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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Description of the Foaming Process during the Extrusion of Foams Based on Renewable Resources
Some polymers based on renewable resources like starch containing materials can be plasticated by extrusion processing. Foams based on theses materials have an increasing importance in packaging applications, but also insulation materials have been developed. Starch contains water, which can work as a physical blowing agent for processing of these foams. The foaming process depends on process parameters like the pressure gradient in the die as well as on material properties like rheology. The main target is the production of foams with low density, high expansion ratio and a homogenous cell structure.The foaming process starts in the flow channel of the die. The cell nucleation process can be investigated by a die design with transparent inserts in the flow channel. The influence of process parameters on cell nucleation was determined. It could be shown that a higher pressure gradient in the die leads to a higher expansion ratio and thus to a later cell nucleation.Furthermore, the rheological properties also have an impact on the foaming behavior of molten starch. Shear viscosity is influenced by melt temperature, water content and mechanical energy input during the extrusion process. In this work, the dependency of the flow properties on process parameters was investigated in order to quantify the differences in pressure build-up caused by changes in screw speed and the resulting consequences on viscosity.
ABS Pipes for Chemical Transport
Polymer pipes for transport of corrosive substances have been widely adopted by the chemical industry, but problems of attack and failure have continued to occur. The present case involved ABS pipe used for carrying concentrated hydrochloric acid, where failure of a blanking plate caused a major loss of acid (2500 litres). One investigator observed that the polymer had become discoloured, and attributed the loss to poor selection of material. However, the failed parts had been lost in the incident and were not available for inspection. Intact blanking plates were available, however, and they showed absorption of impurities, producing softening of the ABS, but no brittle cracking. The problem of assessing resistance of polymers to industrial chemicals remains a problem if long-term exposure tests are not available to designers.
Ozone Cracking of Seals in Microchip Production
Lithography machines for making semiconductor chips use pneumatic circuits for the air bearings which support the tables on which the chips are etched by laser beams. The tables must be absolutely flat and perfectly still to achieve accurate circuits, a function achieved by the air bearings. An air bearing consists of a pressurised chamber enclosed by a nitrile rubber diaphragm. There have been problems however, with ozone cracking of the diaphragm seals, causing extensive machine downtime and loss of chip production. Examination of failed seals showed that very low levels of ozone (ppb) were sufficient to initiate cracks at sharp corners in the seal, the cracks growing until the seal failed. ESEM analysis of the fracture surface showed enhanced oxygen levels from traces of carbonyl compounds on the surface left by ozone attack. The problem has been eliminated by filtering the air flow both before and after the compressors.
Subsurface Anchoring of Fluorescent Probes in Poly(Ethylene-Co-Acrylic Acid) Film
Poly(ethylene-co-acrylic acid) (PEAA) films contain reactive carboxylic acid groups that can undergo chemical coupling after activation. However, the chemistry will occur not only on the surface but also in the subsurface of the film. The aim of this work was to study the surface grafting behavior and penetration reaction of a relatively small fluorescently labeled probe molecule, dansyl cadaverine, in PEAA films. A two-step reaction was conducted. First, PEAA film was activated with PCl5 at room temperature, which could occur throughout the film depending on reaction time. Second, the acid chloride was reacted with dansyl cadaverine to form a modified film. ATR-FTIR spectroscopy and fluorometry were employed to analyze the penetration behavior. Using dichloromethane as a solvent, it was found that the dansyl cadaveine penetrated throughout the analysis region (~400 nm) of the ATR-FTIR evanescent wave in few minutes and the conversion was approximately 90%. As the penetration depth increased with time, so did the amount and fluorescence intensity of grafted dansyl-cadaverine. However, insignificant changes of surface wettability for dansyl-cadaverine-modified film were observed by contact angle measurements.
Prediction of Core Deflection in Ceramic Injection Molding
A full three-dimensional finite element simulation of ceramic injection molding is performed using the PELDOM software. Predicted melt-front advancement, and pressure variation and core deflection for an airfoil-shaped mold are compared with the corresponding experimental data. The power-law-WLF model is used for strain-rate and temperature dependence of the viscosity for a ceramic/polymer mixture. A modified Herschel-Bulkley model is used to include the effect of yield stress in the viscosity model. Pressure from the mold filling simulation is used to predict the deflection of core pins in the mold. Numerical predictions are found to be in good agreement with experimental data.
