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Isothermal crystallization and subsequent melting behavior of metallocene-catalyzed syndiotactic polypropylene resins of varying molecular weights were investigated. Two sets of molecular weight range were synthesized with two different metallocene catalyst systems. Differential scanning calorimetry (DSC) was the main technique used. The kinetics of the crystallization process was assessed by directly fitting the experimental data to the Avrami, Malkin and Urbanovici-Segal macrokinetic models, using a non-linear multivariable regression program. The equilibrium melting temperature of these resins was estimated based on the linear and nonlinear Hoffman-Weeks extrapolative methods.
The ideal stress relaxation experiment is defined as the imposition of an instantaneous strain. In practice, it takes a finite time t1 to reach the constant strain. Various ways in which to account for the finite step time and the subsequent effects on the relaxation modulus G(t) are examined in the present work. First, we consider the “rule of thumb” in which data are ignored until 10 times the strain application time t1. In addition, the Lee-Knauss algorithm is compared with the Zapas-Craft method in which the corrected time of the experiment becomes t-t1/2 where t is the experiment time. A surprising result is that the different correction schemes affect the estimates of the material parameters more than they affect the relative differences between the corrected data and the ideal behavior.
A novel method for studying photo-degradation has been applied to the study of several different polymers including a series of polyethylene (PE) samples containing TiO2 pigments with different photo-activities. Infrared (IR) analysis was used to monitor carbon dioxide emitted from samples exposed to ultraviolet irradiation (UV) in atmospheres of differing composition. The experiments were conducted in a specially constructed cell that permits simultaneous UV exposure of the sample and IR interrogation of the vapour in the cell. A single test on one material occupied about 5 hours – very much less than conventional artificial weathering exposures.The TiO2 pigments used included anatase and rutiles with different surface treatments. Anatase-pigmented material gave significantly higher CO2 emission than unpigmented PE. The rutile-pigmented PEs either gave reduced CO2 emission or enhanced emission, according to the surface treatment. The ranking of the pigments as protectants or pro-degradants coincided with that obtained from much more time-consuming laboratory testing and field experience.
The calorimetric glass temperature of polystyrenes with molecular weights ranging from 3.0 x 103 to 43.7 x 106 g/mol are measured as a function of cooling rate for both bulk material and for samples freeze-dried from dilute solution. We find that Tg is depressed approximately 5 K for samples which can fully entangle and also the same amount for ultrahigh molecular weight samples which cannot achieve full entanglement. The lowest molecular weight samples show only 2 K depression on freeze-drying. Annealing eliminates the depression in Tg. The results indicate that the reduction of the glass temperature due to freeze-drying cannot be due to the reduced entanglement concentration induced by freeze-drying.
In previous work, modification with different diamines was reported and the diamine-grafted polypropylene was used as an adhesion-promoting agent to layer of polycarbonate (PC). A study on the technique of adding reactive is reported in this work. Packets of different aliphatic diamines were reacted with polypropylene modified with maleic anhydride (PPgMA) in melting process. The reaction between amine primary groups and maleic anhydride groups was analyzed by FTIR. Differences in viscosity measurements were evident using packets of diamine, samples obtained by packet of diamine showed a low value of viscosity compared with samples produced by diamine-packet. Two-layered films were prepared using PC film and PPgNH2 film. Adhesion strength was measured using T-peel test. All results permit conclude which diamine is promoting the best adhesion between PPgNH2 and PC layers.
Nano-indentation techniques are being developed for the mechanical testing and physical characterisation of micro-mouldings. A procedure for the embedding, sectioning and testing of micro-mouldings was described at Antec ’02. The technique has been further refined and a systematic evaluation of injection mouldings with micro-dimensions has been carried out. The results from the nano-indentation tests have been supported by atomic force microscopy measurements relating to the dimensions and geometry of the indentations. The results that will be presented will show that the levels of anisotropy of mechanical properties can be measured in micro-mouldings by the methods described.
A range of metallocene and conventional PE resins of various comonomer types, were extruded from a single capillary rheometer, at different melt temperatures and extrusion rates. Analysis shows that die swell increases with increasing extrusion rate and decreasing melt temperature. GPC analysis elucidated the influence of molecular characteristics on die swell. Increased die swell was found for the broader MWD (3.5-3.8) conventional PEs, in comparison with the narrower mPEs (2.1-3.1), and in the higher molecular weight resins. Furthermore, long chain branching was found to increase die swell.
