Biaxial Stretching Research Articles

A Study on the Oxygen Permeability Behavior of Nanoclay in a Polypropylene/Nanoclay Nanocomposite by Biaxial Stretching.

Polypropylene (PP) has poor oxygen barrier properties, therefore it is manufactured in a multi-layer structure with other plastics and metals, and has been widely used as a packaging material in various industries from food and beverage to pharmaceuticals. However, multi-layered packaging materials are generally low in recyclability and cause serious environmental pollution, therefore we have faced the challenge of improving the oxygen barrier performance as a uni-material. In this work, PP/nanoclay nanocomposites were prepared at nanoclay contents ranging from 0.8 to 6.4 wt% by the biaxial stretching method, performed through a sequential stretching method. It was observed that, as the draw ratio increased, the behavior of the agglomerates of the nanoclay located in the PP matrix changed and the nanoclay was dispersed along the second stretching direction. Oxygen barrier properties of PP/nanoclay nanocomposites are clearly improved due to this dispersion effect. As the biaxial stretching ratio and the content of nanoclay increased, the oxygen permeability value of the PP/nanoclay nanocomposite decreased to 43.5 cc·mm/m2·day·atm, which was reduced by about 64% compared to PP. Moreover, even when the relative humidity was increased from 0% to 90%, the oxygen permeability values remained almost the same without quality deterioration. Besides these properties, we also found that the mechanical and thermal properties were also improved. The biaxially-stretched PP/nanoclay nanocomposite fabricated in this study is a potential candidate for the replacement of the multi-layered packaging material used in the packaging fields.

Characterizing Biaxially Stretched Polypropylene / Graphene Nanoplatelet Composites

In this work, polypropylene (PP) nanocomposites containing different weight concentration of graphene nanoplatelets (GNP) were prepared by melt-mixing using an industrial-scale, co-rotating, intermeshing, twin-screw extruder. The materials were then compression moulded into sheets, and biaxially stretched at different stretching ratios (SRs) below the PP melting temperature. The effects of GNP content and biaxial stretching on the bulk properties of unfilled PP and PP/GNP nanocomposites have been investigated in details. Results show that the addition of GNP (>5wt%) can lead to electrically conductive composites due to the formation of percolation network. The GNP have led to increased polymer crystallinity and enhanced materials stiffness and strength. Biaxial stretching process further enhances the materials mechanical properties but has slightly decreased the composites electrical conductivity. The PP/GNP nanocomposites were also processed into 3D demonstrator parts using vacuum forming, and the properties of which were comparable with biaxially stretched composites.

Crystallinity and β Phase Fraction of PVDF in Biaxially Stretched PVDF/PMMA Films.

Polyvinylidene fluoride (PVDF) and poly(methyl methacrylate) (PMMA) blend films were prepared using biaxial stretching. The effects of PMMA content and stretching ratio on the crystallinity and β phase fraction of PVDF in blend films were investigated. The distributions of crystallinity and β phase fraction on variable locations were also studied. The results of FTIR and XRD showed that β phase appeared in PVDF/PMMA blends after extrusion and casting procedures. Although β phase fraction decreased after preheating, there was still an increasing trend during following biaxial stretching. More importantly, the increase in PMMA content improved β phase fraction, and the highest β phase fraction of 93% was achieved at PMMA content of 30 wt% and stretching ratio of 2×2. Besides, the reduction in PMMA content and the increase in stretching ratio improved the crystallinity of PVDF. The mechanical properties of the stretched films were significantly improved by increasing the stretching ratio as well. The uniform stress distribution on different regions of biaxial stretching films contributed to the uniform distribution of β phase fraction and crystallinity of PVDF with the aid of simulation. This work confirmed that biaxial stretching can be a candidate method to prepare PVDF/PMMA blend films with uniform distributions of comparable β phase and crystallinity of PVDF.

Nonlinear Elasticity of Ultrasoft Near-Critical Gels with Extremely Sparse Network Structures Revealed by Biaxial Stretching

Unequal biaxial stretching experiments reveal the unique nonlinear elasticity of ultrasoft near-critical gels with an extremely sparse infinite network that are obtained slightly beyond the gel poi...

