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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Real Time Development of Stress and Birefringence in PET during Uniaxial Stretching as Detected by Spectral Birefringence Technique
The birefringence and stress development of PET films has been measured by our new stretching system that couples the Spectral Birefringence Technique with the stress strain measurements. The tensile stretching machine which is specifically designed such that both clamps of the samples move away from each other. This allows for keeping the midsection of the sample stationary. The birefringence and width of the sample is measured at this location. The width of the sample is measured using laser micrometer through which true strain is obtained real time. It has been found that the birefringence development starts before strain-hardening point. The system is fast enough to follow the deformation at high rates of strains. The increased strain rates results in higher birefringence levels through all stages of deformation
Effects of Biaxial Stretch Ratio and Stretch Mode: The Evolution of on Structural Hierarchy in Polylactic Acid
A series of stretch modes: uniaxial free width (UFW) stretching, uniaxial constant width (UCW) stretching, simultaneous equall biaxial(SEB) stretching and sequential equally biaxial (SEQEB) stretching, were applied to cast amorphous films of PLA in order to investigate the effect of processing on the structure and properties. It is found that UFW stretching leads to higher crystallinity. SEQEB stretching is found to induce very high stress during this resulted in higher crystallinity development in the sequentially stretched films as compared to simultaneously stretched ones of comparable stretch ratios. This was attributed to the increased efficiency of strain induced crystallization in the sequential deformation mode stemming from the first stretching stage.
A Model for the Physical Aging of Semicrystalline Polymers above Tg: Secondary Crystallization Induced Constraining Effects
Semicrystalline polymers exhibit changes in physical properties during storage above their glass transition temperature. According to the current paradigm, physical aging above TG is explained by densification of the rigid amorphous fraction in the vicinity of the crystalline phase. Results from differential scanning calorimetry, X-ray diffraction, atomic force microscopy and creep studies lead us to propose a different model, which considers the formation of secondary crystals and the increase in conformational constraints in the residual amorphous fraction.
Real Time Birefringence Development of Orientation in Polymers during Uniaxial Stretching as Detected by Robust Spectral Birefringence Technique
Development of Stress and Birefringence during uniaxial stretching of Polymers was studied using the newly developed stretching instrument that allows simultaneous recording of stress, spectral birefringence and strain during uniaxial deformation. In this new instrument the stretching mechanism is designed such that both upper and lower sample holding clamps move away from each other simultaneously in order to probe the birefringence at the stationary mid section of the sample. The spectral birefringence technique is robust enough to follow rapid changes in the retardation (and birefringence) as well as the reversals in the trend in birefringence that may be caused by the relaxation, crystallization and/or melting depending on the processing conditions. This deviced unique instrument will allow us to study the details of the structural ordering mechanisms real time at industrially meaningful temperatures and deformation rates.
Kinetics of Rapid Structural Changes during Heat Setting of Preoriented PEEK/PEI Blend Films as Followed by Spectral Birefringence Technique
The influence of composition and pre-orientation on the development of structural hierarchy during heat setting of PEEK/PEI films was investigated using on-line birefringence, X-ray scattering and thermal analysis techniques. When the PEEK/PEI blends are drawn to deformation levels below the onset of strain hardening, the subsequent heat setting at high temperature starts with a large relaxation process followed by fast crystallization stage and long-term slow structural rearrangement process. When the films are pre-drawn beyond a critical structural level (crystallinity and orientation), the initial relaxation stage completely disappears. This signifies that beyond a critical structural order a long-range physical network, where the nodes consist of crystallized domains, is formed. The addition of non-crystallizable PEI chains was found to retard the formation of this network structure"."
