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.
The halo surface defect is one of the surface defects of the glossy products. A sudden change of the flow front speed causes the difference in the cooling condition of the surface, resulting in the halo. In this work, a quantified evaluation method for the halo by image processing was developed. Its feasibility was confirmed by compared with visual observation. The strongest influencing factor to the halo was the injection rate. A strategy of reducing the speed difference around the halo location was tested for eliminating the halo. The location of the halo was found by CAE analysis. As the injection rate was reduced to the minimum level at the location, the halo was successfully eliminated. The elimination of the halo was confirmed by both visual observation and the quantified evaluation method proposed in this work.
In order to conserve resources and at the same time spur economic growth, the European Union is pushing to establish a Circular Economy. For global businesses, including manufacturers of electrical and electronics equipment (E&EE), some of the principles of the Circular Economy will likely be applied globally rather than just within the European Union. This paper describes how the recycling of plastics from shredded waste electrical and electronics equipment (WEEE) fits within the Circular Economy, and provides some guidance to manufacturers looking to incorporate these recycled plastics in new E&EE. Furthermore, we provide recommendations on the design of E&EE such that plastics may be recycled more easily in the future.
Ice is a unique natural substance, whose solid state behavior is deceiving due to the pervasive presence of a liquid-like surface layer, especially at temperatures close to its melting point (>-10°C). As a result, ice is a very slippery, self-lubricating substance on which most materials, thought to give high traction (e.g. elastomers), cannot achieve high coefficients of friction (COF ~ 0.1). Here, we describe the high friction behavior (COF ~ 0.5) of a new class of textured elastomer fiber composites made using a facile fabrication method of cutting and rearranging molded composites. These fibrous TPU composites have uniformly distributed surface protrusions that are capable of penetrating and interlocking with an ice substrate underneath resulting in static COF that are 4- 7X higher the TPU elastomer by itself. Increasing the fiber content improves the surface structure characteristics, namely protrusion density, and hence improves the friction coefficient. Furthermore, increasing the contact pressure increases the depth of protrusion penetration and hence improves the friction force. These structure-property relationships were verifiable through a mechanics model, with the appropriate normalization, that describes the characteristic forces on a single fiber. Strong potential applications of such textured elastomer composites exist for winter safety applications such as footwear and tires.
In this work, biocomposites of agave fibers (Agave tequilana Weber var. Azul) and polylactic acid (PLA) were produced by rotational molding. In particular, a simple dry-blending technique was used to disperse the agave fibers in the biodegradable polymer matrix. The effect of fiber content was studied (0, 10, 20, 30, and 40 wt.%) and the samples were characterized in terms of morphology, density and porosity to relate with mechanical properties (tensile, flexion, impact and hardness). The results showed that rotomolded biocomposites were successfully produced, but had high porosity leading to lower properties for fiber contents above 10%. It was possible to observe that low fiber contents produced the best morphology, indicating that there is an optimum fiber content to get well-distributed fibers in the matrix.
Many effect pigments used in thermoplastics such as those used for pearlescent appearance are comprised of coated mica crystalline platelets. For effective coloration of thermoplastics the mica structure should not be altered. If the mica platelet is reduced in size while being compounded into the plastic it will alter the appearance of the plastic. It is desirable to maintain the mica structure in order to produce the best possible appearance of such pigments. To avoid attrition of the platelet structure exposure to shear during processing should be avoided, particularly when compounding high concentrations of pigment for masterbatch production. Co-rotating twin screw extruders are used for the compounding pigments into thermoplastics. Typical kneading blocks have predominantly been used with this equipment for the compounding of pigments for many decades. The mixing properties of this element include compression and simple shear which causes damage to the mica structure. Avoiding compression through the use of elongational mixing can significantly reduce damage to the crystalline structure of mica and enhance the appearance of mica based pigments. New mixing alternatives are available today that eliminate the shear peaks that are characteristic of typical kneading blocks, and utilize highly effective and efficient elongational mixing for the dispersion and distribution of mica based pigments while preserving the platelet structure.
In this work, ground tire rubber (GTR) was dryblended with linear low density polyethylene (LLDPE) to produce thermoplastic elastomer parts by rotational molding. In particular, different GTR concentrations (0, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50% wt.) were incorporated to determine the effect of the rubber phase on the processability and overall properties of the parts. Each composition was characterized in terms of morphology and mechanical properties (tensile, flexural and impact). The results show that the addition of the rubber phase decreased the tensile and flexural moduli and strengths, but the tensile elongation at break was always above 100%. This good elasticity produced impact strengths higher than the neat matrix with an optimum GTR content around 20% wt.
