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.
Transient thermal conductivity methods have benefited from the rapid nature of the testing. The drawback has been the need to measure density (?) and heat capacity (cp) for the materials in order to calculate thermal conductivity. For speed, nominal values of ? and cp have been used, producing questionable thermal conductivity results. If ? and cp are measured, the increase in time reduced the benefit of the transient measurement. This difficulty has now been removed. A new technique has successfully been demonstrated which produces thermal conductivity directly. The only additional parameter that is necessary is material thickness. This new technique uses existing instrumentation without the need for hardware modification.
The physical aging response of polymers is generally examined in isothermal conditions by following the viscoelastic behavior as a function of aging time. It is then often asked if time-aging time superposition applies at a single temperature. If so, it can then be ascertained if time-temperature superposition applies to the aging time reduced curves obtained at different temperatures. In prior work from this laboratory we showed that isothermal time-aging time superposition did not apply to amorphous PEN. In this work we describe the surprising result that samples aged at 100 °C and then tested at 30 °C, 50 °C, 70 ° and 90 °C, that is iso-structurally (constant fictive temperature) seem to follow time-temperature superposition.
The low temperature impact properties of glass fiber reinforced Polypropylene and polyolefin blends with two different rubbers are investigated. Our results reveal that the impact strength increases with decreasing temperatures when glass fibers are highly loaded. The thermomechanical analysis over a wide range of temperatures is employed to elucidate the possible cause of the pronounced temperature dependence of the impact strength. It is found that the average thermal expansion coefficient of the highly filled composites significantly deviates from the linearity of a simple mixing rule. This significant reduction in the thermal expansion coefficient caused by the addition of glass fibers can provide a useful strengthening of the bond between fiber and matrix by increasing the compressive pressure exerted on the fibers by the matrix at low temperature. Meanwhile, the increase in the impact strength of polyolefin blends with some rubbers was also observed below room temperature. The examination of fractured surfaces of these blends clearly demonstrates the different toughening behaviors at low temperatures. We suspect that the difference in thermal expansion coefficient between rubber and matrix possibly causes the increase in the interfacial stress between rubber and matrix at low temperature.
In blow-moulding, film production and other processes, polymers are biaxially stretched. For the layout of those processes, for Finite-Element Analysis (FEA) and for raw material development, the mechanical material behaviour of the polymer materials must be known. Therefore, the stress/strain behaviour of the material at forming temperatures and high strain rates is investigated in this paper. A new measurement device is described called the Membrane-Inflation Rheometer. It is capable to measure stress/strain behaviour of polymers under equibiaxial deformation and process relevant conditions concerning temperature and strain rate. The algorithm for data evaluation is explained. Some results for different polymer materials are presented.
Single-screw extruders make use of mixing and shearing sections to ensure good thermal and mechanical homogeneity at high mass throughput rates. Nowadays, these sections are usually designed empirically or with very simple estimation formulas. Therefore, important interpretation criteria, like pressure loss, temperature increase, average shear rate or residence time profile are only determined very inaccurately. The 3D finite-element analysis (FEA) can determine these parameters very precisely, but with very long computation times. The network theory allows an economic calculation with a sufficient accuracy of the aforementioned data. This paper describes the modelling of extruder mixing sections and the solution of these models by means of the network theory.
The discontinuous processes in the rubber manufacturing are sensitive to low deviations in the processing method. The main reasons for these deviations are the fluctuations into the process parameters or deviations of the quality of raw materials or the manual operations. The on-line quality prediction of rubber compounds based of the mathematical models for the mixing process in an internal mixer is an important step in direction of quality control. For most applications the models based on regression or neural networks lead to quality predictions of over 90% for various compounds and machine sizes. Such a measure and control unit has been successfully tested at a laboratory mixer.
The wall section of medical press-through blisters may reduce the stability of the packed medicine. A homogeneous wall thickness over the entire capsule chamber enables the manufacturer use a thinner starting foil without a lack of quality, which leads to the saving of raw material and other expenditures. Three thermoforming methods are tested on an industrial form-fill-seal" line. the temperature profile of the raw film before forming the friction coefficient between films and molds or plugs and the biaxial rheological properties of the foil influence the resulting wall thickness distribution."
The recycling of thermoplastics gains more and more importance. For removing the contamination one-or-two step filtration units are state of the art, but due to high material loadings or running costs they often reach their limits. Therefore IKV examines whether a centrifuge, which is fed with polymer melt, might be an alternative. In preliminary tests IKV showed that centrifuges built for low-viscosity materials can also be used for polymer melts. A centrifuge was installed into an extrusion line. Up to 10 weight-% of contamination could be removed out of the polymer melt successfully.
Since multi component injection molding techniques are well established, the development of rigid-flexible combinations is increasing. Besides combinations between thermoplastics and thermoplastic elastomers (TPE) which are used in various applications, the combination of Liquid-Silicone-Rubbers (LSR) and thermoplastics becomes more important because of their better thermomechanical and mechanical properties in comparison with TPE. Concerning the adhesive strength of these combinations which depends on the properties of the materials, the process parameters in the molding process and the mold-technique there is only insufficient knowledge. To solve this techniques are developed to improve the adhesive strength between the materials.
In micro injection molding two different tasks can be distinguished: These are the injection molding of small parts (> 1 g) with microstructured details and the direct production of micro parts, i.e. parts with a part weight down to milligrams (mg). Until now there are no suitable injection molding machines available for the production of single micro parts, so injection molders produce big, but precise sprues to achieve the necessary shot weight. To solve this problem, the IKV is developing a micro injection molding machine that meets the molder's demands. First, the injection molding process with differently manufactured micro cavities is analysed.
