Sunghyun Nam

Enhanced thermal and combustion resistance of cotton linked to natural inorganic salt components

Abstract A comparison of the thermal decomposition and combustion characteristics of raw and scoured cottons has demonstrated a mechanistic link caused by the presence of inorganic salts in raw cotton, which enhances resistance to heat and flame. Thermogravimetry, differential thermogravimetry, and microscale combustion calorimetry were used to examine the thermal decomposition kinetics and thermal stability of cotton. During pyrolysis, both raw cotton nonwoven and woven fabrics exhibited a slower decomposition with a larger initial weight loss and produced a greater char yield, as compared to the fabrics after scouring, which removes most inorganic components from cotton. The activation energy (Ea) values, calculated using the Kissinger method, the Flynn–Wall–Ozawa method, and the modified Coats–Redfern method, were consistently determined to be smaller for raw cotton than for scoured cotton. The analyses of cotton fabrics heated at elevated temperatures by 13C CP/MAS NMR and ATR-FTIR showed that trace quantities of inorganic components promoted the formations of oxygenated moieties at low temperatures and aliphatic intermediate char. In the combustion, raw cotton exhibited a much smaller heat release capacity and a smaller total heat release than scoured cotton, indicating enhanced thermal stability when the inorganic components are intact.

Evaluation of three flame retardant (FR) grey cotton blend nonwoven fabrics using micro-scale combustion calorimeter

Unbleached (grey or greige) cotton nonwoven fabrics (with 12.5% polypropylene scrim) were treated with three phosphate–nitrogen–based flame retardant formulations and evaluated with micro-scale combustion calorimeter. Heat release rate, peak heat release rate, temperature at peak heat release rate, heat release capacity, total heat release and char yield were determined. The peak heat release rate and total heat release results demonstrated that nonwoven fabrics treated with a formulation having higher diammonium phosphate and no dimethylol dihydroxyethyleneurea were superior to those treated with a formulation containing dimethylol dihydroxyethyleneurea. Nonwoven fabrics treated with these formulations were both superior to the nonwoven fabrics treated with a commercially available flame retardant formulation. These results were supported by the percentages of phosphorus and nitrogen on these fabrics, confirming that P–N synergism imparts high flame retardancy to the nonwoven fabrics. Grey cotton (untreated) consistently showed better flame resistance than (untreated) bleached cotton. As a result, its flame retardant products had lower heat release rate/peak heat release rate and other flammability characteristics than those of the bleached cotton. Additionally, grey cotton is softer than bleached cotton and saves the cost of bleaching and waste disposal. These three flame retardant formulations were used primarily to treat the cotton component of the nonwoven blend to make it flame retardant without flame retardant improvement for the polymer component.

Flame-retardant cotton barrier nonwovens for mattresses

According to regulation CPSC 16 CFR 1633, every new residential mattress sold in the United States since July 2007 must resist ignition by open flame. An environmentally benign “green,” inexpensive way to meet this regulation is to use a low-cost flame-retardant barrier fabric. In this study, a nonwoven fabric of grey unbleached cotton was treated with a low-cost phosphate-based formulation. The energy-dispersive X-ray microanalysis showed uniform nitrogen and phosphorus distribution. With 17% add-on, the flame-retardant unbleached cotton barrier showed a limiting oxygen index of 33% oxygen and 83 mm of char length with no after-flame and no afterglow in the vertical flame test. Under air and nitrogen at 500°C, 24% and 35% char remained after thermogravimetric analyses, respectively. This flame resistance is comparable to that of current commercial barrier fabrics made from bleached cotton and Flovan cyanoguanidine or from T-bond grey cotton fiber highlofts (Jones Fiber). Mattresses constructed with a flame-retardant cotton nonwoven barrier fabric are predicted to meet the requirements of 16CFR1633. As a follow-up to this study, a full-scale mattress burn test is recommended.

Flame retardant antibacterial cotton high-loft nonwoven fabrics:

Flame retardant treated gray cotton fibers were blended with antibacterial treated gray cotton fibers and polyester/polyester sheath/core bicomponent fibers to form high-loft fabrics. The high flame retardancy (FR) and antibacterial property of these high lofts were evaluated by limiting oxygen index, vertical flame testing, and antimicrobial tests against S. aureus (ATCC 6538), a Gram-positive bacterium, and K. pneumonia (ATCC 4352), a Gram-negative bacterium. The blended high-loft nonwoven fabrics, apart from the control blend number 5, had high LOI values greater than 24.7. Samples should have a higher LOI value than the threshold value of 20.95. All the blended high-loft nonwoven fabrics passed the vertical flame test and the char length increased with the decrease in the proportion of the SRRC FR cotton in the blends. The blended high-loft nonwoven fabrics were effective in reducing the bacteria by 99.9% for both types of bacteria tested. FR gray cotton fiber obtained from the treatment of SRRC 2 formulation (blend number 4) also showed good antibacterial properties.

Water-based binary polyol process for the controllable synthesis of silver nanoparticles inhibiting human and foodborne pathogenic bacteria

The polyol process is a widely used strategy for producing nanoparticles from various reducible metallic precursors; however, it requires a bulk polyol liquid reaction with additional protective agents at high temperatures. Here, we report a water-based binary polyol process using low concentrations of high-molecular-weight polyethylene glycol (100 000 g mol−1, 2 wt%) and ethylene glycol (5 wt%). The entangled conformation of the polyethylene glycol in water and the increased number of reducing sites by the ethylene glycol cooperatively contributed to the stability and effectiveness of reduction reaction and particle growth, producing uniformly sized silver nanoparticles (15.8 ± 2.2 nm) with no additional protective agents at a mild temperature of 80 °C. The measurement of particle size throughout the reaction and the dependence of the optical density of a silver colloidal solution on the concentration of ethylene glycol revealed three stages of particle growth. The minimum inhibitory concentrations of the purified silver nanoparticles against four representative human and foodborne pathogenic bacteria—S. aureus, P. aeruginosa, S. enterica, and E. coli—were 4.7, 2.3, 2.3, and 1.2 μg mL−1, respectively.