Plastic is a chemical product obtained through processes that involve polymerization, distillation, and mixing of substances. As most of these materials are subject to chemical reactions, when exposed to heat, moisture, and UV rays, it is common for polymer degradation to occur.
To better understand polymer degradation and stability, it is very important to know the physical and chemical properties. Moreover, this process can occur through stress-cracking, radiation, and a mechanical, photochemical, chemical, or thermal reaction. Check out!
What is polymer degradation, and how does it happen?
Although undesirable, polymer degradation processes are common. However, do you know how it happens? This can occur due to different types of chemical reactions, such as cross-linking, depolymerization, fission of chemical bonds, oxidation, among others.
The beginning of the plastic degradation happens by the rupture of a covalent bond (two atoms sharing two electrons), generating free radicals, which are responsible for the continuity of the reaction. One of the most present forms at the beginning of this action is the external source, such as heat or solar radiation.
Aggressive agents, which change physical behavior, causing an increase or loss of stiffness, changes in appearance, etc., can also contribute to degradation. In some cases, this happens through the dissolution of molecules at the beginning of the polymerization or in the breaking of bonds.
What are the problems caused by polymer degradation?
Degradation can generate several negative effects on molded pieces, as is the case with polymers. The main reasons for this are changes in brightness, visual aspects (such as yellowing or color changes), and the appearance of stains.
In addition to the situations discussed above, there is the rheological and mechanical properties change. This is because the fission of the chains decreases the molar mass of the compounds, reducing the mechanical characteristics and viscosity since it also involves the cross-linking of the polymer.
Another issue is the appearance of cracks, which can unite the stresses and increase the probability of failures in materials used in applications that need a good mechanical request. To better understand these types of degradation of polymers, check out more details with the information below!
While some materials have resistance to temperatures above 2,000ºC, the compounds have a processing capacity of around 100 to 200ºC and lower temperatures of use. This is because the atoms are interconnected by covalent bonds, in which the dissociation energy is between 300 to 850kJ mol-¹.
The photochemical reaction happens by the participation of a molecule in an electronic state. The main cause of this type of UV degradation of polymers is excessive exposure to the sun.
This reaction occurs in cases where the polymeric compounds need to be sterilized, as with pharmaceutical products and hospital equipment. In this case, when receiving the radiation, the material acquires greater absorption to light, breaking carbon chain bonds, which decreases the resistance.
How to identify the polymer degradation?
The best way to expand the polymer degradation time is through the correct choice of the material used. Besides, the additives for each application need attention, especially when facing factors such as solar radiation, contact with other substances, and heat.
To facilitate the choice, the chemical industries use tests to analyze the behavior and properties of the compound when subjected to the actions mentioned above. These tests become even more useful when these reactions are considered contributing sources for polymer degradation.
An example of this is the weatherometer (accelerated aging test), an option that submits the samples to different temperatures, UV radiation, and humidity for a certain time. This allows a better comparison between material properties, such as resistance to traction, brightness, and color.
Another test widely used to study the properties of polymers is FTIR (Fourier-transform infrared spectroscopy), an alternative that allows the verification of chemical degradation of polymers.
As the thermal degradation of polymers causes the rupture of covalent bonds, proportioning the creation of other chemical groups, it is possible to verify the content of these groupings in the process. The manufacturer can also compare the intensity of the samples analyzed.
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