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Scope of application
⑴. Applied to unsaturated rubber: such as NR, BR, NBR, IR, SBR and so on.
⑵. Applied to saturated rubber: for example, EPM can only be vulcanized with peroxide, and EPDM can be vulcanized with either peroxide or sulfur.
⑶. Applied to heterochain rubber: such as Q vulcanization.
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Characteristics of peroxide vulcanization system
⑴.The network structure of vulcanizate is C-C bond, which has high bond energy, high chemical stability and excellent thermal oxygen aging resistance.
⑵. Vulcanizates have low permanent deformation, good elasticity and poor dynamic properties.
⑶. The processing safety is poor and the peroxides are expensive.
⑷. It is widely used in static sealing or high temperature static sealing products.
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Key points of peroxide vulcanization
⑴. Dosage: varies with different types of glue
Crosslinking efficiency of peroxides: how many grams of rubber molecules can be chemically crosslinked by organic peroxides of 1g molecules.
If the peroxide of 1 molecule can make the rubber of 1 g molecule cross-linked, the cross-linking efficiency is 1.For example, the cross-linking efficiency of SBR is 12.5, the cross-linking efficiency of NR is 10.5, the cross-linking efficiency of NBR, IIR is 0.
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Using active agents and co-curing agents to improve cross-linking efficiency
The function of ZnO is to improve the heat resistance of the compound, not as an activator. The function of stearic acid is to improve the solubility and dispersion of ZnO in rubber. HVA-2 (N-methylene-o-phenylene-bismaleimide) is also an effective active agent of peroxide.
Add co-vulcanizing agent: mainly sulfur, other co-crosslinking agents such as divinylbenzene, trialkyl cyanurate, unsaturated carboxylate and so on.
- Add a small amount of alkaline substances
such as MgO, triethanolamine, etc., to improve the cross-linking efficiency and avoid using acidic fillers such as trough carbon black and silica (acidic substances passivate free radicals); antioxidants are generally amine and phenolic antioxidants, which are easy to passivate free radicals and reduce cross-linking efficiency, and should be used as little as possible.
- . Curing temperature:Should be higher than the decomposition temperature of peroxide
- Curing time:It is generally 6-10 times the half-life of peroxide.
Peroxide half-life: the time it takes for peroxides to decompose to half of their original concentration at a certain temperature, expressed as T1bin2.
If the half-life of DCP is 1min at 170℃, the positive curing time should be 6~10min.
Formula example: EPDM 100 (matrix)
S 0.2 (auxiliary vulcanizing agent)
SA 0.5 (activator)
ZnO 5.0 (improved heat resistance)
HAF 50 (reinforcing agent)
DCP 3.0 (curing agent)
MgO 2.0 (improve crosslinking efficiency)
Operating oil 10 (softener)
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Characteristics, advantages and disadvantages of peroxide vulcanization system
Advantages:
1. The network structure of peroxide vulcanizate is C-C bond, which has high bond energy, high chemical stability, excellent thermal oxygen aging resistance and low pressure deformation.
2. The curing speed is fast at high temperature, and there is no vulcanization reversion phenomenon.
3. Peroxide vulcanizate has low permanent deformation, good elasticity and poor dynamic performance.
4, good color stability, no pollution, most peroxides do not spray frost, storage without burning danger.
5. The formula is simple, and it is easy to be vulcanized when mixed with different polymers.
Disadvantages:
1. The curing speed is slow at low temperature, so high curing temperature of glue is required.
2. The physical and mechanical properties of vulcanizate are low, such as tension, tear, wear resistance and so on. Especially at high temperature, the tear resistance is poor.
3. Most peroxides have a bad smell and may react with other compounding agents.
4. The processing safety of peroxide is poor, and the price of peroxide is expensive.
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