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.
For the recent years, multi-shot sequential molding is widely applied in various industries. It is a process that uses two or more molds to produce a multi-material component. In principle, the first material is injected into the first mold by standard single-material molding technique and then moved to the next mold where the next material can be injected to combine with it. This complex process is difficult to identify and study correctly by the traditional 2.5D model. In this paper, a three-dimensional numerical approach is developed to simulate the filling, packing and cooling stages in multi-shot sequential molding, as well as the part warpage after ejection. Several cases are reported to indicate the success of the present model.
A novel vibration-assisted metal powder injection molding (MIM) machine was adopted to study the effects of the vibration amplitude and vibration frequency on the cavity pressure. The melt in the cavity could be manipulated dynamically and continuously during the vibration-assisted metal powder injection molding. The experimental results showed that the cavity pressure was decreased with the increase of amplitude/frequency when the average injection velocity was constant. The cavity pressure gradient was lower than that of conventional injection molding processing (without vibration) within our research scope. The metal powder could be molded at a relative lower temperature or a lower injection pressure without the loss of the product quality.
The goal of this contribution is to show the possibilities of utilization of benchmarking and its procedures in the financial management of plastics processing companies. Benchmarking is a significant tool for financial management motivating the company managers to make necessary changes thereby affecting the performance of the enterprise. This contribution contains a benchmarking study of a sample of plastics processing companies operating in the United States and in the Czech Republic. The results of the study identify the areas of financial management of an enterprise that require particular attention in order to increase its performance. The concept of Economic Value Added as a measure of performance has been chosen.
Inorganic flame retardants, such as aluminum trihydrate(ATH) and magnesium dihydrate(MDH), are most widely used fillers in halogen-free flame retardant polyolefin materials, especially for cable. These inorganic fillers, as they used in great amount, influence the rheological properties and extrusion characteristics of resin. During processing, they sometimes raise a problem such as die lip buildup, which refers to the resin accumulation on the open faces of extrusion dies. It commonly deteriorates the processability. The mechanism of die lip buildup is not fully understood, though there are many proposed explanations. The effects of resin composition and processing aids on the rheological and processing performance, including die lip buildup characteristics, were studied here. Also, processing conditions on the extrusion processability were investigated.
Compression tests were carried at different temperatures and constant press pressures on unidirectional GF/PP towpreg preforms. The experimentally determined displacement/time curves were compared to the simulations obtained from a theoretical model that assumes an isothermal process and two different fiber/polymer packing arrangements, one triangular and the other hexagonal.Discrepancies were found between the experimental results and theoretical simulations as consequence of the difficulties found in establishing the real fiber/polymer arrangement and polymer flow conditions during consolidation. This work presents an empirical equation, which includes two constants to be determined experimentally, that allows reducing those discrepancies and predicting with higher accuracy the relationship between the material properties (polymer viscosity and fiber and polymer particle dimensions) and the operational compression molding conditions (press pressure and consolidation time).
In the present work, a carboxylic-acid-anhydridemodified polypropylene additive was used to improve the interfacial properties of low-cost glass fiber/polypropylene (GF/PP) towpregs produced in developed dry coating equipment. The article describes how the use of the additive affects towpreg processing conditions. The towpregs were used to produce composites by compression molding and filament winding.The produced composites were submitted to mechanical testing. Improvements were clearly identified on the fiber/matrix interface by comparing the obtained results with those determined from non-added GF/PP composites.
The chemical structure of crosslinked polyethylene (PEX) prevents easy reprocessability. Crosslinking of the polymer backbone covalently bonds it to another polymer chain. This bond prevents chain slippage and therefore any further melt processing. With an increase in time or temperature the crosslinking reaction will proceed, increasing its molecular weight to a point where it can not be processed a second time. The objective of this research is to determine a time window such that the crosslinked material can be reground and reprocessed using conventional melt processing equipment before the crosslinking reaction proceeds to a point where the material becomes unprocessable.
While addition of block copolymer during melt mixing of immiscible polymer blends has yielded compatibilization in small-scale academic studies, it has not been commercially successful due to thermodynamic and kinetic limitations. We show that addition of a commercially available styrene/ethylene-butylene/styrene triblock copolymer to an immiscible polystyrenepolyethylene blend during solid-state shear pulverization (SSSP) can substantially reduce coarsening in subsequent melt processing. In comparison with blends made by melt mixing, blends mixed by SSSP led to coarsening of the dispersed phase during high temperature annealing that was reduced by more than an order of magnitude. We believe that mixing block copolymer with the blend by SSSP yields greater levels of block copolymer near the interfacial regions as compared to melt processing. By overcoming the thermodynamic limitation of block copolymer micelle formation during melt processing, block copolymer addition via SSSP offers a commercially viable strategy for blend compatibilization.