Gas-Assisted-Injection-Molding (GAIM) was applied to a vacuum cleaner body made of PP that had a higher shrinkage and a lower strength than ABS. The CAE analysis was carried out to examine the factors in the mold design and processing such as the gas injector location, the gas channel size, the gas pressure level and profile, etc. Although the mold was machined according to the analysis result, actual molding conditions were optimized again with Taguchi method because the CAE analysis could not reflect the complexity of the actual process. The optimized molding conditions agreed well with the result of the CAE analysis.
Recycled poly(ethylene terephthalate) (R-PET) used in blends with a fiber grade material (F-PET) has been investigated in this paper. As-spun fibers of R-PET, F-PET, and R/F-PET blends were made at winding speeds ranging from 1000 to 4000 m/min (mpm), and subsequently drawn in the range of 5.4 to 1.35X to bear the same total extension ratio. The properties of fibers spun at high and low wind-up speeds with low and high extension ratios have been compared in terms of the orientation, crystallinity, and mechanical properties. The fully oriented yarns (FOY) prepared from R-PET show a tensile strength of 90% of the fiber grade, with 4.4 g/d (R-PET) to 4.8 g/d (F-PET). On the other hand, R-PET fibers spun at low wind-up speed with high extension ratio show better physical properties than that spun at high wind-up speed with low extension ratio, with 4.4 g/d (1000 mpm/5.4X) to 3.7 g/d (4000 mpm/1.35X). The results indicate that for R-PET material, the low wind-up speed with high extension ratio process provided advantageous environment for developing crystalline fiber structures.
A three-dimensional finite element model combined with a volume tracking technique has been developed to simulate the mold filling phase in gas-assisted injection molding. The model deals with the polymer melt flow having two moving interfaces, i.e., the gas-polymer interface and polymer front. A mixed finite element formulation using four node tetrahedral elements is employed to solve the 3D Navier-Stokes equations. A robust volume tracking technique is developed to track the gas-polymer interface and the polymer front surfaces. When compared to 2D shell models, 3D modeling is capable of predicting accurately the important flow features in complex parts as well as the gas core shapes and locations.
The effects of various waterblocking gels are investigated in relation to swelling behavior of polyolefins. Gel absorption is studied in polyethylene and polypropylene/ethylene copolymers as a function of temperature for a density range of 0.868g/cc to 0.948g/cc for polyethylene and 0.88 to 0.91g/cc for propylene/ethylene copolymers. The effect of swelling on antioxidant extraction is also studied as a function of antioxidant molecular weight and degree of swelling. Both factors show a strong influence on the amount of antioxidant extracted. A direct correlation is found between antioxidant extraction by gels and reduction in thermo-oxidative stability.
The melt viscosity of three commercial polyolefines (LDPE, LLDPE and HDPE) was measured in uniaxial elongational flow at constant extension rate, as well as by the Rheotens and the Entry Flow Methods. The melts showed the same MFI but differed in their extensional properties, reflecting the differences in their molecular structure. The indirect methods could also give meaningful estimates for the extensional viscosity of polymer melts, if the amount of accumulated extensional strain in each case was taken into consideration.
Blends of Polyethylene terephtalate (PET) and Linear Low Density Polyethylene (LLDPE) compatibilized with maleic anhydride-grafted-LLDPE (MAH-g-LLDPE) were characterized. The addition of MAH-g-LLDPE produced a fine dispersed phase morphology and improved processability of blends. A decrease on the crystallization temperature and on the degree of crystallinity of the polyester and an increase on the elastic modulus and on the stress at break were observed. These effects could be attributed to the reduced interfacial tension as a result of the promoted interaction between the polymers by the functionalized polymer.
Blends of Polyethylene terephthalate (PET) and High Density Polyethylene (HDPE) with and without compatibilizing agent have been studied. Both materials are widely used in the soft drink bottle industry. The compatibilizing agent was a copolymer of ethylene and methacrylic acid (surlyn). The olefinic segment of surlyn will be compatible with HDPE, while the acid groups will be affine with the similar groups from PET. The compatibility was investigated using different techniques such as differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy and X-ray spectroscopy.
The effect of chemical exposure on the stress rupture behavior of polyurethane, polyacetal and four acrylic materials was investigated. The polyurethane and polyacetal stress rupture data was used to provide the basis for verification of the expected service life of products made from these materials. The stress rupture data from four different acrylic materials was used to differentiate the materials on the basis of long term strength. The stress rupture data (applied stress vs. failure time) was obtained using a custom designed and built constant tensile load (CTL) testing apparatus.
Polyetheramide tri-block copolymers have been polymerized in a modular counter-rotating twin screw extruder under a range of processing conditions, including temperature profiles and screw speeds. Polyetheramide tri-block copolymers had not been previously polymerized in a twin screw extruder. Thermal analysis and viscosity measurements clearly demonstrated that the formed copolymers have two separated domains arising from two different block segments. Studies were also made of melt spinning polyetheramide tri-block copolymer into oriented filaments. The formed filaments were characterized using birefringence. The melt spun fibers of polyetheramide tri-block copolymer showed higher elongation than those of polyamide 6 due to the existence of elastomers.
When numerically analyzing mixing in polymer processes, there are several difficulties that the engineer will encounter; such as moving boundaries, complex geometries and non-linear material behavior. The Boundary Element Method (BEM), as a technique which requires only boundaries (surfaces) to be meshed, is ideal to simulate problems with moving boundaries and complex geometries. However, the introduction of non-linear material behavior requires domain information. This study applies the Monte Carlo technique to integrate the domain and keep the boundary-only discretization. Results show the influence of non-linear effects, such as shear-thinning viscosity, when characterizing mixing in polymer processing equipment.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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