Preparation,Thermal Stability And Flame Retardant Mechanism Of Novel Polymer/hydroxide Nanocomposites

Polymer/hydroxide nanocomposites is a novel type of advanced composites, which has become the focus of research in recent years because of their demonstrated excellent mechanical,thermal and gas barrier properties compared with their conventional counterparts due to the combinations of the rigidity,dimensional and thermal stability of inorganic component with the toughness, processing and dielectric of polymer.The latest progress in the field of nanocomposites based on one-dimensional and two-dimensional inorganic was reviewed in this dissertation based on the recent literatures.In this thesis, several typical polymer/hydroxide nanocomposites were prepared and characterized by different approaches based on the synthesis and properly modification of hydroxides. Then, the relationships between structure and properties, especially thermal stability and flammability properties of the nanocomposites, using both thermogravimetric (TG) analysis and cone calorimetry experiment, were discussed in detail. The kinetics of the thermal and thermo-oxidative degradation of the nanocomposites were studied, which suggested that besides a charring barrier mechanism of carbonaceous char formation as an insulator to the heat and a mass transport barrier during the combustion of the nanocomposites, there is an active mechanism from the increase of the effective activation energy of the degradation acting as an effect of energy barrier of the process. In general, it was revealed that the influence of preparation on the structure of the nanocomposites resulted in differentia in thermal and flammability properties. It is very important that the preparation procedure should be optimized to obtain the polymer nanocomposites with comprehensive excellent properties.In summary, this dissertation is composed of four parts as follows:Firstly, layered double hydroxide with a high content of hydroxyl groups was prepared by ion-exchange method and organically modified with Dodecyl Sulfate Sodium(DS). Poly(methylmethacrylate) (PMMA)/MgFe-LDH nanocomposites were prepared via in-situ polymerization method. Though the XRD and TEM, the PMMA/LDH nanocomposites were partially interacted and partially exfoliated. The participation of Fe³⁺ ion was found to play an important role in improvement of thermal stability of nanocomposites with small inorganic loading and well-dispersed inorganic components. The thermal degradation mechanism was discussed by microscopic kinetic analysis. This indicated that the naocomposites also possessed an action mechanism of the effect of a charring insulator barrier and the effect of an energy barrier in the combustion behavior of the nanocomposites.Secondly, the flammability and mechanics properties of three series of EVA/MH/LDH nanocomposites as well as the flame retardant synergistic effect between LDH and the conventional flame retardant additive MH were investigated by cone calorimetry and dynamic mechanics analysis.The results demonstrated that the heat release rate (HRR) of the nanocomposites, in particular, their peak HRR value, has a more obvious decrease than that of comparative sample. In addition to the effect of an insulator barrier as other inorganic compounds such as clay, LDH may promote the formation of the carbonaceous char due to the abundant hydroxyl groups between its interlayer. It means that the combustion properties of the nanocomposites were reduced, which may lessen the fire hazard of the materials in use.Thirdly, a novel multicomponent nanoribbon have been synthesized in our group by mixing zinc acetate and hydrazine solution at low temperature. The nanoribbon with abundant functional groups on the surface of ribbons have been prone to interact to groups of polymers.PVA/nanoribbon nanocomposites were prepared by solution blending. All nanocomposites as-prepared were characterized by XRD, TEM, SEM, TG and UV-VIS.All nanocomposites have retained favourable transparence, even the content is up to 11.8%.The char process have possible been promoted by zinc nanoribbons, which also were verified by analysis of char morphology.PMMA/nanoribbon nanocomposites were prepared by free radical polymerization. Experimental results showed that inorganic nanoribbons were uniformly distributed in and bonded to the PMMA host matrix without macroscopic organic-inorganic phase separation. It was found that the thermal stability and glass transition temperature (Tg) of the nanocomposite films increased effectively with increasing inorganic content at low content and remained above 1wt% inorganic content. These results suggest the network formation because of the strong interaction between the inorganic nanoribbons and the polymer matrix, which induces the mobility restriction of polymer chains. The characteristics of the 1-dimensional inorganic nanoribbons we used here may play a key role in the formation of the "cross-link" networks and in the decision of the lower content of inorganic nanoribbon additive.Fourthly, Lanthanide hydroxide nanowires were synthesized by hydrothermal method, a series of characterizations were used to study the structure,morphology and degradation details of nanowires. Poly(methylmethacrylate)/La(OH)₃ nanocomposites were prepared via in-situ polymerization method. Experimental results showed that inorganic nanowires were uniformly distributed in the PMMA host matrix without macroscopic organic-inorganic phase separation and the thermal stability of nanocomposites have remarkably improved. Microscopic kinetic analysis verified the effect of an energy barrier of nanowires in the polymer martix.