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.
Vibration welding glass reinforced nylon compounds is a commonly used joining technique. The butt joint strength achievable with these compounds is significantly lower than that of the bulk compound and is most often comparable to the strength of the polymer matrix. These lower properties are attributed to little glass fiber orientation perpendicular to the weld interface. This research examined introducing a secondary vibratory motion perpendicular to the weld plane during welding in an attempt to promote greater glass fiber orientation normal to the weld plane. The work was performed using 3.2 mm thick plates composed of 33 % glass filled nylon 6 and 66. These plates were butt welded on a lab scale linear vibration welder and then cut into strips before tensile testing. These process modifications resulted in strengths 20% higher than those of samples welded using the standard vibration welding process.
Weldlines, a common feature in injection molded parts, are known to be inherently weak. Vibration molding has been shown to increase shear within the mold thus increasing the strength of weldlines, but with high capital costs. The present experimental study focused on improving weldline strength through the use of a novel idea, the controllable compliance accumulator (CCA). This device works together with the vibration-assisted injection molding technique to increase the local shear at the weldline. Comparisons between the tensile strength of ASTM specimens made with and without the CCA were made and the details of the results will be discussed.
The history of synthetic polymers, albeit a relatively short history only spanning some 100 years, is replete with many outstanding examples of innovation, luck and perseverance. Although science is perceived by most to be a strictly logical endeavor, where serendipity plays no role and well thought out hypotheses are tested by super-human nerds in a precise and systematic manner, this is not reality. We will attempt to show that we can learn something about the complex nature of innovation by drawing upon selected tales of the historical development of some of the most important polymers in use today.
Indentation tests were performed on flat coupons of poly(formaldehyde), three types of reinforced nylon and reinforced poly(ethyl terephthalate). Spherical, conical and cylindrical indenters were selected for this study and the effects of indenter shape combined with the rate of indentation on the behaviour of these materials were examined. The load-depth relationship during the indentation process revealed the emergence of step-like transitions at high indentation rates. The effects of the assessed parameters on the indentation resistance were analysed. The modelling of the data was based on the approach developed by Johnson and the introduction of a modified parameter that took not only the geometrical characteristics of the indenter into account but also the indentation depth. The proposed method has proven to be useful since a steady state of the indentation pressure was observed for all materials.
Sample preparation can greatly influence the results of laboratory testing of packaging sealant materials. Factors such as test strip width, edge uniformity, sealing die temperature and die load are recognizable variables to control.A design of experiments approach was used to explore the rank importance of these factors and any interactive effects that may occur. A generally well-behaved ethylene vinyl acetate (EVA) sealant on a high density polyethylene (HDPE) film was used for these tests. Experimental results indicate that sample width, die temperature and die pressure are the most influential factors. Unexpectedly, edge effects, namely a regular sine wave pattern and a generally random irregular edge had little influence on hot tack results.
The vinyl industry has expressed concern over color changes of vinyl siding that correlate with underlying insulation patterns. Occasionally, homeowners observe visual differences in vinyl appearance when a single extrusion lies over different types of backing used in home construction. This paper reviews weathering-induced color change data from commercially available rigid vinyl exposures in Arizona and Florida. Results from weathering experiments show influences of backing on color change for dark brown and white vinyl during several years' exposure. This paper describes weathering behavior observed in vinyl color change as a function of backing and important considerations regarding effects of backing on vinyl building product weathering appearance.
The cooling phase of the extrusion blow molding process has a large influence on the cycle time of the process as well as on the properties and quality of the molded products. A better understanding of the heat transfer mechanisms occurring during the cooling phase will help in the optimization of both mold cooling channels and operating conditions. A continuous extrusion blow molding machine and a rectangular bottle (motor oil type) mold were used to produce bottles. A high density polyethylene (HDPE) and a metallocene polyethylene (mPE) having different rheological properties were tested. Melt and mold temperatures, cooling time, inflating pressure and die gap were varied systematically. An infrared (IR) camera was used to measure the temperature distribution of the plastic part just after mold opening as well as after part ejection. The wall thickness and dimensions of the bottles of the finished parts were measured in order to determine the shrinkage and warpage. Finally, the temperature fingerprints were used to explain what happens during the cooling phase and correlated with the final part characteristics.
