Preparation And Characterization Of Polymer/Inorganic Nanocomposites Via In Situ Emulsion Polymerization

Polymer/inorganic nanocomposites, maily polymer/montmorillonite (MMT), were prepared by an in-situ emulsion polymerization. The dispersion state of the inorganic particles, especially MMT layers, in the polymer matrix was characterized by XRD and TEM. Furthermore, the effect of MMT dispersion and the interaction between MMT and polymer matrix on the properties of nanocomposites were determined. The structure-property relationship between of the nanocomposites was established.Firstly, PS/MMT nanocomposites were prepared by an in-situ emulsion polymerization using the cationic surfactant of cetyl trimethylammonium bromide (CTAB) as an emulsifier. The results of XRD, FT-IR and TEM showed that polystyrene chains were intercalated into the galleries of MMT. The cationic surfactant CTAB acted not only as the emulsifier but also as an intercalated agent, facilitating the intercalation of polystyrene chains. The DSC curves indicated that the glass transition temperature of the nanocomposites was enhanced in some degree.In order to improve the exfoliation of MMT layers in the polymer matix and to determine the structure-property relationship of the nanocomposites, an inorganic clay (Na-MMT) and two types of organic clays (C₁₈-MMT and VC₁₈-MMT) were chosen in the emulsion polymerization to form the PS/MMT nanocomposites. The predispersion of the organic clays was realized via two methods. One was sonicating the suspension of the clay particles in styrene monomer. The other was sonicating the suspension of the clay particles in an emulsifier solution. The rheology of the clay suspensions was characterized by a rheometer to determine the dispersion state of the MMT layers. The structure of the final nanocomposites was characterized by XRD and TEM. The results indicated that the nanocomposite prepared using the inorganic clay was intercalated, while the nanocomposites prepared using the organic clays predispersed in styrene monomer were partiallyexfoliated and the nanocomposite prepared using the organic clays predispersed in the emulsifier solution were fully exfoliated. Compared to the method in which the organic clays were predispersed in the monomer, the method of the organic clay predispersed in the emulsifier solution had the advantages of lower viscosity and better dispersion state.TGA curves showed that the stability of the polymer was dramatically enhanced by the addition of MMT. Due to the better exfoliation of MMT layers and the chemical link between the layers and polymer, the nanocomposites prepared with VCig-MMT had a thermal stability better than the naonocompoaites prepared with the inorganic clay and Cis-MMT. The dynamic mechanical analysis results showed that the storage modulus G' of the PS/MMT nanocomposites had different enhancement over that of the pure polymer, especially when temperature approached the glass transition temperature (Tg). Meanwhile, the change in the Tg of nanocomposites was different with various types of clay. PS/Na-MMT and PS/VC18-MMT nanocomposites had higher Tg than the pure polymer, while the Tg of PS/Cig-MMT did not change or was slightly lower than that of the pure polymer.The MMT-supported initiator was prepared by the exchange of Na+ and the cationic initiator 2,2'-azobis(isobutyl- lamidine hydrochloride)(AIBA). The clay-supported initiator was used to initiate the emulsion polymerization of styrene to prepare the PS/MMT nanocomposite. During the polymerization, the initiator intercalated in the galleries of MMT layers decomposed to produce radicals that initiated the polymerization of styrene. The decomposition of initiator also caused the exfoliation of MMT. In the final nanocomposites, Some MMT was exfoliated into individual layers and other existed mainly as nano-aggregates with a thickness of around 10²0nm. The results of extraction indicated that many PS chains were grafted on the MMT layers by chemical bonds.Styrene-butadiene rubber (SBR) hybrid nanocomposites were prepared via an in-situ emulsion polymerization using Na-MMT and Cis-MMT. The C18-MMT was predispersed in water with the assistance of emulsifier and then the emulsion polymerization occured in the presence of MMT to form the SBR/MMTnanocomposites. As a comparison, SBR/Cig-MMT nanocomposites were also prepared by a melt intercalation method. The characterization of nanocomposites structure demonstrated that the MMT layers were dispersed in the rubber matrix at a nanoscale and the nanocomposites had different microstructures. Moreover, the nanocomposite based on the organic MMT prepared by in situ emulsion polymerization had the smallest size of dispersion state. The effects of the inorganic and organic MMT on the vulcanization reaction of rubber were determined by a DSC method. The vulcanization curves showed that the existence of the organic MMT accelerated the vulcanization reaction but the activation energy was not changed. However, the vulcanization rate decreased and the sensitivity of reaction to temperature also decreased by the MMT layers, which resulted in a decrease of the apparent activation energy. The results of mechanical property measurements indicated that the physical properties of the rubber such as strength, anti-abrasion and anti-penetrability were dramatically enhanced for the existence of MMT. The nanocomposite based on Cig-MMT prepared by the in-situ emulsion polymerization had a maximal strength and anti-penetrability due to the better dispersion and compatibility. The Attapulgite (AT) and nano-SiC>2 were chosen as the typical inorganic nano-fillers to prepare SBR/AT and SBR/SiCh nanocomposites by an in-situ emulsion polymerization. The dispersion of nano-fillers in emulsion, rubber matrix and the effect of nano-filler on the mechanical properties of rubber were investigated. The modeling of the stress-stain curves showed that for the SBR/AT nanocomposites, the traditional composite theories could be used to predict the stress-strain curves and obtained preferable results. But for the SBR/SiO2 nanocomposites, the traditional theories couldn't work. The "chain group" theories gave satisfied results but the structure parameters should be further studied.