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
Li Cui, Zhaotian Ba, Bingchen Wu, Xinxin Shi, Hui Liu, Lili Ma, Xin Wen, Pingan Song
Abstract
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.