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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The Effect of Recycle History and Processing Temperature on the Weld Line Strength of a Polypropylene Homopolymer
This investigation focuses on the inherent recyclablility of a polypropylene homopolymer by characterizing the mechanical and rheological properties of a multiprocessed resin. The investigation studied molded samples both with and without the presence of a weld line. Several blends of virgin and reground polypropylene homopolymer (consisting of 5 recycle histories) were prepared. The tensile properties (including weld strength) and melt flow rate tests were performed on all molded samples from each of the blends.The results of the study showed that regrind did not affect the tensile modulus, tensile strength at yield, or elongation at yield for samples molded without the weld line to any significant degree. The presence of a weld line had a negative effect on the mechanical properties of the molded sample. The weld line strength also decreased significantly as regrind concentration increased. Melt flow rate tests of the various blends showed the melt flow rate increased by a total of 29% over the entire range of regrind percentages studied. Increasing the processing temperature did have a positive effect on the weld line strength. The addition of regrind did not affect the first stage injection pressure or cavity pressure observed during the molding of the test samples.
Bonding Strength in Micro Injection Assembly Moulding
Polymer materials offer a wide range of properties that can be chosen according to the functional necessities. Therefore these materials are increasingly often used for decisive elements in micro systems. Injection molding as a production process for polymer materials can also be applied as a joining and assembly process in addition to generating micro parts. This approach offers a high potential for micro technology, since an offline joining process can be avoided by overmolding of the components, where it is possible to generate movable and force fit connections. New research at IKV (Institute of Plastics Processing) shows progress made in the attainable bond strength of hybrid micro systems. A specific testing method for different material combinations has been developed. Since plastics/metal bonds possess little adhesion, surface modifications such as increased surface roughness or silane coating show promising results.
Functionalization of Polyolefins through Catalytic Hydrosilylation and Imidation Reactions
Polypropylene and polyethylene were terminally functionalized with anhydride groups through a two-step solution catalytic hydrosilylation reaction. Subsequently, the anhydride group in the functionalized polymers was reacted with 1,6-diaminohexane following an imidation reaction to produce primary amine functionalized polymers. The anhydride functionalization of polyethylene was also carried out in molten state. The functionalized products were characterized by FT-IR and an acid-base titration method, and attempts to prevent crosslinking of polyethylene and the application of the novel anhydride functionalization technique in extruders are discussed.
A Novel Suspension Polymerization Process without Mechanical Agitation, Yielding Mono-Sized Beads
The concept of a novel suspension polymerization technology without mechanical agitation is presented. It aims to yield a practically monosized product, allows the inclusion of a variety of components in the polymer matrix with a potential for broader range of products, compared to a conventional stirred-tank process. The technology is comprised of two stages: dispersion of an organic phase into droplets with the required size, and the subsequent polymerization of the droplets, while preserving their initial size distribution. The dispersion method combines pressure atomization of the organic phase below free surface of a stabilizing continuous phase, with the controlled pressure pulsation imposed on the flowing stream, and yields mono-sized droplets for both Newtonian and Non-Newtonian viscoelastic liquids. The atomized droplets are next polymerized in low shear, low turbulence flow pattern created within the continuous phase, by injecting an inert immiscible gas at selected reactor locations. The process was validated on lab-scale; the results are presented and discussed.
Properties and Applications of Blends of High Melt Strength PP and Linear PP
Polypropylene and its variants by far offers the best balance of cost and performance for wide range of applications requiring flexibility, toughness, rigidity, heat and chemical resistance. However, one major drawback of PP is its low melt strength, which limits its use in blow-molded, thermoformed and extruded and injection molded low-density foams. During last decade, various PP grades with improved melt elasticity have been introduced to overcome this drawback. However, in neat form processors find these HMSPP difficult to process and expensive. This paper describes various approaches to impart high melt strength to PP. It is shown that blending 10-30% of HMSPP with linear PP produces significant and unexpected benefits.
