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.
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Critical items in designs of plastic products are joints. The paper will deal with a number of design aspects about designing reliable plastic products. It will combine the results from our research in the field of stress concentrations, orientation and weld lines around holes, embrittlement of polymers, adhesion and environmental stress corrosion. A number of failures in practice will be presented.
Laura Luna, Yomilka Marcano, Maribel Marrero, Rosestela Perera, May 2004
In this work, the process of recycling high-impact polystyrene, both post-consumer and post-industrial, was studied. Blends of recycled/virgin materials were made and their MFI, mechanical properties and processability (thermoforming) were evaluated. Few differences in the behavior of the materials were found and their use as thermoformed packaging was ascertained.
Industrial designers have problems imagining how their designed plastic products might fail.The paper illustrates how our students are educated about the specific structure related properties that might cause failures.A specific course about designing for reliability of plastic products is outlined. Case studies showing failed products are important.Students must be aware of failure causes like: stress concentrations, low mass and/or mould temperatures, highly stressed weld lines, faulty ribbing and incorrect joining.The course deals also with typical failure mechanisms of plastics like: creep and stress relaxation, stable crack extension, chemical attack and environmental stress - cracking.
Carbon dioxide is widely recognized as an environmental-friendly blowing agent for foam extrusion. However, it is also more difficult to process than other gases because of its low solubility and high diffusivity. In order to improve processing, it might be suitable to use additives. The aim of this work was to study the effect of such additives on the solubility and diffusivity of carbon dioxide in the solid state and to validate their effectiveness in a foam extrusion process.Three “CO2-philic” additives were added to polystyrene and sorption experiments were conducted to measure the solubility and diffusivity at room temperature. Results show that all three additives had a small but measurable effect on gas solubility, which was a consequence of the free volume increase in the polymer blend and in some cases, due to the specific interaction of carbon dioxide with the compounds. Diffusion was also affected depending on the concentration of additive.
J. Yu, Y. Hu, B. Risch, A. Hiltner, E. Baer, May 2004
The effect of an environmental stress cracking agent on slow crack propagation in creep and fatigue of polyethylene resins was studied. At 50°C, fatigue and creep behavior of polyethylene in Igepal solutions followed the same stepwise mechanism as in air. The fatigue to creep correlation was probed by increasing Rratio (defined as the ratio of minimum to maximum stress in the fatigue loading cycle) from 0.1 to 1.0. Unexpectedly, 10% Igepal CO-630 solution, an ASTM standard environmental stress cracking agent, retarded fatigue crack propagation at R-ratio 0.1 but accelerated crack propagation at increasing R-ratios, in comparison with experiments in air. In contrast, fatigue and creep experiments in another longer chain Igepal solution, Igepal CO-997, showed no appreciable effect on crack propagation kinetics at different R-ratio compared to air.
The ratio of a polymer's craze strength to its yield strength is an excellent measure of toughness. It can be used to quantitatively compare materials and to predict how the ductile-brittle transition will change as a function of a variety of environmental and material variables.
C. Daly, D. Leonard, F. Buchanan, J. Orr, N. Dunne, May 2004
The small punch test is a useful technique in the mechanical testing of polymers where limited material is available. This investigation focuses on the latest developments in the small punch test design, including integrated temperature control and environmental conditioning and its use in analysis of polymethyl methacrylate (PMMA) bone cement.
J. Lou, K. Schimmel, A. Shahbazi, V. Harinath, C. Rutkoski, May 2004
Filled biodegradable polymer samples were prepared and exposed to simulated composting environment and the degradation kinetics was characterized. Particularly, the influence of the fillers on the biodegradation kinetics was investigrated.
Yasuo Hashimoto, Tsujii Tetsuya, Kitagawa Kazuo, Machiko Mizoguchi, Yasuhiro Fujita, Hiroyuki Hamada, Umaru S. Ishiaku, May 2004
The heat-sealing machine is a vital tool in plastic bag manufacture. Processing conditions such as heat-sealing temperature and pressure greatly affect mechanical properties of the heat sealed part. In this study, the mechanical properties of the heat sealed part of a biodegradable plastic film were examined. Based on the results obtained from peeling test, circular notch tensile test and DSC measurement, the optimum heat sealing was established at 130-135 °C. The mechanical properties of the heat seals decreased with increasing heat sealing temperature.
