A. Valenza

Characterization of a new natural fiber from Arundo donax L. as potential reinforcement of polymer composites

The aim of this paper is to study the possibility of using of Arundo donax L. fibers as reinforcement in polymer composites. The fibers are extracted from the outer part of the stem of the plant, which widely grows in Mediterranean area and is diffused all around the world. To use these lignocellulosic fibers as reinforcement in polymer composites, it is necessary to investigate their microstructure, chemical composition and mechanical properties. Therefore, the morphology of A. donax L. fibers was investigated through electron microscopy, the thermal behavior through thermogravimetric analysis and the real density through a helium pycnometer. The chemical composition of the natural fibers in terms of cellulose, hemicellulose, lignin, and ash contents was determinated by using standard test methods. The mechanical characterization was carried out through single fiber tensile tests and a reliability analysis of the experimental data was performed. Furthermore, a mathematical model was applied to investigate the relation between the transverse dimension of the fibers and the mechanical properties.

Mechanical behavior of carbon/flax hybrid composites for structural applications

In this work, the influence of an unidirectional carbon fabric layer on the mechanical performances of bidirectional flax fabric/epoxy composites used for structural applications was studied. Two different bidirectional flax fabrics were used to produce flax fabric reinforced plastic (FFRP) laminates by a vacuum bagging process: one is normally used to make curtains; the other, heavier and more expensive than the previous one, is usually used as reinforcement in composite structures. In order to realize hybrid structures starting from FFRP, an unidirectional UHM carbon fabric was used to replace a bidirectional flax fabric. Tensile and three-point bending tests were performed to evaluate the mechanical properties of the laminates investigated (both FFRP and hybrids). Furthermore, the mechanical behavior of the different bidirectional flax fabrics was analyzed by carrying out tensile tests. The experimental tests showed that the structures reinforced with flax fabrics, normally used to make curtains, present better flexural properties than that of others while, in tensile configuration, these last show higher modulus and strength. Moreover, both FFRP laminates show low mechanical properties, which do not allow their use in structural applications while the presence of one external layer of unidirectional carbon involves remarkable increase in their properties. According to this study, the hybrid composites realized could be used in several structural applications (i.e., nautical and automotive).

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.

Relationships between mechanical properties and structure for blends of nylon-6 with a liquid crystal polymer

Abstract Mechanical properties of blends of nylon-6 with a liquid crystal copolyesteramide (LCP) are presented. The improvement of the elastic modulus increases with increasing the draw ratio. Fibrils of LCP are evident when the draw ratio >40. The moduli are lower than those predicted by the theory of short-fibre oriented composites probably because of poor adhesion between the two phases and to incomplete fibrilation of the LCP particles.

Shear viscosity of polybutyleneterephthalate/liquid crystal polymer blends

Viscosity measurements have been carried out on blends of polybuty-leneterephthalate (PBT) and a liquid crystalline copolyesteramide (LCP). The flow curves of the blends with LCP content larger than 20%, show a behavior similar to that of the pure LCP, with a rapid rise of the viscosity at low shear rates. The viscosity-composition curves exhibit a deep minimum at low LCP content which may be mainly attributed to the lack of interactions between the two phases.

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.

Mechanical properties-structure relationships for immiscible blends of low density polyethylene with nylon-6

Abstract Data on mechanical properties of blends of low density polyethylene with nylon-6 as a function of the composition are presented. They suggest that these blends are immiscible in the solid state. However both a theoretical model and scanning electron microscopy seem to indicate some degree of interaction at high content of nylon.

CHARACTERIZATION OF BLENDS OF POLYPROPYLENE WITH A SEMIRIGID LIQUID-CRYSTAL COPOLYESTER

Abstract Blends with a liquid-crystal polymers (LCP) as one component show, in general, very interesting properties. Reduction of shear viscosity and improvement of mechanical properties are very remarkable. High melting temperatures and high costs of the LCP limit the use of these blends. A new class of thermotropic LCPs with flexible spaces, with relatively low melting temperatures, can overcome the first problem. In this work, rheological and mechanical properties of blends of polypropylene with low contents of this LCP are presented. Torque during extrusion and viscosity decrease with LCP content. Elastic modulus is remarkably increased when the LCP phase is oriented.

Recycling of polymer waste: Part II—Stress degraded polypropylene

Abstract Rheological and mechanical properties of blends of polypropylene and degraded polypropylene have been studied. Both properties, and particularly the elongation at break, depend on the composition and on the extent of degradation. The unusual behaviour of the elongation at break is correlated with crystalline phase segregation which appears with decreasing molecular weight of the degraded component.