1.Application scope
(1). Applied to unsaturated rubber: such as NR, BR, NBR, IR, SBR, etc.
(2). Apply to saturated rubber: such as EPM can only be vulcanized by peroxide, EPDM can be vulcanized by both peroxide and sulfur.
(3). Applied to miscellaneous chain rubber: such as Q vulcanization.
2. Characteristics of peroxide vulcanization system
(1). The network structure of the vulcanized rubber is C-C bond, with high bond energy, high chemical stability, and excellent resistance to thermal and oxygen aging.
(2). Vulcanized rubber has low permanent deformation, good elasticity and poor dynamic performance.
(3). Poor processing safety and expensive peroxide.
(4). In static sealing or high temperature static sealing products have a wide range of applications.
3．Commonly used peroxides
Commonly used peroxide vulcanizing agents are alkyl peroxides, diacyl peroxides (dibenzoyl peroxide (BPO)) and peroxy esters. Among them, dialkyl peroxides are widely used. Such as: diisopropyl peroxide (DCP): is currently the most used a vulcanizing agent.
2,5-dimethyl-2,5-(di-tert-butylperoxy) hexane: also known as bis-dipentyl
4. Peroxide vulcanization mechanism
The peroxide group of peroxide is easily decomposed by heat to produce free radicals, which trigger the free radical type cross-linking reaction of rubber molecular chain.
5. Key points of peroxide vulcanization:
(1). Dosage: varies with different rubber species
Cross-linking efficiency of peroxide: 1g molecule of organic peroxide can make how many grams of rubber molecules produce chemical cross-linking.If 1 molecule of peroxide can make 1g molecules of rubber cross-linked, the cross-linking efficiency is 1.
For example: the cross-linking efficiency of SBR is 12.5; the cross-linking efficiency of BR is 10.5; the cross-linking efficiency of EPDM, NBR, NR is 1; the cross-linking efficiency of IIR is 0.
(2). Use of active agent and co-sulfurizing agent to improve the cross-linking efficiency
The role of ZnO is to improve the heat resistance of the adhesive, not the activator. The role of stearic acid is to improve the solubility and dispersion of ZnO in the rubber. HVA-2 (N,N'-phthalimido-dimaleimide) is also an effective activator of peroxide.
Adding auxiliary vulcanizing agent: mainly sulfur yellow, and other auxiliary cross-linking agents such as divinylbenzene, trialkyltricyanate, unsaturated carboxylates, etc.
(3). Add a small amount of alkaline substances, such as MgO, triethanolamine, etc., to improve the efficiency of cross-linking, avoid the use of slot carbon black and silica and other acidic fillers (acid to make free radicals passivation); antioxidants are generally amine and phenolic antioxidants, also easy to make free radicals passivation, reducing the efficiency of cross-linking, should be used sparingly.
(4). Vulcanization temperature: should be higher than the decomposition temperature of peroxide
(5). Vulcanization time: generally 6~10 times of the half-life of peroxide.
Peroxide half-life: at a certain temperature, the peroxide decomposition to half of the original concentration of the time required, expressed in t1/2.
If the half-life of DCP at 170℃ is 1min, then its positive sulphation time should be 6~10min.
Formulation example: EPDM 100 (base)
S 0.2 (auxiliary vulcanizing agent)
SA 0.5 (activator)
ZnO 5.0 (to improve heat resistance)
HAF 50 (reinforcing agent)
DCP 3.0 (Thixotropic agent)
MgO 2.0 (Improves cross-linking efficiency)
Operating oil 10 (softening agent)
