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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Using Molecular Stress Function Theory to Evaluate Strain Hardening of Polyethylene
Strain Hardening of polyethylene in uniaxial extensional flow is evaluated with a focus on its strain rate dependency. The stress growth function data of LDPE and HDPE by a rheometer with dual drum fixture was evaluated with the Molecular Stress Function (MSF) Theory. The model provides evidence that the MSF fit on the data at the lowest available strain rate may be used to obtain reasonable semi-quantitative characterization of the long-chain branching content of LDPE. The rate dependent strain hardening behavior of the LDPE and HDPE samples, on the other hand, is well characterized with the maximum Trouton ratio (Tr) predicted by MSF. All three resins studied show a decreasing Tr with increasing strain rate. The rate dependence is strong when Weissenberg number Wi ó1.
A Case for Round Energy Director: Utilizing Advanced Control Capabilities of Servo-Driven Ultrasonic Welders in Evaluating Round Energy Director Performance
Ultrasonic welding of thermoplastics is widely used in many industries to fuse two parts together in a very short time with no additional consumables. The development of the Dukane?s iQ series Servo-Driven Ultrasonic Welder with patented Melt-Match? technology introduces unprecedented levels of control, which allow to overcome less than optimal weld joint designs, material compositions and processes, that have long been challenging to pneumatically driven welding presses. This study further investigates the capabilities of the servo-driven welder and focuses on experiments evaluating the feasibility of using round energy director (ED) designs for the ultrasonic welding process.
Sterilization Effects on Hard-Soft Combined Polymers for Medical Application
Polymeric hard-soft combinations manufactured by multi-component-injection molding are a suitable way to combine strength properties of a hard thermoplastic component with an elastomer for damping, sealing or haptic functionalities. The use of multi-component injection molding has been transferred to medical applications, mostly applied for sterile products. Consequently, it has to be ascertained that necessary sterilization processes do not affect the adhesion between hard and soft component during the life cycle of the plastic part. So far, there is a lack of sufficient studies on sterilization effects within hard-soft combinations.
For this reason, the adhesion strength of different polymeric hard-soft combinations after sterilization treatment was analyzed in this study. The tested material combinations are different thermoplastic elastomers (TPE) on thermoplastic substrates. Moreover, silicone rubber was combined with thermoplastic substrates after atmospheric pressure plasma treatment. Hot steam sterilization (20 min., 121øC) and gamma irradiation (50 kGy) were applied on the specimens with varied intensities. To quantify the influence of sterilization treatments, adhesion strength was analyzed by 90ø-peel testing. SEM images of the peeled off surfaces were compared for qualitative analysis of the bond strength.
Hot steam sterilization was particularly critical to polar materials as e.g. polycarbonate (PC), resulting in reduced peel force, as well as to heat sensitive material combinations. Gamma irradiation can be applied to nearly all tested polymers, for some thermoplastic ? silicone rubber combinations the peel force can even be enhanced due to post-curing reactions. Beneath the influence of sterilization on adhesion, other effects as yellowing of e.g. PC and TPU or changes in mechanical characteristics have to be respected.
Rheological Characterization of Highly Filled Composite Systems for Injection Molding Applications
The focus of this study is to characterize the rheological properties of boron nitride (BN) composites. A series of boron nitride composites with varying filler loading level were prepared using two different forms of BN fillers blended with polystyrene (PS). The rheological properties of these composites were characterized using a parallel plate rheometer and a capillary rheology. The structure and thermal conductivity of these composites were also characterized. These data were used to identify structure-property relationships for PS/BN composites.
Heat Transfer Simulation for a Continuous Annealing Process of Plastic Sheets
The continuous annealing process in conjunction with an extrusion casting line is of vital importance to reduce the shrinkage level of plastic sheets while maintaining economic competitive advantage. Therefore, it is crucial to accurately predict the temperature profile of plastic sheets during the annealing process to facilitate process design and operational control. In this paper, a heat-transfer model was developed to predict and optimize the continuous annealing process. Through mathematical modeling of the infrared heating process using a finite-difference analysis (FDA) program coded with FORTRAN language, we successfully mapped the temperature profile of plastic sheets. The numerical simulation results were validated and consistent with experimental data.
