Deformation Of Poly Research Articles

Lamellae orientation and structure evolution of reinforced poly(lactic acid) via equal channel angular extrusion

AbstractThe aim of this study was to improve the mechanical performance of biodegradable poly(L‐lactic acid) through equal channel angular extrusion (ECAE). Changes in morphology induced by the ECAE shear deformation in poly(lactic acid) (PLA) were investigated. Differential scanning calorimeter results suggested a significant improvement in crystallinity of ECAE‐deformed PLA depending on its thermal condition and deformation force. Two‐dimensional wide angle X‐ray diffraction measurement and polarized FTIR spectroscopies of ECAE‐deformed PLA revealed a structural network in the crystalline region, and the taut tie molecules (TTMs) connecting lamellae also stretched. Scanning electron microscope results showed that the macro‐fibrils were generated, and the oriented structures were arranged along the nominal shear direction at a certain angle. Both the inclined macro‐fibrils structure and the oriented TTMs within fibrils were beneficial in improving mechanical performance. Finally, the mechanical property tests showed that the mechanical properties of PLA were improved overall. The tensile strength, elongation, impact strength, and bending strength increased by 28%, 123.8%, 224.3%, and 47.6%, respectively. Meantime, a transition from brittle fracture to ductile fracture was observed from the original PLA billet to ECAE‐deformed one. Therefore, the ECAE process represents a promising approach for comprehensively reinforced PLA.

Production of Porous Poly(p-dioxanone) Fibers during the Neck Propagation in Self-Excited Oscillation Mode

Features of the plastic deformation of poly(p-dioxanone) fibers in air were studied. The neck propagation in the deformation speed range 0.2–15 mm/min was shown to occur in the self-excited oscillation mode. It was detected for the first time that this process is accompanied by the formation of areas with an open-pore structure. Impregnation of the fibers with brilliant green with the penetration of the die from the solution into the pores produces fibers with antimicrobial properties against the fungal culture of Candida albicans.

Microscopic Origin of Elastic and Plastic Deformation in Poly(Ether-Block-Amide) Elastomers under Various Conditions

Microscopic Origin of Elastic and Plastic Deformation in Poly(Ether-Block-Amide) Elastomers under Various Conditions

Asymmetric deformation in poly(ethylene-co-1-octene)/multi-walled carbon nanotube composites with glass micro-beads for highly piezoresistive sensitivity

To develop strain sensors with excellent reliability, stability, sensitivity, reversibility, and facile processing still suffers great challenge. In this work, the glass micro-beads (μ-GB) with high modulus were added into poly(ethylene-co-1-octene)/multi-walled carbon nanotubes (POE/MWCNTs) composites to construct modulus mismatching domains, which generated asymmetric deformation in the composites during compression and then improved piezoresistive sensitivity. The μ-GBs with diameter of 45, 75, and 105 μm were used to evaluate the size effect of modulus mismatching domains on the piezoresistive sensitivity of the composites. It was very interesting to find that the composites with different diameter of μ-GBs exhibited different piezoresistive sensitivity. The highest piezoresistive sensitivity was found in the composites with the smallest size of μ-GBs (45 μm). Additionally, the piezoresistive sensitivity was also improved by increasing the content of μ-GBs. For example, the gauge factor of the POE/MWCNTs composites increased from 1.9 to 6.4 by the incorporation of 50 wt% μ-GBs with 45 μm in diameter. The mechanism of the asymmetric deformation in the composites with modulus mismatching domains under cyclic loading was discussed in detail. Furthermore, the strain sensor with μ-GBs had excellent reliability, stability and reversibility, which was attached to a sport shoe and exhibited a good cyclic signal response during walking. Besides, the Young’s modulus and compression modulus were also enhanced by the addition of μ-GBs. For example, the Young's modulus of the POE/MWCNTs composites showed 300% enhancement by adding 50 wt% μ-GBs with 45 μm in diameter.

Homogeneous and Localized Deformation in Poly(Methyl Methacrylate) Nanocutting

Nanoscale manufacturing imposes demands on prediction of cutting processes on small scales. Predictive modeling schemes based on the underlying physical mechanisms could potentially be more generally applicable in manufacturing. In this work, the experimental and numerical studies on polymethyl methacrylate (PMMA) nanocutting are reported. The cutting experiments were performed on an ultramicrotome instrumented with piezoelectric transducers to measure the cutting forces on cutting down to about 60 nm thickness. Using atomic force microscopy, the surface damage was identified as shear yield bands triggered by adiabatic heating. A suitable physical model including these observed phenomena made it possible to link the processing conditions with the onset of damage, i.e., the transition between a high-quality transparent surface and a damaged uneven surface. Finite element analysis was carried out to investigate the deformation modes of PMMA under different cutting conditions and to predict the formation of the undesired shear bands. From an engineering perspective, such an approach could be potentially useful in improving manufacturing control.

