SPE Library
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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Conference Proceedings
Welding Thermoplastic Foams
Foamed thermoplastics display economical potentials due to the material saving and reduced cycle time during the injection molding process. At present neither knowledge of the applicability of different welding methods exists, nor the process parameters to gain the optimum weld quality are known. In this paper an experimental study will be presented to analyze the effects of the process parameters on the attainable strength using the heated tool welding and vibration welding. Via three-dimensional experimental design all process-relevant parameters have been varied including the material density. It was found that the process parameters have a considerable influence on the weld results. Differences in terms of weld strength between the particularly small pores and large pores were found. Comparing to bulk material a major reduction of the cycle time has been observed. Connections between the melting characteristic and the process parameters were deduced.
CDs and Interactive Programs in Plastics Engineering Education
We have developed CDs1,2 and interactive programs that are being used in both polymer science and plastics engineering courses. These CDs contain various interactive programs and numerous animations. These materials can be used as self- learning tools with the aid of workbooks. Initial evaluation has been very positive with a high level of acceptance and use by students. The plastics industry is now the fourth largest manufacturing industry in the United States, accounting for $330 billion in annual shipments and directly employing more than 1.5 million people. A key to this industry remaining competitive with countries where workers are paid a fraction of U.S. wages is a skilled, educated, and flexible workforce. Over the course of the past five years, we have been working to address the need for technical personnel in this field through NSF funded projects whose goals have been the development of new and innovative educational materials and the dissemination and evaluation of this material.
Fibre Orientation Measurement and Prediction within Gates and Ribs of Injection Moulded Parts
Within this paper we discuss the effects of gating systems and ribs on the fibre orientation of injection moulded parts. Three-dimensional analyses were performed using the Moldflow MPI 5.0 commercial software with predicted fibre orientations compared to experimental measurements made at the University of Leeds. For many years thermoplastics have been extensively used in a wide variety of applications due to their relatively cheap cost and high processability, particularly by injection moulding. However, commodity polymers such as polypropylene and Nylon have relatively poor mechanical properties, which limits their use to non-structural applications. The use of short glass fibre reinforcement is a well-established means of significantly improving mechanical performance without compromising processability.
The Effect of Volume Fraction and Particle Size of Polystyrene onto Magneto-Rheological Properties of Inverse Ferrofluid
Inverse ferrofluids are prepared using microsized polystyrene particles dispersed in a ferrofluid. The magnetorheological properties were measured as a function of the particle size, and polydispersity. The measurements are performed in a plate-plate rheometer applying a vertically oriented magnetic field. The obtained flow curves show, that under shear a ”solid” to “liquid” transition take place, which is presumable due to the destruction of chains of the non-magnetic particles. This transition is characterized by an apparent yield stress and compared with theoretical predictions. In the oscillatory mode, the storage and loss moduli reveal, that also the viscoelastic behavior is affected by the particle size and the particle size distribution of the non-magnetic particles in inverse ferrofluids.
Enhanced TPO Thermoforming Using High Melt Strength Polyolefin Elastomers
Hard TPOs have grown rapidly in the automotive industry due to their favorable cost/performance characteristics and injection molding processability. Other plastics processes are now either currently used or under investigation. Processes such as blow molding and thermoforming offer the potential to manufacture large parts with much lower tooling costs than injection molding. However, it is well known that conventional polypropylene exhibits poor melt strength. This deficiency has limited its use in either large part extrusion blow molding or thermoforming.Recently, polypropylene producers have introduced high melt strength polypropylene into the market. These polypropylenes have much higher melt strength than conventional materials. They are being promoted for use in hard thermoplastic olefin (TPO) applications requiring high melt strength.However, other components, particularly the impact modifier, can now play an important role in the thermoforming characteristics of hard TPO compounds. In a series of experiments, significant changes in TPO rheology were observed, depending on the level and type of impact modifier used. The characteristics of ethylene/alpha olefin copolymer impact modifiers and their effect on hard TPO thermoforming performance will be discussed.
Morphological and Electrical Properties of the Adhesive for Lithium Ion Battery
This research intends to investigate the utilization of porous polymer for Li-ion second battery. The phase separation method was used to control the porous condition. Various solvents were used to generate phase separation when epoxy resin was cured. The void distribution of porous polymer was observed by scanning electron microscope (SEM). Furthermore, the porous adhesive was applied to the Li-ion battery. The effects of adhesive on the capacity and the cycle life of Li-ion battery were investigated.Results showed that the porous epoxy adhesive did not change the electrochemical reaction of electrode. The battery properties, such as the capacity, cycle life and the 1st irrev % are significantly affected by the porous adhesive. The ratio of discharge to charge was over 90% in the coin-cell test. The capacity of battery decreased slightly (about 6.91%(23mAh/g)) as the coating area of adhesive reached 20%(1cm2). The real battery cycle life is more than 85% after 250 times test, which meets with the standards of the commercial grade.
