We live in a time of amazing new materials: graphene, plastics, alloys, ceramics, composite materials, carbon fiber… but none have been able to completely replace the humble wood that has accompanied human beings since the beginning of their cultural journey.
The first thing we must keep in mind when faced with this supermaterial is that wood only exists as a general concept, an abstraction with some biological basis… but what there really is are wood, many woods, as many species of woody plants exist on our planet. . And that’s talking about many species, around 100,000. And the wood from them can be enormously different and serve a wide variety of purposes, from building construction to bicycles, watches and numerous musical instruments.
Another element that must be taken into account: wood is considered the most abundant material in the biosphere, and easy access to it, as well as its mechanical performance and sustainability, is returning it to the commercial importance it had in the past. There is still an additional point that is not related to its characteristics as a material, but to climate change. This, on the one hand, requires that no greenhouse gases be emitted into the atmosphere, especially carbon dioxide and methane, and on the other hand, it imposes the responsibility of capturing carbon from the atmosphere, a carbon that was a component of large masses of vegetation in the past that the human being has burned in the form of oil, gas and coal. Well, wood, as it was millions of years ago, is a very attractive option for carbon capture, and can keep this element retained for thousands and thousands of years.
What is it?
As a plant product, wood is primarily defined as a natural composite material. A composite material is one in which two or more components assume different functions to resist the forces to which it is subjected. In the case of wood, the first component is cellulose fibers, a polysaccharide formed by long chains of thousands of D-glucose units that make up around 50% of wood. Cellulose is responsible for withstanding tension and torsion, two of the forces to which any material is subjected.
The second component of wood is hemicelluloses, which are also polysaccharides but are made up of other sugars in addition to D-glucose and are shorter, and instead of being linear, they are cross-polymers or copolymers. Hemicelluloses, which are about 20 to 35% of wood volume, are most abundant in hardwoods.
Cellulose and hemicelluloses fibers are like those of any other plant. What makes them special, what makes them wood, is that they are embedded or embedded in a matrix of lignin, which is the substance that resists compression and makes up between 25 and 30% of the wood. Lignin is a class of organic polymers derived from three cross-linked alcohols: coniferyl alcohol, sinapyl alcohol, and p-coumaryl alcohol.
In the synthetic world, one of the most common compounds is reinforced concrete, where the metal rods fulfill the function of cellulose and hemicelluloses, and the cement is the matrix that supports compression, as is the case of lignin.
As far as scholars have been able to determine with the available data, wood appeared on our planet in the geological period called Devonian (between 409 and 359 million years ago). That was a period of important events. Life had made the transition from the sea to land and plants began to develop roots and the fossil of a specific plant, the Armoricaphyton chateaupannense, identified in western France, is the first to date to show a woody stem. Nature had invented wood.
The wonderful material
If we open a log, we will discover that it has two types of wood. The outermost part, the sapwood, is moist and is made up of living cells that form a xylem or system of very narrow tubes that carry water and nutrients from the roots to the rest of the tree by capillarity. In the outer layer of the sapwood there is a thin layer called cambium, which is where the tree grows outward, a little each year, forming rings that allow us to know the age of the trees as well as data on the climate and conditions. of every year of his life. Below the sapwood is the heartwood, which is not alive, in which the xylem has become blocked with resins and no longer functions as a nutrient carrier.
The structure of the wood gives it enormous resistance, which is one of the reasons why it has been used in construction and for laying railway tracks as sleepers. It is both a solid but very light weight material. It is enormously resistant to compression, which is what makes it possible to make wooden columns that support great weights, and it is also extraordinarily durable. Many medieval cathedrals today have ceilings built with wood from the 12th or 13th centuries that continue to resist without problem. It absorbs and expels water depending on its environment, like a natural dehumidifier, and even when burned, wood maintains a certain structural coherence that neither metals nor plastics present when exposed to heat. An additional advantage is its excellent insulating capacity, which still makes it the preferred material for building in extreme climates.
Wood is also an ecological, renewable, 100% recyclable, sustainable material and, as an additional element that is not insignificant for many applications, it is beautiful. Its touch, its aroma, its veins, knots and rings are enormously attractive and aesthetic to human taste.
That is why today we are beginning to see products such as polymers enriched with wood fibers in car bodies, robots with bamboo arms that move more fluidly, or computer cases for countries with humid environments. And chemistry today uses wood to produce optical and electronic films in addition to exploring its use in the production of plastics.
In 2018, a group of materials scientists at the University of Maryland presented a process to partially remove lignin and hemicelluloses from wood, then compressing it until its cells collapse and chemical bonds form between its components, leaving a much stronger superwood. rigid, resistant to compression, harder and capable of stopping bullets… and it is also cheap to make.
Rather than being a material of the past, for many, wood is one of the most suitable materials for building the future.