The water jet cutting of ACM laminates often causes a serious defect or delamination. This paper describes that water jet cutting can be successfully applied for small bore piercing of advanced composites by an impulse jet. Results of a piercing test on the laminates of continuous carbon and glass fiber reinforced plastics, confirmed experimentally and theoretically that a defect appeared in internal layers of material due to a bending moment of the bottom layer, caused by the high pressure of the jet. The bottom layer deflects to peel or delaminate from the upper layer as if it is a simple beam and finally as a cantilever lever at the bore edges as the hole progresses. Hence, the defect was most effectively prevented by supporting the work material behind the cut edges with a thick plate having a bore smaller than that of the nozzle.
An optical elastomeric system having a nanoscale layered structure was fabricated using a novel continuous coextrusion processing technology. This system was composed of hundreds of alternating layers of two elastomers with different refractive indices. When the layer thickness was on the order of quarter wavelength of visible light, these novel films exhibited reflectivity due to the periodic variation in refractive index (1-D photonic crystal). Nanolayer structure, reflectivity, and its tunability of these films were studied. Results indicated that the wavelength of reflection is tunable and reversible with applied strain. An analytical model was developed that agreed with the experimental data. Potential applications include tunable optical filters and optical strain gauges.
A new method using high intensity ultrasonic wave, instead of peroxide-aided reactive extrusion, was applied to modify a linear polypropylene to a branched structure. To enhance and control the recombination reaction during sonication, multifunctional agent and antioxidant were used. From the rheological property measurements, it was confirmed that the modified polypropylene has nonlinear branched structure. Also, adequate use of antioxidant could control the degradation or recombination of polypropylene by stabilizing the structure during sonication.
The glass transition temperature (Tg) and physical aging behavior of nanoconfined polymer films were investigated by novel fluorescence methods. These studies have revealed that there are large modifications in both Tg and physical aging behavior due to interfacial effects. For example, Tg was observed to decrease compared to bulk in polymers where free-surface effects dominate (e.g., for polystyrene (PS) on silica substrates), while Tg was observed to increase compared to bulk for polymers where strong attractive substrate interactions dominate (e.g., for poly(2-vinylpyridine) (P2VP) on silica substrates). Similar interfacial effects were observed for physical aging, where attractive substrate effects retarded physical aging compared to bulk. Furthermore, the Tg- nanoconfinement effect was observed to be widely tunable by small variations on the repeat unit structure of PS or by the addition of low molecular weight diluents or plasticizers. Finally, Tg and enthalpy relaxation behavior were investigated by differential scanning calorimetry for PS-silica and P2VP-silica nanocomposites. As in the nanoconfined film studies, interfacial interactions were key in dictating the ultimate properties of the nanocomposite, but it was also observed that preparation method plays a significant role.
Science and practice have proven that phthalic acid esters are among the most functional plasticizers for PVC. The performance properties of phthalic acid esters can be modified for an advantageous cost/benefit position by varying the alcohol moiety of the ester molecule in the practical range of C4 through C13 and by specifying the linearity of the alcohol main chain. C8, C9, and C10 alcohols produce esters of most value as PVC plasticizers.Most plasticizer alcohols are produced by the oxonation process from primary olefins, of which ethylene, propylene and butene are the major refinery products available on a world scale at costs acceptable to the application. This paper will introduce a C10 phthalate produced from butene rather than the current route from propylene.
In this work, the viscoelastic properties of acrylic-based copolymer blends with poly (methyl methacrylate) and polycarbonate are investigated in the molten and solid states. Copolymers of MMA-BA with varying molecular weight and composition are used to enhance the rheological properties in shear and extension. The blends were prepared at 200°C using a DSM micro-compounder for up to 15 wt.% copolymer. The samples were characterized by size exclusion chromatography (SEC), dynamic mechanical analysis (DMA). The rheological properties were determined using small amplitude oscillatory measurements (SAOM) in shear and using a Rheotens device for melt strength determination. The results showed that depending on the nature of the copolymer used, the glass transition temperature (composition) and molecular weight, the rheological properties can be fine-tuned to enhance melt strength without a significant change in the shear rheology.
