Preparation And Controlled Release Behavior Of HNTs-Corrosion Inhibitor/Antifouling Agent Composites

In order to better protect structures and ships in the ocean,extending service life and enhancing the ability of corrosion resistance and anti-bioadhesion,environmentfriendly anticorrosive and antifouling coatings have been extensively studied and applied.If corrosion inhibitor and antifouling agent are added directly in paint,the rapid release of active ingredients in the early use will occur,resulting in waste of resources and losing efficacy in the late application.Therefore,it is of great significance to prepare anti-corrosive and anti-fouling composites with sustained and controlled release effect.Thermal treatment of natural halloysite nanotubes was carried out in this paper and SEM,TEM,XRD,BET were used to analyze these samples.It was found that length of samples was shortened and average diameter increased after calcination.When temperature was over 550 °C,dehydroxylation of halloysite would change the structure of HNTs from crystal to amorphous.Heat-treated halloysite was employed as carrier and active ingredients containing benzotriazole,2-mercaptobenzothiazole and capsaicin were loaded into the lumen of nanotubes by means of vacuum load,after which polyelectrolyte layers were synthesized on the surface.The highest load of BTA was 8.4wt% for the sample calcined at 260 °C and continuously increase of diameter was adverse to the preservation of BTA in water,resulting in a sustained decline in loading capacity.For water-insoluble MBT and capsaicin,the samples treated at 550 °C had the highest loading of 8.2wt% and 4.8wt% respectively.The controlled release capacity of synthetic composites was studied subsequently.Release time of BTA in uncoated samples can be extended to a certain extent in neutral water,and release rates in the samples with higher treatment temperatures were faster.After coating polyelectrolyte layers,BTA in composites could be effectively controlled.When the pH in environment changes,polyelectrolyte layers would be destroyed and immediate release of BTA occurred.Polyelectrolyte layers were more sensitive to alkaline environment and made release faster.Although overall release time was prolonged,the primary release rules of MBT insoluble in water was similar to that of BTA before and after coating.Because MBT easily reacted with NaOH in alkaline water to form anticorrosive MBT-Na,promoting release process,the release rate of MBT in coated halloysite was faster in alkaline environment.In order to enhance the anti-corrosion and anti-fouling effect of coatings,avoid waste of resources and extend service life,considering the total loading,controlled release behavior and immediate release effect of composites,the best nanocontainer for BTA in coating research is HNTs-260 and for MBT as well as capsaicin is HNTs-550.