Novel Method for Rapid Determination of Tehrmoformability
The demand for large parts with thick wall, constructed of multiple polymer layers, along with the desire for quick turn around time, lower tool cost, and low pressure processing is making thermoforming very attractive over injection molding. In spite of the long history, thermoforming is still very much an art than science. There are very few reliable tests available to processors and researchers for analyzing and quantifying thermoformability. This paper presents comparison between current methods and a novel test apparatus, which closely simulates thermoforming process under controllable conditions while collecting quantitative information, which can be used to assess, compare, optimize or predict thermoformability of test material.
Collocation Method Solution with Radial Basis Functions of the 2D Energy Equation
This paper describes the collocation method with radial basis functions (RBFCM) of the 2D energy equation for Newtonian and non – Newtonian fluids, These fluids are widely used in polymer processing in various processes like extrusion, blow molding, and injection molding. The 2D energy equation involves specially the variation of the thermal properties with temperature and the viscous dissipation term. The boundary conditions are of Dirichlet, Neumann and Robin Type. The accuracy of the solution is assessed by comparison with well known analytical solutions and numerical procedures, such as, benchmark test, found in the literature. The problem of the fluid between the two parallel plates is completely simulated using RBFCM. It is clear the accuracy of the RBFCM solution assessed by comparison with the analytical solution and the DRBEM numerical solution.
Foaming Polystyrene with HFC-245Fa and Blends of HFC-245Fa and CO2
HFC-245fa is a newly available blowing agent that was developed specifically for the polyurethane market. It is however, sufficiently soluble in polystyrene and polyethylene so that it can be successfully used in the thermoplastic foam extrusion process at moderate concentrations.Higher loadings of gas were tested in polystyrene and were found to generate large holes owing to inadequate nucleation. Blending small quantities of CO2 with HFC- 245fa turned out to be beneficial for foaming and allowed to decrease the foam density further than using HFC-245fa alone. Moreover, it improved the overall morphology of the foam and reduced the incidence of extrusion defects.
The Preparation of TPU /Silica Hybrid Using Sol-Gel Process
Thermoplastic polyurethane elastomer/silica hybrid (TPU/SiO2) using sol-gel process was prepared. This work was undertaken to investigate the thermal and physical properties of this type of hybrid by employing different catalyst systems during sol-gel processing. Two types of catalyst systems including acetic acid (HOAc) and HCl were used to prepare sol particles. The mixing of sol solution and TPU solution was then carried out to form TPU/silica hybrid. Fourier Transform Infrared (FTIR) spectra and dynamical mechanical properties were recorded to depict the enhanced interfacial interaction. Thermogravimetric analysis was used to determine actual silica content forming in the hybrid, and to evaluate the heat resistance of hybrid. Mechanical property such as tensile strength was investigated at various concentrations of in situ silica. Tensile strength increased at all concentrations of silica. HOAc catalyzed system showed better optical property than HCl catalyzed system. Fracture surface was revealed through SEM (scanning electron microscopy) to observe the dispersion degree of SiO2, which in turn confirmed the results of optical property and mechanical properties.
Study of Dynamically Cured PP/Mah-g-PP/Talc/Epoxy Composites
In this paper, an epoxy resin was dynamically cured in a PP/MAH-g-PP/talc matrix to prepare dynamically cured PP/MAH-g-PP/talc/epoxy composites. SEM analysis shows that the maleic anhydride-grafted polypropylene (MAH-g-PP) and an epoxy resin are demonstrated to effectively increase the interaction adhesion between PP and the talc in the PP/talc composites, dynamical curing of the epoxy resin can further increase the interaction in the PP/MAH-g-PP/talc composites. The mechanical properties of PP/MAH-g-PP/talc and PP/MAH-g-PP/talc/epoxy composites are better than that of the PP/talc composites. The dynamically cured PP/MAH-g-PP/talc/epoxy composites have the best mechanical properties in all the PP/talc composites. The suitable content of epoxy resin in the composites is about 5wt%.
