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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Supercritical Carbon Dioxide Assisted Polymer Blending in Twin-Screw Extrusion: Relations between Morphology Evolution and Mechanical Properties
Supercritical carbon dioxide (scCO2) was added during compounding of polystyrene and poly(methyl methacrylate) (PMMA) and the resulting morphology development was observed. The compounding took place in a twin screw extruder. Viscosity reduction of PMMA and polystyrene were measured using a slit die rheometer attached to the twin screw extruder. Carbon dioxide was added at 0.5, 1.0, 2.0 and 3.0 wt.% based on polymer melt flow rates. A viscosity reduction of up to 80% was seen with PMMA and up to 70% with polystyrene. A sharp decrease in the size of the minor (dispersed) phase was observed near the injection point of CO2. However, further compounding led to coalescence of the dispersed phase. De-mixing of the dispersed phase occurred upon CO2 venting. The resulting morphology was similar to that without the addition of CO2. Adding small amounts of fillers (e.g. carbon black, calcium carbonate, or nano-clay particles) tended to slow down the de-mixing of the polymer blend system when the CO2 was released. The comparison of morphology and mechanical properties for various polymer blends with and without CO2 considerations will be reported.
The Effect of Varying Injection Molding Conditions on Cavity Pressure
Obtaining high quality parts in injection molding requires the understanding of the many interactions that exist between the molding parameters. Cavity pressure and part mass are good indicators for maintaining high product quality and obtaining good machine control performance. The effect on cavity pressure and part mass was investigated by varying the molding conditions using a two-phase screw-plunger injection molding machine. The molding parameters that were perturbed included the barrel temperature, injection velocity and hold pressure. The results provided a good understanding of the effect of changing the molding conditions on cavity pressure and part mass for a two-phase injection machine.
Surface Analysis of Polymeric Materials: Roughness Exponent
The self-affine behavior of fracture surfaces of polypropylene, PP, and polystyrene, PS, were analyzed applying the variable bandwidth method to the height profiles generated with an atomic force microscope, AFM. The roughness exponent, ?, obtained with this method was 0.788-0.008 for PP samples and V=0.81-0.023 for PS. These results are in very good agreement with the claimed universal value of V=0.8 reported in the literature for other non-polymeric materials. Melted PP was crystallized following two different cooling rates and the crystalline surfaces were also analyzed, obtaining similar roughness exponents. This fact probably means that, for this case, the self-affine behavior could be independent of the crystallization rate.
Morphology and Thermal Loading in Laser Welding of Thermoplastics
Laser welding, an innovative, flexible technology for joining of thermoplastics, now starts to make its way from scientific laboratories into industrial series production. There has been intense research on weld strength de-pending on polymer, butt design, fillers and absorption behavior. Nevertheless, a considerable lack of knowledge concerning the fundamental relationship between the process and its influence on thermal loading of the weld plane and resulting morphology still exists. Actual results of laser transmission welding experiments - including thermal and microscopic analysis of the weld plane - could contribute to a better understanding of the process itself and to success in practical applications.
Temperature Calculation of Plastic Gears
Plastic cog-wheels may run completely without lubricants. When using plastic cog-wheels a service life dependent on the application is to be guaranteed. Because the service life of the cog-wheel is limited by the wear of the flank of the cog-wheel, the specification of the wear is required for dimensioning plastic gears. Caused by frictional processes at the surface of the cog, heat is produced. Like the mechanical properties of plastics, the wear also strongly depends on temperature. Therefore, it is necessary to determine the temperature of the cog. Plastic gears are tested and the cog temperature is measured by means of a thermal camera. Polyacetal cogwheels with a modulus of 1 mm are examined. It will be shown, that the cog temperature can be calculated on the basis of heat balances with a known coefficient of friction.
Polymer Melt Flow Behavior in the Coinjection Molding Process
An experimental study of the co-injection molding process was carried out. The fingering instability due to the difference in viscosities of the two materials gave rise to early breakthrough of the core material and non- uniform skin layer thickness. The core material was also used as tracer material for flow visualization of the injection molding process. The V formation near the wall as well as the mushroom effect, previously predicted, was observed.