This report will include the way to design, fabricate, and assemble a Polymer Electrolyte Membrane Fuel Cell (PEMFC) to maintain a low voltage source, near one volt, that runs at operating temperatures near 80 degrees Celsius. Creating a stack of cells will provide an energy solution that is more efficient than the system in place today. The PEMFC runs off of pure hydrogen and air (oxygen) and will provide a power source that is non-pollutant and renewable since hydrogen is readily available through the electrolysis of water. The problems with this experiment are maintaining moisture control on both the cathode and anode and the other problem is in controlling the hydrogen gas supply since hydrogen is very explosive when combined with oxygen. With these problems taken into consideration the PEMFC could be the energy source for the future.
This paper discusses a technique for identifying and analyzing defects in plastic compounds. Its primary use is in resin or master batch production or as a general purpose QC or investigative instrument.Initially the resin is processed in a simulation of typical production conditions, by producing blown or cast film on a small scale ( < 2 Kg/hr )The film is passed through the optical field of a CCD line scan camera Data from the camera is processed in hardware and software to capture the continuously moving image.The image data is then analyzed to automatically discriminate and classify a wide range of defects, flaws and process induced variables.The Authors will presentThe special considerations of the extrusion processThe optical design for 5 micron detection resolution of a moving webAlgorithms employed to classify and present data in real time at high speedThe late stage development of this system to detect clear particle contamination in a clear film.
Steady shear rheology of acrylonitrile (AN) terpolymers provides an indication of the melt stability of tailored AN copolymers. It has been found that AN can be copolymerized with methyl acrylate (MA) to produce a material with up to 88 mole percent AN that possesses suitable melt stability at elevated temperatures for processing into carbon fiber precursors. A third copolymer, acryloylbenzophenone (ABP), is copolymerized in 1-2 mole percent to act as a UV stabilizing agent that activates crosslinking following fiber formation. Boric acid (BA) is also added as a “free radical quencher”, which enhances the thermal stability of the terpolymer.
BioComposites are emerging as a viable alternative to glass-reinforced composites. Natural fibers have advantages over man-made fibers (e.g. glass and carbon) in areas such as low cost, low density, competitive specific mechanical properties, reduced energy consumption, carbon dioxide sequestration, and biodegradability. The combination of bio-fibers like kenaf, hemp, flax, henequen and sisal with polymer matrices from both non-renewable and renewable resources to produce composite materials that are competitive with synthetic composites requires special attention to the biofiber-matrix interface, and its resulting adhesion, as well as to the processing methods used to produce these materials. The development of useful biocomposite materials also requires that water-based sizings or dry coupling agents be used to improve fiber-matrix adhesion.. Through bio-fiber surface treatment, biopolymer modification, and adequate processing techniques, novel bio-composites can be designed and engineered so as to substitute/supplement glass fiber composites in various applications.
A range of wood-polymer blends, containing 20, 40 and 60% w/w MDF sawdust (212-850 microns) were prepared using polyethylene, polypropylene and polyvinyl chloride. The blends were melt compounded using a Killion single screw extruder with a barrier type screw design. Over a weathering period of 2 months (fluctuating wet and dry) the mechanical properties decreased in all composites with water retention evident when the composites were “dry”. The rate of water absorption increased during the second wetting period. The diffusivity of water through the wood-polymer composites was found to be greatest for the PVC based composites.
Biodegradable composites were developed by compounding a commercial corn starch polymer with pine and Alfa fibers on a counter-rotating twin screw extruder. Subsequently, the compounds were injection molded under optimized conditions and characterized for the respective mechanical behavior and morphological features.The obtained results establish by evidence that this kind of composites present mechanical performance (in terms of stiffness and strength) within the range of the polymeric systems based on high consumption thermoplastics. In comparison with pine fibers, Alfa based composites presented a better performance as result of various advantageous morphological and interfacial aspects.
It has been established that the production of foamed structure in plastic/wood-flour composites (PWC) is overwhelmingly dominated by the gaseous emissions/volatiles released by the wood-flour. By adopting effective processing strategies, the role of these volatile emissions on foam morphology of plastic/wood-flour composites can be largely suppressed. This paper discusses these strategies, and presents the results obtained from extrusion processing when the chemical blowing agents (CBA) predominantly control the density reduction. The effects of CBAs on extrusion processing of PWC are discussed. Although the used CBAs produced fine-celled structures, the processing window for density reduction was quite narrow.
Wood fiber reinforced thermoplastics are a recent introduction and are finding increased acceptance in a range of industries. Quality control tests for these composites are expensive and time consuming. A quantifiable, reliable method of quality control in real time is increasingly becoming critical with increasing demand and longer production runs.This paper discusses the development of a new method using analytical techniques to monitor quality based on the free, unreacted acid in the composite. The results from this test correlate well to composite physical properties. This test is also useful for process design and optimization studies.
