Back-to-the-future Process Yields ‘Miracle Wood’

A back-to-the-future technology, first used more than 100 years ago, has put a new form of wood on the market – a veritable “miracle wood” that resists the moisture-induced bowing, swelling, cupping, shrinking and cracking that have been downsides of natural wood for thousands of years. The new “acetylated wood” is the topic of a story in the current edition of Chemical & Engineering News (C&EN). C&EN is the weekly newsmagazine of the American Chemical Society, the world’s largest scientific society.

Alexander H. Tullo, C&EN senior editor, explains that production of acetylated wood relies on a process much different from pressure treatment, which infuses insect- and rot-resistant chemicals into wood. Instead, the acetylation process uses heat, pressure and a substance termed acetic anhydride to permanently expand the cell walls in wood into a fixed position that resists water absorption. That absorption of moisture from the air, ground or rainfall underpins the familiar bending, bowing, rotting and other problems with natural wood.

The article points out that acetylation technology has been available for more than a century, and acetylated wood pulp has been used to make photographic film, cigarette filters, coatings for playing cards and other products. It is getting a second life thanks to technological advances made since similar products failed to get off the ground in the 1930s. Manufacturers such as Eastman Chemical and Accsys Technologies attribute its new success to the growing desire for green products. The new wood has similar properties to modern construction materials like aluminum and PVC but a much smaller carbon footprint. And although it costs about three and a half times more than untreated wood, Eastman’s technology manager for acetylated wood says its durability makes it worth it for customers.

Is Acid Anhydride Acidic?

An acid anhydride is an organic compound that has two acyl groups bound to the same oxygen atom. Most commonly, the acyl groups are derived from the same carboxylic acid, the formula of the anhydride being (RC(O))2O. A number of different types of acid anhydride exist, with properties that vary according to their different acyl groups. Many are produced and used in modern industry.

Acid anhydrides differ their properties. While some are liquids, others are solid at room temperature, usually in the form of pellets or flakes. They are generally clear if liquid and white if solid and often produce acrid, pungent odors when exposed to the air. They can cause irritation or burns if they come into contact with the eyes or skin, irritation or damage to the lungs if their fumes are inhaled, and burn to the gastrointestinal tract if ingested. Excessive exposure without proper medical attention can cause serious injury or death.

There are many possible acyl groups that can join with oxygen in this way, and thus many different acid anhydrides with varying chemical properties. Most types of acid anhydride are symmetrical, with an oxygen atom bonded to identical functional groups, but exceptions to this exist. Organic molecules contain groups of atoms called functional groups, which determine the molecule’s chemical properties. Acyl groups are functional groups containing a carbon atom, an oxygen atom, and an alkyl group, which refers to a set of functional groups composed entirely of carbon and hydrogen atoms joined by single bonds. Both acyl groups are in turn single-bonded to an oxygen atom.

Typically, acid anhydrides are generated from chemical reactions involving carboxylic acids, a group of organic acids. The name of the resulting acid anhydride is likewise commonly derived from the name of the original acid. For example, the condensation reaction involving two molecules of a type of carboxylic acid called acetic acid (CH3COOH) results in a single molecule of water (H2O) and a molecule of acetic anhydride ((CH3CO)2O, CAS number 108-24-7). Some forms of acid anhydride are formed from other types of organic acid, such as the phosphonic and sulfonic acids, or from inorganic acids such as phosphoric acid (H3PO4). Another example is maleic anhydride , which is used in the production of the polyester resins in molding compounds and toner for laser printers and photocopiers.

Acetic anhydride is commonly used as a reagent for reactions involving certain organic compounds and is involved in the production of aspirin and cellulose acetate, which is used as a synthetic fiber and as a substrate, or base, for the photosensitive chemicals in photographic film.