Understanding the Impact of UV Rays on Paper

The sun's ultraviolet (UV) rays can have a detrimental effect on paper over time, causing it to yellow and deteriorate. This article delves into the specifics of whether UV rays can penetrate common materials like glass and plastic and how this impacts the integrity of paper documents.

UV Rays and Paper Degradation

UV rays are a part of the electromagnetic spectrum that includes visible light and even X-rays. UV light is further divided into UVA, UVB, and UVC rays. UVA and UVB are the most common types of UV radiation that reaches the Earth's surface, while UVC is largely absorbed by the ozone layer.

Impact of UV on Paper Quality

UVA and UVB rays can cause the breakdown of paper fibers, leading to discoloration and weakening of the document. This yellowing process, often referred to as photodegradation, is a significant concern for preserving the integrity of historical documents and important papers.

Can UV Rays Penetrate Common Materials?

Ordinary Glass

Ordinary glass is effective at blocking most UVA and UVB rays, which are the primary contributors to paper yellowing. However, it allows a small percentage of UVA rays to pass through, which can still lead to degradation over time.

Composition and Protection

Most ordinary glass is designed to block 90–99% of the UVB and nearly 100% of UVC rays. This makes it an effective barrier for UV-induced yellowing. However, the small percentage of UVA that manages to pass through can still contribute to the degradation process.

Plastic Materials

Plastic's ability to block UV rays varies significantly depending on the type of plastic used. Different polymers have different molecular structures that affect how they interact with UV light.

UV Resistance of Polycarbonate and Acrylic

Polycarbonate and acrylic are known for their high UV resistance. However, certain types of polycarbonate and acrylic may still allow some UV light to pass through, leading to the same yellowing effects as seen with ordinary glass.

Scientific studies have shown that ordinary acrylic plastics (types and thicknesses) allow light with wavelengths greater than 375 nm to pass through. This means that UV-C (100-290 nm) is effectively blocked, while UVA (315-400 nm) and some UVB (280-315 nm) may penetrate.

Even very thin acrylic sheets (less than 5 millimeters) do not let UV-C light penetrate. However, the effectiveness of these materials in blocking UVA and some UVB depends on the specific type of acrylic.

Optimal Protection Against UV-Degradation

To maximize the protection of important documents and records, consider storing them in materials specifically designed to block UV light. UV-filtering glass and archival materials designed to block UV rays are excellent choices.

Selecting the Right Protection

When choosing materials for protecting documents from UV-induced yellowing, several factors should be considered, including the type of material (glass vs. plastic), its thickness, and its specific UV-blocking properties.