Comparison of the Structural Evolution of β Polypropylene during the Sequential and Simultaneous Biaxial Stretching Process

In this work, the lamellar structural evolution and microvoids variations of β polypropylene (β-PP) during the processing of two different stretching methods, sequential biaxial stretching and simultaneous biaxial stretching, were investigated in detail. It was found that different stretching methods led to significantly different lamellae deformation modes, and the microporous membranes obtained from the simultaneous biaxial stretching exhibited better mechanical properties. For the sequential biaxial stretching, abundant coarse fibers originated from the tight accumulation of the lamellae parallel to the longitudinal stretching direction, whereas the lamellae perpendicular to the stretching direction were easily deformed and separated. Those coarse fibers were difficult to be separated to form micropores during the subsequent transverse stretching process, resulting in a poor micropores distribution. However, for the simultaneous biaxial stretching, the β crystal had the same deformation mode, that is, the lamellae distributed in different directions were all destroyed, forming abundant microvoids and little coarse fibers.

Pneumatic Experimental Design for Strain Rate Sensitive Forming Limit Evaluation of 7075 Aluminum Alloy Sheets under Biaxial Stretching Modes at Elevated Temperature

A pneumatic experimental design to evaluate strain rate sensitive biaxial stretching forming limits for 7075 aluminum alloy sheets was attempted with the finite element method. It was composed of apparatus geometric design with pressure optimization as the process design. The 7075 aluminum alloy material was characterized by conventional Voce-type hardening law with power law strain rate sensitivity relationship. For optimization of the die shape design, the ratio of minor to major die radius (k) and profile radius (R) were parametrically studied. The final shape of die was determined by how the history of targeted deformation mode was well maintained and whether the fracture was induced at the pole (specimen center), thereby preventing unexpected failure at other locations. As a result, a circular die with k = 1.0 and an elliptic die with k = 0.25 were selected for the balanced biaxial mode and near plane strain mode, respectively. Lastly, the pressure inducing fracture at the targeted strain rate was studied as the process design. An analytical solution that had been previously studied to maintain constant strain rate was properly modified for the designed model. The results of the integrated design were compared with real experimental results. The shape and thickness distribution of numerical simulation showed good agreement with those of the experiment.

Preparation of High-Performance Polyvinylidene Fluoride Films by the Combination of Simultaneous Biaxial Stretching and Solid-State Shear Milling Technologies

Different from the traditional uniaxial stretching films, biaxially stretched films have excellent properties and broad application prospects. In this paper, by adopting simultaneous biaxial stretc...

Highly Sensitive Graphene/Polydimethylsiloxane Composite Films near the Threshold Concentration with Biaxial Stretching.

Uniformly dispersed graphene effectively improves the strain-sensing capability of the composite film under a low graphene load in nanocomposites prepared with polydimethylsiloxane (PDMS) and graphene (GNP) monolayer powder. The threshold concentration of graphene was determined by loading nanocomposites at different temperatures. For different concentrations, when using traditional uniaxial stretching, the rate of resistance change of films near the threshold concentration is five times higher than the rate of films with a high concentration. Compared with traditional uniaxial stretching, the biaxial stretching we introduced can effectively improve the sensitivity of the film by an order of magnitude. The change in the resistance of the film near the threshold concentration is due to the change of the tunnel length and the cross-section of the tunnel, whereas the high concentration of the film is due to the change of the conductive path inside the film. Biaxial stretching has different effects on films with different concentrations, but the final effect of increasing sensitivity is the same. This study provides guidance for improving the strain-sensing sensitivity of GNP/PDMS composite films and the application of biaxial tension in detecting human motions.

Structure Evolution and Deformation Behavior of Polyethylene Film during Biaxial Stretching.

The structure evolution and deformation behavior of tenter-frame biaxially oriented polyethylene (TF-BOPE) films were investigated in this study. For sequential biaxial stretching, the original spherulites were broken into small pieces, and the fibrillar structure simultaneously formed during the machine direction (MD) stretching. Subsequently, the single fibrils were pulled away, and some fine fibrils developed via partial melting–recrystallization or lamellar rearrangement during the transverse direction (TD) stretching, which leads to the formation of the vein structure and nanosized fiber-like network. For simultaneous biaxial stretching, the fractured lamellae and the newly formed crystals were evenly distributed in the MD-TD plane like an isotropous fibrillar network. Moreover, compared with the unstretched sample, both films could achieve up to about 2 times the tensile modulus and 4.5 times the tensile strength and also exhibited the superior optical property.

Instability of a Square Sheet of Rubberlike Material under Symmetric Biaxial Stretching

The purpose of this work is to analyse the stability of the solution of the biaxial stretching test, in the case of Ishihara-Zahorski’s constitutive model of rubber-like material. Two solutions were obtained, the symmetric and asymmetric one. It was shown that the asymmetric solution is possible for significant forces and this solution is always stable. However, the symmetric solution is stable only for relatively small principal stretches. It is worth emphasizing that the stored energy function of the considered model is polyconvex.

