Uniaxial Elongation Research Articles

Effect of molecular structure on film blowing ability of thermoplastic zein

AbstractThe aim of this work was to explore the feasibility of preparing thermoplastic films from commercial zein by film blowing technology. Zein, a cereal protein extracted from maize, was plasticized directly in the extruder, without the time‐consuming and expensive solubilization step, usually utilized in literature for this material. Four different batches of zein were investigated, for it has been observed that properties such as the film‐forming ability of natural polymers strongly depend on several factors such as sources, extraction, and drying conditions. Thermal, rheological, and macromolecular structural characteristics were evaluated for the different materials to establish a correlation among molecular structure, rheological behavior in uniaxial elongation, and film blowing processability. Results indicate that the best films were made by using thermoplasticized zein characterized with a pronounced strain hardening and a large content of α‐helices. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

An experimental study on the “sequential order” rules in generalized two-dimensional correlation spectroscopy

Following our theoretical analysis on the “sequential order” rules in generalized two-dimensional (2D) correlation spectroscopy (H. Huang, Anal. Chem. 79 (2007) 8281–8292), an experimental study was conducted to test the “sequential order” rules using the FT-NIR data of poly(3-hydroxybutyrate) (PHB)/poly( l-lactic acid) (PLA) blends under uniaxial elongation and parallel polarization. The local sequential order concept proposed for the generalized two-dimensional (2D) correlation spectroscopy is now more clearly stated; “the intensity change at ν1 occurs predominantly before ν2” means that the starting time of the intensity change at ν1 is prior to that at ν2. It is this local sequential order which reflects the real and intuitive sequential order between two events in generalized situations. It has been found that the integrated/ overall sequential order results obtained from the 2D correlation analysis may be contradictory to the intuitive local sequential order. In addition, different integrated/ overall sequential orders could be obtained by selection of different sampling intervals from a certain set of experimental data, or choosing different number of the contours for the same sampling interval. These new experimental findings are a perfect reinforcement to our previous theoretical study and have further demonstrated the uncertainty of applying the “sequential order” rules in generalized 2D correlation spectroscopy.

Kinetics of water flow through a polymer gel

The water flow through the poly(acrylamide) gel under a constant water pressure is measured by newly designed apparatus. The Young modulus and Poisson's ratio of the rod shape gels are measured by the uni-axial elongation experiments, which determine the longitudinal modulus independently from the water flow experiments. The time evolution of the water flow in the dilute gel is calculated based on the collective diffusion model of the polymer network coupled with the friction between the polymer network and the water. The calculated results are compared with the time evolution of the flow experiments, and the values of the longitudinal modulus and the friction coefficient are estimated. The estimated values are consistent with the results of our mechanical-response experiments and the light scattering experiments reported previously. We find that the time evolution of the water flow is well described by a single characteristic relaxation time predicted by our model for dilute gels.

Structural evolution of tensile deformed high-density polyethylene at elevated temperatures: Scanning synchrotron small- and wide-angle X-ray scattering studies

The structural evolution of an ice-quenched high-density polyethylene (HDPE) subjected to uniaxial tensile deformation at elevated temperatures was examined as a function of the imposed strains by means of combined synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) techniques. The data show that when stretching an isotropic sample with the spherulitic structure, intralamellar slipping of crystalline blocks was activated at small deformations, followed by a stress-induced fragmentation and recrystallization process yielding lamellar crystallites with their normal parallel to the stretching direction. Stretching of an isothermally crystallized HDPE sample at 120 °C exhibited changes of the SAXS diagram with strain similar to that observed for quenched HDPE elongated at room temperature, implying that the thermal stability of the crystal blocks composing the lamellae is only dependent on the crystallization temperature. The strain at a characteristic transition point associated with the first indication for the occurrence of a fibrillar structure remains essentially constant in spite of the large changes in drawing temperature and crystalline thickness. In addition, WAXS experiments were used to probe the texture changes accompanying the uniaxial elongation and yield the relationship between the orientational order parameters associated with the crystallites and the amorphous chain segments, and the imposed strain. The results support the existence of intralamellar slip processes from the very beginning of tensile deformation.

