Study On The Design,synthesis And Flame Retardancy Of Layered Double Hydroxides Intercalated By Organic Acid Anion

Chinese magnesium resource,especially the magnesium chloride in salt lakes,was in abundant reserve with a low cost.Exploration of high value magnesium-based multifunctional materials manufactured from magnesium chloride,not only has a perspective application potential in various fields,but also can serve as the driving force for integrated utilization of Qinghai magnesium resource at the same time.As a multifunctional layered material which can be easily synthesized and have properties of adjustability for both ions in the hydroxides layer and anions in the layer interval,layered double hydroxides(LDHs)have drawn too much attention from all over the world on the design and synthesis of LDHs oriented by function and application.Organic polymers are now essential materials applied in normal lives and industry and possess different excellent properties,but most of them are flammable in air due to their high carbon composition and have hidden fire peril during the application,which may release toxic smoke and gases during the combustion and commit heavily lives and wealth loss.The flame retardancy modification for organic polymers then become absolutely essential.Even the inorganic hydroxides can realize good smoke and flame retardancy as fillers,the high filling to realize the required flame retardancy rank will lead to a bad fabrication property and a big decreasing in the mechanical properties like tensile strength due the bad compatibility between organic and inorganic phases.Thus,it becomes a key point for changing this situation to realize the mechanical properties conservation at high filling or the high flame retardancy at low filling of the magnesium-based materials.In order to solve the problems mentioned above,three kinds of LDHs were designed and mainly synthesized by coprecipitation with the raw materials of magnesium chloride and aluminum chloride.The first kind LDHs intercalated by cinnamic acid anion(CAa),fumaric acid anion(FAa)and sorbic acid anion(SAa)was designed for the high filling carbon chain polymers(taking polymethyl methacrylate,PMMA as an example),and was named as CLDHs,FLDHs and SLDHs respectively.The second intercalated by gluconic acid anion(GAa)and lactic acid(LAa)anion was for the heterochain polymers(taking epoxy resin,EP as an example),and was named as GLDHs and LLDHs.The third intercalated by diphenyl phosphoric acid anion(DPAa)and phenyl phosphoric acid anion(PPAa)was for realizing high flame retardancy with low filling.The properties such as structural characteristics,formation regulations and flame retardancy were systemic investigated by X-ray diffractions(XRD),Fourier transform infrared spectroscopy(FTIR),scanning electron microscope(SEM),thermogravimetric analysis(TGA),transmission electron microscope(TEM),limit oxygen index meter(LOI),horizon and vertical burning tester,cone calorimeter tests(CCT)and thermogravimetry-mass spectrum analyzer(TG-MS).The main results were as follows.(1)The structures and the Gibbs free energy changes of their related thermodynamical reactions were calculated by density functional methods(DFT).CAa,FAa and SAa can have addition reactions with ethylene and hydrogen radical,and they all can happened spontaneously,suggesting that the LDHs intercalated by them may react with the polymer matrixes with double bonds and realize mechanical reinforcement or strength conservation by the strengthened interfacial interaction between LDHs and polymer matrix.GAa and LAa can form hydrogen bonding with the model molecule isopropanol,meaning that the LDHs intercalated by them can easily interact with groups in polymers to form hydrogen bonding to realized mechanical reinforcement or strength conservation.The decomposition reactions of DPAa and PPAa suggested that it is easier for DPAa to form phosphoric oxides radical comparing with PPAa,and the hydrogen radical released by PPAa was absolutely more reactive,making it may exacerbate the combustion to some extent despite its carbon formation ability.Based on the layer thickness,anion sizes and their electrostatic potential,the possible intercalating structures and the basal distances of the LDHs intercalated by the seven organic anions were theoretically predicted.(2)Based on the structures and basal distance predicted by theoretical calculation,LDHs intercalated by CAa,FAa and SAa with a Mg/Al ratio of 2 were successfully synthesized via precipitation,and the interlayer distance 18.070 ?,11.79 ? and17.698 ? respectively were well consisted with the theoretical proposed ones.XRD patterns of the three LDHs showed that the LDHs intercalated by chloride formed at first and then were anion exchanged by the organic acid anions.The main conditions affecting the successful formation of the LDHs were feeding style,the molar ration of organic anions and aluminum ions,the aging time and the Mg/Al molar ratio.The feeding rate,magnesium and alkali concentrations seem to impact not too much.The flame retardancy tests demonstrated that the flame retardancy of the three LDHs followed the sequence CLDHs > FLDHs > SLDHs,which is in paralleled with their carbonization abilities,and comparing with aluminum hydroxides,all the LDHs can keep more tensile strength of the composites,and the conservation abilities followed the sequence of CLDHs > FLDHs > SLDHs.(3)The LDHs intercalated by GAa can have different basal distance depending on the Mg/Al ratio,which was actually in consistent with the theoretical prediction.The LDHs with a Mg/Al ratio of 2 has a basal distance of 14.3 ?,and it is 9.91 ?when the Mg/Al ratio was 3.The crystallization was not good and formed a bread peak in XRD pattern when the Mg/Al ratio was 2.No matter coprecipitation by chlorides or nitrides,the LDHs with the predicted interlayer distance cannot be synthesized,and anion exchange was finally involved.The results of characterization for EP composites filling with LDHs were as follows.When the addition amount of GLDHs with a Mg/Al ratio of 2 was 40 wt.%,the composites can reach UL-94 V-1rank,and 88% of the prime tensile strength can be conserved in composites,but the LDHs intercalated by LAa cannot realized any UL-94 rank and have a big decrease in the tensile strength.The limit oxygen index of GLDHs/EP composites was 29.8%,which is a little lower than that of LLDHs 31.3%.Both LDHs have little impacts on the DMA test comparing to the prime EP.When the addition content was 40 wt.%,both LDHs can decrease the heat release peak by 70% and the composites all performed excellent in the CCT test.(4)The successfully synthesized LDHs intercalated by DPAa and PPAa had the consistency interlayer distance 18.21 ? and 16.00 ? just as the prediction,but there always appeared a little aluminum hydroxide in the products due to the feeding style itself.The flame retardancy test showed 10 wt.% LDHs intercalated by of DPAa can decrease the peak of the heat release rate to some extent,can efficiently decrease the total heat release and total smoke production and performed good carbonization and flame retardancy at the same time.Though the LDHs intercalated by PPAa can also decrease the total heat release and total smoke production to some extent,it increased the peak of the heat release rate unexpectedly,which means that it may exacerbate the combustion at the beginning.This phenomenon may have relationship with the release of the active radical during its decomposition,which is consistent with result of the theoretical analysis.TG-MS study on the decomposition of LDHs/EP composites showed that the LDHs intercalated by DPAa may perform better in both carbonization and flame retardancy,which effectively confirmed the theoretical analysis.All in all,the anticipated purpose of this dissertation was realized.The method for structural design and synthesis of LDHs intercalated by organic acid anions was constructed.Effect regulations of the key synthesis conditions on the structure of LDHs during the synthesis was discovered.The effects of LDHs intercalated by organic acid anion on the mechanical property and flame retardancy of the composites were identified.The study in this dissertation will definitely supply referential research inspiration and technical routes for the structural design and synthesis of magnesium-based LDHs,lay a theoretical guidance and foundation for the multifunctional composites containing LDHs,and expand the study orientations and application fields for the integrated utilization of magnesium hydroxides.