Rubber tensile strength improvement program.
I. Softening system: adding softening system will reduce the tensile strength of vulcanized rubber
1. In NBR rubber, adding a small amount of softening system can improve the dispersion of carbon black, and the tensile strength may be increased.
2. In natural rubber, adding 10phr or 20phr aromatic oil, the tensile strength of vulcanized rubber decreases by 4% or 20% respectively
3. When 10phr or 20phr aromatic oil is added to SBR, the tensile strength of vulcanized rubber decreases by 20% or 30% respectively.
4. in styrene-butadiene rubber 50/butadiene rubber 50, adding 10phr or 20phr aromatic oil, the tensile strength of vulcanized rubber is basically unchanged
Second, different rubber varieties have selective softeners
1. NR, IR, SBR, BR in the choice of aromatic oil, aromatic oil dosage 5 ~ 15phr
2. butyl rubber IIR, ethylene propylene rubber EPDM in the choice of paraffin oil, naphthenic oil
3. ester plasticizers (DOA, DOS, DOP, DBP) are used first in NBR, CR, Neoprene, and aromatic oils are used second.
4. petroleum resin can ensure the tensile strength of vulcanized rubber is not reduced and improve the processing performance
C. Other methods to improve the tensile strength of vulcanized rubber
Rubber and plastic together
1. NR, SBR/high styrene resin PS
2. NBR/PVC, NBR and polyvinyl chloride
3. NR/PE, natural rubber and polyethylene
4. EPDM/PP, ethylene propylene rubber and polypropylene
5. chemical modification of fillers, especially surface modification of white fillers
6. amine organics such as triethanolamine; polyol organics PEG series
7. metal acid esters such as zirconate esters, titanate coupling agents
8. silane coupling agent
Tensile strength is to characterize the ultimate ability of the product to resist tensile damage. The main factors affecting the tensile strength of rubber are: the main valence bonds of macromolecular chains, intermolecular forces, and polymer chain flexibility.
In testing rubber, the maximum tensile stress during the stretching of the specimen to fracture.
Factors affecting tensile strength.
1, the tensile strength of rubber with small molecular weight increases with the increase in molecular weight. The general molecular weight of rubber between 300,000 and 350,000 tensile strength is the best.
2, the tensile strength of narrow molecular weight distribution is higher.
3, when there are polar substituents on the main chain, the tensile strength increases with the increase of intermolecular forces. For example, in nitrile rubber, acrylonitrile content increases tensile strength increases.
4, with the increase in crystallinity of rubber tensile strength increases. Such as NR, CR, CSM, IIR have higher tensile strength.
5, after the orientation of rubber molecular chain, the tensile strength in the parallel direction increases, and the tensile strength in the vertical direction decreases.
6, tensile strength decreases with the increase of cross-linked bond energy, and the peak occurs with the increase of cross-linked density. The relationship between cross-linked bond type and tensile strength decreases in the following order: ionic bond - polysulfide bond - double sulfur bond - single sulfur bond - -Carbon bond
7, carbon black particles of small and low structure (such as low structure of high wear resistance), surface oxygen groups containing more (such as slot black) its tensile strength, tear strength, elongation is high.
8, filler with small particles, large surface area, and large surface activity, then the reinforcement effect is good. As for the relationship between structure and tensile strength, the relationship between crystalline rubber with high structure is not good for tensile strength, but the opposite for non-crystalline rubber. Soft rubber carbon black dosage is generally between 40-60 parts.
9, the amount of softening agent exceeds 5 parts, it will make the tensile strength of vulcanized rubber is reduced.
10, improve the tensile strength of other methods. Such as NR/PE, HS blending, NBR/PVC blending, EPDM/PP blending, etc.
A, tensile strength and the relationship between the rubber structure
(1) large intermolecular forces, such as polar and rigid groups, etc.
(2) molecular weight increases, Van der Waals forces increase, chain segments are not easy to slide, equivalent to the formation of physical cross-linking points between molecules, so with the increase in molecular weight, the tensile strength increases, to a certain extent to reach equilibrium.
(3) The influence of the microstructure of the molecule, such as cis and trans structures.
(4) crystallization and orientation
Second, the relationship between tensile strength and vulcanization system
(1) Cross-link density: there is a great value.
(2) cross-linked bond type: with the increase of cross-linked bond energy, the tensile strength decreases; polysulfide bond has higher tensile strength, because the weak bond can play a role in releasing the stress in the stress state, reducing the degree of stress concentration, so that the cross-linked network can evenly withstand the larger stress. For NR, etc., which can produce crystallization, the early breakage of cross-linked weak bonds is also beneficial to the directional crystallization of the main chain.
Third, the relationship between tensile strength and filler
A large number of tests show that: the smaller the particle size, the larger the specific surface area, the greater the surface activity, the higher the structure, the better the effect of reinforcement. At the same time with the filler dosage increases, there is a maximum value, and its size is affected by the rubber species and filler type.
Fourth, the relationship between tensile strength and softening agent
The addition of softeners will lose tensile strength, and with the compatibility of softeners and rubber.