A kind of hydrophobic silica with good dispersibility was prepared first.The silica and epoxy natural rubber (ENR) were blended in Haake internal mixer at high temperature in a powerful shear force filed

and so the grafted silica was made through in-situ grafting reaction between the hydroxyl groups of silica and the epoxy groups of ENR.The grafting processes were performed as follows:first

the silica should be dried about 24 h at 100℃ in an oven to remove the free water molecules that absorbed on the surface of silica.Secondly

the grafting reaction temperature was chosen at 170℃ that confirmed by the test result of a Monsanto MDR2000 moving die rheometer

and the weight proportions between silica and ENR were chosen to be 1:1

2:1 and 3:1 separately in this study.Thirdly

ENR was mixed in HAAKE internal mixer about 1 min

then silica was added to react with the ENR for another 15 min before discharged

and the outputs named ENR-grafted silica were obtained as we wanted.In order to obtain an appropriate grafting condition

the effect of different weight proportions between silica and ENR on the stress-strain curves of natural rubber composites reinforced by the grafted silica was discussed.Through analyses of the reinforcement effect

the appropriate proportion between silica and ENR was chosen to be 3:1.FTIR

TGA and TEM analysis results indicated that ENR was successfully grafted onto the silica surface.FTIR result of the grafted silica showed the new absorptions. The peaks at 2966，2929 and 2862 cm-1 are assigned to C—H stretching vibrations.The absorption band at 1660 cm-1 is characteristic of C＝C stretching.The stretching vibration of epoxy groups that should be at 870 cm-1 was missing

suggesting the epoxy groups were almost used up to react with silanol groups.A new shoulder peak appears at 3640 cm-1

which is ascribed to —OH stretching of C—OH which is the result of the reaction of silanol groups and ENR.TGA curves revealed ENR grafted silica showed a new step between 348～449℃ due to the decomposition of ENR

and the grafting rate reached 21.3%.TEM images indicated the size of silica agglomerates became small obviously after modification because of the grafting layer preventing the silica particles from conglomerating.Then

compared with the silica without grafting

the properties of NR composites filled with grafted silica were investigated.The “Payne effect” results indicated that the grafted ENR molecules reduced the silicasilica interaction by enhancing the rubbersilica interaction

and so the grafted silica had better dispersibility in natural rubber (NR) composites.Mechanical properties test of NR composites proved that the grafted silica could more effectively improve the reinforcement effect due to the strong interface combination between silica and ENR.DMA results showed that the temperature of glassy transition of ENR bound to the silica surface shifted to higher temperatures.Consequently

the composite contained the grafted silica had high strength and high hysteresis at the same time on the normal temperature.So the composites have potential application in the shocking absorber products

the tire of racing cars

and so on.