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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Fracture of a Breast Tissue Expander
A silicone breast tissue expander failed suddenly after several infusions of saline solution, causing great distress to the patient. The device had fractured at the junction between the bag and the feed catheter. Examination of the dome attached to the catheter into which the saline is fed showed the number of infusions. The fracture surface when examined using ESEM showed a smooth crack path caused by growth of a single crack. The origin lay at the shoulder of the catheter where it met the bag, and numerous microcracks were found at all parts of the junction. Their presence suggested failure of the adhesive used to join the two parts, with slow crack growth under progressively increasing load leading to catastrophic rupture. Especial care is needed in the design of silicone implants to allow for all possible loading patterns.
Fracture Toughness Measurement of Ductile Polymeric Sheets and Films
Many engineering polymers and their blends are tough and the conventional fracture parameters, such as the critical potential energy release rate Gc and critical stress intensity factor Kc, are inapplicable as they are only valid for linear elastic fractures. Post-yield J-integral or crack-tip opening displacement (CTOD) characterization is problematical due to certain experimental difficulties. To overcome these problems, a review is given on the now accepted essential work of fracture approach, which was developed at Sydney University, to determine valid fracture toughness under these circumstances. The theoretical concept will be presented and examples in support of the theory will be taken from data obtained from a range of ductile polymer sheets and their blends covering the effects of temperature and loading rates under mode I crack opening. We will also extend our fracture analysis and experiments to the out-of- plane tearing mode III that is more relevant for failure of thin films.
Full Field Stress and Velocity Measurements for Polymer Melts in Extrusion Dies
Flow induced birefringence has traditionally been used to determine the stresses in the polymer within extrusion dies. Normal and shear stress components are determined at the intersection of isochromatic and isoclinic fringes. The development of stress fields by this method is laborious and provides a limited number of data points. A modulated birefringence approach has been employed to provide a full field stress measurement, that may be more readily compared to numerical simulations. Comparisons between stress and velocity field simulations and experiments on both lab-scale and mini-recirculating flow cells using a variety of geometrical contractions (e.g. abrupt, hyperbolic) will be presented for one branched and one linear polymer melt.
Gas Barrier Mechanisms in Copolyesters
This paper summarizes the systematic study undertaken to gain an insight on the barrier limitations and potential of the isophthalate-modified PET copolymers. The major variables affecting the barrier performance of the copolyester were studied on the molecular and macroscopic levels. Dynamic Mechanical Analysis and gas permeability measurements were carried out to investigate the barrier properties on the macroscopic level whereas Positron Annihilation Lifetime Spectroscopy was used to probe changes on the molecular level. Films made from copolymers and blends containing various levels of isophthalates were extruded. Some were thermally crystallized whereas others were stretched at different conditions. The stretching conditions included various stretching temperatures, stretching modes and stretching ratios. Molecular and macroscopic measurements were correlated.
Gas Permeation Properties of Soluble Aromatic Polyimides Based on 4,4-Diaminotriphenylmethane
Polyimides are promising polymers for gas separation due to their superior thermal and chemical stability, and excellent mechanical strength. High gas permeability and permeselectivity, however, are the key elements for membrane performance. An enhancement of gas permeability of the polyimide membranes can be achieved via inhibiting of interchain packing leading to higher free volume fractions (FVF). Polyimides based on 4,4'-diaminotriphenylmetahne (DA-TPM) are interesting systems potentially suitable for gas separation applications. These polimides contain high fraction of free volume, and they are also technologically attractive because of the simplicity of monomer synthesis, good processability of the resulting polymers, and possibility of their further modification.Organic soluble polyimides (PI-TPM) were prepared in the present study from DA-TPM and various aromatic dianhydrides using different synthesis methods, and their gas transport properties were studied. Gas permeability of PMDA-TPM membranes was higher than that for the conventional PMDA-ODA polyimide gas separation membranes. The permeselectivity values obtained for practically important gas pairs (H2/CH4, He/CH4, H2/N2, O2/N2, CO2/CH4) were at the same level as for polyimides specially designed for membrane applications. Replacement of PMDA moiety with more flexible binuclear dianhydrides resulted in further improvement of permeselectivity.
