Synthesis Of Poly(methyl Methacrylate)/phosphate And Titanate Nanocomposites And Study On Thermal Stability

Compared with conventional materials, polymer/inorganic compoundnanocomposites is becoming the focus of research. They have excellent propertiessuch as high thermal stability and gas barrier properties due to the combination of therigidity, dimensional and thermal stability of inorganic component with the processingand toughness of polymer. In order to improve the thermal stability of poly(methylmethacrylate) (PMMA), different phosphates and titanate with the hydroxyl groupwere synthesized and incorporated into PMMA with in situ polymerization in thisthesis. The relationships between structures and thermal properties of PMMAcomposites were investigated. It is looking forward to providing experimentalevidence for further investigation of PMMA/inorganic compounds. The detailedoutlines are elaborated as follows:1. The well-crystallized and uniformed hydroxyapatite nanorods (HANR) wereprepared by hydrothermal treatment and then incorporated into PMMA by in-situpolymerization of methyl methacrylate (MMA). The nanorods are well-dispersed inthe matrix and have good interfacial adhesion with PMMA. It is found that thethermal stability and combustion performance of the composites improve effectivelywith enough loading of HANR, and the amount of residues is increased. Experimentalresults show that graphitized carbon is generated after thermal degradation of thecomposites. It is proposed that HANR retards the free radical depolymerization ofPMMA, and then the partial-depolymerized PMMA forms graphitized carbon. Thegeneration of graphitized carbon and the good interfacial interaction between HANRand the matrix lead to a stable, compact and continuous char. The carbonizationbehavior of HANR in PMMA matrix leads to inhibition of heat spreading and theimproved thermal properties.2. Short titanate nanotubes were synthesized with optimized hydrothermaltreatment of anatase titanium dioxide. The obtained nanotubes with abundanthydroxide groups are uniform and clear. It can be dehydrated into anatase titaniumdioxide nanotubes easily at high temperature. The well-dispersed composites wereprepared with incorporating synthesized nanotubes into PMMA by in-situpolymerization of MMA. Thermal properties and the evolved gasified products of thecomposites during thermal degradation were investigated. Experimental results indicate that the thermal stability of the composites was enhanced significantly with aproper amount of nanotube loadings. The glass transition temperatures of thecomposites with proper loadings increase greatly, which indicates the mobilityrestriction of polymer chains. It is demonstrated that the constructed network isformed in polymer and lead to the improved thermal properties. Besides, carbondioxide generated during thermal degradation, and the amount of evolved gasifiedproducts is reduced significantly. It is possibly due to the absorption effect ofnanotubes, which can reduce the generated free-radicals during pyrolysis and inhibitthe depolymerization of PMMA. It is beneficial to the inhibition of thermal spreading.3. The zinc phosphate nanorod clusters were prepared by hydrothermal treatment.Amorphous zinc phosphate hydrate and other transitional zinc phosphate compoundsare obtained by adjusting the condition of hydrothermal treatment and incorporatingpolyvinylpyrrolidone. According to the analysis of the compound, the mechanism ofthe crystal growth is proposed. It is believed that the formation of the one-dimensionalnanorods is due to the directional aggregation of zinc phosphate hydrate microcrystals.The amorphous zinc phosphate dihydrate (ZnP-D) was incorporated into PMMAmatrix by in situ polymerization. The inorganic loadings are well-dispersed in thematrix. The thermal analysis shows that the thermal stability of PMMA/ZnP-Dcomposite is improved effectively with a little loading of ZnP-D, and increases withthe increasing inorganic loading.