Improving Polyethylene Performance - The Use of Metallocene Catalysed Polyethylene in Injection Moulding
A range of medium density, metallocene catalysed polyethylenes (mPEs), and conventional polyethylenes (PEs) were injection moulded using different mould cooling conditions. The results for the metallocene polyethylenes show significant improvements in impact and tensile performance. Increases of over 200% in tensile elongation for metallocene PE resins over the conventional PE resins were recorded. D.S.C. analysis shows the metallocene PE resins to be more crystalline in nature than the conventional polyethylenes.
Orientation Recovery in Biaxially Oriented Amorphous Polymer Films
The dimensional recovery of biaxially oriented polystyrene and high impact polystyrene films was found to follow dual second order kinetic processes that took place in parallel. The early stage of the recovery involved major dimensional changes with a high rate constant and is likely related to the recovery of main chain orientation. The later stage process gave smaller dimensional changes with a low rate constant and is not directly related to the main chain orientation. This study indicated that the orientation in amorphous polymer films could be examined by understanding the kinetics of thermal recovery.
On-Line Material Characterization during Extrusion of Recyclates
Unknown properties of recycles are the problem in the field of recycling thermoplastics. The off-line determination of selected properties (basicpolymer, colour and mechanical properties) is not sufficient to qualify recyclates. Important for the characterization is an almost complete knowledge of the material properties when producing recyclates that are supposed to be competitive as construction materials. Therefore the implementation of tools for the detection and assurance of material properties on-line during extrusion is a promising conception. This presentation shows and discusses the basic ideas of on-line property determination, the achieved results of material determination, and the resulting process control.
Evaluation of the Interfacial Tension between a Low Molar Mass Liquid Crystal and Solid Polymers
The surface tension of a low molar mass liquid crystal (LMMLC) was measured as a function of temperature (56.0°C to 79.5°C), using the pendant drop method. The surface tension presented a behavior described by two distinct curves for the different phases (isotropic and nematic). Also the contact angles of LMMLC on plates of PS and of a liquid crystal polymer were measured at different temperatures (from 62.4°C to 89.0°C). The angle presented a discontinuity nearby the nematic to isotropic transition temperature when measured on PS, whereas it remained constant on the LCP. The interfacial tension between the LMMLC and the polymers were estimated.
Influence of Process Parameters on the Phenomenon of Stress Cracking during Hot Plate Welding
Heating experiments were carried out in order to investigate the significance of the different process parameters on susceptibility to stress cracking. With the help of wetting tests, different crack lengths were generated in the heated sheet and subsequently compared with the various process parameters by means of multiple regression analysis. Another focal point is the estimation of the normal stress difference (?x – ?y) at each point of the specimen by means of 2D photoelastic stress analysis. In both cases the marked correlations between the process parameters and the phenomenon of stress cracking are recognisable, and the results can be used to minimise stress cracking.
Structure-Property Relationship in Poly(phenylene sulfide)(PPS)/Polyethylene Blends-Effect of Metallocene Catalyzed Polyethylene
In this investigation, blends of poly(phenylene sulfide)(PPS) with two types of polyethylene such as linear low density polyethylene(LLDPE) and metallocene catalyzed polyethylene(MPE) were prepared by melt blending. First, rheological behavior was determined using a capillary rheometer. The melt viscosity of PPS/LLDPE and PPS/MPE blends was low when PE was a dispersed phase. However, when PPS was a dispersed phase, increased melt viscosity was observed. This tendency was similarly observed in mechanical properties such as percent strain at break and notched Izod impact strength. Also, the mechanical behavior of PPS/LLDPE and PPS/MPE blends showed negative deviation from the rule of mixtures relationship when PE was a dispersed phase. But the negative deviation for PPS/MPE blend was less than that for PPS/LLDPE blend. Also, the dispersed phase morphology was analyzed using scanning electron microscope(SEM).
Factors Influencing the Sorting Efficiency of Commingled Post-Consumer Bottles Using an Automated Sorting System
This paper examines the effects of high throughput rates in a spectroscopic bottle sorting system, on the purity of PET and HDPE end-products as well as other key factors such as an increase in material loss, decrease in % material yield and the need for extra manual sorting staff at higher throughput rates. Increasing the throughput rate of a wide belt bottle sorting system from 1,000 kg/hr to 2,000 kg/hr decreased the purity of HDPE by 17% and that of PET by 2%. Material loss had more then doubled for PET from 12% to 32% and for HDPE increased from 8% to 9%. The end-product yields for HDPE and PET had decreased by 3% and 8% respectively. One of the key improvements to the sorting operation was the development of an automated sensor cleaning system, which uses an automated film rotating mechanism.
