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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Environmental Stress Cracking (ECS) of Abs (II)
Environmental stress cracking (ESC) of acrylonitrile-butadiene- styrene (ABS) co-polymer caused by two kinds of non-ionic surfactants was studied by edge crack tension (ECT) tests. The dependence of the ESC on temperature and on the kind of surfactant was investigated. The fracture surfaces were investigated by a scanning electron microscope (SEM). It was found that the rise of temperature had a different effect on each surfactant. The crack propagation behavior of each surfactant at different temperatures was understood from the change of morphology at the crack tip.
A Criterion for the Onset of Gross Melt Fracture of Polyolefins: Molecular Structure Effect
In this work, a critical extensional stress is proposed as the criterion for the onset of gross melt fracture. This stress is estimated by means of the entrance pressure drop analyses developed by Cogswell and by Binding. This criterion for the onset of gross melt fracture was evaluated for several constrained geometry catalyzed (CGC) and metallocene, linear low, and high density polyethylenes. The presence of a low level of long chain branching in CGC polyethylene enhances the critical extensional stress, as compared to purely linear polyethylene. High density polyethylene blends having large low molecular weight fractions exhibit higher critical extensional stress than blends with lower amounts of low molecular weight material. Finally, a polymer having a broad molecular weight distribution shows a higher critical extensional stress than a narrow molecular weight polymer. The critical extensional stress for the onset of gross melt fracture is independent of temperature.
Eliminating PVC Degradation during Injection Molding Using Computational Techniques
New vinyl compounds with lower viscosity and increased thermal stability have been developed for injection molding. Furthermore, more advanced and robust computational techniques allow for proper design of molds and determination of process conditions. Yet, even with all the recent advancements, there still exists a need for either expertise or a trial-and-error" approach to optimize injection molding of vinyl compounds. This is due to the limited amount of detail that can be included when designing complex parts in order to reduce computational time. Research was performed in order to gain better understanding of important parameters for injection molding of vinyl compounds. The goal of the research was to increase the level of detail in the thickness direction and include a model of the degradation kinetics by reducing the complexity of the geometry being studied. The parallel plate flow geometry was evaluated in this study using a finite difference scheme to provide detailed information about viscous heating during injection. A "stop-and-go" technique was used to simulate the filling process; the degree of degradation was evaluated by implementing a computational tracer method. The simulation results were compared to experiments performed using a spiral mold."
The Influence of Polymer Rheology on Bubble Penetration in Gas-Assisted Injection Molding
The influence of polymer rheology on the wall thickness and flow dynamics during the filling stage of gas-assisted injection molding is examined. Isothermal experiments are conducted with tailored ideal elastic fluids to isolate the influence of polymer elasticity on the hydrodynamic coating thickness formed during the bubble penetration process. The results indicate that the wall thickness increases with increasing elasticity and extensional viscosity. The results for several tube diameters are scaled onto a single master curve using the Deborah number (De). Flow visualization and particle tracking experiments are conducted to investigate the flow field in the vicinity of the bubble front. It is concluded that the extensional rheology plays an important role in determining the wall thickness in gas-assisted injection molding.
Evolution of Structural Hierarchy in Uniaxially Deformed Poly Lactic Acid Films as Followed by Spectral Birefringence Technique and Others
Polylactic acid, PLA, is a relatively new biodegradable polymer primarily used for biomedical as well as mass-market packaging applications. PLLA is a polyester comprising repeating units of the lactide residue with an asymmetric carbon atom. Because of its biodegradability to nontoxic products and good plastic properties of that polymer makes it suitable for use in film studies. De Santis and Kovacs showed that the unit cell of PLLA is pseudo-orthorhombic with dimensions of a=10.7 Å, b=6.45 Å, c= 27.8 Å and ?=?=?=90°, where the molecules assume a 10/3 helical conformation. (1).Eling et al reported the existence of another modification, which they called ?-crystal modification (2) Hoogsteen et al. studied the influence of the preparation conditions on the presence of the crystal modification (3). Fischer et al investigated solution grown crystals of lactide polymers (4). Also Kalb and Pennings estimated the crystallization of PLLA from bulk state and solution (5). Tadakazu and Masuko investigated the relationship between the fine structure of PLLA and its physical properties (6). The need for polymeric biodegradable films is well established. The use of films occurs in the packaging and disposable article industries. In light of depleting landfill space and adequate disposal sites, there is a need for biodegradable films. Currently films from nylon, polypropylene, polyethylene, polystyrene, PVC, are noncompostable, which is undesirable from an enviromental point of view (7). In this paper, we present our results on the development of structure in uniaxial and biaxial stretching of PLA and subsequent heat setting process as followed by the new spectral birefringence technique we adapted for rapid acquisition of birefringence during the course of heat setting.
Autonomous Arrangement of Cooling Channels Layout in Injection Molding
This paper deals with a methodology for designing an effective layout of cooling channels to make a desired temperature distribution on cavity surface in injection molding. A cooling channel is modeled as several Cooling Elements that remove heat from a cavity surface. These elements move in the mold according to the information that is ordained by Source Elements located on a cavity surface to estimate temperature distribution on cavity surface. A layout of cooling channels is autonomously decided through an interplay between Cooling Elements and Source Elements. Several numerical experiments assuming heat-transfer to be steady-heat conduction have been a good indication that this method can design an effective layout of cooling channels and can estimate the necessary number of cooling channels.
