Studies On The Preparation,Microstructure And Properties Of Halloysite Nanotube/Polymer Latex Nanocomposite Films

This work is mainly concentrated on the film formation from polymer latex which is polymerized from microemulsion, Halloysite nanotube (HNT)/Polymer latex dispersions and the evaluation of the improvement, such as mechanical and thermal properties of the films. The first major topic is the development of methods for solving the cracking problem in latex films. The second important part is the evaluation of the nanocomposite films which are after different way of treatment and of improved properties.Commonly, there is a quandary in polymer film formation:soft polymer particles are needed for preventing films cracking when deform but hard films are expected afterwards for good mechanical properties. It was found that the intermixed layer between two Poly(Methyl methacrylate)(PMMA) particles, widened by increasing the drying temperature, would be helpful for preventing cracking even there are always stress fluctuations in drying polymer dispersions which easily cause the micro crack. The addition of n-Butyl acrylate (BA) is proposed as a method to decrease the hardness but to increase the critical cracking thickness of PMMA latex films. Our results show that the softer P(MMA-BA) latex particles of lower Tg lead to higher critical cracking thicknesses.Another method developed, different from adjusting the forming temperature and hardness of polymer by copolymer to improve the film formation, is the introduction of the Halloysite nanotube (HNT) which could naturally bridge the polymer particles together and form a physical cohesive connection between them. As showed in experiments, the intercalation of organic compounds would be favored when halloysite is hydrated. Theoretically HNTs can both sustain the stress of deformation based on and aid the concomitant interdiffusion of polymer particles during drying, resulted in higher critical thicknesses (up to nearly400%as higher). Thick, crack-free films were made from hard latex. It was found that the dispersion of HNT has a significant effect on the film formation from polymer latex. But here comes a problem. Halloysite nanotube, directly manufactured from the natural minerals and often hard to be refined during processing, will therefore be of a large range of size distribution in micro-scale and burden the polymer-HNT nanocomposites with the nanotube aggregation most of the time. From the observation by microscope, it can be concluded that even applied into the polymer latex which is much more viscous than water, Brownian motion still has a significant effect on the HNT dispersion in the latex. Stirring, high shear mixing, sonication and shaking pre-treatment of HNT suspensions with the help of the coagulant Polyethylene glycol (PEG1500) can sorting the HNTs and make them homogeneously disperse in the latex, and then improve the polymer films'properties at the end. Meanwhile, although after proper treatment, HNTs will still have the trend to cluster together in suspensions because of the strong Van der Waals interaction between tubes and their high specific surface area. As the experiments show that increasing the HNT content can help to decrease the cracking in HNT/PMMA and HNT/P(MMA-BA) nanocomposite films, in order to improve the surface quality of the films, it would be better to decrease the HNT bundles than simply lower the Halloysite content.At last, the nanocomposite films from the latex dispersions mixed with HNT are very white. This can make the materials a candidate of painting without Titania. In the moisture absorption test, polymer films show an increasing water mass fraction in equilibrium with the HNTs. This can also explain to some extent the strengthen mechanism, that is, Halloysite slower the drying of films to supply enough time for the deformation and alleviation of the strain during film formation. And interestingly, with the increasing solid content of HNT, films absorbing water become slower which represent a good moisture resistance.