Gas-Assisted Non-Contact Hot Plate Welding of HDPE
Non-contact hot plate welding offers considerable advantages especially in joining of high temperature polymers. Heating occurs due to a combination of radiation and natural convection. For large and complex samples, the natural convection results in non-uniform heating. In gas-assisted non-contact hot plate welding a heated gas is forced into the gap between the workpiece and the hot plate thereby achieving more uniform heating. In this work, a vertical hot plate was used with assisting and opposing gas flow relative to the direction of the natural convection. The effect of process parameters and the optimization of gas-assisted non-contact hot plate welding of HDPE were studied. In addition, finite element models for the process were developed and found to be in good agreement with experiments. As was shown in previous work with contact and non-contact hot plate welding, the reduced welding parameters of melt layer thickness, welding displacement, and weld displacement ratio offer simple means of optimizing this process.
Generation of Residual Styrene in Injection Molding of Hips
High impact polystyrene is largely applied in the production of food packaging by means of thermoforming or injection molding. Modern processes of HIPS production originate very low levels of residual styrene monomer (SM), which are much lower than the ones permitted by the FDA. Nevertheless, even small amounts of residual SM could affect the taste and odor of the package contents. Therefore, any further increase in the amount of SM is a concern.The present work shows that the amount of styrene can be increased depending essentially on the temperature of injection molding and secondarily on the residence time. A mechanism of generation of that additional SM, based on the reversibility of the trans 1,2- diphenylcyclobutane (TDCB)- styrene reaction, is proposed. Original concentrations of TDCB and SM vary for resins made with different technologies and are directly related to the final content of residual SM.
Gloss Modeling of Injection Molded Rubber-Modified Styrenic Polymers
Gloss models were developed through statistical experimental design for several ABS (acrylonitrile butadiene styrene) and HIPS (high impact polystyrene) materials that span Dow's portfolio of rubber-modified styrenic polymers. The purpose of this work was to benchmark the gloss performance across the portfolio and quantify the influence of molding conditions on the gloss of injection molded parts. Six processing parameters were included in the experimental design: Tmelt, Tmold, tfill, thold, tcool, and Pcavity. A description of the experimental protocol employed for this statistically designed experiment will be given. For the purpose of this communication, the discussion of the results will focus on the observations obtain from three types of ABS materials: emulsion (E-ABS), mass (M-ABS), and a newly developed high gloss mass ABS (HGM-ABS).
Heat Flow Model for Laser Welding of Polymers
ClearWeld™ is an innovative laser welding process that creates strong joints in optically transparent polymers and synthetic fabrics. There is no visible joint line or surface damage using an IR absorbing ink. An analytical heat conduction model is developed to predict the process capabilities and weld characteristics. Experiments using single lap joints in amorphous transparent Polyethylene Terephthalate (PETG) are used to validate this model. Further analysis of failure modes in the joints as a function of processing parameters (power, speed, pressure, etc...) allows the development of process charts to aid in the optimisation of the welding process.
Heat Transfer in Polymer Processing Measured with a Capillary Rheometer
Heat transfer is important to optimise polymer processing. Since recent years model processing is getting more and more important to successfully simulate divers processes. Commercial software requires a range of heat transfer parameters. A triple bore capillary rheometer has been designed to provide one single bore for measurements of the thermal conductivity while the second and the third bore is still available for routine viscosity tests, ideally on the same material. A conductivity probe is placed in the dedicated bore. A heating wire and a thermocouple are placed into the probe. A defined amount of heat is transported to the heating wire. The increase of temperature is measured by the thermocouple. Results will be presented for different polymer melts.
Heat Transfer Properties of Engineering Plastics by Effusivity Measurements
Knowledge of the thermal conductivity of engineering plastics aids in the selection of a candidate polymer. A fundamental property of a plastic material of construction, in a computer or in hot engines of an automobile, is its ability to transfer heat away from hot parts allowing them to cool. Polymer wear and distortion can be minimized when a plastic is chosen with an enhanced ability to draw heat away from friction heated parts.Insulating properties of polymeric materials are well known. The measure of a plastic's ability to insulate is based on its thermal properties. A relatively lower thermal conductivity and higher specific heat capacity polymer, like Styrofoam, expanded polystyrene, is a poor heat conductor.The TC Probe™ that measures effusivity (thermal conductivity) is an effective tool in aiding the design and selection of materials based on their heat transfer properties. Various engineering plastics are differentiated by effusivity measurements and related to real-world performance.
