Plastic is preserved primarily by meticulously controlling its environment, particularly by minimizing exposure to factors that accelerate degradation such as light, heat, oxygen, and certain chemicals, while also ensuring proper physical support and storage.
Understanding Plastic Degradation and the Need for Preservation
Plastics, a vast category of synthetic polymers, are celebrated for their versatility and durability. However, they are not immortal. Over time, plastics degrade through various chemical and physical processes, leading to changes in their appearance, structural integrity, and chemical composition. This degradation can manifest as discoloration, brittleness, stickiness, cracking, and loss of original form. Preserving plastic objects, whether they are historical artifacts, scientific samples, or cherished personal items, is essential to maintain their aesthetic, functional, and historical value.
Effective preservation strategies focus on mitigating the key agents of degradation.
Key Factors Affecting Plastic Preservation
Several environmental and intrinsic factors contribute to the breakdown of plastic materials:
- Temperature: Elevated temperatures accelerate chemical reactions within plastics, leading to faster degradation rates. Even moderate temperature fluctuations can cause stress.
- Oxygen: Oxygen reacts with polymers in a process called oxidation, which can break down polymer chains, causing embrittlement, discoloration (e.g., yellowing), and loss of strength.
- Light (especially UV radiation): Ultraviolet (UV) light provides the energy to initiate chemical reactions that break molecular bonds in plastics, leading to surface crazing, brittleness, and severe discoloration.
- Humidity: Both excessively high and low relative humidity (RH) can be detrimental. High humidity can accelerate hydrolysis (a reaction with water that breaks polymer chains) in some plastics and encourage mold growth, while very low humidity can make some plastics brittle.
- Chemical Pollutants: Airborne pollutants, industrial fumes, and even chemicals off-gassing from unsuitable storage materials can react with plastics, leading to surface damage or accelerated breakdown.
- Physical Stress: Improper handling, inadequate support, or continuous mechanical stress can cause cracking, warping, and deformation.
- Inherent Stability: The chemical composition and manufacturing process of a plastic greatly influence its inherent stability. Some plastics are naturally more prone to degradation than others (e.g., cellulose acetate is less stable than polyethylene).
Strategies for Effective Plastic Preservation
Preserving plastic objects involves a multi-faceted approach focusing on environmental control, physical protection, and proper handling.
1. Environmental Control
Creating a stable and controlled environment is paramount for long-term preservation.
- Temperature Stability: Maintaining a stable low temperature is crucial. Cold storage, often below room temperature, significantly slows down the chemical reactions responsible for degradation, extending the lifespan of plastics. Fluctuations in temperature should be avoided.
- Oxygen Exclusion: Limiting oxygen exposure can dramatically reduce oxidative degradation. Placing plastic objects in oxygen-impermeable bags or sealed containers, sometimes with oxygen scavengers, is an effective method, especially when combined with cold storage.
- Light Management: Store plastics in dark conditions or use storage enclosures that block light. When displayed, use UV-filtering display cases or window films to mitigate the damaging effects of UV radiation. Avoid direct sunlight and high-intensity artificial lights.
- Humidity Regulation: Aim for a stable, moderate relative humidity, typically between 40-60%, to prevent both hydrolysis and excessive drying. Avoid rapid changes in humidity.
- Pollutant Control: Store plastics in clean environments, away from dust, fumes, and sources of chemical off-gassing. Use archival-quality storage materials that are chemically inert.
2. Physical Protection and Storage
Proper physical support and storage materials prevent damage and reduce exposure to harmful elements.
- Archival-Quality Materials: Use storage boxes, folders, and interleaving materials made from inert, acid-free, and lignin-free archival stock. Avoid PVC (polyvinyl chloride) plastics for storage, as they can off-gas plasticizers that damage other plastics.
- Protective Enclosures: Individual enclosures, such as custom-fitted boxes or polyester sleeves, can protect items from dust, physical abrasion, and provide support. For oxygen-sensitive plastics, heat-sealable, oxygen-barrier bags offer superior protection.
- Adequate Support: Ensure objects are properly supported to prevent sagging, warping, or cracking. Use inert padding materials like polyethylene foam or polyester batting where needed.
3. Handling and Maintenance
Careful handling and appropriate maintenance routines contribute significantly to long-term preservation.
- Gentle Handling: Always handle plastic objects with clean, lint-free gloves to prevent transferring oils, dirt, or residues from hands.
- Minimal Cleaning: Clean plastics only when necessary using soft, non-abrasive cloths and mild, pH-neutral cleaners, or distilled water. Avoid harsh solvents, abrasives, or polishes that can damage the surface or react with the plastic.
- Regular Monitoring: Periodically inspect stored plastics for any signs of degradation such as stickiness, discoloration, brittleness, or odors. Early detection can allow for intervention to slow further damage.
The table below summarizes key environmental factors and their corresponding preservation strategies:
| Factor | Impact on Plastic | Preservation Strategy |
|---|---|---|
| Temperature | Accelerates chemical degradation, embrittlement | Stable low temperatures, cold storage |
| Oxygen | Causes oxidative degradation, discoloration, brittleness | Oxygen-impermeable bags, low-oxygen environments |
| Light (UV) | Breaks polymer chains, yellowing, surface damage | Dark storage, UV-filtering materials, low-light display |
| Humidity | Accelerates hydrolysis (high), embrittlement (low) | Stable, moderate relative humidity (e.g., 40-60%) |
| Pollutants | Surface damage, chemical reactions | Clean environment, inert storage materials |
| Physical Stress | Warping, cracking, distortion, abrasion | Proper support, careful handling, protective enclosures |
Practical Insights for Preserving Plastic Collections
- Prioritize Stability: The most critical aspect is creating a stable environment, minimizing fluctuations in temperature and humidity.
- Consider Cold Storage: For highly valuable or fragile plastic items, investing in a cold storage unit (e.g., a dedicated archival freezer) can provide optimal preservation conditions, especially when combined with oxygen-impermeable packaging.
- Identify Plastic Types: Different types of plastics degrade differently. Knowing the composition of an object (e.g., cellulose nitrate, PVC, polyethylene) can help tailor specific preservation approaches.
- Consult a Conservator: For rare, valuable, or already degrading plastic objects, consulting a professional conservation expert specializing in plastics is highly recommended. The Getty Conservation Institute provides valuable resources on plastic preservation: Getty Conservation Institute - Plastics
By diligently managing these environmental factors and employing sound physical protection techniques, the lifespan and integrity of plastic objects can be significantly extended for future generations.
