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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Parison Wall Control Systems for Extrusion Blow Molding Equipment
For a uniform wallthickness and layerthickness distribution even in complex-shaped blowmolded articles the parison has to be adjusted accordingly. Important developments in recent years were: • The Static Flexible Deformable Ring" SFDR and the "Partial Wall Thickness Control" PWDS for sophisticated articles. • The "Wallthickness Location Control" WDLS controls the actual position of wall thickness points which may "wander" e.g. due to changing raw material conditions. • The "Radial Wallthickness Control" RWDS for wallthickness control in bows of 3-dimensionally bent (3D-) parts. • A uniform layer thickness distribution in multilayer parts is achieved with a gravimetric throughput control system. "
Viscoplastic Analysis of Hot Embossing in Microfabrication
In MEMS (micro electromechanical system), the hot embossing process has been mentioned as one of the major fabrication techniques, which is capable of making polymer microstructures for both low volume prototyping and high volume production. This is due to its simple process, relatively low tooling cost, high replication accuracy, and relatively high throughput. In order to minimize the process cycle time, the embossing temperature is set slightly above the glass transition temperature (Tg), while the de-embossing temperature is slightly below Tg. Since the polymer is deformed near Tg, its flow behavior during molding is substantially different from that at high temperature processes such as injection molding and extrusion. Also, the residual stresses resulting from the thermal cycle and compression force will profoundly influence the replication accuracy and optical properties of the molded parts. In order to establish the relationship between the residual stresses, replication accuracy, rheological behavior, and processing variables, we carried out a viscoplastic analysis and a series of hot embossing experiments. Two optical polymers, polyvinyl butyral (PVB) and polycarbonate (PC) were used in this study. The rheological property was characterized through both dynamic and transient shear viscosity measurements using the RMS-800 and a tensile test. Optical and SEM photos of replicates were taken at different processing conditions to determine the replication accuracy and birefringence pattern.
Biodegradable Laminates and Composites Containing Starch and Poly(hydroxyester-ethers)
Poly(hydroxyester-ethers) (PHEE) were added to a variety of thermoplastic starch composites in order to improve the mechanical and water-resistant properties of these systems. Thin film coatings of PHEE's were found to adhere well to starch sheets and foams and provided resistance to cold water over short periods of time (hours-days). Adhesion was decreased by high water or glycerol contents in the starch and was increased by addition of partially hydrolysed polyvinyl alcohol. Extruded starch foam peanuts containing 5-20% PHEE were found to have a thin surface layer consisting mainly of PHEE. This probably explains, at least in part, why the starch/PHEE foams have a higher expansion ratio, greater water resistance and reduced friability compared to foams made from starch alone.
Evaluating the Energetics of Heterogeneous Deformation in LLDPE Films under Biaxial Loading Conditions
Post-yield, heterogeneous deformation (dilatational bands) occurs in linear, low density polyethylene films under certain biaxial loading conditions. The dilatational band evolution occurs primarily by isotropic expansion and the energy release rate is therefore determined using the M integral. A thermodynamic model is used to determine a material property that describes the energy associated with the drawing process. The thermodynamic model and the M integral appear to be appropriate for modeling this process.
Electrical Static Dissipative Composites Made from Coated Fillers
A novel polymerization technique, admicellar polymerization, was used to coat alumina with a thin layer of polypyrrole. A polyethylene composite made from the uncoated material had a conductivity of approximately 10-9 S/cm, well below the useful conductivity range for most applications. However, the conductivity of the composite made with the coated material was approximately 10-5 S/cm, which is in the conductivity range of many electrically static dissipative applications.
Numerical Simulation of Blown Film Cooling
Commercial blown film production is often limited by the rate of cooling that can be achieved in the production line. The flow of the cooling air around the curved bubble is characterized by rather complex aerodynamics. Even for the same air ring design, different set-ups (adjustable air rings) produce significant differences in the air-flow pattern. Numerical simulation suggests that heat transfer rates are affected by all these parameters. Additionally, numerical simulation in the film phase reveals large temperature gradients across the film thickness in the area where the film is emerging from the die.
