Hoang Thi Dong Quy’s research while affiliated with Vietnam National University Ho Chi Minh City and other places

In order to improve fire performance of thermoplastic polyurethane (TPU) material, halogen-free flame retardants (triphenylphosphate- TPP and diamonium hydrogen phosphate-DAP) were studied in an attempt to obtain UL-94V ratings. The fire behaviors and thermal stability properties were evaluated using UL-94 vertical test and thermogravimetric analysis (TGA). The UL- 94V results showed that V-0 ratings were achieved at 5 wt% of DAP or 7.5 wt% loading of TPP. The incorporation of these flame retardant (FR) increases the flame retardant properties as well as the amounts of charred residues protecting the mixture from further degradation. This assertion could be accepted when observing that the char residual of TPU/DAP mixture at 500–600oC was much higher than that of neat TPU. The char layer limited the amount of fuel available and insulate the underlying composite material from the flame and, thus, make further degradation more difficult. The mechanism of flame retardants was also discussed in this study.

Gold nanoparticles (AuNPs) in spherical shape with diameter of 6–35 nm stabilized by dextran were synthesized by γ -irradiation method. The AuNPs were characterized by UV-Vis spectroscopy and transmission electron microscopy. The influence of pH, Au ³⁺ concentration, and dextran concentration on the size of AuNPs was investigated. Results indicated that the smallest AuNPs size (6 nm) and the largest AuNPs size (35 nm) were obtained for pH of 1 mM Au ³⁺ /1% dextran solution of 5.5 and 7.5, respectively. The smaller Au ³⁺ concentration favored smaller size and conversely the smaller dextran concentration favored bigger size of AuNPs. AuNPs powders were prepared by spay drying, coagulation, and centrifugation and their sizes were also evaluated. The purity of prepared AuNPs powders was also examined by energy dispersive X-ray (EDX) analysis. Thus, the as-prepared AuNPs stabilized by biocompatible dextran in solution and/or in powder form can be potentially applied in biomedicine and pharmaceutics.

Colloidal silver nanoparticles (AgNPs) with particle size less than 10 nm and concentration of 2 mM/L (~200 mg/L) were synthesized by gamma Co-60 ray irradiation of Ag+/chitosan solutions with different chitosan concentration of 0.5%, 1% and 2% (w/v). Incorporation of AgNPs onto cotton fabric was carried out by padding method with 100% wet pick-up. The content of AgNPs deposited on cotton fabric and released from cotton fabric after repeated washing was determined by inductively couple plasma-atomic emission spectroscopy (ICP-AES). The results indicated that cotton/AgNPs fabric made from padding into AgNPs solution with 0.5% - 1% chitosan was the best one of AgNPs adhesion ability on cotton fabric. Results on antibacterial activity against S. aureus showed that cotton/AgNPs fabric with AgNPs content more than 100 mg/kg exhibited highly antibacterial activity (η > 98%). The mechanical property (tensile strength and elongation) of cotton/AgNPs fabrics was almost unchanged in comparison with untreated cotton fabric. Thus, the resultant cotton/AgNPs fabric with highly antibacterial activity can be potentially used as bed drapes and/or patient uniforms in hospitals, etc.