Effect of Stretching on the Structure of Cylinder- and Sphere-Forming Styrene−Isoprene−Styrene Block Copolymers

Two styrene−isoprene−styrene block copolymers Vector 4111 and 4113, exhibiting cylindrical (18 wt % PS) and spherical (16 wt % PS) morphology, respectively, have been examined under uniaxial elongation up to 200% strain. On the basis of stress−strain data, mechanical properties are compared for isotropic and oriented polystyrene domains. The structure at various stages of deformation has been determined from SAXS patterns in three planes and two principal deformation directions with respect to orientation. Samples showed a very high degree of hexagonal packing, resulting in an X-ray pattern taken parallel to the cylinder alignment approaching single crystal ordering. Cylinders were aligned with the closest packed planes parallel to film surface. Particular attention has been paid to a lattice deformation process occurring during the first stretching and relaxation cycle. For a copolymer with oriented cylindrical morphology the deformation was affine up to 120% strain. The microdomain spacing was calculated parallel and perpendicular to the stretching direction. The cylindrical microstructure orientation, quantified by Hermans’ orientation factor reduced during elongation of oriented polymer, while the elongation of isotropic sample caused an increase of orientation. Deformation of all studied morphologies was reversible.

Elongational and shear rheology of carbon nanotube suspensions

Rheological behavior of concentrated suspensions of chemical vapor deposition carbon nanotubes in uniaxial elongation and simple shear is studied experimentally and theoretically. Nanotubes are suspended in viscous host liquids—castor oil or its blends with n-decane. The elongational measurements are performed by analyzing self-thinning (due to surface tension effect) liquid threads of nanotube suspensions. A quasi-one-dimensional model is used to describe the self-thinning process, whereas corrections accounting for thread nonuniformity and necking are introduced a posteriori. The effects of nanotube concentration and aspect ratio, viscosity of the suspending liquid, and initial diameter of the self-thinning thread in uniaxial elongation are elucidated. The results for uniaxial elongation are compared with those for simple shear. The correspondence in the results of the shear and elongational measurements is addressed and interpreted. The results conform to the Herschel–Bulkley rheological constitutive equation (i.e., power law fluids with yield stress). However, the yield stress in elongation is about 40% higher than in simple shear flow, which suggests that the original Herschel–Bulkley model need modification with the yield stress being a function of the second invariant of the deviatoric stress tensor. The present effort is the first to study capillary self-thinning of Herschel–Bulkley liquids, which are exemplified here by suspensions of carbon nanotubes.

Coarse-grained molecular dynamics simulation of nanofilled crosslinked rubber

A bead-spring model was applied to a crosslinked polymer with nanofillers for coarse-grained molecular dynamics simulation. Two nanofillers consisting 561 tightly connected beads and a crosslinked polymer with about 3000 beads were used as a simulation model. The strength of interactions between nanofiller and polymer based on the Lennard-Jones potential were varied. In order to investigate the effects of crosslinking and nanofiller on reinforcement, uniaxial elongation behavior was studied by coarse-grained molecular dynamics simulation with deformation function. From the uniaxial elongation simulation results and the analysis of polymer dynamics around nanofiller, it was confirmed that the degree of reinforcement depends on the strength of filler–polymer interaction, and one of the factors which influenced the stress was attributed to the existence of a low mobility phase around the nanofiller.

On Hadamard stability and dissipative stability of the molecular stress function model of non-linear viscoelasticity

We study the stability characteristics of the molecular stress function (MSF) model, i.e., a molecular constitutive theory for stress that extends the original Doi–Edwards model for linear polymers to the case of branched polymers, by repeating the assumption that the tension in the deformed chain is equal to its equilibrium value. We derive analytical, closed-form conditions for Hadamard stability under general 3-D high-frequency, short-amplitude wave disturbances in bi-quadratic form, which reduce to simple algebraic criteria for the cases of 1-D and 2-D disturbances. Application of the derived conditions in the case of general biaxial extension, which provides a simplified description of many processes encountered in industry and nature, shows that the MSF is Hadamard unstable for strains beyond 2. This casts doubts on its ability in predicting correct elastic response under rapid extensional deformations. The region of instability widens with the strengthening of network connectivity or the alignment strength of the flow. Dissipative stability of the MSF is examined using two necessary criteria: the first and less restrictive criterion requires the stress to be monotonically and unboundedly increasing function of strain in uniaxial elongation and simple shear. The second criterion requires the free energy and the rate of energy dissipation to be bounded functions of deformation. We find that while MSF satisfies the first stability criterion, violates the second, thus revealing thermodynamic inconsistencies in formulating the dissipative terms of the constitutive equation.

