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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Ioan I. Negulescu, Codrin Daranga, Zhong Wu, William H. Daly, Louay M. Mohammad, Chris Abadie, May 2004
Since polymer modified asphalt cements (PMAC) have been employed for a decade, the lifetime and wear on of some of these roadbeds are reaching a stage where resurfacing will be necessary. This paper considers the potential problems associated with recycling of polymer modified asphalt cements, PMAC's, in particular blending aged PMAC with tank PMAC. A standard PMAC was selected and characterized using typical asphalt binder qualification techniques, i.e., the Superpave Strategic Highway Research Protocol. Procedures were developed to separate the PMAC into its asphalt resin and polymer additive components as well as to characterize the relative concentrations of each component. Infrared and chromatographic techniques were used to identify changes in the components as a result of aging. The impact of the extraction and recovery process on binder properties has been ascertained and found to be minimal.The standard PMAC was aged under accelerated aging conditions in a Pressure Aging Vessel (PAV) that produced a material equivalent to 5-8 years in the field. The aged PMAC was then reanalyzed both chemically and rheologically and all changes in its properties due to aging were noted. Finally blends of the PAV aged PMAC with fresh PMAC, as well as blends where the PAV aged PMAC was replaced with road-aged binder, were prepared and analyzed. Our initial results indicate that aged PMAC can be blended successfully with fresh PMAC. Thus we anticipate that resurfacing of aging PMAC roadbeds can proceed, but further tests will be required to establish the precise conditions necessary to conduct this process.
Woo-Hyuk Jung, Nathan Tortorella, Charles Beatty, May 2004
The front cover of cellular phone housing collected was grounded to be as the same size as the original particles before use, using knife mill. The unprinted glass fiber reinforced epoxy circuit boards were size reduced and pulverized using knife mill and hammer mill. The separated epoxy powder and glycidyl methacrylate (GMA) were added as the additive and the reactive species for reactive process using the batch mixer and the twin screw extruder. Izod impact strength at various temperatures, tensile test, particle size distribution analyses for the ground circuit board, SEM on the fracture surface, and dynamic mechanical spectroscopy were performed to characterize the reactive alloys and mixtures compounded by the batch mixer and the twin screw extruder.
Pittsburg State University has worked on the development of biodegradable blends for low temperature, durable applications in bull castration clips for use in the farm industry. These clips are biocompatible, to ensure that meat is not contaminated. At the same time they also exhibit biodegradability and strength in temperatures as low as –20 °C; temperatures that can be experienced in the North American farm belt. The blends contained the following materials, Eastar Bio Copolymer, Polycaprolactone, Polyethylene glycol (Carbowax), Hydroxypropylcellulose (Klucel), Cornstarch, and Titanium Dioxide. Table 1 shows the ingredients of each blend. In vitro results show degradation of the samples from 5% to over 25% of its’ original mass over a 28- day period. Differential Scanning Calorimetry results showed the Tg of the blends reaching –24.15 °C, well below the targeted value of –20 °C.
Christopher C. Ibeh, Dhirendra Bhattarai, Mark Schultz, May 2004
A prior advanced materials selection process via the digital logic approach (DLA) yielded five materials as suitable choices for the housing of the Signal Detector Control Head Unit (SDCHU), with ABS (acrylonitrile-butadiene-styrene) terpolymer and aluminum 1100 as the top two choices. In an effort to study the long term perspective, durability and environmental impact of the SDCHU, a life cycle value analysis (LCVA) was performed on the SDCHU with ABS as the housing material and then with aluminum 1100 as the housing material. The LCVA results indicate that ABS is the choice material in seven of the eight impact categories studied such as costs, energy usage, conventional pollutants, green house gases released, fuels used, ores used, hazardous waste generated and water used. Normalized environmental impact data show that the 5.6% increase in hazardous waste is offset by the 8 - 52% reduction in the other seven categories due to ABS use in the SDCHU housing.
The attractiveness of high molecular mass poly(lactide), PLA, as a packaging material has increased in the last few years due to its natural biodegradability. PLA is a thermoplastic and compostable polymer produced from annually renewable resources, which can be totally degraded in aerobic or anaerobic environments in six months to five years. As PLA is now potentially available for use as food packaging polymeric material, one of the main concerns is to evaluate its durability with respect to the product shelf life. Since moisture sorption isotherms of polymeric materials are one of the controlling factors in the preservation of moisture-sensitive products, the aim of this research was to study the moisture-sorption characteristics of two poly(lactide) polymers at 5, 23, and 40°C for water activities (aw) from 0.1 to 0.9 as a function of short time storage. The PLA films were stored for one month at the same temperatures, and the glass transition and melting temperatures were monitored by Differential Scanning Calorimetry every week. It was found that PLA films absorb very low amounts of water, and the variation of the glass transition temperature as a function of time was statistically significant (P<0.05).
