Ana Ares

Effects of silane functionalization of alumina whiskers on high-density polyethylene composites

New polyethylene matrix and alumina whiskers composites have been designed in order to combine the processability of common thermoplastics with improved physical properties. This work analyzes the influence of the composite formulation on the morphological, rheological and thermal properties of the new materials. Concerning rheological properties, a significant increase in viscosity and storage modulus is observed for high alumina whiskers content. Furthermore, the whiskers were functionalized with silane coupling agent in order to improve compatibility with the matrix. Two surface treatments were used for comparison purposes, and Fourier transform infrared spectroscopy was applied for evaluating the chemical changes on the surface of whiskers. Pre-treatment with the silane coupling agent brought about beneficial changes in morphology and rheology, related with improved dispersion of whiskers and increased filler–matrix interface. Finally, the inclusion of only 5 wt.% filler, functionalized with 100 wt.% silane, increased the thermal stability of matrix around 37%.

Alumina Whisker Selection to Design Fiber-Reinforced Polyethylene Composites

New polyethylene composites with α-Al2O3 whiskers are produced using four fibers (unpurified, cleaned, ribbon-shaped and silica-coated) differing in their purification level or surface. The influence of different fibers on the morphological, thermal and rheological properties of composites is analyzed. The composites with the ribbon-shaped and the silica-coated whiskers show the most suitable morphology and the best rheological properties together with a lower cost. The nucleating action of these fibers increases the crystallization temperature and the crystallinity of polyethylene. The enhancement in degradation temperature and flexural parameters prove that both types of alumina whiskers produce a clear reinforcement in polyethylene matrix.

Barrier and physical properties of polypropylene/highbarrier ethylene vinyl alcohol copolymer blends compatibilized with a sodium ionomer

Abstract The aim of this work is to investigate the properties of the PP/EVOH films for their potential use in the packaging industry. Besides, the barrier properties, the mechanical parameters and the morphology of the PP/EVOH films have been studied as function of their composition and the processing technique used for their manufacture. In these applications, the package is frequently in contact with humidity environments and for this, it is necessary to know how environments with different humidity contents, affect the O2 permeability of the polymer material. For these reasons, the influence of the moisture in the values of permeability was evaluated too. The data showed that the oxygen transmission rate (O2TR) decreased with the amount of EVOH, and if the copolymer mass is maintained constant, the O2TR diminished with the quantity of the ionomer in the compositions. Besides, the films obtained by extrusion and following unidirectional stretching, presented better barrier properties to the oxygen molecules than the compression moulded films. When the ionomer is added to the compositions the permeability is reduced even for the films maintained in wet atmosphere. The micrographs obtained by SEM showed that the films have a biphasic structure, where the EVOH particles are dispersed in the PP matrix.