Does vulcanization time affect the properties of rubber?

The vulcanization time of rubber has a crucial effect on the properties of rubber. The length of curing time will directly affect the degree of cross-linking of rubber, and then determine its physical and mechanical properties, heat resistance, chemical resistance and other key characteristics. The following is a detailed analysis of the effect of rubber vulcanization time on rubber properties:

1. Physical and mechanical properties

Hardness:

When the vulcanization time is insufficient, the cross-linking density between rubber molecules is low, and the hardness is low.

With the increase of vulcanization time, the hardness of rubber gradually increased, and reached a peak in the positive vulcanization stage.

Overvulcanization will lead to a further increase in rubber hardness, but at this time the increase in hardness is often accompanied by a decline in elasticity.

Tensile strength and elastic modulus:

When the vulcanization is insufficient, the tensile strength and elastic modulus of the rubber are low, the material strength is insufficient, and the elasticity is poor.

In the positive vulcanization stage, the tensile strength and elastic modulus reach the best state.

Overvulcanization can cause the tensile strength and elastic modulus to decrease, and the rubber becomes stiff and brittle.

Elongation at break:

Under vulcanization, elongation at break is higher.

The elongation at break decreased gradually with the increase of curing time.

Overvulcanization will further reduce the elongation at break and make the toughness of rubber worse.

Second, dynamic performance

The vulcanization time also has significant influence on the dynamic properties of rubber. Dynamic performance is an important index to measure the performance of rubber products under cyclic load, including dynamic modulus, hysteresis loss and fatigue resistance.

When the vulcanization is insufficient, the dynamic modulus is low, the hysteresis loss is large, and the rubber is easy to heat and age under cyclic load.

In the positive vulcanization stage, the dynamic performance reaches the best state.

Overvulcanization will cause the rubber to become stiff and lack sufficient elastic response, resulting in decreased dynamic performance.

Third, heat resistance and aging resistance

Vulcanization time also significantly affects the heat resistance and aging resistance of rubber products.

When the vulcanization is insufficient, the crosslinking bond is less, the molecular chain is easy to degrade, and the heat resistance and aging resistance are poor.

In the positive vulcanization stage, the heat resistance and aging resistance of rubber reach the best state.

Overvulcanization will lead to embrittlement of the internal structure of the material, which is easy to crack at high temperatures, thereby reducing heat resistance and aging resistance.

Fourth, chemical corrosion resistance

The chemical resistance of rubber depends on the integrity of its molecular cross-linking network.

When the vulcanization is insufficient, the intermolecular void is large, the chemical medium is easy to penetrate, and the chemical corrosion resistance is poor.

In the appropriate vulcanization time, the chemical corrosion resistance of rubber reaches the best state.

Overvulcanization may weaken the corrosion resistance due to molecular chain breakage.

Vulcanization time is one of the key factors affecting the properties of rubber products. Reasonable vulcanization time should ensure that the crosslinking density is moderate, so that the rubber products can achieve the ideal state of high strength, high elasticity, high heat resistance, and high chemical resistance. At the same time, it is also necessary to take into account production efficiency and economy to achieve the best comprehensive performance of rubber products.

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