Silica-Polypropylene Nanocomposites for Film Capacitors: Structure–Property Studies and the Role of Biaxial Stretching Conditions

Biaxial-stretching-induced morphology development anddielectric properties of hydrophobic fumed silica-BOPPnanocomposite films were investigated. The precursor (cast)film morphology, pre-heating as well as biaxial stretchingtemperature and stretch ratio were found to profoundly affect thesilica-BOPP film bulk morphology, surface texture and theformation of particle/agglomerate-induced cavitation uponbiaxial stretching. Isothermal high-field conductivity andthermally stimulated depolarization current measurementsindicated decreasing high-field/high-temperature conductivityand modification of trap density of states upon incorporation ofnanosilica in comparison to neat BOPP. Large-area DCdielectric strength is, however, sensitive to thermal/mechanicalstresses upon biaxial stretching, hence necessitating carefuloptimization of the nanocomposite formulation and processing.

Structure Evolution of Polyethylene in Sequential Biaxial Stretching along the First Tensile Direction

Two linear low-density polyethylene samples (PE-A and PE-B), with similar melt index and molecular weight but different molecular structures, were used to explore the structural evolution during sequential biaxial stretching. Only PE-A could be successfully stretched into a film with the biaxial draw ratio of 6 × 6. The interlamellae crossing adjacent lamellar stacks were observed in PE-A but not in PE-B, which could increase the lateral tie connection. Moreover, the amount of fibril was less in PE-A than that in PE-B and the fibrillar structure lacked tie chains between each other. In addition, the newly formed lamellae in PE-A (derived from fine lamellae) could lock the molecular chains of different crystals, which increased the lateral connection via anchoring the tie chains from adjacent lamellae. Therefore, the above specific structures increased the lateral connection and were beneficial for biaxial stretching. Furthermore, the relationship between molecular structure and condensed structure was als...

Three-Dimensional Bioconvection Nanofluid Flow from a Bi-Axial Stretching Sheet with Anisotropic Slip

A theoretical study is presented for three-dimensional flow of bioconvection nanofluids containing gyrotactic microorganisms over a bi-axial stretching sheet. The effects of anisotropic slip, thermal jump and mass slip are considered in the mathematical model. Suitable similarity transformations are used to reduce the partial differential equation system into a nonlinear ordinary differential system. The transformed nonlinear ordinary differential equations with appropriate transformed boundary conditions are solved numerically with the bvp4c procedure in the symbolic software, MATLAB. The mathematical computations showed that an increase in Brownian motion parameter corresponds to a stronger thermophoretic force which encourages transport of nanoparticles from the hot bi-axial sheet to the quiescent fluid. This increases the nanoparticle volume fraction boundary layer. Fluid temperature and thermal boundary layer thickness are decreased with increasing stretching rate ratio of the bi-axial sheet. The present simulation is of relevance in the fabrication of bio-nanomaterials and thermally-enhanced media for bio-inspired fuel cells.

Grain Size Effect on Mechanical Properties Under Biaxial Stretching in Pure Tantalum

This paper reports the mechanical properties and formability under biaxial stretching in pure tantalum as a function of average grain size. The grain size of pure tantalum was adjusted from submicron to tens of micron using the high-pressure torsion process and subsequent annealing. The stretch formability was evaluated using a miniaturized Erichsen tester. Under uniaxial tension, the mechanical properties of pure tantalum followed the typical strength-ductility trade-off behavior according to the average grain size. Nevertheless, the stretch formability became rather significantly inferior in the coarse-grain tantalum, which was primarily attributed to the poor resistance to strain localization and limited work hardening capacity. This deterioration was supposed to be due to the intensified strain localization with increasing the average grain size, based on the in-grain deformation heterogeneity within individual grains and the surface roughening after the Erichsen test. Consequently, this study suggests that the excellent stretch formability and work hardening capacity under biaxial loading can be achieved at a certain range of the average grain size (8.25–19.3 μm in this work).

