Sangmook Lee

Effect of ultrasound on the properties of biodegradable polymer blends of poly(lactic acid) with poly(butylene adipate-co-terephthalate)

This study investigated the effect of ultrasound irradiation on the blend of poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT). The blends of PLA/PBAT(50/50) (PBAT50) were prepared in a melt mixer with an ultrasonic device attached. Thermal, rheological, and mechanical properties, morphology, and biodegradability of the sonicated blends were analysed. The viscosity of the sonicated blends was increased by the ultrasound irradiation owing to the strong interaction. The morphology of the sonicated blends was significantly dependent on the duration of the ultrasound irradiation. For PBAT50, the phase size reduction was maximized when the blends were ultrasonically irradiated for 30 sec. At longer duration of ultrasound irradiation, the PBAT phase underwent flocculation. Measurement of the tensile properties showed an increased breakage tensile stress and an enhanced Young’s modulus when the blends were properly irradiated. This improvement was ascribed to better adhesion between the PLA matrix and the PBAT domain and to better dispersion of the PBAT phase. However, the tensile properties were maximized after excessive energy irradiation, which was ascribed to an emulsifying effect leading to coalescence of the PBAT phase. Impact strength was increased to reach a peak with the ultrasound irradiation, and was higher than the untreated sample for all sonicated samples due to the difference of failure mechanism between the tensile test and the impact test.

Microcellular foaming of silicone rubber with supercritical carbon dioxide

In spite of great concern on the industrial application of microcellular silicone rubber foams, such as in electric and medical devices, only a few works can be found about the foaming of silicone rubber. In this study, microcellular silicone rubber foams with a cell size of 12 μm were successfully prepared with curing by heat and foaming by supercritical CO2 as a green blowing agent. The microcellular silicone rubber foams exhibited a well-defined cell structure and a uniform cell size distribution. The crosslinking and foaming of silicone rubber was carried out separately. After foaming, the silicone rubber foam was cross-linked again to stabilize the foam structure and further improve its mechanical properties. Foaming process of cross-linked silicone rubber should be designed carefully based on the viscoelastic properties because of its elastic volume recovery in the atmosphere. The basic crosslinking condition for small cell size and high cell density was obtained after investigating the rheological behavior during crosslinking.

Thermal degradation kinetics of antimicrobial agent, poly(hexamethylene guanidine) phosphate

The thermal degradation of poly(hexamethylene guanidine) phosphate (PHMG) was studied by dynamic thermogravimetric analysis (TGA) and pyrolysis-GC/MS (p-GC). Thermal degradation of PHMG occurs in three different processes, such as dephosphorylation, sublimation/vaporization of amine compounds and decomposition/ recombination of hydrocarbon residues. The kinetic parameters of each stage were calculated from the Kissinger, Friedman and Flynn-Wall-Ozawa methods. The Chang method was also used for comparison study. To investigate the degradation mechanisms of the three different stages, the Coats-Redfern and the Phadnis-Deshpande methods were employed. The probable degradation mechanism for the first stage was a nucleation and growth mechanism, An type. However, a power law and a diffusion mechanism, Dn type, were operated for the second degradation stage, whereas a nucleation and growth mechanism, An type, were operated again for the third degradation stage of PHMG. The theoretical weight loss against temperature curves, calculated by the estimated kinetic parameters, well fit the experimental data, thereby confirming the validity of the analysis method used in this work. The life-time predicted from the kinetic equation is a valuable guide for the thermal processing of PHMG.

Effect of supercritical carbon dioxide as an exfoliation aid on bio-based polyethylene terephthalate glycol-modified/clay nanocomposites

Bio-based PETG (bio-based glycol modified polyethylene terephthalate, Ecozen T95) / clay (organo-modified montmorillonite, OMMT, C10A) nanocomposites were prepared by co-rotating twin screw extruder attached with supercritical carbon dioxide (scCO2) injection system. The effects of nano-clay and scCO2 on the properties of PETG/clay nanocomposites were investigated by measuring thermal, rheological, tensile, impact, and barrier properties. The thermal and mechanical properties decreased with increasing nano-clay content, but they recovered or even exceeded the properties of neat PETG as scCO2 was added. It was verified due to a good dispersion of the nano-clay in PETG matrix for PETG/clay nanocomposites by XRD, SEM, and TEM. It was thought that scCO2 could be an effective exfoliation agent for many nanocomposites systems as well as for bio-based PET/clay nanocomposites.

Electrical conductivity enhancement of polycarbonate/poly(styrene- co -acrylonitril)/carbon nanotube composites by high intensity ultrasound

AbstractPolycarbonate (PC)/poly(styrene-co-acrylonitrile) (SAN)/carbon nanotube (CNT) nanocomposites were prepared using an intensive melt-mixer equipped with an ultrasonic device. The effect of CNT content and sonication time on the electrical conductivity and other properties was investigated by DSC, TGA, rheometer, Izod-impact tester, surface resistivity meter, TEM and SEM. 1 min of sonication could considerably lower the percolation threshold of nanocomposites. Two different methods, a one-pot method and a master batch method, were compared to each other in regard to the effectiveness of CNTs. The expected mechanism of the two methods was proposed. The electrical conductive nanocomposite was obtained with even a small amount of CNTs by using incompatibility between polymers, affinity differences with CNTs, and a proper high-intensity ultrasound together.

