As one of the earliest materials used in the rubber industry, the role of zinc oxide has been changing with the development of rubber technology.
From the initial coloring agent, reinforcing agent to the vulcanization system can shorten the vulcanization time of the active agent, chloroprene rubber and carboxy rubber in the vulcanizing agent, dynamic conditions of the rubber products used in the thermal conductivity of the filler, etc., which as a vulcanization system of the active agent, zinc oxide is still the most effective kind of material. Magnesium oxide can also be used as an active agent in the vulcanization of rubber, but because of the lower activity and the physical properties of the rubber material is poor, so magnesium oxide is mainly used as a vulcanizing agent and heat stabilizer in halogen-containing rubber.
Peroxide vulcanization is peroxide and rubber in the vulcanization process occurs free radical addition reaction to form a higher bond energy c-c bond.
Compared with sulfur yellow vulcanization, it has the advantages of good heat resistance, excellent compression permanent deformation performance, not easy to spray frost, and simple coordination, etc. In recent years, it has been widely used in rubber products under high temperature conditions. From the cross-linking mechanism, peroxide vulcanization system can not be activated by metal oxides, but in the actual production process, people still often add about 5 parts of metal oxides in the formula, and its specific use of the effect of different opinions. The study shows that nano zinc oxide, magnesium oxide, calcium oxide and unsaturated acid can be used as a new co-crosslinking agent in peroxide vulcanized hydrogenated nitrile butadiene rubber (HNBR), which can shorten the vulcanization time and improve the crosslink density and physical properties, but the effect on the heat resistance of the rubber is not mentioned.
1. The effect of zinc oxide or magnesium oxide on the properties of rubber material
Compared with the blank sample, the addition of zinc oxide or magnesium oxide rubber M have increased, and zinc oxide rubber ML is higher, this is due to the zinc oxide has a larger surface area and a strong interfacial effect, in the rubber matrix is not easy to disperse, easy to cohesion, agglomeration, which causes the rubber ML increased, poor fluidity. The addition of metal oxides also increases the MH-ML of the compound, which indicates that metal oxides can promote crosslinking, improve the degree of vulcanization, but also shorten the T10 but have little effect on the T90. In addition, the MH-ML of zinc oxide compounds was higher than that of magnesium oxide compounds at the same dosage, which indicates that zinc oxide has a greater activating effect on vulcanization than magnesium oxide in the peroxide vulcanization system.
With the increase of zinc oxide and magnesium oxide dosage, the tensile strength of vulcanized rubber first increases and then decreases, the 100% constant elongation stress overall tendency to increase, while the elongation at break and tear strength is a decreasing trend, and in the same dosage of zinc oxide rubber material constant elongation stress is higher than the magnesium oxide rubber material, this is the same with the vulcanization characteristics of the MH-ML trend, but when the dosage of zinc oxide is 10 parts of the 100% constant elongation stress of vulcanized rubber is a decreasing trend, which may be caused by poor dispersion of zinc oxide. However, when the dosage of zinc oxide was 10 parts, the 100% constant elongation stress of the vulcanized rubber showed a decreasing trend, which might be caused by the poor dispersion of zinc oxide. In summary, the addition of metal oxides can improve the crosslinking density of HNBR rubber under the peroxide vulcanization system, and the degree of crosslinking of zinc oxide-containing rubber is higher than that of magnesium oxide under the same dosage, but when the dosage of zinc oxide is 10 portions of the poor dispersion, which causes the decrease of the constant elongation stress. From Table 2, it can also be seen that the addition of metal oxides can improve the hardness, but with its dosage does not change much, and the effect on the rebound value is not significant, in which the zinc oxide dosage does not have a significant effect on DIN abrasion, magnesium oxide vulcanized adhesive abrasion with its dosage increases and tends to increase, but the overall abrasion is still in the lower level, which also fully demonstrates that the HNBR adhesive has excellent abrasion resistance.
The aging of HNBR belongs to the chain cross-linking type, which is manifested in the decrease of tensile elongation and the increase of hardness and tensile strength after aging. This indicates that the cross-linking reaction continues during the aging process, which increases the cross-linking density, and the tensile strength of all the rubbers increases after aging, indicating that HNBR has excellent high temperature tensile properties. In addition, the addition of zinc oxide and magnesium oxide significantly improved the
In addition, the addition of zinc oxide and magnesium oxide can significantly improve the rate of change of tensile elongation after heat resistance, and the rate of change of tensile elongation of the rubber material decreases with the increase of the dosage of the material, which shows excellent high-temperature resistance, which may be attributed to the fact that metal oxides themselves belong to the thermally stable substances and can increase the cross-linking density of the rubber material, which can further impede the attack of the molecular chain of oxygen, and improve the high-temperature resistance performance of the rubber material. At the same time, the addition of zinc oxide can significantly reduce the compression permanent deformation of the rubber, but with its dosage does not change much; magnesium oxide on the compression permanent deformation of the impact is not very significant. Therefore, the addition of appropriate amount of metal oxides in the peroxide vulcanization system helps to improve the heat resistance of the rubber.
