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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A New Approach for in-Mold Finishing: The Valyi Surface Finishing/Compression Molding Process
The Valyi SFC molding process for surface finishing/compression molding (SFC) provides an economical route to molding and Class A finishing of large thermoplastic parts in one step. In the Valyi Process, decorative film or fabric is placed over a mold cavity in a press. Plastic melt is then deposited onto the film which subsequently heats the film to a formable temperature. Positive air pressure may be supplied to support the film/molten plastic. The press is then closed to form the final finished part. The process is similar to the textile back molding process. The Valyi Process uses much lower pressures than conventional injection molding. Molding (cavity) pressures for the Valyi Process are <<10 MPa (1450 psi) as compared to conventional injection molding which is typically >30 MPa (4350 psi). The in-mold lamination of paint film achieves the paint appearance and protection without the environmental and cost impact of conventional painting. Also, heating the film using the heat from the deposited melt eliminates the pre-heating step in the in-mold injection molding process. This paper describes the Valyi SFC Molding Process and reveals the advantages such as the mechanical performance of the part, reduction in cost and reduction in paint pollution, which can be achieved over the conventional injection molding - painting process.
Dynamic Mechanical Thermal Analysis (DMTA) of Barrier Materials Immersed in Automotive Fuel Components
EC legislation has ordered vehicular hydrocarbon emissions to be drastically reduced by the year 2000. New polymeric materials must be used to manufacture fuel storage / delivery components. Such materials must offer increased barrier performance without loss of mechanical properties. Samples of poly butylene terephthalate (PBT), two types of poly vinylidene fluoride (PVdF) and THV, a terpolymer of tetrafluoro ethylene, hexafluoro propylene and vinylidene fluoride, were immersed in pure methanol, ethanol and toluene. The effect of the degree of solvation on the glass transition temperature (Tg) and the storage modulus (E') of each material were measured using dynamic mechanical thermal analysis (DMTA). Significant changes in Tg and E' were evident in each case, but behavioural differences were apparent between different polymers in a given solvent, and also for a given polymer in different solvents. In all cases, the Arrhenius activation energy changed on solvation.
Determination of Optimum Extrusion Conditions for Multilayer, Low Emission Plastic Fuel Line Systems Using Dual Capillay Rheometer Techniques
Multilayer co-extrusion of plastics is fast becoming a very cost effective method of improving the barrier properties of plastic products. In this process individual polymers are melted and conveyed by separate extrusion systems, into a common distribution block and through a forming die where the polymer melts merge to form an integral multilayer structure. Many of these polymers do not form a mutual bond in the melt and so specially formulated tie layers have been developed in order to facilitate melt bonding and so prevent delamination. Multilayer polymer tube structures have recently been developed for use in automotive fuel lines. These multilayer structures are proving difficult to extrude because of their widely different temperature profiles required during extrusion, and the fact that all the melts enter a common die which can only be maintained at one particular temperature. The melt rheological characteristics of a range of commercially available barrier materials, polyvinylidene fluoride (PVDF), a terpolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene (THV), plasticised Nylons and tie layer materials have been studied using Dual Capillary Rheometric techniques. The relative change in shear viscosity with temperature, up to 270°C and shear rates up to 103 sec-1 have been investigated, for these materials, in order to determine optimum extrusion parameters during manufacture. The findings are confirmed by pilot plant tube extrusion trials using various multilayer structures. Arrhenius flow activation energies are also reported.
The Effect of Fuel Components and Standard Test Fuels on the Mechanical Properties and Glass Transition Temperature of Polymers Used in Mult-Layer Fuel Line Tubing
With the advent of more stringent legislation for fuel and fuel vapor emissions from vehicles, it has been necessary to introduce a barrier polymer into the fuel line as a means of reducing emissions. This paper investigates the changes in mechanical properties, such as tensile modulus, of a range of plasticized nylons, tie layer polymer systems and fluoropolymers which were immersed in various mixtures of fuel components and standard fuels at a temperature of 25°C. The percentage mass uptake and extent of swelling were also determined in addition to changes in glass transition temperature up to a period of 31 weeks.
Reactive Blends of Polyvinyl Chloride and Polyurethane
Effects of PVC resin and PVC stabilizer on thermoplastic polyurethane (TPU) polymerization kinetics are studied using DSC and adiabatic temperature rise measurements. Addition of PVC results in partial absorption of the unpolymerized polyester component of the TPU mixture resulting and lowers the rate of reaction. Thermal characterization of melt and reactive blends of PVC and TPU showed one glass transition indicating miscibility. However, SEM revealed that the PVC/TPU melt blend contained small PVC primary particulates dispersed in the TPU matrix. The PVC/TPU reaction blend exhibited no observable PVC particulates under the same magnification.
