Lignin, Ink and the Scent of Paper

Lignin and the Life of Paper

Paper has a scent before anything is printed on it. With the addition of ink, coatings, glue, and time, every publication develops a slightly different olfactory profile. These combine into that wonderful scent we smell when visiting a bookstore, library, or our own shelves at home.

One of the materials behind that scent is lignin, a complex natural substance found in the cell walls of trees and other plants. It binds plant fibers together, gives wood its rigidity and helps it resist water.

What happens during papermaking?

Wood is made largely from cellulose fibers held together naturally by lignin. During papermaking, the wood is chipped and turned into pulp, either by mechanically separating the fibers or by using heat and chemicals to dissolve much of the lignin around them. The pulp is then washed, formed into a wet sheet, pressed and dried. Mechanical methods leave more lignin in the paper, while chemical methods remove more of it. The scent you might smell from a papermill isn't lignin, its volatile sulfur compounds produced while lignin is being separated from wood.

Lignin is therefore best understood as something naturally present in wood and removed to varying degrees during papermaking.

Different publications, different amounts of lignin

You can often find clues to a paper’s lignin content in how it looks, feels and changes.

Newsprint usually contains a high proportion of mechanical or recycled pulp. It retains more lignin than most book and writing papers. Its thin, porous, uncoated surface also places the paper fibers and ink directly in contact with the air. The familiar scent of a newspaper is therefore a close mixture of wood-derived compounds, ink and whatever the paper has absorbed during printing, transport and display.

Inexpensive paperbacks use paper containing substantial lignin. You’ve seen it, these are the books whose pages can become cream-colored, then yellow or brown, particularly around the exposed edges. Their scent may become drier, woodier and sweeter as the paper changes.

Trade paperbacks and hardcovers are more often printed on chemically pulped paper from which most of the lignin has been removed. Their pages generally remain brighter and more stable. What you smell may come less from lignin and more from ink, sizing, binding adhesive and the materials used in the cover.

Magazine paper varies considerably. A mass-market magazine or catalog may use lightweight coated mechanical paper that still contains lignin beneath its smooth mineral coating. A higher-end art, fashion or design magazine may use coated chemical-pulp paper containing far less lignin. In these publications, the immediate scent can be dominated by heavy ink coverage, varnish, coating and binding adhesive.

An uncoated magazine offers another experience. Without a sealed or polished surface between the nose and the sheet, the paper fibers, absorbed ink and surrounding air can feel more present. This may help explain the especially rich scent of thick, matte, heavily saturated pages.

How lignin becomes something we can smell

Lignin itself is a large molecule that does not simply float off the page and into the nose. It becomes noticeable as oxygen, light, heat and moisture gradually alter its structure. As it breaks into smaller molecules, some become airborne.

These airborne molecules are called volatile organic compounds, or VOCs. “Volatile” here simply means they evaporate readily enough to move through the air. When they reach receptors in the nose, we experience them as smell.

Lignin can produce molecules with vanilla-like, almond-like, woody or lightly smoky characteristics. Other parts of the paper release sharper, vinegary, warm or toasted notes as they change. You do not normally perceive these as separate chemicals. They arrive together and become a single impression.

That impression also includes VOCs from outside the paper:

• Printing ink can contribute oily, mineral, resinous or solvent-like notes.
• Coatings and varnishes may smell waxy, plastic-like or faintly sweet.
• Binding adhesives can add rubbery, milky, sharp or synthetic notes.
• Paper can absorb traces of perfume, tobacco, cooking, humidity, dust and the room in which it has been stored.

Lignin therefore does not create the entire scent of a publication. It contributes one group of materials to a much larger mixture.

How the scent develops over time

When a publication is new, its most noticeable VOCs often come from production: freshly cured ink, coatings, laminates and glue. Many of these compounds gradually disperse once the object is exposed to air.

Meanwhile, slower changes are taking place inside the paper. Oxygen and light alter lignin and cellulose. Large structures gradually form smaller airborne molecules. The paper may yellow, lose flexibility and develop a scent that is less overtly inky and more woody, dry, sweet, dusty or acidic.

This is not a simple progression from “new” to one universal mature scent. A lignin-rich paperback kept near a sunny window will develop differently from a chemically pulped hardcover stored in a cool room. Humidity, ventilation, ink coverage, paper thickness and binding method all affect what is produced, trapped and released.

Even within a single book, the scent can vary. The exposed edges receive more light and oxygen. The gutter may hold adhesive and trap less-circulated air. A heavily printed image contains more ink than a blank page. The cover may introduce cloth, board, laminate or varnish.

What we casually identify as the smell of paper is rarely just paper. It is wood that has been pulped in a particular way, printed with a particular ink, assembled with particular materials and allowed to change in a particular place.

Lignin is one part of that story, the part of the tree that remains in the page and continues to make itself known when you open a book or step into an old bookstore or library.

Photo by Rita Morais