Microcellular foams (MCFs) of polycarbonate (PC) with relative densities of 0.9 and 0.7 (MCF-0.9 and MCF- 0.7) were produced by solid-state foaming. Microstructural characterization showed that they had bi-modal distribution of spherical cells, with median cell sizes of 3- 4 ?m and 6-9 ?m for both cell populations. Tensile testing showed that ultimate tensile strength and Young’s modulus approximately ranked with relative density, although MCF-0.9 had a modulus similar to unfoamed PC (uPC). Toughness measurements showed that, when compared to uPC on a critical stress intensity factor basis, MCF-0.9 showed no reduction in toughness and MCF-0.7 showed a ?35% reduction. When compared to uPC on an strain energy basis, 12-15% increases in toughness were measured for both MCFs. Their fracture occurred by multiple initiation, growth and coalescence of voids formed at cells acting as stress concentrators. A fine cell morphology resulted in prolonged growth and coalescence phases, thus improved fracture toughness.
The production of polymer nanocomposites with excellent dispersion of nanofillers has proven to be a major challenge using conventional polymer processing methods. As a result of commonly poor dispersion of nanofillers, the promise of enhanced properties in nanocomposites has often gone unrealized. We have recently demonstrated that a process called solid-state shear pulverization (SSSP) can yield well-exfoliated polymer-clay nanocomposites and well-dispersed polymer-multiwall carbon nanotube and polymer-alumina nanoparticle composites. Furthermore, the exfoliation of dispersion achieved via SSSP is stable during subsequent melt processing of the nanocomposites made via SSSP. The connection between synergistic macroscopic properties, from modulus to thermal stability to conductivity, and dispersion of nanofiller is illustrated by the results obtained in this study.
According to the homogeneous classical nucleation theory, the nucleation free energy barrier in the foaming process can be calculated by W =16??3/3(Pbubble – Pmelt)2. Currently, almost all the simulation results simply substitute the bubble pressure, Pbubble, with the saturation pressure, Psat, and the curvature-dependent surface tension, ?, with the experimentally measurable surface tension, ??. This paper engages a brief discussion of the above two approximations. The consequence of substituting Pbubble with Psat on the free energy barrier will be considered with respect to equations of state. The effect of the curvature dependence of surface tension on the prediction of free energy barrier for bubble nucleation, and thereby on the calculation of nucleation rate is explored using the recently proposed scaling function approach.
Solubility and diffusion coefficients of Carbon Dioxide (CO2) in polylactic acid (PLA) (poly-L-lactic acid (PLLA) and poly-DL-lactic acid (PDLLA) copolymer) have been measured at room temperature and pressures up to 5.8 MPa. Based upon x-ray diffraction analysis it was found that CO2 induced crystallinty in the samples. The results indicated that the crystallinty increased with processing pressure with the largest increases noted at pressures between 2.1 and 2.8 MPa under room temperature conditions. These findings were used to investigate the effect of different saturation conditions on the cellular structures of foams produced using various processing temperatures. Samples saturated at 2.8 MPa and room temperature for two days, followed by foaming at 100°C gave a uniform cellular structure with a cell diameter in order of 30-40 ?m and a cell density of 7.93x107 cell/cm3.
The susceptibility to mechanically-induced surface damage in neat and clay-reinforced polymer nanocomposites is examined by combining the lateral resolution of scanning electron microscopy and vertical resolution of atomic force microscopy. The surface damage in neat polymers is characterized by ‘psiloma-type’ morphology indicative of compressive plastic deformation, while in clay-containing nanocomposites, ‘ironing,’ a less severe surface damage was dominant. Also, clay-reinforced nanocomposite experience significantly reduced stress whitening, and characterized by lower change in gray level in the stress-whitened zone. This behavior is attributed to the effective reinforcement by clay particles that increase the tensile modulus of the composite and restricts plastic deformation of the polymer matrix.
An experimental investigation of the flow behavior of a glass fiber reinforced polypropylene in an injection molding machine revealed that it was possible to reduce the extent of fiber breakage occurring through the addition of a blowing agent. With the increased addition of a chemical blowing agent, from 0 to 5 wt%, the fibre length distribution was found to increasingly resemble the virgin resin. Rheological study of this phenomenon with an inline rheometer showed that the blowing agent changed the pseudoplasticity of the composite. As a result of the change in pseudoplasticity, less glass fibers were exposed to shear flow and therefore did not experience rotation normally leading to fibre breakage.
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