Aging mechanism of Handern polyethylene shed film in Wuhan
DATE：2020/5/13 8:23:21 / READ： / SOURCE：This station
Aging mechanism of Handern polyethylene shed film in Wuhan
1) Mechanical properties decline (tensile strength and elongation at break significantly decrease); www.handern.com breathable membrane equipment, melt-blown non-woven fabric equipment, plastic building templates.
2) The shed film loses part of its transparency, and its light transmittance decreases significantly; often small
3) Discoloration (shed film becomes gray or earthy yellow);
4) The relative molecular weight of the polymer decreases (the melt flow rate of the shed membrane increases significantly); www.handern.com breathable membrane equipment, melt-blown non-woven fabric equipment, and plastic building templates.
5) Brittleness (the shed film is broken with a little pinch).
In fact, like other polymers, polyethylene is subjected to high temperature, mechanical shear stress and oxygen during the molding process, which starts the polymer degradation process. In the process of use, it is exposed to sunlight, oxygen, natural disasters and pesticides to accelerate its aging rate. The polyethylene shed film without any protection treatment can only be used for 3 to 6 months in the sunny season. After years of research, there are now a variety of compounds used to protect the polymer and prevent its aging. The effective service life of polyethylene shed film can be increased to 3 to 5 years. www.handern.com breathable membrane equipment, melt-blown non-woven equipment
1. Thermal oxidation of polyethylene shed film
In the synthesis process of polyethylene resin, the forming process of the shed film, and the use process of the shed film, the polyethylene generates excessive heat and oxygen, and its carbon-carbon chain and carbon-oxygen chain are easily broken or oxygen directly attacks the macromolecular chain Oxides and another alkyl radical: alkyl radicals can also combine with oxygen to generate more free radicals, and this cycle is repeated continuously. The chain reaction of free radicals causes the polyethylene chain to break and degrade, the relative molecular mass decreases, and the melt flow rate increases. In this reaction, the peroxide formed is cleaved to produce an alkoxy radical and a hydroxyl group, both of which can in turn increase the chain reaction. www.handern.com breathable membrane equipment, melt-blown non-woven equipment
We have noticed that if the polyethylene is heated (heated to 290 ° C) in the absence of oxygen, the performance of the polyethylene will remain stable; on the contrary, in the presence of oxygen, the temperature of polyethylene exceeds 100C Time, and after a short induction period, the rate of thermal oxygen aging will accelerate. Therefore, it can be considered that the coexistence of heat and oxygen is an important condition for thermal oxygen aging of polyethylene. Due to different molecular structures, each type of polymer compound has a unique degradation method. www.handern.com breathable membrane equipment, melt-blown non-woven equipment
Author：admin