Rheological behavior and mechanical properties of sawdust/polyethylene composites

AbstractWe have characterized the melt rheological behavior and the solid tensile properties of sawdust/polyethylene composites prepared in an internal mixer. Various concentrations (from 0 to 60 wt %) and three particle sizes have been tested, in presence of a coupling agent (maleic anhydride grafted polyethylene). In the molten state, for each particle size, a mastercurve of the complex viscosity as function of frequency can be plotted, using a shift factor depending on weight fraction. We show that the shift factors can be described by a Krieger‐Dougherty law, leading to a “universal” viscosity law of the Carreau‐Yasuda type. In the solid state, the presence of sawdust increases Young modulus in uniaxial elongation, mainly for small size particles, but reduces dramatically deformation at break and tensile strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

모재의 방향성에 따른 마찰교반용접 판재의 성형성에 관한 실험적 연구

In order to investigate the formability of friction stir welded(FSW) tailor welded blanks(TWB) with respect to the base material`s directional combination, aluminum alloy AA6111-T4 sheets were welded with three different conjoining types: RD-RD, TD-RD and TD-TD. Here, RD and TD represent rolling and transverse directions, respectively. For experimental formability study, three tests with gradual complexity were performed: the simple tension test with various weld line directions for uni-axial elongation, the hemisphere dome stretching test for biaxial stretching and the cylindrical cup deep drawing test. As a result, all three forming tests showed that RD-RD type samples exhibited the best formability, while TD-TD type sheets showed the least formability performance.

Modeling of Structure Evolution of Filled Elastomers under Uniaxial Elongation

The evolution of filler network structure in elastomers during elongation is investigated on the basis of computer modeling. The filler network is represented by spherical particles of different sizes, which are randomly filling a prismatic volume. No physical interaction forces between the particles on the molecular level are considered. The modeling is based on geometrical obstructions of particle ensembles. Interpenetrations of rigid particles during modeling of filling and subsequent stretching are forbidden, and only a minimal finite distance between the particles is allowed. The material is assumed to be incompressible. It was found that the number of nearest neighbors (coordination number) in a loosely filled material increases during stretching; however, in a densely filled material, this value decreases. The analysis of the size of unfilled spaces in the matrix has shown the occurrence of essential structural heterogeneities in the filler network. Stretching of a densely filled material results in appreciable mixing of particles whereby changes of the distances between originally neighboring particles exceed the macroscopic elongation of the material by several times. An analytical relation between the elongation of the composite and polymer chains via transmission ratio is proposed.

Effect of Blended Ionomers on the Strain Hardening of Polyester-Type Elastomer/Ionomer Blends

A Na-type ionomer based on poly(ethylene-co-methacrylic acid) (EMAA-Na ionomer) was blended with thermoplastic polyester elastomer (TPEE) and the effect on uniaxial elongational viscosity was investigated. To clarify the effect of the degree of neutralization (ND) by the EMAA-Na ionomer on strain hardening of TPEE/ionomer blends system, EMAA-Na ionomers with different NDs were prepared and blended with TPEE above their melting temperature using a twin screw extruder. An unexpected strong strain hardening was observed for a ND above 40% for a TPEE/EMAA-Na blend ratio of 80/ 20 wt %, which corresponds to the critical ND for the formation of ion aggregates. The results can be explained using the acid-cation exchange mechanism proposed by Vanhoorne and Register. It is considered that blending EMAA-Na ionomers is an effective method for the modification of TPEE with respect to the intensity of strain hardening under uniaxial elongation.

Rheo-optical FT-IR spectroscopy of poly(3-hydroxybutyrate)/poly(lactic acid) blend films

The orientation of poly(3-hydroxybutyrate) (PHB) and poly(lactic acid) (PLA) segments in PHB/PLA blend films cast from chloroform solutions with compositions PHB < PLA was studied during uniaxial elongation up to 250% strain at 50 °C by in-situ rheo-optical FT-IR spectroscopy. From the orientation functions of the ν(C O) bands of the blend components, it was derived that the PLA chains orient in the direction of elongation while the PHB chains orient perpendicular to the drawing direction. PHB homopolymer and PHB/PLA blend films with PHB > PLA compositions could only be oriented by cold drawing in ice water after quenching from the melt. The IR-dichroic effects of films drawn under these conditions indicate for both blend components a chain alignment parallel to the drawing direction.

First-Principles Constitutive Equation for Suspension Rheology

Using mode-coupling theory, we derive a constitutive equation for the nonlinear rheology of dense colloidal suspensions under arbitrary time-dependent homogeneous flow. Generalizing previous results for simple shear, this allows the full tensorial structure of the theory to be identified. Macroscopic deformation measures, such as the Cauchy-Green tensors, thereby emerge. So does a direct relation between the stress and the distorted microstructure, illuminating the interplay of slow structural relaxation and arbitrary imposed flow. We present flow curves for steady planar and uniaxial elongation and compare these to simple shear. The resulting nonlinear Trouton ratios point to a tensorially nontrivial dynamic yield condition for colloidal glasses.

Structural, mechanical, and electronic properties of ultrathin ZnO nanowires

We report a structural transformation between the regular wurtzite and the unbuckled wurtzite (hexagonal) structure for ultrathin single-crystalline [0001] ZnO nanowires under uniaxial elongation and compression. Our density functional calculations show that hexagonal structure corresponds to a distinct minimum on the transformation path. Young’s moduli of the ZnO nanowires with the hexagonal structures are larger than those with the wurtzite structures at the same size. Within the nanowire size range considered, Young’s moduli of the ZnO nanowires decrease with increasing wire diameter. The electronic properties of these two types of ZnO nanowires exhibit distinctly different behaviors.

