Browsing by Author "Nunes, Bernardo"
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- Cork-based composites: studies on binder replacement and incorporation of biomass-derived additivesPublication . Rafael, Helder Martins; Fernandes, Isabel P.; Nunes, Bernardo; Pinto, Vera; Ferreira, Maria José; Barreiro, M.F.; Rafael, Helder MartinsThe Portuguese footwear industry is an important economic sector once it is one of the most active national business areas. The investment made in the production of footwear with high technological performance, and high technical-scientific requirements, evidences the valorization of the footwear industry during the last years. In addition, the evolution of consumers' environmental awareness, allied to the demand for bio-products, is considered a challenge for this sector. Therefore, the development of novel composites, based on natural materials and by adopting green productive processes, represents an area of great interest. In fact, cork, the natural material selected for this application, has properties such as impermeability, good compressibility and resilience, as well as low density, being usually applied in the form of composites for the production of footwear components like shoe insoles and soles. Cork is the bark of a cork oak (Quercus suber L.), which is normally harvested every 9-12 years. Among the corkproducing countries, Portugal has the largest annual production, with around 100.000 tons, which represented 49.6% of the worldwide production in 2016. Traditionally, the cork agglomeration process uses a reactive polyurethane-based adhesive, which results on composites with low flexibility and poor water absorption/desorption characteristics, generating products with low comfort properties. In addition, this adhesive is based on toluene diisocyanate (TDI), which is classified as a high toxic compound, thus motivating its replacement by environmental friendly products. Herein, the use of green adhesives such as water-based polyurethanes dispersions can be envisaged. Furthermore, the low water absorption capacity of the generated composites is related to the hydrophobic character of the cork itself and the used binder, which results in low absorption of the sweat, promoting a sensation of discomfort when footwear incorporating these materials is used. Considering all the above mentioned, the present work is focused on the production of novel cork-based composites, where the traditionally used adhesive was replaced by commercial water-based polyurethane adhesives. In addition, the effect of incorporating residual biomasses on the water absorption/desorption properties will be tested.
- Development of new footwear materials within the extralight safe shoe projectPublication . Fernandes, Isabel P.; Rafael, Helder Martins; Fernandes, Albano M.; Nunes, Bernardo; Pinto, Vera; Ferreira, Maria José; Barreiro, M.F.At present, footwear is considered as one of the most internationalized sectors of the Portuguese industry, having a major importance for the national economy, as it is proved by 2017 economic data: 83.3 billion shoes pairs were exported, representing an average value of 1.96 billion euros. The remarkable progress of the footwear sector is strongly related with the investment in research and technological development made in the last years, along with an attentive surveillance of the market opportunities, which in its turns, allows the identification the latest consumer demands and of new business opportunities. One example of these novel tendencies is the actual society demand for lightweight and comfortable footwear, which prompted the development of ultralight (low-density) materials. Additionally, the evolution of consumers' environmental awareness, allied to the demand for bio-products, is considered a challenge for the footwear sector. Thus, both challenges motivated the development of new materials within the scope of the Extralight Safe Shoe project, namely ultralight microcellular polyurethanes and natural composite-based materials. In this context, the work performed was focused on: (i) the development of ultralight microcellular polyurethanes (PUs) with suitable properties for the production of midsoles for technical footwear, and (ii) the development of lighter and more flexible PU/cork composites for production of insoles.