Synthesis, Performance Evaluation, and Plasticization Dynamics of a Dual-Green Components Flame-Retardant Plasticizer for Poly(vinyl chloride)

The toxicity of phthalate plasticizers poses serious threats to human health and the environment. Biobased plasticizers have been widely developed to address sustainability issues, but the flammability problem of flexible polyvinyl chloride (PVC) products remains unresolved. Therefore, there is an urgent need for a solution that balances the flame retardancy, flexibility, and migration resistance of flexible PVC products. The present work synthesized a biobased flame-retardant plasticizer (LA7-P) containing dual-green components through a two-step method using biomass lactic acid (LA), heptanol, and phenyl dichlorophosphate (PDCP). The use of strong acid catalysts was avoided, and the product structure was confirmed by various spectral methods. Scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) indicated that LA7-P produced more char residue during thermal degradation. These dense char layers reduced the heat release by 28% and achieved a VTM-0 rating in the UL-94 test. LA7-P significantly lowered the glass transition temperature of PVC, resulting in a 630% increase in the elongation at break of plasticized PVC compared to neat PVC. Plasticization dynamics simulations demonstrated the secondary bonding interaction between the ester groups of LA7-P and the PVC chain, with calculated binding energy stronger than that of the PVC/dioctyl phthalate (DOP) system. Due to these interactions, the migration rate of LA7-P into n-heptane was reduced by 90% compared to DOP. LA7-P containing dual-green components exhibited similar plasticizing performance to commercial DOP while demonstrating significant advantages in flame retardancy and migration resistance. The development of LA7-P fills the gap left by lactic acid-based plasticizers in the field of flexible PVC flame retardancy, offering a solution for this application.