Advanced Development of Molded Expanded Polypropylene and Polyethylene Bead Foam Technology for Energy Absorption
Recent advancements in the field of polyolefin resins in the area of PP+PE copolymers, impact co-polymers, and homopolymers have allowed for the creation of a new class of thermoplastic foam products. These new products are capable of improved performance due to the advancements that have been made in the area of polyolefin resin catalyst systems. These new Metallocene catalysts are being used to create resins with improved mechanical properties that otherwise were not available using the traditional Ziegler- Natta catalyst systems currently being used to produce a majority of the thermoplastic materials available today.This paper describes these recent advancements and how they allow for improved properties in the area of moldable expanded bead foam used in the automotive, marine and recreational occupant safety and cushioning system designs. This technology allows for improvements in the mechanical properties of these thermoplastic foam components, while allowing them to be produced on existing processing equipment. This paper will also compare these advancements to those currently being used, and demonstrate how improvements in performance, system integration, and cost can be realized. Compliance to existing and new environmental substance regulations and restrictions are also addressed.
Numerical Simulation of Deformations for Injection Molded Parts
Thermally induced stress and the relevant warpage cause by inappropriate mold design and processing conditions are problems that confounded the overall success of injection molding. A thermorheologically simple thermoviscoelastic material model is used to simulate the residual stress and warpage within injection molded parts generated during the cooling stage of the injection molding cycle. The initial temperature field corresponds to the end of the filling stage. The fully time-dependent algorithm is based on the calculation of the elastic response at every time step. Numerical results are discussed with respect to temperature and pressure.
The Investigation of the PTFE Wall Slip Effect in Paste Extrusion
Polytetrafluoroethylene (PTFE) is a remarkable material having high melting temperature, high chemical resistance, low frictional and dielectric coefficients. However, PTFE fine powder cannot be processed without understanding the rheological behavior of paste powder. In this study, a simple PTFE rheometer was built and the PID control technology used to control the extrusion pressure and extrusion speed (from 2mm/s to 0.5mm/s). Different extrusion length from 45mm to 94mm to change the L/D ratio were also utilized. After analysis of measured data, it was founded the viscosity of PTFE paste basically follows the power law with shear thinning behavior similar to thermoplastics melt. Because of wall slip effect, the pressure drop was one order of magnitude less than that without wall slip and wall slip becomes more significant at high extrusion speed. Lower extrusion speed also results in a better performance in extrudate.
3D Simulation and Verification for Mold Temperature Control Technologies
Three new temperature control technologies: 1) high and low temperature coolant switchover for heating/cooling, 2) electrical heater combined with medium temperature coolant, 3) induction heating combined with low temperature coolant, have been simulated and verified in the paper. Traditional injection molding software of temperature field usually cannot deal with any heat source item multi-processing cycles, e.g. heating/cooling switchover in the same coolant channel, electrical heater and induction heating. Therefore, fully 3D temperature simulation technology for different heating system was constructed. To verify the simulation technology, a mold plate temperature field of each heating/cooling control system has been simulated first. Temperature heating/cooling cycle with selected points on mold plate surface variation ranges within 50--100--50-and 50--110--50-, were designed and experiment data were measured by thermometer, and infrared radiation thermal imaging (IRTI) system. The predicted results show quite precise predictions in accordance with experimental results. Finally, an actual lens mold with combined temperature control system of heater and coolant switchover has been simulated by coupled-field solution. All studies indicate that the simulation technologies are reasonable accurate and feasible.
Crystal Structure and Crystalline Orientation Behavior of Cold Drawn Metallocene Poly(Ethylene-CO-1-Octene) Filaments
A basic study on the crystal structure and crystalline orientation behavior of cold drawn metallocene ethyleneoctene copolymer with different octene content (with density as 0.958, 0.916, 0.902, 0.885 and 0.870 g/cm3) is described. All polymers were first melt spun under different draw-down ratios and subsequently received cold drawing with different cold draw ratios. The crystal structures were characterized by wide angle x-ray diffraction (WAXD). For as-spun filaments, an orthorhombic unit cell was found in all polymers, but an extra peak was found for the polymers with densities of 0.885 and 0.870 g/cm3. This was tentatively assigned to a hexagonal phase. For cold drawn filaments, besides orthorhombic crystal structure, several reflection peaks from a monoclinic unit cell were found for the polyethylene without octene (density is 0.958 g/cm3). For the three filaments with higher octene levels (with densities as 0.916, 0.902, 0.885 g/cm3), only one additional peak was found. For the copolymer filament with the highest octene level (with density 0.870 g/cm3), the WAXD pattern reflections are similar to those of as-spun filaments. Orientation factors for the a, b and c axes of orthorhombic crystal and birefringences of cold drawn filaments were also determined.