In this study, we report on the influence of semi-crystalline morphology on the physical aging characteristics of poly (phenylene sulfide). The physical aging rates were observed to depend on the relative amounts of the mobile-amorphous and rigid-amorphous phases, with accelerated aging rates measured in specimens with higher rigid-amorphous phase fraction. We suggest that the rigid-amorphous phase, which includes chain segments that are more tightly packed relative to the mobile-amorphous phase, is able to accelerate physical aging due to its relative proximity to a state of lower configurational entropy.
Adding small amounts (0 to 5 wt.%) of a broad molecular weight distribution, free-radical polymerized low density polyethylene (LDPE) to a Ziegler-Natta catalyzed linear low density polyethylene (LLDPE) led to a reduction in haze of the resulting blown films. While the surface haze decreased with increasing LDPE content, the haze resulting from the internal or bulk structure remained fairly constant. The surface haze was caused by the spurious scattering of light from a rough film surface, which decreased linearly with decreasing r.m.s. roughness within the range of 0 to 5 wt.% LDPE. The presence of LDPE in the blend triggered a different morphological structure on the surface of the final films. The surface of the neat LLDPE blown film contained a bumpy morphological superstructure composed of small lamellar aggregates as observed by atomic force microscopy. Increasing the LDPE content in the blend (up to 5 wt.%) led to a transformation from this aggregate superstructure to the row nucleated structure when blown under the same processing conditions. The row nucleated structure was inherently smoother than the lamellar aggregate superstructure, yielding films with lower haze.
In this work, we report on the influence of lamellar morphology and orientation on the dart impact strength of linear low-density polyethylene (LLDPE) blown films. Characterization of the solid-state morphology of a wide variety of LLDPE blown films reveals the importance of lamellar anisotropy on the impact strength performance of such films. Specifically, we find that lower degrees of lamellar orientation (more random lamellar orientation) favor higher impact strengths. Further, we also report on the solid-state deformations that take place as the films are stretched during the impact test and how these deformation modes discern blown films of high and low impact strength.
The current research is focused on the carboxylation of poly(L-lactide) through a free radical grafting process utilizing an asymmetric functional peroxide within a co-rotating twin screw extruder. Similar experiments, as well as free radical maleation reactions, have been successfully carried out on polypropylene and PLLA. In order to maximize the grafting efficiency and minimize chain degradation, the effects of the extrusion conditions (screw design, screw speed and melt temperature) on the carboxylation reaction and molecular weight of the polymer are investigated. This report focuses on molecular weight and thermal analysis as well as titration to quantify the level of acid functionality grafted onto the PLLA chains.
The rheological behavior of Polypropylene (PP) modified with Styrene-Butadiene-Styrene copolymer (SBS), within the composition range of 10-40 wt % SBS content, was studied based on blend ratio, vulcanization agents (sulphur, peroxide) and curing times. The rubber phase was statically cured and blends with PP were mixed in a twin screw extruder. Results indicate all unvulcanized systems show an increasing melt viscosity on SBS content. Regarding vulcanizing agents, sulphur shows no variation on melt viscosity neither with shear strain nor with curing time, while peroxide shows significant changes on melt viscosity at low shear strain ranges when varying curing times from 2 to 6 min.
An investigation has been conducted to analyze the influences of two important parameters, solubility and viscosity, to the polystyrene/CO2 extrusion foaming process. The solubility, which decides CO2 concentration limit and the nucleation onset, is measured by an improved volumetric method. Experimental data are then fitted with the Sanchez-Lacombe equation of state that will be applied to calculate the solubility at any temperature and pressure. The viscosity reduction by injecting CO2 in the polystyrene melt is studied by connecting a slit die with backpressure control to the extruder. Therefore, the viscosity of the polystyrene/CO2 solution at any temperature, pressure, CO2 content and shear rate can be obtained. Cell structures of two polystyrenes with different viscosities are compared.
