Alfonso Maffezzoli

Synthesis of a novel cardanol-based benzoxazine monomer and environmentally sustainable production of polymers and bio-composites

A novel pre-polymer deriving from cardanol—a well known renewable organic resource and harmful by-product of the cashew industry—in combination with cellulose based materials (i.e. jute fibres) has been used to produce bio-composites having a high percentage of renewable materials. Cardanol and its derivatives are considered nowadays very attractive precursors to developing new materials from renewable bio-sources to use in eco-friendly processes. This paper deals with the synthesis and characterization of a novel cardanol based benzoxazine monomer used for the preparation of new bio-composites. The new cardanol-based benzoxazine was characterised by 1H and 13C NMR, FT-IR spectroscopies and LC mass spectrometry analysis, while a differential scanning calorimeter was used to study and monitor the polymerization process. Different bio-composites have been obtained by thermal cure of jute fibres impregnated with a cardanol based benzoxazine resin.

Degradation behaviour of a composite material for thermal protection systems Part I-Experimental characterization

Thermogravimetric studies and combined thermal analysis techniques have been used to characterize an ablative composite for thermal protection systems. The aim of the work was to utilize these techniques to obtain the main parameters used in the computer simulation of the space re-entry. In particular, a phenomenological model of the degradation kinetics of a silicon-based ablative composite has been developed using thermogravimetric analysis coupled with mass spectroscopic analysis. Simultaneous thermal analysis has also been used to calculate the ablation heat. The results are used as input for a computer model, developed in Part II, to enable calculation of the temperature profiles inside a thermal protection shield during the re-entry into the earths atmosphere. Such a program can also be used in materials selection.

Characterization of antibacterial silver coated yarns

Surface treatments of textile fibers and fabrics significantly increase their performances for specific biomedical applications. Nowadays, silver is the most used antibacterial agent with a number of advantages. Among them, it is worth to note the high degree of biocompatibility, an excellent resistance to sterilization conditions, antibacterial properties with respect to different bacteria associated with a long-term of antibacterial efficiency. However, there are only a few antibacterial fibres available, mainly synthetic with high production cost and limited effectiveness. Cotton yarns with antimicrobial properties are most suitable for wound healing applications and other medical treatments thanks to their excellent moisture absorbance while synthetic based fibres are most suitable for industrial applications such as automotive tapestry and air filters. The silver-coated fibers were developed applying an innovative and low cost silver deposition technique for natural and synthetic fibers or yarns. The structure and morphology of the silver nanoclusters on the fibers was observed by scanning electron microscopy (SEM), atomic force microscopy analysis (AFM) and XRD analysis, and quantitatively confirmed by thermogravimetric analysis (TGA) measurements. Good silver coating stability has been confirmed performing several industrial washing. Antimicrobial tests with Escherichia coli were performed.

The challenge of high-performance selective emitters for thermophotovoltaic applications

We present a brief survey of the most significant contributions to the study and the development of selective emitters for high-temperature applications. After a brief introduction and some necessary notes on definitions and experimental methods, this review presents the many different solutions proposed so far from the point of view of both the optimization of the functional properties of selective emitters and the fulfilment of the severe thermostructural requirements imposed by most high-temperature applications such as thermophotovoltaics.

Influence of crystal and amorphous phase morphology on hydrolytic degradation of PLLA subjected to different processing conditions

Isothermal and non-isothermal crystallization kinetics of poly-l-lactide (PLLA) were studied in order to analyse the effect of crystalline and amorphous morphology on hydrolytic degradation. A modification of the nucleation/growing mechanism was observed in both isothermal and non-isothermal analysis. Samples isothermally crystallized at Tc 110°C). The effect of hydrolytic degradation on the amorphous and crystalline phases depends upon the initial morphology developed during the isothermal crystallization. The larger crystals developed at Tc=130°C are more resistant to erosion compared to the less perfect and smaller crystals developed at higher levels of undercooling (Tc=90°C).

A model for the thermal and chemorheological behavior of thermoset processing: (II) Unsaturated polyester based composites

Abstract The rheological and thermokinetic aspects of the cure of unsaturated polyester based composites are analyzed by means of a computer program developed by using the heat transfer and heat generation characteristics of polymerizable systems. The temperature and extent of reaction profiles, calculated according to an appropriate kinetic and heat transfer model, have been used to predict the corresponding viscosities by an empirical model. A commercial polyester system commonly used in resin transfer molding. (RTM) has been characterized by differential scanning calorimetry (DSC) and dynamic viscosity measurements and the results have been processed to construct the corresponding sub-model. Experimental temperature profiles measured during the processing of the systems studied are compared with theoretical values obtained from the master model.

