Preparation And Performance Of IPBC Bamboo Preservatives Supported On Nano-sized Halloysite

The long-term protection of bamboo materials is an important research aspect of bamboo protection.Halloysite nanotube（HNT）is a viable and inexpensive nanoscale container with a hollow tubular structure,which possess high aspect ratio,specific surface area,excellent chemical and thermal stability.The special lumen of HNT can be used for loading IPBC mildew preservatives to have more functionality of controlled release properties under certain conditions.However,the guests exhibit a low loading capacity and limited loading space on halloysite,which have severely limited the application of halloysite as an effective carrier in the field of bamboo protection.In this study,an acid etching method was used to remove the alumina layer for highly loading of IPBC,and the preparation of the HNT/mildew preservatives（HDI）was carried out in this study.The polyelectrolyte multilayer film coated on HDI composites were fabricated using the layer-by-layer（LbL）self-assembly technique by positively charged poly allylamine hydrochloride（PAH）and negatively charged poly styrene sulfonate（PSS）,which absorbed on the surface of HNT and form polyelectrolyte multilayer.The influences of encapsulation layers and pH values on the release of IPBC were studied and applied it into the coating of bamboo and bamboo plastic composite（BPC）,the effects of washing and UV irradiation on antifungal performance of HDI fungicide were also discussed.The main work includes the following aspects:（1）The effect of acid etching on the lumen and surface morphology of HNTWith the increase of acid concentration,the alumina layer in HNT was gradually dissolved,the aluminum hydroxyl was reduced,and most of the impurity elements were expunged.After3M acid treatment,the content of Al2O3 in HNT is only 21.29%（XRF dates）,and the content of SiO₂ composition is as high as 69.56%,3M acid solution could increase the diameter of HNT inner lumen from 10-25 nm to 19-35 nm,greatly increase the specific surface area and pore size,and do not destroy the complete tubular structure of HNT,which is suitable for highly loading mildew preservatives.As the acid concentration exceeded 3M,the wall of HNT became thinner,and even some perforations were appeared,and a large number of HNT have lost their tubular structure.（2）The highly loading and release property of IPBC on etched HNTThe 3M acid etched HNT has the largest loading（24.4%）,almost three times as much as the loading of the unetched HNT（8.4%）.However,under the condition of more than 4M acid concentration,the loading of IPBC began to decline.The IPBC was mainly loaded in the inner cavity of HNT,showing blurred and invisible tube structure on the TEM images.The hysteresis loop of the nitrogen isothermal adsorption-desorption curve of HDI-3M was reduced,the maximum adsorption capacity of nitrogen was reduced,and SBET and VPore were reduced to 43.21m²/g and 0.24 cm³/g respectively,and the pore diameter distribution of 6.3 nm and 26nm were completely disappeared.The release time of HDI in ethanol solution（about 90 h）was 80 h longer than that of pure IPBC.The release time of HDI in the buffer solution environment was greatly prolonged compared to ethanol solution,which reached a stable release after 30 days,the cumulative release rate amount of HDI in acidic and alkaline buffer solution are 37.3%and 39.5%respectively,slightly faster than the neutral solution（33.8%）,the release curves of IPBC from HDI are accorded with pseudo-first-order kinetic model and the modified K-P model,the release mechanism of IPBC in HDI fungicide is Fick diffusion.（3）The encapsulation and release of IPBC from HDI/Polyelectrolyte compositePAH and PSS have a good encapsulation features for HNT,the Zeta potential and the layer number of present a rule of positive and negative variations.With the increase of the encapsulation layers,the encapsulating layer was gradually thickening.When six layers were encapsulated,the lumen ends of HNT have been completely blocked by polyelectrolyte.With the increase of encapsulation layers,the release rate of IPBC from HDI dropped significantly in the neutral aqueous solution.The cumulative release amount of HDI2,HDI4 and HDI6 were 5.9%,4.8%and 4%respectively within 30 days,which is far below the cumulative release amount（33.8%）of unwrapped HDI.After encapsulation,the release time of IPBC was greatly extended,and the cumulative release of IPBC in HDI₂,HDI₄ and HDI₆ was 9.70%,7.69%and 6.55%in90 days,respectively.The encapsulation of polyelectrolytes has obvious influence on the sustained release of IPBC.The order of release rate for IPBC in different pH environments:alkaline（pH=8.6）>acid（pH=4.2）>neutral（pH=7.0）.The encapsulation of polyelectrolyte can slow the release rate and controll the release rate of IPBC from HDI.When the HDI preventive was used in a neutral environment,the less release of IPBC can avoid the invalid release.When the woodiness materials were used in meta-acid or leaning alkalinity,where the materials are easy to moldy,encapsulated HDI can release more effective ingredient IPBC,preventing or reducing the mildew phenomenons.（4）The anti-fungal performance of HDIThe inhibition zone diameters of HDI under different concentration of IPBC to mold and blue stain fungus are different.With the increase of IPBC concentration,the inhibition zone diameters increased.In the same condition of IPBC content,inhibition zone diameter of HDI is a bit less than pure IPBC,which illustrated the block and slow-release effect of HNT to IPBC.The minimum inhibitory concentration of HDI for Trichoderma viride,Penicillam citrinum,Aspergillus niger,Botryodiplodia theobromae were 0.05%,0.03%,0.01%and 0.03%respectively.When the HDI was added into the coating of bamboo and bamboo plastic composite,the washing process has little effect on the antifungal performance of HDI,because of the protection and slow-release effect of HNT and polyelectrolyte layer for IPBC,only a very tiny IPBC in washing process was washed out.The same results were founded after UV irradiation process.The antifungal performance of bamboo coating products and bamboo plastic materials with pure IPBC decreased greatly after washing and UV irradiation,illustrating the good prevention of IPBC from ultraviolet decomposition by HNT and polyelectrolyte layer.