Research On Preparation And Properties Of PH-responsive Halloysite Nanomaterials

With the widespread application of metal material in industrial manufacture and daily life,the metal corrosion is becoming a serious problem and need to be solved.So the researchers pay more attention on the metal protection technology.In the traditional field of metal anticorrosion,physical coating and corrosion inhibitor are the most common means,both of which have a good protective effect but each has its own drawbacks.The physical coating is susceptible to mechanical damage which causes the coating to peel off to expose the metal substrate and accelerate the process of metal corrosion when exposed in the air and corrosive media for a long time.For corrosion inhibitor,it can not continue to be effective in the flowing corrosive media.In view of the shortcomings of the above two methods,a composite material with pH-responsive function is proposed by the researchers.The researchers load the inhibitor into the the appropriate nanocontainer and then mix them into coating.The pH-responsive material is stimulated by the changes of pH and release from the nanocontainer to achieve the anticorrosive effect when the metal corrosion occurs.In this research,halloysite nanotubes?HNTs?were employed as the carrier,L-valine?L-Val?and 2-mercaptobenzothiazole?MBT?as inhibitor.Meanwhile,two kinds of pH-responsive materials were prepared by different methods and tested for various properties,the conclusion is as follow:?1?The MBT/HNTs pH-responsive material was prepared by layer self assembly?LbL?.SEM and TEM tests show that HNTs have a special hollow cavity structure and can be used as excellent nanocontainer.TGA test demonstrates that the loading capacity of MBT loaded HNTs is 7%through loading under the vacuum.HNTs were coated with polyacrylic acid hydrochloride?PAH?and sodium polystyrenesulfonate?PSS?.By infrared and ultraviolet visible test,PAH and PSS show the great good encapsulation effect on HNTs when the assembly time is 5 min,the NaCl concentration of NaCl and polyelectrolyte are 0.5mol/L and 4mg/mL via FT-IR and UV-vis tests,respectively.UV-vis test also shows that MBT/HNTs have a good pH-responsive release property under different pH solutions.The MBT release rate is 7%at pH=6.5 within 120 h,85%at pH=2.9 and 94%at pH=10,respectively.?2?The difference of isoelectric point between L-Val and HNTs was used to prepare L-Val/HNTs pH-responsive material,and isoelectric point of L-Val and HNTs is 6.0 and 3.0,respectively.The loading capacity of L-Val loaded HNTs is 12%,which is higher than MBT and measured by TGA test.Furthermore,in the pH-responsive release test,the release rate of L-Val is much than MBT,15.4%at pH=5 within 300 min,83%at pH=3 and 98%at pH=10,respectively.?3?At room temperature,the polarization curves show that MBT and L-Val have an excellent anticorrosion effect on copper,the best concentration of both is 20mM,and the inhibition efficiency is99.76%and 70.36%,respectively.The MBT/HNTs and L-Val/HNTs pH-responsive materials were mixed into the epoxy resin to prepare the self-healing coating and compared with the pure epoxy resin coating sample.Through artificial scratch test,it is found that the self-healing coating shows the better anticorrosion property than pure epoxy resin coating,especially the coating which mixed with L-Val/HNTs.The impedance of it decrease from 5.8×10⁴ to 2.1×10⁴?while capacitance increase from 2.2×10^-55 to 5.9×10^-5 F·cm^-2 after immersion in 3.5 wt.%NaCl solution for 96 h.In conclusion,the results of the experiment show that the two new pH-responsive materials we fabricated exhibit great self-healing performance when mixed witn coating.As the release rate of L-Val is faster,the self-healing property of L-Val/HNTs material is better in the actual performance test.