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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Failure Analysis of High Density Polyethylene in Engineering Applications
Comparative failure analysis of extruded HDPE potable water tubing and rotational cast HDPE automotive gas tank has been performed. Both structural elements have comparable wall thickness and similar sandwich type structure of the wall: a brittle core and relatively ductile outer and inner skin. A peculiar mode of brittle fracture related to the variation of material morphology across the wall has been found in both parts. Optical microscopy of fracture site reveals cracks initiated and propagated in the brittle core. Large deformation (necking) and resulting ballooning was found on the outer skin. The observed mechanism of failure is most likely related to material formulation and processing conditions. Application of fundamental principles and procedure of HDPE testing for lifetime are used for interpretation of the premature failure of structural elements in durable applications.
Optimization of PVC Dry Blend Productivity through Double Batching
Attempt has been made to optimize the PVC dry blend productivity by adopting Double Batching". PVC resin was mixed with additional quantities of additives in heater mixer and subsequently remaining PVC resin added in cooler mixer before discharging. Both horizontal and conventional vertical cooler mixers were used and performances compared. The dry blends were tested for rheological properties physical properties and extrudability in the twin screw extruder for rigid PVC pipe manufacturing. Various sizes of the pipes were tested as per standards and compared with the pipes made by normal "Single Batching". The study revealed increased dry blend productivity and cost savings on power and labour when "Double Batching" was adopted."
Developments of Polypropylene (PP) Homopolymer Compounds for Automotive Exteriors
The objective of the present work was to develop compounds from PP homopolymer using a combination of elastomer, glass fibre, filler and other additives to match properties of 15% Wollastonite filled nylon currently in use. The automotive component identified for this material substitution exercise was the front end of a two-wheeler called nose-cone". Blends were prepared by twin-screw melt compounding and later assessed for physical and mechanical properties on standard ASTM test specimens. The results obtained indicate that 15% Wollastonite filled nylon-6 can be easily substituted by low cost PP compounds. PP compounds can also be painted to match those nylon-based materials."
Studies in Polypropylene (PP) / Polybutylene Terephthalate (PBT) Blends for Extruded Products in Refrigerators
Mineral filled PP and blends and alloys of PP with High Impact Polystyrene (HIPS) or Acrylonitrile Butadiene-Styrene (ABS) or Polybutylene Terephthalate (PBT) are acquiring increased importance as innovative materials for sheet extrusion applications. The objective of this work was to develop an alloy of PP for sheet extrusion applications for refrigerator interiors. As a preliminary study, a blend of homopolymer PP, high impact copolymer PP, polyolefin elastomer and fillers together with anhydride modified PP and PBT was prepared by twin-screw compounding. The resultant product was characterized for physical and mechanical properties and these were compared with those of PP homopolymer.
Polyamide-Imide + Montmorillonite Nanocomposites
A Polyamide-imide (PAI) + montmorillonite nanocomposite was investigated. The material has a potential application in magnetic wire enamel coatings. Montmorillonite was introduced into an uncured PAI + aromatic solvent suspension. Curing of the sample was achieved by step-wise heat treatment. Polarized optical microscopy was used to confirm uniform distribution of the montmorillonite in the PAI. Transmission Electron Microscopy (TEM) and x-ray diffraction was used to examine clay dispersion. The results showed that a new nanocomposite was developed having a concentration dependent dispersion throughout the PAI matrix. Differential Scanning Calorimetry (DSC) was used to ascertain the impact of the clay on glass transition (Tg) of the resulting nanocomposite.
Potential Commercial Opportunities for New Inherently Conducting Polymer Compounds in ESD Control Applications
Thermal stability and dispersion have long been the two major limitations to the use of inherently conducting polymers in thermoplastic applications. Recent advances have overcome these problems and allowed the development of novel compounds containing inherently conducting polymers that exhibit useful electrical properties. In particular, the surface resistivity is tunable into the ideal range for electrostatic dissipation protection. Thermoplastic compounds have been developed for injection molding, blow molding, and extrusion in polypropylene, polyethylene, and polystyrene. Potential applications include but are not limited to tote boxes, strapping, carrier tape, blown film, or thermoformed sheet where control of electrostatic discharge is required.
Standard Reference Materials: Non-Newtonian Fluids for Rheological Measurements
The National Institute of Standards and Technology (NIST) develops Standard Reference Materials® for calibration, quality assurance and for research into improved measurements. Two fluid standards are being developed to exhibit shear thinning and normal stresses typical of polymeric fluids. SRM 2490 is a solution of polyisobutylene dissolved in 2,6,10,14-tetramethylpenta-decane. SRM 2491 will be a poly(dimethylsiloxane) melt, giving less temperature dependence than SRM 2490. NIST will certify the shear-rate dependence of the viscosity and first normal stress difference at 0 °C, 25 °C and 50 °C, and the linear viscoelastic behavior over the same temperature range. A round robin with the fluids will investigate variability in rheological measurements.
