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 simulation of thermally and flow induced crystallization behavior of semi-crystalline polymers is of great engineering significance in polymer processing like injection, blow molding and extrusion. However, its key technology for practical application remains to be difficult. In the study, the mathematical model of three- dimensional thermally and flow induced crystallization of polymer melts obeying Phan-Thien and Tanner (PTT) constitutive model is established. A penalty finite element/finite difference method is introduced to solve the nonlinear governing equations. The computation stability is improved by using the discrete elastic-viscous split stress (DEVSS) algorithm incorporating the streamline upwind scheme. A modified Schneider’s approach is employed to discriminate the relative roles of the thermal and the flow state on the crystallization phenomenon. Two driving causes for the crystallization of polypropylene in extrusion process including the thermal and the flow state are investigated. Both the crystalline distribution and crystalline size of polypropylene are obtained based on the proposed mathematical model and numerical scheme.
Liquid Crystal Polymers (LCPs) are advanced high temperature processing polymers with unique physical properties. It contains rigid rod like molecules, which exhibit structural orientation during the flow process at one or two dimensional level. Rheological behaviour of unfilled LCPs and filled (glass fibre) LCPs were characterized with ARES and Capillary rheometer at low and high shear rates. The complex viscosities (h*) as well as shear viscosities (h) showed a typical shear- thinning behaviour. LCPs exhibit anomalous rheological behaviour with shear and temperature. Viscosity reduced at low shear rate region because of the tumbling nature of rod like molecules. The abnormal temperature dependence of the viscosities can be explained by the transition of anisotropic rod-like molecules to isotropic molecules with increase in temperature. In steady shear flow, it was observed that rotational transformation occur from direction of flow to surface direction, which leads to first negative normal stress difference (N1) with shear rate. Stress relaxation conducted after cessation of shear flow to prove the molecular dynamics. Multiple overshoot observed due to tumbling, which was varying with temperature and shear rate.
Tri acetyl cellulose (TAC) is not a good material for the chain stretching due to its main chain rigidity. Plasticizers were introduced to increase the chain flexibility and the effect of plasticizer on physical properties of TAC film was studied. The lowering of glass transition temperature, melting temperature and crystallinity were found and this was understood that plasticizer provided the main chain mobility by reducing interaction between TAC molecules. These made possible to stretch the TAC chain under low stretching temperature and resulted in the development of birefringence in TAC film which indicated the characteristic of retardation film
Quality is the key to injection-molded plastic optical lenses. To improve the lens quality, a systematic model-free optimization (MFO) method is proposed to minimize the part quality subjected to specified range of focal length. Rather than building a model to correlate the relations between process variables and quality variables, this method online optimize the process by directly using the measurement for function evaluation. An iteration termination control methodology is developed and integrated for the quality optimization. The effectiveness of the MFO has been demonstrated through experiments.
From micro featured optical products made by conventional injection molding(CIM) the defects of inhomogeneous shrinkage and incomplete filling of micro pattern can be found easily because of concentrated residual stresses near gate and the formation of frozen layer. To reduce the inhomogeneous shrinkage in thickness direction injection/compression molding(ICM) can be used by applying compression of mold rather than applying packing pressure through the gate. To achieve better transcription of micro pattern on the product from the mold rapid heating and cooling molding(RHCM) has shown the advantages by heating the mold surface above glass transition temperature of polymer used. In the present study a series of experiments using ICM combined with RHCM named RICM(RHCM+ICM) was conducted to increase both the transcription ratio of micro pattern and the uniformity of thickness for 7 inch sized BLU-LGP(Backlight unit-light guide plate). As a result, the standard deviation of thickness was reduce from 0.024(ICM)~0.025(RHCM only) mm to 0.005(RICM) ~0.007(ICM) mm by apply compression process. In the cases of CIM and ICM average transcription ratio of micro pattern showed 42.0% and 63.2%, respectively. On the other hand, the transcription ratio of micro pattern in the cases of RHCM and RICM showed almost 100% while the mold temperature reached above glass transition temperature. By the application of ICM combined with RHCM both the transcription ratio of micro pattern and the uniformity of thickness can be improved dramatically even the maximum mold temperature of RICM was 10°C lower than the case of RHCM only.
