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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Practical Guidelines for Predicting Steady State Cure Time during Sheet Molding Compound (SMC) Compression Molding
The longest part of the molding cycle during SMC compression molding is the curing stage. Thus it is extremely important to be able to predict its duration to estimate the cost of manufacturing a part. To avoid blistering, the cure time must be increased with consecutive moldings until a steady state value is achieved (tcss). In this paper, we present a series of charts that can be used to estimate the steady state cure time for new parts. These values can then be used to estimate the manufacturing cost.
Method to Estimate Vibration Behavior of Fiber Reinforced Thermoplastic Parts
Until now it has been difficult to estimate quantitatively the vibration behavior of FRTP parts using computer simulation. The reason was that the conventional simulation model did not express appropriately the damping properties of vibration (dependence on the temperature, amplitude, frequency and moisture content) and the orthotropic Young's modulus. Therefore, a new simulation model was proposed through measuring the damping factor of the specimen and the experimental modal analysis of the parts. Based on this model, the simulation result of the realistic vibration behavior on the FR-nylon product (e.g. air intake manifold) proved to be in good agreement with the experiment.
Crystalline Transitions in Nylon/Clay Nanocomposites
Nylon 6-clay hybrid is a molecular composite of Nylon 6 and uniformly dispersed silicate monolayers of synthesized saponite. Nylon 6 has two crystalline forms, ? and ?. The a phase is the thermodynamically most stable crystalline form but the ? phase is not. In this study, the nylon 6/synthesized saponite has prepared by the intercalation of e-caprolactam and then exfoliating the layered synthetic saponite by subsequent polymerization. The DSC thermal analysis and X-ray diffraction methods were used to investigate the crystal structure change of nylon 6/synthesized saponite. The results indicate the presence of crystalline transition in nylon 6 nanocomposites. The effect of thermal annealing on the crystalline structure of nylon 6 nanocomposites in the range between Tg and Tm is also discussed.
Characterization of the Interfacial Regions in Multilayer Coatings by NEXAFS Microscopy
Characterization of polymer interfaces is an important analytical need in many areas of technology. Many techniques, that provide the requisite spatial resolution, provide limited quantitative chemical information. On the other hand, techniques, that provide the desired level of quantitative chemical information, have limited spatial resolution. A relatively new analytical tool, Near-Edge X-ray Absorption Fine Structure (NEXAFS) microscopy [1- 4], provides a unique combination of chemical specificity and spatial resolution that is particularly well-suited for characterization of interfaces in polymer coating, blends and composites. In this paper, the application of NEXAFS microscopy to a multilayer polymer coating is discussed.
Rheological and Blown Film Characterization of Binary Blends of Metallocene-Catalyzed LLDPEs
The advent of metallocene catalyst technology has created several opportunities in the worldwide packaging film marketplace. In this work, we explore the effects of blending two metallocene-catalyzed LLDPEs of reasonably differing molecular weights. Specifically, the shear rheology, quiescent and shear-induced crystallization characteristics, and blown film performance were investigated as a function of blend composition. The presence of small amounts of longer molecules was found to have significant effects on the shear-induced crystallization kinetics and blown film orientation of the blends; this was explained in terms of an increasing number of extended chain nuclei for crystallization with increasing molecular weight. Lastly, the biaxial orientation features in the crystalline and non-crystalline phases of the blend blown films were also characterized and used in explaining the Elmendorf tear and dart impact performance of the blown films.
High Performance Rigid Flexible Combinations Made of Thermoplastic and Liquid Silicone Rubber
The injection molding of LSR represents a cost-efficient process for the production of high quality rubber parts for technical applications. Due to excellent material properties at extreme temperatures silicone rubbers offer various advantages for the production of soft/rigid combinations in comparison to thermoplastic elastomers. A new kind of LSR is presented which exhibits excellent adhesion properties to engineering thermoplastics. The process and the adhesion mechanism is designed in a way that no mold coating is required. A systematic analysis of the injection molding process points out suitable material combinations and indicates the influence of process parameters on adhesion strength.
Welding of Plastics: Introduction into Heating by Radiation
For welding of plastics, various procedures of heat transfer are presently in use. Non-contact heating by radiation allows heating e.g. without contamination of a heated tool and makes heating faster by volume-absorption of the material. Presently infra-red lamps and infra-red laser beams are in use for welding of plastics. This paper wants to give an introduction into the physical principles of heating by infra-red radiation, wants to divide between surface and volume absorption of different materials and wants to give a survey about the advantages and disadvantages of infra-red lamps and lasers.
Melt Rheological Properties of Natural Fiber-Reinforced Polypropylene
The melt viscosities and mechanical properties of 3 different natural fiber-polypropylene composites were investigated. Coir (coconut), jute, and kenaf fibers were compounded with polypropylene at 30% by weight content. A capillary rheometer was used to evaluate melt viscosity. The power-law model parameters are reported over a shear rate range between 100 to 1000 s-1. Effects on melt viscosity with the use of a coupling agent and different fiber types were also evaluated.
Injection Molding Tie Bar Extension Measurements via Strain Gauge Collars for Optimized Processing
The measurement of the clamping force in injection molding can give valuable insight for optimization of the process. Problems in production are often related to the level and the distribution of the clamping force. A novel measuring system that employs strain gauges that are clamped around the tie bars make a precise measuring method applicable in a rugged industrial environment. It was the objective of this work to evaluate the performance of the device in practical use.
Dielectric Relaxation Spectroscopy of Reactive Network-Forming Polymers
Dipole dynamics in network-forming polymers were investigated by broadband dielectric relaxation spectroscopy (DRS). The changes in reorientational dynamics during the advancement of reactions were used to (1) describe the molecular origin of various relaxation processes (?,?), (2) describe the dynamics in terms of the location and intensity of relaxation spectrum, and (3) advance an interpretation of network dynamics in terms of intermolecular cooperativity. The chemical state of network at various stages of cure was identified by simultaneous DRS and remote fiber-optic FTIR.
Simulation of the Filling and Curing Phase in Injection Molding of Liquid Silicone Rubber (LSR)
The injection molding of Liquid Silicone Rubber (LSR) represents a cost-efficient process for the production of high quality rubber parts. Due to the extreme thermal conditions in the mold and the very low material viscosity a precise subvolumetric filling of the cavity is required to avoid flash formation. Modeling flow properties, curing characteristics and as the pvT-behavior creates the basis for an unified simulation of the injection molding process. The implementation of these models into a process simulation software makes it possible to calculate the filling phase considering a subvolumetric filling and to simulate the course of cavity pressure during the heating phase.
Thin-Wall Injection Molding
A precision monitoring system for high speed thin-wall injection molding machine was build so that hydraulic pressure, nozzle pressure, injection speed, filling to packing switchover and cavity pressures can be monitored during the whole molding process. Tensile test specimens of 2.5 mm, 1.2 mm, 1 mm and 0.8 mm thick were molded. It was found that as part becomes thinner the pressure prediction of CAE simulation gets worse and the errors range from about 50% to more than 100%. Filling time, proper filling to packing switchover, gate size, holding pressure and mold temperature were found to be the critical factors to successful molding and part quality. When part becomes thinner, residual stress is higher and affects part strength more significantly. When molding industrial thin parts, the residual stress concentrates around gate area, bosses and area where part thickness varies. Thickness reduction for the housing of computer dictionary can be achieved without great reduction in structural performance when localized thinning design is implemented.
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.
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