Wood fiber reinforced thermoplastics are a recent phenomena. Their usage has been growing with increasing acceptance in a variety of industries. Applications range from non-structural to load bearing structural components.The multitude of applications requires diverse performance attributes. Performance of these composites is based on the efficiency of coupling the non-polar thermoplastic matrix to the polar wood fibers. Maleic anhydride grafted polymers are widely used for achieving this coupling. Selection criteria for appropriate performance attributes are based on a complex web of process, material and design variables.This paper presents the results of a designed experiment wherein the best combinations of compatibilizer characteristics, molecular weight and percent maleic anhydride grafting level and wood fiber moisture level were determined, to achieve the optimum balance of responses.
In this paper the complete design and the manufacturing of an innovative composite bicycle frame is presented. The initial target and the concept are described to produce a lightweight frame using unsaturated polyester, glass fiber preforms, closed foam core and metal inserts. The final composite body frame has comparable weight and stiffness with a corresponding aluminum tube frame. For the mass production of the frame the resin transfer molding technique with a closed mould has been explored. Furthermore the extension of the method to use epoxy resins and carbon fibers is straightforward resulting in considerable weight reduction and strength increase but also to a moderate increase of the material costs.
The objective of this research is to determine the effect of thermal cycling on the development of microcracks in BMI-carbon fiber composites (5250-4 RTM / IM7 6K 4-harness satin weave fabric). By clamping composite specimens on the radial sides of two half cylinders having two different diameters (127mm and 70mm), two different pre-stresses (-0.4 to 0.4 GP and -0.7 to 0.7GPa) are applied to the composites. Three different thermal cycling experiments, 1) –196°C to 250°C, 2) 23°C to i)150°C ii) 200°C iii) 250°C, and 3) -196°C to 250°C were performed as a function of pre-stress, number of thermal cycles, heating or cooling rate, and humidity conditions. An in-situ monitoring microscope is used to observe the microcrack development under synergistic stress, time, and temperature conditions. The experimental results suggest that there is a higher probability of microcracking with increasing number of thermo-cycles, higher pre-stress and humidity. A mathematical model considering residual stress and pre-stress is suggested to predict the microcracking under environmental conditions.
The effect of temperature, moisture and thermal spiking on the performance of Cycom 8 HS carbon fibre epoxy laminates was investigated. Cured laminate samples were preconditioned (65°C, 95%R.H.) and these samples were exposed to various thermal spiking (150°C/2min) programmes. DMTA techniques measured the changes in glass transition temperature (Tg), storage modulus (log E’) and damping (Tan ? max) of the laminates as a result of exposure to these environments. The thermal spiking programme was shown to cause an increase in both the amount and rate of moisture absorption of the laminates. These increments were accompanied by a significant decrease in Tg, log E’, and Tan ? max. SEM analysis also showed the progressive growth of both interlaminar and translaminar micro-cracks as a result of thermal spiking.
Polymers filled with carbon fibers have recently received attention due to their remarkable conducting and dielectric properties. The fibrous character of the filler causes that the percolation threshold of these systems is reached at 1 – 2 vol. % of conducting component. Coating the fibers with a non-conducting layer can substantially increase the percolation threshold, thus enabling to broaden the range of concentrations where the DC conductivity of material is low and its behavior is not affected by the instabilities in the vicinity of the percolation threshold.As far as dielectric properties are concerned, at high frequencies they are mainly controlled by the polarization of induced dipoles of the fibers or their clusters. Thus, by increasing filler loading, i. e. with higher number of induced dipoles, an improvement of dielectric properties can be expected. The present study has been aimed at electromagnetic interference shielding properties of epoxy resin composites containing short carbon fibers coated with a layer of non-conducting polyaniline base. Due to the coating, the percolation threshold shifted to 16–20 vol. % of the filler. Such high concentration caused a considerable increase in complex permittivity and AC conductivity of investigated material below the percolation threshold. The evaluation of shielding effectiveness and the skin depth the radiation can penetrate, however, have revealed that the material is still not suitable for commercial applications. Nevertheless, the composites of short carbon fibers coated with non-conducting polyaniline base show a high AC conductivity in high frequencies (10 MHz –1300 MHz) and low DC conductivity at the same time. They can thus be used for transmitting high-frequency signals, and for shielding of low-frequency ones. Moreover, they do not short-circuit the surface of electronic systems.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
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