In recent years, polymer nanocomposites have fascinated scientists, engineers and industrialists on the premise that the creation of new and more performing polymeric materials is possible by the combination of different building blocks with controlled dimensions at the nanoscale. Unfortunately, uniform dispersion of the hetero-phase domains within the plastic matrix or on its surface often fails due to the unfavorable thermodynamics, thus resulting in migration and irreversible aggregation phenomena. In-situ generation of a dispersed hetero-phase within the same polymer matrix or in its precursors increases the chances of achieving a better control of morphology by eliminating the often critical harvesting and re-dispersion steps in the manufacturing process. Strong interaction at the interface must be also provided to avoid aggregation and coarse phase-separation in usage.With this purpose, radiation grafting of a functional monomer onto polypropylene film has been applied to modify the molecular structure and properties of the otherwise chemically inert film. The radiation-grafted film has become permeable to the precursors of polymerization of a conducting polymer, namely polyaniline that can grow as a thin skin from its surface as well as an interpenetrated network into the film. Chemical attachment of the conducting polymer to the polyolefin has been demonstrated. The nanocomposite film shows an increase of electrical conductivity of several orders of magnitudes and amenability to be used as flexible electrode. In consideration of the well-known possibility of controlling the extent and depth of chemical modification of a substrate by radiation grafting, by tuning both system composition and irradiation conditions, this approach can enable a good degree of control of the morphology of the heterophase that forms on or within the substrate and thereby of the nanocomposite film.The recourse to suitable carriers, as chaperones of active molecules or nanoparticles into structurally different polymer matrices, is another possible strategy to obtain more uniform and stable dispersions. For this purpose, the possibility of obtaining colloidally stable micro-/nanoparticles from a partially degalactosylated xyloglucan (Deg-XG) has been investigated. 60Co γ-irradiation was applied to reduce the size of polymeric clusters in water. Irradiation was performed on the solid powder in air, up to a maximum dose of 60 kGy. FTIR and GPC analyses do not evidence any significant change of functional groups of the polymer and its average molecular weight, respectively. Deconvolution of GPC curves point to a change in the proportion between two main fractions of different molecular weight clusters, with a prevailing contribution of the lower over the higher MW clusters at the increase of the absorbed dose. Aqueous dispersions of the irradiated materials at low concentrations were characterized by dynamic light scattering measurements as function of the time and at different temperatures. For all systems an increase of scattered light intensity as function of the time at 37°C was observed. The fastest kinetics and the highest pseudo-plateau were shown by the 20 kGy irradiated system. Globular particles with 300-400 nm hydrodynamic diameters are formed. Their propensity to incorporate hydrophobic small guest molecules or high molecular weight biomolecules was assessed. The possibility of preparing optically transparent films from native xyloglucan incorporating these particles by solvent casting was demonstrated.
|Title of host publication||IAEA TECDOC SERIES: Radiation curing of composites for enhancing their features and utility in health care and industry|
|Number of pages||10|
|Publication status||Published - 2015|