This paper describes the mechanical behavior in compression, at both low and high strain rates, of several low density open cell polyolefin cellular materials with different gas phase tortuosity of the cellular structure. Due to the high tortuosity of some of the polyolefin foams under study they have a mechanical behavior similar to that of open cell polyurethane foams at low strain rates (i.e. they could be used for comfort applications) and they have a similar mechanical behavior to that of closed cell polyolefin foams at high strain rates (i.e. they could be used in body protection applications). Therefore, these new materials with high tortuosities have an unique mechanical performance strongly influence by the strain rate.
For modeling the flow of non-Newtonian polymer melts in single screw extruders numerical methods are required in general. In this study the viscous dissipation and the conveying characteristics in the melt channel of single screw extruders are analyzed for a two-dimensional, fully developed flow of power law fluids. Therefore three different numerical methods are presented and the results are compared. Furthermore, a comprehensive parametric design study is shown, analyzing the viscous dissipation depending on three independent parameters: (i) pitch to diameter ratio, (ii) power law exponent, and (iii) dimensionless pressure gradient. The derived results for the viscous dissipation can be used to calculate the mean melt temperature profile more precisely.
In this paper, we consider a two-dimensional model of the foam nucleation process of CO2 in polystyrene (PS) matrix by random initiation of growing bubbles in time and space. The model was extended to account for the simultaneous cell nucleation, growth, and collapse processes of the foaming bubbles at two different viscosities of PS resins. By means of connection among neighboring bubbles, secondary nucleation behaviors emerged from a multi-bubble system were attempted in simulations. The resulting cell size distribution (CSD) of bubbles shows power law behaviors for both simulations and experiments. The cell size distribution and morphologies obtained from the numerical simulation agreed with the snapshot pictures of the experiments qualitatively and quantitatively. Finally, different nucleation and growing rates were investigated to understand the relationship between the bubble nucleation /growth and final morphology of the foam structure. Potential applications lie in the analysis of the resulting micro-/nano-cellular structures due to secondary nucleation and the foam stabilization.
The adhesion properties of liquid silicone rubber (LSR) and different thermoplastics (PC, PA, and PP) were examined in this investigation. In order to guarantee the adhesion of both components, an activation (silicatization) of the TP surface, which is a conventional method, was carried out. Furthermore, the long-term stability of the silicatization (storage of the activated surfaces) as well as the wetting behavior were investigated. Moreover, microscopic investigations were performed to analyze the activated thermoplastic surfaces. The test specimens were produced on a 2-component injection molding machine. In accordance with the guideline VDI 2019, the peeling resistance was determined and the results were compared.
Advanced material is developed by using continuous fiber reinforcement to achieve higher strength than can be obtained with injected composite material. High forming performance has been achieved by using the cloth-like textile fabric material, made from combined filament yarn. By applying the developed textile composite, parts can be molded with deep drawing and complex shapes with ribs. Moreover, high weld strength has been achieved between the materials of compression molded textile composite and injection molded short fiber reinforced material in hybrid molding.
Incorporating liquid fillers in additive manufacturing processes can produce liquid-filled solid parts with unique properties. To develop this, the behavior of immiscible droplets in a polymer matrix subject to different kinds of flows is explored. Castor oil droplets, with a range of capillary numbers much higher than the critical capillary number, were injected in a matrix of Silicone oil and subjected to flows within a converging channel. The rate of change of capillary number as the droplet moves down the channel was measured to illuminate the effect of the die design. The affine state was not reached when the droplets were deployed in the center but was achieved when injected in an offset position. This data is valuable to understand the effect of the die on the deformation induced on immiscible droplets and is one of the preliminary steps to incorporate liquids in additive manufacturing.
Ultrasonic welding of thermoplastics is widely used by many industries to fuse together two parts in a short time without introducing additional consumables such as fasteners, adhesives, or solvents. The recent development of servo-driven ultrasonic welders, as opposed to pneumatically driven welding machines, introduces unique levels of control throughout the welding cycle. This study focuses on the final phase of the welding process, i.e., the hold cycle, and the benefits that the servo-driven ultrasonic welders can provide to this final phase by controlling both hold distance and the velocity at which this final phase is accomplished.
Traditional polymer powder and micropellet based processes, such as powder bed fusion and rotational molding, have been in increased demand in modern processing industries. These processes require polymer powders and micropellets with a small particle size, narrow size distribution and defined geometry for a variety of polymer resins. Therefore, micropelletization technologies, where particles in the size range of 50 to 1000 µm are generated, have been attracting growing attention over the past decade. A new technique, developed at the Polymer Engineering Center, yields micropellets with a controlled morphology and narrow particle size distribution. In this process, a polymer melt is extruded through a capillary and is subsequently stretched with a hot air stream until flow instabilities cause it to break up into particles. Small changes in process conditions result in different size distributions and particle shapes, such as lentil-like pellets, fibers and thread segments. This work shows how material properties and processing parameters influence the produced micropellets. Besides the processing of virgin thermoplastic material, recycled high density polyethylene flakes are used as feedstock for the micropelletization process in order to show the capability of this process to contribute to current polymer recycling efforts.