High Barrier Blow Molded Containers Based on Nano Clay Composites
The current study deals with application of nano-clay technology to high barrier blow molded high-density polyethylene (HDPE) containers for storage of hydrocarbon solvents and fuels.The approach in preparation of the polymer nano composite was based initialy on melt compounding of the nano clay filler into appropriate polymer materials following a specific treatment of the clay particles to achieve high degree of exfoliation and use of a compatible carrier. The blow molding process was optimized to obtain high degree of orientation of the exfoliated clay particles parallel to the wall surface.Experimental results have shown that incorporation of small amount of nano clay particles (2-5%) under optimized processing conditions, led to significant reduction of permeation of hydrocarbon fluids by a factor of 70 to 100, compared to neat HDPE. Moreover, the container stiffness in top load conditions and its dimensional stability were increased without loss of impact resistance.This novel single wall nano clay composite technology has been commercialized for the production of high barrier extrusion blow molded containers.
High Flexibility EMA Made from High Pressure Tubular Process
The comonomer distribution and mechanical properties of two ethylene/methyl acrylates (EMA's), one made in a tubular reactor and the other in an autoclave reactor, are compared using thermal fractionation and Dynamic Mechanical Spectrometry. Both EMA's contain 24 wt % methyl acrylate. The pair has the same number of MA branches on ethylene chains. The result points that the tubular EMA has broader MA distribution than the autoclave EMA. For example, the tubular tube-produced EMA has long ethylene run lengths, melting at 100ºC and 95ºC, which are not seen in autoclave EMA. The mechanical beta relaxation region shows two peaks. In addition to the conventional cooperative relaxation of the glass transition at -30ºC and -32ºC, for autoclave and tube, respectively, we noticed a higher temperature shoulder at 8ºC and -4ºC for the latter. Oscillatory rheometry study suggests that tubular EMA has a higher melt flow activation energy than autoclave EMA. Additionally, examination of the melt elasticity reveals differences that suggest differences in long-chain branching but which may be due, at least in part, to the comonomer distribution. The TEM image reveals the tubular EMA are well dispersed in either PP or nylon 6. In contrast, the autoclave EMA shows a much coarse dispersion in PP with larger particles and obvious particle agglomeration.
High Output PVC Extrusion Benefits with Acrylic Impact Modification
The continuing trend toward high output extrusion has contributed greatly to the growth of rigid vinyl applications, particularly siding and window profiles. The development of large diameter twin-screw extruders, advances in die design, and improvements in extruder downstream efficiencies are among the factors that have enabled PVC to achieve a dominant share in the building and construction market.The PVC formulation plays a key role in achieving productivity improvements. Considering how susceptible PVC is to thermal degradation, it is important to choose formulation ingredients that facilitate the processing and flow of the PVC melt at the high shear conditions generated from high throughput. Typically, acrylic impact modifiers are used in siding and window formulations to improve ductility, weatherability, and, to some degree, appearance. In developing new acrylic impact modifiers, emphasis is generally placed on making changes to the polymeric structure in order to improve impact efficiency in PVC. However, the polymer's rheology characteristics must be considered. The typical acrylic polymeric additive, whether it be impact modifier or processing aid, contributes to the melt viscosity of the PVC formulation. High viscosity produces pressure build-up which, in turn, raises melt temperatures high enough to degrade the PVC. To show that both high extrusion rates and improved impact efficiency can be attained with acrylic impact modified PVC formulations without excessive viscosity, pressure or temperature increases is the intent of this paper.
High Performance Barrier Films from Polyacrylonitrile Homopolymers
Polyacrylonitrile homopolymer films were produced by melt extrusion in the presence of a fugitive plasticizer followed by post-extrusion operations involving biaxial orientation and heat setting. In the stretching and annealing processes, the plasticizer is expelled, leaving a high purity monolayer polyacrylonitrile film with residual levels of acrylonitrile and plasticizer below the levels required to meet FDA regulations for these substances in food contact applications. The films were characterized for mechanical properties and transmission rates for oxygen, carbon dioxide, water vapor, hydrogen and fuels. The preliminary results indicate that the experimental films have extraordinarily low oxygen permeability, lower than those of commercial barrier films. Film characteristics are discussed in terms of resin type, plasticizer concentrations and choice of extrusion and post-extrusion conditions.
