt-blended polypropylene (PP)/single wall carbon nanotube (SWNT) composites has been studied using optical microscopy and differential scanning calorimetry. Polypropylene containing 0.8 wt% SWNT exhibits faster crystallization rate as compared to pure polypropylene. PP/SWNT fibers have been spun using typical polypropylene melt spinning conditions. The PP crystallite orientation and the SWNT alignment in the fibers have been studied using X-ray diffraction and polarized Raman spectroscopy, respectively.     

Barrier property and morphology of polypropylene/polyamide blend film

The barrier property of polypropylene (PP)/polyamide (PA) blend film produced by the extrusion casting film process was studied by investigating the effects of rheological properties of each components, compatibilizer content, screw rpm, and the absorbed moisture, and by performing morphological analysis and permeability modeling. The oxygen barrier property of blend film with ellipsoidal structure of PA dispersed phase was significantly improved by a factor of 5.4 with the addition of only 20 wt% PA, when compatibilizer was added by the content of 7 phr and the PP matrix resin and process condition was selected to induce lower viscosity ratio less than unity. Using Fricke’s model with the value of 19.6 of aspect ratio of the ellipsoid, the permeabilities of blend films as a function of PA content could be predicted and exhibited a good agreement with the experimental results. The absorbed moisture had a significant influence on the barrier property of the PP/PA blend system, suggesting that the hygroscopic PA resin should be incorporated with the high water barrier PP resin by the amount below about 20 wt% to minimize the deterioration of the barrier property in the humid atmosphere.     

Molecular orientation behavior of mesomorphic isotactic polypropylene under uniaxial and biaxial deformation

The molecular orientation behavior of mesomorphic isotactic polypropylene films under biaxial extension was investigated at room temperature. The birefringence was measured not only for drawn films but also simultaneously with biaxial stresses. It was found that there exists a yield point at which the neck is initiated on the biaxial deformed films and necking occurred and propagated in only one stretching direction, resulting in mosaic structures consisting of necked blocks. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

PVC-U双轴取向管材生产技术现状

介绍了PVC-U双轴取向管材的生产技术概况和拉伸机理，对它们的特点进行了说明，对实现工业应用具有一定的指导作用。