Thermal Behavior during Thermoplastic Composites Resistance Welding
Two- and three-dimensional heat transfer finite element models of the resistance-welding process for joining thermoplastic composite laminates were developed. The models simulated a resistance welded single lap-shear joint using 16-layer unidirectional APC- 2/AS4 laminates. The heating element consisted of a stainless steel metal mesh sandwiched between neat PEEK films. The heat was generated at the bond surface by applying current to the heating element, using a controllable DC power supply. The 2-D model was used to investigate the effect of the length of the exposed areas of the heating element to air (clamping distance) on the local overheating at the edges and the effect of various input power levels on the thermal behavior of the welds. It was found that controlling the clamping distance could improve the thermal uniformity of the weld. The 3-D model showed that heat conduction along the length of the laminates had a great influence on the thermal uniformity of the weld interface.
Novel Coupling Agents for PVC/Wood-Flour Composites
Effective interfacial adhesion between wood fibers and plastics is crucial for both the processing and ultimate performance of wood plastic composites. Coupling agents are added to wood plastic composites to promote adhesion between the hydrophilic wood surface and hydrophobic polymer matrix, but to date no coupling agent has been reported for PVC/wood composites that significantly improved their performance and was also cost effective. This paper presents the results of a study using chitin and chitosan, two natural polymers, as novel coupling agents for PVC/wood-flour composites. Addition of chitin and chitosan coupling agents to PVC/wood flour composites increased their flexural strength by approximately 20%, their flexural modulus by approximately 16%, and their storage modulus by approximately 33-74% compared to the PVC/wood flour composite without the coupling agent. Significant improvement in the composite performance was attained with 0.5 wt% chitosan and while 6.67 wt% chitin used.
A Comparison of Rheological and Thermal Measurements of Cure in Three Epoxy Resins
Cure kinetics of 3 different thermosetting resins were investigated using differential scanning calorimetry (DSC) and oscillatory rheometry, with smooth and grooved plates. For the latter, a fractional conversion was defined based on the maximum storage modulus achieved at a given temperature, and compared to the fractional conversion calculated from enthalpy measurements. As expected, the rates of reaction for the DSC measurements were much factor than those calculated from rheometry, while the rate of reactions were identical with smooth and grooved plates. However, our measurements showed that the torque for the grooved plates was independent of sample thickness, indicating that the grooves were being deformed rather then the whole resin.
Optimization of Parts with Rib Using Gas Assisted Injection Molding Technique
Gas-assisted injection molding (GAIM) offers a cost effective means of production of plastic parts and a solution to the problems associated with conventional injection molding (CIM). GAIM process utilizes compressed gas as the packing medium, hence a lower injection/packing pressure and clamp force are required than CIM. Especially, GAIM has less residual stress and warpage, and better surface finish than CIM in produce plastic parts with ribs geometry.So, A shell of embroider-machine with lots of rids across its bottom was used to analysis by CIM and GAIM numerical simulation software. In order to gain a set of optimize processing condition for GAIM, a L9(34) experimental matrix design based on the Taguchi method was conducted. The results show GAIM effectively lessen weight of the part, significant reduce the packing pressure, and provide a good surface finish. So GAIM has shown considerable advantages in the production of parts with ribs in the industry.
Blend Compatibilization via the Use of Sodium Neutralized Ionomers
An ethylene-methacrylic acid copolymer partially neutralized with sodium (Na-EMAA), was successfully used to compatibilize nylon 6 (Ny6) and low-density polyethylene (LDPE) blends. The phase morphology and thermal behavior of these blends were investigated over a range of compositions using a variety of analytical techniques. The addition of small amounts (0.5 phr) of Na- EMAA improved the compatibility of Ny6/LDPE blends as evidenced by a significant reduction in dispersed phase sizes. TGA measurements demonstrated an improvement in thermal stability when Na-EMAA was added to either LDPE or Ny6. DSC results of Ny6/Na-EMAA binary blends showed that with increasing Na-EMAA content, the crystallization temperature of Ny6 phase decreased indicating that Na-EMAA retarded crystallization of Ny6. TGA and DSC results indicate that chemical reactions might have taken place between Ny6 and Na-EMAA, a hypothesis confirmed by the Molau test.
