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.
It has been known for many years that both types of acetal plastic are susceptible to oxidative attack, or stress corrosion cracking (SCC) when in contact with chlorine. It was thought that high levels (>30ppm) of free chlorine in cold water are needed to initiate attack, so that acetal injection moulded fittings could be used quite safely in potable water supplies where free chlorine levels are very much lower (<1 ppm). The case study to be described here of a fracture in a water supply which caused substantial damage, indicates that attack probably can occur at such levels, especially if the fittings exhibit extensive weld lines near stressed zones. High chlorine concentrations can arise due to chlorine surges in the water supply, especially when the water company overdoses the supply after a major leak.
The molecular structure of randomly branched polymers is understood using percolation theory. Once the chain length between branch points and the extent of reaction relative to the gel point are specified by synthesis, both the molecular structure and the linear viscoelastic response can be determined using simple models. We demonstrate these ideas using randomly branched polymers with known chain lengths between branch points. Then we exploit this finding to characterize the chain length between branch points for polyethylenes from knowledge of their weight-average molecular weight and zero-shear-rate viscosity.
This paper presents a finite element algorithm for solving gas-assisted injection molding problems. The solution of the three-dimensional (3D) equations modeling the momentum, mass and energy conservation is coupled with two front-tracking equations, which are solved for the polymer/air and gas/polymer interfaces. The performances of the proposed procedure are quantified by solving the gas-assisted injection problem on a thin plate with a rib. Solutions are shown for different ratios polymer/gas injected. The effect of the melt temperature, gas pressure and gas injection delay, on the solution behavior is also investigated. The approach is then applied to a thick 3D part.
This paper presents a finite element algorithm for solving polymer injection molding problems. The methodology consists in solving for the three-dimensional (3D) equations modeling the momentum, mass and energy conservation. The packing and cooling stages of the injection molding process are modeled by including the compressibility effects. The procedure is aimed by problems in which three-dimensional effects are important but is also effective for thin parts. The performances of the proposed approach are quantified for the injection of a thin plate for which experimental data are available. The procedure is then applied to a thick 3D part. The method results in accurate solutions and it proves to be a useful tool to quantify the solution behavior on cases otherwise difficult to investigate.
A process has been developed to compact fillers commonly used in plastics to improve mechanical properties - mica, nanoclays and wollastonite -and flame retardance - magnesium and aluminum hydroxides. Such fillers are produced in very fine particle size or high aspect ratio. They are fluffy, entraining much air, which must be removed. Aerated fillers do not flow well and require special feed devices. Voluminous filler takes up machine capacity, limiting the production rate of filled compounds. Entrained air reduces thermal conductivity and thus the flux rate of the polymer. Compaction improves the handling, feeding and incorporation rate of such fillers into compounds.
It is already known that the use of Boron Nitride (BN) in the extrusion of molten polymers may eliminate surface melt fracture and postpone the critical shear rate for the onset of gross melt fracture to significantly higher values depending on resin type and additive content. In this work several new Boron Nitride powders (Carborandum Co.) are tested that exhibit superior behavior from the previous studied ones. Critical parameters for this unique behavior (elimination of gross melt fracture) are good dispersion, small average particle size and free of agglomeration. The equipment used for the testing of the new powders include both an Instron capillary rheometer with special annular dies (Nokia Maillefer wire coating crosshead) attached to the rheometer, and a parallel-plate rheometer. A metallocene polyethylene with all types of boron nitride is tested at various additive concentrations. The additive having the finest particle size and that is free of agglomeration was found to have the greatest influence on the gross melt fracture performance of the polymer tested in crosshead dies and tips. Moreover, one of the additives was found to enhance melt slippage and as a result relieved internal shear stresses. This action is believed to eliminate surface melt fracture and postpone the critical shear rate for the onset of gross melt fracture to significantly higher values depending on the additive concentration. The influence of the boron nitride type and its concentration on the polymer rheology is also discussed.
