Behavior Of Polymethyl Methacrylate Research Articles

Investigation on brittle-ductile transition of PMMA mode-II fracture using time-temperature superposition principle

The rate-temperature dependent brittle-ductile transition (BDT) behavior of PMMA (polymethyl methacrylate) mode-II fracture was investigated through tensile-loading shear fracture (TLSF) tests. The dimensionless ratio KJC/KIIC was chosen as the index to identify the brittle/ductile state. Assuming the fracture property to be viscosity-dominated, the time-temperature superposition principle based on the Arrhenius equation was adopted. The master curves of KJC/KIIC in a wide range of loading rate and temperature were constructed with the experimental data obtained under limited test conditions. With the derived critical BDT band from the master curve, the BDT state of PMMA’s fracture under complex loading conditions was successfully predicted and experimentally validated. The results are helpful to describe the BDT behavior and provide an equivalent approach to investigate the mode-II fracture which can substantially save the experimental cost and time.

γ-ray effects on PMMA polymeric sheets doped with CdO nano particles

The present work aimed to study the γ-ray irradiation effects on the physical and chemical behavior of poly methyl methacrylate (PMMA) thin polymeric sheets doped with different concentrations of nano CdO (0.3–1.8 wt. %). Co-precipitation technique was used to prepare CdO nanopowder, while casting-solution method was applied to prepare thin sheets of PMMA/CdO. The XRD analysis of CdO, PMMA and their composites confirmed their formation in pure phase. The particle size distribution of the CdO powder was estimated using TEM imaging and found to be 3–20 nm. According to optical microscopy investigation, good homogeneous distribution was obtained for the CdO powder inside the PMMA sheets. Different sets of the prepared samples were irradiated by γ-ray of 60Co source with gradually increasing doses (20–120 kGy). The irradiated samples were analyzed using XRD, FTIR and UV/Vis spectroscopy. Comparative study was done on pristine and irradiated samples at different CdO concentration. The visual appearance of the samples showed chromatic degradation with increasing both CdO concentration and absorbed γ-ray doses. A color map of the irradiated PMMA/CdO samples was presented for monitoring the absorbed dose. The changes in the samples color was attributed to conversion of CdO (reddish brown) to Cd(OH)2 (clear white) as a result of γ-ray irradiation. The unirradiated samples showed slight decrease in their optical band gap with increasing CdO concentration. Furthermore, a linear correlation between the optical band gap and γ-ray dose was deduced for all the irradiated samples. Electrical permittivity and conductivity of pristine and irradiated samples were measured as a function of frequency at room temperature using LCR bridge. A relative increase in the dielectric constant and AC conductivity of the irradiated samples by about 5–25% was observed for the highest CdO concentration. The electrical parameters of the irradiated samples showed significant changes at high γ-ray dose of 120 kGy. The obtained experimental data were discussed in view of γ-ray interaction with the medium using the suitable models and theories of polarization mechanisms. The results are promising for using the prepared samples as γ-ray dosimeters in addition to enhancement of their electrical properties for various applications.

An experimental study of the mechanical and fracturing behavior in PMMA specimen containing multiple 3D embedded flaws under uniaxial compression

This paper studies the mechanical and fracture behavior of poly methyl methacrylate (PMMA) specimens containing multiple embedded flaws, under uniaxial compression. The initiation, propagation, coalescence of cracks, and failure of specimens are captured by a high-speed digital video camera system. Six types of cracks and three modes of crack coalescence are captured in the PMMA specimens. The experimental observations show that the effects of the flaw angle on crack propagation and coalescence are stronger than the non-overlapping length. Furthermore, the peak strength and crack initiation stress show regular change with increasing in the flaw angle and the non-overlapping length.

Glass transition temperature of PMMA/modified alumina nanocomposite: molecular dynamic study

In this study, the effect of alumina and modified alumina nanoparticles in a PMMA/alumina nanocomposite was investigated. To attain this goal, the glass transition behavior of poly methyl methacrylate (PMMA), PMMA/alumina and PMMA/functionalized alumina nanocomposites were investigated by molecular dynamic simulations (MD). All the MD simulations were performed using the Materials Studio 6.0 software package of Accelrys. To obtain the glass transition temperature, the variation of density versus temperature was obtained. The temperature at which the slope of the density-temperature curve observably changes is defined as the glass transition temperature (Tg). The effect of alumina nanoparticles on the Tg was related to the free volume and the mobility of chain segments and the interaction between the alumina nanoparticles and the polymer. The mobility of the chain segments was investigated based on the mean square displacement and radius gyration. The results show that the incensement the Tg of the PMMA/functionalized alumina nanocomposite is more than that of the PMMA/alumina nanocomposite due to the modification of the alumina nanoparticles.