A Novel Method with Improved Economics for Preparing Polymer Blends
Polymer blends are, with few exceptions, made in extruders. However, extrusion can be costly and requires that the previously made starting materials (blend components) be isolated (and dried in the case of polar polymers) and handled, adding to expense. A novel method has been discovered wherein polyester/acrylate polymer blends are prepared in the polyester reactor itself. This is accomplished by emulsion polymerizing acrylate monomers in the presence of a diol continous phase. The diol can then be used to synthesize a polyester. This technology allows for blending and compatibilization strategies accessible and inaccessible through conventional methods at a reduced cost. In addition to polyesters and polyacrylates, we have expanded this technology to include other condensation polymers such as polyamides and other dispersed phase polymers such as silicone and butadiene rubbers.
Simulation of the Puncture Resistance of a Thermoformed Syringe Pack
A potential material change for a medical packaging thermoformed pack requires costly and time-consuming re-validation. One of the major issues associated with this is the puncture resistance of the pack. This study considers a non-isothermal computational fluid dynamics (CFD) analysis of the thermoforming process of a syringe pack, followed by a non-linear structural analysis of the formed pack to estimate puncture resistance. In this way the final shape and thickness distribution of the thermoformed pack are included in the structural analysis. Two reference materials will be used in validating the usefulness of the technique.
Processing and Benefits of Commingled Glass Fiber Reinforced Thermoplastic Composites
Despite continuous growth over the years, thermoplastic composites suffer from rather low mechanical properties due to low levels of glass reinforcements and random fibers. The breakthrough of commingling thermoplastic and glass fibers during the glass forming process addresses that issue. When comparing commingled wovens to long fiber reinforced PP the significant improvement in properties opens the door to new applications. Recent developments have focused on combining woven fabrics and molding compounds in both injection and compression molding tools to take advantage of the benefits of both material forms.
Processing of Glass Fiber Mat Reinforced Thermoplastic Composites
In this paper, information relating to the processing of glass fiber reinforced thermoplastic composites by compression molding techniques is presented. Glass Mat Thermoplastic (GMT) composites have been used in bumper beams and other structural applications by the automotive industry since 1980. In this paper, information that will act as a processing and design guide for engineers and designers involved with thermoplastic composites is presented. Various molding parameters for successful processing, critical processing parameters, fundamental design criteria, equipment requirements for molding and other secondary operations, material selection and the differences between the various grades with advantages and disadvantages are discussed.
Polyester Polyols for Polyurethanes from Recycled PET
Plastic packaging forms a significant portion of household waste, and PET soft drink bottles represent a major percentage of the waste. Consequently, PET bottle grade material makes up a significant portion of the feedstock in the recycling plant at Visy plastics. The end uses are theoretically many, however, there are few applications for less purified grades of recycled PET. This paper presents the preliminary results of an industry based collaborative research project which aims to investigate the breaking down of recycled PET into its chemical building blocks using glycolysis. The main objective is to produce a polyester polyol for the polyurethane industry from recycled PET and to compare the properties with that of a virgin resin.
The Effect of Surface Energy of Boron Nitride Powders on Gross Melt Fracture Elimination
Boron Nitride (BN) powders have been used successfully to eliminate gross melt fracture in the extrusion of polyethylenes. It is believed that the surface energy of BN powders plays a key role to attain this significant effect. In this work, the surface energy of BN powders is measured using capillary rise experimental methods, based on Washburn's equation. Experimental setup includes a special column-packing device that allows uniform compaction of powder and a computer data acquisition system for liquid penetration rate measurement. Many past experimental difficulties, which have led to inaccurate wettability measurements, have been controlled. Finally, the dispersive and non-dispersive components of the surface energy were determined using polar and non-polar liquids and the results are correlated with the performance of the BN powders as processing aids.
Modern Developments in PVC Pressure Pipes for Cost Effective Water Supply
The objective of this paper is to describe the properties of a modified PVC alloy (MPVC) which offers substantial cost savings and other benefits over conventional uPVC and other pipe materials. The paper deals with pipe design principles including creep rupture regression, long term strength, creep strain and the important property of toughness. The concepts of 'strength' and 'toughness' are discussed together with tests for toughness which lead to the predictable performance properties of MPVC. The unique combination of properties offered by this material is supported by a program of rigorous performance testing which ensures the correct balance of strength and toughness and a minimum 50 year design life. The technology has proven itself over several years with many thousands of kilometres of MPVC pipes having been installed in Southern Africa and elsewhere.
