Paper degradation is the natural process by which paper, an organic material primarily composed of cellulose fibers, breaks down over time. This process involves complex changes to its physical, chemical, and mechanical properties. The rate at which paper degrades varies significantly, depending on a range of internal and external influences.
Understanding Paper Degradation
Paper degradation occurs through both biological and chemical mechanisms that dismantle its cellulose structure. Microorganisms, such as bacteria and fungi, produce enzymes called cellulases. These enzymes break down the long chains of glucose molecules that form cellulose, converting them into simpler sugars. Moulds, for instance, release enzymes that chemically attack cellulose macromolecules within the paper fibers.
Chemical reactions are also fundamental to paper’s deterioration, with hydrolysis and oxidation being the primary pathways. Hydrolysis involves water reacting with acidic components in the paper to break chemical bonds in cellulose. This shortens cellulose chains, leading to a loss of strength and increased brittleness. Oxidation, often driven by oxygen or pollutants, causes discoloration and weakening. These chemical processes can also promote each other, accelerating overall degradation.
Factors Influencing Paper Degradation
Numerous factors significantly influence the speed at which paper degrades. Environmental conditions, such as moisture and humidity, facilitate hydrolytic reactions and support microbial growth. Higher temperatures accelerate chemical reactions, while light exposure, especially ultraviolet (UV) radiation, can catalyze oxidation and cause structural damage. The availability of oxygen also contributes to paper weakening.
The composition and type of paper itself are also critical determinants. Papers with higher lignin content, like those made from wood pulp before modern processing, are more susceptible to oxidation and yellowing. The presence of inks, coatings, and glues can introduce acidic components or react with the paper, accelerating degradation. Acid-free papers resist acid hydrolysis by neutralizing internal acids, whereas acidic papers degrade more quickly. Paper thickness and the length of its cellulose fibers also affect durability, with longer fibers providing more strength and resilience.
Microbial activity, encompassing bacteria, fungi, and insects, also contributes to paper degradation. The presence of these organisms can lead to direct consumption of paper fibers or the production of enzymes and acidic waste products that break down cellulose. Mould growth can result in fragile and discolored spots on paper surfaces. Insects like silverfish and termites physically damage paper by feeding on it, causing holes and material loss.
Typical Paper Degradation Timelines
The timeline for paper degradation varies widely depending on the environment and paper type. Under optimal conditions, such as those found in archival storage with controlled temperature and humidity, acid-free paper can last for centuries or even thousands of years. Conversely, paper in a compost pile, exposed to high moisture, warmth, and abundant microorganisms, can break down rapidly, often within weeks to a few months.
In typical outdoor environments, paper degrades at a moderate pace, usually over several months to a few years. Newspaper, with its high lignin content, tends to yellow and become brittle quickly, degrading faster than higher-quality office paper. Cardboard, being thicker, might take longer than thin sheets of paper to fully decompose.
Paper in a modern landfill, however, degrades extremely slowly due to the lack of oxygen and moisture, creating anaerobic conditions that inhibit microbial activity. In such environments, paper can persist for decades, sometimes even centuries, with very little change. Historical documents, if not properly preserved, often show significant degradation within decades to a century, particularly if they were made using acidic manufacturing processes prevalent in the 19th and 20th centuries.
The Fate of Discarded Paper
Once paper is discarded, its degradation journey depends largely on how it is managed. Recycling provides a path that delays the degradation process by transforming used paper back into new products, thereby extending the life cycle of the cellulose fibers. This process reduces the demand for new pulp and postpones the eventual breakdown of the material.
If not recycled, discarded paper typically ends up in landfills. In this environment, the conditions are often unfavorable for rapid degradation. The tightly packed layers of waste, combined with a lack of oxygen and moisture, create an anaerobic setting that significantly slows down the activity of microorganisms responsible for decomposition. This means that paper in landfills can remain intact for very long periods, contributing to the volume of waste rather than quickly returning its components to the natural cycle.