Correction to Strain-Induced Crystallization during Relaxation Following Biaxial Stretching of PET Films: A Real-Time Mechano-Optical Study

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to Strain-Induced Crystallization during Relaxation Following Biaxial Stretching of PET Films: A Real-Time Mechano-Optical StudyMohamed K. HassanMohamed K. HassanMore by Mohamed K. Hassanhttp://orcid.org/0000-0001-6453-0383 and Mukerrem Cakmak*Mukerrem CakmakMore by Mukerrem Cakmakhttp://orcid.org/0000-0001-9128-7833Cite this: Macromolecules 2019, 52, 6, 2627Publication Date (Web):March 14, 2019Publication History Published online14 March 2019Published inissue 26 March 2019https://doi.org/10.1021/acs.macromol.9b00244Copyright © 2019 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views733Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (202 KB) Get e-Alerts Get e-Alerts

Characterization and modelling the mechanical behaviour of poly(l-lactic acid) for the manufacture of bioresorbable vascular scaffolds by stretch blow moulding

Bioresorbable Vascular Scaffolds (BVS) manufactured from poly (l-lactic acid) (PLLA) offer an alternative to metal scaffolds for the treatment of coronary heart disease. One of the key steps in the manufacture of these scaffolds is the stretch blow moulding process where the PLLA is biaxially stretched above glass transition temperature (Tg), inducing biaxial orientation and thus increasing ductility, strength and stiffness. To optimise the manufacture and performance of these scaffolds it is important to understand the influence of temperature and strain rate on the constitutive behaviour of PLLA in the blow moulding process. Experiments have been performed on samples of PLLA on a custom built biaxial stretch testing machine to replicate conditions typically experienced during blow moulding i.e. in a temperature range from 70 °C to 100 °C and at strain rates of 1 s−1, 4 s−1 and 16 s−1 respectively. The data is subsequently used to calibrate a nonlinear viscoelastic material model to represent the deformation behaviour of PLLA in the blow moulding process. The results highlight the significance of temperature and strain rate on the yielding and strain hardening behaviour of PLLA and the ability of the selected model to capture it.

Structural Evolution of Two-Phase Blends of Polycarbonate and PMMA by Simultaneous Biaxial Stretching.

We investigated the structural evolution of the two-phase blends of polycarbonate (PC) and poly(methyl methacrylate) (PMMA) at various blend compositions by simultaneous biaxial stretching, using optical microscopy and SEM observation. The spherical PMMA domains and PC matrix of 30/70 PC/PMMA were enlarged uniformly at the all in-plane direction, while the anisotropic-shaped co-continuous structure in 50/50 PC/PMMA was deformed to a crosshatched structure by the in-plane bimodal orientation. In 70/30 PC/PMMA, the phase inversion was found to occur by simultaneous biaxial stretching; that is, the spherical PMMA domains were changed to a crosshatched matrix by the in-plane bimodal orientation due to coalescence of the PMMA domains during the stretching. Owing to the phase inversion, the surface hardness estimated by the pencil hardness test became harder, from 2B to 2H, increasing the strain from 1.0 to 2.0.

A Comparative Study of the Structure and Mechanical Properties of Uniaxially and Biaxially Stretched PA6-66/Montmorillonite Films

A Comparative Study of the Structure and Mechanical Properties of Uniaxially and Biaxially Stretched PA6-66/Montmorillonite Films

Effects of Reorientation of Graphene Platelets (GPLs) on Young's Modulus of Polymer Composites under Bi-Axial Stretching.

Effects of bi-axial stretching induced reorientation of graphene platelets (GPLs) on the Young’s modulus of GPL/polymer composites is studied by Mori-Tanaka micromechanics model. The dispersion state of the GPLs in polymer matrix is captured by an orientation distribution function (ODF), in which two Euler angles are used to identify the orientation of the GPLs. Compared to uni-axial stretching, the increase of the stretching strain in the second direction enhances the re-alignment of GPL fillers in this direction while it deteriorates the re-alignment of the fillers in the other two directions. Comprehensive parametric study on the effects of the out-of-plane Young’s modulus, stretching strain, strain ratio, Poisson’s ratio and weight fraction and GPL dimension on the effective Young’s moduli of the composites in the three directions are conducted. It is found that the out-of-plane Young’s modulus has limited effects on the overall Young’s modulus of the composites. The second stretching enhances the Young’s modulus in this direction while it decreases the Young’s modulus in the other two directions. The results demonstrate the increase of Poisson’s ratio is favorable in increasing the Young’s modulus of the composites. GPLs with larger diameter-to-thickness ratio have better reinforcing effect on the Young’s modulus of GPL/polymer nanocomposites.

Influence of Strain Ratio on Surface Roughening in Biaxial Stretching of IF Steel Sheets

Influence of Strain Ratio on Surface Roughening in Biaxial Stretching of IF Steel Sheets