The main factors affecting the tensile elasticity of rubber include molecular structure, crosslinking system, filler system, softening system, processing technology and usage environment. The detailed analysis is as follows:
1. Molecular structure:
Molecular chain flexibility: The more flexible the molecular chain is, such as natural rubber (NR), the better its elasticity. Rigid rubber with a large molecular weight, such as ethylene propylene rubber (EPM/EPDM), has good heat resistance but slightly lower elasticity.
Molecular weight and distribution: High-molecular-weight rubber generally has better tensile strength and elasticity because long-chain polymers facilitate the entanglement and extension of molecular chains. When the molecular weight distribution is narrow, the performance is uniform but the processing property is slightly weaker; when the distribution is wide, the processing property is good but the performance uniformity is slightly worse.
Polar groups: Rubber containing polar groups, such as nitrile rubber (NBR), has good oil resistance but slightly lower elasticity.
2. Crosslinking system:
Crosslinking density: As the crosslinking density increases, the elasticity of the vulcanized rubber increases, but after reaching the maximum, further increasing the crosslinking density will lead to a decrease in elasticity. Appropriately increasing the degree of vulcanization is beneficial to elasticity.
Crosslinking bond type: Multiple sulfur bonds have better elasticity. The type and amount of vulcanizing agent affect elasticity; sulfur vulcanization provides good elasticity, while peroxide vulcanization increases hardness and heat resistance.
3. Fillers system:
Filler type: Carbon black enhances strength and wear resistance, but excessive use will reduce elasticity; white carbon black provides low friction coefficient and wear resistance, with a relatively smaller impact on elasticity.
Filler dosage: The dosage of carbon black in soft rubber is generally between 40-60 parts. Excessive dosage will reduce elasticity.
Filler particle size and surface activity: Smaller particle size, larger specific surface area, and higher surface activity of fillers have better reinforcing effect, but may have an adverse impact on elasticity.
4. Softening system:
Softening agent type: The solubility of the softening agent is related to the rubber. The smaller the solubility, the worse the elasticity. For example, natural, butadiene, and butyl rubber with paraffin oil is superior to adding naphthenic oil; nitrile rubber with DOP is superior to using naphthenic oil or aromatic oil.
Softening agent dosage: Increasing the dosage of the softening agent will reduce the elasticity of the vulcanized rubber. Therefore, in the formula of high-elasticity rubber products, it is necessary to avoid using softening agents or reduce their dosage as much as possible.
5. Processing technology:
Extrusion and mixing: Reasonable plasticizing and uniform mixing can obtain better elasticity.
Sulfurization temperature and time: Sulfurization temperature and time are the key to controlling the crosslinking degree. Excessive or prolonged sulfurization leads to excessive crosslinking and a decrease in elasticity.
6. Operating environment:
Temperature: High temperature intensifies the movement of molecular chains, reducing elasticity; low temperature limits the freedom of molecular chains, also reducing elasticity.
Humidity and oxygen: Moisture and oxygen affect rubber properties. Some rubber absorbs water in high humidity, resulting in performance changes; oxygen accelerates aging and reduces elasticity.
Ultraviolet rays and ozone: Long-term exposure to ultraviolet rays and ozone leads to chain breakage, reducing elasticity, and even brittleness.
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