Factors Affecting Weathering of Plastics
Plastics have indeed been a revolutionary development in the domain of materials science, transforming industries and everyday life through their remarkable versatility. The advent of commercial production and use of plastics near the industrial revolution post the world war marked a gradual shift from traditional materials, offering a range of properties that have allowed them to seamlessly substitute and, in many cases, outperform their predecessors. However, as versatile as plastics are, they are not immune to the effects of weathering – the gradual deterioration caused by environmental factors. The weathering performance of plastics stands as a critical benchmark that directly impacts the longevity and reliability of a vast array of products. The persistent exposure to environmental elements poses a formidable challenge to the structural integrity and aesthetic appeal of these polymers. As an engineer, manufacturer or designer who is involved with plastics to strive and create resilient and enduring solutions in a technology advancing world, it is important to understand how plastics respond to weathering factors. In this blog, we will investigate the key factors influencing the weathering of plastics and explore how these materials respond to challenges posed by the elements.
Plastics weathering and the environment (Credits: https://www.ufz.de/index.php?en=50173)
Let us first look at the factors affecting weathering in plastics.
1. UV Radiation: Exposure to ultraviolet (UV) radiation poses a formidable challenge to plastics, inducing a cascade of effects that compromise their structural integrity. The energy from UV rays initiates photodegradation, causing polymer chains to break and leading to a reduction in mechanical strength. Additionally, chromophores within the polymer structure can absorb UV light, triggering discoloration and a phenomenon known as photobleaching. Furthermore, the embrittlement of plastics is a consequence of the alteration in the molecular structure induced by prolonged UV exposure. To mitigate these issues, the incorporation of UV stabilizers and absorbers into plastic formulations becomes crucial, acting as a shield against the deleterious effects of sunlight.
2. Change in Temperature: The physical and mechanical properties of plastics are significantly influenced by temperature fluctuations, making thermal stability an important consideration. Exposure to varying temperatures during day-night cycle or season cycles can result in thermal expansion and contraction, impacting the dimensional stability of plastics. This can lead to stress concentrations and affect the material's mechanical properties, such as strength and flexibility. The industries which are reliant on making plastic products to perform in extreme temperature environments must prioritize materials with good thermal stability to ensure optimal performance and longevity.
3. Humidity and Moisture Exposure: High humidity and exposure to moisture can bring in a host of challenges for plastics, particularly through processes like hydrolysis. Hydrolysis involves the breakdown of polymer chains in the presence of water, compromising the material's long-term integrity. There are certain chemistries that have functional groups as a part of the repeating polymeric chain such as amides, esters, etc. that are hydroscopic in nature. Additionally, the absorption of moisture can lead to dimensional changes, causing plastics to swell or shrink. Engineers and material scientists address these issues by incorporating moisture-resistant additives or utilizing coatings that act as barriers, safeguarding plastics against the detrimental effects of humidity.
Summary of the primary weathering processes and changes occurring in significant plastic debris or primary microplastics, leading to the formation of secondary microplastics in marine environments (Credits: https://www.mdpi.com/2305-6304/8/2/40)
4. Chemical Exposure: The interaction between plastics and a diverse range of chemicals and pollutants can instigate changes in the chemical structure of these materials, resulting in degradation and alterations in physical properties. Chemical exposure may lead to discoloration, weakening of the material, and a shift in its mechanical characteristics. Protective coatings and the selection of chemically resistant polymers such as HDPE, vinyl esters, epoxy, etc. become imperative strategies to safeguard plastics in environments prone to exposure to corrosive substances.
5. Ozone Exposure: Ozone exposure in the atmosphere can induce oxidative degradation in plastics, particularly affecting unsaturated polymer bonds. This process initiates the formation of cracks and surface deterioration, compromising the material's structural integrity. Plastics susceptible to ozone degradation may experience reduced mechanical strength and exhibit changes in appearance. The incorporation of ozone-resistant polymers and antioxidants into plastic formulations serves as a pivotal strategy to counteract the detrimental effects of ozone exposure.
6. Mechanical Stress and Cracking: Mechanical stress, when combined with environmental factors, contributes significantly to the initiation and propagation of cracks in plastics. Stress concentrations, coupled with factors like UV radiation and temperature fluctuations, can accelerate the deterioration of plastics. To mitigate the effects of mechanical stress, designers and engineers employ strategies such as distributing stress more evenly across components, incorporating reinforcing materials, and optimizing designs to enhance durability and longevity.
7. Airborne Particles and Abrasion Resistance: The presence of particulate matter and airborne debris in the environment can lead to surface wear and degradation in plastics, emphasizing the importance of abrasion resistance. Plastics exposed to abrasive conditions may experience scuffing, scratching, and a loss of gloss or clarity. In response, the development of polymers with high hardness and/or abrasion resistance and the application of protective coatings have become important to ensure the longevity and visual appeal of plastic products subjected to abrasive environmental conditions.
8. Microorganisms and Biodegradation: Biological degradation, often overlooked in discussions about plastic weathering, involves the activity of microorganisms, including bacteria and fungi, contributing to the breakdown of polymer chains. This less-discussed factor can lead to structural changes and compromise the integrity of plastics over time. Mitigating strategies encompass the use of antimicrobial additives and the exploration of biodegradable polymer alternatives, aiming to address the intricate challenge of biological degradation in plastics.
9. Light Exposure and Its Effects on Plastics: Light exposure, encompassing both visible and infrared light, can trigger color changes and material degradation in plastics. Specific wavelengths have the potential to induce chromatic effects, affecting the transparency and clarity of plastics. The incorporation of UV absorbers and stabilizers acts as a protective measure, shielding plastics from the deleterious effects of light exposure. Understanding the nuanced impact of light on plastics is crucial for industries where the aesthetic and functional properties of materials are paramount.
10. Material Composition and Weathering Resistance: The composition of plastics, including the type of polymer and additives incorporated, plays a pivotal role in determining their resistance to weathering factors. Different polymer types exhibit varying chemical structures, influencing their inherent weathering characteristics. Additives such as stabilizers and UV absorbers are key components that enhance the weathering resistance of plastics. Engineers and manufacturers must carefully consider material composition, tailoring formulations to specific environmental conditions and balancing performance requirements with cost considerations.
The weathering performance of plastics is hugely dependent over the environmental factors and material characteristics. Each factor presents unique challenges that necessitate thoughtful mitigation strategies such as UV radiation, mechanical stress, etc. Whether through the incorporation of additives, the selection of resistant polymers, or the implementation of protective coatings, understanding and addressing these weathering factors are critical for ensuring the longevity, durability, and sustainability of plastic materials in diverse applications. As industries continue to innovate, the responsible consideration of weathering challenges will be paramount for the continued success of plastics in an ever-evolving world.
If you have any other questions or would like to suggest topics for us to write about, please feel free to contact us at prashant.gupta@polymerupdateacademy.com
Author
Dr. Prashant Gupta
Faculty, Polymerupdate Academy
