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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Surface Recovery of PDMS after Exposure to UV/Ozone
Controlled surface oxidation of polydimethylsiloxane (PDMS) is commonly used in manufacturing of microfluidic devices since it is a very effective method of both bonding PDMS components together, and altering the surface properties of PDMS. The stability of these modified surfaces is crucial in determining the lifetime and reliability of the device. This paper investigates the stability of UV/ozone modified PDMS surfaces using x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM).
XPS Analysis of Uv Curable Adhesive and its Adhesion to PDMS
Adhesive joints were prepared between polycarbonate (PC) and polydimethylsiloxane (PDMS). This paper presents an x-ray photoelectron spectroscopy (XPS) investigation into the chemistry of adhesion between the adhesive and PDMS. UV pretreatment of the PDMS surface proved essential in obtaining strong adhesion.
Formulation of Optimally Stabilized Poly(Vinyl Chloride) Systems with the Aid of the Chemiluminescence Technique. Part II
The Chemiluminescence (CL) technique has been shown to be an accurate method to detect the formation of polyene sequences in the degrading PVC compounds. This part 2 of the paper analyzes the functions and performances of different classes of thermal stabilizers and co-stabilizers, i.e. mixed metal carboxylates, mercaptides, organic and inorganic HCl absorbers, phosphites and antioxidants by their CL. The ways of formulation of well rounded stabilization are offered.
Preparation of Poly(Methyl Methacrylate) and Carbon Nanofiber Composites by Chaotic Mixing
Composites of poly (methyl methacrylate) and carbon nanofibers were prepared in a chaotic mixer, and electrical conductivity and quality of dispersion were compared with those produced in conventional mixers. The threshold for electrical conductivity was about 1.5 wt. % for materials prepared in a chaotic mixer, while those produced in batch and continuous mixers were not conductive up to a loading of 4 wt. %. Thermogravimetric analysis revealed that the presence of carbon nanofibers delayed thermal degradation of the polymer.
Nanomechanical Properties of Viscoelastic Polymers
The surface mechanical properties of ethylene vinyl acetate (EVA) with various vinyl acetate (VA) contents have been investigated. These nano mechanical properties, obtained from the nanoindentation technique, were compared with bulk results from the conventional tensile test. Agreement in Young's modulus as a function of VA content is found between two data. The discrepancy in modulus value between surface and bulk was also found in EVA with higher VA content. We speculate that this is due to macroscopic structure effect on bulk modulus as well as intrinsic viscoelastic deformation behavior of EVA.
An Investigation into Hesitation Effects in Oscillating Flows
The hesitation effect is well known to adversely affect the appearance of molded products. In this paper, the effect of hesitation on aesthetics and dimensional properties is investigated via a design of experiments varying the materials, melt temperature, coolant temperature, injection velocity, and oscillatory time. Analysis and molding validation indicate that hesitation is related to solidification of the melt front rather than changes in melt shear stress.
Performance of a Self-Regulating Melt Pressure Valve
Injection molding has been limited by the lack of direct flow and pressure control of the polymer melt at multiple points in the mold during the molding cycle. A selfregulating melt pressure valve has been developed whereby the outlet melt pressure is proportional to the control force on the valve pin. This paper validates the capability to provide melt pressure control proportional to the supplied pneumatic pressure without melt pressure transducers.
Design and Performance Analysis of a Self-Regulating Melt Pressure Valve
A design for a self-regulating pressure valve is analyzed using a 3D flow analysis that utilizes independent shear and elongational viscosities for the polymer. The regulator is derived from a low force valve design that enables the outlet pressure to be directly regulated by a provided force on a valve pin without need for pressure sensors or a closed loop control system. Analytical and experimental results indicate an excellent level of response and consistency given the simplicity of the design.
Validation of On-Line Molding Process Simulation
Plastics injection molding has been limited by the lack of observability and controllability, such that it has not been possible to know or control flow rates and pressures at multiple locations in a mold. Using cavity pressure transducers and faster than real time process simulation, the described system provides estimates of the flow rates, part weight, melt temperature, and apparent viscosity before the mold opens and the parts are ejected. Validation results for part weight are provided for a two-cavity family mold with a valve-gated hot runner system.
