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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Mold Filling and Curing Analysis in Scrimp
In recent years, vacuum-assisted resin transfer molding (e.g. Seemann Composite Resin Infusion Molding Process - SCRIMP) has been widely used for marine, civil infrastructure, transportation and defense applications. Unsaturated polyester and vinylester resins are two major resins used in these processes. Their kinetic and rheological behaviors were investigated experimentally. A model was developed to quantify the effects of different curing agents on the gel time and reaction rate. This model, in conjunction with fluid flow and heat transfer models, was used to determine the effects of resin type and composition, curing temperature, and part geometry on mold filling and curing. SCRIMP experiments were carried out to verify the simulation results.
Improving the Performance of Rotomolding Resins
Rotational molding is one of the fastest growing processes in the plastics industry today. However, this growth has been somewhat restricted by the number of and types of resins available to the molder. Polyethylene has traditionally been the workhorse for the industry because of its ease of processing. Unfortunately polyethylene lacks stiffness, along with other mechanical properties, compared to the resins used in competitive processes. This paper outlines methods to improve the performance of rotomolding resins using processing techniques, modifying the design of the part and by the inclusion of strengthening additives in the polymer matrix.
Laser Surface Modification of Polymers to Enhance Adhesion Part II-PEEK, APC-2, LCP and PA
Excimer lasers have been employed to modify the surfaces of a range of polymers to enhance adhesion. Considerable increases in joint strength were achieved as a result of laser treatment. Many lap shear joints, exposed to hot/wet environments, provided high retention of joint strength and durability. Laser-treated PEEK and APC-2 joints exposed at 50°C and 96%RH for several weeks, showed excellent resistance to ageing.
Stereolithography Inserts - Pros" and "Cons" to Use Tin as a Backfilling Material"
Stereolithography inserts shells for injection molding tools are filled in the backside, aiming to support high pressures and to improve the cooling efficiency on the mold. A common backfilling material used is an alloy of bismuth. However, there are other alternatives, such as tin, which has a higher thermal conductivity. This article discusses the pros" and "cons" to use tin as a backfill and investigates if it provides a better cooling condition improving mold's life."
Enhancement of Natural Fiber-Epoxy Interaction Using Bi-Functional Surface Modifiers
Enhancement of fiber-matrix interaction for a jute-epoxy composite system was attempted by surface modification of the fibers. The surface modification of jute fibers was achieved using bi-functional amines, which were capable of bonding with both the fiber and the matrix. The changes in interface bonding were observed by measuring the flexure modulus of the composite samples.
Effects on Mechanical Properties of LLDPE after Modification with Organic Peroxides
The action of two differents organic peroxides at 290°C on the mechanical properties of linear low density polyethylene (LLDPE) viewing its application as internal pipeline coating was studied. When the amount of crosslinking agent increased on polyolefin it was observed that for both peroxides a decreasing of elastic modulus and stress at yield. The stress at break raised and the drop of elongation at break cocurred from 0,5% of peroxide.
High-Performance Poly Metal Composites Replace Lead in Many Applications
A new injection moldable thermoplastic composite has been developed to eliminate problems associated with lead. This nontoxic polymer-metal composite can be formulated to meet the density, mass, and radiation-shielding properties of lead, while offering superior strength and design flexibility. The use of this material eliminates lead-toxicity issues encountered in handling, fabrication, and disposal. Target applications include: nontoxic projectile cores and shot, radiation shielding for medical and nuclear power, counterweights, sporting goods, ballast systems, vibration dampening, sound proofing, and many other applications where a nontoxic, high-density, high-strength material is required.