High Toughness Vinylester/Epoxy-Based Thermosets of Interpenetrating Network Structure
The curing and fracture mechanical performance of resin combinations containing a bisphenol-A type vinylester (VE) and various epoxy (EP) systems were studied in the entire composition range. VE was crosslinked by free-radical induced copolymerization with styrene, whereas the EPs of aliphatic (Al-EP), cycloaliphatic (CAl-EP) and aromatic (Ar-EP) nature were hardened by an aliphatic diamine compound. Curing and chemorheology of the resin compositions were assessed by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR) and plate/plate rheometry. It was found that the curing of VE is faster than that of the EPs and thus it is the controlling parameter of the resulting morphology. Dynamic-mechanical thermal analysis (DMTA) showed a broad mechanical loss peak between the glass transitions (Tg) of the pure resins at least in a given composition range (25/75..75/25). It was supposed that the related materials possess an interpenetrating network (IPN) type structure. The fracture energy (Gc) of the VE+Ar-EP combinations followed the additive rule. On the other hand, combining VE with Al-EP and CAl-EP in the composition range 40/60... 60/40 yielded synergism in Gc the values of which reached 6 to 10 kJ/m2 . The toughness improvement was explained by the enhanced shear deformability of the network which was confirmed by fractographic results.
Highly Crystalline EPDM Terpolymers as Cure Enhancers in Radiation Cured Polyolefin Compounds
It is well known in the cross-linked polyolefin industry that conventional ethylene/propylene/diene (EPDM) rubber can enhance the cure response of polyolefins to electron beam irradiation. Some EPDM rubber, having ethylene content from 50 to 80 weight percent, is used to boost polyethylene cure response in irradiated systems. Unfortunately, these blends can have limited use due to the EPDM rubber;s low softening point.Single site metallocene constrained geometry catalyst (CGC) technology enables the manufacture of EPDM terpolymers at higher reactor temperature and catalyst efficiency than standard Ziegler Natta catalyst systems. The unique combination of monomer, catalyst and process technology enables the manufacture of highly crystalline EPDM's (HCEPDM) having ethylene contents from 85 to over 90 weight percent. This study investigated these new HCEPDM terpolymers and their differentiation from commercially available EPDM's. The results indicated that these new HCEPDM's exhibited mechanical and thermal properties similar to linear low-density polyethylene, yet exhibited very high gel response to electron beam radiation. These new HCEPDM polymers demonstrated utility as blend additives to enhance the gel response of polyethylenes to electron beam irradiation. Good cure response was also observed in blends with polypropylene.
Highly Filled Calcium Carbonate/Polyethylene Porous Films for Water Vapor Breathable Applications
Thin LLDPE films containing high loadings of fine particle size, ground calcium carbonate (GCC) were prepared in a single screw extruder from precompounded pellets. The films were then biaxially stretched to about 25-50 microns thickness to produce porous structures suitable for water vapor breathable applications. The films were characterized for filler dispersion by SEM elemental dot mapping analysis and surface texture by SEM. The cumulative pore volume and pore size data obtained by Mercury Intrusion Porosimetry analysis confirmed the SEM observations and were in good agreement with water vapor transmission values as per ASTM procedures. The resultant breathable film morphologies are discussed in terms of resin/filler properties and choice of extrusion and post-extrusion conditions.
Horizontal Turntable and Stackmold Technologies - Inovative Technologies in Multi Component Injection Molding
Turning a part of the mold is the classical, most widely used, method of transporting preforms in multiple component engineering molds. Up until now, turning was carried out exclusively with vertical turntables which were mounted on the moving machine platen and which have a horizontal turning axis.However, because the machine has to provide turning space according to the diagonals of the mold, the problem of a very large machine clamping unit is encountered. In addition to the turning space, a high clamping force is needed for the injection of preform and finished part in one cycle.This situation looks much more advantageous if the over-molding-stack mold system is linked with a horizontal turning device. This process has been developed by Ferromatik Milacron in close co-operation with Foboha GmbH Formenbau, Haslach.
A Hot Runner Manifold as a PvT Apparatus
PvT data are used in closed-loop injection machines to control the process and achieve uniform quality of the parts. In CAE software for injection molding, the PvT data are used for compressibility calculations during the filling phase, and for volumetric shrinkage calculations during the holding phase. The predictions made by the software are only as good as the input data. Therefore, to generate data that are more realistic is necessary to use an apparatus that reproduces the actual molding conditions. To approach these conditions, a hot-runner manifold is attached to an injection-molding machine to determine PvT properties.
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