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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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.
How Increased Control in Plastic Melt Delivery Increases Productivity
In modern injection molding all of the process control is established and controlled in the barrel of the injection-molding machine. This paper explores the benefits of providing independent, real time, closed loop, process control at each hot runner gate location in a mold. This new approach to injection molding allows for a separate injection fill and pack profile to be established at each gate location, creating a best practice in plastic melt delivery control. The higher level of localized control opens the door to increasing quality and productivity. We will demonstrate how higher productivity is realized through producing higher cavitation-precision (parts) molds, as well as family molds and/or modular mold systems.
Hybrid Magnetic Materials Based on Polymers and Magnetic Fillers
In this work the mechanical, magnetic and rheological properties are analyzed. The influence of different magnetic powders onto a polyethylene was studied. The magnetic characterization of isotropic plastic bonded magnets, based on strontium ferrite (SrFe12O19) and Nd2Fe14B onto polyethylene, as a function of composition was analyzed in a magnetometer at room temperature. The rheological properties were studied in a capillary rheometer; it was found that viscosity increased as the magnetic powder concentration increased in the composite.
Hygro-Thermal Effects on the Physical Aging Response of Glassy Polymers
Physical aging experiments are being performed in epoxy glasses subjected to relative humidity jumps. The premise of the study is that a change in moisture (plasticizer) content in the material is equivalent to a change in temperature because in both cases the distance from the glass transition is changed by either a constant relative humidity jump in temperature or an isothermal jump in relative humidity. As did Kovacs in his classic work on Poly (vinyl acetate) we are creating a data set of volume recovery for the epoxy. We have begun the determination of the intrinsic isopiestics--the RH-jump equivalent to the Kovacs' intrinsic isotherms. Similarly, we are determining the asymmetry of approach in up- and down-jump conditions as well as the memory response that results after in a two-step experiment. Finally, work is underway to model the material response by extending the KAHR model to the case of changing relative humidity.
The Impact Behavior of Injection Molded Plates with and without Weld Lines
A box-like part was injection molded in a polypropylene copolymer with systematic variations of the processing conditions (melt and mould temperature, injection flow rate and holding pressure), based on a design of experiments approach (L9 Taguchi orthogonal array). Due to the gating options (hot runner with two gate points), the major box surface shows a central weld line. This work studies the influence of the processing conditions on the impact behavior of the molded plates at two locations: in and away from the weld line. Both local processing thermomechanical environments were computed from mould filling simulations (thermal and stress levels), and characterized by thermomechanical indices (aiming at interpreting locally the microstructure development). The falling weight impact tests were performed at 2 m/s with a lubricated striker. The impact behavior was characterized by the peak force and energy. The experimental results are analyzed by ANOVA statistical tool. The dependences of the impact response upon the thermomechanical indices at the two locations are compared.
Impact Enhancement of High Melt Flow HDPE
The modification of impact properties of High Density Polyethylene (HDPE) having high flow to meet impact, stiffness and processability of heterophasic polypropylene copolymers (CPPs) was studied using a variety of impact modifiers like : high impact HDPEs, Low Density Polyethylenes (LDPEs), Linear LDPEs (LLDPEs) and Ethylene Vinyl Acetate (EVA) copolymers.Taking into account both the resultant properties (impact and stiffness), the flow properties and cost, it was shown that EVAs provide the most cost-effective solution to impact modification of HDPE with stiffness levels compared to CPPs. Experimental results showed that addition of up to 5.6% Vinyl Acetate (e.g.20% EVA with 28% VA content) yielded the optimum properties of the HDPE blends.Addition of LLDPE to HDPE though resulted in the sought mechanical properties, exhibited a major reduction in flow properties at the content level needed (40%) for properties modifications.
Impact Modification of Polypropylene
This paper compares the modification mechanism provided by ethylene-octene (EO) copolymer to that of ethylene propylene diene terpolymer (EPDM) rubber. Within the limits of this study, the highest impact strength was achieved at 30-40% rubber content, regardless of the rubber type. An increase in rubber melt viscosity resulted in overall greater impact strength. At the optimum concentration, the high viscosity (MFI = 1 to 5) EO rubber provided modification mainly via crazing mechanism, while the EPDM rubber by energy dissipation through the three-dimensional network structure formed with the polypropylene matrix. This paper also discusses the effect of the processing conditions on physical properties of PP/EPR copolymer. An increase in processing temperature and screw speed resulted in a reduced number of discreet rubber particles, nearly no or very slight increase in impact strength, but a very significant reduction in tensile strength and tensile modulus.
The Importance of Monitoring Mold Pressure during Rotational Molding
During the rotational molding of plastic parts, the pressure inside the mold can become positive or negative depending on a variety of factors such as the size of the vent, the quality of the mold, the heating rate, etc. In commercial molding, the pressure is likely to vary in an arbitrary manner, depending on particular combinations of key variables. This leads to conflicting reports about the causes and cures of problems such as warpage, residual stress and shrinkage. This paper reviews the effects of pressure variations on the quality of rotomoulded parts and using experimental data, demonstrates the importance of monitoring the pressure inside the mold throughout the cycle. Methods of doing this are illustrated and the benefits in terms of reduced cycle times and improved part quality and consistency are demonstrated.
Important Parameters for Operating and Selecting Dynamic Mechanical Thermal Analyzers
Dynamic mechanical thermal analysis (DMTA) is used to measure the stiffness (modulus) and mechanical damping (tan delta) of polymers rapidly over a range of temperatures. It is one of the best methods for examining the glass transition and other viscoelastic relaxations in materials. A sinusoidal mechanical perturbation (force or amplitude) is applied and the resulting sinusoidal response (amplitude or force) is measured. The three basic parameters of the measurement are force and displacement amplitudes, and time delay between the force and displacement signals. Several instrument and sample parameters must be considered when designing DMTA experiments including deformation mode and amplitude, sample strain target and ranges of stiffness and force that the instrument can measure. With good control of the operating parameters DMTA can provide good measurements of modulus. A common sense approach is given to setting experimental parameters for linear drive DMTA instruments.
Improved Screw Design for Maximum Conductive Melting
New advances in screw designs and mixing sections have allowed processors to take advantage of new resins, higher production rates, and improved product quality. Until now, the basic single screw geometry has changed little over the past 15 years. With the advances in new material formulations, additives and fillers, the screw design must be able to fully melt and disperse the additives in the polymer matrix without destroying the properties from excess shear. This paper will present data on the melting performance of a new screw design with a unique flight geometry that maximizes the conductive melting mechanism (low shear) in the screw channel.
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