Ballistic Impact Resistance of Thermoplastic Composites
The correlation between adhesive strength, stiffness, flexural properties and ballistic impact resistance of Kevlar-KM2 composites with polysulfone (PSU) resin matrix was studied through examination of the failure of the composites on different processing conditions. Processing temperature greatly changed resin molecular conformation. Resin molecular conformation directly influenced composite flexural properties as well as ballistic impact energy absorption. Composites processed at 260°C showed significantly higher ballistic impact resistance than composites processed at 350°C. Significantly different failure mechanisms of these composites that are induced by different processing conditions are considered to be responsible for this result. The former exhibited mainly tension mode of failure whereas the later failed mainly shear cut. Fiber straining accompanied with delamination due to the tension mode of failure is the preferred failure mechanism for better ballistic impact energy absorption.
New Thermally Conductive Thermoplastics Offer Freedom of Design in Heat-Management Applications
A new thermally conductive compound available in a variety of crystalline thermoplastic matrices can be used to improve material management in a variety of industrial and consumer applications, including heat sinks, thermostats, heat exchangers, and as radiant heating coils. Replacing heavy metal shrouds and non-recyclable metallized plastics, the new compounds are non-corrosive, can be processed on all conventional thermoplastic equipment, and can even be melt reprocessed for in-plant recycling. A variant on the technology also produces compounds that are simultaneously thermally and electrically conductive.
Parameters Affecting the In-Line Measurement of Gas Solubility in Thermoplastic Melts during Foam Extrusion
The knowledge of gas solubility at processing conditions is of paramount importance for the understanding and optimization of extrusion foaming by gas injection. A recently developed in-line optical method is used to generate data of the solubility of atmospheric gases in PS and PET in single or twin screw extruders with gas injection capabilities. Overall, the in-line data compare favorably with off-line data where Henry's law constants were obtained from the slope of solubility/equilibrium gas pressure plots. Results obtained with the twin-screw extruder configured for improved mixing indicate: a) better data consistency, presumably as a result of enhanced homogenization/dissolution and longer residence time, and, b) a higher degree of sensitivity in detecting differences in the solubility of different gases.
Improved Organotin Stabilizers: Continuing Health and Environmental Research
Years of experience and significant research support using organotin mercaptides as PVC stabilizers. Safe use of organotin stabilizers involves following Material Safety Data Sheet instructions and using adequate engineering controls and/or personal protective equipment. Modifications of stabilizers to develop more efficient formulations continue. Product stewardship includes continued development of data to improve our understanding of the effects of materials. An overview of stabilizer trends in the industry, existing data, and planned health/ environmental research is presented.
Preparation of Microporous Films from Immiscible Blends via Melt Processing
Microporous films from immiscible blends were produced via melt processing and post-step treatments. Polystyrene (PS)/polypropylene (PP) and poly(ethylene terephthalate) (PET)/polypropylene (PP) blend systems with different viscosity ratios were studied. The blends were first compounded in a corotating twin-screw extruder and subsequently extruded through a sheet die to obtain the precursor films. These were uniaxially or biaxially drawn (100-400%) with respect to the original dimension to induce microporous structure and post treated at elevated temperature to maintain the porous structure which consisted of uniform microcracks in the order of a few hundred nanometers. The fabrication process here is shown to be a promising technique for producing microporous films that can be used for liquid and gas separations, as suggested from permeability measurements.
Polyethylene Synthesis Using Zeolites as Support Material for Metallocene Catalysts
In the synthesis of polyethylene, sodic mordenite and acid ZSM-5 zeolites were evaluated as support material for bis (cyclopentadienyl) zirconium dichloride catalyst system. The zeolites were calcinated at 300°C before treatment with methylaluminoxane (MAO) and Cp2ZrCl2. The supported catalyst systems were evaluated in terms of polymerization activities by varying the temperature of Cp2ZrCl2 impregnation on the support and the MAO and Cp2ZrCl2 concentrations.
Use of Contact-Atomic Force Microscopy in Plastic Material Surfaces
The operating conditions of an atomic force microscope in contact mode (C-AFM) were determined for polymer surface analysis. Isotactic polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS) film surfaces were analyzed. The most important restriction was to obtain sharp and clear 3-D images of the polymer microstructure without causing any harm to the specimens by the microscope tip. The obtained operating conditions were a force around 10-9 N and a scanning frequency range from 1.0 to 1.5Hz. These operating conditions are very far from the normal ones used for other rigid materials.
