Prediction of the creep behavior of reinforced plastics

The time-dependent deformation of orthotropic and transversely isotropic viscoelastic materials under biaxial constant load is given in the range of linear and reversible stress-strain behavior for isothermal processes. This allows one to calculate the deformation of plastics on the basis of isochronous stress-strain diagrams. In addition, a method is presented which allows a calculation of the creep moduli of mat-reinforced unsaturated polyesters and their dependence on glass content, temperature, and time. This calculation requires only specific creep data of matrix material and the elastic modulus of the reinforcement.     

Prediction of environmental stress cracking of polycarbonate from solubility considerations

Simple thermodynamic relationships as well as semiempirical solubility parameter plotting techniques were examined as methods for predicting critical crazing strains of polycarbonate exposed to linear and branched alkanes. In general, measured critical strains correlated with predicted solubilities based on the Flory–Huggins equation. Solubility parameters could also be used to predict critical strains if molecular size differences between specific alkanes were taken into account. These techniques were then extended to polar and hydrogen bonding liquids using two-dimensional solubility parameter plotting representations. A comprehensive listing of critical strains for polycarbonate exposed to over 80 liquids and liquid mixtures is included.     

Prediction of mechanical properties of weather-induced degraded plastics in saudi arabia

Empirical equations have been developed to predict the mechanical properties of greenhouse films when exposed to natural weather conditions for long durations. Tensile strength and percent elongation data obtained for the Dhahran site was used to develop empirical equations. Prediction models were developed with exposure time as independent parameter for both tensile strength and percent elongation, which were taken as dependent parameter. The mean deviations for tensile strength and percent elongation were found to be 2.5 and 1.2%, respectively. Weather data of Dhahran for the period of natural exposure is also presented. © 1995 John Wiley & Sons, Inc.     

Prediction of mechanical properties of polymers. Tensile strength of glass-reinforced plastics

Tensile strength data at high and low rates of loading were obtained for a glass-reinforced polyester and a glass-reinforced epoxy. Analysis of the data by a rate method indicated that such a method may be used to predict behavior of polymers from limited test data.     

Prediction of combined effects of fibers and cement on the mechanical properties of sand using particle swarm optimization algorithm

In this research, a series of laboratory tests have been performed to investigate the effects of cement and polyvinyl alcohol (PVA) fiber on the performance of sand. Unconfined compression strength and compaction are also assessed in the present study. The cement contents were 0.5, 1, 2, 4, and 6% by weight of the dry sand. Fiber length and diameter were 12 and 0.1 mm, respectively, and were added at 0.0, 0.3, 0.6, and 1% by weight of dry sand. Finally, the obtained results from the experimental data with particle swarm optimization algorithm are used to generate a polynomial model for prediction unconfined compression strength, modulus of elasticity, and axial strain at peak strength. The results of the study indicate that the inclusion of PVA fiber increases the unconfined compressive strength and the peak axial strain. The elastic modulus of specimen decreased with increase in fibers. Maximum dry density of the sand–cement–fiber mixture increases with the increase in cement content and decreases with the increase in fiber content.     

Prediction and evaluation of the susceptibilities of glassy thermoplastics to environmental stress cracking

Glassy, amorphous thermoplastics experience a nearly universal susceptibility to crack and craze formation in the combined presence of stress and a chemical environment. This susceptibility has been evaluated for styrene-acrylonitrile copolymers according to the factors which effect craze initiation and those which limit the rates of flaw propagation. Molecular weight, styrene-acrylonitrile ratio, rubber content, and rubber phase morphology are variables which were found to affect flaw initiation and propagation. Fundamental characterization of the chemical parameters which control the initiation of craze formation in polysulfone and polycarbonate is also presented. In particular, “3-dimensional” solubility parameters have been observed to be a reasonable means of characterizing susceptibility to environmental stress cracking.     

