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Styrene/methyl methacrylate (St/MMA) copolymer-silica nanocomposite foams were prepared using supercritical C[O.sub.2] as blowing agent, and the relationships between their cellular microstructure and mechanical properties were investigated. The effects of nanosilica content, size, and surface chemistry on the foam's microstructure and properties were examined. Dispersion and distribution of silica nanoparticles with different surface chemistry in St/MMA copolymer nanocomposites were discussed. To determine the most suitable copolymer composition for incorporating silica nanoparticles, some operating conditions such as temperature and pressure were primarily examined to study their effects on the microstructure of resulting foams. In compressive mechanical properties of final foams, a considerably high value was obtained for the compressive strength of the foams of up to 9.5 MPa. The prepared low-density (below 0.2 g/[cm.sup.3]) St/MMA copolymer microcellular foams can be used in green lost foam iron casting processes. Highlights * Styrene/methyl methacrylate copolymer-silica nanocomposite foams were prepared via supercritical C[O.sub.2]. * Foams' cell size was changed by changing silica nanoparticle surface chemistry and size. * The uniform cellular microstructure was achieved by nanosilica size increment. * Increasing nanoparticle size improved the foam's mechanical properties. * Low-density foams were achieved for potential application in lost foam casting. KEYWORDS cellular microstructure, lost foam foundry, mechanical properties, nanosilica, St/MMA copolymer, supercritical C[O.sub.2], 1 | INTRODUCTION Because of the world energy crisis, scientists are very much interested in the development of lightweight and high-mechanical-property materials. (1-4) Producing such materials is viable by the [...]

Diamond nanoparticles/urethane-based bio-adhesives (ND-U-BA) were synthesized via in-situ polymerization. Chemical structure and curing kinetics of the samples were studied by Fourier-transform infrared spectroscopy. Results showed NDs controlled the curing profile of samples. Thermal and crystalline properties were studied using differential scanning calorimetry and X-ray diffraction analyses. Results indicated hard segments had higher ordering levels in the presence of NDs which is due to the lower hydrogen bonding among polyurethane chains. Mechanical results showed ND-U-BA had higher adhesion strength due to the formation of chemical crosslinks and a controlled curing mechanism. MTT and biodegradation studies showed ND-U-BA had acceptable cell viability and degradation content. • Urethane and diamond nanoparticles/urethane-based bio-adhesives were synthesized. • Results showed ND nanoparticles had controlling effect on curing kinetic of samples. • Cell viability of bio-adhesives was improved with the ND nanoparticles' addition. • Incorporation of ND nanoparticles increased the adhesion strength of bio-adhesive. [ABSTRACT FROM AUTHOR]

This research investigated the synthesis of thermoplastic polyurethane (TPU) with a hard segment content (HSC) of 30% weight. The chain extender, the polyols, and the diisocyanate utilized 1,4-butanediol (BDO), and the polycaprolactone diol (PCL-diol) with molecular weights of 2000, 4000, and 10,000 and isophorone diisocyanate (IPDI), respectively. Differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), hydrogen nuclear magnetic resonance (1H-NMR), and X-ray diffraction (XRD) were used to examine the chemical microstructure and physical properties of PCL diol and thermoplastic polyurethanes (TPUs). The molecular weight of the PCL diol as soft segments affected the crystallinity and glass transition temperature (Tg) of TPUs. An increase in PCL diol molecular weight resulted in a reduction in elongation at failure and an increase in ultimate tensile strength. This study was conducted to investigate the permeability and the permselectivity of CO2 and N2 gases over pressure ranges (3 to 9 atm). It was determined that the gas permeability of each sample increased in response to an increase in the pressure of the supplying gas. An elevation in the molecular weight of PCL-diols in TPU samples resulted in a reduction in selectivity and an increase in CO2 and N2 gas permeability. Although IPDI is a non-aromatic cyclic diisocyanate with a significant impact on thermoplastic polyurethane phase morphology, the goal of this paper is to create a change in the molecular weight of PCL-diol and investigate the effect of molecular weight on the resulting morphology as well. [ABSTRACT FROM AUTHOR]

Styrene/methyl methacrylate (St/MMA) copolymer‐silica nanocomposite foams were prepared using supercritical CO2 as blowing agent, and the relationships between their cellular microstructure and mechanical properties were investigated. The effects of nanosilica content, size, and surface chemistry on the foam's microstructure and properties were examined. Dispersion and distribution of silica nanoparticles with different surface chemistry in St/MMA copolymer nanocomposites were discussed. To determine the most suitable copolymer composition for incorporating silica nanoparticles, some operating conditions such as temperature and pressure were primarily examined to study their effects on the microstructure of resulting foams. In compressive mechanical properties of final foams, a considerably high value was obtained for the compressive strength of the foams of up to 9.5 MPa. The prepared low‐density (below 0.2 g/cm3) St/MMA copolymer microcellular foams can be used in green lost foam iron casting processes. Highlights: Styrene/methyl methacrylate copolymer‐silica nanocomposite foams were prepared via supercritical CO2.Foams' cell size was changed by changing silica nanoparticle surface chemistry and size.The uniform cellular microstructure was achieved by nanosilica size increment.Increasing nanoparticle size improved the foam's mechanical properties.Low‐density foams were achieved for potential application in lost foam casting. [ABSTRACT FROM AUTHOR]

Thermoplastic elastomer polyurethanes (TEPUs) were synthesized for orthodontic ligature application and the relationship between various properties and structure of the synthesized TEPUs were studied. Polyethylene glycol and 1,4-butanediol were utilized in various weight ratios as chain extender. Fourier-transform infrared spectroscopy, differential scanning calorimetry, and X-ray diffraction were used to study the chemical and physical properties and also, tensile, stress relaxation, and elasticity analysis were performed to evaluate the mechanical properties of the prepared samples. Shape memory and stress relaxation analysis with temperature variation showed that the samples could recover the relaxed force due to the shape memory capability. [ABSTRACT FROM AUTHOR]