Effect of Rheology on the Morphology of Coextruded Microcapillary Films
This paper reports, for the first time, the successful implementation of microcapillary coextrusion technology with an emphasis on the fundamental understanding of the effect of rheological properties of polymers in both film matrix and microcapillaries on the morphology of coextruded microcapillary films. Four different polymer pairs were judiciously selected for coextruded microcapillary films, indicating that the microcapillary shape may be circular, oval, or even rectangular depending on the viscoelastic properties of the respective polymer pair as well as the processing conditions. The area percentage of microcapillaries in the film cross-section was dependent on the screw speed (i.e., extrusion rate) of the extruder. The average film thickness decreased with increasing line speeds, while the aspect ratio of microcapillary dimension held the reverse trend.
Numerical Simulation and Experimentation of Water-Assisted Co-Injection Molding of a Non-Circular Tube
Water-assisted co-injection molding (WACIM) is a complex, innovative injection molding process. A three-dimensional model for WACIM was setup and a turbulence model was adopted to deal with the turbulent flow of the water. A free interface of the skin?inner melt and the inner melt?water were tracked by the volume of fluid (VOF) method. Numerical simulations for the filling stage of WACIM parts with four types of cross-sections were carried out using the computational fluid dynamics (CFD) method. Experiments were conducted to verify the simulation results. The results of the experiments were in agreement with those of the simulations. The shape of the cavity cross-section had an obvious effect on the penetration section of the inner melt, while the shape of the water penetration ended up being round. The penetration area of the water increased in the flow direction, and the residual thicknesses of the inner melt downstream was thinner than the melt upstream.
Precise Injection Molding of Thermoplastics Elastomers -Evaluation of Surface Replication and Metal Adhesion-
New thermoplastic elastomer (TPE)s with different polymer content and additive were injection-molded onto line-and-space micro pattern and sand-blasted aluminum plates. The thermal shrinkage and micro surface replication of molded elastomers were revealed after injection molding. These properties of elastomers were dependent on the composition of polymer and additive. Moreover, the sand-blasted aluminum substrate was joined with the molten elastomer as the elastomers were developed to precise seal parts for electronic devices. The joining strength of the aluminum/elastomer interface was sufficiently strong as the elastomers themselves were fractured while the interface was held when the joined part was stretched.
A Walk around the Color Sphere: Effect of Titanium Dioxide Particle Size Distribution on Color of Plastics
?Black? and ?White? pigments are often referred to as colorants because they can influence the color properties of finished products in the plastics industry. One of the most common ?white? pigments used in the plastic industry is rutile titanium dioxide. This review provides an example of how various types of titanium dioxide materials can impact the overall color of plastics. Three different titanium dioxide (TiO2) grades were compounded into a soft PVC containing with a fixed amount of carbon black and the resulting CIE L*a*b* tri-stimulus values were measured. The primary difference amongst the titanium dioxide samples was their median particle diameter. Each titanium dioxide material resulted in a unique color space, As the amount of each pigment was increased in the soft PVC formulation, it was interesting to observe that the tri-stimulus values march towards the ideal white co-ordinates of L*= 100, a* = 0, and b* = 0, but follow different paths. In other words, the tri-stimulus values walk along the color sphere in different paths, but all tending towards the same point. At a given concentration of titanium dioxide, the smaller particle diameter pigment approached the ideal white the most amongst the three pigments. The highest Whiteness Index (WI) was achieved by the titanium dioxide with the smallest particle size diameter.
Fiber Orientation Measurements Using a Novel Image Processing Algorithm for Micro-Computed Tomography Scans
Based on previous work at the Polymer Engineering Center, Madison, a novel image processing algorithm has been developed that accurately analyzes fiber orientation distribution in discontinuous fiber-reinforced composites. The developed algorithm is an accurate and time-efficient method to measure the fiber orientation distribution of micro-computed tomography (?CT) scans. In this work, the image processing algorithm is described and verified experimentally. Additionally, the algorithm is compared to a commercially available benchmark software package. In this test case, ?CT scans of samples extracted from compression molded parts were used to evaluate the performance of the algorithm by comparing it to the benchmark. In all cases, the algorithm shows highly accurate fiber orientation measurements and the results show that it can compete with the benchmark software.
