The vulcanization system of rubber commonly used is sulphur-yellow vulcanization system and organic peroxide system. Sulphur-yellow vulcanization is mainly used in the diene rubber, and the vulcanized adhesive with sulfur crosslinking bond is obtained. Organic peroxide is a kind of vulcanization system which has been developed rapidly and applied widely in recent years [1-2]. Organic peroxide system can be vulcanized diene rubber and non-diene rubber, the resulting cross-linking bond is the C bond, the bond can be produced by the sulphur-yellow vulcanization system of the single sulfur, double sulfur and disulfide bond is large, Organic Peroxides so the organic peroxide vulcanizate excellent heat resistance, compression permanent deformation small, with simple, not easy to spray frost, not like sulphur vulcanization system to produce the phenomenon of vulcanization; but the tensile stress-strain performance and fatigue resistance of vulcanized rubber are poor.
In addition to butyl rubber and halogenated butyl rubber, almost all other rubber can be organic peroxide. The most commonly used organic peroxide is silicone rubber (VMQ), EPDM (EPDM), Nitrile Rubber (NBR), hydrogenated nitrile rubber (HNBR), chlorinated polyethylene (cm), thermoplastic elastomer (TPV), Neoprene (CR) and so on. Although the organic peroxide system is easy to cooperate, but in the formula component, the type of rubber, Organic Peroxides the variety and dosage of peroxide and cross-linking agent, the interaction of other coordination agents have a great effect on the crosslinking of the adhesive and the performance of the vulcanizate; the process conditions of rubber processing also need to be compatible with the vulcanization system. The authors use the methods of adding multifunctional active crosslinking agent and compound vulcanization system to improve the organic peroxide system to meet the overall requirements of the product's performance, processing technology and cost [3-5].
1 Organic peroxide system
The mechanism of peroxide crosslinking is mainly: The free radicals are produced by splitting of peroxide and rubber, and then the crosslinking reaction is made through free radicals plus reactive or ɑ-methylene active hydrogen on the chain of rubber molecule, thus forming C crosslinking bonds in the reaction process. Organic Peroxides The vulcanization process of peroxide on elastomers, it is mainly divided into three steps: (1) The peroxide occurs in the split, forming two alkyl oxygen free radicals, (2) The alkyl oxygen radicals take the hydrogen atom from the polymer chain, and (3) The free radical binding of two adjacent polymer chains to form a carbon-carbon bond.
Peroxide used for vulcanization of rubber is a class of substances containing O bonds. At present, the main industrial production of five types of peroxide is: Two acyl peroxide, Organic Peroxides tert-alkyl peroxide acid ester, alkyl hydroperoxide, dimethyl peroxide, dimethyl acetal. The most commonly used is the peroxide of diisopropyl benzene (DCP), Benzoyl peroxide (BPO), 1, 1-di-tert-butyl peroxide-3, 3, 5-three methyl cyclohexane (BPMC), 2, 5-Two-2, 5-bis (tert-butyl) hexane (DBPMH), 1, 3-bis (tert-butyl oxygen isopropyl) benzene (BIPB), etc. Their basic characteristics are listed in table 1.
In the organic peroxide system, the decomposition temperature of peroxide is very important, which is mainly related to the stability of the oxygen-peroxide bond. The stability of the over oxygen bond depends on the group around it. The degree of decomposition of peroxide depends on the time and temperature of heating. When peroxide decomposes, Organic Peroxides the lower the temperature of the heat, the longer the decomposition time . A method for characterizing peroxide stability is known as the half-life temperature. The half-life temperature varies greatly with peroxide. At any temperature, the decomposition rate of peroxide with lower half-life temperature is faster than that of peroxide with higher half-life. The peroxide with higher half-life temperature has better scorch resistance, Organic Peroxides slow vulcanization usually requires slower processing speed, and peroxide with lower half-life temperature, faster vulcanization rate and faster processing speed, but may cause coke burning. This equilibrium relationship is often considered when choosing peroxide.
crosslinking time and crosslinking temperature were correlated with the half-life of peroxide. For the typical peroxide used in the rubber industry, the temperature increases by 10 ℃ and the half-life is reduced to 1/3 of its original.
2 cross-linked agent
Compared with sulphur-yellow vulcanization, the wear-resisting property and dynamic performance of organic peroxide adhesive are worse. The addition of some functional monomers with free radical polymerization properties in organic peroxide systems, to a certain extent, can overcome these shortcomings, while improving the crosslinking efficiency of peroxide, speed up the vulcanization, Organic Peroxides reduce the decomposition temperature of peroxide, maintain the excellent performance of vulcanizate, some of the cross-linking agent can effectively reduce the odor of vulcanizate. The commonly used active crosslinking agents include two types:
The first type of cross-linking agent is usually a group of low relative molecular weight compounds with polar groups, which can be clustered or grafted onto a polymer chain. such as tri-hydroxy methyl propane ester (TMPTA), tri-hydroxy methyl methacrylate (tmptama), ethylene glycol acrylate (EGDA), dimethyl methacrylate (EGDMA), N, n′-to phenyl bismaleimide (PDM or HVA-2), Zinc (ii) acrylate (Zda), zinc dimethacrylate (ZDMA), etc. Among them, Tmptma and Tmpta are also called hardening agents, in the use of organic peroxide, can effectively increase the hardness of vulcanizate, the general dosage of 1 can increase the hardness of 1 units; PDM is a multifunctional vulcanizing additive, which can increase the crosslinking efficiency and increase the tensile stress of vulcanized rubber in sulphur yellow vulcanization, Organic Peroxides organic peroxide or resin oxime vulcanization.