Orthogonal Dynamic Model of Viscoelastic Deformation Under Variable Concentration and Loading

Abstract In the present work, a generalized mathematical model is considered for describing the process of viscoelastic deformation of poly- mer materials. The model is applied for describing the creep of poly- ethylene in the conditions of diffusion in liquid environment interacting chemically with the polymer and variable loading. The orthogonal expansions method is used and is extended for a process with integrating properties (without self-settling). In this case, it is necessary to separate the integral component, which is also presented as parameter-dependent on loading and saturation. The output experiments are executed with samples which possess reached beforehand different levels of saturation with cyclohexan and have been afterwards submitted to mechanical testing with brief creep in pure torsion at various constant levels of loading.

Structure and stability of oligomer-polymer blends based on poly(ethylene terephthalate) deformed by crazing mechanism

Deformation of poly(ethylene terephthalate) films in high-viscosity poly(ethylene glycol) (PEG 600) and poly(propylene glycol) (PPG 3000) is investigated. It is established that the deformation is realized by the classical crazing mechanism, is accompanied by the formation of a finely dispersed fibrillar-porous structure and results in the formation of blends with high concentrations of the incorporated components (as high as 52–57 wt %). The stability of samples that occur in the free state after stretching is studied. Prolonged release of PEG 600 from the crazed poly(ethylene terephthalate) matrix is revealed, the intensity of which depends on the ambient humidity.

Metrology for characterizing scratch resistance of polymer coatings

Current methods for scratch resistance assessment are often based on “relative but not quantitative” types of measurements, such as visual inspection, gloss changes, and changes in gray scale level or lightness. Most results are used for qualitative assessment purposes, which result in the lack of a repeatable and reliable standardized test method for the polymer materials community. To implement a scientifically based standardized test method for quantifying scratch resistance, it is vital to understand the relationships between material mechanical properties, morphology, and appearance (optical properties) of surface and subsurface deformation. In this article, preliminary results from a scratch testing protocol to identify the “onset” of plastic deformation in poly(methyl methacrylate) and poly(propylene) commercial samples are presented. Recent advances in optical scattering measurements to identify the onset of plastic deformation by analyzing specular and off-specular intensities are also presented.

Deformation of poly(methyl methacrylate) after exposure to radiation and magnetic fields

It is demonstrated that prolonged treatment in a constant magnetic field considerably increases the creep rate under compression of poly(methyl methacrylate) samples irradiated with gamma-ray doses as high as 100 kGy. For higher irradiation doses, the effect of the magnetic field on the creep rate is insignificant.

On deformation of poly(ethylene terephthalate)/polyethylene and polycarbonate/polyethylene blends with high interfacial contact during elongation

On deformation of poly(ethylene terephthalate)/polyethylene and polycarbonate/polyethylene blends with high interfacial contact during elongation

Deformation of Poly(o-methoxyaniline) Film Induced by Polymer Conformation on Electrochemical Oxidation

Deformation of Poly( o -methoxyaniline) Film Induced by Polymer Conformation on Electrochemical Oxidation

Conditions of homogeneous deformation of poly(ethylene terephthalate) films during uniaxially drawing

Amorphous poly(ethylene terephthalate) film was uniaxially drawn over a wide range of temperatures from below to above the T g at a constant strain rate. The geometry of the deformation in macroscopic dimensions of the sample demonstrates that homogeneous deformation can be obtained when the drawing temperature (T def ) is not lower than 69°C. The change of the cold crystallization peak temperature (T cc ) and crystallinity determined by differential scanning calorimetry and density measurement, respectively, were studied in terms of the T def and the draw ratio (A). The orientation, relaxation, and crystallization during drawing were investigated as a function of T def as well as of A. The results suggest that 69°C is the critical temperature at which the sample with the highest orientation and the least slippage of the molecular chain and without obvious crystallization can be obtained.

Deformation of Poly(dimethylsiloxane) Oligomers under Uniaxial Tension: Quantum Chemical View

The response of a silicone polymer fragment to external stresses is considered in terms of a mechanochemical reaction. The quantum chemical realization of the approach is based on a coordinate-of-reaction concept for the purpose of introducing a mechanochemical internal coordinate (MIC) that specifies a deformational mode. The related force of response is calculated as the energy gradient along the MIC, while the atomic configuration is optimized over all of the other coordinates under the MIC constant-pitch elongation. The approach is applied to a set of linear silicone oligomers Sin with n = 4, 5, and 10 subjected to uniaxial tension, followed by the molecule breaking and a postfracture relaxation. Three stages of deformation, differing by structural transformation, have been detected. The observed peculiarities of the oligomer mechanical behavior are well attributed to the characteristic modes of vibrational spectra. The oligomer strength and the related Young's moduli are obtained. A cooperative radical-driven mechanism of silicone polymer fracture is suggested.