Influence of a Surfactant Additive on the Crystallization of Syndiotactic Polystyrene and Sulfonated Polystyrene
Syndiotactic polystyrene (sPS) was mixed with dodecylbenzene sodium sulfonate (DBSNa), benzene sodium sulfonate (BSNa) and dodecylbenzene (DB), to investigate the influence of these additives on the crystallization behavior of sPS. The crystallization of sPS containing DBSNa was significantly slower than that of sPS containing DB or BSNa. Since SAXS investigations indicated the presence of DBSNa aggregates within sPS/DBSNa samples, the observed decrease in the rate of crystallization is attributed to a slow expulsion of the bulky DBSNa aggregates from the crystalline growth front. In comparison, sulfonated syndiotactic polystyrene (SsPS)/DBSNa mixtures crystallized faster than SsPS, due to a disruption of the electrostatic crosslinks by DBSNa.
Flow Instability Reduction of PP through Blending of EVA
Flow instabilities are often encountered during extrusion of high molecular weight Polypropylene homopolymers. Traditional techniques of flow instability reduction such as addition of fluoropolymers or compatibilizers significantly increase the cost of the finished product. During this study it was found that blending small amounts of Poly (Ethyl Vinyl Acetate) EVA into the Polypropylene PP matrix eliminates melt fracture fonnation within a reasonable operating window, maintaining acceptable mechanical properties. A wide range of EVA concentrations was tested using capillary rheometry, microscopy and mechanical analysis. The acceptable operating window without instabilities was determined by analyzing the extrudate surface under the microscope.
Molecular Modeling Studies of the Molecular Components of Starch. I. an Atomistic Model of the Double Helical Structure of Amylose and Amylopectin
Starch is made of amylose and highly branched (amylopectin) ?-linked chains of D-anhydroglucose. A detailed atomistic model for the amylose and amylopectin components of starch was simulated using established molecular modeling methods. In particular, attention is paid to the formation of A and B amylose in the double helix configuration, and to the formation of the double helix configuration after the branch point in amylopectin. Molecular dynamics simulations are carried out over extended periods of time, and calculations suggest that the observed crystallographic parameters for the A and B forms of amylose can be reproduced with water molecules either inside the core of the double helix or with the core devoid of water. In both cases the strand repeat distance of ~2.14 nm is found. Models of the amylopectin macroscopic formation are described and speculation as to the molecular details of the amorphous high solvent and crystalline starch structure are made.
Use of a Hexafunctional Coupling Agent to Control Free Radical-Induced Molecular Weight Degradation during Reactive Processing of Polypropylene
Variable quantities of a hexafunctional coupling agent were reacted with polypropylene (PP) in a twin-screw extruder. An increase in the z-average molecular weight was observed, and attributed to the formation of PP crosslinks through the coupling agent, which tended to offset molecular weight degradation due to ?-scission. The mechanical properties and morphologies of the resultant extrudates were analyzed. Notched Izod impact and tensile strengths were enhanced over those of the control, which lacked added coupling agent. The presence of coupling agent crosslinks resulted in increased nucleation and growth rate during crystallization from the melt.
Fill Length Determination for a Non-Intermeshing Twin-Screw Extruder
This paper describes the effect screw speed and material throughput have on the filled regions in front of restrictive elements on a Non-Intermeshing Twin-Screw Extruder (NITSE). Fill length, operating conditions, material properties, and the pressure over the cylinders are all measured and compared to a model of pressu fill lengths can be predicted for a non-transparent barrel from geometric terms and material properties."re buildup in the screw elements of a NITSE. Experiments are performed over a range of operating conditions in a clear barrel ?0.8 NITSE. By determining the relationship between fill length and pressure across the cylinders
Fill Length Determination for a Non-Intermeshing Twin-Screw Extruder
This paper describes the effect screw speed and material throughput have on the filled regions in front of restrictive elements on a Non-Intermeshing Twin-Screw Extruder (NITSE). Fill length, operating conditions, material properties, and the pressure over the cylinders are all measured and compared to a model of pressure buildup in the screw elements of a NITSE. Experiments are performed over a range of operating conditions in a clear barrel ?0.8 NITSE. By determining the relationship between fill length and pressure across the cylinders fill lengths can be predicted for a non-transparent barrel from geometric terms and material properties."
Amorphous Orientation in Polymers Determined Using Two-Dimensional X-Ray Diffraction Data and its Significance
Amorphous orientation in polymers is described in terms of the fraction of the amorphous chain segments which are oriented, and the degree of alignment of the amorphous chain segments. The method for evaluating these two features using two-dimensional x-ray diffraction data is described. Whereas the unoriented amorphous component contributes to an isotropic amorphous halo, the oriented component gives rise to enhanced scattering near the equator. The method is illustrated using the data from PET and nylon 6. The role of amorphous orientation in determining dimensional stability, diffusion behavior and glass transition temperature is discussed.
