G. Spadaro

Influence of the irradiation parameters on the molecular modifications of an isotactic polypropylene gamma-irradiated under vacuum

Isotactic polypropylene was irradiated under vacuum in a complete set of experimental conditions. The influence of the irradiation parameters, total absorbed dose, D, and dose rate, I, was analysed in order to verify the theoretical predictions of a simple kinetic model, already presented (Sarcinelli L, Valenza A, Spadaro G. Polymer 1997;38:2307), based on the rates of the main reactions occurring during irradiation, i.e. β-scission, addition to double bonds and termination. The concentration of free radicals and double bonds formed during irradiation is detected together with a comparison to their dependence on the irradiation parameters. A quantitative determination of the “inversion curve”, forecasted by the model, i.e. an implicit function of D and I, which gives the dose values enhancing chain branching and molecular weight increase at fixed dose rate and vice versa, was also performed.

Influence of morphology and chemical structure on the inverse response of polypropylene to gamma radiation under vacuum

Abstract In this work the influence of the chemical structure and of the morphology on the gamma-radiation effects on polypropylene based polymers is studied on the basis of a previously discussed kinetic model [1] . For this aim an isotactic polypropylene and a random ethylene–propylene copolymer were irradiated under vacuum at one dose rate and several absorbed doses after well defined solidification conditions. We show that the model is reliable varying both the chemical structure and the morphology of the polypropylene based polymer. An inversion of the response of the material to gamma radiation under vacuum is always observed, and the inversion conditions depend on the irradiation parameters. In particular at a fixed dose rate we check an absorbed dose, depending on the ethylene and mesomorphic phase content in the polymer, in correspondence of which a significant change in the molecular response to gamma irradiation occurs.

Blends of polyamide 6 and linear low density polyethylene functionalized with methacrylic acid derivatives

Abstract Morphological, calorimetric, rheological, dielectric and mechanical behaviour of blends made with polyamide 6 (PA6) and linear low density polyethylene (PE) are presented. The PE was functionalized grafting ester and alcohol groups in a Brabender mixer with methacrylic acid derivatives. These groups induce “compatibilization” effects in the blends with respect to blends made with the unfunctionalized polyethylene. The difference effects on the behaviour of the blends of the various functional groups are shown. In particular, the interactions at the interface change depending on the chemical nature of the grafted groups. Ethyl and isobuthyl-methacrylate essentially cause dipolar interactions and hydrogen bonding whereas hydroxyethyl-methacrylate gives rise to condensation reactions with the functional groups of polyamide. This last blend presents the highest increase of the elongation at break.

Cytarabine release from α,β-poly(N-hydroxyethyl)-dl-aspartamide matrices cross-linked through γ-radiation

Abstract α,β-poly( N -hydroxyethyl)- dl -aspartamide solutions were cross-linked through γ-radiation and the systems obtained were tested as matrices for drug sustained release, using cytarabine as model drug. We performed the characterization of the cross-linked polymer, both drug-loaded and unloaded, through water swelling measurements, scanning electron microscopy and X-ray analysis. Finally, we investigated the in vitro release behaviour of cytarabine.

Physical and structural characterization of blends made with polyamide 6 and gamma-irradiated polyethylenes

Abstract Morphological, calorimetric and rheological results of blends made with polyamide 6 and polyethylene gamma irradiated in air are presented. The polar oxidized groups grafted in the poliolefin chains through gamma-radiation induce “compatibilization” effects in the blends with a more uniform and finer distribution of the polyethylene “phase” in the polyamide matrix, with respect to blends made with the unirradiated polymer. This effect, observed with polyethylenes of different molecular structure, i.e. low density, linear low density and high density, was attributed to the presence of interactions among the functional oxidized groups of the polyethylene chains and the polyamide. Tests done at different mixing times indicate that short times are enough to allow these interaction to occur.

Inverse response of polypropylene to gamma radiation under vacuum

Abstract The effect of gamma radiation under vacuum on polypropylene is analysed on the basis of a simple kinetic model. The influence of the irradiation parameters, total absorbed dose and dose rate, on the rates of the main reactions occurring during irradiation, i.e. β-scission, addition to double bonds and termination, is studied. Using kinetic equations, and free radical and double bond balance relationships, we show that it is possible to rationalize the response of polypropylene to gamma radiation. In particular, on the basis of the mathematical solutions of these equations, we obtain the equation of an ‘inversion curve’, implicit function of the irradiation parameters, which gives the dose values enhancing chain branching and molecular weight increase at fixed dose rate and vice versa. These ‘inversion conditions’ are also found experimentally analysing the rheological behaviour of a commercial polypropylene irradiated under vacuum.

Tensile properties of γ-irradiated LDPE-iPP blends

Abstract Low density polyethylene-isolatic polypropylene have been irradiated in vacuum in the dose range 0–150 Mrad. The structural modifications induced by irradiation were the subject of a previous work. Tensile tests have been performed on the same materials and the results are here discussed in the light of their physico-chemical properties.

Physico-chemical properties of γ-irradiated LDPE-iPP blends

Abstract Low density polyethylene-isotactic polypropylene blends have been irradiated in the dose range 0–150 Mrad. Structural modifications have been investigated by means of solubility, calorimetric and density measurements. Slight interactions between the effect of irradiation and the effect of blending have been observed for the blends containing small amounts of one component.

Dielectric behaviour of LLDPE/PC blends

Dielectric characterization of blends of linear low density polyethylene (LLDPE) with bisphenol-A polycarbonate (PC) is presented. The obtained results show that these measurements are a useful tool to obtain information about the structure of incompatible systems. In particular the experimental data are discussed in relation to the prediction of a statistical mixture type equation and specific rheological, thermal and morphological results are also included.

Synthesis and characterization of water-swellable?,?-polyasparthydrazide derivatives: II. Hydrogels at low crosslinking degree as potential systems for anticancer drug release

Abstractα, β-polyasparthydrazide (PAHy) was crosslinked by glutaraldehyde to form water-swellable materials possessing a three-dimensional molecular network. Different crosslinking degrees were prepared varying glutaraldehyde/PAHy ratio and samples containing 5-fluorouracil were obtained by incorporating the drug into the polymer networks during the crosslinking reaction. All samples were characterized by swelling tests, thermal, x-ray and SEM analysis. Their microstructure was observed through scanning electron microscopy. Furthermore, for samples containing the anticancer drug,in vitro release studies were performed in pH 7.4 buffer solution.