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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Thermoplastics Materials and Foams
Extrusion Foaming of Newly Developed High-Melt-Strength Polypropylene
We report systematic studies on the foamability of our novel high-melt-strength long-chain branched polypropylene under supercritical CO2. Continuous foaming experiments were conducted using a tandem extrusion system and a set of filamentary dies with similar pressure drops but different pressure drop rates. The foam expansion was controlled by varying the temperature at the die exit. Under identical CO2 loadings, the expansion ratio plotted as a function of die temperature exhibited similar shapes across multiple pressure drop rates. However, the shape of the curve varied across different amounts of CO2, under which the highest achievable expansion ratio occurred at a lower die temperature with increasing CO2 content. The cell density displayed strong dependence on both the pressure drop rate and the amount of dissolved CO2. The effect of the latter became more apparent at lower pressure drop rates. The average cell size decreased with increasing CO2 loading but generally showed weak dependence on pressure drop rate except at the highest value.
Design and Engineering of Insoluble, High Performance Starch Foams Via Extrusion Technology
Insoluble, high performance starch foams with high resistance to moisture were prepared by ZSK-30 twin screw extruder using additives such as chitosan, polyvinyl butyral (PVB) and sodium trimetaphosphate (STMP). Under the optimized extrusion conditions, water acted as a plasticizer and a blowing agent breaking up the hydrogen bonds within the starch granules and releasing the starch polymer chains without significantly reducing their molecular weight. The pressure drop at the die led to expansion and formation of closed cell foams. A screw configuration made up of 3 kneading sections was found to be the most effective for better mixing and foaming. The use of PVB was extremely effective in minimizing moisture sensitivity and made the foams hydrophobic and insoluble in water. Crosslinking of starch with STMP gave anionic mono and di-starch phosphates which formed an insoluble polyelectrolyte complex with cationic chitosan due to electrostatic attraction. This also increased the compressive strength of the foams by 3 times compared to the control foams. STMP also reduced the cell size and gave more uniform cell size distribution. It was found that properties like density, expansion ratio, compressive strength, resiliency, and cell size distribution of foams can be controlled by adjusting feed rates of starch, chitosan, and the crosslinking agent. These insoluble composite foams absorbed over 600% by weight water and formed a gel kind structure; a property which could be useful in hemostatic applications. Densities of foams were found to vary from 21 to 51 kg/m3 for different compositions studied. A maximum expansion ratio of 74.5 was obtained for the formulation containing 10% PVB and 4% chitosan.
Injection Moldable 5G Plastic Antenna Dipole
In the past decade, the wireless communication technology has expanded rapidly over the globe, thus stipulating higher data rates and lower latency communication. The advancement in wireless technology has led to drastic increase in number of end users, demanding higher efficiency. To fulfil the requirement of data traffic, the unexplored millimeter wave frequency region is being studied which is recognized as the 5th generation of wireless communication system. This range of frequencies of millimeter waves can facilitate larger bandwidth, higher data rates, lower latency and can connect large number of devices. New technologies emerging for the foundation of 5G include massive MIMO, small cells, beamforming that plays an important role in revolutionizing the cellular network technology. Miniaturization, lightweight trends lead for utilization of thermoplastic materials being used for the antennas. The dielectric properties of thermoplastic materials are measured & used in building simulation models for antennas. A broadband dual polarized, injection moldable base station antenna with crossed dipoles, balun, feeding connectors and reflectors is designed to operate in the 5G spectrum at frequencies up to 10GHz. Sensitivity analysis is performed to examine the antenna performance and most efficient antenna design is chosen.
In situ Visualization of Microstructure of Polypropylene under Shear and CO2 Pressure
Crystallization and foaming behaviors of a semi-crystalline polymer in conditions comparable to those found in polymer processing, where the polymer melt experiences shear under elevated pressures, are key for modeling polymer processes and predicting the final structure and mechanical properties of polymer products. We investigate the crystallization behaviors of a newly developed high-melt strength polypropylene (PP) resin using a novel high-pressure visualization system. Overall crystallization kinetics can be easily controlled through the effect of induced-shear stress and the presence of pressurized CO2.
3D Numerical Simulation and Experimental Observation of Bubble Growth and Collapse in Nitrogen-Gas Saturated Molten Polymer for the Core-Back Foam Injection Molding
We have demonstrated the dynamics of bubble growth and collapse in the visual observation experimental and foam injection simulator in physical foaming of molten plastics. The modified Han and Yoo model can predict the bubble size for both the situation of bubble growth and collapsed. Our modified model is promising for the application of core-back foam injection molding.
