József Hári

Competitive interactions and controlled release of a natural antioxidant from halloysite nanotubes

Halloysite nanotubes used as potential carrier material for a controlled release stabilizer in polyethylene were thoroughly characterized with several techniques including the measurement of specific surface area, pore volume and surface energy. The high surface energy of the halloysite results in the strong bonding of the additive to the surface. Dissolution experiments carried out with eight different solvents for the determination of the effect of solvent characteristics on the amount of irreversibly bonded quercetin proved that adsorption and dissolution depend on competitive interactions prevailing in the system. Solvents with low polarity dissolve only surplus quercetin adsorbed in multilayers. Polyethylene is a very apolar polymer forming weak interactions with every substance; quercetin dissolves into it from the halloysite surface only above a critical surface coverage. Stabilization experiments confirmed that strong adhesion prevents dissolution and results in limited stabilization efficiency. At larger adsorbed amounts better stability and extended effect were measured indicating dissolution and controlled release.

Nanocomposites: Preparation, Structure, and Properties

Publisher Summary The general idea of nanocomposites is based on the concept of creating a very large interface between the nanosized-building blocks and the polymer matrix. The main problems of nanocomposites are usually the homogeneous distribution of the particles in the polymer matrix and interfacial interactions. Compared to the basic idea behind nanocomposites, interfacial interactions are treated rather superficially the available information is limited and very often contradictory. Very little unambiguous information exists about the relationships among the interaction of a coated nanoparticle surface, the size and characteristics of the available uncoated area, the strength of interfacial adhesion, and the macroscopic properties of the nanocomposites. The main purpose of this chapter is to overcome issues. Nanocomposites can be classified in many ways; in this chapter they are classified according to the dimensionality of the nanosized heterogeneity. The size is in the nanometer range in all three dimensions for particles like silica (SiO2), titanium dioxide (TiO2), calcium carbonate (CaCO3), or polyhedral oligomeric silsesquioxane (POSS); nanotubes and fibers are small in two dimensions but can be micrometer long; while the individual platelets of layered silicates are approximately 1 nm thick, their other two dimensions are usually much larger.