Design And Fabrication Of Flame Retardant System Based On MOFs@GO And Its Flame Retardancy For Polylactic Acid

In this paper,four novel flame retardant systems were designed and prepared,which were applied to the flame retardant modification of polylactic acid（PLA）.The mechanical and flame retardant properties of PLA composites were measured.The related mechanisms of flame retardancy were discussed in detail.This paper mainly includes the following parts.The binary hybrid flame retardant of ZIF-8@GO（ZG）was prepared by loading metal-organic frameworks（ZIF-8）on graphene oxide（GO）.The PLA/ZG flame retardant composites were prepared by solution blending using polylactic acid（PLA）as matrix.The mechanical properties,crystallization,flame retardancy and flame retardant mechanism of the prepared composites were studied.The experimental results showed that the nanoparticle size of ZIF-8 loaded on GO was about 32⁴5 nm.ZG could act as a heterogeneous nucleating agent in PLA matrix and accelerate the crystallization of PLA.When the content of ZG was 0.05 wt%,the crystallinity of PLA composites was 69.5%.The mechanical and flame retardant properties of PLA were obviously improved with the addition of ZG.When the content of ZG was 0.5 wt%,the tensile strength and LOI value of the composite reached 49.63 MPa and 24.0%,respectively.Besides,UL-94 of the composite reached V-2 grade.Chitosan salt（CHP）containing a large amount of phosphorus and nitrogen was synthesized by the modification of chitosan with 2-carboxyethyl phenylhypophosphite（3-HPP）.Then,ZG was compounded with CS or CHP to form two composite flame retardant systems of CS/ZG and CHP/ZG.The flame retardant composites of PLA/CS/ZG and PLA/CHP/ZG were prepared by combining CS/ZG or CHP/ZG with PLA,respectively.The effects of CS,CHP and ZG on the mechanical and flame retardant properties of PLA were studied.The experimental results showed that ZG could play a role of compatibilizer,promoting the dispersion of CS or CHP in PLA matrix.The mechanical properties and flame retardancy of the PLA/CHP/ZG composites were significantly improved compared with that of the composites adding unmodified chitosan.When adding 4.2 wt%CHP and 0.8 wt%ZG,the tensile strength and LOI value of the composites was 61.5 MPa and 26.0%,respectively.Moreover,the continuous and compact char layer was formed after burning of the PLA/CHP/ZG composites.GO-g-PPA was prepared by grafting phenylhypophosphite（PPA）on GO due to the rich oxygen-containing functional groups on the surface of GO.Then the GO-g-PPA/ZIF-8（GPZ）ternary hybrid flame retardant was prepared by loading nano-ZIF-8on GO-g-PPA.The experimental results showed that the content of P,N and Zn atoms in GPZ was about 2.5%,14.0%and 4.0%,respectively.The GPZ had good thermal stability and its contact angle was about 95°,which was very close to that of PLA.The PLA/GPZ flame retardant composites were prepared by adding GPZ into PLA matrix.GPZ had good interface effect on PLA matrix,which endowed with the good performance of flame retardancy for the composites.When adding 2 wt%GPZ,the PHRR,HRC,THR and LOI value of the composite was about 316.2 W·g^-1,322.4 J·g^-1·K^-1,17.53 kJ·g^-1 and 27.0%,respectively.The PLA/GPZ composites reached the commercial standard in practical application,such as plastic parts for automobile passenger seats.