Cell Dissolution in High-Pressure Foam Injection Molding: Towards a More Efficient Packing
Packing/holding stage as one of the most important stages during foam injection molding is often overlooked in the industry. It not only influences the part’s geometrical accuracy and stability, and the residual stress distribution but also has a significant impact on the production time, machine tonnage, etc. In this work, we attempted to predict the evolution of the cell size during packing using a previously developed model. The model predicted dissolution profile was then compared with measured cell size obtained from visualized high-pressure foam injection molding. Moreover, the use of the visualization mold granted us access to characterize the dissolution time for gate nucleated cells, thereby systematically study the efficiency of each individual packing parameters (i.e. gas concentration, packing pressure, and injection speed).
Melting and Crystallization Behaviors of Polyphenylene Sulfide Blended With Thermoplastics: A Review
Recent research about the melting and crystallization behaviors of Polyphenylene sulfide (PPS) blended with thermoplastics are reviewed in this paper. Thermoplastics discussed herein are mainly polyamide (PA) and Liquid Crystal Polymer (LCPs). Other thermoplastics including high-density polyethylene (HDPE), polycarbonate (PC), polyethylene terephthalate (PET), polyetherketone (PEK), polyether ether ketone (PEEK), polysulfone (PSF), polystyrene (PS), and polyvinylidene fluoride (PVDF), etc. are also discussed. The recent literature shows that by blending with certain content of thermoplastic polymer, the crystallization rate and crystallinity of PPS can be improved.
3D Chemical Foaming Simulation For Transfer Molding Process
This study presents the recent development of three-dimensional prediction of cross-linked ethylene propylene diene monomer rubber (EPDM) with chemical blowing agent azodicarbonamide (ADCA) in transfer molding process. Plunger retraction is applied after transfer process is completed. The reaction kinetics model, density model, and viscosity model are applied to describe the complex foamed rubber system in the simulation study. The experimental investigation of material properties into EPDM/ADCA system are studied to make physical parameters in simulation model more realistic. The flow front behavior, the density of foamed rubber, the reaction behavior in foaming and curing conversion are examined to understand the dynamic behavior of the rubber material in both transfer and foaming stages. Furthermore, we study the effect of foaming and plunger retraction. Simulation results show that foaming effect make clamp force larger, however, plunger retraction effect make the back flow occur from cavity to pot to avoid high pressure in the cavity and therefore eliminate the mold clamp force. This study is of great relevance to light weighting application and should reduce the product-to-market cycle time by eliminating the need for the traditional trial-error method.
A Review of Impact Modification Technologies for Different Thermoplastics using Ethylene Copolymers
Thermoplastics have been blended with reactor-based and grafted-ethylene copolymers for over 50 years to improve room temperature and low temperature ductilityfor many applications, including those in the automotive, appliance, sporting goods industries. The compatibilityof the modifier with the thermoplastic matrix and the rheology of the blend components are key factors in controlling blend morphology. The amount of modifier used and the morphology obtainedaffect the balance of critical properties, including stiffness,impact toughness, and flow. Compatibility of the modifiers with the thermoplastic matrix can be controlled by composition of the modifier produced in-reactor, use of additional compatibilizers (such as diblock copolymers), and by in-situcompatibilization achieved through reactive blending. This paper reviews commercially practiced technologies for impact modification of various thermoplastics based on ethylene copolymers.
Fibrillated and Highly Interconnected Porous PCL Scaffolds by Supercritical Foaming and Leaching
Highly porous and interconnected 3D structures are crucial elements for tissue engineering scaffolds since they can support the mass transport of cell nutrients and waste. Supercritical foaming technology is an environmentally-friendly and solvent-free way of manufacturing porous scaffolds. In this research, highly porous, interconnected poly(ɛ-caprolactone) (PCL) scaffolds combined with supercritical carbon dioxide (SCCO2) foaming and a polymer leaching process were fabricated by blending PCL with water-soluble poly (ethylene oxide) (PEO) as a sacrificial material. The effects of phase morphology of PCL/PEO blend on foaming behavior and pore morphology were investigated. The incorporation of PEO not only facilitated the foaming of PCL by increasing its viscosity, but also improved the porosity and interconnectivity of the post-leached PCL scaffolds. The fibrillated porous scaffolds with open-pore content up to 91% were obtained after the leaching process because of two different cell-opening mechanisms. Cell-opening on surface of scaffolds is difficult in preparing porous materials. In the end, a novel method for improving surface porosity and producing the so-called outer and inner porous PCL scaffolds is described. The information gathered in this study may provide a theoretical basis for research into porous tissue engineering scaffolds.
