Than đen là chất độn gia cường phổ biến cho cao su, giúp sản phẩm tăng cơ tính và kháng mài mòn tốt. Hai thông số kỹ thuật quan trọng nhất đối với than đen là diện tích bề mặt than đen và lượng dùng. Tuy nhiên, diện tích bề mặt lớn và lượng dùng nhiều không nhất thiết sẽ mang lại cơ tính tốt cho cao su vì hai thông số trên đều có mức tối ưu khi sử dụng. Phần tài liệu bên dưới sẽ trình bày cụ thể vấn đề này.

Regarding tyre applications, the most important contribution of carbon black to tyre performance is the tremendous improvement in tread wear resistance. The amount and type of carbon black play major roles in tread wear. Shieh and Funt [27] examined the effects of carbon black surface area, aggregate size distribution, aggregate complexity, surface activity and the dispersion of carbon black on wear resistance of tyre tread compounds. The surface area of carbon black is the most important parameter affecting tread wear. For a given carbon black loading, the wear resistance passes through a maximum with increased carbon black surface area level as shown in Figure 5.13. For a given carbon black surface area, an optimum loading exists as shown in Figure 5.14. Three possible reasons are responsible for the existence of optimum surface area and optimum loading. First, higher surface area carbon black will create more heat during service, which may induce thermal degradation of the compound. Second, higher surface area blacks will be more difficult to disperse, especially at high loading. Third, higher surface area blacks will have a smaller particle to particle spacing.

In this situation, the polymer chain will not have enough room to change its configuration upon deformation or will be restricted from free motion due to the adjacent carbon black particle, causing higher local stress. Polymer chains will become more susceptible to break because of the higher stress. When the elastomer coil size Dg is greater than the particle-to-particle spacing, uniform dispersion will also be difficult to obtain. The reason behind the optimum loading and optimum surface area for tread wear resistance is mainly attributed to the third factor, spacing between particles. From this point of view, going to a very high surface area black does not necessarily result in improved wear resistance no matter how well the black is dispersed.

Trích đăng từ sách Rubber Technologist’s Handbook, Sadhan K. De và Jim R. White, Smithers Rapra Technology, trang 151 – 153


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