Bio Based Active Barrier Materials and Package Development
The food and packaging industry are interested in approaches to reduce the permeability of oxygen in Polyethylene terephthalate (PET) to extend product shelf-life. The purpose of this work is to investigate use of unsaturated fatty acids as O?2 scavengers to reduce the permeability in PET. The focus was to characterize the scavenger and to develop methods to incorporate them within PET packages. Linoleic acid was chosen based on oxygen capacity and uptake kinetics. Reactive extrusion was utilized to make pellets of PET/scavenger and blown into bottles. The presence of the scavenger in the polymer was determined using TGA and extraction. Permeability of O?2 through bottle sidewall in PET/scavenger system was measured and compared with base PET. The PET scavenger system exhibited decreased O?2 permeation with little changes in thermal and mechanical properties.
How Is Electrical Percolation Achieved in Nano Doped Materials? Direction towards More Efficient Doping
One route to create electrically conductive polymeric material is to dope them using highly conductive nanoparticles such as carbon nanotubes. It is well known that, when a threshold volume fraction is reached, a percolated network is achieved in which efficient conduction can take place. In such a network, inter particles charge transfer takes place over a very short distances, when particles become close enough to each other so a tunneling mechanism becomes possible. It follows that most of the introduced particles are not linked to the percolated path, thus not participating in the doping mechanism. The spatial arrangement of the particles plays a major role in the way they are participating in the increase in macroscopic electrical conductivity. We propose here to go further than the usual method of quantifying filler content based on weight/volume fractions by studying in detail the topology of the particle arrangement. This provides an in-depth understanding about how the conductive path develops when increasing the filler content and paves the way for an optimal use of the doping particles.
Thermal and Rheological Analysis of Nucleated LLDPE Resin. Determination of Crystallization Kinetics Parameters
The effect of a commercial nucleating agent i.e HPN20E on the thermal and rheological properties of LLDPE M500026 resin was successfully studied. The crystallization temperature increased by about 7§C and the crystallization % decrease when a NA is added. Non-isothermal crystallization parameters were determined. The lower Ea value for LL50-NA indicates easier crystallization in the presence of a nucleating agent.
Time sweep rheological experiment proved to be a powerful technique to evidence the effect of a nucleating agent. Hot stage microscopy confirmed the role of a NA in reducing the size of crystallite
Modeling of Tension-Compression Asymmetry in Fiber-Filled Engineering Thermoplastic Materials Using LS-DYNA
Fiber-filled engineering thermoplastic (ETP) materials such as THERMOCOMP?, VERTON? and STAMAX? compounds are used across various domains such as aerospace, automotive and fluid engineering. For such materials, Young?s modulus (E) in tension may be very different than that in compression. Most of the commercial simulation software used for non-linear static analysis does not have a material model to simulate the structural deformation of a component having differential mechanical properties under tension and compression. The assumption of using the lower value of E, between that of tension and compression, in the material model leads to an over prediction of the design deformations. On the other hand, the usage of higher E value leads to an under prediction of the actual deformation which could result in an unsafe design condition. This paper explores advanced material modeling capability available within the LS-DYNA commercial code to simulate the aforementioned material behavior. In this work, a methodology to perform a quasi-static simulation using LS-DYNA explicit solver for materials with unequal tension-compression modulus is proposed and is validated against a practical field problem.
Development of Electrically Conductive PVDF/PET Systems
Polyvinylidene fluoride/poly(ethylene terephthalate) (PVDF/PET) based composites for proton exchange membrane fuel cell (PEMFC) bipolar plates (BPs) were prepared at different crystallization temperatures and characterized by X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and resistivity setup. Composite conductivity was made possible by using a mixture of carbon black (CB) and graphite (GR). To improve composite processability, its viscosity was reduced by adding a small amount of cyclic oligomers of butylene terephthalate (c-BT) and thermoplastic polyolefin elastomer. In the PVDF/PET based composite, it was found that PVDF phase could crystallize easily but PET crystallization was difficult. Due to CB/GR additives, the formed crystals in PVDF/PET phases had a poor perfection degree and showed a lower melting temperature compared to pure PVDF and PET. It was observed that PET nucleation was accelerated but not that of PVDF. According to through-plane resistivity results, composite crystallization temperature range was divided into two parts (below/above 170oC) where there was a different variation behavior of through-plane resistivity. It has been proved that the resistivity was mainly governed by the network of CB/ GR developed inside the PET phase, and decreasing the crystallinity of PET led to a decrease of through-plane resistivity, which is desirable for BPs.