Study of the Optical Performance of Injection Molded Light Guide Plates
Display panels of various sizes are important components for many 3C devices. However, their optical performances are sensitive to optical design, material selection, molding conditions. In the present study, optical design software (Trace Pro™) is used to simulate the optical performance of light guided plate designed with the micro-featured circle array so that the light distribution characteristics within the plate from the side LED source light can be understood in a better manner. PMMA and PC were used as materials for injection molded light-guide plate. For PMMA parts, the measured optical performance is quite consistent with simulated prediction due to the lower value of residual stress and birefringence. The optical property in PC plate shows deviation from prediction due to high level of birefringence. By properly modified the micro-featured array via the aid of simulation, optimum light uniformity are improved in both PMMA and PC light-guide plate.
Micro Injection Molding of Micro Fluidic Platform
In this study, micro injection molding was applied to mold micro fluidic platform used for DNA/RNA test. LIGA like process using UV light aligner was applied to prepare silicon based SU-8 photoresist followed by electroforming to make Ni-Co based stamp be the mold insert. The micro features in the stamp with a size of 80 mm by 40 mm by 0.4mm includes 30?m by 100?m micro-channel size and 50?m pitch size. COC, PC and PS were utilized as molding materials. Micro channel depth and width in stamp can achieve an accuracy of about +1.5?m (+5%) and -14.1?m -14.1% . For micro injection molded parts, the dimensional accuracy are about -0.58?m (1.8%) and +1.16?m (+1.4%) for depth and width , respectively. Vacuum during melt filling provide a better replication of micro features. Among injection processing parameters, the mold temperature and holding pressure are found to affect the molding accuracy significantly.
Study on the Rheological Behavior of Polymer Melt for Micro Molding
Determination of polymer melt rheological behavior within micro structured geometry is very important for the accurate simulation of micro molding. Yet its investigation is difficult due to the lack of commercial equipment. In this study, melt viscosity measurement within micro channel was established using a micro channel embedded mold operated at a mold temperature as high as the melt temperature. From measured pressures drop and volumetric flow rate both capillary flow model and slit flow model were used for the calculation of viscosity utilizing Rabinowitsch and Walters corrections. It was found that the measured viscosity values in the test ranges are significantly lower (about 30% to 90% lower) than those obtained from macroscopic rheometer. As micro channel size decreases, the derivation in viscosity is increases. This may be attributed to the melt slip occurs on the micro channel wall and the extend of wall slip increases when size of micro channels decreases. In addition, the higher the melt temperature, the effect of wall slip also becomes more significant. The result indicates that current simulation packages are not suitable for micro molding simulation without considering this effect.
Variable Mold Temperature on the Part Qualities of Injection Molded Parts
In this study, electromagnetic induction heating is utilized to achieve a rapid mold surface heating. Mold surface temperature was raised to above glass transition temperature instantly within few seconds (2 to 3 seconds) then mold is closed for melt injection and cooled down to regular mold temperature before the next cycle starts. Varied mold temperature was applied to injection molding and the associated part qualities including weld line appearance, weld line strength and residual stress were examined. It was found that surface appearance of weld line can be eliminated and the associated weld line strengths are enhanced for molding double-gated tensile test parts. For thin-wall parts, applying variable mold temperature also reduces the injection molding pressure and the part residual stress. The rapid heating and cooling of mold surface temperatures using induction technology combined with low coolant temperature cooling was successfully illustrated.
Breathing Tube Failures
Polysulphone is a useful high-temperature resistant material but demands high quality moulding methods. It was chosen for use as the transparent tube of breathing apparatus for use by hospitals with patients, but the first prototypes were rejected by the manufacturer for defects found in the tube. The manufacturer initiated proceedings against the toolmaker, claiming that the tool was poorly designed for its intended purpose. However, detailed examination of many such tubes showed that the defects were caused by faulty moulding. The case went to a full trial but failed when the plaintiff could not withstand cross-examination. Documents produced in his case against the toolmaker had also been doctored, and the judge ordered the original copies, which were never produced. The case exonerated the toolmaker, who won his full costs.
