The phenomenon of plastics becoming sticky over time can be attributed to several factors. Here are a few possible reasons:
Plasticizers: Plasticizers are additives used in the manufacturing of certain types of plastics to enhance their flexibility, durability, and other properties. These plasticizers are typically small molecules that can leach out or migrate from the plastic over time, especially when exposed to heat, humidity, or certain chemicals. When the plasticizers escape, the plastic material can become dry and brittle, leading to a sticky residue on the surface.
Degradation: Plastics can undergo degradation due to exposure to environmental factors like sunlight (UV radiation), heat, moisture, or chemicals. This degradation can result in the breakdown of the polymer chains that make up the plastic material. As a consequence, the surface of the plastic may become sticky, tacky, or gummy.
Oxidation: Some plastics are susceptible to oxidation, a chemical reaction that occurs when they come into contact with oxygen in the air. Oxidation can break down the polymer chains and cause changes in the plastic's properties. In certain cases, oxidation can result in a sticky or tacky surface.
Contamination: External factors such as dust, dirt, oils, or other substances can accumulate on the surface of plastics over time. These contaminants may interact with the plastic and form a sticky layer or attract moisture, leading to a sticky feel.
It's important to note that not all plastics will become sticky over time. The susceptibility to stickiness depends on the specific type of plastic, its composition, and the environmental conditions to which it is exposed. Additionally, some plastics are intentionally designed to have a tacky or sticky surface for specific applications, such as adhesive tapes or certain types of grips.