Thermal and mechanical properties of plastics molded from urea-modified soy protein isolates

Soy protein has been considered as a potential alternative of some petroleum polymers in the manufacture of plastics. The purpose of this investigation was to characterize the thermal and mechanical properties of plastics made from urea-modified soy protein. Soy protein isolate was separated from the defatted soy flour, modified with various urea concentrations, and compression-molded into plastics. Differential scanning calorimetry showed that the temperatures of denaturation and the enthalpies of denaturation of the modified soy protein decreased as urea concentrations increased above 1 M. At the same urea concentration, molded plastics made from the modified soy proteins showed a similar temperature of denaturation as the modified soy protein, but a lower enthalpy of denaturation. Tensile strength and Young's modulus of the molded plastics from the modified soy proteins increased as urea concentration increased and reached their maximum values at 8 M urea modification. Both storage modulus and glass transition temperature of the plastics from the modified soy proteins increased as urea concentration increased. The plastics made from the 2 M urea-modified soy proteins showed improvements in elongation, tough fracture behavior, and water resistance. The urea may function as a denaturant, a plasticizer, and a filler.     

The incapacitative effects of exposure to the thermal decomposition products of polyurethane foams

The mechanisms of incapacitation resulting from exposures to the thermal decomposition products of flexible and rigid polyurethane foams (PUF) were studied over a range of different temperatures under pyrolytic or non-flaming oxidative decomposition conditions. Individual cynomolgus monkeys were exposed to atmospheres increasing in separate experiments from very low concentrations until early physiological signs of incapacitation were detected. When flexible PUF was pyrolysed at 900°C and rigid PUF was oxidized at 600°C, clear atmospheres containing CO and HCN were produced and the signs of toxicity were very similar to those produced by HCN gas alone, consisting of an episode of hyperventilation followed by a semi-conscious state. Pyrolysis of flexible PUF at 600°C and 300°C produced a dense yellow smoke but no HCN. The signs, consisting of hyperventilation throughout exposure and dyspnoea afterwards, were consistent with pulmonary irritation, Since TDI monmer is not present at 600⁰ C it is concluded that some as-yet unidentified but highly irritant chemical species is present in smoke from flexible PUF.     

The sward number and mechanical properties of plastics

A Sward rocker tester is used to obtain the Sward number for glass, mild steel, copper, poly(methyl methacrylate), polyethylene of various densities, and natural rubber. A relationship between the number and mechnical properties is investigated. It is shown that with metals and glass the number is essentially a frictional factor. With plastics and rubber it is a true hardness factor, involving dynamic Young's modulus, Poisson's ratio, and damping capacity. The aim of the investigation is to encourage the development of the Sward test as a nondestructive quality test for plastics.     

Prediction of environmental stress cracking resistance in linear low density polyethylenes

Recently it has been shown that the strain hardening modulus (G_p) at 80°C can be used to predict the environmental stress cracking (ESC) resistance of polyethylenes. The advantage of using strain hardening to determine ESC resistance is that the data may be obtained relatively easily and quickly using simple tensile test equipment. In this article, the strain hardening modulus has been used to predict the ESC resistance of three grades of linear low‐density polyethylene. Unlike in the previous research, the measurements were conducted at room temperature enabling tests to be performed without the need of a temperature‐controlled oven. This was achieved by reducing the strain rate to increase the sensitivity of the technique and increasing the thickness of the specimens to improve the repeatability. The strain hardening modulus data were found to correlate well with the ESC results obtained from long‐term full notch creep tests and are consistent with the known molecular structure of the polyethylene grades. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

Coupling effects of spinodal decomposition and crystallization on mechanical properties of polyolefin blends