The blow molding process offers the possibility of reproducible, fully automatic and therefore cost-efficient mass production of complex hollow bodies. Due to the poor mechanical properties of uncured rubber, it has not yet been used for the manufacturing of elastomeric hollow parts. In this contribution, it is shown that with a defined pre-cross-linking of solid silicone rubber the blow molding of the material is possible. With pre-cross-linking the mechanical material properties can be adjusted precisely. This allows parison extrusion without strong drawdown. During the forming, it provides the necessary elasticity while maintaining the weldability and formability of the material. But pre-crosslinking also influences the materials rheological properties. Preliminary investigations showed pre-crosslinking has to take place in the blowing head bevor the material leaves the die. Therefore, changes in rheological material behavior are investigated and considered for the flow channel design. It is shown that the pre-cross-linking allows the blow molding of elastomeric hollow bodies with a surface stretch ratio of 3.6 to 1. However, precross- linking can also lead to flow instabilities such as wall slippage and melt fracture.
Due to their complex flow and curing behavior the quality of parts made from thermosetting molding compounds depends to a high degree on the reactive and viscous characteristics during their processing. In the presented studies a continuous kneader was used to investigate how those characteristics depend on the filler content of the fluid molding compound, the grain size distribution and the present material humidity. Therefore, the grain size of different batches of three thermosetting molding com-pounds was examined, they were purposefully impinged with high air moisture and their flow resistance was measured using various kneader temperatures. The results display a strong dependence of the flow resistance on the filler content, the respective composition of the molding compound and the water content within the material. They will be discussed and interpreted according to their influences within the injection molding process.
Injection molding simulation is taking an increasingly important part in the development of new plastic components and in tool and mold making. However, in particular, the results of the filling pressure simulation frequently deviate from the filling pressures occurring in the injection molding process, so that injection molding tools are often oversized and too large injection molding machines are used for serial production in order to ensure the complete filling of the component cavity. The aim of this paper is therefore to define a correction factor which can be used to infer the pressure losses of an injection molding simulation to the real pressure loss that occurs in the injection molding process, the under- or over-dimensioning of injection molding tools and the use of injection molding machines which are too large or too small to avoid. For this purpose, a correction factor has been defined which consists of three individual correction factors, each taking account of the influence of the material used, the influence of the injection molding machine used and the influence of the component geometry to be produced. In addition, an addendum has been defined which maps the pressure loss of the screw of the injection molding machine used. The tests were carried out with five plastics: polypropylene (PP), acrylonitrile-butadiene-styrene (ABS), a blend of acrylonitrile-butadiene-styrene and polycarbonate (PC/ABS), polycarbonate (PC) and polyamide 66 (PA 66). Four factors from the control variables were defined and their influence on the injection molding process was systematically investigated using the means of statistical experimental planning. These factors are the melt temperature of the plastic, the coolant temperature, the injection speed, and the residual cooling time. Factor levels have been defined in order to examine the effects in a defined process window.
We investigated the solidification behavior and foaming behavior of a grade polypropylene in high-pressure foam injection molding process by means of an in-situ mold visualization technique. We observed that the solidification behavior of polypropylene had a clear influence on the cell nucleation and on the final cellular morphology of the foam injection molded parts. By adjusting the processing condition, we could control the sequence of the cell nucleation and melt solidification such that either would occur earlier, influencing the final cell morphology and structure.
The failure of an elastomeric resistance band used in performing physical exercises can often result in human injury. This paper investigates the cause(s) of failure and attempts to identify designs, materials, and manufacturing methods that can prevent failures in elastomeric resistance bands. This paper discusses three separate failure analysis case studies involving elastomeric resistance bands to identify failure modes. It also provides evaluation of six different elastomeric resistance bands to identify design, manufacturing, and material characteristics that are important in prevention of elastomeric resistance band failures.
Poly (vinylidene fluoride) (PVDF) matrix hybrid nanocomposites incorporating MnO2 nanowire (MnO2NW) and Carbon nanotubes (CNT), were fabricated by melt mixing in a batch mixer followed by hot pressing. Dielectric properties of fabricated nanocomposites were studied in X-band frequency (8.2-12.4GHz). The conductive CNT increased the dielectric permittivity of the PVDF by serving as a nanocapacitor. Increasing CNT loading enhanced dielectric loss due to the formation of a conductive network. Adding MnO2NW increased the dielectric permittivity while decreasing dielectric loss. Rheology coupled with dielectric properties and electrical conductivity measurements of the nanocomposites showed the effect of MnO2NW, as secondary nanofillers, on the CNT percolative network. We attribute the superior dielectric properties of the hybrid nanocomposites to the role of MnO2NW on improving the dispersion state of CNT (confirmed by rheology) and also its barrier role on hindering the CNT network formation.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
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