Predictive Control of Melt Temperature Incorporating the Effect of Screw Rotation
Controlling the plastic melt temperature along the barrel of an injection molding machine is important for the overall product quality. In order to achieve good control performance, other process interactions such as the rotating screw should be incorporated into the controller design. The use of model-based predictive control (MPC) allows coupled processes to be model in a dynamic matrix in order to calculate the control moves to each process. By applying this control approach, higher rotating screw speeds and melt plastization back-pressure can be utilized without the effects of temperature oscillations and material degradation.
Interfacial Anchoring in Semi-Crystalline Blends
We demonstrate that anchoring of entangled interfacial chains is responsible for toughness in immiscible blends containing a semi-crystalline component. Interfacial anchors are formed when entangled chains crystallize into lamellae, creating entanglements in the phase boundary that have chain ends secured in crystallites. The proposed toughening mechanism was demonstrated with isotactic polypropylene and polyethylene. Both scattering experiments and imaging showed that non-crystalline material placed at the phase boundary decouples the interface, diluting the number of interfacial anchors. As the degree of interfacial anchoring was reduced, the failure mode changed from bulk iPP failure to interfacial failure, reducing the tensile toughness and elongation by 40%. The interfacial structure was probed directly with peel tests. When an interfacial crack was propagated through a highly anchored interface, the 90° peel strength was 15 times greater than for a crack propagated through an interface that had no significant interfacial anchoring.
Characterization of Polyethylene Blends by Using Novel Techniques Such as the Successive Self-Nucleation and Annealing (SSA) and the Fourier Self-Deconvolution IR Spectroscopy (FSD-IR)
At the present, the plastic film industry has been using complex blends of Polyethylene to meet the demands of better mechanical properties, excellent sealability and adequate runnability in the processing machinery. Thus the characterization and the evaluation of processing properties are of great importance for the plastic industry. According to the present study successive self-nucleation and annealing SSA and the Fourier Self Deconvolution IR Spectroscopy, is a valuable tool for characterization of complex blends of Polyethylenes. By using the above mentioned techniques it is possible quantify metallocene Polymers and traditional LLDPEs from LDPE binary and ternary blends.
Application of the Crack Layer Model for Understanding of the Correlation between Lifetime and Creep Behavior in Polyethylene
A closely coupled system comprising of a crack and a process zone (PZ), i.e., a domain of crazed material ahead of the crack, commonly observed in polyethylenes (PEs), constitutes the crack layer (CL). According to the CL theory, slow crack growth in polyethylenes is largely a result of degradation of the process zone material. The CL theory has been applied to model some features of slow crack growth in PE, such as the discontinuous manner of the process, the widely reported specifics of fracture surface morphology, the stress and temperature dependence of lifetime, as well as the crack speed-stress intensity factor (SIF) relation. In the present work, a simplified version of the CL theory is employed to explain and generalize the correlation between the lifetime of PE pipes in brittle mode fracture and the so-called Creep Rate Deceleration Factor (CRDF) of drawn PE.
Ductile Failure and Delayed Necking in Polyethylene
Analysis of polyethylene (PE) pipes ductile failure (ballooning) suggests that it is directly related to the delayed necking phenomena and time to ductile failure of PE pipe can be evaluated as the time to delayed necking. The necking in polyethylene (PE) is studied under displacement control (ramp test) and load control (creep) conditions. In ramp tests the dependence of the yielding and drawing stresses on strain rate are established using specimens of a European PE 100 pipe grade HDPE, It is shown that both stresses decrease with decrease of strain rate and approach a common value, the characteristic stress. In creep tests of the above material, the relation of time-to-necking vs. applied stress is obtained. It is proposed to employ the testing procedure on tensile specimens for estimation of time-to-ductile failure in PE pipes. The characteristic stress is suggested to be an indicator of the ductile-to-brittle transition in failure mechanism.
