Preparation Of Core-shell Aluminum Hydroxide Based Composites And Their Flame Retardancy

Aluminum hydroxide as one of the most widely used inorganic flame retardants are attracting more and more attention due to non-toxicity,high whiteness,abundant sources and no secondary pollution.However,when aluminum hydroxide is used as a separate component for flame retardancy,the efficiency is relatively low.Therefore,in order to achieve,the added amount of aluminum hydroxide needs to reach 60 wt%for achieving the UL94-V0 flame retardant level.But the filling amount is so high that the mechanical properties of composite plastic become serious deterioration.Aiming to solve the problem,this dissertation proposes the idea based on the preparation of aluminum hydroxide base"core-shell structure"type flame retardant to improve the aluminum hydroxide flame-retarding efficiency.Firstly,The in-situ growth method was used to synthesize an efficient halogen-free composite flame retardant composed of aluminum hydroxide core and aluminum phosphate multi-stage flower-like shell.Furthermore,a secondary layer of silica or dodecylamine is coated on the surface to prepare a core-shell aluminum hydroxide composite synergistic flame retardant that has different flame retardant components.Composites based on core-shell aluminum hydroxide flame retardant and matrix material vinyl acetate（EVA）exhibit high-efficiency flame-retardant properties and excellent mechanical properties.The main contents are summarized as follows:（1）The in-situ growth method was used to synthesize an efficient halogen-free composite flame retardant composed of aluminum hydroxide core and aluminum phosphate multi-stage flower-like shell（Marked as Al（OH）₃@AlPO₄）.The standard spline was prepared by melt-blending the flame-retardant system with polymer materials to test its mechanical properties and flame-retardant properties.Compared with pure aluminum hydroxide and physical mixtures of aluminum hydroxide and aluminum phosphate,the flame retardancy and mechanical properties of EVA/Al（OH）₃@Al PO₄ have been relatively improved when the same amount is added.When the added amount is 55 wt%,the flame retardant reaches UL94-V1 level,and the elongation at break increases by 71%compared with EVA/Al（OH）₃.It shows that the existence of flower-like core-shell structure has a favorable lifting effect on mechanical properties and flame retardancy.（2）The SiO₂ layer was further coated on the surface of the multi-level flower structure AlPO₄ shell（denoted as Al（OH）₃@AlPO₄@SiO₂）and the standard spline was prepared by melt blending Al（OH）₃@AlPO₄@Si O₂ with EVA and tested for its mechanical properties and flameretardancy.ComparedwithAl（OH）₃@AlPO₄andphysicalmixturesof Al（OH）₃@AlPO₄ and SiO₂,the flame retardant performance of EVA/Al（OH）₃@AlPO₄@SiO₂has been obviously improved.When added amount is 55 wt%,the flame retardant performance reaches UL94-V0 level.This may be due to the fact that the silica cladding and aluminum hydroxide can better produce a synergistic flame retardant effect.（3）Finally,Considering there is better synergistic flame retardant effect between dodecylamine containing"nitrogen"source and phosphorus flame retardants（at the same time,dodecylamine,having long chain structure,can also be well compatible with EVA polymer chains）.Dodecylamine as surface modifier was used to modify the surface of Al（OH）₃@AlPO₄(Marked as Al（OH）₃@AlPO₄@C₁₂H₂₇N),And Al（OH）₃@AlPO₄@C₁₂H₂₇N was used as flame retardant additive for EVA.The results show that the mechanical properties can reach the standard of processing compared with Al（OH）₃@AlPO₄ and Al（OH）₃@AlPO₄@SiO₂,The elongation at break was 724.9%and the tensile strength was9.39 MPa when the added amount was 55 wt%,and the filling amount can be reduced to 54wt%to reach the V-0 level.