A Comparison of Process Configurations for Compounding Woodfiber-Plastic Composites
The market for woodfiber-plastic composites is growing at an astounding rate. Subsequently, numerous machinery manufacturers and individual processors have been scrambling to develop unique methods for continuously mixing, devolatilizing, and extruding these materials, in an attempt to increase manufacturing efficiency and to optimize finished products properties.A wide variety of devices, including parallel twin screw extruders (co- and counter-rotating), conical twin screw extruders, continuous mixers, batch mixers, and even single screw extruders are being used for compounding woodfiber-plastic composites. This paper will identify those devices, and the various process configurations currently being utilized in the manufacture of woodfiber-plastic composites. In commodity thermoplastic operations, these mixing devices have traditionally produced intermediate pellets, which are then processed in a separate operation on single screw extruders to make an extruded part. With woodfiberplastic composites, however, the trend (although not the rule) is to bypass the pelletizing step and to combine compounding/devolatilizing with direct sheet or profile extrusion.
Evaluation of Classical Nucleation Theory Using Visualization Data
Numerical modeling of the microcellular polymeric foaming process often employs the classical nucleation theory. Although many previous theoretical studies of cell nucleation and cell growth have attempted to verify the theoretical models through experimental observations, most studies have been limited to the comparison of simulation results with the final cellular structures after the foams were stabilized. In this work, visualization data obtained by Guo et al [1] for the in situ foaming processes was utilized to evaluate the theoretical model for the polymeric foaming process based on the classical nucleation theory. Unintentional heterogeneous nucleation and nucleus-size dependent surface tension were discussed to narrow the gap between theoretical and experimental results. Simulation results indicated that contact angle and surface tension had significant effects on the final foam structures.
Heated Die Energy Saving Enhancement through Thermoset Polyester Mold Insulation
The energy consumption of a heated die can be significantly decreased by using mold insulation. Two different types of insulation applications will be evaluated to determine the significance of the energy savings by insulating the shear bars and platens as opposed to just the platens in a compression molding process. The applications being compared are, mold platen insulation versus mold platen and shear bar insulation. The most productive application will also be established in order to maximize energy cost savings. The insulating media was chosen due to its low thermal conductivity and high compression strength.
Study on RTD of S Element in Co-Rotating Intermeshing Twin-Screw Extrusion
S element is a new screw element. It takes the shape of the character ‘S’ in the cross section and is always consisted of positive and negative components. In this paper, a simulation method of residence time distribution in intermeshing co-rotating twin-screw extrusion was put forward. According to the velocity profiles simulated and the marker particle tracking method, the functions of the resident time distribution (RTD) are fit. The functions of RTD demonstrate that lognitudinal mixing ability of S is better than that of common screw elements. The theoretical RTD is agreement with the experiment results.
Shear Imbalance Effects on Gas Distribution in Gas-Assist Injection Molding
This paper presents a study about the way in which shear, developed in the perimeter of the runner, affects the distribution of gas in gas-assisted injection molding. The high shear regions created in the perimeter of the runner continues into the mold cavities. These high shear regions within the cavity create variations in the melt’s viscosity within that cavity and will control the distribution of the gas within the formed parts. This study evaluates the sensitivity of this phenomena in a variety of different plastic materials. The study further evaluates means to control the gas distribution through use of melt rotation technology.
Resistance Welding of Conductive Thermoplastic Composites
Resistance welding is a common metal joining process wherein electrical current is dissipated as heat as it passes through a high resistance boundary between mating parts. This process can also be used with thermoplastic composites rendered electrically conductive by the addition of carbon reinforcement. In this study, two conductive thermoplastic composite plates were resistance welded without external electric heating elements to form a complex box-like structure. The influence of welding conditions on mechanical and physical properties of the assembly was studied. Weld strength and meltdown were strongly dependent on the welding current, and pressure. A minimum energy, equal to the product of current, pressure-induced contact resistance and welding time, was required for meltdown. It was also observed that, regardless of the current, a critical pressure must be applied to achieve acceptable mechanical properties.
Modification of Physical and Chemical Properties of Polyethylene Resins through Electron Beam or Gamma Irradiation
Polyethylene resins have been modified with electron beam or gamma radiation to adjust some of their physical and chemical characteristics before their conversion into formed parts, with positive impact on the properties of end products produced from these resins. This paper provides results from characterization studies which give evidence of structural changes, including long-chain branching and oxidation, from the modification of certain polyethylene resins, as well as data on important property enhancements in extruded, injection molded and blown film end products produced from these resins. The property enhancements allow the material to be more competitive with other resins and offer good prospects for overall cost savings.
