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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Effect of the Skin/Core Ratio on the Flow Behaviour during Co-Injection Moulding
The effect of the core/skin ratio on the overall flow behaviour in the co-injection molding process was studied. A 7.6x16.4x0.7 cm3 rectangular plaque was moulded using a 150-ton Engel co-injection machine. ABS was used both for the skin and core material and PC were used only as the skin material. For visualization purposes, a black pigment was added to the core material. The results are discussed in terms of the relative viscosity, injection speed, melt and mould temperatures.
Thermal Stability of Polyurethanes Based on Vegetable Oils
A series of polyurethanes from polyols derived from soybean, corn, safflower, sunflower, peanut, olive, canola and castor oil were prepared and their thermal stability in air and nitrogen assessed by thermogravimetric analysis, FTIR and GC/MS. Oil based polyurethanes generally had better initial thermal stability in air than the polypropylene oxide based polyurethane, while the latter was better in nitrogen. If a higher conversion is taken as the criterion of stability then all oil based polyurethanes have better thermals stability both in air and in nitrogen.
Wall Slip of Polypropylene/EP Rubber Blends
The wall slip flow behavior has been determined for different blends of a polypropylene with an EP rubber. This is done by analyzing capillary flow data with several dies of different diameters. Mooney plots drawn from this data are strongly curved. This is attributed to viscous heating effects and to a more complex slip velocity relation for the blends. The relevant mass, momentum, and energy equations for flow of a power-law fluid through a capillary are solved numerically to incorporate the combined effects of slip and viscous heating, for fitting the capillary flow data.
Recent Advances in Ultrasonic Monitoring of the Injection Molding Process
Ultrasonic pulse-echo techniques were used to monitor the entire injection molding process including the flow front advancement, the end of filling, the packing phase, the solidification and the detachment of the part from the mold. Compared to conventional pressure and temperature sensors, ultrasonic sensors are non-intrusive, have very fast response and can provide unique capabilities such as monitoring of filling and solidification, and detection of part/mold detachment from both sides of the cavity.
Rod Strength Analysis for Polyethylene/Gas Systems
Roller pull-off experiments have been performed to investigate the rod strength with and without blowing agent. Low density polyethylene was melted to mix with physical blowing agent, or to liberate inert gas by decomposing chemical agent to form a homogeneous melt in the extruder. The extrudate exit a capillary die and went through a driven nip roll for force measurement at a given speed. Extensional viscosity was calculated from the pulling force and roller speed. It appears that plasticization and foaming are important factors in the stretched strength analysis.
Study of Surrounding Temperature Effects on Extruded Foam Structure
Foam extrusion experiments were performed to study the effects of surrounding temperature variation on cell structure. Linear low density polyethylene was used with endothermic chemical blowing agent on a single screw extruder to exit from a capillary die into environments with different temperatures. Cell density, foam density, and cell morphology were investigated. The amount of chemical blowing agent and the surrounding conditions have to be viewed together to correlate with the cell density. Foam density appears to be related to gas escape from the surface during foaming.
Effect of Formulation Variables on Rheology of Rigid PVC
The effect of lubricants, impact modifier, and process aid on the processing and physical properties of a rigid PVC compound have been modeled using a Central Composite designed experiment. Capillary rheology was used to evaluate the flow properties of the various formulations in the study. By modeling the rheological properties it is possible to simultaneously optimize flow, extruder conditions, and final part properties.
Mold Wear vs. Wall Thickness: Critical Information for Thin Wall Molding
The plastics industry is under increasing pressure to reduce the wall thickness of molded parts. Thin wall molding provides a host of concerns not present in standard molding applications. An analysis of the relationship between tool wear and wall thickness was conducted as part of the long-term copper alloy mold wear studies at Western Michigan University (WMU). This analysis suggests tool design for the proactive reduction of high shear erosive wear associated with thin wall molds.
Moulded Part Design for the Gas Injection Technique
In gas assisted injection moulding the melt front advancement has a considerable effect on the gas penetration. The evaluation of an appropriate melt filling is an important step to avoid instabilities in the process sequence. Taking a sample moulded part a procedure is presented that enables the part designer to evaluate required melt and gas injection points according to the gas injection technique. Using finite element simulations different calculations for the melt front advancement lead to the correct gate location in correspondence with the gas nozzle and the part geometry.
Thermoplastic and Elastomeric Toughened Cyanate Esters for Composite Applications
Cyanate ester resins were modified using thermoplastic and elastomeric materials to study their effect on properties and long term durability when used as high temperature matrices in glass fiber composites. Toughness improvements without significant sacrifices in flexural properties were only observed for the systems that did not phase separate. Conversely, the thermal properties of these materials were more seriously affected after exposure to a high temperature environment.