Derivation of Process Windows
Selection of set-points is of vital importance to the quality and economics of manufacturing processes. However, most recipes are developed from recursive trial and error interpreted via prior human experience. A new analytical procedure based on the Extensive Simplex Method is presented that derives the global process window for an arbitrary number of process parameters and quality specifications that requires minimal process experimentation. The methods are applied to an injection molded component with width, length, and flash specifications and shown to provide excellent results.
Concept Design of a Wireless Pressure, Temperature, and Flow Rate Sensor for Injection Molding
A new concept design for a self-energizing, wireless sensor is presented. The sensor extracts energy from the polymer melt and transmits discrete acoustic signals whose timing indicates a pressure change and whose frequency indicates the melt temperature. A receiving system outside the mold receives the transmitted signals and reconstructs the melt pressures and temperatures. It then utilizes mapping and simulation techniques to estimate the pressure, temperature, and flow rates in the entire mold in real time.
A Review of In-Mold Pressure and Temperature Instrumentation
A survey of commercially available and broadly used pressure and temperature sensors for injection molding is presented. The various pressure and temperature sensing means are reviewed along with the geometry and performance of common transducers. Usage and trade-offs in sensor design and selection is discussed.
Modeling of the Film Blowing Process for High Stalk Bubbles
A simple equation with only a few physical parameters for the description of the high stalk bubbles has been derived from variational principles. The proposed equation was used in modeling of the film blowing process and a very good agreement between measured and simulated data was found.
Investigation of Zig-Zag Type of Interfacial Instabilities in Coextrusion
Modified Leonov model has been used for the viscoelastic stress calculation in the flat multi-manifold coextrusion die used for LDPE film casting process. It has been shown that specific type of high stress area occurs around the interface at the end of the converging section. This total stress has been found to be nonmonotonic along the interface and related for the onset of zig-zag type of interfacial instabilities when the total stress achieved 200 kPa.
Effect of Impulse Heat Sealing Process Parameters on Bond Strength of Low Density Polyethylene Films
In this paper, process and film parameters affecting the peel strength of impulse heat sealed thermoplastic polymeric films are investigated. In particular, the roles of film thickness and duration/temperature of application of impulse heat sealing tool are investigated for low density polyethylene. The data obtained are particularly useful in flexible packaging and film sealed container applications.
Plastic Piece Stress Analysis Using Simulation Software
The objective of this work was to evaluate mechanical properties of a cellular phone. Evaluation was made employing two commercial simulation programs. Acting bonds and external forces to simulate the phone opening action were determined. Programs used were capable of modeling static loads for the stress analysis by finite element mesh creation. Maximum wall shear stress and residual stresses showed maximum values in the gate area, in smaller thickness sections.
Finite Element Analysis of Living Hinge Behavior
The study investigates the high deformation and resulting high strains occurring during the flex of living hinge designs by putting a finite element model through the full range of motion. It investigates the ability of this technique to predict feature alignment after fully closing by comparing to actual molded parts. It investigates the feasibility of obtaining accurate simulation results from a model that undergoes high element distortion and material model at very high strains.
Visualisation and Analysis of Polyolefin Multilayer Coextrusion Flows
Flow visualisation studies were preformed to determine process parameters initiating interfacial instability in the coextrusion of polyolefin melts. Slit coextrusion visualisation cells with 30° and 90° convergent streams were studied. Studies were performed using two different extruder arrangements. Stress fields, quantified using birefringence. Concomitant velocity and layer ratios leading to wave type interfacial instability in the polyolefin melts are presented.
Electrically Conductive Immiscible Polymer Blends as Sensors for Chemicals
Sensors produced as extruded filaments based on HIPS/ABS/CB and HIPS/LLPE/CB blends were exposed to ethanol, acetone, heptane and benzene. The solubility parameters of the liquid and the blend components are important in determining the sensing level. Sensors based on proper immiscible polymer blends exhibit reproducible and recoverable electrical resistance behavior upon exposure to liquid/ drying air cycles, selectively responding to different liquids or liquid mixtures of different ratios.
Influence of Die Design on Interfacial Instabilities in Coextrusion
Fully viscoelastic FEM together with flow visualization technique are employed to quantify the effect of the die design on the wave type of interfacial instabilities in coextrusion. It has been shown experimentally that the minor channel geometry has a strong impact on the wave type of interfacial instabilities and the results can be correlated through novel criteria called as Total Stress Difference (TSN), which takes in to account the bulk change of the total stress in normal as well as tangential direction with respect to the interface.
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