Research On Properties Of Nitrogen/Phosphorus/Bimetallic Hydroxide Synergic Flame-retardant Polypropylene

As a common thermoplastic plastic,polypropylene(PP)has been widely used in medicine,automobiles,home appliances,construction and so on due to its low density,easy processing,good mechanical properties,and chemical corrosion resistance.Nevertheless,its inflammable property poses a great threat to people’s life and property safety.In general,incorporation of flame retardant additives is one of the most efficient ways to improve its flame retardant performance.In recent years,as a halogen-free flame retardant,bimetallic hydroxide has the advantages of non-toxicity,smoke suppression,and low price,and has been widely used in flame-retardant polyolefins.However,due to the inherent hydrophilicity of the bimetallic hydroxide surface,it was easily to agglomerate in PP matrix,thereby reducing the flame retardant efficiency and mechanical properties of PP.In addition,when bimetallic hydroxide is used as a single flame retardant,its flame retardant efficiency is often lower than the “synergistic flame retardant” efficiency of multiple flame retardants.Therefore,in order to develop a halogen-free synergistic flame retardant with good compatibility in PP and high flame retardant performance,this study designed and synthesized three new types of nitrogen/phosphorus/bimetallic hydroxide hybrid flame retardant.The main research work is as follows:(1)Based on the excellent flame retardancy and compatibility of polyphosphazene and the ability of nickel-cobalt-based bimetallic hydroxide(Ni Co-BH)to convert PP to char,the polyphosphazene encapsulated Ni Co-BH was perpared through in-situ polymerization,and added it to PP matrix.The results show that the flame retardant and mechanical properties of PP/PZN@Ni Co-BH are better than PP/Ni Co-BH.In the case of PP/PZN@Ni Co-BH composites,with 20 wt% of PZN@Ni Co-BH filler,29.5% LOI value and UL-94 V-0 rating were obtained.Compared with pure PP,the peak heat release rate(p HRR),total heat release(THR)and total smoke production(TSP)of PP/PZN@Ni Co-BH decreased by 56.3%,40.9% and 58.7% respectively.(2)Through the polymerization of tannic acid and hexachlorocyclotriphosphazene on the surface of magnesium-aluminum hydrotalcite,a core-shell structure flame retardant(LDH@TA-HP)was prepared.On the surface of LDH@TA-HP,tannic acid provides carbon source,phosphazene provides gas source and acid source,the “shell”formed by the cross-linking of the two constitutes an intumescent flame retardant system.Hence,the combination of intumescent flame retardant and layered metal hydroxide flame retardant is realized.Whereafter,the flame retardant properties of PP/LDH@TA-HP were studied.The result showed that the “shell” formed by tannic acid and phosphazene significantly improved the hydrophobicity of LDH,and enhances the compatibility and dispersion of LDH@TA-HP in PP.PP/LDH@TA-HP has better mechanical properties and flame retardancy than PP/LDH.At only 20 wt% of LDH@TA-HP,PP/LDH@TA-HP achieved a UL-94 V-0 rating and a LOI of 30.1%during burning tests.Compared with pure PP,the p HRR,THR and TSP of PP/LDH@TA-HP were decreased by 63.5%,16.8% and 47.6% respectively.(3)Due to the adjustable anion in the interlayer of magnesium-aluminum hydrotalcite(LDHs)and the positively charged nature of the laminates,the bio-based phytic acid(PA)is intercalated in the interlayer of LDHs through the “one-pot method”,at the same time,phytic acid and melamine self-assemble on the surface of LDHs to form a phytic acid-melamine supramolecular network(PA-MEL).Subsequently,the modified LDHs(LDH@PA-MEL)was incorporated into PP matrix.The results showed that the modified LDH@PA-MEL had better compatibility and dispersibility in PP matrix,and PP/LDH@PA-MEL had better mechanical properties and flame retardant properties than PP/LDH-C.With only 20 wt% LDH@PA-MEL,the LDH@PA-MEL composite reached a LOI of 29.6% and UL-94 V-0 rating.Compared with pure PP,the p HRR,THR and TSP of PP/LDH@PA-MEL were decreased by 63.5%,26.2% and 43.7% respectively.