Why does newsprint paper yellow and become brittle over time, and how can this process be slowed down?

Newsprint paper is notorious for its tendency to yellow and become brittle over time, a characteristic that often leaves old newspapers looking aged and fragile. The science behind this process is rooted in the paper's composition and the natural chemistry of the materials used in its production. Let's dive into why this happens and how it can be slowed down.

The Culprit: Lignin
The primary reason newsprint yellows and deteriorates is the presence of a natural compound called lignin. Lignin is a complex organic polymer found in the cell walls of wood and plants. It acts like a natural glue, giving wood its rigidity and strength. In the process of making newsprint, wood pulp is mechanically ground to separate the fibers, but this process does not remove the lignin content.

When newsprint is exposed to light and oxygen, the lignin undergoes a chemical reaction known as oxidation. This reaction breaks down the molecular structure of lignin, leading to the formation of chromophores, which are molecules that absorb certain wavelengths of light. The chromophores absorb blue light and reflect yellow, giving the paper that familiar yellowed appearance. This same oxidation process also weakens the bonds between fibers, making the paper brittle.

Why Newsprint Is Different from Other Papers
In higher-quality papers, such as those used in books or fine stationery, the wood pulp is chemically treated to remove most of the lignin. This extra step is known as chemical pulping and helps produce a more durable and longer-lasting paper. Because newsprint is intended for temporary use, such as daily newspapers that aren't meant to be archived, it undergoes a mechanical pulping process. This method is more cost-effective, but it retains most of the lignin in the fibers, making newsprint more prone to yellowing and brittleness.

How to Slow Down the Process
While it's impossible to stop the natural aging process of newsprint entirely, several strategies can help prolong the life of the paper and keep it in better condition:
Limit Exposure to Light
Ultraviolet (UV) light from the sun or artificial light sources accelerates the oxidation of lignin. Storing newspapers in a dark place or using UV-filtered glass in picture frames can help slow down the yellowing.
Control Temperature and Humidity

Heat and moisture also speed up the degradation of lignin. Keeping newspapers in a cool, dry environment—ideally at a temperature below 70°F (21°C) and humidity between 30% and 50%—can help reduce the rate at which the paper becomes brittle.
Use Acid-Free Storage Materials

Acid in the air or from other materials can further break down the fibers in newsprint. Archival storage boxes and acid-free paper sleeves can protect newspapers from acidic contaminants, preserving their integrity for a longer period.
Deacidification Treatment

For valuable or historically significant newspapers, a process called deacidification can be used. This treatment neutralizes the acids in the paper and can be performed by professional conservators to slow the aging process.

The yellowing and brittleness of newsprint are inevitable outcomes of the chemical properties of lignin and the way it interacts with light, air, heat, and moisture. While the mechanical pulping process used in newsprint production makes it more susceptible to these changes, understanding the science behind it can help us better preserve newspapers when necessary. Simple measures like controlling exposure to light, temperature, and acidity can go a long way in slowing down the aging process, allowing a little bit of history to last just a bit longer.