Relative Dimensional Change of Various Nylon Products Due to Moisture Absorption
In plastic materials published data, moisture absorption is almost always expressed in terms of percent weight gain. While this information is important for comparison purposes, it doesn't truly relate to the design engineers' application and use of these materials. This study will quantify and compare the relative dimensional changes which occur in parts as they are exposed to a humid environment and move from the dry-as-molded state toward saturation using nylon types 6, 66 and 46.
Effects of Various Fillers on the Coefficient of Thermal Expansion of Epoxy Resins
It has long been recognized that the predictive ability of the rule of mixtures for coefficient of thermal expansion (CTE) is less than desired. It ignores the elastic interaction and restraint between the matrix and the filler, hence yielding values that are too high. The predictive ability of the rule of mixtures and three other theories are compared to actual measured CTE values of over 90 particulate filled epoxy formulations. It has been found that the Kerner theory can predict the CTE within 8 ppm/°C at the 95% confidence interval for the epoxy systems evaluated.
Injection Molding Cycle Time Reduction Using an Advanced PC/ABS Blend
An advanced PC/ABS blend has been developed offering reduced cycle times for injection molding applications, and thus creating economic value for the molder. This material has improved flow as compared to traditional PC/ABS blends, yet it is designed for high toughness. The results of molding trials demonstrate injection pressure and melt temperature can be reduced, ultimately resulting in reduced cycle time and improved manufacturing cost. Physical properties and desired part performance criteria, such as heat resistance and low temperature ductility, are maintained.
The Development of Weld Line Strength in Injection-Molded Poly(methyl methacrylate)
An experimental investigation has been conducted to evaluate various approaches to modeling weld line development during the injection molding of amorphous plastics. A series of poly(methyl methacrylates) (PMMA) representing several different molecular weights were molded both with and without weld lines over a range of processing parameters. Results were compared with the predictions of several previously proposed isothermal models. These were found to be insufficient to explain all the phenomena observed. A non-isothermal model is developed to provide an improved predictive capability. This non-isothermal approach combined with fracture mechanics leads to a new physical interpretation of weld line morphology and its contribution to the resultant strength of the welded part.
Rheological Characteristics of Polymer Blends
This work presents an experimental observation of the rheological characteristics of the TPE/SB blend (Thermoplastic Elastomer / Styrene-Butadiene) used in the plastic transformation industry for medical applications. The flow curves (shear viscosity x shear rate) of the blend were investigated at different temperatures and in a wide range of shear rates. During the extrusion, the instability phenomenon (melt fracture) and its relation with the shear rate and temperature parameters was also investigated. All the experiments, the flow curves and melt fracture observation, were performed in a Capillary Rheometer ( a Rosand Rh-2100 capillary rheometer) working with a 1 x 16 mm rod capillary die.
Evaluation of Liquid Gas-Assisted Injection Molding
Gas-Assisted injection molding has been applied successfully in plastic industry within last 10 years. Liquid gas-assisted injection molding (LGAI) is a good alternative of conventional gas-assisted injection molding process. In LGAI process, a liquid is injected under low pressure into the melt stream. The liquid vaporizes and pushes the melt downstream and creates hollow channels within part. HELGA® patents this process originally. We had evaluated this process with different-type molds and liquid nozzles that we develope. Finally, we compared the LGAI process to the conventional gas-assisted injection molding process.
Surface Enrichment in Polymer Blends Involving Hydrogen Bonding
Poly(4'-hydroxyl-4-ethylphenylsiloxane)(PHEPS) has been synthesized via hydrosilylation followed by hydrolysis. This polymer, hydrogen bonding donor, was blended with three kinds of hydrogen bonding acceptors that include poly(4-vinylpyridine) (PVPy), poly(acrylonitrile) (PAN) and poly(ethylmethyacylate) (PEMA). The surface enrichment with PHEPS, which has lower surface energy, was characterized by X-ray Photoelectron Spectroscopy (XPS). The effect of the strength of hydrogen bonding interaction on the surface compositions of the blends was studied. The results showed that surface enrichment in miscible polymer blends was responded to the balance between the differential in the surface energy of the constituents and the bulk enthalpic interactions.
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