Chemical degradation
Solvolysis
Step-growing polymers such as polyester, polyamide and polycarbonate can be degraded by solvolysis") and mostly hydrolysis, to give rise to molecules with low molecular weight. Hydrolysis takes place in the presence of water, which contains an acid or a base "Base (chemical)") as a catalyst.[3].
Polyamide is sensitive to degradation by acids and therefore the molds of this compound will break when attacked by strong acids. For example, the fracture of the surface of a fuel connector showed the progressive growth of the fracture generated from the attack of the acid (Ch) to the top of the polymer (C). The problem is known as cracking corrosion stress") and in this case it was caused by the hydrolysis of the polymer. It was the opposite reaction of the polymer synthesis:[1].
Ozonolysis
Breaks can be formed in many different elastomers by ozone attack. Small traces of the gas in the air attack double bonds in the rubber chains, with natural rubber"), polybutadiene, styrene-butadiene rubber and HNB") being the most sensitive to degradation. Ozone breakdowns generate stressed compounds, but the critical stress is very small. The breaks are always oriented at angles directed towards the axis of tension, in such a way that a twisted rubber tube is formed around the circumference. These breaks are dangerous when they occur in fuel pipes because they will grow from the outer surfaces to puncture the pipe and cause a fuel spill and fire. The problem with "ozone cracking" can be prevented by adding anti-ozonants to rubber before vulcanization. Ozone cracks are commonly seen in the sidewall of automobile tires, but are now rarely seen thanks to these additives. On the other hand, the problem is repeated with non-protective products such as rubber tubes and seals.[1].
Oxidation
Polymers are susceptible to attack due to atmospheric oxygen, especially at elevated temperatures encountered during the shaping process. Many processing methods (such as extrusion and injection molding) involve pumping molten polymer into tools and the high temperatures required for casting can result in oxidation unless precautions are taken. For example, a forearm crutch suddenly broke and the user was seriously injured by the failure. The crutch fractured through the polypropylene inside the device's aluminum tube and infrared spectroscopy of the material revealed that it rusted, as a possible result. of the poor molding to which it was subjected.[1].
Oxidation is usually easy to detect due to the strong absorption by the carbonyl group in the polyolefin spectrum. Polypropylene has a relatively simple spectrum with some peaks at the carbonyl position (like polyethylene). Oxidation tends to be generated in tertiary carbon atoms since the free radicals formed here are more stable and last much longer, making them more susceptible to attack by oxygen. The carbonyl group can subsequently be oxidized to break the chain, this weakens the material by reducing its molecular weight and the breaks tend to begin in the affected regions.[1].
Galvanic action
Polymeric degradation by galvanic action was first described in the technical literature in 1990.[4][5] This was the discovery that "plastics can corrode", for example, polymer degradation that occurs by galvanic action is similar to that of metals under certain conditions. Normally when two metals of different species such as copper (Cu) and iron (Fe) are brought into contact and then immersed in water with salts, the iron will experience corrosion or rust. This is known as a galvanic circuit where copper is the noble metal and iron is the active metal"), for example, copper is the cathode or positive electrode (+) and iron is the anode or negative electrode (-). A battery "Battery (electricity)") is formed. Plastics are made stronger by impregnating them with small carbon fibers, only a few micrometers in diameter known as carbon fiber reinforcing polymer (RPFC"). This in order to produce materials that are strong and resistant to high temperatures. Carbon fibers act as a noble metal similar to gold (Au) or platinum (Pt). When brought into contact with a more active metal, for example aluminum (Al) in water with salts, the aluminum corrodes. However, in the early 1990s, it was reported that imide resins in RPFC compounds degrade when a simple compound is paired with an active metal in salt water environments. This is because corrosion occurs not only on the aluminum anode, but also on the carbon fiber cathode in the form of a very strong base with a pH of approximately 13. This strong base reacts with the chain structure of the polymer degrading it. Affected polymers include bismaleimide") (BMI), condensation polymides, triazines and a mixture between these. Degradation occurs in the form of dissolved resin and fibers. The hydroxyl ions generated at the graphite cathode attack the O-C-N bond in the polymide structure. Standard corrosion protection procedures were found to be accepted to prevent polymer degradation under most conditions.[6].
Induced chlorine cracking
Another highly reactive gas is chlorine, which attacks susceptible polymers such as polyacetal and polybutylene pipes. There have been many examples of acetal pipes and joints failing at certain US properties as a result of chlorine-induced cracking. In essence, the gas attacks sensitive parts of the chain of molecules (especially secondary, tertiary or alicyclic carbon atoms), oxidizing the chains and causing them to split. The root of the problem is portions of chlorine in the water supplement system, adding the antibacterial action, the attack occurs in proportions of parts per million of the dissolved gas. Chlorine attacks weak parts of the product and in the case of a polyacetal cross in water supplement system, it is the root threads that are attacked firstly, causing a slight breakage and some fragility. The discoloration on the fractured surface was caused by the deposition of carbonates from the heavy water supply, such that the joint was in a critical state for several months. Problems in the USA also occur in polybutylene pipes, causing the material to be removed from the market, however it is still used in other parts of the world.[1].