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 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  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 , 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.
Study on the Properties of Gear Disk in Co-Rotating Twin Screw Extruder
Gear disk is one of the most important mixing screw elements. It can meet the demand in distribution mixing of filler in polymer, and can be used in co-rotating twin-screw extruder with other screw elements in different configurations. In order to study which screw configurations can get the best mixing capability, flow fields of different configurations of gear disk and common screw elements were studied. Pressure profile and shear stress profile were calculated. The mixing ability of different flow fields was compared. The result can be concluded that alternate short mixing zones have better mixing ability than a whole long mixing zone. The simulation results of the flow field in different screw configurations of gear disk and common screw elements were verified by experiments.
Development of Thermoplastic Polyurethane Electrolytes and Their Ionic Conductivity
The ionic conductivity of linear segmented thermoplastic polyurethane (TPU) in-situ reacted with alkali metal salts is investigated. The kinetics of thermoplastic polyurethane (TPU) electrolytes complexed with varying molar concentrations of lithium perchlorite (LiClO4) salt has been studied at various temperature (100, 120, 140, and 160°C) by differential scanning calorimeter (DSC). The relationship between ion conductivity and cationic size in TPU electrolytes is discussed with different salts including LiClO4 and KI. Fourier transform infra-red (FTIR) spectroscopy was used to determine the interaction of LiClO4 and KI salts with TPU. The temperature dependency of TPU electrolytes is also studied by using the modified LCR meter.
Erosion and Continuity Development in High Viscosity Ratio EPDM/PP Blends
Blends of EPDM and PP provide an interesting model system to examine continuity development in very low interfacial tension systems. In this work an emphasis is placed on the study of high viscosity ratio blends. The SEM micrographs of the dispersed phase, after matrix dissolution, demonstrate a variety of unusual morphological features including: isolated nanometer-scale fibers, very large particles, and numerous particles interconnected by fibers. It is found that the high viscosity EPDM phase slowly erodes during melt blending by a number of different mechanisms: i) simple erosion, at low compositions, ii) via droplet alignment, elongation in the direction of first normal stress and the subsequent strangulation in the flow direction, and iii) collisioncoalescence- separation type erosion, at higher compositions of the dispersed phase. It is found that the unique morphologies generated enable the dispersed phase to percolate and become cocontinuous at unexpectedly-low compositions of the dispersed phase.
Dimensional Stability of Pre-Shaped Nylon-6 Tubes
During the fuel tank assembly process, preshaped Nylon-6 vapor lines were subjected to 148.9°C. At this elevated temperature the bent tubes tended to return to their original straight shapes, which created undesirable contact with the tank shell. A series of experiments were performed in lab to quantify the effect of several design and processing variables – bend radius, angle, and orientation; forming temperature; and storage temperature – on the tube dimensional stability. Experimental results indicated that the bend radius, forming temperature, and storage temperature affected the tube dimensional stability significantly while the other factors did not. Curved beam theory was employed to calculate the equivalent bending moments associated with the radius change measured in the experiments. Those bending moments were then applied to FEA models to predict the dimensional change of vapor lines at assembly positions. The CAE predictions correlated well with the assembly test results and successfully resolved the contact issue.
Rapid Thermal Response Mold Design
Rapid thermal response (RTR) technology has been successfully applied to the injection molding and hot embossing processes. This technology was found to be durable and reliable for manufacturing disposable plastic parts with micro/nano scale features. This paper focuses on the mold design challenges. Thermally induced surface deflection and stress of the mold were simulated and used for optimal mold design with respect to thermal fatigue failure. A mold was constructed and tested to verify simulation results by experimental study. In a thermal fatigue test, the optimal designed mold showed no signs of fatigue after 10,000 thermal cycles.
Development of a Technology for Large Scale Production of Continuous Fiber Reinforced Thermoplastic Composites
New highly economical process technologies for long-fiber reinforced thermoplastics such as the LFT-D process are the current trend of the market in the automotive industry in Europe. The next step on the way to enhanced LFTs is the use of engineering thermoplastics (e.g., PA66, SAN and PBT) as well as co-molding with local reinforce ments and tailored fiber placement [1, 2, 3, 4]. The process described in this paper shows how continuous fiber reinforcements such as fabrics, profiles, and preforms are co-molded with an LFT material in one step (Tailored LFT). Process parameters for a sufficient bonding of the thermoplastic preform with LFT-material as well as an example of an automotive application are given in the paper. A pilot-scale production plant has been built to demonstrate the ability of serial production.
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