The influences of preferentially occurred liquid-liquid phase separation (LLPS) and following crystallization processes on the mechanical properties of statistical copolymer blends of poly(ethylene-co-hexene) (PEH) and poly(ethylene-co-butene) (PEB) have been investigated in detail through tensile deformation tests with a relatively high extension rate to avoid the effect of interfacial properties of the blends. Crystallinity and lamellar thickness of the samples are estimated by using the wide-angle X-ray diffraction and small-angle X-ray scattering techniques, respectively. The tensile modulus and yield stress are found to increase with LLPS time up to 6 h, but decrease afterwards, under the conditions of temperature of 120 °C and isothermal crystallization time of 10 min. It is considered that the instantaneous tensile properties are substantially largely affected by the much perfect lamellar structures formed during crystallization with a long time prior LLPS step. This finding is further experimentally substantiated by the scanning electron microscope observation. Whereas the strain-hardening modulus described by a simple neo-Hookean relation increases with LLPS time and reaches a plateau after 6 h, which can be accounted for by the cooperation effect between amorphous entanglement density, insensitive to LLPS time, and crystallinity redistribution. The similarity of the results observed on the blends experiencing the spinodal decomposition (SD) process supports that the redistribution of crystallizable components contributes to the tensile stress increase, which is primarily controlled by the development of LLPS process. This simple relationship gives us a new insight of what controls the mechanical properties of the phase separated polymer blends and of how we might be able to predict the mechanical properties of as yet unmixed polymer pairs.     

Thermal decomposition behavior and mechanical properties of elastomeric composites based on polyolefinic thermoplastic elastomer and organomontmorillonite

The elastomeric composites based on organomontmorillonite (OMMT) and Santoprene thermoplastic elastomer were prepared by melt processing. Maleic anhydride grafted polypropylene (PP-g-MA) was used as a compatibilizer for the composite system. By adding optimum content of PP-g-MA, the fracture surface of the composites observed by SEM was smoothened as a result from compatibilizing effect. From XRD results, the measured d-spacing data proved a good dispersion of nanoclay along with compatibilizer. Thermal decomposition behavior of the neat components and its composites obtained from simultaneous TG and DSC profiles indicated that the incorporation of OMMT into the matrix polymer improved the thermal stability in air but not in nitrogen. No significant change in thermal stability of the composites with addition of PP-g-MA. The incorporation of clay significantly enhanced in dynamic mechanical and tensile properties of the composites. The dynamic storage modulus, tensile modulus and yield stress of the composites with the presence of PP-g-MA were remarkably improved.     

The effects of residual stress on the mechanical properties of glassy polymers

Residual stresses can have either beneficial or detrimental effects on the mechanical properties of plastics. Manufacturing processes frequently impose residual stresses on plastics. In this study, controlled thermal processes were used to impose surface compressive stresses on polycarbonate beam samples (6.4 by 12.5 by 80 mm). Resistance strain gage and photoelastic techniques were developed to measure the magnitude of these stored stresses. The compressive surface stresses were found to be between 14 MPa (2000 psi) and 31 MPa (4500 psi) and to vary with process method and cooling rate. The mean fatigue life (in bending) of the treated beam samples was found to improve by a factor of 10 over that of untreated samples. The increase in the fatigue life of the treated samples appears to be directly related to the magnitude of the surface compressive residual stress in the samples. The imposed residual stress, as determined by photoelastic measurements, has not appreciably relaxed after 1 year of storage at room temperature.     

Dynamic mechanical response of adhesively bonded beams: Effect of environmental exposure and interfacial zone properties

The dynamic mechanical response of adhesively bonded metal beams has been examined over a broad temperature range using a dynamic mechanical thermal analyzer (DMTA). The measured dynamic mechanical response of the bonded beam contains rich information about the viscoelastic properties of the adhesive resin such as glass transition temperatures. The measured storage moduli and loss factors of the bonded beams are very sensitive to changes in the properties of adhesive induced by exposing the beam specimens to environmental attack. Dynamic mechanical responses associated with dry adhesive resin, water plasticized resin, and aggregated water were observed for an electro-galvanized steel/epoxy beam exposed to water. The effect of the presence of an interfacial accommodation zone (IAZ) between adhesive resin and metal substrate was also examined; measured properties were very sensitive to the presence of a low modulus IAZ. It was successfully demonstrated in this study that the DMTA testing of bonded beams is a potentially useful tool for studying dynamic performance and durability of automotive adhesive joints.     