Light stabilization of polyamides for automotive applications remains a challenge. In this paper various stabilization systems (hindered amine light stabilizer, antioxidant, phosphite) were evaluated in black and white glass-filled nylon-6. The properties being examined were color change and gloss retention of injection molded plaques during exposure in a xenon arc weatherometer under exterior automotive conditions per SAE J1960 and interior automotive conditions per SAE J1885. Light stabilization systems meeting the interior automotive requirements were identified.
Pressure dependent viscosity and juncture loss were measured by means of a new capillary rheometer developed at pressure up to 100 MPa and over wide shear-rate range from 5.0E+02/s to 5.0E+05/s for four polymer melts (HDPE, GPPS, HIPS, and PC) through simultaneous measurement of pressure at the entrance and exit of the capillary during applying counter pressure to the exit by means of a needle valve located in the downstream. Pressure dependent viscosity and juncture loss play an important role to improve the accuracy of simulation with a CAE program. However, there are few data in high shear-rate range corresponding to actual molding. Pressure loss in the flow path increases unexpectedly with increase of hydraulic pressure applied. The most adequate equation for fitting viscosity seems to be the Cross-WLF equation. The magnitude of the pressure parameter D3 lies in the range of 10E-07 K/Pa for these polymers.
Using a special tool designed with the purpose to visualize the melt flow across the thickness dimension of the mold cavity [l], an experimental investigation was made to assess the polymer melt behavior in specific processing conditions. The aim of the work is to visualize some unexpected flow front behaviors in the selected injection molding conditions. The design of the mold enables to adjust the location of a special glass window along the material flow path. The mold feed is based on a hot runner system. The results presented are direct visualization images of the melt front.
Today's conditions in business activities, only short-term planning possibilities, necessity for everyday adaptation to situations within the company, require new organisational forms, new ways of managing the companies and, in a way, new people. Since today's companies are the target of constant selection, comparable to the one in nature, and their environment is unpredictable, it is no wonder that knowledge acquired by natural sciences is being increasingly implemented in the field of organisation. Modern business conditions have forced the managers to search for similarities with those scientific fields that have just begun to develop, and that try to establish some kind of order in the haphazard phenomena. Recognising similarities between the world of nature and an enterprise have led to the creation of numerous new organisational concepts, which have found their application also in plastic companies.
This paper investigates the use of a Helical Barrel Rheometer to measure the viscosity of filled polymer systems. A Helical Barrel Rheometer is an online rheometer developed at the Polymer Processing Institute. The HBR allows us to measure the viscosity of polymer systems under conditions close to that encountered in processing. The viscosity measurement does not require measuring either the torque or the flowrate. The rheometer does not require an entrance correction, avoids bridging of filler particles during measurement and also takes care of the orientation of fillers encountered in processing. This paper uses polypropylene/talc as a filled polymer system. Three different concentrations of three different grades of talc were used to measure the viscosity and a comparison with conventional capillary viscometer was made.
Hot water plumbing applications can often be a severe environment for both metals and plastics. Continual exposure to elevated temperature as well as the oxidative effects of disinfectants such as chlorine can reduce the lifetime of plumbing components. A study was recently conducted to determine the potential degradation effects of hot chlorinated water on several engineering thermoplastics. Weight loss, tensile strength and elongation properties, burst strength retention and microscopy were used to examine the material behavior as a function of exposure time. This data will provide a basis for determining which engineering thermoplastics will be suitable for long-term exposure in hot, potable water.
Since the first measurements of the reduction of the glass transition of small molecule liquids in nanometer pores, there has been an increasing number of studies of the effects of size and confinement on the glass transition of both small molecules and polymers. The measurements coming from different groups often give apparently conflicting results. This paper surveys the state of the field and provides insights into possible reasons for the apparent discrepancies that suggest paths for further investigation.
Screw design is often the main factor in polymer processing equipments to achieve better quality products or higher outputs. This work presents a new screw design tool based on the use of extrusion softwares and statistical methods that provides a reliable basis for screw design. This method is versatile, not time consuming, and can be applied to many cases in the plastic industry. A specific case in the field of PVC profile extrusion is discussed in detail. Experiments support the new screw design proposed for this application.
