Synthesis Of Carbon Microspheres @Mg-Al Hydrotalcite Based Hybrid Flame Retardants And Their Flame Retardant Properties In Polypropylene

Polypropylene(PP),a semi-crystalline thermoplastic,has been widely used in daily life and industry because of its excellent mechanical properties,chemical resistance,excellent electrical insulation properties,easy processing and so on,and is one of the top five general-purpose plastics.However,the strong flammability of PP itself has brought many major fire accidents to people's life health and property safety.Therefore,it is of great importance to modify PP with flame retardant.At present,traditional halogen flame retardants reveal many defects,which are harmful to the environment and people's health.Therefore,the development of new flame retardants with halogen-free and environmentally friendly features has become the current research hotspot of PP flame retardant.As an emerging class of flame retardants,carbon-based flame retardants have shown the advantages of"halogen-free,environmental protection and high efficiency"in the flame retardant modification of polymers.Some common carbon materials such as fullerene,graphene,graphite,carbon black and so on have been applied in flame retardant PP,and excellent flame retardant performance can be achieved with a small amount of addition.Carbon microspheres,a member of the family of carbon-based flame retardant materials,have attracted much attention in the field of polymer flame retardancy because of their simple preparation and low price.Studies have shown that they have excellent flame retardant efficiency,however,they cannot achieve smoke suppression requirements when added to polymers.Hydrotalcite,also known as anionic clay,is a halogen-free,environmentally friendly flame retardant with excellent smoke suppression,but it has the disadvantages of low flame retardant efficiency and poor compatibility with polymers.Therefore,combining the high smoke suppression properties of hydrotalcite with the high flame retardancy of carbon microspheres is expected to build a class of highly effective flame retardants with significant smoke suppression.In this paper,hydrotalcite was loaded on the surface of carbon microspheres to form core-shell hybrid flame retardant CMSs@LDH by co-precipitation method,and then it was applied in PP as flame retardant,and its flame retardant performance,smoke suppression performance and mechanical properties were systematically studied.After that,CMSs@LDH was modified separately with bio-based copper lignosulfonate and nitrogen-phosphorus flame retardant phosphazene to improve its hydrophobicity,and then the effects of modified CMSs@LDH on the flame retardant properties,smoke suppression properties and mechanical properties of the composites were investigated.The specific research work is as follows.(1)Carbon microspheres(CMSs)were prepared from xylose by hydrothermal method,and then hydrotalcite was coated onto the surface of carbon microspheres using co-precipitation method to prepare core-shell hybrid flame retardant carbon microspheres@hydrotalcite(CMSs@LDH),which was applied to PP.The morphological characteristics,microstructure and so on of CMSs and CMSs@LDH flame retardants were tested by XRD,FTIR,SEM,TG/DTG and contact angle characterization,and the flame retardant and mechanical properties of PP composites were characterized by TGA and CCT.The results showed that LDH successfully coated the surface of CMSs and improved the hydrophobicity of CMSs to some extent.When CMSs and CMSs@LDH were added to PP separately as fillers,the flame retardant properties,smoke suppression properties and mechanical properties of PP/CMSs@LDH were better than those of PP/CMSs.When the addition amount was 4wt%,the LOI of PP/CMSs@LDH was 27.1%and UL-94 V-1 grade was achieved.Compared with Neat PP,the peak heat release rate,total heat release and total smoke of PP/CMSs@LDH decreased to 934.6 k W·m^–2,84.5 MJ·m^–2 and 10.7 m²,respectively,which decreased by 16.8%,10.7%and 12.3%.(2)In order to improve the compatibility and interfacial bonding between flame retardants and PP substrates,a layer of copper lignosulfonate capsule was wrapped on the surface of the core-shell flame retardant CMSs@LDH to make a flame retardant with a double-shell structure CMSs@LDH@CLS by using the chelating effect of lignosulfonate on metal ions.The results showed that the method effectively improved the compatibility of CMSs@LDH@CLS with PP,enhanced the flame retardant properties of PP composites and improved the mechanical properties of the composites.When the addition amount of flame retardant was 4.0 wt%,the LOI of PP/CMSs@LDH@CLS was 29.3%and achieved UL-94 V-0 grade.Compared with Neat PP,the peak heat release rate,total heat release and total smoke of PP/CMSs@LDH@CLS decreased to 863.2 k W·m^–2,74.5 MJ·m^–2 and 9.3 m²,respectively,which decreased by 23.2%,21.6%and 23.1%.(3)To further investigate the improvement of the compatibility between the flame retardant CMSs@LDH and PP matrix,an in situ polymerization method was used to prepare a double-shell flame retardant CMSs@LDH@PZN by coating a polyphosphonitrile shell on the surface of CMSs@LDH.The results showed that the method effectively improved the compatibility of CMSs@LDH with PP,enhanced the flame retardant properties of PP composites and improved the mechanical properties of the composites.When the addition amount of flame retardant was 4.0 wt%,the LOI of PP/CMSs@LDH@PZN was 29.6%and achieved UL-94 V-0 grade.Compared with Neat PP,the peak heat release rate,total heat release and total smoke of PP/CMSs@LDH@PZN decreased to 797.2 k W·m^–2,77.5 MJ·m^–2and 9.9 m²,respectively,which decreased by 29.0%,18.4%and 18.2%.