Preparation Of Polybenzoxazine And Nanoclay Composite Coating And Study On Corrosion Resistance

Metallic corrosion leads to the loss of metal all over the world,which reduces the life of metal materials and metal mechanical strength,causes a series of safcety and environmental problems,and increased the maintenance cost.Among many anti-corrosion technologies,the organic coating can effectively isolate the metal from the surrounding corrosive environment,and the electron transfer is also hindered by the insulating coating,the organic coating is wildly applied in corrosion resistance.Polybenzoxazine is a new type of resin that has been developed recently.It has many characteristics,such as low water absorption,small volume shrinkage during curing,hydrophobicity and electrical insulation.Therefore,two series of polybenzoxazine and nanoclays composites were synthesized,which were applicated as anti-corrosion costings on mild steel(MS).Research were concentrated on the relationship between benzoxazine structure and its anti-corrosion resistance.The effect of nanoclay structure on the properties of the composite coatings were also studied.Firstly,2,2-bis(3-n-butyl-3,4-dihydro-2h-1,3-benzoxazine)isopropane(BA-b)was synthesized from butylamine,polyformaldehyde and bisphenol A,and applied to the corrosion protection of low carbon steel.The structure of BA-b was confirmed by FTIR and 1HNMR spectra.The electrochemical tests showed that when the curing temperature of BA-b was 200 C and the curing time was 2 h,corrosion current density reached minimum value(2.71 ×10-10 A cm-2),which is nearly five orders of magnitude lower than that of blank steel(1.09×10-5 A cm-2).Secondly,four kinds of nanoclays(NaMMT,I.30P,I.34TCN,I.44P)with the same amount were added to polybenzoxazine poly(BA-b).The influence of benzoxazine monomer on the structure of nanoclay was clarified by comparing the XRD diffraction patterns of nanoclay and polybenzoxazine/nanoclay composite coatings before and after curing.The electrochemical test showed that the composite coating with I.44P performed the highest corrosion resistance than other nanoclays when the contents was 0.6wt%all the same.The corrosion current density reached 5.60 × 10-10 A cm-2,which was 67.2%lower than that of the poly(BA-b)coating without nanoclay.Finally,silanized benzoxazine 2,2-bis(3,4-dihydro-2,3-trimethoxysiloxane-n-propyl-1,3-benzoxazine)-isopropane(BA-aptms)was synthesized from bisphenol A,3-aminopropyltrimethoxysilane and polyformaldehy de.In order to improve the shielding ability of polybenzoxazine coating,the poly(BA-aptms)was doped with two organic modified nanoclays.The relationship between the microstructure inside the composite coating and the macroscopic corrosion resistance was investigated.For the sample with 3 wt%organoclay,corrosion rate reduced 3 and 4 orders of magnitude compared to that of poly(BA-aptms)and bare MS,respectively.The improvement of corrosion resistance was strongly correlated with the clay intercalation structure dispersed in the composite system,but the effect of the addition amount was not significant.