Environment and resources are the most compelling topics in the world today. Scientific and rational use of limited resources is fundamental to environmental protection.
The world has consumed a lot of resources due to corrosion of materials, causing huge losses to human beings, hindering the development of productivity, and further leading to the deterioration of the global environmental conditions. According to statistics from some industrial countries, the direct loss due to corrosion reaches 2% to 4% of the gross national product (GNP), and the most developed United States is as high as 4% or more. China’s annual direct economic losses due to corrosion are at least 20 billion yuan.
As a new class of materials, plastics have excellent chemical inertness and other good comprehensive properties, and have been widely used in the field of anti-corrosion. Plastic anti-corrosion is an edge discipline. Studying and mastering the principle and application of plastic anti-corrosion has a very positive significance for further promoting and expanding the application of plastics in anti-corrosion fields and saving social wealth and resources.
1. Definition of plastic corrosion
Corrosion is a phenomenon in which a substance is destroyed and deteriorated due to its interaction with the environment. The appearance of plastic and its deterioration due to deterioration of mechanical properties under the action of a chemical medium environment is called corrosion or chemical aging of plastics. Chemical aging is one of the forms of plastic aging.
2. Type of corrosion of plastics
Different types of plastics, different degrees of chemical aging and erosion, may occur depending on the type, chemical medium and environmental conditions. Such as: appearance (extinction, discoloration, wrinkling) changes, and mechanical properties (optical properties, electrical properties, weight) changes and changes in chemical structure and properties, research to master the laws of plastic chemical aging, can be more scientific and more reasonable Use plastic to make better use of plastics to solve corrosion problems.
The basic reason for plastic corrosion is that the chemical medium penetrates into the plastic interior, and the diffusion causes swelling, dissolution, cracking or chemical reaction between the medium and the plastic, which leads to various corrosion phenomena.
Plastic corrosion can be roughly divided: the destruction of the main valence bond in the macromolecule of the polymer, and the destruction of the subvalent bond between the macromolecules. However, it is common to use both types of composite damage and the destruction of sub-valent bonds between macromolecules.
3. Factors influencing the chemical reaction of polymer corrosion and its effect on polymer properties
The chemical reaction of a polymer is mainly determined by the genes contained in the environment, medium and macromolecular chain, but the reaction will also be affected by neighboring group effects, probability effects, aggregation states, chain conformations, and media diffusion.
Polyolefin does not contain hydrolyzable groups in the molecular chain, so hydrolysis reaction is not easy to occur, acid and alkali resistance are good. Plastics such as polyester and polyamide contain heteroatoms in the main chain of the macromolecule, which are prone to acidic and alkaline hydrolysis. As a result of the reaction, the hydrolysis softens the material and the tensile strength decreases. The macromolecular chain of chlorinated polyether consists of easily hydrolyzable ether linkages, but the chloromethyl group regularly arranged on the t-butyl groups on both sides of the main chain causes steric hindrance to the erosion, and the chloromethyl polarity leads to The high crystallinity hinders the penetration of the medium, so that the hydrolysis resistance of the chlorinated polyether is good.
Ordinary unsaturated polyester resin has high ester group content, easy hydrolysis and poor corrosion resistance, but when it changes from ortho system to meta-line, bisphenol system, corrosion resistance is obviously increased, such as bisphenol a type Unsaturated polyester. The hydrolysis reaction of polyacrylonitrile fibers occurs on the side groups and has little effect on the main chain, so its performance changes are small.
4 temperature
As the temperature increases, the polymer macromolecule energy increases, the movement increases, the molecular gap increases, the chemical medium permeates and diffuses faster, the adsorption increases, and at the same time, the reaction speed increases and the corrosion is intensified.
Sometimes the temperature is slightly higher, but it contributes to the relaxation of the internal stress, reduces the stress concentration, and the temperature changes too much and the frequency will generate thermal shock. Reduces the life of the device or even damages it. Thermal and stress damage to the plastic can also produce synergistic effects. For example, wet nylon is brittle at 70 degrees for two months, and the dried nylon is still stable after two years of use at the same temperature. Because the former undergoes an oxidation reaction, a main chain hydrolysis reaction also occurs. This is the result of a combination of heat and water media. Usually, the heat resistance temperature of most plastics is not too high. When the plastic is used in the medium at a critical temperature, attention must be paid to the damage caused by the triple synergy of heat, stress and environmental media.
Partitioning Systems,Urinal Division Rounded,Unisex Ceiling Braced,Custom Overhead Braced Floor
PRO CABINET SOLUTION PTY LTD , https://www.pcscabinet.com.au