Hygrothermal Aging of Recycled-PET Sandwich Injection Moldings
Thermal instability and hydrolysis have been the major factors and driving force behind the continued efforts by researchers to improve the properties of recycled poly(ethylene terephthalate) (RPET) in order for them to be considered useful. This study aims at enhancing the resistance of RPET moldings to hygrothermal aging without making any chemical modifications to the resin. The only means of modification that is done here is through alterations in terms of processing conditions and techniques. The sandwich injection molding technique is capable of producing specimens with a distinctive skin and core structure. Water absorption rate of the sandwich moldings was found to be much lower compared to conventionally molded specimens. Tensile and bending properties have also shown significant improvement favoring the sandwich specimens. The change in morphology due to ‘double-resin-flow’ in sandwich injection moldings could have created a layer between the skin and core that has excellent barrier properties that prevents water absorption into the inner parts of the specimens.
Single-Step Foaming of Polypropylene in Rotational Molding
It is well known within the plastics industry that foaming of polypropylene is a very challenging process. A new generation of polypropylene, offering improved processability, has been produced recently by using a metallocene catalyst technology. A fundamental study of single-step foaming of the newly developed polypropylene in rotational molding was conducted, using polymer microspheres as a blowing agent. The influence of polymer rheology on tensile properties, flexural modulus, and cell morphology of the foamed polypropylene parts was investigated. Comparisons are made between conventional and metallocene polypropylene materials.
Quantification of Melting Progression during Twin Screw Extrusion Using the Pulse Perturbation Technique Part I: Method, Experiment and New Insights
Steady state and pulse perturbation monitoring of the melting process in a twin-screw extruder has been carried out. While steady state measurements quantify the total mechanical energy input, they provide no information about the melting progression in the working section. Previously [2], Polypropylene and Polystyrene data were presented for several operating conditions. In this paper, the behaviors of four different resins are examined in more detail. Quantification of melting time and intensity using pulse perturbation power and RTD responses has been attempted. The effects of operating conditions and simple changes in screw design are examined. Multivariate statistical analysis using Principal Components Analysis of independent operating variables, monitored and derived parameters is described.
Using Synchrotron Radiation to Follow Structure Development in Commercial and Novel Polymeric Materials
The crystallinity in a polymer material influences its aesthetic and mechanical properties and so to develop useful materials it is essential to have a deep understanding of the kinetics involved with this process. Exploring the macro and micro-structure development associated with crystallization in polymer materials such as polyethylene and polypropylene can be achieved using Small-and Wide- Angle Scattering techniques (SAXS/WAXS). Here, SAXS probes the long range ordering or macrostructure and WAXS gives information on the atomic level of ordering (microstructure). Following the structure development and hence the crystallization process in polymers, is particularly important as it leads to the stabilisation of the final product.
Melt Fracture of Polyethylene and the Role of Extensional Flow Behavior
The melt fracture and extensional flow behaviors of a series of linear polyethylenes were characterized from capillary extrusion and uniaxial extension melt rheology experiments with the SER Universal Testing Platform. Based on the experimental results it was determined that the critical shear rates for the onset of both sharkskin and gross melt fractures were found to correlate with the highrate extensional flow behavior of the polymer melts. These findings were found to mechanistically support the generally accepted observations of melt fracture phenomena occurring at the exit (sharkskin) and entrance (gross) regions of the capillary die. In addition, it was found that the presence of a small amount of boron nitride (BN) filler behaves as an energy dissipater that acts to suppress the rapid increase of extensional stress associated with gross melt fracture, and enables the BN to act as an effective processing aid in postponing the onset of gross melt fracture.
Quantification of Melting Progression during Twin Screw Extrusion Using the Pulse Perturbation Technique Part II: Physics of Melting
Further analysis of steady state and pulse perturbation monitoring of the melting process in a twin-screw extruder discussed in Part I has been carried out with respect to the physics of melting. This paper examines why the total specific energy changes with operating conditions. New parameters are defined, the differential specific energy, ?P/?Q and ?P/?N, that can be determined from either monitoring method. It is proposed that the differential specific energy may be used to characterize an extrusion system and applied to the prediction the total specific energy at any rate and screw speed. From pulse and RTD responses, a modified description of the progression of melting based on plug and fluid flow regimes is made using concepts advanced previously. Energy input related to back mixing or mass spreading during melting is discussed.
Structure-Property Correlations for PE Blown Films
In order to develop correlations between the properties and microstructural characteristics of polyethylene (PE) blown films, three polymers were evaluated in this study: LDPE, LLDPE and HDPE. Series of blown films were produced at different process conditions. Morphological characteristics of the films were analyzed using SEM and AFM. Herman’s orientation factors of the films were determined via both wide angle X-ray diffraction pole figures and FTIR. DSC, WAXD and SAXS were used to determine the degree of crystallinity, lamellar thickness and crystal dimensions. Finally, key mechanical properties including Elmendorf tear, dart impact, tensile properties in both MD and TD and optical properties such as haze and clarity have been measured. By using the statistical design of experiments and multivariate modeling, the properties of PE films are correlated to the microstructural parameters including; lamellar thickness, crystal size and Herman’s factors.
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