The Influence of Polypropylene Content on the Properties of Post Consumer Recycled High Density Polyethylene
Polypropylene (PP) from bottle caps is present in High Density Polyethylene (HDPE) in post consumer recycled resin, and it acts to reduce the overall toughness. This study is concerned with quantifying the influence of PP on the physical properties of recycled HDPE resins and evaluating toughening recycled HDPE/PP blends by the addition of metallocene catalysed linear low density polyethylene (m-LLDPE). The toughness of HDPE was found to decrease significantly with as little as 5 wt% PP, and at 20 wt% the toughness was reduced to levels comparable to that of PP alone. The addition of m-LLDPE was effective in increasing the toughness of the blends to values comparable or greater than those of recycled HDPE alone. The principal mechanism seems to arise from the suppression of crystallinity of HDPE matrix for levels of up to 20% m-LLDPE, and the introduction of amorphous phase content within the samples.
Prediction of Plasticizer Solvency Using Hansen Solubility Parameters
The solvating strength of a plasticizer for poly (vinyl chloride) resin is a measure of the interactive forces between these two materials. Hansen’s three dimensional solubility parameters provide a quantitative measure of these interactive forces. Using COACTSM service, a computer program designed for solvent systems with various resins, plasticizers were found to lie near the edge of the solvency “sphere” of PVC. The relative positions of various plasticizer structures are in the expected order, while known solvents show strong association and lubricating additives fall outside the solvency sphere of PVC.
Plasticizer Factors Influencing Take-Up by PVC Resins
The ease with which plasticizer is combined with poly (vinyl chloride) resin is a measure of processing characteristics critical in the dryblending of suspension PVC, and the gelation of plastisols. Using commercial grade plasticizers, this study developed predictive equations for the following processing parameters of dialkyl phthalates in PVC: • Relative dryblend rates in suspension PVC as a function of plasticizer viscosity. • Relative initial gelation temperatures in plastisols as a function of plasticizer molecular weight and solvating strength. • Relative final gelation temperatures in plastisols as a function of plasticizer solvating strength. This information allows one to predict the relative processing characteristics of any dialkyl phthalate plasticizer for PVC on the basis of its chemical and physical properties.
Hot Plate Welding of Blow Molded Parts: Influence of the Blow Molding Process on Weld Strength
The manufacturing process of complex blow molded parts does not only consist of the extrusion blow molding process but is finished of by hot plate welding. Especially with plastic fuel tanks more and more parts such as nipples, holders for hoses or clips, etc. are being welded on. The strength of the weld seam does not only depend on the welding parameters but also on the quality of blow molding such as wall thickness, wall thickness distribution or warpage. These characteristics result in different deformation during the heating and the joining phase. The correlation between the blow molding process, the quality of the blow molded part and the weld strength is shown.
Processing and Mechanical Properties of Co-Continuous Polymer Blends
Blending poly(ether-ester) and SEBS thermoplastic elastomers (TPEs) with ordinary pseudoplastics, at temperatures where the TPEs are microphase separated, results in stable co-continuous morphologies over a wide composition range. Processing the same blends at temperatures where the TPEs have a single phase melt, showing normal pseudoplastic behaviour, results in a much smaller range of co-continuity. Therefore, dispersed as well as co-continuous morphologies can be obtained at given compositions. The mechanical properties of dispersed blends are compared to those of co-continuous blends and it is shown that the elastic moduli of co-continuous blends are significantly higher than the moduli of the dispersed blends. No significant difference in tensile strength or impact strength was found.
Melt Spinning of Syndiotactic Polypropylene: Structure Development and Implications for Oriented Crystallization
Stereoregular polypropylenes can be prepared using metallocene-based catalyst systems. The objective of this work is to investigate structure development during melt spinning of syndiotactic polypropylene. The fibers are well crystallized at low spinning speeds, but are only poorly crystallized at higher speeds. The helical nature of the preferred crystal form is responsible for the substantial differences in crystallization behavior of the syndiotactic PP compared to isotactic PP. Implications regarding crystallization kinetics in oriented systems with conformation-dependent crystallization are also addressed.
High Quality Flax Fibre Composites Manufactured by the Resin Transfer Moulding Process
In this work the use of high quality natural fibres as reinforcements was studied using the resin transfer moulding (RTM) processing technique. The fibres were unidirectional high quality ArcticFlax and the matrix was an epoxy resin. The mechanical properties of the composites were compared to conventional RTM manufactured glass fibre composites, traditionally retted UD-flax fibre composites and to the pure epoxy. The results from mechanical testing showed that the (50/50) high quality ArcticFlax/epoxy composite has a stiffness of about 40 GPa compared to the stiffness in pure epoxy of 3.2 GPa. The same composite has a tensile strength of 280 MPa compared to 80 MPa of the epoxy. RTM showed to be a suitable processing technique for natural fibre composites when high quality laminates are preferred.