Orientation, Structure and Properties of Double-Bubble Oriented LLDPE Films
Biaxially oriented linear low density polyethylene films were produced using the double-bubble process with different machine direction (MD) orientation levels and the same transverse direction (TD) blow-up ratio. Their mechanical behavior was characterized in terms of the tensile strength and tear resistance. The microstructure and orientation were characterized using microscopy, Xray diffraction and Fourier Transform Infra Red spectroscopy. The results indicate that MD tensile strength increases with MD stretching ratio while TD one decreases. Tear resistance remained mainly constant in TD and decreased in MD with draw ratio. Morphology analysis revealed that over stretching lamellae tend to align perpendicular to machine direction with an increase of their lamellar dimensions. c-axis orientation in MD direction increases with draw ratio while a- and b-axes orient towards normal and transverse direction respectively. A good correlation was observed between caxis orientation and MD tear resistance and tensile strength.
Studies of Creep and Fatigue Crack Growth in HD-PE Pipe Materials
An experimental observation and an approach to thermodynamic modeling of creep and fatigue crack growth (CCG and FCG) in High Density Polyethylene (HDPE) is reported in this work. The experimental investigation was carried out at elevated temperatures (80 °C) using the Tapered Double Cantilever Beam (TDCB) test specimen allowing the observation of crack growth at constant stress intensity factors (SIF). Both, stepwise and continuous crack growth was recorded with a regular and highly reproducible pattern of crack growth after initiation. The continuous vs. discontinuous crack growth is observed to be dependent on R-ratio. The observations provide the basic data for thermodynamic analysis and application of crack layer (CL) approach to modeling of the fracture propagation process. The thermodynamic forces responsible for process zone (PZ) formation and crack growth are computed as the derivative from Gibbs potential of loaded TDCB specimen with respect to PZ and crack characteristic sizes respectively. A comparative analysis of CCG and FCG suggests a rather complex relation between the two that is not as simple as commonly assumed.
Study on the Weld Line Strength of Injection Molded Nylon6 Nanocomposites
Nanocomposites have been attracted great attentions in recent years. However, most efforts are focused on the preparation and layer structure modification and very few mentioned about the properties of molded parts. In this study, molding conditions including melt temperature, mold temperature, packing pressure and injection speed on the mechanical properties particularly the weld line strength of injection molded Nylon6/Fluoromica nanocomposites were investigated. It is found that with the addition of nano-fluoromica particles the weld line strength becomes significantly weakens as compared to that of pure Nylon6 parts and non-welidline Nylon6/Fluoromica nano- composites. As melt temperature, mold temperature, packing pressure and injection speed increases the weld line strength of molded nanocomposites also increases. Among processing conditions, packing pressure exhibits most significant effect on weld line strength.
Beam Shaping with Diffractive Optics for Laser Micro-Welding of Plastics
This paper reviews the use of diffractive optics for beam shaping of high-power lasers (100 W) for micro-welding of plastics. By using Fourier transformations on twodimensional complex arrays, spatial domain images were transformed into phase domain images. These images were then used to produce a mask for the microlithography etching of a glass diffractive optical element (DE). A 40 W YAG laser with a wavelength of 1064 nm was coupled in air to the lens to shape the beam into predetermined patterns. These patterns were then reduced with standard optics to a desired size. The images were focused at the faying surface of two plastic components in a through-transmission weld configuration. Weld quality was assessed on fidelity. In both cases, reasonably good results were obtained.
A Novel Approach to Manufacture Formaldehyde-Free Wood Based Biocomposites
This study examined the differences between wood composite panels made with maleated polyethylene (MAPE) and maleated polypropylene (MAPP) binding agents. Specifically, the study investigated the contrasts of (i) base resin type, PE or PP, (ii) molecular weight and maleic anhydride content in MAPP binding agents, and (iii) the manufacturing methods (reactive extrusion vs. hot press) on the physico-mechanical properties of the composites. Results showed that while extruding the particles before panel pressing gave better internal bond strength, superior bending properties were obtained through compression molding alone. MAPP based panels outperformed MAPE based panels in stiffness, likely due to the higher stiffness of the PP base resin. MAPE enhanced the IB strength compared to MAPP, attributed to better melting and flow of the polyethylene. Polymer base resin had no effect on MOR or screw holding capacity. Differences between the two maleated polypropylene compounds were not significant for any of the mechanical properties tested. Formaldehyde-free wood based biocomposite panels manufactured in this study often outperformed standard requirements for conventional particleboard, regardless of material composition or manufacturing method used.
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