Definition:

Degradation: Polymers are subjected to high temperature and strong shear force in the process of processing. Under these strong effects, the chain of polymer is broken, so the molecular weight decreases, which is degradation.

Type:

The first is degradation caused by physical factors such as heat and stress. Under the influence of thermal or shear stress, the degradation of polymers is usually carried out by irregular selection. This is because the energies of all chemical bonds in polymers are very close to each other.

It is important to control its thermal or shear stress to reduce degradation.

Secondly, at high temperatures, polymers containing trace water, acid or alkali are selectively degraded. Degradation generally occurs in carbon-heterocyclic chains (such as C-N, C-O, C-S, C-Si, etc.), which is due to the low energy and poor stability of carbon-heterocyclic bonds.

The higher the temperature, the faster the degradation of the automatic forming machine; the longer the residence time at high temperature, the more severe the degradation. Oxygen often exists in the process of processing. Oxygen can oxidize the polymer to form peroxide structure at high temperature. The peroxide decomposes briefly to produce free radicals, and then triggers chain degradation reaction, which is called THERMO-OXYGEN degradation. It is the primary process of polymer degradation.

In the process of processing, the polymer is subjected to repeated stress (mainly shear stress). When the energy of shear stress exceeds the bond energy, the chemical bond will be cracked and degraded. Shear and heat together play an important role in the degradation of polymers.

Trace moisture is the most important factor in the degradation of some polymers, such as PC, PA, ABS, polyester and so on. Therefore, the monotony before processing is the required process.

The first step is to control the monotony of the material to reduce degradation.

Specific operation:

Strict control of raw material technical indicators, as far as possible to remove impurities such as catalyst residues in polymers.

Before application, the polymer is monotonous, especially the storage process of polyester, polyether and polyamide, which absorbs moisture from the air. Before application, the moisture content should be reduced to less than 0.01-0.05%.

Acknowledging the reasonable processing technology and conditions, the polymer can be processed under conditions that are not easy to degrade.

Processing equipment and dies should have excellent structure. First of all, it is necessary to eliminate the dead angle or gap that may exist in the part touched by the polymer in the equipment, reduce the excessive length of the runner, improve the heating equipment, display the sensitivity of the moving temperature equipment and the cooling power of the cooling system.

In the formulation, antioxidants and stabilizers are considered to enhance the resistance of polymers to degradation.