Hydrophobic Modification Of Aluminum Hypophosphite With (Rare Earth) Aluminate For The Research On Flame Retardant Epoxy Composites

In this paper,aluminum hypophosphite（AHP）was designed and prepared by surface hydrophobic modification with aluminum acid ester-based AHP（Al AHP）and rare earth aluminum acid ester-based AHP（Ra AHP）to AHP for the poor water resistance issue.The physical and chemical features,hydrophobicity,charring properties,water resistance,and thermal stability of Al AHP and Ra AHP were investigated,EP/AHP,EP/Al AHP and EP/Ra AHP composites were prepared,the effects of AHP,Al AHP and Ra AHP have been investigated on the laws and mechanisms of action on the interfacial properties,curing behavior,ignition properties,flame retardant properties,hydrophobicity,water resistance and mechanical properties of epoxy resin composites.The specific research contents and conclusions are as follows:（1）The AHP flame retardant was treated with a dry mechanical grinding process to achieve refinement,and then the AHP was applied to the flame retardant of epoxy resins.The refined AHP has a uniform particle size and excellent thermal stability,the residual char of AHP was 75.22%at 600°C.The refinement of the AHP improves the total heat release（THR）of EP/AHP reducing by 23.3%.The maximum peak value of CO production dropped to 0.021 g/s,decreased by 36.4%.The phosphorus-containing carbon layer is stable and continuous,acting as a physical barrier to slow down mass and heat transfer.The AHP also acts as an inhibition in the gas phase.Overall,the EP/AHP composite acts as a flame retardant in both the gas phase and condensation.（2）Prepare hydrophobic aluminate modified AHP（AlAHP）by surface modification of AHP with aluminate coupling agent（ACA）by surface modification of AHP by mechanical force surface compounding and apply Al AHP to flame retardant epoxy resin composites.Al AHP has excellent hydrophobic properties,water resistance,charring ability and thermal stability,and the water contact angle of Al AHP-8 was129.10°,the residual char of Al AHP-2 was 78.86%at 600°C.Al AHP improves dispersion of EP/Al AHP composites.Compared to pure EP,the THR of the EP/6Al AHP-8 composite was reduced from 163 MJ/m² to 99.11 MJ/m²,a decrease by 39.20%.In addition,Al AHP clearly reduced the release of volatile gases from EP/Al AHP and improved the hydrophobicity and water resistance of EP/Al AHP composites.（3）Rapid preparation of rare earth based AHP（RaAHP）by mechanical surface compounding using a rare earth aluminate coupling agent（REA）surface modified AHP for application to flame retardant epoxy resin composites.Ra AHP-4 water contact angle was 94.58°.Ra AHP enhances the effect of flame retardancy,thermal stability and hydrophobicity for EP/Ra AHP composites.In comparison with pure EP,the peak heat release（PHRR）and THR of EP/6Ra AHP-4 were decreased by 50.44%and 35.59%respectively.Compared with EP/6AHP,the maximum peak value of CO production rate from EP/6Ra AHP-4 decreased by 62.64%.With the catalytic effect of Y₂O₃,Ra AHP induces more P elements in the condensed phase in the form of P-O-C.The densities,swelling and graphitization of the char layer of the EP/Ra AHP composite have been significantly improved,which provides a good barrier to heat and mass transfer.In addition,Ra AHP improves the hydrophobicity,water resistance and mechanical properties for EP/RaAHP composites.