Scaleup of Melt Conveying Parameters in Counter-Rotating Non-Intermeshing Twin Screw Extruders
Extruder screws incorporate restrictive elements as melt seals for heating, mixing, shear and separation of devolatilization zones. To overcome the backpressure caused by the melt seals and convey the melt through the extruder, the screw channels upstream of the seal fill and pump the melt. The screw fill length is an important parameter in determining the residence time and ultimate capacity of the extruder. Experimental data on screw fill length was obtained on counter-rotating, non-intermeshing, CRNI twin screw extruders of different sizes. Model equations similar to single screw models were developed and applied to predict the screw channel drag and pressure flows and the apex leakage flow of the CRNI. Scaleup rules and screw design concepts to give equivalent screw fill and melt conveying performance were determined using the model equations.
An Adjustable Pressure Barrel for Counter-Rotating Non-Intermeshing (CRNI) Twin Screw Extruders
Extrusion processing requires screw modifications during process startup, process optimization and product changes. Downtime and expenses are required to change out the critical screw elements that provide shear, heating and mixing to the product. The CRNI twin screw extruder uses cylindrical compounding elements in the screw design to add shear, heating and mixing to the process. The performance of these cylinders determines the optimum performance of the screw. Varying the cylinder diameter changes the clearance between the barrel wall and changes the shear and the backpressure developed. In order to optimize the screw and make changes in the cylinder/barrel gap while operating, the AP (Adjustable Pressure) barrel was developed. Using the AP barrel can eliminate the down time and expense of changing cylinder elements. Experimental data was obtained comparing the processing characteristics of the AP barrel with varying diameter cylinder compounding elements. Similar performance was obtained using the new AP barrel demonstrating its viability for commercial operations.
The Effect of Residual Impurities on the Rheological and Mechanical Properties of Engineering Polymers Separated from Mixed Plastics
This paper reports the results of an investigation of the effects of purity level and nature of impurities on the properties of recycled polycarbonate and recycled acrylonitrile-butadiene-styrene polymers blended with the corresponding virgin resins. The relevant thermal, mechanical and flow properties were measured. It is concluded that properties of recycled polymers depend not only on the amount of impurity present but also on the kind of impurities and contaminants that are present. The latter factor even plays an important part in relation to compatibility of polymers. However, polymer melt rheology seems less sensitive to impurities than some mechanical properties such as impact strength. More than 99% purity is needed for recycling these polymers back into their original, high-value applications.
Numerical Simulation of Co-Injection Molding
In the co-injection molding process, two (or more) different polymers are injected into the cavity simultaneously or sequentially. Different properties of these two polymers and their distribution in the cavity greatly affect the applications of this molding process. The skin layer can use special polymers to provide good appearance and texture, strength, chemical resistance, EMI shielding and other functions. The core layer can use recycled or inexpensive materials. Together these can improve part quality and lower the cost. However, due to the dynamic interaction of two polymers in the manufacturing process and their difference in properties, process control becomes more complicated and process design becomes a challenge. The rules used for the traditional injection molding process design may not always be useful for co-injection molding any more. An integrated CAE software can be used to simulate the co-injection molding process. In this study, the capability and usefulness of the CAE tool will be shown. The control of polymer distribution will be discussed. The effects of polymer properties and their distribution on part quality will also be studied.
Large Part Blow Molding (LPBM) of HDPE Resins: Parison Extrusion Behavior and its Relationship with the Resins’ Rheological Parameters
In order to find the right combination of material properties and processing conditions (blow moldability) for the production of a molded part that has a set of predetermined final properties, it is necessary to characterise the material behaviour under the actual processing conditions. Relating this to the rheological properties (under controlled experimental conditions) of the material, it is possible to design the molecular characteristics of the material in such a way as to attain the desired processing characteristics. This paper presents the results of a study examining the relationships between some basic rheological properties and the key processing material behavior parameters (swell and sag) governing the blow molding process. The technique has been applied to the intermittent extrusion of three HDPE LPBM resins manufactured using three different catalyst and process technologies.
Injection/Stretch Blow Moulding of Polymer/Clay Nanocomposites
Injection/stretch blow moulding is expanding into new markets such as packaging of fruit juices, beer and other food products. These new applications demand better material performance that the one's presently available on traditional materials such as polyethylene terephtalate (PET), polycarbonate (PC) or polypropylene (PP). The development of polymer/clay nanocomposites has shown that the addition of a small amount of clay (2 to 5% by weight) to a polymer matrix can improve greatly impact strength, and barrier performance. In this work we have studied the injection/stretch blow moulding of polyethylene terephtalate (PET) and polypropylene (PP) nanocomposites. The effect of clay content on top load, hot filling ability and barrier properties has been established.
