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.
Exfoliated graphite nanoparticles (EGN) have the potential to be a low cost, high performance reinforcement for polymers due to their platelet structure and predicted physical properties. Thermoplastic films were prepared containing different EGNs at different loading levels. Barrier and physical properties of these EGN/polymer nanocomposite films were then compared to similar nanocomposite films having either comparable filler morphology, such as smectite clays, or similar chemical composition, such as carbon nanotubes and conventional carbon black. Barrier testing included permeation of selected organic permeants, water vapor, and oxygen utilizing a number of different vapor and liquid permeation methods. Relationships between the properties of the nanocomposites and the nanoparticle composition and morphology are presented.
Ethylene co-vinyl alcohol (EVOH) nanocomposites incorporating montorillonite layered silicates (MLS) were examined in this study. EVOH with 3% MLS loading was melt compounded and later extruded into blown film. The morphology, as well as mechanical and thermal properties were examined. Morphology analysis confirms an intercalated system, with a higher degree of dispersion and alignment in the blown film as opposed to the compounded material. Thermal analysis shows an improvement in thermal stability with the addition of MLS. An increase in Young's modulus is also observed in the nanocomposite film.
Cellulose microfibrils obtained by the acid hydrolysis of cellulose fibers obtained from different sources were added at low concentrations (2-10% w/w) to polymer gels and films as reinforcing agents. Significant changes in mechanical properties, especially maximum load and tensile strength, were obtained for fibrils derived from several cellulosic sources, including cotton, softwood, and bacterial cellulose. For extruded starch plastics, the addition of cotton-derived microfibrils at 10.3% (w/w) concentration increased Young's modulus by 5-fold relative to a control sample with no cellulose reinforcement. Preliminary data suggests that shear alignment significantly improves tensile strength. However, addition of microfibrils does not always change mechanical properties in a predictable direction. Whereas tensile strength and modulus were shown to increase during addition of microfibrils to an extruded starch thermoplastic and a cast latex film, these parameters decreased when microfibrils were added to a starch-pectin blend, implying that complex interactions are involved in the application of these reinforcing agents.
Economic and environmental forces are providing an impetus for the development of biocomposites from renewable agricultural byproducts. In pursuit of this goal, we are developing biocomposites from wheat-, kenaf-, and corn-byproducts without external additives. Our differential scanning calorimetry (DSC) measurements suggest that micronized wheat straw and inner kenaf fibers have similar thermal characteristics at 50°C < T < 400°C, thus they can be co-processed. The flexural strength of the composites formulated from micronized wheat straw and kenaf fibers increases as the concentration of straw in the composite increases. Postcuring the composites at 190°C also decreases the strength.
The renewable polymers are environmentally friendly and naturally biodegradable, and could serve as an inexpensive source of raw material for single-use engineered products. Efforts are underway to develop ecocompatible consumer plastics by incorporating renewable polymers as an alternative to petroleum-derived chemicals. Therefore, gaining fundamental understanding of biobased polymers is critical for the design and development of consumer products. The research efforts at the USDA laboratory pertaining to the development of biopolymer blends, polymer processing, characterization and lifetime evaluation are presented.
Functionalization of PHB was successfully achieved by free radical grafting of maleic anhydride using a peroxy initiator by reactive extrusion processing. The crystallization behavior and morphological changes in the PHB upon maleation were followed from the DSC, TGA, FTIR and Optical Microscopy measurements. The presence of succinic anhydride groups was substantiated by stretching vibration at 1782 cm-1 in FTIR. For maleated sample the Tm and Tc decreased up to 20 degree celsius and 10 degree celsius, respectively, indicating a decrease in its crystallinity and rate of crystallization. Decrease in the crystallinity was quantified from the enthalpy of melting (Tm endotherms). These trends were further substantiated by reduction in the crystallinity sensitive peak at 1185 cm-1 in the FTIR spectrum. Moreover, larger the graft degree smaller is the spherulite size and slower is their growth rate as observed in the optical micrographs. Disordered spherulite structure upon maleation also implies the structural changes in the polymer backbone, imperfect crystal formation. These functionally modified PHB can be used as modifiers for variety of applications.
The heat-sealing machine is a vital tool in plastic bag manufacture. Processing conditions such as heat-sealing temperature and pressure greatly affect mechanical properties of the heat sealed part. In this study, the mechanical properties of the heat sealed part of a biodegradable plastic film were examined. Based on the results obtained from peeling test, circular notch tensile test and DSC measurement, the optimum heat sealing was established at 130-135 °C. The mechanical properties of the heat seals decreased with increasing heat sealing temperature.