Monitoring Wood Degradation during Weathering by Cellulose Crystallinity

The degree of crystallinity of cellulose was used for assessing the degradation level of coated and uncoated samples of pine wood after weathering. X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy measured the changes in the surface crystallinity of cellulose resulting from weathering, both natural and artificial. Both techniques revealed an increase in the crystallinity index (CI) of cellulose when wood was subjected to weathering. An increase in the size of crystallites was also observed by XRD measurements. These results were related to the reduction of the amorphous fractions of wood, and, consequently, to the enrichment of the relative crystalline content. Thanks to FT-IR analysis, the degradation of hemicellulose was observed for uncoated samples after exposure to artificial weathering. The effect of weathering was less evident on coated samples because of the protective action of the coating. A good correlation between the crystallinity indexes obtained from FT-IR and XRD was found. The experimental results proved that the proposed method may be a very useful tool for a rapid and accurate estimation of the degradation level of wood exposed to weathering. This methodology can find application in the field of conservation and restoration of wooden objects or in the industry of wood coatings.

Use of steel fibres recovered from waste tyres as reinforcement in concrete: Pull-out behaviour, compressive and flexural strength

The increasing amount of waste tyres worldwide makes the disposition of tyres a relevant problem to be solved. In the last years over three million tons of waste tyres were generated in the EU states [ETRA, 2006. Tyre Technology International - Trends in Tyre Recycling. http://www.etra-eu.org]; most of them were disposed into landfills. Since the European Union Landfill Directive (EU Landfill, 1999) aims to significantly reduce the landfill disposal of waste tyres, the development of new markets for the tyres becomes fundamental. Recently some research has been devoted to the use of granulated rubber and steel fibres recovered from waste tyres in concrete. In particular, the concrete obtained by adding recycled steel fibres evidenced a satisfactory improvement of the fragile matrix, mostly in terms of toughness and post-cracking behaviour. As a consequence RSFRC (recycled steel fibres reinforced concrete) appears a promising candidate for both structural and non-structural applications. Within this context a research project was undertaken at the University of Salento (Italy) aiming to investigate the mechanical behaviour of concrete reinforced with RSF (recycled steel fibres) recovered from waste tyres by a mechanical process. In the present paper results obtained by the experimental work performed up to now are reported. In order to evaluate the concrete-fibres bond characteristics and to determine the critical fibre length, pull-out tests were initially carried out. Furthermore compressive strength of concrete was evaluated for different volume ratios of added RSF and flexural tests were performed to analyze the post-cracking behaviour of RSFRC. For comparison purposes, samples reinforced with industrial steel fibres (ISF) were also considered. Satisfactory results were obtained regarding the bond between recycled steel fibres and concrete; on the other hand compressive strength of concrete seems unaffected by the presence of fibres despite their irregular geometric properties. Finally, flexural tests furnished in some cases results comparable to those obtained when using ISF as concerns the post-cracking behaviour.

The principles of dielectric measurements for in situ monitoring of composite processing

Abstract The fundamental concepts of dielectric behavior of polymers and the utilization of dielectric measurements for in situ monitoring of cure of polymers and composites are discussed. Information is presented on currently used dielectric sensors and the procedure for calculation of dielectric parameters from the monitored signal. The review is written to accommodate both the fundamental and the pragmatic aspects of dielectric monitoring of cure. In the final part of the review, a critical assessment is offered of the advantages and disadvantages of dielectric measurements for the in situ monitoring of processing of polymers and composites.

Photopolymerization of dental composite matrices

The kinetic behaviour of dental composite is traditionally studied, considering only the isothermal behaviour, whereas a fast and highly non-isothermal bulk polymerization is expected as a consequence of the significant heat developed due to the exothermic nature of the polymerization reaction. In this paper the photopolymerization kinetics of a commercial dental composite activated by visible light are analysed by differential scanning calorimetry. This technique is applied to determine the degree of reaction and the glass transition temperature of thin layers of the composite matrix, at different isothermal cure temperatures. A phenomenological kinetic model is then integrated with an energy balance in order to analyse the cure behaviour of thicker composite layers. The full model results indicate that non-isothermal cure conditions may be achieved, obtaining higher values for the glass transition temperature and the degree of reaction.