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Heat and Plastics: What Are the Hidden Dangers in Processing?
With the widespread use of plastics in daily life, people are paying more and more attention to their performance and possible environmental impacts. During the production and use of plastics, thermal energy and chemical changes can cause material aging and degradation. If these processes are not taken seriously, they may cause major safety hazards. This article takes an in-depth look at the heat-related degradation risks that plastics may face during processing.
Polymer degradation is the process by which a polymer's physical properties, including strength, are reduced and can be affected by changes in its chemical composition.
Polymer degradation and its effects
Polymer degradation refers to the decline in physical properties caused by changes in chemical composition. Plastics may be degraded at all stages of their product life cycles, including processing, use, disposal and recycling. The rates of these degradation processes vary widely, with biodegradation potentially taking decades to some industrial processes that can completely break down polymers within hours.
Technologies for degradation have been developed aimed at inhibiting or promoting this process. For example, polymer stabilizers ensure that plastic products have the desired properties, extend their service life, and facilitate recycling. Meanwhile, biodegradable additives accelerate the degradation of plastic waste. The main influencing factors of degradation include heat, light, air and water. Chemical changes are mainly oxidation and chain cracking. These changes will lead to a reduction in the molecular weight and degree of polymerization of plastics, thereby affecting its physical properties such as strength and plasticity.
Generally speaking, the reason why plastics are easy to degrade is because of their structural characteristics. Most plastics, such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), etc., are thermoplastic plastics. More fragile than thermoset plastics.
Thermal energy effects during processing
In the production and processing of plastics, the role of heat energy is inevitable. Thermoplastic polymers need to be heated to a molten state to form the desired shape, usually at temperatures ranging from 150 to 320 degrees Celsius. Under these conditions, polymers can experience oxidation problems, and these temperatures are high enough to initiate thermal degradation of the material, even in the absence of air.
During processing, molten plastics are often subjected to strong shear stresses that are sufficient to cause the polymer chains to break, thereby introducing chemical weaknesses into their overall structure and further exacerbating degradation.
Risk of degradation in the environment
Plastics do not biodegrade easily in the environment, but they can be degraded by the influence of ultraviolet light, oxygen, water and pollutants, a process commonly known as polymer weathering. Chain breaks caused by weather can make plastic increasingly fragile, eventually causing it to break and form microplastics.
Photooxidation is one of the main factors affecting the degradation of plastics. It is caused by the combined effect of ultraviolet light and oxygen, which triggers complex free radical chain reactions.
Degradation during use
Most plastic products, such as packaging materials, are often used only once and experience little or no significant degradation during their use. However, some plastics may experience long-term use in harsh environments, which can exacerbate changes in their physical properties. In this context, the risk of polymer degradation in plastics cannot be ignored, especially those used under high temperatures or chemical attack.
The safety hazards of polymer degradation in use cannot be underestimated. Real incidents caused by pipeline cracks in history tell us that degradation may have dire consequences.
Challenges in the recycling process
The recycling process of plastics also inevitably leads to some degree of polymer degradation. Although mechanical recycling is widely used, the process often cannot avoid thermal damage to the plastic chain and can lead to deterioration of product properties. While recycling technology continues to innovate, balancing environmental needs and cost-effectiveness remains a challenge.
When faced with these potential dangers and challenges, can we find more sustainable solutions for plastic applications and recycling?
