Wood is an amazing material that is naturally produced through photosynthesis from the sun’s energy, water, and nutrients. It is biodegradable, renewable, and stores carbon for the life of the product.
But what is wood? Wood is a natural composite of cellulose fibers and lignin, which is an organic polymer that makes wood rigid. There are two main kinds –
a) hardwoods are angiosperms, which are plants such as oaks, walnut, and maple that produce flowers and bear seeds in fruits. The wood is complex consisting of vessels having visible pores, fibers, and parenchyma, which are cells arranged radially and vertically that function primarily for carbohydrate storage.
b) softwoods are gymnosperms, which are plants such as conifers and cycads that have “naked seeds” borne in cones. The wood is simple, being formed mostly (90%) of tracheids that are long, narrow water-conducting cells plus parenchyma.
In both hardwoods and softwoods the wood is typically divided into sapwood (live cells) and heartwood (dead cells performing structural function). And, confusingly, the terms do not imply ‘hardness’ – some hardwoods are ‘softer’ than wood from softwoods.
Wood is commonly laid down in annual rings that vary in width depending on growth rate in that year – wide rings indicate rapid growth and narrow rings indicate slow growth. The analysis of ring width is a field known as dendrochronology, and a particular cross section when matched against reference sequences can be used for aging the wood sample. Changes in ring width can be correlated with changes in climate conditions when the wood was laid down. Ring width is also related to changes in competition between trees due to neighboring tree death or thinning. Rings near the center of the tree (pith) are juvenile and are commonly wider whereas rings produced when the tree is mature have narrower rings. Within any one ring the wood produced in the spring is commonly composed of larger, thin-walled, lighter-colored cells whereas wood produced late in the season is composed of smaller, thicker-walled, darker-colored cells. Not all trees show annual growth rings – some tropical trees may grow continuously throughout the year.
What’s especially interesting is the amazing variety of uses for wood – it really is a wonderful material. It has been used for millennia for fuel, fencing, boat building, and construction. The oldest wooden building in the world is the Horyuji Temple in Japan built in 607 AD. Wood has numerous uses, not only for construction but for tools, furniture, toys, packaging, and paper. And of course different species of wood are favored for particular uses.
The early development of Rayon (1924) and Nylon (1934) ushered in the use of cellulose-derived fibers in cordage, ‘silk’ fabrics, and textiles. This was followed by the production of Tencel in 1980, which is commonly used blended with cotton to increase ‘breathability’ and softness in sportswear.
And it might surprise you to know that wood cellulose is also used in a wide variety of products including fast food, bath towels, toothpaste, nail polish, ping pong balls, LCD screens, some paints, medication and supplements, sunscreen, cosmetics, ice cream, coffee filters, ketchup, textiles, bioplastics, and on and on. And current research is aimed at using nanocellulosic materials for making printed electronics, water filters, air purification, flexible batteries, and insulation. It has been claimed that any product made from petrochemicals can be made from cellulose.
And then there is the whole new world of building with wood using the new techniques of cross-laminated timber (CLT) and Mass Timber. These buildings are not only cheaper to build, but are fire- resistant due to their solid wood construction and have a far smaller carbon footprint than equivalent structures using steel, concrete, or aluminum. The best examples of multi-story buildings made of wood that are 2-15 stories high are in Scandinavia, but there are also CLT and Mass Timber buildings in British Columbia, Oregon, and elsewhere in the US.
Confidence in using wood in construction has been demonstrated by the Consortium for Research on Renewable Industrial Materials (CORRIM) in their work on Life Cycle Assessment, which consistently shows that wood products that come from renewable resources have lower environmental impact and carbon footprint than using alternative materials such as steel, concrete, plastics, and aluminum.
So, wood is an amazing, renewable, and biodegradable material. Far from being old-fashioned and surpassed by alternative materials, it is now considered to be at the forefront of modern sustainable materials.