Preparation Of Bio-based Nano Flame Retardant And Its Application Research On High-efficiency Fire Retardant Polypropylene

Polypropylene（PP）is an excellent thermoplastic polymer material,but its inherent structure is extremely flammable,which limits its application in many fields requiring flame retardancy.In order to widen the application field of PP,it is necessary to carry out flame retardant modification.At present,the traditional intumescent flame retardant（IFR）system ammonium polyphosphate（APP）/ pentaerythritol（PER）has been widely used in flame retardant PP composites due to its halogen-free,anti-melt dripping,low smoke,low toxicity and non-corrosive gas generation.However,some accompanying disadvantages need to be solved urgently: APP is difficult to be uniformly dispersed in the PP matrix,and a large number of agglomerated flame retardants will affect the flame retardancy of PP composites;The traditional IFR system is highly hygroscopic and easily migrates to the surface of the PP matrix over time,affecting the stability and durability of its flame retardancy;the APP/PER system is so inefficient that a 25 wt% loading or more is required to pass the UL-94 V-0 rating for flame retarding PP composites;Most importantly,APP is derived from non-renewable phosphate rock resources.In the study of this subject,in order to address the problems exposed by the application of the traditional IFR in the PP system,based on renewable bio-based materials phytic acid（PA）and traditional IFR gas source melamine（MA）,a simple and environmentally friendly hydrothermal synthesis method was used to obtain melamine phytate（PAMA）supramolecular nanosheets,and combined with transition metal ions(Mn²⁺,Zn²⁺,Ni²⁺)having strong catalytic charring ability,a class of transition metal doped bio-based flame retardants（PAMA-Mn,PAMA-Zn,PAMA-Ni）with high flame retardant efficiency was prepared.Then the APP in the PP/IFR system was largely replaced by it by means of melt blending,and it is expected that the excellent flame retardant effect will eventually be achieved.Through a comparative analysis of the fire retardancy of PP composites before and after replacement,it is found that when the replacement rate of APP in the PPI system by PAMA-M is 33 wt% and the total amount of flame retardant is 18 wt%,its limiting oxygen index（LOI）value and vertical burning UL-94 rating have reached maximum values.Among them,PPMn33 has the best flame retardancy,its LOI value is 31.9%,and it can pass the UL-94 V-0 rating.However,under the premise of meeting the requirements for basic flame retardant performance（UL-94 V-0 rating）,the replacement rate of APP by PAMA-Zn or PAMA-Ni nanosheets can reach 67 wt% or even higher.In addition,PAMA-M nanosheets not only have excellent dispersibility in PP matrix,but also help optimize the dispersion state of APP in PP matrix.By analyzing the flame retardant mechanism of PPMn33,PPZn33 and PPNi33 through various characterization methods,the following conclusions can be drawn: Due to the in-situ catalytic cross-linking charring effect of transition metal ions,PP composites quickly generate high-quality char layers.At the same time,the pyrolysis products entering the gas phase contain some diaromatics,polycyclic aromatic hydrocarbons and soot,so they are not easily ignited.Therefore,PPMn33,PPZn33 and PPNi33 have higher LOI values and can pass the UL-94 V-0 rating.However,the catalytic charring capacity of Zn²⁺ and Ni²⁺ is weaker than that of Mn²⁺,so the residual char yield of PP composites is lower,which makes it difficult to function as a physical barrier for a long time in the continuous heat flow of the cone calorimetry（CONE）test,and the char layers may crack,so the heat release values of PPZn33 and PPNi33 are large.In addition,another type of bio-based nano flame retardant was successfully prepared in this subject,namely bio-based modified layered double hydroxide（LDH）.The bio-based materials PA and folic acid（FA）were used to modify Zn Ni Al-LDH by one-step co-precipitation method to obtain PA-LDH and FA-LDH nanosheets.Then,XRD and FTIR characterization methods proved that PA-LDH and FA-LDH were successfully prepared.Finally,the micromorphology of PA-LDH and FA-LDH nanosheets was confirmed by TEM characterization.