Polyurethanes (PUs) are versatile and widespread, particularly as flexible and rigid foams. To avoid isocyanates and other toxic reagents required for synthesis, such as phosgene, alternative synthetic routes have been utilized to produce non-isocyanate polyurethanes (NIPUs). A thermally and flame-resistant rigid NIPU was produced from environmentally benign and bio-sourced ingredients, requiring no catalyst or solvents. A foamed structure was obtained by the addition of glutaraldehyde and four different carboxylic acids: malic acid, maleic acid, citric acid, and aconitic acid. The resulting morphology, thermal degradation, and flame resistance of each foam were compared. The properties vary with each carboxylic acid used, but in each case, peak thermal degradation and peak heat release are postponed by >100 °C compared to commercial rigid PU foam. Furthermore, in a butane torch test, NIPU foams exhibit an 80% higher remaining mass and a 75% reduction in afterburn time, compared to commercial polyurethane. This bio-based polyurethane eliminates the hazards of traditional PUs, while imparting inherent thermal stability and flame resistance uncharacteristic of conventional foams.
Poor antimicrobial activity and lack of protection against UV irradiation are weaknesses of cotton textiles. In an attempt to impart superior antimicrobial and UV-protective properties to cotton, layer-by-layer deposition of chitosan and magnesium lignosulfonate, and in situ synthesis of silver (Ag) nanoparticles (NPs), was performed. Lignin, in a chitosan/lignin multilayer, simultaneously acts as a UV protective macromolecule and natural reducing and stabilizing agent, allowing formation of Ag NPs. Four bilayers of this coating is sufficient for fabrication of a chitosan/lignin/Ag-NP textile nanocomposite treatment with 50+ UV protection. 100% reduction of Gram-negative bacteria Escherichia coli, gram-positive bacteria Staphylococcus aureus, and yeast Candida albicans can be achieved with a 12-bilayer coating, when 20 mM silver nitrate solution and sodium borohydride are applied. On the other hand, four bilayers impregnated with Ag NPs, using 10 mM silver nitrate solution, provides sufficient antimicrobial activity independent of an added reducing agent. This treatment exhibits no inhibition of human keratinocyte cells growth on the skin, indicating low cytotoxicity.
Cellulosic paper (from wood bers) is a highly ammable material that is used in corrugated carboard, packaging, printing, and construction. While there is signi cant work focused on depositing a ame retardant coating onto the individual wood pulp bers, there are very few studies that apply ame retardant coatings to already-cast paper. In an effort to improve the ame retardant properties of paper, a polymer-dense coacervate composed of polyethylenimine (PEI) and poly(sodium phosphate) (PSP) was deposited in a single step and subsequently crosslinked with glutaraldehyde. In a vertical ame test, the crosslinked PEI/PSP coacervate-coated paper achieves self-extinguishing behavior, and an average char length of 3.4 in, with only a 35% weight gain. Additionally, the crosslinked coating retains its ame retardant properties after water immersion and conditioning tests. This coacervate system is the rst polymeric coating to be successfully deposited onto commercially available cellulosic paper for the purpose of ame retardancy.
Cotton-based raw paper, made of 100% cellulose, is used to make humidity-sensing, cottonid for bio-architecture applications. Despite its renewability and excellent mechanical properties, it is inherently flammable. In an effort to reduce its flammability, thin films of fully renewable and environmentally benign polyelectrolytes, chitosan (CH) and phytic acid (PA), were deposited on raw paper via layer-by-layer (LbL) assembly. Only four bilayers (BL) of the CH/PA coating are required to achieve self-extinguishing behavior, with a 69% reduction in peak heat release rate measured by microscale combustion calorimetry. These results demonstrate that this renewable intumescent LbL-assembled film provides an effective flame-retardant treatment for these environmentally friendly, climate-adaptive construction materials and could potentially be used to protect many cellulosic materials.
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