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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A NEW FAMILY OF STYRENIC BLOCK COPOLYMERS FOR ELASTOMERIC FILMS IN PERSONAL CARE APPLICATIONS
Styrenic block copolymers are increasingly being used in the production of elastomeric films for personal care and hygiene applications. In recent years, with severe fluctuation on the supply side regarding availability and price for isoprene, butadiene, and styrene monomers, manufacturers and end-users of block copolymers have searched for ways to reduce their costs and maintain high levels of elastic performance. This paper introduces a new family of styrene-isoprene-butadiene-styrene (SIBS) quador tetra-block polymers to produce lower cost high performance products when compared to styrene-isoprene-styrene (SIS) copolymers. These new SIBS quad-block polymers are compared to triblock polymers with mixed isoprene-butadiene S(I/B)S structures.
A STUDY OF THERMALLY AND FLOW INDUCED RESIDUAL STRESSES IN INJECTION MOLDING
During the injection molding process, mold filling may introduce residual stresses. And the sequential cooling process may result in thermal stresses. Some cases show flow induced residual stresses dominate the final stresses. Sequential multi-component molding is one of good examples of thermal stresses. On the other hand, in the higher speed injection molding cases, higher shear stresses may be the major contribution to final residual stresses.In this study, both CAE simulation and real experiments will be conducted and compared for some cases. Specifically, how the polymer properties and process conditions affect the stresses and warpage will be discussed.
PROCESSING INTEGRAL-SKIN POLYPROPYLENE FOAMS UTILIZING EXTRUSION- ASSISTED DIRECT-FOAMING ROTATIONAL MOLDING
The extrusion-assisted direct-foaming rotational foam molding process maximizes the synergistic effects resulting from the recently-invented deliberate conjunction of extrusion melt-compounding and rotational foam molding aiming towards introducing timeand- energy efficient manufacture of integral-skin rotomolded foams. Multiple polypropylene (PP)-based foamable and non-foamable formulation combinations were subjected to a battery of planned experimental trials utilizing a custom-built industrial-grade lab-scale experimental setup. The obtained foam morphologies were characterized in terms of foam density, average cell size, and average cell density.
A NEW ELECTROMAGNETIC DYNAMIC MICROCELLULAR FOAMING TECHNOLOGY FOR PP/HDPE BLENDS
Polypropylene (PP) has poor foamability because of its low melt strength and high crystallinity. To obtain fine microcellular foams, a new electromagnetic dynamic microcellular foaming technology was used in this paper. A dynamic shear in the axial direction induced by the rotor vibration was vertically superposed on the melt flow direction, and its effects on the microcellular foaming process and cell structure were investigated theoretically and experimentally. The results showed that the shear rate and melt strength enhanced as the vibration amplitude and frequency increased, which led to great improvement of the foamability and ultimate microcellular structure.
STATISTICAL MODEL PREDICTING WATER VAPOR TRANSMISSION RATES OF HIGH-BARRIER-COATED PAPERS
Moisture barrier properties of extrusion-coated papers including EVOH-layer were investigated. The moisture barrier of EVOH is considerably compromised in the presence of moisture because the highly polar water molecule tends to hydrogen bond with the EVOH polar groups followed by plasticization of the polymer. To prevent the moisture effect the EVOH-layer is typically covered with a non-polar skin layer. In addition to its own barrier the skin layer improves the barrier of EVOH by decreasing its moisture concentration. This study introduces a practical model that estimates water vapor transmission rates (WVTR) of high-barrier-coated papers with an extrusion-coated EVOH-layer. The skin layer effect is taken into account when the WVTR is estimated as a function of coating structure at specific atmospheric conditions.
STATISTICAL MODEL PREDICTING WATER VAPOR TRANSMISSION RATES OF HIGH-BARRIER-COATED PAPERS
Moisture barrier properties of extrusion-coated papers including EVOH-layer were investigated. The moisture barrier of EVOH is considerably compromised in the presence of moisture because the highly polar water molecule tends to hydrogen bond with the EVOH polar groups followed by plasticization of the polymer. To prevent the moisture effect, the EVOH-layer is typically covered with a non-polar skin layer. In addition to its own barrier, the skin layer improves the barrier of EVOH by decreasing its moisture concentration. This study introduces a practical model that estimates water vapor transmission rates (WVTR) of high-barrier-coated papers with an extrusion-coated EVOH-layer. The skin layer effect is taken into account when the WVTR is estimated as a function of coating structure at specific atmospheric conditions.
INFLUENCE OF PULSATILE PRESSURE INDUCED INJECTION MOLDING ON PARTS PERFORMANCE
A self-made pulsatile pressure induced injection molding machine was adopted to explore the relationship between mechanical property and morphology for low-density polyethylene injected moldings. The main processing variables for pulsatile pressure induced injection molding are vibration frequency and vibration pressure amplitude. The experimental results show that the weights of the parts increased with the introduction of pulsatile pressure. The mechanical properties improved. The melt peak became wider and the melt point moved to high temperature with the increase of piston rod vibration amplitude/frequency.
