Clear plastic typically turns brown due to iron contamination or the natural aging process of certain plastics.
Here's a more detailed breakdown:
Iron Contamination
- Source: Iron can leach into the plastic from manufacturing processes, environmental exposure, or even from the substances the plastic is in contact with (e.g., water pipes).
- Process: The iron undergoes oxidation, similar to rusting, which results in a brownish discoloration.
Natural Aging and Degradation
- Types of Plastic: Certain plastics are more prone to yellowing or browning over time.
- UV Exposure: Ultraviolet (UV) light from the sun can break down the polymer chains in the plastic, leading to discoloration. This is a form of photodegradation.
- Oxidation: Exposure to oxygen can also cause the plastic to degrade and change color.
- Heat: Elevated temperatures can accelerate the degradation process and cause browning.
- Chemical Reactions: Plastics can react with chemicals in their environment, leading to discoloration.
Examples:
- Old plastic containers: Often turn yellow or brown over time, especially if exposed to sunlight.
- Clear plastic tubing: Can develop a brownish tint if used with iron-rich water or exposed to UV light.
Preventing or Slowing Discoloration:
- Use UV-resistant plastics: Opt for plastics formulated to withstand UV exposure.
- Store plastics properly: Keep plastics away from direct sunlight and extreme temperatures.
- Clean regularly: Regularly clean plastics to remove potential contaminants.
- Avoid harsh chemicals: Use gentle cleaning agents to prevent chemical reactions that can cause discoloration.
In summary, the browning of clear plastic is often caused by either iron contamination leading to oxidation or the degradation of the plastic polymers due to factors like UV exposure, heat, and oxidation during the natural aging process.