Self Adhesive Liquid Silicone Rubbers (LSRs) for the Injection Molding of Rigid Flexible Combinations
Liquid Silicone Rubbers (LSRs) exhibit outstanding material properties at extreme temperatures and are processed fully automatically by injection molding. Therefore, LSRs offer high productivity for the manufacturer. Selfadhesive LSRs as presented here are designed in a way that no mold coating during the injection molding process is necessary and are ideally suitable where high performance combinations of rigid flexible combinations for technical applications are required. The adhesion properties to a broad range of engineering thermoplastics have been improved and a highly reproducable method for testing the adhesion properties of injection molded rigid flexible parts is presented.
Effects of Blending of Branched and Linear Polypropylene Materials on the Foamability
The foaming behaviours of blends of linear and branched propylene polymers are presented in this paper. The effects of increasing the amount of branched propylene polymer materials on the expansion ratio and cell density of extruded foam were examined. In foam processing of linear polypropylene resins, the quick loss of blowing agent from the foam, promoted by cell coalescence, causes foam contraction, and results in low expansion. On the other hand, the branched propylene polymer resins are well known to retard cell coalescence, to increase the expansion ratio, and to increase the processing window. Due to the high cost of branched resin and in order to design foam properties, the use of blends of linear and branched propylene polymers has been of interest to the foam industry. This paper presents the changes in the processibility and foam qualities as a function of the amount of the branched resin. The foam morphologies of propylene polymer blends at various processing temperatures were investigated using a tandem foam extrusion system, and their volume expansion and cell nucleation behaviours were compared. As expected, increasing the percentage of branched resin in the blends promoted the volume expansion and cell density that resulted in an increase in the processing window for the maximum achievable volume expansion, and a finer cell structure.
Measurement of the Swelling of Propylene Melts with Dissolved Butane
In thermoplastic foam processing using physical blowing agents, the degree of swelling that occurs is determined by the amount of the blowing agent dissolved in the polymer. From an analytical point of view, the swelling that occurs due to gas dissolution can be determined by obtaining the pressure-specific volume-temperature (PVT) data of the polymer/gas solution. The basic principle involved in the measurement of PVT properties of polymer/gas solutions is to measure the specific volume of the solution by determining the mass and volume flow rates of the polymer/gas solution at different temperatures and pressures. This paper presents a dilatometer based on a foaming extruder with a new degassing oven to facilitate the measurement of the mass flow rate of polymer/gas solutions from the foaming extruder. The degassing oven allowed us to completely remove traces of a blowing agent with a low diffusivity from a foam sample while simultaneously measuring the mass of the foam. A series of parametric experiments revealed significant swelling of the propylene due to the dissolved butane. At 15 wt% of butane the swelling of the propylene materials was observed to be as much as 20%. With identical butane concentrations, it was also observed that the swelling of linear propylene was generally greater than the swelling of branched propylene under similar temperature and pressure conditions. The effects of temperature and pressure on the specific volume were also observed to be different for the pure polymer and the polymer/gas solution.
In Line Compounding/Injection Molding with a Discontinuously Operating Twin Screw Extruder
For standard injection molding a granule length of 10 - 12 mm is used in long glass fibers applications to achieve an optimum fiber length distribution in the part. The resulting fiber length in the part is limited to approximately 3 - 5 mm. To increase the fiber length in the molded part it is necessary to directly compound the glassfibers into the polymer on the injection molding machine. The presentation describes a very cost effective way to produce injection molded parts with long glass fibers on a system where a discontinuous running twin screw extruder fed with glass rovings is directly mounted on a two stage injection unit. The advantages of this configuration compared to a continuously running twin screw extruder and discontinuously running single screw extruder mounted on a two stage injection unit were evaluated and are described in depth.