Uniaxial Stretching above the Glass Transition Temperature of Poly(Ethylene Terephthalate) and its Effects on the Structure Development

This work deals with an experimental investigation of the strain-induced crystalline microstructure that develops under uniaxial elongation of amorphous poly(ethylene terephthalate), PET, above its glass transition temperature, as an approach for industrial stretch-blow moulding processes. The present study aims at: a) defining the most relevant processing parameters which govern and are of significance for the induced morphology, and b) establishing of relationships between processing and morphology. Compression moulded amorphous PET was uniaxial stretched with variations of following stretching parameters: stretching temperature, Tst, stretching velocity, Vst, and stretching ratio, λst, that were varied in two levels according to a L8 Taguchi orthogonal array. The developed morphologies were characterized by differential scanning calorimetry (DSC) and birefringence measurements. Obtained results were analyzed by ANOVA statistical tool. The glass transition temperature, Tg, is influenced mainly by the stretching ratio. The cold crystallization temperature, Tcc, is determined by complex influence of all stretching variables and the interaction Tstxλst. The degree of crystallinity, χc, mainly depends upon Vst and Tstxλst interaction. The birefringence, n, is essentially determined by λst and the interaction Vstxλst. The distinct morphological parameters are then related with the purpose of understand the structure development upon polymer stretching.

&lt;sup&gt;2&lt;/sup&gt;H NMR Study of Deformed Natural Rubber Networks

The orientational order generated in a cross-linked elastomer by uniaxial stress is probed with deuterium NMR spectroscopy. Spectra of technical unfilled natural rubber (NR) vulcanisates (cis-1,4-polyisoprene), locally swelled with o-dichlorobenzene-d4, exhibits quadrupolar doublets under elongation, which have an explicit dependence on the extension ratio and cross-link density. A new mechanical device was designed to fit into an NMR probe-head to permit the elongation of the networks in the interior of the magnet without removal of the sample thus avoiding the effect of the relaxation of the network chains after each step of uniaxial elongation and the observation of always the same section of the stretched sample. A molecular model of rubber elasticity was applied to describe the behavior of rubber network in mechanical and NMR experiments.

Sieve mechanism estimations for microfiltration membranes with elliptical pores

An established sieve mechanism model for microfiltration was modified to incorporate elliptical pore shapes that arise from uni-axial elongation of track-etch (TE) membranes. The particular membranes investigated were poly(ethylene teraphthalate) TE membranes with an average pore size of 0.6 μm and elongations up to 35.6%. The modified sieve theory predicts that a membrane that has undergone a 35.6% elongation allows for twice the throughput compared to the original membrane with circular pores, while maintaining the same removal ability for a solution containing 1 μm particles.

The piezoresistance effect of FIB-deposited carbon nanowires under severe strain

This paper reports the piezoresistance effect of carbon nanowires (CNWs) deposited by focused ion-beam-assisted chemical vapor deposition (FIB-CVD) using phenanthrene gas for the development of novel nanomechanical sensors. CNWs with diameters ranging from 88 to 129 nm were fabricated on electrostatic actuated nano tensile testing devices (EANATs) by FIB-CVD. EANATs can stretch CNWs using electrostatic comb drive actuators, and simultaneously measure the uniaxial tensile load and elongation of CNWs using the lever motion amplification system integrated into the EANATs. The average Young's modulus and fracture stress obtained for the CNWs were 69.2 GPa and 6.2 GPa, respectively. The resistance change in the CNWs with increasing uniaxial tensile strain indicated that the total gauge factor of CNWs was 0.7 below a tensile strain of 4%, but changed to −0.9 above 4%. An electrical conduction model for CNWs proposed in this paper was able to explain the resistance change in the nanowires and predict that the gauge factor for only the hydrogenated amorphous carbon region of CNWs ranged from −27.8 to −56.8.

Bread dough rheology in biaxial and step-shear deformations

We consider the use of a Lodge-type model with a damage function for the description of some bread dough rheology. The model has been reasonably successful in uniaxial elongation and shearing, and here, we investigate biaxial stretching, using a bubble method, and some step strain shear motions. The damage function, previously regarded as a function of the largest Hencky strain, is shown to be inadequate to describe biaxial stretching, and a modification is proposed. The sequence of step strains, with both reversing and steadily increasing steps, is reasonably well described by the model. The revised model can therefore describe small-strain motions, steady shearing, steady uniaxial and biaxial elongations, recoil, stress relaxation and step strain motions.