Research On Properties Of Aramid-pulp Surface Modified Reinforced Nitrile Rubber Composites

Aramid Pulp(AP) is a kind of products but different from PPTA fiber, which has unique ultrafine short fiber structure. A mas of ultrafine fibrils structure on the surface of AP, results in an increase of the potential specific surface area between AP and substrates such as rubber, which is desirable for improving mechanical interlocking and increased bondable surface area. However the more ultrafine fibrils, the stronger physical tangle ability, which leads to a decrease of the dispersion property to some extent. AP can be modified on the surface and be dispersed in Pre-dispersion(PD), which can improve the surface performance and improve the interface between AP and composite material, such as the nitrile rubber(NBR).Poly-dopamine(PDA) can be deposited on the surface of AP via dopamine(DOPA) oxidative self-polymerization in the weak alkaline environment. The results of XPS, FT-IR, SEM and EA confirmed that PDA had been coated on the surface of AP successfully via the DOPA oxidative self-polymerization. The effect of DOPA concentrations, dipping time and the modified AP(DOPA-AP) content on the properties of composites with nitrile rubber(NBR) were investigated. The results confirmed that PDA was deposited on the AP surface successfully. Under the reaction conditions of the concentrations at 2.0g/L for 24 h, DOPA-AP concentrations at 1phr, the effect of modification was best and the tensile property increased 2.85 times, storage modulus increased 100% at 80℃, oil resistant increased 85%.The surface of AP was modified by Phosphoric acid solution(H3PO4), which was the traditional method. The results of XPS and SEM confirmed that the crack on surface appeared, O/C ratio and functional group –OH content increased. Under the reaction conditions of the concentrations at 30%, the tensile property increased 2.45 times. And the results also confirmed that properties of the composites via DOPA modified were superior to H3PO4 modified.PD was prepared by DOPA-AP and matrix sizing agent(MSA), which was mixed in laboratory. We got 4 kinds composited: DOPA-AP-PD/NBR, DOPA-AP/NBR, AP-PD/NBR, AP/NBR.The results of OM confirmed that DOPA-AP was distributed well in PD and the physical tangle ability was weaken. The results supported that the infiltrating ability of sizing agent to DOPA-AP was good. When AP concentrations at 1phr, the tensile property of DOPA-AP-PD/NBR increased 1.70 times than DOPA-AP/NBR, 4.90 times than AP/NBR. At the same experimental conditions, thermos-mechanical properties of DOPA-AP-PD/NBR was best, and DOPA-AP/NBR took second place; the oil resistant of DOPA-AP-PD/NBR was best, and DOPA-AP/NBR took second place.Through the research, we can find that the surface properties of AP is improved effectively by DOPA and dispersion property of AP in NBR is increased by PD. Rubber composite reinforced by modified AP not only has high mechanics performance, but also improve the oil resistant property, which can be used as sealant, strengthening material and friction material.