The Development of a Consumable Container for Built up Roofing Asphalt
An injection molded container has been developed for built up roofing asphalt. The container is consumable in the roofer's kettle unlike the paper carton it supplants. The development of the container consisted of three elements. The first element was the development of a compound that could be injection molded, withstand filling with molten asphalt, and later melt completely in the roofer's kettle. The second element was the design of a container that met processing, cost and customer requirements. The third element was the development of a cost-effective injection molding process.
Permeation of Thermoplastics through Random Fiber Mats
The permeation of fiber mats by thermoplastics has not been studied in depth. In order to address this issue, the permeation of nylon 6 and polypropylene through random glass, carbon, and sisal fiber mats has been studied. A transverse Kozeny constant of 4.6 was calculated for the permeation experiments, and a non-Newtonian permeation model was found to predict the permeation rate of the thermoplastics into the fiber mats well.
New Halogen-Free Fire Retardant for Engineering Plastic Applications
A comparative study of the fire retardant efficiency of three commercial aryl phosphates: triphenyl phosphate (TPP), resorcinol bis(diphenyl phosphate) (RDP) and bisphenol A bis(diphenyl phosphate) (BDP) in PC/ABS blends, was carried out. The thermal and hydrolytic stability of the fire retardant resins as well as their physical properties was also studied. The use of RDP and BDP is preferred over TPP because of superior properties, whereas BDP shows better fire retardant efficiency, hydrolytic and thermal stability than RDP.
Durability Study of Conductive Copper Traces within Polyimide Based Substrates
Flexible printed circuitry (FPC) is a patterned array of conductors supported by a flexible dielectric film made of high strength polymer material such as polyimide. The polyimide core is the premier dynamic structure membrane with an extraordinary ability to withstand continuous. Flexing for hundreds of millions of flexing cycles, fatigue performance and reliability are paramount issues in the design and manufacturing of FPC. In the composite structure, the conductive layers are more vulnerable to failure due to their lower flexibility compared to polyimide film. This paper is focused on the reliability assessment of FPC based on the high cycle fatigue resistance. Fatigue resistance of various material systems has been analyzed as a function of temperature and frequency. The fatigue characteristics of selected material systems are summarized in the form of S-N diagrams. Failure mechanism observations are discussed and complete fracture analysis is presented. In various FPC systems, it has been found that the changes take place in FPC failure mechanisms from well developed and aligned through the width cracks at low temperature to an array of multiple cracks with random sizes and locations at high temperature. Comparative analysis of various material systems based on fatigue performance is presented.
True Stress-Strain-Temperature Diagrams of Polyolefins and Their Application in Acceleration Tests for Lifetime Prediction
True stress - strain - temperature (TSST) diagrams are being used as a tool for characterizing thermo-mechanical behavior of polymers. TSST diagrams are developed for materials that undergo necking by consideration of a material point perspective. In the present work TSST diagrams of three polyolefin types, Polyethylene, PE, polypropylene, PP, and polybutylene, PB, are constructed and their relevance to accelerated lifetime testing discussed. It is found, in contrast to PE and PP, the changes in PB deformation behavior raises the issue of validity of lifetime predictions of PB at temperatures below 70°C based on testing at temperatures above 70°C.
The Effect of Chemical Degradation on Physical Properties and Fracture Behavior of Poly(ethylene-co-carbon monoxide) and Poly(1-butene)
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.
Notch Sensitivity of Pipe Grade Polyethylene and Polybutylene
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.
An Anamoly in the Lifetime-Temperature Relation of a Polybutylene for Pipe Applications
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
An Integrated Process for Medical Design Success
Customer driven medical product development is a process to shorten the development cycle time and drive speed to market. It focuses on the product concept and the design freeze to develop a manufactureable assembly with built in quality while lowering manufacturing costs.
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