Cork-based composites: studies on binder replacement and incorporation of biomass-derived additives
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resumo
The 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.
