The fabrication of conventional or biodegradable polymers with improved thermal and fire-resistant properties is an important task for their successful application in various branches of the industry. In this work, few-layered molybdenum disulfide was functionalized with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and introduced into polyethylene and poly(lactic acid) matrixes. The obtained polyethylene composite samples displayed improved thermal stability, significant reduction in CO emissions, improved fire-resistant properties, and over 100% increases in thermal conductivity. Poly(lactic acid) composites displayed less impressive results, but have managed to improve some values, such as CO emissions, peak heat release rate, and total heat release in comparison to pristine polymer. [ABSTRACT FROM AUTHOR]