The second kind of cross-linking agent can form the free radicals with weaker reaction performance, and only have effect on the degree of vulcanization. They form free radicals mainly by taking hydrogen. such as cyanuric acid allyl ester (TAC), cyanuric acid allyl ester (TAIC), 1, 2-polybutadiene (1, 2-PBR), sulphur yellow and so on. Among them, the most commonly used are TAC and taic, commonly used as peroxide 50%~100%, sulphur yellow can be used as EPDM effective crosslinking agent, to a certain extent, improve the tensile and tearing properties of vulcanizate, but the addition of sulphur yellow will make the odor of vulcanizate increased.
The mechanism of the cross-linking agent is generally considered to have the following two kinds: The molecule contains two or more unsaturated groups, under the condition of free radicals, these unsaturated groups may be polymerized, forming similar resin-enhancing substances. The elastic modulus of the plastic material increases more than the individual use of peroxide. The mechanism of this reaction is not very clear. One hypothesis is that, in the presence of free radicals, active auxiliaries are polymerized into multiple branched-chain resin-reinforced fillers; Another hypothesis is that the active agent and the polymer on the free radicals, become the polymer branched-chain. Organic Peroxides The actual mechanism may be the combination of two mechanisms [7-8].
Although adding some additives can improve the safety of Coke burning, but has a great effect on vulcanization properties, such as Grima [9-10] adding bismaleimide as N in DCP vulcanization system, n-m-bismaleimide (BMI-MP) and sulfur-giving body, such as the six-vulcanization double-methylene brace Autumn Lamb (DPTT), this coordination can be very good to prevent scorch, while improving the mechanical properties of vulcanizate. Organic Peroxides They also found that the mechanical properties provided by N-n-p-bismaleimide (BMI-PP) in Bismaleimide were better than BMI-MP. The effect of the content of the crosslinking agent and the sulfur-giving body on the ignition time and the mechanical properties of the adhesive is greater, when the crosslinking agent is 4 and the sulfur-giving body is 0.7-0.9, each performance achieves the best value.
Chen  The effects of active crosslinking agent N, n′-bis-furfuryl Acetone (VP-4) on vulcanization properties, mechanical properties, heat-resisting air ageing, crosslinking density and permanent deformation of DCP vulcanizate were studied. When the VP-4 dosage is low (0. 5-2.0), the vulcanization time of the compound was shortened, the maximal elastic torque and crosslink density increased, and the compression permanent deformation value decreased obviously, which indicated that VP-4 had the obvious promoting crosslinking effect. VP-4 can effectively improve the heat-resisting air aging performance of vulcanizate, especially the heat-resisting air aging performance of high temperature (150 ℃).
Jelencic et  studied the action mechanism of TAC in the organic peroxide system on EPDM. It is found that the TAC can hinder the decomposition of EPDM chains, and the TAC can react with other bonds that are cracked in the vulcanization process by forming a bridge-type structure that aids the cross-linking agent. Huangminglu , such as in the organic peroxide cm, the addition of auxiliary crosslinking Agent TAC or taic will cause a slight delay in scorch time, with the prolonged vulcanization time, the cross-linking agent appears to promote the cross-linking effect obviously. The difference of the effect between TAC and taic depends on the different molecular activity, which is not obvious due to the similar structure. Zhang Yong et  The effects of peroxide system composed of DCP and crosslinking agent taic on the crosslinking and product tensile properties of liquid EPDM were studied. The results showed that the gel content of the liquid EPDM had no significant change with the increase of DCP, but it increased with the increase of taic, and the tensile properties of the crosslinking products had a similar trend. Organic Peroxides It is indicated that when the peroxide quantity reaches saturation, the crosslinking agent does increase the efficiency and tensile properties of the cross-linking.
Yang et  investigated the vulcanization properties, crosslinking density and physical properties of epdm/vinyl Polybutadiene rubber (1, 2-PBR) and epdm/br with adhesive in organic peroxide system. After the discovery of EPDM with 1, 2-PBR and BR, the crosslinking density, 100% stretching stress, shore type a hardness and tearing strength of vulcanizate increased, and the former increases greatly. Through differential scanning calorimetry, the results showed that: EPDM/1, 2-PBR and 1, and 2-pbr the degree of total vulcanization. Organic Peroxides This is because the cross-linking efficiency of organic peroxides depends mainly on the degree of susceptibility of the rubber molecule to dehydrogenation. Due to the difficulty of dehydrogenation is: 1, 2-pbr> BR >EPDM, and therefore with 1, 2-PBR and BR will lead to the increase of EPDM crosslink density, and EPDM/1, 2-PBR and the increase of the rubber is greater than epdm/br and glue. Hongmei  think that in the TPV of high EPDM dosage, 1, 2-PBR can improve the crosslinking density of the material, and in the TPV with low EPDM dosage, 1 and 2-pbr play a role as plasticizers. With the increase of PP dosage, the effect of EPDM crosslinking degree on the performance of TPV system is no longer obvious.
Yang Wenliang et  studied) vulcanizing agent Tmch (1-1-Two (tert-butyl oxygen)-3, 3, 5-three-methyl cyclohexane and vulcanizing Agent two Furfuryl acetone (VP-4), taic, Tmptma, HV-268 (bismaleimide) alone and the use of the case, found that HV2268 as a total crosslinking agent (1.2 phr, with taic and 1.0 phr), vulcanized rubber physical and mechanical properties of good, thermal aging performance or, fast, Good demoulding. At the same time, because the vulcanization temperature is lower than the general peroxide, the thermal tearing damage is alleviated to some extent. Sulfide products non-toxic, smell light (again after 150℃x20 min about two pieces of treatment after the basic smell), in line with the requirements of the food industry.