The surface activity of most non-asbestos fibers is very poor, which leads to the lower wettability between fibers and rubbers. Therefore, in order to obtain a good interface bonding strength, the reinforcing fibers must be pretreated by suitable surface treatment methods. The commonly used surface treatment methods include surface activating treatment and dipping treatment.
Some NASC were developed by the molding process with aramid short fiber as reinforcing fiber, and NBR and NR as elastic binding material. Three surface treatment methods were adopted to pretreat aramid fiber; they are RFL latex dipping, HRH binding agent treatment and silane coupling agent dipping. The results of SEM observation of the developed NASC are shown in Fig. 5.
It can be seen that the surfaces of the aramid fibers without treatment are very smooth, and there are only a few rubber particles adhering on the fiber surfaces. After surface treatments, the adhesion effect between fiber and rubber matrix was obviously improved.
Carbon short fiber can be treated by coupling agent dipping process or epoxide resin coating process after pretreating by air oxidation process or low temperature plasma process. The transverse tensile strength of NASC developed by the calender process was
tested after aging treatment at 623 K, and the results are shown in Fig. 6. It can be seen that surface treatments have improved the reinforcing effects of carbon fiber.
The treatment effect of glass fiber by coupling agent is also distinctive, as illustrated in Fig.
7. The glass fiber should be firstly dipped in a silicon coupling agent water solution for pretreatment, and then immersed into an epoxide resin methylbenzene solution (2wt%) for further coating treatment. Finally, they must be dried at 423 K to solidify impregnated layer.
Aging treatment time (h)
Fig. 7. Transverse tensile strength of glass fiber reinforced NASC after aging at 623 K
The SEM photos of transverse tensile fracture sections of carbon/ glass hybrid fiber reinforced NASC aged at 623 K for 5 hours are shown in Fig. 8. It can be seen that the intertwined and the rubber coating conditions of fibres are obviously improved after the surface treatment of the fibers by the coupling agent/epoxide resin coating process.
(a) Treated by coupling agent/epoxide (b) Without surface treatment
resin coating process
Fig. 8. SEM photos of transverse tensile fracture sections of carbon/glass hybrid fiber reinforced NASC