When the dosage of zinc oxide is 5 parts, the TG-DTG curve of HNBR rubber material, such as the thermal decomposition of the rubber material appeared a very obvious two stages, which is mainly due to the two different groups of the HNBR molecular chain decomposition temperature is different. The first stage is mainly the butyl
The first stage is mainly caused by the thermal cleavage of the double bond in butadiene, and the second stage is caused by the cyclization of the acrylonitrile chain segment during the heating process to form a chelate compound, which can only be cleaved at a very high temperature , so there are two obvious thermal cleavage stages, and the maximum decomposition temperature of the rubber material appeared at 468.49 ℃, which shows a high thermal stability.
The initial thermal decomposition temperature (when the mass loss rate is 5%) and the maximum decomposition rate temperature of the rubber material have basically the same trend, and the addition of metal oxides can reduce the maximum mass loss rate of the rubber material, in which the initial thermal decomposition temperature of 5 parts of zinc oxide rubber material is increased by nearly 15 ℃ compared with that of the blank rubber material, which indicates that the 5 parts of zinc oxide can significantly improve the thermal stability of the rubber material, but when the dosage of zinc oxide is 10 parts, the initial thermal decomposition However, when the dosage of zinc oxide was 10 parts, the initial thermal decomposition temperature decreased. This may be due to: (1) the poor dispersion of zinc oxide; (2) too much zinc oxide in the peroxide vulcanization system produced cross-linking bonds detrimental to the thermal stability. The exact reason for this remains to be further investigated.The initial thermal decomposition temperature of the 5-part magnesium oxide rubber material was reduced compared to that of the blank rubber material, and the thermal decomposition temperature of the rubber material could only be increased when the amount of magnesium oxide was 10 parts. The use of TG analysis to characterize the heat resistance of silicone rubber, the results show that the heat air aging performance of silicone rubber and the thermal decomposition temperature in an oxygen atmosphere of the trend of change is more consistent, but in this test the two did not form a certain correspondence, but rather is the maximum rate of mass loss and the trend of change in the performance of the hot air aging is more consistent, which may be due to the thermal decomposition of the different types of rubber and the different thermal decomposition mechanism and the TG analysis of the conditions (such as gas atmosphere). This may be due to differences in the thermal decomposition mechanism of different rubber types and different conditions of TG analysis (e.g. gas atmosphere), so if TG analysis is used to evaluate the hot air aging resistance of the rubber, the actual formulation and test conditions should be considered comprehensively.
2. zinc oxide / magnesium oxide and the use of adhesives on the heat and air aging resistance and compression permanent deformation effect
When the ratio of zinc oxide/magnesium oxide is 7/3, there is a synergistic effect on the hot air aging performance of the adhesive, and the adhesive has the best heat resistance, while the addition of magnesium oxide has a negative effect on the compression permanent deformation resistance of the adhesive.
Conclusion
(1) )The addition of zinc oxide or magnesium oxide in HNBR peroxide vulcanization system can produce activation effect on the rubber material and improve the degree of crosslinking of the rubber material, and the activity of zinc oxide is higher than that of magnesium oxide, and the degree of crosslinking of the rubber material shows an upward trend with the increase of its dosage, but when the amount of zinc oxide is 10 portions, it may result in the decrease of the constant tensile stress because of the poor dispersion, but the fluidity of the rubber material deteriorates, which has little effect on the rebound value and the abrasion resistance. Abrasion resistance has little effect.
(2) Single use of zinc oxide or magnesium oxide can significantly improve the heat and air aging resistance of peroxide vulcanized HNBR compounds, and with the increase of the amount of heat resistance, heat resistance and abrasion resistance.
The amount of heat resistance increases, while the addition of zinc oxide can improve the compression permanent deformation resistance of the rubber, while magnesium oxide has little effect on it.
(3)The thermal decomposition of HNBR rubber is in two stages, the addition of metal oxides can reduce the maximum rate of mass loss, 5 parts of zinc oxide can significantly improve the thermal stability of the rubber.
(4) When zinc oxide / magnesium oxide and the ratio of 7 / 3, the best heat resistance of the rubber, but the magnesium oxide has a negative impact on the rubber's resistance to compression permanent deformation performance.