Foam Sheet Extrusion with Blowing Agent Mixtures and Correlation Analysis With Dimensionless Numbers
In foam extrusion, the blowing agent has a significant influence on the process parameters and the resulting foam properties. Low-density polystyrene foam sheets are usually produced with aliphatic hydrocarbons or alkanes as physical blowing agent. Due to the necessary safety precautions and the environmental impact, there is great interest in using alternative blowing agents such as carbon dioxide (CO2). The sole use of CO2 often leads to corrugation, open cells or surface defects on the foam sheet and therefore requires modifications to the process technology. The aim of this work is to investigate the effect of blowing agent mixtures of CO2 and organic solvents on the production of foam sheets. In particular, the interactions between the blowing agent formulation, the process parameters and the foam sheet properties are analyzed. The knowledge of the interactions can allow a systematic influencing of the foaming behavior without modifying the polymer itself. For a systematic evaluation, an existing process model for describing the melt flow in the extrusion die is extended and applied to an annular gap die. Based on the model, dimensionless numbers can be calculated to describe the foaming behavior. The characteristic numbers enable the direct comparison of different recipes, process settings and die geometries.
incorporating Unmodified Lignin into Flexible Polyurethane Foams Formulation
Industries that use polyurethane foam are looking for new sustainable and greener material to replace the petroleum-based polyols. Lignin produced as byproduct of pulp and paper and bioethanol industries is a suitable natural polymer to replace petroleum-based polyol in formulation of PUs. The emphasis was to study effect of different lignins obtained from different chemical processes and plant sources on the structural, mechanical and thermal properties of PU flexible foam and to achieve maximum lignin substitution. Additionally, we were interested to find correlation between lignin properties and performance of lignin-based PU foams to identify which lignin properties would affect the performance of developed lignin-based flexible PU foams and find the most suitable lignins for this application. It was seen that lignins isolated through organosolv process were better for PU fiexible foam applications. Overall, substitution of polyol with lignin increased compression strength, support factor, tear propagation strength and tensile strength of the developed PU foams.
Numerical Analysis of Polymer Micro-foaming Process in Extrusion Flow
In this paper, effects of microviscosity and wall slip were considered, and a mathematical model of isothermal extrusion micro-foaming process was adopted based on classical nucleation theory and cell model. A simulation scheme of the extrusion micro-foaming process was conducted combining with the cross-section/imaginary area method and the Runge-Kutta method. The simulation program of the extrusion micro-foaming process was realized on MATLAB. The effects of inlet pressure on evolution of cell morphology and cell size distribution during the extrusion micro-foaming process were analyzed by the numerical examples. The results indicate that the higher the inlet pressure, the higher the maximum nucleation rate, and the closer to the die outlet the nucleation spot, the shorter the growth distance of the bubble, which is more conducive to formatting smaller cell radius and higher cell density.
‘Plug-and-Play’ Weight Reduction Solution by Hollow Glass Microspheres
Fillers have been in use since the early days of plastics. Today’s enormous growth of the polymer industry is due to the unique properties of fillers they impart to polymers. Glass bubbles (low density hollow glass microspheres) as fillers have been incorporated into thermoset polymers for decades. They are tiny hollow spheres and are virtually inert. These glass bubbles are are compatible with most polymers. Until recently, their use with thermoplastic polymers has been limited because of high rates of bubble breakage from the high shear forces to which they are exposed during such thermoplastic processing operations as extrusion compounding and injection molding. At issue has been the strength of the glass microspheres.
Wood Plastic Composite
Wood and plastic are best friends these days. They can be combined to give the aesthetics of wood with the added durability of plastic. Termed as wood/plastic composites - WPCs' are a relatively new family of thermoplastic composites based on wood-fibres and the commodity thermoplastics. The polymers used for WPCs' are the high volume, low cost, commodity thermoplastics - polyethylene, polypropylene and PVC.
A Breakthrough in Foaming Technology
MuCell process by Trexel Inc. has been touted as a breakthrough technology. The process offers new foaming capabilities. If your business belongs to the categories such as Extrusion (PP, PS sheet & PVC proﬁles), Blow (HDPE bottles) or Injection moulding (PP, PS, Nylons, PC/ABS and TPEs) then you will proﬁt from MuCell process. The process produces microcellular foams (5-50 micron ranges) using supercritical ﬂuids (SCFs). These ﬂuids like carbon dioxide or nitrogen mix thoroughly in plastic melt since they have the viscosity of gases and the density of liquids. Being environmentally benign, SCFs eliminate the need for chemical or hydrocarbon-based blowing agents. CO2 or N2 are in ﬂuid state as opposed to gas (in gas assist injection moulding); the process generates evenly distributed microscopic cells throughout the plastic. This makes MuCell technology to foam very thin sections (0.5mm/0.20inch).
Mix & Match: New Developments Offer New Applications
Injection molding process imparts a complex thermal deformation history to polymer melts. The complexity rises with multiphase blend systems. How about development in areas of new materials? Can we not get new resins that would give faster cycle times, high ultimate strength and elongation values combined with a wide spectrum of shore A and shore D hardness grades?
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