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.
The sandwich injection molding technique can be used in wide range of engineering applications. In this study, the developing behavior of core materials and break through phenomenon in the sandwich injection molding was investigated. The samples were preferred using a spiral-flow mold by changing the viscosity ratio and the melt temperature of skin and core materials. Developing behavior of the materials in sandwich injection moldings divided four regions, and it is noted that core material tends not to completely penetrate through the skin material at a stretch point, and it resulted in break through phenomenon. It is considered that break through phenomenon depends on the melt strength of the freezing layer of the skin material at flow front.
Interface construction is very important in the design of composite materials. Composites that consist of same materials but different shape such as fiber shape and matrix phase can create high interfacial strength. Call this composite Interface-less Composites". In this study knitted fabric was chosen as reinforcement configuration which has good drapability expandability and high productivity. Knitted polyethylene (PE) fiber reinforced PE film (PE/PE composite film) by film stacking method was prepared. Injection molding specimens were prepared by inserting this PE/PE composite film and PE was injected as matrix. Tensile properties of Interface-less composites by using injection-molding method were investigated."
The damage mechanisms in uni-weave/satin-weave hybrid IM7/BMI composites under uniaxial static tension loading have been investigated. The results reveal that hybridization effects on the damage mechanisms largely depend on the degree of waviness. For low waviness composites, the damage process is not affected significantly by hybridization. The damage patterns in the woven and hybrid composites are similar to those found in tape laminate. However, the large waviness composites exhibit complex damage behavior. Hybridization has a significant effect on the damage process.
The interfacial structure and mechanical properties of polypropylene (PP/PP) composites consisting of homo-PP fiber and propylene-ethylene random copolymer matrix were investigated. In PP/PP composites, the transcrystalline structure grows on PP fiber, which influences the mechanical properties. The two types of unidirectional PP/PP composite with different impregnating system were fabricated. In the well impregnated PP/PP composites, there were many transcrystalline layers, and the tensile modulus and strength were higher than those of badly impregnated PP/PP composite. Particularly in the transverse direction, well impregnated PP/PP composites had good adhesive properties. Therefore, it is supposed that the mechanical properties of PP/PP composites are influenced by trenscrystalline.
'Micro-braided yarn' has been proposed as a means of overcoming the difficulty of manufacturing long fiber reinforced thermoplastic composites. Micro-braided yarn is intermediate material for long-fiber reinforced thermoplastic composite. In the Micro-braided yarn a reinforcement fiber is covered by a matrix fiber. In this study, unidirectional carbon-fiber/ PA6-Nylon composites manufactured from micro-braided yarn with different strand diameter were molded in order to investigate the effect of the molding conditions on impregnation mechanism. Through this the mechanical properties of micro-braided composites were understood. A microscopic observation was performed with optical microscopy to understand the impregnation mechanism of thermoplastic resin into the fiber bundle. A parameter for the impregnation property was proposed based on the impregnation volume. 3-point bending test was carried out to investigate the effects of diameter of reinforcements strand in micro-braided yarn and molding condition on the mechanical properties.
The fiber/resin interface can be considered to have three-dimensional region, so that technical term of interphase has been often used instead of interface. Interphase should be considered as the third component in fiber reinforced composite materials, and is generated during composite manufacturing. The authors have tried to apply a new function to interphase and called Affordable Interphase". As an example of affordable interphase we have developed the composites with more flexible interphase than matrix resin. In this study we applied the concept of flexible interphase to the woven fabric composites. As a result it was cleared that tensile strength was improved because flexible interphase restrained generation of cracks at interphase inside of fiber bundles."
Dairy and fruit juice bottles are a major source of post consumer recycled high density polyethylene (PCR HDPE). The recycled HDPE has limited post-consumer applications due to its poor stress crack resistance (SCR). This paper presents a review of a test method for SCR and some preliminary results of the development of recycled HDPE blends with improved SCR. The improvement has been achieved with the addition of a modifier, and results indicate that there is a potential to incorporate the use of recycled HDPE in non-pressure pipe applications. These customised blends have been tested for SCR according to the Notched Constant Ligament Stress (NCLS) test. The NCLS test is a new test method (ASTM F17.40) which is currently under development. The NCLS test will be used to determine the susceptibility of HDPE resins to slow crack growth (SCG) under a constant ligament stress in an accelerated environment. The results from the test will subsequently be correlated with field performance results.
