The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
Chemical degradation is one of the dominant mechanisms of aging in polymers. To prevent a premature catastrophic failure of polymers in durable applications, an understanding of the causes and kinetics of chemical degradation are required. UV accelerated oxidation has been applied in this work to study the effect of oxidative degradation on physical and mechanical properties, such as crystallinity, density, toughness and deformability of unpigmented, unstablelized Poly (ethylene-co-carbon monoxide), ECO, and Poly (1-butene), PB. The correlations between the variation of physical, mechanical properties, and reduction of molecular weight are reported. The effect of oxidative degradation on fatigue crack growth rate and build-up of residual stresses due to densification is also addressed.
To characterize the notch sensitivity for short-term (e.g. notch sensitivity under dynamic impact conditions, sensitivity to failure under rapid crack propagation conditions) and long-term (e.g. slow crack growth resistance, pipe lifetime under creep conditions) strength of thermoplastics, the ratio of the energy-to-break in tensile impact test for notched and unnotched specimens (short term notch sensitivity factor) and the similar ratio for the time-to-failure in tension creep test (long term notch sensitivity factor) are introduced. The limits of these ratios as the notch length approaches zero are called the notch sensitivity factors. The test procedure is developed and applied to determine the factors for one pipe grade polyethylene (PE) and one pipe grade polybutylene (PB). The results indicate that both materials show short term notch sensitivity, and that PB shows very high long term notch sensitivity in contrast to PE.
A comparative analysis of polyethylene (PE) and polybutylene (PB) tensile behavior at various temperatures is reported. It is noted that PB exhibits different tensile behavior below and above 70 °C (transition temperature). This is in contrast with PE that does not change its tensile behavior over the entire temperature range considered. PB also exhibits different crack growth mechanisms at 110 °C (above the transition temperature) than that at 50 and 23 °C (below the transition temperature). The fatigue lifetime for PB at 110 °C is observed to be more than ten times the fatigue lifetime at 23 °C. Thus the commonly accepted opinion that temperature is always an accelerating factor of fracture process is not applicable for PB within the above range of temperatures. It is suggested that the observed anomaly in temperature acceleration of fracture in PB is related to the reported transition of tensile behavior around 70 °C
It has long been known that polymers have a structural order intermediate between that of insulators and that of amorphous materials. We show how this intermediate type of order leads to anomalous charge conduction properties for insulating, semiconducting, and metallic polymers. Concepts such as fractal dimensionality and mesoscopic order are introduced and their unusual predictions for variation of conductivity and dielectric constant with temperature and frequency are presented. A comparison with experimental results for undoped and doped polymers is presented.
A comprehensive analysis of the heat exchanges between an instrumented Aluminum mold and various thermoforming materials were made during controlled heavy gauge production trials. Five materials Impact Polystyrene, High Density Polyethylene, PETG, ABS and Impact Polypropylene Copolymer were evaluated. Heat flux was calculated. Experimental variables were quiescent and circulated ambient air, mold and coolant temperatures.
This study demonstrated that a variety of fluoro-containing polyimides with hydroxyl groups, simply incorporated with a copolymerization of 2,2'-bis(3- amino-4-hydroxyphenyl)hexafluoropropane (BAHHF), 2,2'-bis(4-aminophenyl)hexafluoropropane (BAHF), and 2,2'-bis(1,3-dioxo-1H,3H-isobenzofuran-5-yl)hexa-fluoropropane (BIFHF), were responsible for the good solubility in organic polar solvents. These polyimides exhibited optically transparent at a wavelength of 365nm with respect to the UV-visible spectroscopic determination. Measurement of differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) indicated that these polymers, having the glass transition temperatures (Tgs) varied from 306°C to 317°C, were quite thermally stable. In addition, the inherent viscosity as well as refractive index of the polymers was studied and potential applications of photoresists in terms of photosensitivity were also discussed.
Most nanocomposite materials are initially prepared by modifying the hydrophilic clay or hydrophobic clay. Related investigations emphasize the compatibility between clay and polymer, but overlook the factor of the monomer diffusing into the interlayer to proceed with polymerization. This treatment causes most of the polymer/clay nanocomposites being only the intercalated dispersion of clay instead of exfoliated dispersion in the substrate of polymers. Therefore, this study applies the catalyst after a unique polymerization process to make the stratiform inorganic mineral materials disperse proportionally in the polymer materials and form nanocomposites. Doing so significantly enhances the mechanical properties, thermal deformation temperature, and CO2 gas barrier of polymer/clay nanocomposites.
Thermoplastic elastomers are materials that combine the processing characteristics of thermoplastics with the physical properties of conventional thermoset rubbers. The combination has been sufficiently attractive that thermoplastic elastomers have become commercially successful. This success has led to their extension as specialty compounds for applications requiring increased electrical conductivity. In order to achieve desired conductivity, carbon and metal powders are typically employed. To a lesser degree, carbon and metal fibers are also utilized. New thermoplastic elastomer compounds have been recently developed that contain intrinsically conductive polymers. The properties of these novel materials are compared to conductive thermoplastic elastomers with traditional conductive additives.
The volume resistivity threshold for maximum paint transfer efficiency via electrostatically painting was determined to be in the range of 105 to 107 ohm-cm. Thermoplastic compounds have been developed for electrostatic painting which do not meet this threshold (greater than 107 ohm-cm) and still exhibit good transfer efficiencies without a conductive primer. Further, these compounds do not contain metal or carbon-based additives. As a result, they may be pigmented to any desired color. A comparison is made between electrostatically painted carbon based substrates and color-matched substrates. New options are now available for property selection while still retaining the economic benefits of electrostatic painting.