Reactive extrusion of polypropylene/polystyrene blends with supercritical carbon dioxide

AbstractsA reactive extrusion process for immiscible polypropylene/polystyrene (PP/PS) blends with peroxides and multifunctional agents in the presence of supercritical carbon dioxide (scCO2) was studied. The PP/PS blends were investigated by rheological measurement, scanning electron microscopy, thermal analyzer, and mechanical testers. The results show that the complex viscosity and the storage modulus of the blends increase with the addition of peroxides and multifunctional agents, which might represent the formation of copolymer during melt processing. From the morphology analysis of the blends, the size of the dispersed PS domain decreases significantly. Moreover, the analysis of the blends also reveals that the use of supercritical carbon dioxide leads to an increase of complex viscosity and a decrease of domain size. It was believed that the use of scCO2 improved the compatibility of the blends. The interfacial tensions of the PP/PS blends were predicted theoretically from the rheological data using the Choi and Schowalter model and the Palierne model. The values of the interfacial tension decreased as the compatibility of PP/PS blends was improved. From the results above, we strongly suggest that the use of supercritical carbon dioxide-assisted reactive extrusion is an effective way to improve the compatibility of the PP/PS blends.

Polyurethane curing kinetics for polymer bonded explosives: HTPB/IPDI binder

The kinetics of polyurethane reaction and the effect of catalysts on the curing behavior were studied. The mixtures of hydroxyl terminated polybutadiene and isophorone diisocyanate with different reaction catalysts were dynamically cured in a differential scanning calorimeter. The activation energies were evaluated by the Kissinger and the Ozawa methods. The Chang plot was also used to determine reaction order and rate constant. The results showed that the activation energies were influenced remarkably by the choice of catalysts. The degree of cure and the cure time at given temperatures were calculated by direct integration of modified auto-catalytic kinetic model. It would give valuable information like pot-life estimation during manufacturing polymer-bonded explosives.

Effect of manufacturing condition in PC/PMMA/CNT nanocomposites extrusion on the electrical, morphological, and mechanical properties

Polycarbonate (PC)/poly(methyl methacrylate) (PMMA)/carbon nanotube (CNT) nanocomposites were prepared using a twin screw extruder. The effect of CNT content, screw speed, and manufacturing method on the electrical conductivity, morphology, and mechanical properties were investigated using a surface resistivity meter, SEM, XRD, and UTM. There existed the processing condition which lowered the surface resistivity of nanocomposites considerably. Three different manufacturing methods were tested on the effectiveness of CNTs and the expected mechanism was proposed. The electrical conductive nanocomposites were obtained using the incompatibility between the polymers, the difference of affinity of the polymers to CNTs, an optimum processing condition, and a proper manufacturing method.

Color Stabilization of Low Toxic Antimicrobial Polypropylene/Poly(hexamethylene guanidine) Phosphate Blends by Taguchi Technique

The color stabilization of antimicrobial blends was studied by using poly(hexamethylene guanidine) phosphate (PHMG) as a highly efficient biocidal and nontoxic agent. The Taguchi method was used to determine the optimum conditions for the blending of PHMG in polypropylene (PP) matrix. To improve the yellowing phenomena, two kinds of stabilizer were used together: tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)](IN1010) from phenol and tris(2,4-di-t-butylphenylphosphite) (IF168) from phosphorus. According to blend composition and mixing condition, six factors were chosen, with five levels being set for each factor. The orthogonal array was selected as the most suitable for fabricating the experimental design, L25, with 6 columns and 25 variations. The-smaller-the-better was used as an optimization criterion. The optimum conditions for these parameters were 10 phr for PHMG, 2 phr for IN1010, 1 phr for IF168, 10 min for mixing time, 210 °C for mixing temperature, and 30 rpm for rotation speed. Under these conditions, the yellowness index of the blend was 1.52. The processibility of the blends was investigated by Advanced Rheometric Expansion System (ARES). The blend with 0.5 w% PHMG content, diluted with PP, exhibited an antimicrobial characteristic in the shake flask method.

Detecting changes in arthritic fibroblast‐like synoviocytes using atomic force microscopy

The morphological and quantitative differences between arthritic fibroblast‐like synoviocytes (FLS) and normal FLS were determined as an effective diagnostic tool for rheumatoid arthritis (RA), and confirmed using atomic force microscopy (AFM). Collagen‐induced arthritic (CIA) mice and normal mice were prepared and FLS were isolated by enzymatic digestion from the synovial tissue of sacrificed mice at 5‐week and 8‐week pathogenesis periods. Analysis of cell morphology using AFM revealed that the surface roughness around the nucleus and around the branched cytoplasm was significantly higher in CIA FLS (P < 0.05) than that in normal FLS. In addition, the roughness of two different sites on the arthritic FLS increased with an increase in the duration of pathogenesis. These results strongly suggest that AFM can be widely used as a diagnostic tool in cytopathology to detect the early signs of RA and various others diseases at the intercellular level. Microsc. Res. Tech. 78:982–988, 2015.