Influencing factors and testing methods for testing plastics in large ageing tes

The ageing of plastics is one of the factors that measure the life of plastic products. The ageing rate and ageing performance of plastic products in different environments are different. In accordance with international standards such as GB/T15596, the ageing performance of plastics can be evaluated.

 

1) Ozone has a much higher chemically active oxygen and is also more destructive. It also breaks molecular chains, but the effect of ozone on rubber and plastics changes as they are deformed. When used as a deformation rubber (mainly unsaturated rubber), cracks appear perpendicular to the direction of stress, called "ozone cracking"; when acting on deformed rubber, only an oxide film forms on the surface without cracking.

 

2) Oxygen reacts with the rubber and plastic molecules in rubber and plastic in a free radical chain reaction, resulting in a break in the molecular chain or excessive cross-linking, leading to a change in the properties of rubber and plastic. Oxidation is one of the major causes of rubber and plastic ageing.

 

3) Increasing the temperature can lead to thermal cracking or thermal cross-linking of rubber. But the basic function of heat is to excite|activate. Increase the rate of oxygen diffusion, excite|activate the oxidation reaction, thus accelerating the rate of oxidation reaction of rubber and plastic, which is a common aging phenomenon - thermal oxidation aging.

 

4) The role of water is twofold:When wet air is showered with rain or soaked in water, rubber and plastic are easily damaged. This is because the water-soluble substances in rubber and clear water are extracted and dissolved by water. Caused by hydrolysis or absorption. In particular, the alternating effects of water immersion and atmospheric exposure can accelerate the damage to rubber and plastics. In some cases, however, water has no damaging effect on rubber and plastics, and even has a delaying effect on ageing.

 

5) Mechanical stress: Under the repeated action of mechanical stress, rubber develops a mechanical-chemical process. This mechanical molecule, then, is the one that causes rubber chain breakage and mechanical activ|ation of oxidation, which process is more advantageous? Which has the advantage depends on its conditions. In addition, stressful conditions tend to cause ozone cracking.

 

6) The shorter the light wave, the greater the energy. Damage to rubber and plastics is caused by the higher energy UV light. Rubber and plastics generate free radicals by absorbing light energy, which trigger and accelerate the oxidation chain reaction process. External light plays a role in heating. Another characteristic of photosynthesis (unlike heat) is that it grows mainly on the surface of the rubber. Samples with high rubber content show a web of cracks on both sides, the so-called "smooth outer layer cracks".

 

7) The factors that act on rubber and plastics include chemical media, altered metal ions, high energy radiation, electricity and biology.

 

The common methods are appearance change method; mechanical property change method; other property change method.

 

Mechanical property change method:It mainly evaluates the retention of mechanical properties of plastics after ageing. Typically, the life of a plastic is measured in terms of the time it takes for the mechanical properties to decline to 50%. Other property changes:These include size, density, mass, electrical properties, thermal properties, activity rate, molecular weight, etc.