Kluthe Magazine
« Mitigating the Effects of Influencing Factors on Plastic Aging »
The aging of plastics is a slow process during which irreversible changes occur within the material. Although aging cannot be prevented, appropriate measures can delay it. This requires an understanding of the scientific principles underlying the material’s properties and the impact of factors that lead to the loss of these properties.
Why Use Plastics?
Plastics offer three key advantages:
- They can be easily molded into parts with complex shapes.
- They are lighter than other materials.
- They are resistant to many aggressive substances.
However, the downside is that plastics age, a fact that was not immediately identified because the aging processes occur so slowly that people had grown accustomed to the conveniences of plastics before realizing their temporal limitations. Now, intensified efforts are required to keep these consequences within limits.
What Happens When Plastics Age?
Eventually, all plastics deteriorate. . Before this happens, their internal structure changes due to the effects of UV radiation, oxygen, and moisture. Heat and varying mechanical stresses accelerate these processes. The materials yield to external forces and decompose . Continuous varying stresses lead to fatigue. Additionally, variations in mechanical stress within the material, caused by the manufacturing process, gradually even out, a phenomenon often referred to as relaxation. To achieve specific properties, additives are mixed into some plastics. Well-known additives include plasticizers that prevent the material from becoming brittle. These additives sometimes distribute unevenly within the material or escape from it which also contribute to the aging of plastics.
Focus on Researching Aging Processes
With the goal of delaying deterioration, individual processes are studied. Understanding these processes helps in slowing deterioration. To usefully categorize research findings, a system is needed that distinguishes between chemical and physical deterioration as well as internal and external deterioration. Defining these terms is challenging because these processes often occur simultaneously, influence each other, and sometimes cannot be clearly separated. Reliable results can only be obtained based on practical experiments. In long-term studies, material samples are exposed to weather conditions or other stresses to observe the progression of deterioration. The slow progression of material deterioration hinders rapid insights. Employing artificial deterioration methods, which create higher stresses on the material than those experienced in real time, provide a solution.
Chemical Aging
All plastics consist of macromolecules. Depending on the type of plastic, the individual atoms form either long or branched chains. These long-chain molecules are either entangled with each other or lie stretched out side by side. The behavior of a specific plastic is determined by these structures and the chemical properties of the individual molecules. Chemical processes lead to the breakdown of these macromolecules. Light, especially UV light, impacts these chains from the outside, breaking them apart. Water, nitrogen, and oxygen from the atmosphere penetrate the material and either form new chemical bonds with the fragments or cause the existing fragments to react with one another. . This often results in the detachment of small molecules such as water, hydrogen chloride, or nitrogen compounds, which gradually migrate out of the material and escape into the environment. These processes result in the loss of mechanical strength or embrittlement and eventually lead to crumbling.
Physical Aging
Even if the composition of the macromolecules is preserved, environmental influences and areas of different structure or stress distribution within the material contribute to the aging of plastics. Naturally, nature always strives for equilibrium. Artificially created materials disturb these balances, and nature attempts to restore them. Additionally, changes in temperature and the application of mechanical forces in plastic parts create mechanical stresses that alter the structure. The penetration of water and other substances disrupts the cohesion of the material because they deposit between the molecules. Physical aging processes are also driven by very high or very low temperatures, which either embrittle or soften the material. The macromolecules change their shape and cannot return to their original structure.
Internal and External Aging
Effective measures to delay aging processes must always counteract the causes of these processes. For this purpose, internal and external aging are differentiated. Internal changes result from irregularities that occur during the manufacturing of materials. For example, insufficient mixing of components leads to concentration differences and side reactions with disruptive reaction products. During the processing of the material, too rapid cooling, and significant differences in temperature between areas of the material accelerate the aging processes. These relationships must be considered during the manufacturing of plastics. External influences, such as UV light, moisture, or aggressive agents, must be countered during the use of plastic parts. They can be blocked, for instance, by suitable surface coatings. Careful material selection, tailored to the intended use, and consideration of expected temperature and stress distributions in the design of the parts also contribute to delaying material aging.
How to Mitigate the Effects of Influencing Factors on Aging?
Four strategies can be followed to reduce the effects of influencing factors:
- Avoid influences entirely.
- Block influences
- Increase resistance to influences.
- Timely replacement of damaged parts
Completely avoiding influences is only possible in exceptional cases. Environments such as air-conditioned, UV-protected rooms, enclosed devices, or dry, oxygen- and nitrogen-free protective atmospheres are conceivable. Coatings block external influences. Aging protectants added to the reaction mixture during the manufacturing of plastics and care products that keep the plastic resistant during its use serve to increase resistance. The consequences of the failure of a relevant part on the overall system can be avoided by timely replacement of this component. This requires developing and applying criteria to assess the failure.
Avoiding the Consequences of Plastic Aging for People
Because plastics age, its lifespan is limited. Thus, it joins all naturally occurring and artificially created things and beings. Nature limits the growth and accumulation of substances. It accomplishes this with cycles in which substances are broken down and new things are formed from the components. Plastics push nature to its own limits – it fails to convert them back into water, carbon dioxide, oxygen, and nitrogen. With the United States generating over 35 million tons of plastic waste annually and only about 9% being recycled, we face a significant challenge. The path forward involves not only collecting all used plastic parts for proper disposal or burning, when necessary, but also focusing on regeneration through specialized recycling programs that can manage degraded plastics appropriately. This is particularly crucial as many American landfills are reaching capacity, making proper management of aging plastics increasingly important.