Experimental study of polymethyl methacrylate: damage under corona discharge

In high-voltage applications, insulators may be exposed to corona discharges during long periods. In this experimental work, corona discharge tests of different durations are carried out in air at atmospheric pressure on polymethyl methacrylate (PMMA) samples. The resulting surface degradation is studied with several techniques. The surface damages are observed with environmental scanning electron microscope and atomic force microscopy. The results show that electrical trees occur on the surface of material and their distribution depends on the corona discharge duration. The chemical changes on PMMA surface are analyzed by Fourier transform infrared spectroscopy and a chemical degradation mechanism is proposed. Evolution of surface resistivity with corona aging is also implemented by using a classical I(V) method. In addition, to study the dielectric behavior of PMMA, the monitoring of kinetics of the trapped charge under electron irradiation in a scanning electron microscope is performed. The charging ability of PMMA under electron irradiation and its time constant of charging decrease with electrical aging.

Influence of Titanium Oxide Nanoparticles on the Physical and Thermomechanical Behavior of Poly Methyl Methacrylate (PMMA): A Denture Base Resin

Influence of Titanium Oxide Nanoparticles on the Physical and Thermomechanical Behavior of Poly Methyl Methacrylate (PMMA): A Denture Base Resin

The response of polymethyl methacrylate (PMMA) subjected to large strains, high strain rates, high pressures, a range in temperatures, and variations in the intermediate principal stress

This article presents the response of polymethyl methacrylate (PMMA) subjected to large strains, high strain rates, high pressures, a range in temperatures, and variations in the intermediate principal stress. Laboratory data from the literature, and new test data provided here, are used in the evaluation. The new data include uniaxial stress compression tests (at various strain rates and temperatures) and uniaxial stress tension tests (at low strain rates and ambient temperatures). The compression tests include experiments at e = 13,000 s−1, significantly extending the range of known strain rate data. The observed behavior of PMMA includes the following: it is brittle in compression at high rates, and brittle in tension at all rates; strength is dependent on the pressure, strain, strain rate, temperature, and the intermediate principal stress; the shear modulus increases as the pressure increases; and it is highly compressible. Also presented are novel, high velocity impact tests (using high-speed imaging) that provide insight into the initiation and evolution of damage. Lastly, computational constitutive models for pressure, strength, and failure are presented that provide responses that are in good agreement with the laboratory data. The models are used to compute several ballistic impact events for which experimental data are available.

A fluorescence study for the critical behavior of polymethylmethacrylate doped by multiwalled carbon nanotube (PMMA–MWNT) composite bulk gel systems

Polymethylmethacrylate (PMMA) doped by multiwalled carbon nanotube (MWNT) bulk gels were prepared with different amounts of MWNTs varying in the range between 1 and 20 wt%. Free-radical cross-linking copolymerization of PMMA–MWNT composite bulk gels was characterized by the steady-state fluorescence technique. Ethylene glycol dimethacrylate (EGDM) and pyrene (P y ) were introduced as cross linker and fluorescence probe, respectively. Changes in the viscosity of the pregel solutions due to glass formation dramatically increased the P y fluorescent intensities, which were used to study the glass transition of PMMA–MWNT composite gels for various MWNT contents. The fluorescence intensity of P y is proportional to the average size of the glassy regions below and to the strength of the infinite network above the glass transition point. Observations around the glass transition point show that there are three regimes for MWNT concentration in which the gel fraction exponent, β, and the weight average degree of polymerization exponent, γ, differ drastically from percolation results, given in three dimensions as β=0.41 and γ=1.80.

An Experimental Study of Tissue Reaction to Hyaluronic Acid (Restylane) and Polymethylmethacrylate (Metacrill) in the Mouse

The aging skin is a challenge for medical science. Plastic surgeons and dermatologists are called every day to solve problems like filling wrinkles or folds. The material used must be biocompatible because abnormal reactions may cause catastrophic results. This study analyzes the biological behavior of polymethylmethacrylate (Metacrill) and hyaluronic acid (Restylane), using a histopathologic study in mice. A prospective study was performed using 40 mice for each substance: polymethylmethacrylate or hyaluronic acid was injected into the right ear, the left ear been used as a control. Histopathologic analyses of the right ear, liver, and kidney were performed at intervals during the study and revealed the development of a granulomatous reaction with fibrosis and absorption of spheres and signs of liver and kidney sistematization for polymethylmethacrylate. A discrete cellular reaction, with less formation of fibrosis, and no giant cells were seen in the mice injected with hyaluronic acid.