In-Line Monitoring of Particles in a Polymer Melt during Extrusion Using a Scanning Particle Monitor
The development and application of an in-line scanning particle monitor is described. The monitor consists of an interface, telecentric lens, CCD camera, and computer. The interface provides a window into the process through which the optical system obtains images of particles, such as microgels, as small as eight microns in size. An exceptionally novel aspect is that the monitor can focus upon any depth in the stream to provide images of particles across the flow. Programmable image analysis software yields information on particle concentration, size, color, shape and velocity. The system is useful for both quality control and research.
The Effect of Die Entry Flow on the Rheology of Linear Polymers
It is well known that secondary flow will occur in the stagnant area near the die entrance of an extrusion die. The secondary flow may produce large-scale waviness on the extrudate surface if it propagates into the die land. For polymers that exhibit well-defined stick-slip transitions, propagation of the entry flow into the die is usually facilitated by slip flow. In this paper we show how the entry flow can quicken the sharkskin dynamics while only having a subtle effect on the rheology. This phenomenon is observed first hand using a flow birefringence technique. It is also shown how the effect of the die entry angle changes the slip behavior.
Temperature Rise in a Single Screw Pump-Extruder
The focus of this investigation was to determine the effect of barrel rotation and screw rotation on the flow rate and viscous dissipation inside the screw pump-extruder. The experimental results can be summarized by noting that the pumping capacity of the device was independent of which element was rotated at constant angular velocity and that barrel rotation generated higher temperature rise than screw rotation. Also this analysis suggested that a large amount of viscous dissipation inside this extruder arises from the clearance flow. A new analytical model was proposed to evaluate the viscous dissipation for screw rotation and has good agreement with data.
Structure Development during Film Blowing
The use of simultaneous on-line SALS (Small Angle Light Scattering) and IR (Infrared) temperature measurements to study structure development during tubular blown film extrusion of LLDPE is described. SALS patterns were recorded at various vertical positions along the bubble. For LLDPE, an undeformed spherlulitic structure is formed if the stress level during processing is not too high. The change in average scattered intensity with axial position can be described using multiple step crystallization process. The first step accounts for crystal growth and corresponds to the well-known temperature plateau. The later processes may reflect secondary crystallization and orientation processes. By allowing the processor to track the crystallization process, this on-line SALS system is potentially a useful tool for monitoring process-property interactions.
High Shear Rheology of Calcium Carbonate Slurries
Several sizes of calcium carbonate were investigated because of their extensive use in the polymer industry as fillers. The investigation focused on developing an analytical tool which would lead to understanding and predicting the flow characteristics of slurries which have a Newtonian continuous phase but have high enough filler concentration to exhibit shear thinning or power law characteristics. We focus on concentrations where the initial yield behavior in not dominant A new function was found which linearly correlates the power law constant, n, to the concentration of the filler. The behavior of this function suggests that the Newtonian to Power-law behavior may be dominated by percolation processes.
Effect of Oil Additives and Injection Molding Process Parameters on the Tensile and Impact Energy of Polypropylene
A factorial designed experiment was run to evaluate the interactions of processing parameters, polymer chemistry and proton irradiation on the tensile and impact properties of polypropylene. Polymer chemistry was the greatest contributor to differences in material properties. Base flake polymers with nucleating agent gave the best tensile properties, followed by the base flake polymer alone, the alternative base polymer and the polypropylene with oil, in that order. Polymers with oil gave the best impact properties with an increase in impact energy of 6000 %. Irradiation had significant impact on most polymer systems with some irradiation/processing interactions. In general proton irradiation was beneficial to tensile properties and detrimental to impact properties. Irradiation/processing parameter interactions were present and were highly dependent on the material chemistry and the material property tested. Those polymers with nucleating agent have a drop in material properties across the experiment, suggesting a time dependent material property change.
Low-Velocity Impacts in Continuous Glass Fiber/Polypropylene Composites
The low-velocity impact behavior of a continuous glass fiber/polypropylene composite has been investigated. Optical microscopy and ultrasonic scanning were used to determine the impact-induced damage. Damage mechanisms were found to be matrix cracking, delamination and a small amount of fiber breakage at the edge of the indentation on the front face. Tensile and flexural tests showed that the post-impact residual strengths and flexural modulus decreased with the incident impact energy, whereas effect on the post-impact residual tensile modulus was negligible. The dynamic fracture toughness was evaluated from the critical strain energy release rate during impact of specimens with an embedded insert used to simulate a delamination. Results are compared with fracture toughness values obtained during steady crack growth.
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