Showing papers by "María José Abad published in 2014"

Effect of carbon nanotube type and functionalization on the electrical, thermal, mechanical and electromechanical properties of carbon nanotube/styrene–butadiene–styrene composites for large strain sensor applications

Abstract: Thermoplastic elastomer tri-block copolymer, namely styrene–butadiene–styrene (SBS) composites filled with carbon nanotubes (CNT) are characterized with the main goal of obtaining electro-mechanical composites suitable for large deformation sensor applications. CNT/SBS composites with different filler contents and filler functionalizations are studied by morphological, thermal, mechanical and electrical analyses. It is shown that the different dispersion levels of CNT in the SBS matrix are achieved for pristine or functionalized CNT with strong influence in the electrical properties of the composites. In particular covalently functionalized CNTs show percolation thresholds higher than 8 weight percentage (wt%) whereas pristine CNT show percolation threshold smaller than 1 wt%. On the other hand, CNT functionalization does not alter the conduction mechanism which is related to hopping between the CNT for concentrations higher than the percolation threshold. Pristine single and multiwall CNT within the SBS matrix allow the preparation of composites with electro-mechanical properties appropriate for strain sensors for deformations up to 5% of strain, the gauge factor varying between 2 and 8. Composites close to the percolation threshold show larger values of the gauge factor.

Fracture and thermal behaviour of biomass ash polypropylene composites

Abstract: In this work, the fracture and thermal behaviour of environmentally friendly composites based on polypropylene (PP), an olefin block copolymer (OBC) and ash from biomass combustion was investigated. PP/OBC/ash composites with different ash contents and 10 wt% OBC were prepared by extrusion followed by compression moulding. Ash particles were treated with a silane coupling agent before blending to promote interfacial adhesion between polymer matrix, OBC and ash. An approach to fracture mechanics was investigated and showed that the fracture parameters increased when OBC was used. Fracture surface analysis by scanning electron microscope revealed that the presence of OBC promotes the material ductile failure and that one of the main failure mechanisms was fibrillised debonding of ash particles encapsulated by OBC from the matrix and its subsequent elongation around them. Free OBC inclusions distributed within the PP matrix would have also induced toughening in the composites investigated. The crystalline st...

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

Abstract: 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

Abstract: 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.