Cork: a strategic material

Cork is a material whose applications have been known since Antiquity, especially in floating devices and as stopper for beverages, mainly wine, whose market, from the early twentieth century, had a massive expansion, particularly due to the development of several cork based agglomerates (Gil, 2011). Cork is closely related to the maintenance of biodiversity, the heart of sustainable development, and the reduction of emissions and sequestration of CO2, aspects that, additionally to the environmental importance, are also economically very important (Gil, 2011). Other services such as the formation of the landscape, soil protection, regulation of hydrological cycle, are also very sound (Pereira, 2007). Cork regenerates after each stripping, and the cork tree survives the lost of an important quantity, often more than 50% of the total trunk and branches’ surface. The fact that corks are made of the bark harvested from living trees has lead environmentalists to encourage the use of cork over other, less natural, alternatives. Cork oak forests (known as “montados”) are a habitat for many animal and plant species. At a meeting of experts it was announced that the “montado” is integrated in one of the 34 “hotspots” of biodiversity worldwide, featuring a number of species per square meter even higher than the Amazon rainforest, usually stated as reference in this field. Cork oak is one of the best examples of real sustainability through the environmental, economic, and social functions within the various forest types, aspects currently placed on the agenda of the world public opinion. In addition to forest products’ production and activities associated with the extraction of cork, other activities such as hunting, bee-keeping, livestock, harvesting of mushrooms, and herbs and medicinal plants, reflect a multi-functional system which has a great social and economic importance in regions where the cork oak grows (Pereira, 2007; Gil, 2010, 2011). Significant reductions in emissions of greenhouse gases in the construction sector can be achieved through various measures for energy savings, an area where cork derivatives can have a very important role, particularly regarding the thermal performance of buildings, but not only. Cork used in floor coverings, wall coverings, and other decorative applications also contribute to this. Also considered are green building and sustainable materials which are concepts that are increasingly considered by engineers, architects and other technicians and even by consumers. Almost all cork products can be recycled and the main advantage of this procedure is that this material incorporates carbon fixed by the cork tree that remains there during the lifetime of the products (long life products), thus increasing the delay of the emission of this carbon back to the atmosphere. Besides this if there is no more use after their useful life, cork products can be used in energy production, having a high calorific value and, when incinerated, the CO2 produced is equivalent to the one which was fixed in the material, what is commonly referred to as being “carbon neutral” (Gil, 2010, 2011). In addition to this, the periodic extraction of cork oaks for cork production, produces between 250 and 400% more cork than they would produce if it they were not explored (when the bark is harvested the tree produces rapidly new bark for protection) increasing the fixation of CO2. Therefore, the consumption of cork products that leads to the exploitation of this material promotes the formation of more cork and thus more CO2 is sequestered, beyond the stated fact that such products are long-life products retaining the carbon during their useful life and being “carbon neutral” at the time of decomposition or energy use. Some studies refer that cork oak forests make a sequestration of until 5.7 ton CO2/ha/year. The 2.3 million ha of cork oak forests worldwide are seen as promoting the retention of about 14.4 million tonnes CO2/year. It should be noted also that according to data from a supplier 0.379 kg of CO2/kg of cork are emitted but each kg of final product is responsible for fixing 1.833 kg of CO2. Besides this, e.g., to produce 1000 cork stoppers 1.5 kg CO2 are emitted, but 14 kg of CO2 are emitted for the same amount of plastic stoppers or 37 kg CO2 for 1000 screwcaps (Gil, 1998, 2011; Pereira, 2007; Corticeira Amorim, 2008). According to the Cork Portuguese Association Annuary 2012 (APCOR, 2013) the European countries where cork is produced, Portugal (715,922 ha, 100,000 ton/year), Spain (574,248 ha, 61,504 ton/year), France (65,228 ha, 5200 ton/year), and Italy (64,800 ha, 6161 ton/year), have more than 67% of the total cork forest area and produce more than 85% of the global cork production. The exports of cork products in 2011 where: Portugal—805 million euros; Spain— 216 million euros; France—51 million euros; Italy—50 million euros, contributing for the economy of these countries. The exportation of cork products is worldwide. Several European countries are great importers of cork products, as for example, in 2011, Germany (104 million euros).