The Use of Nucleators and Clarifiers in Polypropylene
Polypropylene is one of the most common plastics, and its use in many applications is a result of the excellent balance of physical properties that PP displays. The solid state properties of polypropylene are very dependent on the crystal morphology of the final part. One common way of controlling the crystal structure and the overall crystallinity of PP is through the use of nucleating agents. These additives provide surfaces on which polypropylene crystallites can form when the molten polymer is cooled. The chemical and surface characteristics of the nucleating agent affect the type of polymer crystals that form, the size and distribution of the polymer crystals, and the percent crystallinity in the final part. Nucleating agents also influence the appearance of the part, and they can have a dramatic effect on processing behavior and the rate of crystallization.
In this talk we will review the basic principles of polymer crystallization and nucleation. This discussion will include examples of nucleating agents that induce the formation of the more common alpha crystal form of PP as well as the less common beta form. Many examples of nucleated products ranging from molded parts and oriented films to extruded and thermoformed plastic parts will be included in this discussion. A particular type of alpha nucleant known as a clarifier, which is used to produce high clarity parts, will also be discussed.
Virtual Fine-Tuning of a Profile Coextrusion Die using a Three-Dimensional Flow Simulation Software
Die geometry of a bilayer die for coextrusion of a PVC window profile is fine-tuned for a uniform exit velocity distribution by using a flow simulation software. Besides the flow inside the die, the post-die flow of extrudate, including the flow in the calibrator of the profile die, is simulated. The pressure drop and the changes in the extrudate shape predicted by the software are in good agreement with the corresponding experimental data. It is estimated that the virtual fine-tuning of the die using the software saved two fine-tuning cycles in the experiments, resulting in a significant saving in the cost and the lead time for the profile die development.
Filtration Media Using a Melt-Based Processing Technique
Fibrous filtration media were produced using a novel melt-based co-extrusion and two-dimensional multiplication technique combined with a high-pressure-water delamination technique. These cross-plied, fibrous filters have integrity and mechanical strength in two dimensions. The orientation procedure greatly improves the fiber orientation, decreases the fiber sizes, and enhances their mechanical performance. In comparison with the commercial product, the filters produced from the oriented tapes have superior mechanical properties, larger surface area, smaller pore size and higher porosity, which are indicative of improved filtration performances. This melt-based, versatile technology is applicable to any melt-processable polymers, and allows tunability of the filters? surface area, pore size, and porosity, and makes these filter materials good candidates for various filtration applications.
Continuous Extrusion of Nanocellular Foam
Nanocellular foams are typically produced with supercritical CO2 by a solid state batch foaming process. Low temperatures allow for the stabilization of a high number of nuclei that can be generated by controlling the pressure and pressure drop rate. Yet such a process is not easily applicable to future commercial production due to long saturation times and finite autoclave volume.
This limitation can be removed by adapting the nanofoaming process to continuous production. Modifications to a simplified foam extrusion system made it possible to produce sub-microcellular acrylic foams with bimodal and monomodal cell distributions. Optimization of extrusion conditions led to homogeneous nanofoams with four-fold expansion and cell nucleation densities over 1014/cm3.
Nucleation of Polypropylene during High Speed Processing
Nucleation is one important tool for tailoring mechanical and optical properties of polypropylene (PP) as well its processability in various conversion technologies. Especially the latter aspect is gaining more and more importance in the light of sustainability and energy efficiency discussions, as shorter cycle times and high line speeds are aspired. The efficiency of a nucleating system is commonly determined by the crystallization temperature (Tc) of the resin as measured by differential scanning calorimetry (DSC), typically at 10 K/min. However, Tc is strongly dependent on the cooling rate. Thus, at processing relevant conditions (cooling rate 100-6000 øC/min resp. up to 100 K/s) a suppression of the nucleation effect is frequently observed, and in certain cases the nucleating agent can become completely ineffective. In this study, the crystallization behavior of polypropylene heterophasic copolymers, containing state-of-the-art nucleating systems has been compared. Non-isothermal and isothermal crystallization experiments were performed by DSC and by fast scanning chip calorimetry (FSC) at cooling rates between 0.02 and 3.000 K/s. The data obtained suggest significant differences regarding the crystallization rate. The results are discussed in light of the molecular architecture of the polymer and the type of nucleating system.
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