DEVULCANIZATION OF RECYCLED TIRE RUBBER CRUMB WITH SUPERCRITICAL CO2: CURING BEHAVIOR MECHANICAL PROPERTIES AND DEGREE OF DEVULCANIZATION
In this work the devulcanization of tire rubber crumb was studied by using an industrial scale twin screw extruder. A reasonably high throughput extrusion process has been developed and the effect of processing conditions has been studied. The effects of different screw configurations screw speed and feed rate on the stability of process have been investigated. Crosslink density and percent of devulcanization of different samples are measured. Curing behavior tensile strength and elongation at break of different compounds consisting of blends of virgin rubber with devulcanized crumb have also been evaluated.
DEVULCANIZATION OF RECYCLED TIRE RUBBER CRUMB WITH SUPERCRITICAL CO2: CURING BEHAVIOR, MECHANICAL PROPERTIES AND DEGREE OF DEVULCANIZATION
In this work the devulcanization of tire rubber crumb was studied by using an industrial scale twin screw extruder. A reasonably high throughput extrusion process has been developed and the effect of processing conditions has been studied. The effects of different screw configurations, screw speed and feed rate on the stability of process have been investigated. Crosslink density and percent of devulcanization of different samples are measured. Curing behavior, tensile strength, and elongation at break of different compounds consisting of blends of virgin rubber with devulcanized crumb have also been evaluated.
NATURAL FIBER REINFORCED THERMOPLASTIC FOAMS A NEW MATERIAL GROUP FOR LIGHTWEIGHT STRUCTURES
Injection molding of thermoplastic foams is not new, e.g. /1 4/. Nevertheless it is well known, that the tensile properties are decreasing due to the weakened cross section of a stressed foamed structure. Putting glass - fibers into the compound to compensate this disadvantage means an increasing weight. A part of the lightweight performance will be lost. A solution could be, to take natural fibres as reinforcement for thermoplastic foams to compare this disadvantage. The main task of the recent studies was to foam compounds made of different natural fibers and polypropylene. Blowing agents of different producers have been taken to process the polymer specimen. The results of the material tests show that composites made of natural fiber foam have a potential to become a suitable material for lightweight constructions.
CHARACTERIZATION OF PE RESISTANCE TO RAPID CRACK PROPAGATION
A small-scale test methodology for the determination of plastic pipe resistance to rapid crack propagation (RCP) is proposed. Like the full-scale and S4 tests, this test determines the critical pressure (pc) and transition temperature (Tc) of RCP. At the same time it is an inexpensive and safe small-scale alternative to the standard tests. The internal pressure in the proposed test is kept constant with practically no decompression. Therefore the pressure and crack length involved in the evaluation of dynamic toughness of material are directly measured at the crack arrest. Thus it allows for the evaluation of the material resistance to RCP (dynamic toughness) in terms of the energy release rate (ERR) at crack arrest, in addition to the determination of pc and Tc. Applications of the proposed characterization of the RCP resistance for PE-100 are discussed.
TEMPERATURE EFFECTS ON SLOW CRACK GROWTH IN PIPE GRADE PE
Temperature strongly affects the mechanical properties of pipe grade polyethylene (PGPE), such as strength and toughness. It is observed in this study that the temperature also affects the mechanisms of slow crack growth (SCG). A change in the mechanism of SCG is observed at certain temperature, named Crack Growth Transition Temperature (CGTT). The CGTT of the cold drawn (oriented) PGPE appears to be significantly higher than room temperature. At the temperature above CGTT the crack propagates discontinuously, stepwise, whereas at the temperature below CGTT the crack grows continuously. The slope of crack growth rate vs. stress intensity factor (SIF) is also noticeably different for temperatures above and below CGTT. The existence of CGTT implies certain limitations for commonly used extrapolation of SCG and lifetime data from the elevate temperature of an accelerated testing to the room temperature across CGTT.
NEW MODEL AND METHOD FOR THE DETERMINATION OF THE THERMAL DIFFUSIVITY IN SEMICRYSTALLINE POLYMERS UNDER DIFFERENT PROCESSING CONDITIONS IN INJECTION MOLDING
The most recent results for the measurements and modeling of thermal diffusivity of thermoplastics under injection molding conditions are presented. The method is based on the inverse numerical solution of the differential equation that describes the cooling process of the injected part. The effect on the thermal diffusivity of different cooling rates across the thickness of the injection part the cavity pressure the thickness of the part the wall temperature of the mold and the melt temperature were investigated and included as parameters in the improved mathematical model for the description of the thermal diffusivity. The model was validated for polypropylene in a wide processing window.