High Molecular Weight Film Resins with Increased Stiffness
High Molecular Weight High Density Polyethylene resins for film markets typically fall into a relatively narrow range of densities to provide the desired product functionality. For example, resins targeted for the tee shirt bag market require tear and puncture properties that require melt indices of around 0.05 and densities around 0.950. Development of these resins and their respective bags has allowed for substitution of HMW-HDPE for paper in many markets. Additional substitution appears available, but require resins with both high strength and higher modulus. Using technology to produce bi-modal molecular weight distributions, film resins meeting these requirements have been produced. The resins and their end-use applications will be discussed.
Properties and Applications of Sandwich Panels Based on PET Foams
PET foams of variable densities, (1 g/cc to 0.2 g/cc), based on virgin and recycled material were produced by extrusion with physical or chemical blowing agents and evaluated as low density core in sandwich panels having M/F impregnated paper or flame retardant mineral reinforced PET as skin faces. Flexural and shear stiffness of the laminates were determined by variable span three point bending. Panels were also tested for thermal and moisture stability and compared with competitive sandwich constructions based on PVC foam, flake board, particleboard and plywood. Potential applications of the PET based laminates in building and construction are presented.
On the Experimental Investigation of High-Frequency Dielectric Sealing of PVC
This feasibility study deals with the investigation of welding Polyvinyl Chloride (PVC) sheets of different formulations, using high dielectric frequency technique. The experimental work consisted of PVC formulation (rigid sheet), mold design (new products), experimental design to quantify the effect of process parameters, mechanical characterization (tensile, peel testing) of the weld area, and process optimization. Rigid PVC formulation was selected based on two primary mechanical properties, tear resistance and shear modulus. The weld was well achieved within the studied range of parameters, while the processing conditions were experimentally optimized. Finally, new office items were successfully produced as a result of the design of new molds combined with new process layout (sheets).
Comprehensive Study of a New Extensional Flow Mixer
A patented Extensional Flow Mixer (EFM) (1) has been developed in which plastics is hydrodynamically mixed by flowing through a series of convergent and divergent regions so that very efficient dispersive and distributive mixing can be achieved. The EFM can be attached to any plastics pumping machine, such as single-screw and twin-screw extruders, for injection molding, blow molding, extrusion, and compounding. Comprehensive laboratory and industrial tests have been conducted especially for film applications, which indicate the mixing of a single-screw extruder (SSE) with an EFM can outperform that of a twin-screw extruder (TSE) in certain aspects. Results of gel elimination, strength enhancement and morphology changes are presented.
Pressure-Volume-Temperature Dependence in Polyvinylidene Fluoride and Polyvinylidene Fluoride-Hexafluoropropylene Copolymers
The relationship between pressure, volume and temperature (PVT) of polyvinylidene fluoride homopolymers (PVDF) and polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) copolymers was determined in the pressure range of 200 to 1200 bars and in the temperature range of 40°C to 230°C. Differential scanning calorimetry (DSC) analysis was performed on each resin to simulate the cooling process during the PVT experiments and to determine the crystallization and melting temperatures at atmospheric pressures. The TAIT state equation describing the dependence of specific volume on the zero-pressure volume (V0,T), pressure and temperature has been used to predict the specific volume of PVDF and PVDF-HFP copolymers.
On the Prediction of Crystallinity Distribution in Injection Molded Semi-Crystalline Thermoplastics
Injection molded semi-crystalline thermoplastic parts show variable morphologies across their thickness. Process parameters such as injection speed, mold temperature, and melt temperature, play important role in forming these morphologies. The heat and shear history has great effect on the crystallization process of the semi-crystalline plastics. In this study, different available crystallization models were used to predict the crystallinity distribution, and capabilities of the models compared. Based on the results from these models, a more realistic model, which considers stress relaxation during the crystallization process, is proposed.
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