The Study Of The Preparation Of Oyster Shell-based Flame Retardant In Aqueous Phase And Its Application In Epoxy Composites

Epoxy resin（EP）has been wide used in coatings,electronic materials,and engineering plastics due to its chemical corrosion resistance and thermal stability.However,EP exhibited high flammability and released harmful smoke particles during the combustion process.The introduction of flame retardants improves the flame retardancy,smoke suppression,and toxicity reduction of EP composites,but the complex preparation process and non-renewable raw materials have attracted wide attention.Meanwhile,bio-based flame retardants show great potential in the field of flame-retardant polymers.In this paper,based on the resource utilization of oyster shell powder（OSP）,several flame-retardant systems were constructed by mechanochemical strategy with water as the ball-milling agent,and corresponding flame-retardant EP composites were prepared and the possible flame-retardant mechanism was speculated.The main research contents and conclusions are as follows:（1）A phosphorus-free,green,organic-inorganic hybrid flame retardant（TOSP）was constructed using OSP as raw material through a mechanochemical strategy.The EP composite with TOSP showed a short combustion time in UL-94 vertical burning test,and the limiting oxygen index（LOI）increased from 24.4%to 27.3%of EP.Notably,TOSP significantly enhanced the flame retardancy of EP composites（peak heat release rate（p HRR）and total CO production（TCOP）decreased by 41.8%and 55.0%with 4wt%content）.The result of the condensed phase products and gas phases pyrolysis products revealed that TOSP played a flame-retardant role in the condensed phase,catalyzing the formation of char layers and inhibiting the generation of combustible gas and smoke particles.（2）Based on OSP and ammonium polyphosphate（APP）,an efficient organic-inorganic hybrid flame retardant（TOSP@APP）was successfully constructed by an aqueous mechanochemical strategy.The introduction of TOSP@APP improved the thermal stability of EP composites.The results of UL-94 and LOI tests showed that the EP composite with 8 wt%TOSP@APP-2 reached V-0 rating,and the LOI value of EP/TOSP@APP-2 increased from 24.4%to 30.3%.The introduction of TOSP@APP significantly enhanced the flame retardancy of EP composites.Compared with EP,the p SPR and p HRR of EP composites with EP/TOSP@PAPP-2 reduced by 69.4%and78.2%,respectively.In addition,compared with the EP composite with APP,the TCOP of the EP composite with TOSP@APP-2 decreased by 44.9%.The result of the condensed phase products and gas phases pyrolysis products revealed that TOSP@APP changed the structure of the char layers and catalyzed the generation of residual chars with good compactness and high expansion,which acted as a thermophysical barrier and inhibited the volatilization of combustible gases.（3）Based on OSP and phytic acid（PA）,a bio-based organic-inorganic hybrid flame retardant（TOSP@PAA）was successfully constructed by an aqueous mechanochemical strategy.TOSP@PAA is a flocculent nanosphere with a cross-linked structure formed by the-NH₃⁺-O^-P-bond.TOSP@PAA exhibited excellent self-charring performance and rapidly formed highly intumescent protective char layers at high temperatures.The EP composites with TOSP@PAA demonstrated excellent thermal stability and lower flammability:the EP composites with TOSP@PAA achieved a V-0rating at the UL-94 test,and the LOI value of EP/TOSP@PAA-8 increased from 24.4%to 30.2%.The EP composites with TOSP@PAA showed remarkable flame retardancy（reduction of 74.0%in p HRR and 60.2%in total heat release rate（THR）at 8 wt%content）.EP/TOSP@PAA-8 showed excellent thermal shielding performance by catalyzing the formation of char layers to isolate external thermal radiation.Through the analysis of residual char in condensed phase and gas phase pyrolysis product,it is speculated that the possible flame-retardant mechanism is that the degradation product of TOSP@APP catalyzed the cross-linking of residual chars and played a role of thermal shielding.The EP with TOSP@PAA revealed good mechanical properties and significantly improved flexural properties.