Correlation of Step-Wise Fatigue and Creep Slow Crack Growth in Polyethylene
The correlation in mechanism and kinetics of slow crack growth between fatigue and creep of high density polyethylene was studied. The step-wise crack propagation mechanism characteristic of long-term failures in polyethylene was observed over all fatigue and creep loading conditions examined. Fatigue fracture kinetics allowed for extrapolation to the case of creep failure, which suggested that short-term fatigue testing can be used to predict long-term creep fracture properties. Under high stresses the presence of shear deformation retarded crack growth.
Utilization of Dynamic Feed Control in Family Tools
Just-in-time business agreements have forced molders to become more flexible in the way they produce parts. One way to improve efficiency in the production of complete assemblies is to mold all of the components at once in a family tool. This paper examines the ability of Dynamic Feed Control to produce high quality parts in family tools with widely varying parts in regards to wall thickness and volume.
Effect of PP-GMA on Properties of Talc Filled Polypropylene
Glycidyl methacrylate grafted polypropylene (PP-GMA) was used as a coupling agent in a PP/talc blend. Two coupling agents with GMA grafting levels of around 0.34 %wt. and different molecular weights were used. It was found that the use of PP-GMA at concentration between 1 and 10 %wt. increased the tensile strength and impact resistance of PP/talc composites. The performance of the PP-GMA was comparable to commercial PP-MAH modifiers. The chemical or physical effect of the coupling agent are discussed.
Optimization of the Weld Line in Injection Molding via an Experimental Design Approach
Weld lines are sometimes inevitable when processing large and complex parts by injection molding. In this paper, a design of experiments approach (Taguchi Method) was utilized to study the influence of seven processing variables (melt and mold temperatures, injection and hold pressures, cooling and holding times, and back pressure) on the weld line width and the tensile impact properties of injection molded dog-bone bars. The important processing variables affecting the weld line behavior are identified.
Effects of Additives on Scratch Resistance of Polypropylene Materials
Pigmented mineral-filled polypropylene (PP-PMF) is marketed as a potential alternative to ABS (acrylonitril-butyldiene-styrene) and ABS/ PC (acrylonitril-butyldiene-styrene/ polycarbonate) for interior automotive components. PP-PMF is more easily damaged by surface scratch & mar, thus limiting its acceptance for interior applications. This study investigates the scratch and mar mechanisms of talc-filled PP and the effects of various additives on the scratch and mar resistance of PP-PMF. Talc filler provides higher modulus for PP. The addition of nucleation agent and lubricant showed beneficial effects.
Observation and Characterization of Slow Crack Growth in Water Pipe Grade Polybutylene
Polybutylene (PB) piping has been widely used in portable water distribution systems. Premature brittle fracture constitutes the major limitation for PB in its application. The fracture process of PB consists the well recognized three stages: crack initiation, slow growth and fast propagation. In present work, the observations of crack initiation in service, fatigue slow crack growth (SCG) at elevated temperature, strain localization in front of the crack constituting the process zone (PZ) as well as variability of the strength of PB are reported.
The Time Dependency of the Necking Process in Polyethylene
Characterization and comparative analysis of necking phenomena in HDPE under load (creep) and displacement (ramp) control conditions are reported. For creep tests a simple exponential dependence of delay time to necking on the applied stress is observed. The applied stress and strain rate dependence of yield stress for both creep and ramp tests are presented.
Rheological Study of Soy Protein-Based PRF Wood Additives
The gelling of soy protein-based PRF wood adhesives is studied. Soy protein isolate, in combination with phenol resorcinol formaldehyde (PRF) resins is useful in the finger joining of lumber. This unique technology has several advantages including an ability to bond green lumber, very rapid set at room temperature, excellent water resistance, and reduced formaldehyde emissions. The goal of this study is to quantify the effect of soy protein hydrolysis conditions and amine functionality on the gelling and ultimate modulus of soy-derived wood adhesives.
The Effect of Fillers on the Properties of Rotationally Moulded Polyethylene
This paper describes the effects of talc and mica as fillers in rotationally moulded medium density polyethylene-MDPE. Adhesion between the filler and the matrix was enhanced using maleic anhydride modified polyethylene. Results show a clear increase of the modulus and in some cases an improvement in the tensile strength, but a decrease in the elongation and impact properties. Shrinkage of the moulded articles was reduced, and internal air temperature measurements show a reduction in the cycle time.
Computer Simulation of the Rotational Moulding of Plastics
This paper describes the development of a computer simulation for the rotational moulding of plastics. Two separate aspects of the process - the kinematics of the mould rotation and the heat transfer to the plastic powder - are modelled separately and then combined into a complete simulation. The simulation is capable of reading CAD files of real rotomoulded components, and variables such as speeds, speed ratios, material bulk density, etc can be set by the user. The program will then predict and display the wall thickness distribution in the moulded article.
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