Starch acetates with degrees of substitution (DS) of 1.68 and 2.3 were extruded with 10, 20 and 30% (w/w) cellulose and 20% (w/w) ethanol in a twin screw extruder at 150, 160 and 170 °C barrel temperatures with 170, 200 and 230 rpm screw speeds. X-ray diffractogram (XRD), differential scanning calormetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the morphological properties of extruded foams. A central composite response surface design was applied to analyze the effects of starch type, cellulose content, barrel temperature and screw speed on specific mechanical energy requirement of extruding foams and the radial expansion ratio and compressibility of the extruded foams. XRD showed losses of DS starch and cellulose crystallinity and the formation of new complexes. FTIR spectra revealed that functional groups and chemical bonds were maintained after extrusion. Melting temperatures changed significantly when higher DS starch acetate was used. Cellulose content, barrel temperature and screw speed showed significant effects on thermal, physical and mechanical properties of extruded foams and the specific mechanical energy requirement.
Here, we have reported the successful preparation of the smallest nanopolymer, high density polyethylene, which has a diameter of about 0.17 ?m (but the number average molecular weight is greater than 1,00,000). The success of obtaining very small nanopolymer opens the door to unprecedented applications of this fascinating material as a true 1D material. This nanopolymer is characterized using particle size analyzer, scanning electron microscopy, infrared spectroscopy, X-ray diffraction, viscoelastic properties, etc. Similar synthesis strategies, involving careful selection of desired conditions and smart manipulation of favorable thermodynamic properties could be extended for the preparation of various nanopolymers: low density polyethylene, polypropylene, polystyrene, etc. To the best of our knowledge, this is the first demonstration for a preparation of nanopolymer in the literature.
Polystyrene nanopolymer (Number average molecular weight greater than 1,00,000), which has a diameter of about 0.17 ?m is prepared for the first time. This observation is confirmed using scanning electron microscopy. Infrared spectroscopy, X-ray diffraction, viscoelastic properties, etc are used to characterize it. The novel technique produces nanopolymer within a range of 0.17 to 51 ?m measured by particle size analyzer. BET surface area shows its minimum surface area of 17.7 m2/gm. We have elucidated the thermodynamic parameters for formation of nanopolymer.
Low density polyethylene nanopolymer is characterized by scanning electron microscopy, particle size analyzer and BET surface to prove the formation of nanopolymer over a range of diameter from 0.17 to 70 ?m. BET surface area reveals that its mimimum surface area is 17.0 m2/gm. The findings prove that the small diameter low density polyethylene nanopolymer is proved to be able to show good properties without any confinement that limits its material dimensions. Infrared spectroscopy and X-ray diffraction studies are also used to characterize it.
Gas solubility and transport properties control cell structure during polymer foam processing. This study reports the sorption and diffusion kinetics of sub and supercritical CO2 gas in nanocomposites of poly(methyl-methacrylate) containing organically modified smectite clay. Various methods for preparing the PMMA-clay nanocomposites were investigated and a solution co-precipitation method was selected. PMMA-clay nanocomposites containing 2, 4 and 6 wt. % nanoclay loadings were prepared. Using wide-angle X-ray diffraction (XRD) and scanning electron microscopy (SEM) the resulting materials were found to have well dispersed intercalated clay structures. CO2 solubility studies at 45°C and pressures up to 60 atm using an in situ gravimetric technique were performed on compression molded films. From the results diffusion coefficients were determined using the appropriate transport models for these test conditions.
The effects of moisture absorption on dimensional stability and mechanical properties of various polyamide/polyolefin blends are being studied. The morphology of the blends has also been investigated by using transmission electron microscopy (TEM). Furthermore, the correlation between the morphology of the blends and their moisture absorption rate and dimensional changes upon absorbing moisture has been examined as well.Results of this investigation indicate the moisture absorption rate, dimensional stability and mechanical property retention of polyamide and polyolefin blends are strongly affected by the degree of compatibility of the blend. The finer the dispersion polyolefin particles, the slower the water absorption rate, and the lower the dimension changes after being equilibrated at 50%RH or 100%RH.
