Application Of Vulcanizing Agent DTDM In Rubber

The semi effective vulcanization system can make the proportion of sulphur and polysulfide bonds in vulcanizates moderate, so that the tensile strength and fatigue resistance of vulcanizates are balanced, and the heat resistance and aging resistance are good.

The curing agent DTDM, also known as 4,4 "- two thio two morpholine, is a sulfur donor which is widely used in semi effective vulcanization system. It can release single sulfur or disulfide free radicals. When vulcanized rubber is formed, it mainly forms a single sulfur bond or disulfide bond, and the vulcanizate has good heat and oxygen aging resistance.

Therefore, the effective vulcanization system or semi effective vulcanization system of DTDM can meet the stringent requirements of high temperature vulcanization.

Because sulfur in DTDM is combined with sulfur, it can avoid the problem of "frosting" caused by excessive coordination.

In addition, DTDM can also decompose the morpholine radical with secondary amine in the process of chemical reaction. This radical not only has the heat and oxidation resistance of amine antioxidant, but also delays the scorching.

Therefore, it becomes an important vulcanization system.

NBR is vulcanized by sulphur vulcanization system, but the vulcanized rubber has large compression deformation and poor heat aging resistance.

This can be improved with other materials, such as fluorocarbon resin, etc., and hydrogenation of NBR can also improve its compression permanent deformation and thermal aging resistance.

Liu Yuzhen and others have studied in detail the effects of DTDM vulcanization system, CZ effective vulcanization system, DCP vulcanization system and sulfur curing system on the compression deformation, compression heat generation, modulus of elasticity and other physical and mechanical properties of NBR, as shown in Table 1.

However, Li Zhonghai's research shows that adding DTDM will adversely affect the bonding strength between NBR and metal.

Nitrile rubber and metal can also produce good adhesion when nitrile rubber is vulcanized by accelerator TMTD. The vulcanizates have excellent heat resistance and less compression permanent deformation. Only vulcanizates are prone to frost phenomenon and affect the appearance of products.

The influence of sulfur curing system, accelerator TMTD vulcanization system and curing agent DTDM curing system on the peel strength of NBR and metal is shown in Table 2.

If DTDM and TMTD are used together, the peeling strength of NBR and metal will increase with the decrease of the dosage of vulcanizer DTDM when the effective total sulphur content of the curing system is basically unchanged.

The vulcanizing system with vulcanizing agent DTDM and accelerator TMTD can not only eliminate the frosting phenomenon, but also improve the bonding strength of vulcanizates. At the same time, vulcanizates also have good heat resistance.

The curing agent DTDM can not only greatly improve the storage stability and processing safety of neoprene compound, but also play a role of heat resistant antioxidant in neoprene, and the effect is obvious.

The physical and thermal aging properties of DTDM and DTDM vulcanizates are shown in Table 3 and table 4.

Different curing systems will have a direct effect on the crosslinking bond types and physical and mechanical properties of vulcanizates.

Peroxide vulcanized vulcanizates have good thermal stability, but their tear properties are poor. In addition, the peroxide price is high and the odor is not good, so its application is restricted to a certain extent.

The sulphur vulcanization system is safe and vulcanized at moderate speed and has good physical and mechanical properties. It is the most widely used vulcanization system in EPDM three.

However, the use of sulphur vulcanization system is likely to cause frosting.

When DTDM is used as vulcanizing agent, DT-DM will decompose active sulfur in the sulfuration process and form a crosslinking bond which is mainly composed of double bonds, so that the vulcanizate has good heat aging property and can avoid the problem of "frosting" caused by the high volume of the product.

Sun Lijun also systematically studied the effect of DTDM on the mechanical properties and thermal aging properties of EPDM compound in the vulcanization system, semi effective vulcanization system and effective vulcanization system.

Through research, they found that in the semi effective vulcanizing system of S=0.5 part, the scorching time of EPDM increased when the amount of DTDM increased, and the comprehensive mechanical properties of EPDM compound decreased with the increase of DTDM dosage (as shown in Figure 1). When DTDM dosage was about 3.5 parts, the tensile strength retention rate and elongation at break rate of aging were better (as shown in Figure 2).

In commonly used curing systems and effective vulcanizing systems, when the amount of DTDM is between 0 and 0.2 parts, the comprehensive mechanical properties of EPDM compound are better. With the increase of DT-DM content from 0.2 to 1 parts, the comprehensive mechanical properties of the rubber material decrease (as shown in figures 3 and 4).

When the dosage of DTDM is 0.4 to 0.6 parts, the thermal aging property of the compound is excellent. In the S=0 effective curing system, the comprehensive mechanical properties of EPDM compound decrease with the increase of DTDM dosage.

When the dosage of DTDM is between 3 and 3.5, the EPDM vulcanizate has good thermal aging resistance.

A comprehensive analysis of many research results shows that if the DTDM vulcanization system is used alone, the curing speed is slow, the scorching time of EPDM compound is prolonged, and the trend of DTDM influencing the mechanical properties and heat aging properties of EPDM vulcanizates is different. It is necessary to select suitable DTDM dosage according to actual needs.

If a small amount of sulfur is added, the effect is better, and has the advantages of safe operation, no frost spray, no color change, no pollution, etc., and the vulcanizate has good heat resistance and aging resistance.

In synthetic rubber, DTDM and other complementary vulcanization systems can improve the comprehensive properties of rubber products. For example, the semi effective vulcanization system consisting of sulfur / accelerator DTDM/CZ/TMTD used in the fuel oil special rubber hose NBR/PVC of the car can effectively integrate the relationship between the mechanical properties and the production process of the rubber.