In this study, the aliphatic or aromatic isocyanates and poly-alcohols was used to synthesize polyurethane with shape memory function, which the polyol was derived from the biomass polylactic acid (PLA). The recycled PLA was degraded into the low molecular weight PLA (Mw 1,000) and the chain extension agent (1,4-butanediol, BDO) reaction was added to form biomass polyol. The analysis of Fourier transform infrared spectroscopy (FTIR) and Gel permeation chromatography (GPC) were proved the synthesis of polyol. The recovery ratio of shape memory and mechanical properties of polyurethane were improved significantly due to the urea structure, the biomass polyurethane with shape memory could be increased up to 95% of recovery ratio. Different isocyanate (hexamethylene diisocyanate, HDI, or 4,4- diphenylmethene diisocyanate, MDI) were compared and found that the functional group of aromatic was better than that of aliphatic in the synthesis of polyurethane with shape memory behavior.
As a typical batch process, injection molding has the following unique features compared to traditional continuous processes: repeatability, two-dimensional dynamics and stages based operations. A sophisticated control algorithm shall exploit all these features. In this paper, a systematic two-dimensional model predictive iterative learning control algorithm is introduced to control the injection molding process with the injection velocity as an application example. The experimental results prove that the control algorithm has good performance and robustness.
Polylactic acid and polypropylene were melt blended and extruded into 3-10 mil films. Differential scanning calorimetry studies showed the polymer blends, unlike the neat PP and PLA materials, exhibited crystallization exotherm in heating scans with a crystallization point varied with the ratio of PLA to PP. This melt crystallization behavior was enhanced with the increase of the content of PLA from 25 to 75%. The polymer blends also showed multiple melting points ranging from approximately 140 to 175°C depending on the ratio of the two polymers and the heating rate. The formation of a new crystallization temperature, the shifting of the melting points, and/or the formation of new melting points suggested some compatibility between PP and PLA. Upon uniaxial stretching, the originally translucent films showed strong stress-whitening phenomena with widespread porous structure developed in the whitened region. SEM showed fibrils with a typical diameter of 2 micron and voids or pores of approximately 5 micron developed in the whitened region. The partial compatibility between PLA and PP could have contributed to the homogeneity of the stress-whitening and the porous structure in the film. The porous films provided two folds or higher increase in oxygen transmission rate depending on the material composition and draw ratio. The structural development and the potential use of the porous PLA/PP films in packaging application are discussed.
Nowadays, most manufacturing companies store their data electronically. The selection of the appropriate data mining algorithm for exploration of this data can quickly identify issues leading to process improvement and cost reduction. In this paper, The Decision Tree Classifier (DTC) is used for plastic color mismatch parameters analysis. Especially, the relationship between polymer grade, color, type, line of production, and ingredients supplier is analyzed. DTC Results showed interesting and evident relationships between certain parameters.
Poly(vinylidene ?uoride) (PVDF)/graphene composite was successfully fabricated by a solution-cast and hot- pressing method. The composite material with graphene as conductive ?ller exhibited a very low percolation threshold (0.0018 volume fraction), but the dielectric constant was enhanced signi?cantly. The largest dielectric constant of 7940 was observed for the PVDF/graphene composite with 0.0177 graphene volume fraction at 100 Hz. Large enhancements of the ac conductivity and loss tangent were also observed for the composites with graphene content near the percolation threshold. The percolation theory was used to explain the dielectric behavior of the composite.
A semicontinuous process was used to prepare copolymers varying the feed composition profile, to vary in a gradual manner the composition of the copolymer chains being formed through an emulsion reaction, for the (50/50, w/w) styrene/butyl acrylate system. With the cumulative composition of the copolymers (1H-NMR), the weight distribution of chains composition (WCD) was estimated, constructing a histogram that is used to elucidate the mechanical behavior (DMA, stress-strain and, impact strength) of the synthesized copolymers.
To expand use of photovoltaic generation, there is a real need for reducing cost of generating by photovoltaic panels. One of cost-cutting of power generation is to prolong its service life. It is very important to prevent moisture from penetrating the back-sheet for insuring the long-life operation of photovoltaic panels. In this study, the correlation was evaluated between mechanical property and partial discharge of degraded polyethylene terephthalate film for the back-sheet.
Reducing the weight of thermoplastics and rubber parts has been a paramount objective in various industries such as transportation, aerospace, hand-held electronics and sports and leisure. 3M ™ Glass Bubbles (hollow glass microspheres) are light weight micro additives specially engineered to withstand temperature, stress, and deformation gradients in a wide range of polymer processes ranging from liquid phase polymer processing to high viscosity melt compounding and high pressure injection molding. We will present factors influencing glass bubble survival and discuss processing methodologies to achieve the highest level of bubble survival for a given polymer grade, specifically during twin screw extrusion compounding and injection molding. We will then analyze application examples and demonstrate how the plastics industry and associated OEMs can exploit the light weight advantages of these novel additives while improving the processing and end-product properties without resorting to costly equipment modifications.
