Preparation And Microstructure Of Polymer-based Nanocomposite

In this dissertation, the epoxy/rectorite and epoxy/montmorillonite nanocomposites were prepared successfully. The effects of clay content, epoxide equivalent and curing temperature on microstructure of the nanocomposites were studied by X-ray diffraction (XRD), infrared spectrometry and positron annihilation lifetime spectroscope (PALS), and the properties of the nanocomposite also were investigated. The main results are as follows.1. Nanocomposites with different rectorite content were prepared. At low contents, mechanical and thermal properties of the nanocomposites have significant improvements in terms of the impact strength, the breaking elongation and the glass transition temperature compared to the neat epoxy, and it is found that the rectorite with low content is easier to form exfoliation structure compared to that with high contents. FT-IR spectra showed that the reaction between the rectorite and epoxy matrix occurred, and at the same time, the PALS measurements indicate that the free-volume concentration in nanocomposites is decreased with the increase of the clay content and the size of free volume holes isn't affected by the clay content.2. The epoxy/rectorite nanocomposites with different epoxide equivalent ranged from 188g/mol to 1110g/mol were prepared. In nanocomposites, the formation of exfoliated structure was observed from XRD pattern at epoxide equivalent > 263. The PALS measurements indicate that the fraction of free volume holes in nanocomposites was strongly affected by epoxide equivalent, in paticular, the free-volume concentration was dramatically decreased with the increasing epoxide equivalent from 188 to 263. And the interface layer between epoxy and rectorite layers was formed and rapidly increased also from epoxide equivalent 188 to 263. The increased percentage of impact strength in nanocomposite compared with neat epoxy is bigger with the increase of epoxide equivalent , and this result can be explained as the proportion of exfoliated structure in epoxy matrix become higher with the increase of epoxide equivalent, and because exfoliated nanocomposites have higher phase homogeneity than the intercalated counterpart, the exfoliated structure is more desirable in enhancing the properties of the nanocomposites. The S parameter indicates the rectorite structure change and the high sensitivity of positron annihilation to the entry of rectorite into epoxy. The low momentum part of CDB ratios of the nanocomposite of epoxy 1110 can be ascribed to the contribution of the momentum of electrons in polymer, and the high momentum part can be ascribed to the contribution of the momentum of electrons in rectorite.3. The epoxy/rectorite nanocomposites at different curing tempeature ranged from 70°C to 200°C were prepared. We find that the formation of exfoliated structure is difficult when the curing temperature is low(<90°C). At the range from 90°C to 200°C, the clay in matrix can all be exfoliated . The nanocomposite cured at medium temperature possess highest storage modulus and high glass transition temperature . The PALS measurements show that the size of free volume holes isn't affected by curing temperature and the free-volume concentration was decreased with the increasing cure temperature. The positron lifetime distribution in nanocomposite has been obtained by the new computer program-MELT, and the results suggest that the distribution of free-volume-hole size is narrower when the composite is cured with medium temperature.4. The epoxy/rectorite nanocomposites and epoxy/ montmorillonite with different clay content were prepared. The rectorite is more easily exfoliated compared with montmorillonite. Only small amount of rectorite(<0.8%) can improve the mechanical and thermal properties of the nanocomposites, but in order to improve the properties of composite , higher montmorillonite content is needed(>2%). The size of free volume hole isn't affected by the two kinds of clay. Rectorite with higher surface area has more chances to interact with epoxy matrix, so it has stronger restriction on the motion of the molecule chain, which lead to smaller free volume concentration. Only small amount of rectorite(3.0%) can prevent the phase seperation.