Previous product quality models based on cavity pressure suffer from being geometry and polymer specific and requiring large amounts of data to develop. The present study focuses on the development of geometry/polymer independent models to predict part weight with a minimum of experimental data. Several product geometries were created using inserts in a standard ASTM tensile specimen cavity. Both amorphous and semi-crystalline polymers were utilized. Real-time cavity pressure data was collected, quantified via pressure curve attributes" and used to develop predictive models through multivariate linear regression. Future work will apply the model results to the molding of a typical commercial electrical connector."
The injection molding process has several inherent problems associated with the constant temperature mold. A basic solution is the rapid thermal response molding process that facilitates rapid temperature change of the mold surface thereby improving quality of molded parts without compromising cycle time. Rapid heating and cooling systems consisting of one metallic heating layer and one oxide insulation layer were investigated in this paper. Design issues towards developing a mold capable of raising surface temperature from 25°C to 250°C in 2 seconds and cooling to 50°C within 10 seconds were discussed. To reduce thermal stresses in the layers during heating and cooling, materials with closely matched low thermal expansion coefficient were used for both layers. Effects of various design parameters, such as layer thickness and material properties, on the performance of the mold were studied in detail with the aid of heat transfer simulation and thermal stress simulation. Several rapid thermal response mold inserts were constructed on the basis of the simulation results. The experimental heating and cooling response agrees with the simulation and also satisfies the target heating and cooling requirement.
The simulation of polymer viscoelastic flows is a complicated problem and until now it is not possible to perform simulations that are relevant from an industrial perspective. One of the limiting factors is the degree to which elasticity plays an important role in the flow. For a given constitutive equation and numerical technique, a higher material relaxation time, will result in a lower maximum deformation rate for which convergence is possible. Since industrial processes typically involve very large deformation rates, a practical way to allow their simulation might be to truncate the longest relaxation times. In this work the Leonov constitutive equation was used to simulate flow through an abrupt contraction. The possibility of truncating the relaxation spectrum was explored and the impact of using truncated spectra on simulations is described. Finally we propose a technique for obtaining a truncated relaxation spectrum that will be useful for flow simulations.
Blends of polyethylene terephthalate (PET) and ethylene-ethyl acrylate-maleic anhydride terpolymer (E-EA- MAH) were dynamically crosslinked in a one-step extrusion process. An amine-terminated glycol reacting with MAH moieties was used as the crosslinking agent. Systems were compatibilized by addition of ethylene-methyl acrylate-glycidyl methacrylate terpolymer (E-MA-GMA). The tensile properties and dynamic mechanical thermal analysis response of the unvulcanized and the dynamically vulcanized systems were studied. The effect of blend composition, compatibilization, dynamic crosslinking and processing conditions on the microstructure and tensile properties were investigated.
Mechanical deformation induced experimentally using a T. M. Long stretcher enabled an investigation of the effect nano size platelets can have on the clarity, barrier and mechanical properties of a polymerized nano polyamide 6. Clarity of cast film specimens did show a direct correlation between %Haze and nano platelet concentration. Non nano containing films biaxially stretched 2 times its original dimensions had a 1% - 3% haze reading. Nano containing films ranged from 5% -~ 20% over a nano concentration of 1.0% - 4%, respectively. The oxygen transmission rate, OTR , of 2% and 4% nano films had a 3X and 6X improvement in OTR compared to the unfilled polyamide 6 film, respectively. Biaxed nano polyamide 6 film did not significantly improve OTR, as is the case with non-nano containing polyamide 6 films. There was only a 6% improvement in OTR, which was due primarily to the minimal increase in molecular orientation or packing, which is shown by the small change in the degree of orientation ~77% to 83% for as cast nano films compared to biaxed nano containing films, respectively. The nano containing films do have improved modulus and yield strength and an expected reduction in elongation at break. By taking advantage of molecular orientation mechanical properties were modified via biaxially orientation.
The effect of varying the feedstock shape on the output performance of groove-feed extruders was examined. Pellets of five different aspect ratios were run, as were five different levels of bottle regrind blended with virgin pellet. The different feedstock materials were compared on two different screw designs with differing feed zone geometries. The results showed that different aspect ratios or bulk densities had no effect on the locking action of solids within the grooves, but can have a dramatic influence on the filling and packing unless a screw of appropriate design is used.
