Study On Functionalized Modification Of Expandable Graphite And Its Flame Retardant Rigid Polyurethane Foam

Due to its highly cross-linked,almost closed three-dimensional structure,rigid polyurethane foam(RPUF)has low apparent density,low thermal conductivity and good mechanical properties,which makes it widely used as an external insulation material for building walls.However,RPUF material has a great possibility of easily causing fire safety accidents,harmful to lives and property safety of humans.Expandable graphite(EG)is a halogen-free green intumescent flame retardant commonly used to improve the combustion behavior of polymers.In the process of polymer combustion,EG can absorb a large amount of heat to effectively slow down the degradation rate of the polymers.More importantly,EG will rapidly expand into a“worm-like”structure,blocking the“fuel flow”that transports the flame during the combustion process.Thus,the combustion of polymers is inhibited and flame retardancy is realized.However,EG also has its inherent shortcomings,such as“popcorn effect”,large addition amount,and poor compatibility with polymer matrix,etc.In order to solve the above problems,EG is used as flame retardant to prepare RPUF composites,and the influence of different foaming agent content on the structure and properties of RPUF/EG flame retardant composites is investigated in this thesis.On this basis,EG is modified by two methods respectively,and the combustion behavior,morphology and flame retardant mechanism of RPUF flame retardant composite system are systematically studied.On the one hand,an environment-friendly flame retardant with simple preparation method is prepared by chemical modification.It greatly improves the flame retardant efficiency of EG and the interfacial compatibility between EG and matrix.On the other hand,a second flame retardant is introduced into RPUF/EG composites by physical blending,which not only reducing the amount of EG but also improving the fire safety of RPUF by synergistic effect.The main findings of this thesis are as follows:(1)The RPUF/EG composites with different n-pentane contents are prepared.The morphological characterization(SEM)results of RPUF and RPUF/EG composites with different n-pentane contents show that adjusting the content of n-pentane causes changes in the cell structure of the RPUF.Thermogravimetric analysis(TGA),flame retardancy tests(LOI and UL-94)and physical and mechanical tests show that the thermal stability,flame retardancy and specific compressive strength of RPUF/EG composites decrease with increasing the n-pentane content.(2)The hybrid modification of EG with hexachlorotripolyphosphazene(HCCP)is successfully achieved,and the composite expandable flame retardant(HCCP@EG)is prepared and used for the flame retardancy of RPUF.The SEM results show that the compatibility between organically modified EG and RPUF is significantly improved.RPUF/15HE achieves a higher specific compressive strength than RPUF/15EG in the test of physical and mechanical properties.In addition,it can be seen that HCCP plays a flame retarding role in both gas phase and condensing phase,and obviously inhibits the“popcorn effect”of EG through the analysis of the flame retardant mechanism of HCCP@EG,which successfully makes RPUF/15HE reach V-0 grade in the UL-94 test.(3)A novel phosphorus and nitrogen-containing flame retardant is synthesized(Zr MP),and the successful preparation of Zr MP is proved by FTIR,XRD and SEM characterization.Then it is blended with EG in different proportions for the flame retardant of RPUF.The UL-94 test shows that when the addition of Zr MP is 2.5%and the addition of EG is 12.5%,the RPUF composite reaches V-0 level.At the same time,the specific compressive strength of RPUFs4 reaches 4.31 MPa/(g/cm~3),and there is no further deterioration of the specific compressive strength of RPUF compared with RPUFs1.Moreover,the analysis of the flame retardant mechanism of Zr MP/EG reveals its dual-phase flame retardant effect in inhibiting the combustion of RPUF.