The aging caused by natural rubber or natural rubber products can be divided into two kinds of reactions: degradation and cross-linking. Thermal oxidative aging is a typical degradation-type aging. However, aging degradation and cross-linking of natural rubber or products usually occur simultaneously, but degradation dominates. It is characterized by degradation and aging, and there are problems such as a decrease in molecular weight, a sharp drop in elasticity, and a sticky surface of a natural rubber product. In the actual production and application process, many physical factors can also cause aging degradation or cross-linking of natural rubber.
3. Physical factors lead to aging of natural rubber
Natural rubber or natural rubber products may cause the main chain or side group of the rubber macromolecule to break under the physical action of high temperature, light, radiation or mechanical force, and the natural rubber will be aging.
1 high temperature causes natural rubber aging degradation: theoretically, in the state of inert gas or air isolation, the natural rubber will reach the chemical bond decomposition bond energy when the temperature reaches 200 °C, the macromolecular main chain begins to break and produce degradation; and the degradation rapidly occurs above 300 °C.
2 Photoaging: Natural rubber is sensitive to light in vacuum or inert gas. Under ultraviolet irradiation, gelation problems occur at temperatures below 150 °C, and hydrogen gas is also precipitated. Therefore, natural rubber products are basically unacceptable. The light of time.
3 Radiation aging: Under the action of X-ray or γ-ray, natural rubber and natural rubber products will have ionization and free radicals inside the cross-linking, leading to the breakage of the main chain of the natural rubber molecule, the detachment of the side groups, or cross-linking, etc. The problem is that the natural rubber or product ages and the service life is shortened until the use value is lost.
4 natural rubber fatigue aging: the internal molecular structure of natural rubber or natural rubber products changes under certain frequency or cyclic stress will produce fatigue aging, mainly due to the continuous friction of the molecular chain, the accumulation of intramolecular friction heat causes the molecular chain The weak bond breaks to form a crack, and the stress concentration at the crack leads to the crack growth, and the natural rubber or product loses its use value. In the actual application process, natural rubber undergoes fatigue aging and is generally affected by aging factors such as temperature, oxygen, ozone, light and chemical media.
5 contact with the medium leads to the aging of natural rubber: natural rubber products are generally not exposed to air or sea water for a long time. The fundamental reason is that these media will accelerate the aging process of natural rubber, mainly because the tensile strength and elongation at break of natural rubber are decreasing. The higher the temperature in the same medium, the faster the mechanical properties decrease.
As the most traditional rubber variety, natural rubber has its own unique advantages and is widely used in various industries. However, the poor aging resistance of natural rubber is obvious to all, and it is difficult to use in many special occasions; research on the causes of natural rubber and products aging It can give effective measures, such as the use of anti-aging agents, or with styrene-butadiene rubber, butadiene rubber, recycled rubber, etc., to improve the aging resistance of natural rubber or natural rubber products, expand the use of natural rubber, extend natural rubber Product life.