The dispersion of nano filler in rubber matrix has a decisive impact on the comprehensive properties of rubber. Effectively improving the dispersion of nano filler in rubber is the key to the development of high-performance tire rubber. Epoxidized natural rubber (ENR) is the product of natural rubber (NR) modified by epoxidation. Under the condition of not using any coupling agent, nano silica (white carbon black) is added to ENR. Through the interaction (hydrogen bond or chemical bond) between the epoxy group on the molecular chain of ENR and the silicon hydroxyl group on the surface of white carbon black, the agglomeration of white carbon black is inhibited and the white carbon black is uniformly dispersed in the rubber matrix, so as to improve the performance of the compound.


The application of silica in epoxidized natural rubber (ENR) without any coupling agent was studied. Silica will agglomerate obviously in natural rubber (NR), while the agglomeration in ENR can be significantly improved. The higher the epoxidation degree of ENR, the better the dispersion of silica. ENR silica compound showed good wet skid resistance and low rolling resistance. When the amount of silica was more than 20 phr, the compression heat generation of ENR / silica compound was significantly lower than that of NR / carbon black compound.


Silica agglomerated obviously in NR compound. When the amount of silica was more than 20 phr, a large number of agglomerates appeared in the compound. This is because white carbon black has very large surface energy and there are a lot of silicon hydroxyl groups on the particle surface. Without any coupling agent, the dispersion of white carbon black in NR is poor. In ENR compound, due to the introduction of epoxy group in NR molecular chain, the agglomeration of white carbon black has been significantly improved. White carbon black is uniformly distributed in ENR matrix, and the dispersion of white carbon black in enr40 compound is better than enr25 compound, indicating that the higher the content of ENR epoxy group, the better the dispersion of white carbon black in ENR.


Dynamic mechanical property analysis

After epoxidation modification of some double bonds in NR molecular chain, the flexibility of molecular chain decreased and the glass transition temperature (TG) increased. Rubber loss factor (tan) of NR and ENR without silica δ）。

Tan of rubber at 0 ℃ δ With the increase of ENR epoxidation modification degree, it shows that the dynamic lag loss of the compound becomes larger and the wet slip resistance is improved. Tan of enr25 and enr40 compounds at 0 ℃ δ (characterization of wet skid resistance) greater than NR compound, tan at 60 ℃ δ (characteristic rolling resistance) is less than NR, indicating that its wet sliding resistance and rolling resistance have been improved at the same time.


After the addition of silica, the wet slip resistance of enr40 compound is better than that of NR compound, and the rolling resistance of enr25 is less than that of NR compound; When the amount of silica is 20 phr, the rolling resistance of enr40 rubber is equivalent to that of NR rubber. When the epoxidation degree of silica rubber increases, the compression heat generation of rubber increases. This is because NR molecular chain contains a large number of double bonds, the flexibility of molecular chain is good, and the internal friction between molecular chains is low; After the double bond on the rubber molecular chain is modified into epoxy group, the flexibility of the molecular chain decreases and the friction internal friction between the molecular chains increases. Therefore, the heat generation of the rubber increases with the increase of the epoxidation degree of the rubber. With the addition of silica, under dynamic stress-strain conditions, the relative motion between rubber macromolecular chains, between rubber molecular chains and filler particles, and between filler particles is not synchronous. Because the friction between rubber molecular chains belongs to small inter structural friction, the friction between filler particles belongs to nano particle friction at least. Relatively speaking, the addition of filler makes the friction more intense, As a result, the overall dynamic heat generation of the compound is greatly improved. The influence of filler on the dynamic properties of rubber compound mainly comes from the following two aspects: the contact interface between filler and rubber molecules and the amount of filler. Generally speaking, the smaller the particle size of the filler, the larger its specific surface area, the greater the surface energy, and the easier it is to agglomerate to reduce the surface energy. The harder it is to disperse the filler after agglomeration, the worse the dispersion, the worse the dynamic performance of the rubber, the greater the heat generation, and the easier it is to be destroyed by high-temperature ablation in the process of use; The larger the amount of filler, the more friction parts between filler particles and rubber molecules, and the greater the dynamic heat generation.


With the increase of the amount of silica, the compression heat generation of NR / silica rubber increases rapidly, which is due to the serious agglomeration of silica in NR rubber, and the friction between fillers is dominant under the dynamic action. When the amount of silica is 20 phr, the heat generation of NR compound is greater than enr25 compound and lower than enr40 compound; Without using any coupling agent, silica agglomerates obviously in NR matrix, while the aggregation of silica is obviously inhibited by introducing epoxy group into NR molecular chain, and the higher the content of epoxy group, the better the dispersion of silica. ENR / silica compound has good wet skid resistance and low rolling resistance; When the amount of silica is more than 20 phr, the compression heat generation of ENR / silica compound is significantly lower than that of NR / silica compound, which is of great significance for high-performance green tire.