Bio-inspired construction of hydrophobic Mg(OH)2/Co-MOF/DOPO hybrids for simultaneously improving flame retardancy and mechanical properties of poly(L-lactic acid) composites

• Bio-inspired strategy was developed to synthesize MH@MOF- g -DOPO hybrids. • The synthesized MH@MOF- g -DOPO was hydrophobic with the water contact angle of 113.7°. • PLA/MH@MOF- g -DOPO composites exhibited significantly improved flame retardancy. • The PLA composites also displayed outstanding mechanical properties via uniaxial pre-stretch. The design of environmentally friendly flame retardants to achieve the balanced flame retardancy and mechanical properties of poly(L-lactic acid) (PLA) is a critical challenge. Herein, inspired by the micropapillae adorned with hydrophobic wax crystals structure of lotus leaf, Mg(OH) 2 /Co-MOF/DOPO hybrids (MH@MOF- g -DOPO) were successfully constructed through in-situ growth of Co-MOF and chemical grafting of DOPO . Thermogravimetric analysis (TGA) revealed that the Co-MOF content in MH@MOF was approximately 27.3 wt%, while the grafted DOPO in MH@MOF- g -DOPO was about 19.5 wt%. Owing to the unique microstructure, the water contact angle of MH@MOF- g -DOPO reached to 113.7°, implying its hydrophobic surface. Subsequently, the as-synthesized MH@MOF- g -DOPO was used to prepare PLA composites, which exhibited significantly improved flame retardancy, as indicated by the LOI value of 30.2 %, UL-94 V0 rating, and the reduction on PHRR by 70.1 %. The flame retardant mechanism was attributed to the synergistic effects of multiple flame retardant units (MH, Co-MOF and P) in MH@MOF- g -DOPO hybrids. Furthermore, the flame retarded PLA/20MH@MOF- g -DOPO achieved the brittle-tough transformation via uniaxial pre-stretch process, thus displayed outstanding mechanical properties (good stiffness and excellent toughness). Notably, compared to the pristine undraw PLA, the Youngꞌs modulus, tensile strength and the elongation at break PLA/20MH@MOF- g -DOPO increased by 35 %, 38 % and 1957 %, respectively. This work proposes an innovative and efficient method to achieve the excellent balance on flame retardancy and mechanical properties of PLA composites, benefiting to promoting their real-world applications as functional polymer materials.