M.S. Huda, A.K. Mohanty, M. Misra, L.T. Drzal, E. Schut, May 2004
Green composites were made from poly (lactic acid) (PLA) and cellulose fibers by extrusion followed by injection molding processing and their physico-mechanical properties were evaluated. The properties of PLA reinforced with varying amounts of wood pulp-based cellulose materials were studied. These composites possess superior thermal and mechanical properties based on the strong interaction between the PLA matrix and the cellulose fibers. It was found that the wood pulp-based cellulose fiber could be a good reinforcement candidate for the high performance biodegradable polymer composites.
Kevin G. Cai, Charles G. Reid, Satchit Srinivasan, Norbert Vennemann, May 2004
The elastomeric properties of polyolefin thermoplastic vulcanizates (TPV) have been characterized by compression set, recoverable strain after hysteresis, and thermal scanning stress relaxation (TSSR) analysis. Unlike a thermoset rubber, a TPV is a two-phase system with highly crosslinked fine rubber particles dispersed in a thermoplastic matrix. Compression set, which was originally designed to characterize the elastomeric properties of a thermoset rubber, does not truly characterize the unique elastomeric properties for a TPV. Compression set for a TPV is not only highly dependent on the crosslinking density and structure, but also very sensitive to the orientation of the two phases in the TPV. For the same TPV with a fully crosslinked rubber phase, the compression set value can vary substantially depending on sample preparation and thermal history. Elastomeric properties can be better characterized by the recoverable strain after hysteresis and TSSR stress-temperature curve. The thermal-mechanical properties or stress relaxation behaviors provides more useful information for designing and producing all-thermoplastic parts, such as automotive seals, from TPV.
Bret H. Calhoun, Jeremy Swanson, Graham Behringer, Robert B. Moore, May 2004
Nanocomposites are materials that exhibit a change in composition and structure over a nanometer length scale. In many cases, these systems have shown remarkable property enhancements compared to traditional polymers. Recently, poly (L-lactide) (PLLA) has received considerable attention because of its “green” nature. However, the end-use properties of this biodegradable polymer typically fall short of typical petroleum based polymers. Therefore, PLLA/montmorrilonite nanocomposites have been prepared via solution blending in an attempt to enhance the properties of PLLA.
S. Chung, J. Couch, J.D. Kim, K. Oliphant, P. Vibien, May 2004
Environmental factors are known to significantly impact the oxidative failure mechanism of materials. For example, the chlorine present in potable water as a disinfectant is an oxidant that has been reported to impact the failure mechanism of materials in potable water applications. In this paper, the relationship between various potable water qualities, with different oxidative potentials, and chlorine induced oxidative failures of plastic piping materials is examined. The primary factors of potable water quality affecting oxidative strength are reviewed. Laboratory exposed pipe samples tested at various water qualities to ultimate failure are examined to determine the impact of water quality on the failure mode. The chlorine in potable water is seen to attack the inner pipe wall causing oxidation and degradation of this inner surface. The stresses on the inner wall lead to micro-crack formation in this degraded layer. These micro-cracks are seen to propagate radially through the pipe wall resulting in a brittle slit type failure. The failure mode is shown to be the same over a range of water qualities. The impact of chlorine is shown to be simply one of oxidation with the rate of degradation primarily related to the oxidative strength of the potable water. For the PEX pipe material examined, it is projected that material performance can significantly exceed the excellent performance predicted based on testing at the aggressive water qualities typically employed in validation testing, depending on the specific water quality of the end use application.
A compressed air line exploded suddenly and caused extensive damage to property, fortunately without casualties. The air line was used as part of a plant for annealing glass, and so was pressurised regularly up to about 10 bar. When the pressure was released, a blast of cold air was directed over the hot glass surfaces. Most of the pipework for the system was made of ABS pipe and solvent-welded fittings. The explosion was caused by catastrophic growth of an internal axial crack in one of the pipes of the system. The inside surface of the pipe was covered with deep cracks, and the first investigators concluded that the cracks had been caused by fatigue. However, a separate investigation of the remains indicated that traces of fluid from the oil of the air pump compressor had created environmental stress cracks.
Gediminas Markevicius, Vivak M. Malhotra, May 2004
Economic and environmental forces are providing an impetus for the development of biocomposites from renewable agricultural byproducts. In pursuit of this goal, we are developing biocomposites from wheat-, kenaf-, and corn-byproducts without external additives. Our differential scanning calorimetry (DSC) measurements suggest that micronized wheat straw and inner kenaf fibers have similar thermal characteristics at 50°C < T < 400°C, thus they can be co-processed. The flexural strength of the composites formulated from micronized wheat straw and kenaf fibers increases as the concentration of straw in the composite increases. Postcuring the composites at 190°C also decreases the strength.