Extrusion of Oil Extended Thermoplastic Vulcanizates
When some thermoplastic vulcanizates (TPVs) or dispersions of crosslinked rubber particles in a polypropylene matrix were extruded through a slit die at 200°C, spots or lumps 50 microns or more in diameter appeared above a critical flow rate on both sides of the extrudate. When the lip of the die was wetted with oil on one side, a decrease in spot formation was observed on the lubricated side of the extrudate. This suggests that insufficient lubrication of TPVs during extrusion is a key factor in spot formation. Analysis of the disperse phase morphology from AFM images revealed that larger and more stretched rubber particles lead to better lubrication in such flows.
Effect of Chaotic Mixing on Catalyzed Thermoplastic Polyurethane Polymerization
We investigated the effects of catalyst concentration on chemical reactions at the interfaces between the diisocyanates and diols in a bulk polymerization system where self-similar mixing microstructures were produced by chaotic mixing. It was observed that chaotic mixing conditions exerted strongest influence when the time scale of mixing and the time scale of chemical reactions were of comparable magnitude. For example, at moderate catalyst concentrations, the chemical reactions in the chaotic mixer occurred much faster than in a conventional mixer, such as in the mixing chamber formed by the kneading block elements of twin-screw extruders. It was found that chaotic mixing had almost no influence on conversion at lower catalyst concentrations.
Structure-Property Relations in Visbroken (Peroxide Treated) Impact Polypropylene Copolymers
Impact polypropylene (PP) copolymer (reactor blend) or a postreactor blend of PP and ethylene-propylene rubber (EPR), is an immisible two-phase system consisting of PP as a matrix and EPR as a dispersed phase. When the amount and the molecular weight of EPR in such a blend exceed certain limits, then visbreaking of such a blend leads to an unusual melt rheological behavior – namely, a viscosity up-turn at low frequencies as seen in the dynamic measurements of the molten polymer. We attribute this unusual behavior to the formation of an “interacting network structure” between the two immisible phases via grafted molecules created during the visbreaking process.This melt network structure is carried over into the solid state as evidenced from the optical micrographs of the isothermally crystallized samples. The control of this network structure is important because it affects such properties as stiffness, impact strength and bruise resistance. This paper describes the relation between the extent of viscosity up-turn with the impact resistance and flex modulus of the injection molded samples.
Processability and Film Performance of Single Site Bimodal sLLDPE Resins
Fractional Melt Index (MI) linear low-density polyethylene (LLDPE) resins are used in the polymer extrusion industry to manufacture films. These fractional MI resins provide excellent melt strength for bubble stability on high throughput lines as well as excellent film physical properties. Until now, most fractional MI film resins were made using Ziegler-Natta type multi-site catalysts producing unimodal MWDs. With the advent of single site dual reactor process technologies, it is now possible to produce single site bimodal sLLDPE resins. This paper will discuss the effects of molecular architecture and film processing conditions on the performance characteristics of films made from fractional MI, single site bimodal resins.
Numerical and Photoelastic Research on Residual Stress/Warpage of PC Plank
The clear plastic injection-molded parts are extensively employed in optical, optoelectronic and electronic applications. But the molded residual stress can deteriorate the optical properties of the final product. In this research, the distribution of residual stress of the transparent molded polycarbonate plank with 6.5mm thick have been inspected firstly under polarized light to understand effects of flow-induced and thermal-induced stresses and their interaction. Then based on optical experiment results of photo-elasticity, thermal-induced residual stress of different mold cooling conditions was investigated by numerical methods. A series of multicolored band or fringed pattern and simulation results showed the effect of non-uniform temperature distribution was the main cause of residual stresses/warpage of thick parts. In-molded constrain and mold deformation effects on parts warpage were also discussed by numerical method.
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