Injection molding of thermoplastics with small feature size is needed in many medical and bio-chemical applications, i.e., bioMEMS. Three types of mold inserts, CNC machined steel mold, photoresist molds, and photolithography produced nickel molds are tested in high speed and high pressure (i.e., thin-wall) injection molding. The feature size covers a range of 5 micrometers to several hundred micrometers. Two optically clear thermoplatics (PMMA, PC) were processed under different molding conditions including mold temperature, injection speed, shot size, and holding pressure. The replication accuracy, molded-in stress, and mold wear were measured. Numerical simulation was carried out to calculate flow front profile and stress distribution. The simulation and experimental data were compared and the results can be used to design the process window for micro-injection molding.
An investigation of the transient, steady and dynamic flow properties of the thermotropic liquid crystalline polymer Vectra A950 (Ticona) is presented. The steady viscosity curve shows the typical three-region flow curve of LCPs. In the transient shear experiments, the shear stress grows during the start-up of constant shear rate flow and goes through a maximum at approximately ?=2. Dynamic mechanical experiments show the existence of a linear viscoelastic region at small strains, and that the onset of nonlinearity varies with frequency. In the linear viscoelastic region, the storage and loss modulus, G'(?) and G(?) do not display the typical dependence on ?2 and ? respectively. The results obtained for a frequency sweep using constant strain and constant stress instruments are qualitatively different."
In addition to universal filler/pigment to polymer coupling, two parts of thermally stable neoalkoxy titanates and zirconates per thousand parts of polymer provide for in situ metallocene-like repolymerization catalysis of the filled or unfilled polymer during the plastication phase resulting in: significantly faster injection molding production cycles at lower temperatures while maintaining or increasing mechanical properties; the in situ regeneration of regrind polymer to virgin properties; the lowering of polymer recrystallization time; and the copolymerization of dissimilar polymers. Examples: both 40% CaCO3 filled and unfilled PP compounds experienced respective reductions of 35.5% and 42% in injection mold cycle time and 22% and 11% in process temperature; a 39.7% reduction in the recrystallization time of PPS; and a ten-fold increase in the elongation of a PET/PC alloy. The effect is shown to be permanent and recyclable.
Three-dimensional batch chaotic mixing of short carbon fibers (SCF) and low-density polyethylene (LDPE) is investigated as a means to obtain thermoplastic composites with directional electrical properties. Previous studies investigated carbon black filled systems and revealed that anisotropic electrical properties can be obtained by chaotic mixing at various filler concentrations. The present study focuses on network formation among short carbon fibers used as the conducting filler. The directional electrical properties in terms of static dissipation times and volume resistivities are related to microstructures. These properties are compared to the properties of composites obtained by conventional mixing processes.
In this paper, the effect of polymer rheology, injection speed, mold geometry, melt temperature, mold temperature and lubricant on flow marks was studied. The results show that the most important factor affecting the flow marks is injection speed. It is found that the flow marks did not occur at high injection speeds. Mold geometry also has an effect on the flow marks. However, mold temperature and melt temperature were determined to have little effect on the flow marks. It is also found that the polymer with the highest dynamic viscosity, elastic modulus and first normal stress difference, and longest relaxation time exhibits flow marks over the widest range of processing conditions.
As with other forms of rapid prototyping, fused deposition modeling (FDM) creates parts by depositing a thermoplastic in layers. The mechanical properties of these parts are anisotropic due to this layering, with the part being weaker than the published material properties. Since FDM parts are sometimes used as working prototypes, it is important to understand the degree of these variations. This investigation studied the effect of six different build orientations on six mechanical properties for test parts built of ABS. While parts built on end were understandably the weakest in all tests, properties were the best for parts built on edge versus parts built flat. Also, specimens oriented parallel to the x-axis of the FDM had improved properties over specimens built with a 45° rotation, regardless of layer orientation.
Mode I Tear resistance in high density polyethylene (HDPE) blown film has been characterized using a single specimen J-Integral approach. This method measures the load on the sample, crack initiation, and crack growth in a double-edge notch tensile specimen pulled at a constant extension rate. Tensile tests were performed to determine basic mechanical properties of the HDPE film. A systematic characterization of film morphology has also been performed. This work focuses on the use of a thorough morphological investigation to describe the fundamental aspects of deformation and tearing as they relate to different processing conditions.
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