Lawyers and judges have, most of the time, little understanding about the mechanical, chemical and physical behavior of plastics. A selection of legal cases will be presented and it will be emphasized that presentation is sometimes rather an art than a science. This is illustrated by three examples of legal cases.1. Water storage tanks, consisting of an outer and an inner stainless steel tanks with insulation between the tanks. In order to prevent freezing of the wastewater a heating mat is adhered using silicon kit to the outside of the inner tank. PE tanks were ordered to substitute the expensive stainless steel tanks. The heating mats became overheated because of the poor adhesion to PE. It is rather easy to convince court that the bonding between silicon kit and PE is absent and that this is the reason that containers for silicon kit are of PE.2. Scratches on textured plastic panels. A supplier promised to manufacture panels of high surface quality, but was not able to meet the requirements and painted the panels. The supplier billed the customer for $ 400 000 and in court this claim was rejected on the basis of strict contractual liability. The lawyers even did not want to have the technical explanation, why the scratched occurred, in my failure report.3. Fatigue of flexible covers for cupboards made of ABS. The manufacturer of the cupboards covers specified ABS with a rubber content (polybutadiene) of 40 % to avoid fatigue of the covers that were subjected to bending during opening and closing of the cupboards. The covers often did to satisfy the surface gloss requirements and the manufacturer of the covers proposed ABS and PS with a lower polybutadiene content. These covers met the surface gloss requirements, but failed in surface due to the low polybutadiene content. This resulted in a loss of confidence of the Cupboard Company and almost resulted in a bankruptcy. The final solution was to use ABS from another supplier and stricter quality control.
Poly (l-lactide) (PLLA) has received considerable attention recently because it is environmentally friendly, derived from agricultural sources, and biodegradable. However, the mechanical properties of PLLA are typically low compared to other petroleum-based plastics. Recently, properties such as modulus and heat deflection temperature have been improved by creating polymer/clay nanocomposites. This study focuses on the effect of different organic modifiers for montmorrillonite clay on the thermal and mechanical properties of PLLA. Upon the addition of a small amount (1-10 wt %) of these modified clays, the storage modulus and Tg increases for all types of clays. The greatest increase in properties is found using quaternary ammonium ion having a pendant benzyl group.
M. Misra, A.K. Mohanty, P. Tummala, L.T. Drzal, May 2004
This paper focuses on the development of a new technology and process in order to manufacture natural fiber reinforced engineering thermoplastics like nylon 6. Natural fibers are not suitable reinforcements when high temperature melting (above 200°C) engineering thermoplastics is used as matrix materials because natural fibers start to degrade thermally at above 200°C. Small quantities of inorganic salts like lithium chloride were added to the nylon 6 during melt extrusion processing to depress its melting temperature. The final composites are injection molded into test specimen at the reduced processing temperatures of nylon 6. The molded plastics and composites are tested for mechanical and thermal properties. Natural fiber reinforced nylon 6 composites show improved tensile and flexural properties. The morphology of the fracture surfaces is observed using Environmental Scanning Electron Microscopy.
Biodegradable composites were developed by compounding a commercial corn starch polymer with pine and Alfa fibers on a counter-rotating twin screw extruder. Subsequently, the compounds were injection molded under optimized conditions and characterized for the respective mechanical behavior and morphological features.The obtained results establish by evidence that this kind of composites present mechanical performance (in terms of stiffness and strength) within the range of the polymeric systems based on high consumption thermoplastics. In comparison with pine fibers, Alfa based composites presented a better performance as result of various advantageous morphological and interfacial aspects.
Many injection molders when processing high temperature amorphous resins like Polyetherimide (PEI) use oil cooled molds to enhance the mold filling process and achieve the best mechanical properties attainable. The practice of molding with high mold temperatures is generally recommended by material suppliers in order to reduce molded-in stress, which can have a negative effect on final molded part performance. While it is still good molding practice to use oil cooled molds, there are many instances in which PEI can be molded into acceptable parts using water as the heat transfer fluid. Water cooled molds offer several advantages over oil and includes reducing environmental and personnel safety concerns in addition to lower capital cost and ease of operation.
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Brown, H. L. and Jones, D. H. 2016, May.
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Society of Plastics Engineers
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