Flame-Retardant Plasticizer Derived from Renewable Acids for Poly(Vinyl Chloride) Improved Toughness and Flame Retardancy

Biobased plasticizers have gained significant attention for their potential to replace conventional petrochemical-based additives in the production of flexible poly(vinyl chloride) (PVC) products, offering an environmentally friendly alternative. However, the incorporation of biobased plasticizers can render PVC materials highly flammable and produce substantial smoke, posing significant safety and environmental concerns. To address these challenges, this study developed a biobased biodegradable flame-retardant plasticizer (PLRCL) synthesized from renewable acids, namely, ricinoleic acid, l-lactic acid, and levulinic acid, along with 9,10-dihydro-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The innovation of this study lies in the successful synthesis of PLRCL and its integration into PVC films, which not only enhances the flame retardancy but also improves the toughness of the material. The PLRCL-endowed PVC films achieved a UL-94 V-0 grade and a significantly higher limited oxygen index of 37.9%, compared to the commercial plasticizer dioctyl phthalate plasticized PVC films. The pyrolysis of PLRCL was found to facilitate the formation of a complete and continuous char layer, thus improving the thermostability and fire resistance of the PVC films. This char layer acts as a protective barrier, suppressing the release of smoke and toxic gases during combustion, thereby improving the overall safety of the PVC materials. Mechanical testing revealed that the elongation at break and tensile strength of plasticized PVC films with 40 phr PLRCL reached 302.59% and 28.34 MPa, exhibiting outstanding flexibility. Meanwhile, the good volatilization and migration resistance of PLRCL endowed the long-term stability of PVC films. Besides, the loading of PLRCL could keep good optical transparency and improve the processability of the PVC products. Soil degradation experiments demonstrated that PLRCL is biotransformed by the microorganisms present in the soil into nontoxic and innocuous lipid molecules, highlighting the environmental benefits of PLRCL. In all, PLRCL is a promising green sustainable multifunctional plastic additive, offering a viable alternative to traditional petroleum-based plasticizers and providing insights into the design of sustainable flame-retardant plasticizers.