Relation between impact strength and dynamic mechanical properties of plastics

A simple theory is developed which correlates the Izod impact strength of polymers with (G′₁₀₀-G′₃₀₀)²/G′₁₀₀, where G′₁₀₀ and G′₃₀₀ are dynamic shear moduli at 100°K. and 300°K., respectively. The theory assumes the Maxwell element for the material and the fracture time smaller than the relaxation time. The theory is verified by experimental data for numerous polymers. Another approach which correlates the impact strength with the integrated loss factor from 0 to 300°K. is also proved valid.     

硫对环境介质中重金属环境行为的影响研究进展

主要介绍了水体沉积物中硫与重金属的赋存形态,阐述了沉积物中硫与重金属之间迁移转化的耦合关系,综述了沉积物/土壤重金属潜在风险评价方法,以及硫在重金属污染治理方面的应用。     

The stress relaxation behavior and mechanical properties of polypropylene and polypropylene/CaCO3 in mechanical vibration injection molding

The influence of vibration pressure and frequency on the mechanical properties and stress‐relaxation was investigated via stress‐relaxation test and tensile test. First, it had been observed in the tensile test that the tensile fracture elongation reached the maximum at 20 Hz for polypropylene (PP) and 15 Hz for polypropylene/calcium carbonate (PP/CaCO₃), respectively. With the increasing vibration pressure, the tensile fracture elongation would decrease. Second, the dynamic mechanic analysis has been used to test loss angle tangent value of the material. After the dynamic mechanic analysis, the simples have been installed in the universal tensile testing machine which applies the 2% strain on the simples. From these experiments, it has been discovered that the trend of the changes of stress‐relaxation is similar with the trend of the changes of loss angle tangent value. When the vibration frequency reaches the 20 Hz for PP and 15 Hz for PP/CaCO₃, the stress‐relaxation is larger than that of other materials prepared at the same pressure (10 Mpa); meanwhile, the stress‐relaxation of these materials, which has been prepared at the same frequency (10 Hz), decreases with the increasing vibration pressure. According to above tests, it is also very useful to improve the stress relaxation properties via changing the condition of the vibration field. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

The effect of environmental exposure upon the mechanical properties of coir or oil palm fiber reinforced composites

Polyester matrix composites reinforced using nonwoven coir or oil palm empty fruit bunch fiber mats were manufactured. Fibers were used unmodified, chemically modified by acetylation, or treated with silane or titanate coupling agents. Composite test pieces were exposed to decay fungi in unsterile soil for up to 12 months, along with samples made of unreinforced, or glass fiber reinforced, resin. Water exposure tests were also performed. The effect of such exposure on the mass loss, tensile and flexural properties of the samples was evaluated. Mechanical properties deteriorated as a result of exposure. However, acetylation of fibers, or treatment with silane coupling agent was found to afford a significant degree of protection. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1322–1330, 2000     

Fatigue behavior and modeling of thermoplastics including temperature and mean stress effects

An experimental investigation was conducted to evaluate fatigue behaviors of two thermoplastics. The effects considered include mold flow direction, thickness, mean stress, temperature, and frequency. Tension‐compression as well as tension?tension load‐controlled fatigue tests were performed at room temperature, ?40°C and 85°C. Incremental step cyclic deformation tests were also performed to generate cyclic stress?strain curves to determine strain‐life fatigue properties. The effect of mean stress was modeled using various parameters. The Walker mean stress model and a simple model with a mean stress sensitivity factor proved to be the most effective models to correlate the wide range of experimental data generated. POLYM. ENG. SCI., 54:725–738, 2014. © 2013 Society of Plastics Engineers     

The effect of chemical exposure on the EMI shielding of conductive plastics

The electrical properties of a number of filled plastics were examined after subjecting the materials to exposure to isopropyl alcohol, a 25°C detergent/water solution, an 80°C detergent/water solution, and at various chemical plant sites. Compositions which contained metal fillers maintained their conductivity only when a high temperature thermally stable polymer was used as the polymer matrix, while compositions which are made conductive through a carbon filler network maintained their conductivity under most of the exposure conditions examined even when low temperature polymers were used as matrices.