Antiflaming poly(L-lactide) by synthesizing polyurethane with phosphorus and nitrogen

A novel polyurethane containing phosphorus and nitrogen (PU) was synthesized and characterized with 1 H-NMR, FTIR, and GPC. It was served as flame retardant to blend with poly(L-lactide) (PLLA) through solution casting technique. PU particle dispersed in PLLA substrate irregularly and improved the crystallinity of PLLA. The initial decomposition temperature of PLLA composite was significantly lower, but char residue increased. Flame retardancy and mechanical properties of PU/PLLA blends were evaluated. When the blend ratio of PU/PLLA was 10 wt%, LOI was 26.8%, and UL94 test reached V-2 grade. The inflaming retarding mechanism was outlined. The tensile strength of PLLA blend was 42.8 MPa, while its elongation at break was only 2%. By adjusting PU and adding compatilizer, the balance between flame retardancy and good mechanical properties of PLLA would be controlled.