Heated tool welding is a highly reliable, well established process for joining thermoplastic semi finished products in plant engineering and tank construction. The weld seam quality may be impaired by residues on the heated tool, and high welding temperatures cannot be applied via the tool without damaging its non-stick coating. Non-contact heating, by e.g. infrared radiation, does not have these drawbacks. In this paper, the examinations with different types of infrared emitters and different materials are presented. A medium wave metal foil IR emitter shows good results and also allows a high reproducibility of the process. Not only good weld seam qualities, but also a faster process can be realized.
Polymer nanocomposites (PNC) are emerging as a new class of industrially important materials that offer improvements over conventional composite systems. The high aspect ratio of the nano particles leads to higher reinforcement efficiency and therefore higher specific modulus, strength and HDT. The low organoclay content (< 5% by weight) also guarantees good processabilty as well as higher recyclability potential.In this study, short (2-3 mm) glass fiber composites with of 7, 14, 20 & 27 % by weight glass fiber content were prepared using both pure PA-6 and 2% organoclay/PA-6 PNC. These glass fiber reinforced composites were injection molded using a dog bone" mold with weld line. Mechanical properties and resulting microstructure were evaluated to ascertain the effect of fiber orientation fiber length matrix crystallinity and the fiber/matrix interface on the overall performance of the composites."
Thermal welding is a well established method for producing complex parts. However it requires a complex industrial logistics because the previously molded components has to be handled and positioned in the machine.For the production of a bacteriological filter, a one-step manufacturing process, combining injection molding of two polypropylene components, the insertion of a filter paper, and the joining of the plastic components by injection welding, was developed. In this paper, the process is described and the influence of processing variables (temperature, injection speed and pressure) is related to the morphology and properties of the welded product.
A new version of a unique microphotometric inline/realtime particle process sensor PMP 691 for analyzing particle dimensions and for detecting different types of inhomogenities in flowing plastic melts during extrusion processing will be presented. As examples flowing blend melts from Polystyrene and Polypropylene as matrix phases and a Polyamide 6 and two PMMA- grades of different viscosities as disperse phases have been investigated. In both blend systems the concentration range of disperse phase was varied between 0.5 to 30 Vol.-%. Depending on the optical behaviour of both blend components (relative refractive index in melt state as a function of temperature) it is possible to determine average particle diameters up to higher particle volume concentrations in comparison to light scattering, light blocking technique, focused beam reflectance analysis and light optical methods. Application of quantitative imaging analysis (QIA) on SEM- images from blend cross sections after complete dissolving the blend particles from the blend matrix results in a good agreement to the microphotometric particle measurements. Additionally the application of the PMP691 for the inline/realtime detection of seldom/stochastic particle events in flowing plastic melts like gels, bubbles, impurities will be shown. Furthermore the inline/realtime control of the homogenity of plastic melts during plastification/melting of pellets are observable.
In-Line" compounding is defined as any process in which both the compounding and the forming steps are performed at the same time. For these applications line stability is crucial and greatly affected by equipment selection and design particularly the melt pump. Presented is a performance comparison for the two most common styles of melt pumps: a gear pump and single-screw extruder. Performance will be characterized in terms of pressurization efficiency pressure stability response to system upsets power consumption melt temperature generation residence time distribution and process limitations."
The objective of this work is to monitor the concentration of thermal stabilizers, ultraviolet (UV) stabilizers, antioxidants and various other additives in polyolefins and in poly(vinyl chloride) during extrusion. The monitoring system consists of an inexpensive charge-coupled- device (CCD) UV spectrometer connected to an extruder by a fiber optic cable. Software has been developed on a notebook computer to enable spectra, continuously obtained from the polymer melt flowing through the die, to be immediately interpreted to provide additive concentrations. At this point, initial trials have been done using a mixed metal heat stabilizer in low-density polyethylene. These results are encouraging but issues related to spectra sensitivity need to be overcome before quantitative concentration values can be obtained. This paper will summarize the current situation and work planned for the near future.
The objective of this study was to evaluate the thermal diffusivity for foams and glass-filled resins during the cooling phase of the injection molding cycle and compare the experimental values with the standard values obtained by other methods.An aluminum mold having three cylindrical shaped cavities were fabricated. A special channel cut was machined and extended to the cavity edge to insert the thermocouple co-axially at the center of the cavity. The melt temperature obtained by the data acquisition set up and analog output converted to the digital signal and thermal diffusivity data calculated from the collected signal output.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
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