Cork: Sustainability and New Applications

Cork is a strategic material used in multiple applications and its use has accompanied mankind since the days of Ancient Egypt. The cork oak forests are extremely well adapted to the semi-arid regions of southern Europe and northern Africa (western Mediterranean). These forests help to prevent the advance of desertification, improve water penetration into the soil and hydrological regulation, promote soil conservation, and being the perfect habitat for many animal and vegetables species. Consequently, these forests promote biodiversity (Pereira, 2007; Gil, 2011, 2014). Save the cork forests, increasing the area and the quantity and quality of cork produced and develop new products with high added value are essential actions. The loss of the economic importance of the cork activity would lead to an uncertain future of cork oak forests, promoting biodiversity loss, land abandonment (social desertification), and also social imbalance. This could lead to the disappearance of one of the most sustainable industries based on forest products, beyond the environmental and nature problems created. One of the ways to decrease the amount of carbon dioxide in the atmosphere is the production of long-life products based on plant biomass, which include without doubt, cork products. Furthermore, these materials are “carbon neutral” at the time of decomposition or energy recovery. A very important aspect has to do with the increase in production due to cork extraction. This is caused by the need of the tree to be rapidly protected from the environment after the removal of its bark. This operation will serve as a stimulus to the production of new suberous material, particularly in the early years after the extraction. During the tree lifetime in operation, an average cork oak produces about four times more cork bark than the cork tree would produce if it were not subject to stripping. The sum of the various layers of cork produced and harvested is greater than the single layer of cork produced if there was no extraction during the life of a tree (Gil, 1998, 2011). Related to environmental aspects of the transformation of the cork raw material, it can be mentioned the production of expanded cork agglomerate. The manufacture of this cork product only uses superheated steam, using generators fueled with cork waste, not introducing any other products not exclusively cork, and giving up agglomeration based on resins of the cork itself. So, this is a completely natural and ecological product. In addition, in the processing of this and other cork products an important residue is produced, cork powder. This powder is commonly burned to produce steam and/or power used in the factories themselves, given the high energy content of this material. Also, all other industrial cork wastes are reused or valorized in another way (Gil, 1998). So, there is really no wasted cork. Meanwhile, cork products for the construction industry, are ones of the most suitable for sustainable and efficient energy construction, given its mentioned ecological characteristics. These materials are good thermal insulators, conferring to the buildings good thermal quality and good thermal behavior according to the energy certification systems. In addition, these products contribute to the general comfort and also indoor air quality (Gil, 2007). In this regard, it should be noted that there are a number of new derivatives products of cork or incorporating new technologies applied to traditional products, which are still in various stages of development. These may have or be adapted for use in construction, one of the most interesting areas of application although several other fields of applications are also under consideration. These are new products that may eventually contribute to a greater sustainability in the construction business and also in the cork sector. A short selection on these new materials that can be foreseen for building applications is as follows. For example, we can start by addressing a new product derived from cork that is being introduced in the market, consisting of a flexible tubular cork pipe coating obtained by extruding a mixture of granulated cork with a polyurethane resin binder (Esteves, 2010). This product is intended for industrial and residential applications for mechanical, thermal, and acoustic insulation. Its application is foreseen particularly under conditions where the outer wear caused by photo-degradation, chemical, physical, and biological conditions is very heavy, resisting better than competing insulation materials. It is anticipated a widespread use in piping insulation, e.g., in air conditioning and central heating, water heating systems, solar energy and water pipes, etc. This material may also be buried in the ground or embedded in construction. Another product that is also being developed is a block of concrete with cork, with optimized geometry, light weight and good thermal and acoustic performance, maintaining good physical and mechanical behavior (Branco et al., 2008). This block can be used as a construction element, e.g.,