John F. O’Gara, Michael G. Wyzgoski, Glen E. Novak, May 2004
During injection molding of glass-filled thermoplastics, the flow of the molten polymer causes preferential orientation of the fibers, which leads to the development of anisotropic mechanical properties across a part. These anisotropic properties pose a significant challenge to part designers, who normally assume isotropic properties measured on tensile bar samples. This paper describes the background information and test data used to prepare an ISO standard plaque (ISO 294-5: 2001) for measuring anisotropic properties and developing a relevant materials property database for plastic part design.
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.
Pistons and cylinders in hydraulically systems are separated using plastic guidance strips, positioned in grooves of the piston. The total compression and wear of the strip under transversal loading is critical for avoid metallic contact between pistons and cylinders. If the compression of the strip is larger than expected, severe damage occurs and, even in Europe, high liability claims are likely.The paper is about a design in which the compression of the strip was critical. The designer relied on the stress-deflection curves in the brochure of the manufacturer of plastic guidance strips. The designer was convinced to be on the safe side, but in practice metallic contact occurred.The stress-deflection curve of the guidance strip has been measured again and the difference with the values in the brochure was significant. Interesting, from the engineering standpoint, was the ambiguity of some of the data. The assumptions made by the designer of the hydraulic system and the manufacturer of the strips has been tested using FEM calculations.The predictions have been made with the FEM-program MSC/MARC using the contact option. The predictions have been compared with results of full-scale experiments.
In a previous publication1, I showed that root cause analysis was an effective method in revealing the true cause(s) of polymer failures and in proposing the corrective actions needed to avoid future failures. In this current work, I will discuss two polymer failure cases that explain the basic steps of root cause analysis. In these cases, I will talk about the effect of the four common factors that influence failure: part design, material choice, processing factors, and end-use conditions. An explanation of each case will be offered. Subsequently, the suggestion of the probable failure cause(s) and the exploration of the most likely cause will be presented. Finally, some corrective actions will be recommended.
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.
Byoung-Ho Choi, Wen Zhou, Alexander Chudnovsky, Pak M. Cham, Thoi Ho, May 2004
The fracture initiation in polybutylene (PB) tubing is usually observed in the form of a microcrack network within a layer of degraded PB at the inner surface of the tubing exposed to flowing water. Chemical degradation of PB is manifested in a reduction of molecular weight, increase of crystallinity and density of the material, a subtle increase in yield strength, and a dramatic reduction in toughness. An increase in material density, i.e., shrinkage of the degraded inner layer of the tubing constrained by the outer layer of unchanged material results in a buildup of tensile stress due to an increasing incompatibility between the inner and outer layers of the PB tubing. These stresses combined with preexisting manufacturing and service stresses, as well as reduction of toughness, result in fracture initiation. A mathematical model of the foregoing process is presented in this paper. An equation for determination of the critical level of degradation at the onset of fracture is derived. The critical level of degradation leading to fracture depends on the rates of toughness deterioration and buildup of the degradation related stresses as well as on manufacturing and service stresses. A method for the evaluation of the time interval prior to fracture initiation is also outlined.
A number of water utilities in various states of USA have reported a persistent premature failure of polybutylene (PB) tubing in water distribution system. A methodology of reliability analysis of PB tubing in potable water distribution application and probabilistic model for predictions of future leaks are presented in this paper. The predictive power of the proposed methodology is validated by comparison of predicted number of failures in Harford County Water District, Maryland between 1996 and 2001 with actual events reported by the District in 2002. The proposed methodology also accounts for the effect of preventive replacement program on the reduction of emergence replacements and thus allows a rational planning of replacements. The needs to understand the failure mechanisms for proper interpretation of both descriptive and inferential statistics are also discussed.