Thermal stability and deformation of poly(acrylic acid)–metal oxides

Thermal stability and deformation of poly(acrylic acid)–metal oxides

Thermal stability and deformation of poly(acrylic acid)-metal oxides

In this work, we investigated the thermal stability and deformation of the compound of poly(acrylic acid) (PAA) and metal oxides (ZnO, CaO, CuO, Al2O3, and Cr2O3). The kinetic parameters of the desorption of water from PAA–metal oxide were calculated. The activation energies of the water desorption of PAA–metal oxide were less than 5 kcal/mol. The order of bonding capability of oxygen (PAA–O–metal) and water was PAA–CaO > PAA–ZnO > PAA–CuO > PAA–Cr2O 3 > PAA–Al2O3. The reaction types of the composites were clarified. Incorporating metal oxide into PAA increased the thermal stability. The factors which influence the mechanical properties of the composites, e.g., the chemical compositions, curing environment, and curing time, were also studied. The various curing environments (pure water, 0.1N HCl, 0.1N NaOH, and methanol) decreased the compressive strength of PAA—metal oxide. Moreover, the thermal stability and compressive strength of PAA–ZnO and PAA–CuO reached an optimum because of their crosslinking nature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2021–2027, 1997

Influence of bond interchange reactions on mechanical behavior of solid poly(ethylene terephthalate)

Reported are a pair of studies exploring the possible role of transesterification during the deformation of poly(ethylene terephthalate) (PET) near its glass transition temperature. SANS experiments on PET-D/PET-H blends were carried out on films drawn according to the method of Petermann and Gohil at 70 and 90°C. In order to avoid effects of orientation on the SANS pattern, the measurements were made on liquid solutions made from the drawn material. The results show a decrease in the D-sequence length upon deformation, while the molecular weight of the chain is unchanged. This result indicates that bond exchange has taken place. Based upon the SANS results, an approximate activation energy in the 8-24 kcal/mol range is reported for bond interchange. To test the hypothesis that transesterification may play a role in the mechanical behavior of PET near T g , creep measurements were carried out over a temperature range on either side of T g . Activation energies obtained from time-temperature superposition shift factors showed a dual behavior: above T g the activation energy matches those for diffusive processes in PET ; below T g the activation energy coincides with activation energies reported for exchange reactions in this material. The role of annealing prior to deformation is also reported, and it is shown that the activation energy increases rapidly with increasing annealing temperature.

Mechanisms of plastic deformation in poly(diethylene glycol bis(allyl carbonate))

The plastic deformation of a highly crosslinked glassy polymer, poly(diethylene glycol bis(allyl carbonate)) (ADC resin) at different temperatures was investigated. It is found that both compressive yield stress σ y and Young's modulus E decrease as temperature is increased. The relationship between σ y and E has been analysed using Argon's and Bowden's theories of plastic deformation in glassy polymers. Molecular parameters derived from each theory have been discussed in terms of the chemical structure of the resin.

Bending of ionic polymer gel caused by swelling under sinusoidally varying electric fields

AbstractDeformation of poly(vinyl alcohol)–poly(sodium acrylate) composite hydrogel (PVA–PAA gel) under sinusoidally varying electric fields was studied in electrolyte solutions. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixed solution of PVA and polyacrylic acid. A cyclic bending–straightening motion of the PVA–PAA gel rods of about 1 mm in diameter have been observed in Na2CO3 aqueous solutions under the fields. The PVA–PAA gel had a response time of less than several hundreds milliseconds. The bending has also been observed in organic solvents containing an electrolyte when the organic solvent is electrolyzed. It was found that the motion of the gel under electric fields of less than 1 Hz occurred mainly through swelling due to the change of the osmotic pressure based upon the difference of the ion concentration. However, it has not been determined whether the motion at higher frequencies is caused by the osmotic effect. © 1993 John Wiley & Sons, Inc.

Experiments on polymer gels: Swelling and deformation of poly(vinyl acetate) networks in equilibrium with a θ-diluent

Deswelling of chemically cross-linked poly (vinyl acetate) gels swollen by isopropyl alcohol at the θ-temperature (T=52°C) was induced by two independent methods: (1) the activity of the diluent around the stress-free gels was lowered by dissolving a polymer in the equilibrium liquid phase and (2) gels equilibrated with pure diluent were subjected to unidirectional compressive stress. In addition, shear modulus measurements were performed on the gels at different stages of deswelling.The results are described by relationships derived between the swelling pressure, shear modulus, deformation ratio and polymer concentration. The concentration dependence of the shear moduli of poly (vinyl acetate) gel homologues in the fully swollen state exhibits a power-law exponent 2.96, which is close to the theoretical value of 3. It is shown that for gels subjected to unidirectional compressive stress, the difference in chemical potential between the pure diluent and the diluent in the deswollen gel, Δμ1, is given by the equation Δμ1=G(φ) (1 — Λ−89e), where G(φ) is the shear modulus and Λe is the deformation ratio relative to the length of the freely swollen undeformed sample.

Deformation of poly(ethylene terephthalate) films of various thickness in liquid adsorption-active media

The effect of initial thickness of PETP films on the process of their deformation in liquid adsorption-active media was investigated by the methods of liquid permeation under a pressure gradient, dynamometry and electron microscopy. It was found that the geometry of the initial sample substantially affects both the process of initiation and growth of crazes, and the process of their immediate coagulation in a liquid under strain.