Coextrusion Blow Molding with LCP
Because of their high barrier properties, high temperature capability, and resistance to chemicals, liquid crystal polymers (LCPs) are ideally suited for use in multilayer containers. This paper will describe a coextrusion die and process for orienting the LCP layer in a PET-tie-layer/LCP three-layer container with approximately 13 percent LCP, showing oxygen barrier properties over 10 times better than a PET container of equal volume and wall thickness. Low shrinkage after hot fill, and excellent resistance to flavor loss will also be demonstrated. The process is applicable to other thermoplastics with LCP, and applications for packaging of beverages, fragrances, solvents, and other chemicals will be discussed, along with comparison against alternative multilayer containers.
Relaxation Phenomena in Liquid Crystalline Epoxies
Liquid crystalline (LC) epoxies have been of great interest to academic and industrial communities because they combine the performance of epoxies with the anisotropic properties of LC polymers. In this study, we investigated the effect of structural changes on the frequency dependent dielectric relaxation in a series of aromatic thermotropic main chain LC epoxies by broadband dielectric relaxation spectroscopy and differential scanning calorimetry. Various polarization mechanisms were identified over a wide range of frequency and temperature. The molecular origin of these relaxations was assigned and dipole dynamics was described in terms of the location and intensity of relaxation spectrum.
Systemic Development Models of Polymer Mouldings and the Appropriate Injection Moulds
Many activities during the manufacturing of mouldings and the appropriate mould are carried out simultaneously. This proves the need to apply the basic principles of systemic technology theory to the development and production system of polymeric mouldings. The development of an appropriate mould for injection moulding can be regarded as a real sub-system of the development and production system of the mouldings. The planning of a systemic model in this case means defining of the exact sequence of activities during the mould development. Thus the guidelines for mould development are created, which can serve especially to inexperienced mould designers.
Joining of Nylon Based Plastic Components - Vibration and Hot Plate Welding Technologies
Previously we reported to SPE'96 the optimized mechanical performance of linear vibration welded nylon 6 and 66 butt joints. Under the optimized vibration welding conditions (amplitude, pressure, meltdown, thickness of interface), the tensile strength at the nylon butt joints was equal to or 14% higher than the tensile strength of the base polymer (matrix). H. Potente and A. Brubel presented to SPE'94 and SPE'98 an analysis of the welding performance in a family of amorphous and semi-crystalline thermoplastics including nylon 6 using hot-plate welding technologies. For hot-plate welded nylon 6 with a range of glass-fiber reinforcement from 0 to 40% (by weight), the tensile strength at the weld was 40-60% less compared to the tensile strength of the base polymer. We performed a comparative study of mechanical performance of welded nylon's butt joints. In this study we analyzed the efficiency of both widely used joining technologies: vibration welding and hot plate welding. Under the optimized hot plate welding conditions, tensile strength of both nylon 6 and 66 joints is close to or slightly higher than the tensile strength of the base polymers. Presented results will help plastic parts designers, material developers and manufacturers, by giving them alternatives when choosing types of nylon (6, 66, 66/6, 46, etc.) and welding technologies for a wide range of applications.
Direct Measurement of Slippage Induced by a Polymer Processing Additive
Flow profiles of a linear low density polyethylene (LLDPE) were measured in an optical slit die situated at the exit of a twin screw extruder. The velocities of tracer particles were measured as a function of position across the slit die at various flow rates. The results show that the presence of a PPA (Dyanmar) in the polymer melt induces slippage on the surfaces of the die. The occurrence of slippage indicates that the process improvements obtained with this high energy additive occur via migration to the polymer-metal surface and subsequent reduction in the effective friction" between the polymer and the wall."
Relaxation Processes in Polymer Networks by Dynamic Light Scattering and Dielectric Spectroscopy
Isothermal chemical reactions of network forming monomers or functional polymers produces a continuous increase in the systems Tg and the accompanying cooperative segmental relaxation time (? process). Both broad-band dipolar relaxation spectroscopy (DRS)-probing the ? process via dipolar reorientational mobility, and dynamic light scattering (DLS)-probing the ? process via correlation times of density fluctuations, were used to monitor the system in-situ (to our knowledge, the first study of its kind). An excellent agreement was found between DRS and DLS for the ? process characteristic parameters: relaxation time and KWW stretched exponential parameter (characterizing the relaxation breadth). It was concluded that the broadening of the ? process is due to a general phenomenon: the microscale heterogeneous nature of glass formers.
Dielectric Relaxation Spectroscopy of Reactive Network-Forming Polymers
Dipole dynamics in network-forming polymers were investigated by broadband dielectric relaxation spectroscopy (DRS). The changes in reorientational dynamics during the advancement of reactions were used to (1) describe the molecular origin of various relaxation processes (?,?), (2) propose a methodology for evaluation of the kinetics of network formation, (3) describe the dynamics in terms of the location and intensity of relaxation spectrum, and (4) advance an interpretation of network dynamics in terms of intermolecular cooperativity. The chemical state of network at various stages of cure was identified by simultaneous DRS and remote fiber-optic FTIR.
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