Small transformer plugs are widely used for consumer electrical and electronic products, designed to be fitted to mains electricity sockets by the user. Problems occurred when plugs injection moulded in Noryl started cracking at or near the weld zone on first use, exposing the user to danger. A quality audit showed that the base and cover had been moulded in mainland China in two specific weeks of 1999. Although records for that period were not available, those from adjacent batches showed that low tool temperatures (ca 55°C) had been used for the base moulding , which also showed the greatest incidence of brittle cracking. An alternative theory by a Japanese investigator that the material was faulty could not be sustained by EDAX analysis.
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.
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.
S. Wu, K. Sehanobish, A. Chudnovsky, Yu. Shulkin, Z. Zhou, May 2004
Laboratory studies of slow crack growth (SCG) that mimics the field conditions experiments (ambient temperature and relatively low quasi-static load) would take decades and therefore would be useless for PEs ranking and an evaluation of PE life expectance. Thus it is desirable to develop a methodology for prediction of SCG behavior of PE based on a short-term test. An accelerated test for SCG resistance proposed in the present work is based on the analysis of micro-mechanisms and quantitative modeling of SCG. The test provides a comprehensive characterization of the craze material (fibers) creep and time to fiber fracture dependence on stresses, since SCG in PEs is in a large extant controlled by a process zone (PZ), i.e., a craze, formation and rupture in front of the crack. The proposed experimental procedure includes relatively short-term creep tests at various stress levels, which address only the basic properties of a particular polyethylene. The creep characteristics of craze fibers and the stress dependence of the time to craze fiber rupture are employed for SCG modeling described in the previous presentation. The details of the test procedure and examples of the test results are discussed.
Witold Brostow, Ricardo Simões, António M. Cunha, Júlio Viana, May 2004
We investigate the behavior of polymeric materials at the molecular level by the use of computer simulations. We create one and two-phase materials on the computer with varying degrees of chain orientation, second phase concentration, and defects.The simulated materials are subjected to various patterns of tensile force. The true stress developing along the simulation can be calculated and compared with the engineering stress. Free volume can also be monitored and related to the formation of internal micro-cracks during deformation.Computer simulations provide us detailed information about molecular phenomena. This knowledge can be used to create materials with improved properties.
The authors have earlier identified crack patterns that are generic to a range of rubber-modified polymers as well as homogeneous and other heterogeneous systems. This is in the form of overlapping parallel cracks that are found repeatedly in different materials. In this study, a complex stress function method has been used to study the micro-mechanics and damage stability that exists in this generic pattern. It is shown that the interaction between the cracks in the overlapping crack pattern can lead to arrest of crack growth. The damage is also modeled as a doubly periodic infinite array of cracks. The differences between the two crack growth criteria namely, stress intensity factor and energy release rate, are explained by considering the effect of the cracks on the overall stiffness of the material.
A. Chudnovsky, Y. Shulkin, Z. Zhou, S. Wu, K. Sehanobish, May 2004
It has been well recognized that slow crack growth in polyethylene leading to long-term brittle failure is associated with behavior of a process (craze) zone in front of the crack tip. The concept of crack layer (CL) as a system of strongly interacting crack and process zone (PZ) was introduced and analyzed in a number of publications by Chudnovsky with co-authors. The present paper is an extension of the model, which includes: (i) a new approach to determination of PZ size that accounts for stress relaxation along of the PZ boundary and (ii) evaluation of PZ lifetime under variable stress at each stage of CL growth. Analysis of stresses and strains in a vicinity of the crack layer is based on (i) the compatibility condition between bulk polyethylene and PZ material along the PZ boundary and (ii) determination of material elastic and creep characteristics obtained from tests on an original polyethylene and its craze modification. A stepwise process of slow fracture propagation is considered. The time to ultimate failure is evaluated as the duration of slow CL growth from load application to ultimate instability. An experimental procedure to rank various polyethylenes with respect to resistance to fracture propagation (toughness) is discussed.
M. Hassan, A.B. Khairy, S.M. Fayommi, M.G. Abou-Ali, May 2004
Defect diagnosis of tires during manufacturing and service is one of the very complicated issues in dealing with the tire manufacture. This is due to the big number of raw materials and processing steps involved in the manufacturing of a tire. Each raw material and process quality parameter is affecting the final quality of the tire. The manufacturing history data of that particular tire is essential, with the raw materials inspection results, as the starting point, and going through all manufacturing steps, to the final inspection results and failure mode in service. This study presents a TIRE Defects Diagnostic eXpert system, which we called (TIREDDX) as a part of an integrated TQM system that can be applied to achieve an effective diagnostic procedure for tires and elastomers defects, which may cause a company a lot of money, effort and time to resolve it.
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