Paulo J.R.O. Nóvoa

Magnetic nanocomposites obtained using high evaporation rate magnetic nanofluids

In this paper, we study the influence of the addition of small amounts of nanomagnetic fluids in resins, some specific properties of these fluids and the possibility to produce a new category of magnetisable nanocomposite materials. The research was focused on the compatibility between the various types of nanomagnetic fluids and resins. Samples were prepared varying the resins, carrier liquids and volume fraction of magnetic nanoparticles. The polymerisation process of nanocomposites was investigated under the influence of applied magnetic field. Results of investigations presented in this paper refer to the microstructure of the samples (optical and/or electronic microscopy), and to the mechanical properties corresponding to different preparation methods (three points bending test, elastic properties, gel time determination).

Low Velocity Impact of Thermosetting Composite Systems Modified with Rubber and Cork Powders

The increasing use of composite materials in technology applications over classic metallic materials, in particular where high specific mechanical properties are considered valuable, has drawn composite related research efforts towards sensitive features of composite materials, such as low-velocity impact phenomena. This paper describes a first attempt to enhance the toughness of carbon fibre/epoxy quasi-isotropic laminates, when subjected to low-velocity impact. The work consisted in introducing, cork powder or KratonTM rubber particle layers between specific laminate plies, to take advantage of the well known elastic properties and shock absorbing capacities of cork and rubber. The outer layers structure was also investigated considering the case of two unidirectional plies in a [0°, 90°] configuration, or single twill woven fabric ply. The impact resistance was evaluated by measuring the indentation depth after drop-weight low velocity impact tests. The all-unidirectional ply based laminate compositions give consistently better results. In general, interleaved powders had a positive contribution. In the sense of evaluating the influence of the toughening mechanisms in other properties, results of tensile tests and DMTA arc also be discussed. Analyzing the experimental results it is possible to say that interleaving seems to lead to encouraging results on the topic of CFRP laminates toughening.

Fire Reaction and Mechanical Performance Analyses of Polymer Concrete Materials Modified with Micro and Nano Alumina Particles

In the present study, fire reaction and mechanical behaviour improvements of an epoxy polymer mortar (PM) formulation, induced by binder modification with alumina particles at micro and nano-size levels, were analysed and quantified. For this purpose, several series of PM specimens, modified with different types of microparticles, nanoparticles and nanodispersion of aluminium oxide were manufactured and tested for fire reaction, flexural and compressive load carrying capacities. Obtained results were compared with those obtained for plain epoxy polymer mortars. Fire reaction properties, such as time to ignition, heat release rate, smoke extinction area, carbon monoxide and carbon dioxide yield rates were assessed by means of cone calorimeter test. Test results revealed that the addition of alumina particles to binder matrix of polymer mortars, even in small amounts (3.9 % in weight of total mass), are effective in improving flexural and compressive behaviours of resultant polymer mortars, especially in the case of alumina nanoparticles. However larger amounts of aluminium oxide nanoparticles will be required to attain effective levels of fire retardancy.

Dynamic Mechanical Thermal Analysis of Flame-Retardant Unsaturated Polyester Nanocomposites: The Effect of Aluminum Hydroxide (ATH) and Nanoclays

This work reports the effects of nanoclays and aluminium hydroxide (ATH) on the thermomechanical properties of an unsaturated polyester resin. Dynamic mechanical thermal analysis in the temperature range from 25 to 150 °C has indicated the formation of different structures for the different clay (1, 5 and 10 wt. %) and ATH loadings (50 and 100 wt. %) investigated. The rubbery modulus increases with nanoclay and ATH content which indicates that both nanoclays and ATH act positively on the final network density and consequently lead to systems showing higher stiffness at higher temperatures. The mechanical loss peak value decreases with either nanoclay or ATH content which seems to indicate that both nanoclays and ATH improve network density. The glass transition temperature and the mechanical loss peak value changes linearly with ATH content.

Mechanical Performance of Unsaturated Polyester Resins Modified with Powder from Scrap Tyre Rubber

Unsaturated polyester resins are extensively used in the automotive industry as matrix for polymer based composite materials, but have poor impact resistance. Toughness can be improved dispersing a softer phase in brittle polymers. Scrap tyres constitute a significant waste problem and are a low-cost source for rubber. The objective of this work is the mechanical characterization of matrix systems containing solid rubber particles obtained from scrap tyres. Several pre-treatments were tested based on contact time and temperature. The flexural and Charpy impact behaviour of the modified resins showed a decrease in performance. Dynamic mechanical tests did not result in clear evidence of phase mixing. Optical microscopy showed the presence of contaminant particles, which were considered the cause for the low performance. Among the modified resins, a positive shift in flexural behaviour occurred when pre-heating was used. It is thought the strategy may prove effective in enhancing resin toughness, if the waste rubber is purified prior to its utilization.

Polymer Composite Materials modified with Nano-Oxides and Phosphinates Hybrid Flame Retardant Systems

Unsaturated polyester based composites materials present several improved properties over conventional materials. However, these composites show great sensitivity to high temperatures and poor fire behaviour. In the present study, an effort is undertaken to develop new unsaturated polyester composites with improved fire reaction behaviour by matrix modification with hybrid flame retardant systems based on nanooxides and phosphinates. For this purpose, a series of composite formulations containing different contents and types of both metal oxide nano/micro particles and organic phosphinates were manufactured, with basis on the Taguchi L9 orthogonal array, and tested for fire reaction and mechanical properties. The data treatment was carried out through analyses of variance. Fire reaction properties were analysed and quantified by the vertical flammability test (UL-94), and the mechanical properties were studied by flexural, Shore D, and Charpy impact tests. The results were compared with those obtained for plain resin specimens. Test results revealed that the addition of hybrid flame retardant systems introduced reasonable improvements in at least one fire reaction property. However, it was verified that the filler addition led to a decrease in mechanical properties, probably due to poor matrix-filler adhesion. Further studies are required in order to improve the mix design formulations.