Energy transport in deforming polymeric materials, despite its technological significance, is poorly understood from both experimental and theoretical standpoints. Simple arguments suggest that thermal conductivity is anisotropic in a deformed polymer. In this study we have developed a sensitive and non-invasive optical technique known as Forced Rayleigh Scattering to measure anisotropic thermal diffusivity in both static and dynamic (relaxing) polymers subjected to deformations. Results for a polymer melt in step-shear strain flow and a cross-linked elastomer in uniaxial extension indicate that the thermal diffusivity is enhanced in the flow (or stretch) direction compared to the equilibrium value.
The goal of this study was to determine the degree of degradation during PVC injection molding and to compare the results with a computational model. It was found that a good agreement between experimental and computational results was obtained only if the reaction was assumed to be more thermally sensitive than found in literature. The results from this study show that during injection the activation energy for degradation was 65 kcal/mol, compared to 17-30 kcal/mol found in literature for quiescent systems.
This work reports the results of CAE simulation of thin-wall injection molded part by 3D TIMON. The model used in this simulation was a speaker grille that has thin wall and many tiny openings (net) for sound through them. These openings cause unfavorable weld lines. Effects on weld lines and effects of the number and location of gates were discussed.
Rotational molding is a fast growing process with a constant demand for new materials. As a result of the recent advances in the metallocene single site catalyst systems, a new generation of polyethylenes with unique molecular structure has been developed. The present study compares the rotomolding characteristics of polyethylenes made by metallocene and conventional catalysts.
Recycled high density polyethylene (HDPE) filled with up to 70 wt% rice hulls was compounded and tested for dynamic shear properties on a parallel plate rheometer. A 60 wt% formulation was extruded through two profile dies. Extrudate tearing occurred at all throughputs. The magnitude of the tearing increased with increasing throughput and decreasing land temperature. Observations, 2-dimensional finite element and fully 3- dimensional finite volume simulation suggest the tears are most severe where the wall shear stress is relatively lower.
Although thermoplastic polyolefins (TPOs) have been considered as costwise and environmentally attractive materials, they face the difficulty in being used as potential automotive applications because of poor scratch resistance and oil resistance. The new thermoplastic vulcanizates (TPVs) composed of thermoplastic polyurethane (TPU) / polypropylene (PP) /polystyrene-block-poly(ethylene-co-propylene)- block-polystyrene copolymer (SEPS) systems have been found out to have outstanding oil resistance and scratch resistance. Now they can be used for various kinds of automotive applications such as injection molded, blow molded, extruded, calendered and further, slush molded automotive parts, particularly for automotive interior skins without any coat. The essential issue is conceivably just prolonged weathering resistance and durability. In this paper, this new TPVs are evaluated from the standpoints of weathering stability, long term heat aging and fogging as well as the mechanical and physical properties.
Thermoplastic vulcanizates (TPVs) of polypropylene (PP)/polystyrene-block-poly(ethylene-co-propylene)- block-polystyrene copolymer (SEPS) are able to become much more fascinating for automotive and architecture industry by using polystyrene-polybutylene-polystyrene copolymer (SBS) together. While SBS decreases tensile strength in these systems , it does improve compression set and oil resistance greatly and furthermore, overall balance of properties improve in proportion to the amount of peroxide as coupling agent and acrylic ester as coupling coagent. The goal of this study is to investigate the interaction between SEPS and SBS, which are dynamically crosslinked and microdispersed in PP matrix from the point of mechanical behavior and morphology.
The crystalline texture in selected high-density polyethylene (HDPE) blown films was studied using transmission electron microscopy, small-angle X-ray scattering and infrared dichroism. An orthogonally oriented dual crystalline texture was found. This structure appears to consist of two superimposed uniaxial crystalline textures. In one texture the lamellae are stacked along the machine direction, while in the other, the lamellae are stacked along the transverse direction. The lamellar populations in the two textures are affected greatly by the neck height of the film blowing process. The mechanical properties of the HDPE films can be well correlated with the dual crystalline texture observed.
Local residence time and distributive mixing were measured in conveying sections and kneading blocks of a twin screw extruder. The residence time measurements were completed using carbon black as the tracer and an infrared temperature probe to detect the temperature decrease caused by the changing surface emissivity. A mixing limited interfacial reaction between polymer tracers was used to directly measure the distributive mixing. Possible relationships between mixing and residence time in the sections of the twin screw extruder were investigated by combining these two measurements.
Blends and copolyesters of poly(ethylene terephthalate)/poly(ethylene naphthalate), PET/PEN, have shown promise in high performance container applications. Both rheology and degradation kinetics of these blends have been studied as a function of material composition. Melt viscosity loss was measured as a function of time and temperature. Activation energies for degradation were calculated from experimental data. Results show that blends containing a minimum of 10% PEN by weight are as stable as PEN. Addition of low amounts of PEN to PET causes a depression in melt viscosity. A critical composition of 10% PEN by weight is required before we observe an increase in blend viscosity.
Thickness effect on impact parameters is studied and a model is developed for flat-ended drop weight impact testing of visco-elastic materials. The model represents a relationship of specimen thickness with impact force/stress and impact energy. A polymeric material, ethylene-vinyl-acetate (EVA), was used for experimental verification. Experimental results for a thickness range of 1 to 9 mm at impact energy levels of 0.42, 0.96 and 1.54 Joules have been found to be in good agreement with predictions based on the model.
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Brown, H. L. and Jones, D. H. 2016, May.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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