Formulating Foamable Resins for Achieving a Given Volume Expansion Ratio in Rotational Foam Molding
The rotational foam molding process is suitable for fabricating rotational moldings intended for applications that require their internal volume to be entirely or partially occupied with a cellular structure. Whether the outcome of this process will result in articles having a fully foamed core or just a foamed layer with a given thickness depends on the volume expansion ratio for which the foamable resin has been formulated and the shot size the mold has been charged with. Although the amount of chemical blowing agent (CBA) that should be introduced into the polymer in order to prepare a foamable resin that would be suitable for satisfying the required expansion characteristics can be theoretically calculated, in practice, due to various reasons, a portion of the generated blowing gasses during the rotational foam molding cycle is often inevitably lost via the mold's vent(s). As a consequence of this unaccounted loss of blowing gas, a discrepancy exists between the theoretically calculated and the practically achievable volume expansion ratio of a particular foamable resin. Thus, in order to compensate for the loss of the blowing gas that takes place during the foaming stage, the amount of CBA introduced into the polymer while preparing the foamable resin should be greater than the theoretically calculated. This paper establishes the relationship between the theoretically calculated level of CBA concentration in the foamable resin formulation and the actual experimentally-obtained volume expansion ratio in order to predict the necessary CBA concentration correction factor for a given volume expansion ratio and polymer material-blowing agent combination.
Importance of Timely Polymer Sintering Versus Blowing Agent Decomposition in Rotational Foam Molding of Polypropylene
Producing polypropylene (PP) foams with satisfactory cell morphologies in rotational foam molding is feasible. However, the narrow interval between the melting temperature of PP and the onset decomposition temperature of the suitable chemical blowing agent (CBA), together with the low melt strength of PP at elevated temperatures, often represent the greatest obstacles in the foaming of PP. Experimental results revealed that the morphology of the foams obtained by processing PP pellets that have been pre-compounded with a CBA could be governed by either pellet sintering or cell coalescence. The viscosity of the basic PP resin and the processing temperature determine which of these two key factors will assume a predominating influence towards the foaming process. Desirable PP foam structures in compounding based rotational foam molding could be obtained only if pellet sintering takes place prior to the decomposition of the CBA and if the processing temperature during the foaming process is kept lower than the temperature of cell coalescence.
Load Oriented One-Step-TWINTEX®-Sandwich-Structure for Large Scale Production of Automotive Semi-Structural Components
In a joint project with the German automotive industry, the Fraunhofer Institute, material suppliers, component-and mold manufacturers, a thermoplastic sandwich material has been developed. The goal is to offer a cost-effective material with increased mechanical properties to combine the advantages of In-Line-Compounded long fiber reinforced thermoplastics (LFT-ILC) or well-established thermoplastic semi-finished products like GMT and advanced thermoplastic TWINTEX® woven fabrics. These requirements are fulfilled by a sandwich which consists of outer layers of woven fabrics and a core layer of recycled material mainly of shredded TWINTEX®, GMT or LFT components or production waste. The foot support for the smart vehicle has been selected to evaluate the sandwich system.
Phase Separation Behavior of Ethylene-Styrene Interpolymer Blends
Blends of ethylene-styrene interpolymers (ESIs) are a model system for studying the miscibility of a-olefin copolymer blends. The phase behavior of partially miscible ESI blends, with styrene content difference 9-10 wt%, was characterized by phase diagrams. Blends were rapidly quenched from the melt to retain the phase morphology, and the volume fractions of the two phases were obtained from AFM phase images. Assuming monodisperse polymers, the phase composition was approximated by extrapolation of the relationship between blend composition and phase volume fraction. The blends exhibited an upper critical solution temperature (UCST). The UCST decreased with decreasing molecular weight and decreasing styrene content difference. Phase compositions were also obtained with an analysis that considered the molecular weight distribution. Calculated results indicated that phase compositions depended on the initial blend composition. The interaction parameter obtained with this approach was independent of molecular weight and was proportional to the square of the styrene content difference. The solubility parameter, extracted from the interaction parameter, agreed with literature values.
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