Compositional Effect on Phase Behavior and Uniaxial Deformation Properties for Polyethylene Naphthalate/Polycarbonate Cast Films
The influence of Polycarbonate on the deformation behavior of PEN at temperatures between the glass transition and cold crystallization was investigated at PEN/PC compositions containing 5-30% Polycarbonate. Deformation studies revealed that the addition of as little as 5% Polycarbonate eliminates the neck formation that occurs in stretching of 100% PEN films at intermediate stretch ratios. This neck formation is responsible for narrowing the processing window of 100% PEN to high stretch ratios where the films become uniform after all the necks are eliminated. This neck formation was attributed to the cooperative reorientation of the naphthalene planes parallel to the film surface that occurs at highly localized regions upon stretching1. In this paper, the effect of PC concentration, processing temperature, deformation mode, and ratios on the dynamics of film formation and the structure and properties.
Advances in Thermoforming through the Use of ESPOR, a Micro-Porous Aluminum Mold Alloy
ESPOR is a new product that uses micro-porous casting technology for the production of tooling for the thermoforming industry. Some unique characteristics of ESPOR are: • The ability to cast off an existing pattern due to the absence of material shrinkage. • The porous microstructure of the material (10-15% air by volume) eliminates the need for drilling vacuum holes through the core or cavity area. In addition to the above, by having metallic cooling properties, excellent machining properties, and castable water lines, all in a package that weighs approximately 36% less than an aluminum mold, ESPOR promises to be a major tooling option in the future thermoforming industry.
Measuring the Diffusivity of Additives in Polymer Films Using In-Situ FTIR-ATR Spectroscopy
In many polymer-film applications, additives migrate from the bulk of a film to the film surfaces. For these cases, it is more realistic to measure the additive diffusivity in a diffusion-out mode rather than using a mass-sorption (diffusion-in) experiment. This is particularly true for additives that are solids at the testing temperature. This research focuses on the evaluation of additive diffusivity in a diffusion-out mode via in situ FTIR-ATR spectroscopy, which has the advantage of requiring only small samples of thin films. The technique will be described, including methods to obtain reproducible contacting pressure between a film sample and an ATR crystal and to perform in situ experiments at elevated temperatures. Diffusivity results are presented for the migration of an erucamide slip agent in LLDPE films.
The Use of Morphology Data in the Design of Injection Moulded Flat Products
Thermoplastics are one of the first choices that engineers consider for many practical applications. Most of those parts, often used in automotive or appliance products, are required to have high mechanical performance and are mostly made by injection molding. Strength and dimensional stability under stress are common requirements. Moreover, the quick completion of the development and production process before entry in the market is a mandatory specification for many plastic products. The design process of plastic parts follow the general pattern of the engineering design activity, which was partially reorganized for time-delivery shortening by implementing the concept of concurrent or simultaneous engineering . The overall process flow chart can be structured as shown in Figure 1.
Microwave and Optical Applications of Metallic Conductive Polymers
Recent progress obtained in the synthesis of conductive polymers with a well controlled structure have shown that high levels of conductivity can be achieved with a metal like character. The consequence is a large modification of their dielectric properties, especially in the microwave and optical range. So far, applications such as EMI shielding, microwave absorption or optical modulation have been developed with this class of materials. We are presenting here a survey on these works and we shall show how metallic conductive polymers represent, beyond their pure scientific interest, strong potentialities for microwave and optical applications.
Solubility of HFC-134A, HCFC-142B, and HFC-152A in Polystyrene
The vapor-liquid phase equilibria of HFC-134a, HCFC-142b, and HFC-152a in polystyrene were measured at temperatures from 348 to 473 K and pressures up to 3.2 MPa by using a volumetric method. The solubility of these blowing agents decreased with temperature. Amount of HCFC-142b, HFC-152a, and HFC-134a in polystyrene decreased in that order. The solubilities measured were correlated by the Sanchez-Lacombe equation of state. Agreement between the experimental solubilities and the correlations with a temperature-dependent binary interaction parameter was satisfactory. The interaction parameters linearly varied with temperature.
Evaluation of Additive Concentration Profiles in Multilayer Films
The diffusion of additives in single-layer polymer films has been characterized using FTIR microspectroscopy. This research extends that work to multilayer films. In particular, this investigation focuses on the diffusion characteristics of an erucamide slip agent in press-laminated bilayer and coextruded trilayer LLDPE films. The objective was to monitor the extent of additive partitioning between the various layers and to the outside surfaces of the multilayer films. Results demonstrate the effect of initial additive loading on the spatial distribution of additive and the apparent surface concentration as a function of time.
Proper Utilization of Porous Mold Steel to Solve Venting Problems
Since its introduction to the North American mold making market, this porous, self-venting mold steel has proven remarkably successful. This porous steel has allowed molders to reduce injection pressure, cycle times, shot size and scrap rates. Additional benefits have included elimination of flow lines, short shots, and material burning and ghosting on edges of textured parts. Design consideration should include: 1. Resins Used 2. Tool size 3. Prevention of Problems 4. Whether to use 3 micron, 7 micron or 20 micron porosity Additional considerations should be given to regular maintenance and cleaning of porous inserts.
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