Injection pressure, an important factor in injection molding process, should be minimized to enhance injection molding quality. In this study, we decided the locations and open timings of valve gates to minimize the maximum injection pressure. To solve this problem, we integrated MAPS-3D (Mold Analysis and Plastic Solution-3Dimension), a commercial injection molding analysis CAE tool, using the file parsing method of PIAnO (Process Integration, Automation and Optimization) as a commercial process integration and design optimization tool. In order to reduce the time for obtaining the optimal design solution, we performed an approximate optimization using a meta-model that replaced expensive computer simulations. To generate the meta-model, computer simulations were performed at the design points selected using the optimal Latin hypercube design as an experimental design. Then, we used micro genetic algorithm available in PIAnO to obtain the optimal design solution. Using the proposed design approach, the maximum injection pressure was reduced by 35.1% compare to the initial one, which clearly showed the validity of the proposed design approach
This paper describes a novel approach to achieve swirl-free foamed plastic parts using the microcellular injection molding process. With a better understanding of the cell nucleating behavior, which is governed by the degree of supersaturation, one can delay the onset of cell nucleation during mold filling, thereby allowing a solid skin layer to form on the part surface prior to foaming. The theoretical background of this approach as well as the experimental results are presented.
Banana microfibrils were prepared from banana fibre obtained from the pseudo stem of the banana plant by steam explosion process. Alkali and acid treatment coupled with high pressure defibrillation was found to be effective in the depolymerization and defibrillation of the fibre to produce the microfibrils. The different stages of steam explosion process were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Atomic Force microscopy studies (AFM) revealed that the surface of the microfibrils were rough. The prepared micro fibrils were subjected to chemical treatments with potassium permanganate (KMnO4) and benzoyl chloride. Low density polyethylene (LDPE)/microfibril composites were prepared by injection molding. The dielectric and mechanical properties of composites and chemically treated microfibril composites were investigated. Dielectric constant of LDPE/microfibril composite was found to be greater that of neat LDPE. Chemical treatments reduced the dielectric constant of the composite. The mechanical properties were found to be increasing upto 20% microfibril loading. Chemical treatments further enhanced the mechanical properties of the composite.
In recent years, injection molding technologies have been developed which use variable mold heating and cooling to improve surface finish and general part quality without significantly increasing cycle time. Simulation of these processes requires a transient time dependent mold thermal analysis. This paper presents the further development of a 3D finite element based transient mold cooling simulation capability to include the rapid heating and cooling cycling of the mold. The various rapid heating and cooling stages are explained as well their effect on the part during filling.
POM or polyoxymethylene is an engineering resin used primarily for injection molded parts that replace metal. POM’s usefulness is derived from the combination of strength, stiffness, toughness, creep resistance, and lubricity. POM homopolymer and copolymer compete in this market space. Homopolymer grades have some mechanical advantages while copolymer grades have better thermal and chemical stability. In 2010 Ticona introduced a new high strength, high viscosity POM copolymer with the mechanical properties of a typical homopolymer, while maintaining copolymer stability. This paper introduces an improved flow, high strength POM copolymer, its property profile, salient features and potential applications.
The primary objective of this study was to investigate the effect of damp heat (DH) and ultraviolet light (UV) exposures on the properties and performance of polymeric materials in photovoltaic (PV) modules. The study covers the evaluation of ethylene vinyl acetate (EVA) encapsulant, TPE (PVF/PET/EV A) substrate, and laminate coupons and modules as a function of exposure time to DH (85°C, 85% RH), and UV (100W/m2, ~2 suns UV irradiance). The results showed that DH exposure had a greater aging effect than UV, and the materials exhibited a greater degree of degradation with increasing exposure time.
Tribological parameters are results of a complex system; therefore their behavior can not easily be predicted. This paper suggests a model for characterizing tribological behavior by the distinct contribution of basic friction, and wear modes. These modes and the transition from one to another are influenced by material, geometric, and other system properties. The presented model is based on broadly accepted, mostly two-dimensional, correlations and supported with own pin-on disc friction and wear experiments.
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