Acrylic Acid (AA) was grafted onto LDPE to modify its properties by reactive extrusion process. In this study, a co-rotating twin screw extruder and Banbury were mainly used for the reactive grafting process. By changing the configuration of the screw elements, different degrees of shearing effects gave various degree of grafting. It was found that the ratio of LDPE/AA/DHBP=100/10/0.5 with a medium shearing in the extruder gave an optimal result, and the ratio of grafted AA was 4.7%, which was measured via a standard titration process.
Polypropylene tensile bars were hot plate welded and analyzed by microscopy and mechanical tests. The welding process originated deep modifications in the microstructure and shape of the bars at the weld zone. It was observed that the weld morphology was affected not only by the welding parameters but also by the thermal history of the components. The occurrence of oriented textures, coarse spherulites, voids or sharp notches at the beads are determinant morphological factors on the weld quality. The performance of the welds is dependent on the type of testing method used. The tensile impact test showed to be potentially good for quality control, as the fracture behavior was affected by the overall morphology.
Elastomeric Thermoplastic (ETP) is a patented alloying technology that utilizes ethylene copolymer resins to modify flexible thermoplastic polyolefin (TPO) systems. It is based on the reactive blending of a partially neutralized acid copolymer (ionomer), an epoxy functionalized ethylene copolymer, and a standard TPO. The reaction between the epoxy groups of the ethylene copolymer and the free acid groups of the ionomer results in a partially cross-linked system that forms an in-situ alloy with the TPO. This alloy imparts increased melt strength to the TPO, permitting significant increases in thermoforming performance and grain retention. By varying the amount and type of Surlyn® ionomer within the alloy, a desired mix of mechanical properties, forming performance, and hand can be obtained. As the automotive industry moves toward developing interior components based on thermoplastic polyolefins (TPOs), this ability to customize a TPO-based material for specific applications provides a key advantage for the design engineer. For example, instrument panel skins can now be produced with reduced weight, reduced fogging, and better resistance to heat and UV radiation relative to PVC/ABS, but yet possess the ability to undergo deep draws during thermoforming while maintaining grain definition. Alternatively, formulations have been developed specifically for molded-in-color injection-molded soft-touch surfaces, which require a different balance of melt behavior and physical properties. In this study, we report on the relationship between ionomer content and physical properties in ETP modified TPO systems. The effect of incorporating an ionomer containing a softening acrylate comonomer on the feel" of the modified TPO material as quantified by flexural modulus and durometer is also discussed."
Usage of Thermoplastic Olefin (TPO) is a common trend for automotive interior parts. TPO is a copolymer of Polypropylene (PP) and Polyethylene (PE) for rubber constituent and the TPO evaluated contains 20% of talc. Considering the facts that PP and PE are semi-crystalline thermoplastics with high molecular weight and that TPO contains rubber, talc, and reground material, weldability of the material has been always in question. Especially since the ultrasonic welding process deploys several tens of microns of vibration amplitude for welding, energy from ultrasonic vibration can be dissipated easily before effective heating of materials for welding. Therefore, evaluation of material weldability is an important requirement for material selection.
The mechanical properties of injection molded parts in glass reinforced materials is sensitive to processing. A successful design requires a good estimate of performance before production. The product performance is strongly affected by the fiber orientation field. It is complex and varies tri-dimensionally in the moldings. Some commercial simulation programs already allow the prediction of the fiber orientation induced by the injection flow. However the simulations depend on the definition of the fiber interaction coefficient. C-Mold simulations were made to determine the best fit to experimental results varying the interaction coefficient between neighboring fibers in center gated circular flat discs.
Searching for an advance in mechanical performance, two monomers of high functionality with different spatial structure, were used in this study to crosslink a general purpose reinforced unsaturated polyester resin. Varying the concentration of Divinyl benzene (DVB) and 1,6 Hexanediol diacrylate (HDDA), different crosslinking structures and properties are expected.
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