Biomechanical In Vitro Testing of Human Osteoporotic Lumbar Vertebrae Following Prophylactic Kyphoplasty With Different Candidate Materials

Biomechanical study of human osteoporotic lumbar vertebrae following prophylactic kyphoplasty. To evaluate the potential benefits of different resorbable candidate materials for use in prophylactic kyphoplasty compared with the behavior of polymethylmethacrylate cement. Kyphoplasty using PMMA bone cement for the stabilization of fractured osteoporotic vertebrae has been established as a useful clinical tool. In several studies, consecutive compression fractures have been reported in vertebrae caudal or cranial to those augmented with bone cement. Consequently, some physicians have begun to treat adjacent vertebrae by means of prophylactic augmentation. Biomechanical in vitro testing was performed on 40 human osteoporotic nonfractured lumbar vertebrae. Three types of bone cement (PMMA, 2 different calcium phosphate cements) and one silicon derivative were assessed during compressive and cyclic sinusoidal testing. Each candidate material was applied bipedicularly under fluoroscopic control. Differing processing qualities of the materials led to substantial differences during cement injection, in particular in the amount of cement filling of the vertebrae. However, in comparison to native vertebrae, augmented specimens showed significantly higher compressive failure. No significant differences between vertebral bodies treated with PMMA and those treated with either type of calcium phosphate cement were documented. The biomechanical properties of the vertebrae could not be significantly improved by the silicon derivative. This study demonstrated that calcium phosphate cements displayed identical behavior to PMMA cement with respect to in vitro mechanical qualities. Consequently, from a mechanical viewpoint, calcium phosphate cements may be used in addition to PMMA cement for kyphoplasty and prophylactic kyphoplasty. Silicon derivatives are apparently not recommendable as candidate materials for kyphoplasty.

Creep behavior of poly(methyl methacrylate) with growing damage

A simple optical technique is used to quantify creep crazing damage in a uniaxially stressed transparent glassy polymeric sheet of polymethyl methacrylate (PMMA) at room temperature. The areal craze densities are taken as a measure of the crazing damage. It is shown that the crazing damage increases with nominal applied stress and creep time. The crazing initiation time and the crazing damage evolution equation for PMMA is modeled from a mechanical viewpoint and the results are used to predict the nonlinear creep behavior of PMMA with growing damage. The predictions are in good agreement with the test results.

Dielectric, Thermally Stimulated Discharge Current, Pyroelectric and Surface Morphology of Pmma Thin Films Prepared by Isothermal Immersion

Metal–Insulator–Metal structure was used to investigate the dielectric, thermally stimulated discharge current(TSDC)and pyroelectric behavior of poly methyl methacrylate(PMMA)thin films prepared by isothermal immersion method. The surface morphology and the structure of the above said films were studied by using atomic force microscopy(AFM)and X-ray diffraction(XRD)respectively. The XRD spectrum of as grown and films annealed at 513 K indicated the amorphous nature. No pits and dendritic features were observed from the AFM spectrum. The only important topographic features observed is the hillocks of about 10–12 nm large with a peak to valley vertical distance of about 0.5–1 nm. Both as grown and films annealed at 513 K showed very smooth surface and amorphous nature. From the TSDC spectrum activation energy(E), capture cross-section(σ), escape frequency(ν)and relaxation time(τ)were calculated. The observed amorphous phase, low loss, dielectric and thermal behavior imply the feasibility of utilizing PMMA thin films as gate dielectric insulator layer in organic thin film transistors(OTFTs), which can find application in flat panel display.

28. The behavior of polymethylmethacrylate during kyphoplasty and vertebroplasty in the primate spine—a gross and histologic analysis

28. The behavior of polymethylmethacrylate during kyphoplasty and vertebroplasty in the primate spine—a gross and histologic analysis

Structural and Mechanical Behavior of Polymethylmethacrylate Containing Diethyl Siloxane Oligomer

Using the method of positron annihilation, structural changes induced by introduction of diethyl siloxane oligomers to PMMA were studied. The effect of these structural changes on the mechanical behavior of PMMA was discussed in terms of structural inhomogeneity of PMMA: existence of structural sublevels with different packing density and ordering. Deformation of glassy polymers at low strains as well as such mechanical characteristics as yield stress and contribution of low-temperature component to the temperature-induced relaxation of plastic deformation were shown to be controlled by segmental mobility in structural sublevels with a lower packing density.