CLOSED LOOP CONTROL IN LASER WELDING OF PLASTIC COMPONENTS
A new laser welding process that uses a real time closed loop control system of the process by monitoring thermal emissions directly from the weld region. These emissions are captured, measured, interpolated, and thus correlated to a known temperature. The process has been applied on laser welding a test box molded from thermoplastic PBT material, Ultradur B4300G6.Robustness of the process and the quality of the weld joint is evaluated by performing burst testing of the welded boxes, after welding the box samples at various surface temperatures. The experiment has identified optimum surface temperature regime for laser welding a material for a given weld section design. Microscopy study shows microstructure of good weld joint and poor weld joints
IMPACT OF CRIMS DATA ON THE ACCURACY OF MOLDFLOW WARPAGE PREDICTION
This paper evaluates several simulation approaches in Moldflow, including the use of CRIMS (Corrected Residual In-Mold Stress) data, to better predict warpage in injection-molded parts. The evaluation includes a simulation matrix in which warpage is predicted by part geometry, process conditions, material and simulation method. In addition, selected injection-molded parts are scanned at high resolution to gather actual 3-D warpage data. The paper additionally describes novel methods for making comparisons between the predicted and actual data sets within an interactive CAV environment to determine the effectiveness of CRIMS.
PREDICTION OF PE LONG-TERM CREEP PROPERTY AND LIFETIME IN DUCTILE FAILURE BASED ON SHORT-TERM TESTS
A large number of different formulations of PE have been tested in load (creep) and displacement controlled (ramp) conditions. A certain symmetry (ƒ??mirror reflectionƒ?) between the stress ?Ÿ vs. log ?æ‹?? in ramp and creep tests and the stress ?Ÿ vs ductile failure tf in creep is observed. A procedure for prediction of PE long-term creep behavior and lifetime in ductile failure based on ramp and a short-term creep tests is formulated. The procedure employs Eyringƒ??s model for connecting stress, strain rate and temperature in yielding combined with the observed symmetry. A theoretical basis for the procedure and its experimental validation is presented.
A NEW MECHANISM FOR FLAME RETARDED, NON-HALOGEN WIRE AND CABLE COMPOUNDS
The use of mica as a filler to produce fire resistant tapes for the wire and cable industry is well known. Mica, which is a platelet inorganic filler, promotes the safety and integrity of electrical circuits under fire conditions by an exfoliation mechanism in which the cable is protected from the heat of the flame by the formation of an inorganic thermal insulation barrier. This insulating barrier is formed by the exfoliation or expansion of the mica filler under fire conditions.Unfortunately, mica can be difficult to process and is prone to premature exfoliation during extrusion wire coating.This paper presents the utilization in wire jacketing applications of a unique intumescent coating technology long used to protect steel beams during fire conditions. This technology uses organic components that intumesce and form a carbonaceous, non-flammable char in a fire environment. This char composition has sufficient physical integrity to prevent flaking off and provides thermal insulative protection. This new flame retardant technology is much easier to process than mica, is cost effective, and is efficient enough to formulate nonhalogen, flame retardant, polyolefin based jacketing compounds without sacrificing fire resistance performance
THERMAL STABILIZATION OF BIODEGRADABLE POLY-HYDROXYBUTYRATE (PHB) IN MELT EXTRUSION PART 1: POLY-OLIGOMERIC-SILSESQUIOXANE
Poly-Oligomeric-Silsesquioxane POSS nano modifier was examined as a thermal stabilizer for PHB.Melt compounding of Poly-Hydroxy-Butyrate PHB copolymers with different POSS moieties was performed.Reactive and non-reactive POSS nano modifiers were used. The effect of modification on PHB thermal stability was evaluated by changes in rheology and molecular weight. POSS modifiers with unique core-shell structures were found to significantly reduce the loss in molecular weight during melt mixing possibly by decreasing viscous-heating effects.
PREDICTION OF POLYPROPYLENE LONG-TERM CREEP BASED ON A SHORT-TERM TESTING
A method for prediction of polypropylene long-term creep behavior is proposed based on mirror symmetry between stress vs strain rate in ramp tests and stress vs. ductile-failure-time tf in creep. Such methodology has been previously proposed for polyethylene on the basis of power law creep behavior of polyethylene. Here we use more general approach based on Zhurkov-Eyring model that relates strain rate, stress and temperature with help of parameters having physical meaning such as activation energy of the process. The prediction of long-term creep of polypropylene is made based on the tensile ramp tests with variable strain rate and a short-term tensile creep testing. An analysis of the proposed methodology in view of the set of experimental data is presented. Validation of long-term creep predictions based on the short-term testing by comparison with conventional long-term creep data is discussed.
EVALUATION OF ENVIRONMENTAL STRESS CRACKING RESISTANCE IN POLYETHYLENES: BENT STRIP VS. CONSTANTTENSILE- LOAD METHODS
For a group of 14 polyethylenes (PE) with different densities (0.924 to 0.966 g/cm3) and melt flow index MFI (0.38 to 42 dg/min) the Environmental Stress Cracking Resistance (ESCR) of each PE was determined by the typical method of bent strip or ESCR at constant strain. The results were compared with those obtained by the evaluations of ESCR by constant-tensile-load method. For both methods the effects of the density and MFI on ESCR were similar and in agreement with those reported in the literature. However the failure time spread measured in the ESCR at constant load is smaller although both methods lead to high experimental errors attributed to limitations or omissions in the experimental protocols described in the standards used for these measurements.
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