Carbon dioxide is widely recognized as an environmental-friendly blowing agent for foam extrusion. However, it is also more difficult to process than other gases because of its low solubility and high diffusivity. In order to improve processing, it might be suitable to use additives. The aim of this work was to study the effect of such additives on the solubility and diffusivity of carbon dioxide in the solid state and to validate their effectiveness in a foam extrusion process.Three “CO2-philic” additives were added to polystyrene and sorption experiments were conducted to measure the solubility and diffusivity at room temperature. Results show that all three additives had a small but measurable effect on gas solubility, which was a consequence of the free volume increase in the polymer blend and in some cases, due to the specific interaction of carbon dioxide with the compounds. Diffusion was also affected depending on the concentration of additive.
The fundamental transport parameters for Acrylonitrile-butadienestyrene, ABS – CO2 system was determined using a high pressure gravimetric technique. Solubility in the range 0 to 65°C and pressures up to 55 atm were determined and values as high as 25wt% were obtained at 0°C and 34 atm. Diffusion coefficients derived from the sorption kinetic data resulted in determination of the plasticized glass transition temperatures. The existence of the retrograde vitrification for this system was confirmed and thus used to develop nanofoams. The favorable interaction of CO2 with ABS has resulted in foams with average cell size of 0.47 ?m and cell density of 2 × 1012 cells/g at a processing temperature of 60°C. Heat of sorption and activation energy for diffusion of CO2 in ABS was determined from the experimental data and found to be -15.5 and 28.3 kJ mol-1 respectively.
The purpose of this study was to investigate the effect of MuCell processing on the structure-property relationships of critical engineering thermoplastics. Such techniques as differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM) as well as a variety of standard testing equipment were used to show that through an effective design of experiment, the expected decrease in performance of key physical, mechanical and thermal properties can be minimised, and even improved in some cases.
This paper focuses on gaining a fundamental understanding of the bubble growth and collapse phenomena occurring in a CBA-based foaming of plastics under atmospheric pressure. The behavior of CBA-blown bubbles exposed to various processing conditions was observed using a hot-stage optical microscope-based digital image processing system. A mathematical model that accounts for the effects of diffusion, surface tension, viscosity, and elasticity has been employed. It has been found that the processing temperature, diffusivity, and gas bulk concentration have dominant effects on the lifespan of CBA-blown bubbles.
The conditions that induce the bubble nucleation for the thermoplastic foam extrusion process in which physical foaming agents (PFA) are involved are obviously linked to the solubility parameters, i.e. temperature and pressure at a given PFA content, conditions that can be modified adding a nucleating agent. An in-line detection method based on ultrasonic sensors, sensitive to the onset of the phase separation, was used to investigate the influence of both talc and HFC-134a blowing agent concentrations on the nucleation cell density and degassing conditions for polystyrene foaming.
Most solubility data that is available has been determined by taking into account the swollen volume, which is estimated by the Sanchez-Lacombe (SL) equation of state (EOS). The swollen volume is typically determined with an interaction parameter that is chosen to minimize the differences between the experimentally measured and theoretically calculated solubility data.This paper presents a similar approach to ascertain the solubility based on the Simha-Somcynsky (SS) EOS. As a case example, we measured the apparent solubility of CO2 in a polystyrene melt at elevated pressure using a magnetic suspension balance. The solubilities determined by the two EOS were observed as being the same value below 1500 psi. When the pressure was above 1500 psi, the buoyancy effect was enhanced significantly because of the increased swollen volume and increased CO2 density. Consequently, the corrected solubilities that were determined by the two EOS at elevated pressures were observed to be different and the difference was 10% at 3000 psi.
The process of polymerization of syndiotactic polystyrene formed in presence of catalysts CpTiCl2(OC6H4Cl)/MAO was investigated. At the moment syndiotactic polystyrene is produced in pilot plant. The yield of syndiotactic polystyrene obtained in the reactor 240 dcm3 was about 7- 15 kg/charge. The molecular weight of syndiotactic polystyrene was about 200 000 g/mole and syndiatacticity about 96%. After process of synthesis composites based on syndiotactic polystyrene have been obtained. The powder of syndiotactic polystyrene has been granulated with stabilizers, and modifiers in twin-screw extruder with double degassing. Irganox 1076 have been used as the stabilizer. Syndiotactic polystyrene was reinforced by glass fiber or talc. Syndiotactic polystyrene was modified by polyoxyphenylene, linear polyethylene and hydrocarbon resin. The structure and physical and mechanical properties of composites were investigated.
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