The Role of Dilatation in the Nonlinearly Viscoelastic Behavior of PMMA under Multiaxial Stress States

In order to better understand phenomena related to “yield-like” behavior of polymers, the nonlinear thermo-mechanical behavior of Polymethyl Methacrylate (PMMA) under combined axial (tension, compression) and shear stress states (torsion) is investigated on thin walled cylindrical specimens at temperatures between 22 and 110°C. In contrast to the mutual independence of shear and dilatational response under conditions appropriate for linearized viscoelasticity, one observes an increasingly strong influence of the first stress or strain invariant on shear creep at shear strains in excess of 0.5%. While shear stresses alone elicit nonlinear response in creep (rates) as “intrinsically nonlinear shear response”, the superposition of small positive dilatation accelerates shear deformations while negative dilatation retards it in qualitative agreement with free volume arguments when comparison is effected via maximum shear. In addition, an isochronal representation of the “intrinsically nonlinear shear response” demonstrates that the nonlinear behavior becomes more pronounced the closer one approaches the glass transition temperature from below.

Rain erosion behaviour of polymethylmethacrylate

Mass loss, optical transmittance and the microscopic erosion sequence have been monitored for polymethylmethacrylate exposed to a 2.54 cm h−1 rainfall of 1.8 mm diameter water drops at an impact velocity of 222 m sec−1. Initial drop impacts produced well-defined fracture patterns consisting of a circular area free of damage surrounded by an annulus containing a dense array of fine, short cracks together with a sparse distribution of deeper fractures initiated along surface scratches. Continued exposure to the rainfield produced crack grown and crack intersections at sites of fracture annuli overlap followed by crevice growth as these fracture systems were enlarged by a hydraulic penetration mechanism. An extensive network of subsurface fractures continued to be produced within the expanding cavities with longer exposures. The transient stress distributions generated during a water drop impact on polymethylmethacrylate are considered in terms of their potential for producing circumferential fractures.

The strain-rate behavior of ductile polymers

The stress-strain-strain-rate behavior of polycarbonate is presented. It is demonstrated that the material does not exhibit a double-yield-point phenomenon, as others have reported, if true stress is plotted against actual strain. Also, the behavior of polycarbonate is presented under constant strain rate and relaxation conditions. The observed behavior of the material is discussed in relation to elements of recent theories of viscoelasto-plasticity due to Nagdi and Murch and Crochet. Simple mechanical models of the Bingham type are presented and are discussed with respect to the constitutive equation characterization of polycarbonte. The advantages and disadvantages of more general models are mentioned. Finally, the strain-rate behavior of PMMA (Polymethylmethacrylate) and a poylester given by others is presented and discussed, relative to polycarbonate and the characterization procedures used.

The dynamic mechanical behavior of polymethyl methacrylate

In order to investigate the short time response of solid polymers, a high resolution laser interferometer has been employed to observe the detailed structure of stress waves produced by the impact of polymeric plates. From the observed stress waves the loading and unloading stress-strain paths followed by the material can be determined. For the polymer, polymethyl methacrylate, over the stress range from 0–60 kbar such observations have disclosed a stress-strain behavior which exhibits large strain nonlinearities and significant rate-dependence. For stress levels below ≈7 kbar and above ≈40 kbar, rate-effects are of secondary importance and the observed wave profiles may be modeled using a nonlinear elastic description of the material behavior. However, at about 7 kbar, a transition is observed in the dynamic stress-strain behavior which is characterized by greater stress relaxation and significant hysteresis upon unloading. This transition, which we attribute to a yield phenomenon, requires a rate-dependent description of the material behavior to be used in the stress range of approximately 7–40 kbar.

Dynamic behaviour of polymethyl methacrylate between 60 and 300 °K

The resonant frequency and the coefficient of energy dissipation have been measured as a function of temperature in the interval (60÷300) °K for several specimens of polymethyl methacrylate of the plasticized and unplasticized type. The specimens have the shape of circular plates, and the measurements have been made for flexural vibrations in the frequency range (6÷40) kHz, with a strain amplitude smaller than 10−7. A thermally activated relaxation effect gives rise to a peak in the dissipation-temperature curve. For the above frequency range the temperature of the peak is about 110 °K. At the same temperature a slight inflexion is observed in the frequency-temperature curve, in accordance with the theory of linear dynamic deformations. The relaxation effect, which is probably due to the rearrangement of side chains, is superposed to another cause of energy dissipation which cannot be explained by means of the above theory in its present state, as the corresponding dissipation coefficient increases not only with temperature but also with frequency. The frequency-temperature curve exhibits aknee near 230 °K. This temperature is apparently independent of the vibration frequency, and the knee seems to be due to a second order transition.

Breaksown of methyl methacrylate polymer by high-energy radiation.

THE behaviour of polymethyl methacrylate (‘Perspex’) when exposed to high-energy radiation is markedly different from that of many other longchain polymers such as ‘Polythene’ and polystyrene1. These latter develop cross-links forming a thermosetting material, whereas polymethyl methacrylate shows rapid breakdown after relatively short radiation doses. The nature of the changes produced is complex, and appears to vary with the temperature as well as the radiation dose.