细菌纤维素纳米晶稳定液体石蜡Pickering乳液的制备

摘要

Bacterial cellulose (BC )was prepared by biological method,and bacterial cellulose nanocrystals (BCN)were prepared by hydrolysis of the BC with concentrate sulfuric acid. Then O/W Pickering emulsions were prepared by liquid paraffin as the oil phase and BCN as the solid emulsifier under the assistance of ultrasonic wave. BC and BCN were characterized by SEM,TEM,FT -IR,XRD,contact angle meter,laser particle size and Zeta potential analyzer. The effects of BCN mass concentration,pH value of the aqueous phase and ionic strength on the stability of the Pickering emulsions were also investigated. Experimental results showed that oxidation of BC occurs during the process of acid hydrolysis and the hydrolysis mainly occurs in the amorphous region,making the crystallization index of BCN be as high as 97%. BCN suspension with the size of 462.5 nm,the Zeta potential value of-40.8 mV and the three phase contact angle of 95.7°,exhibits good emulsifying performance. The particle size of the emulsions prepared under the assistance of ultrasonic wave is 8.6-17.3 μm. Adjustment of pH value of aqueous phase could change the surface charge density of BCN,thereby changing the stability of the emulsions. With the increase of pH value,the volume fraction of the emulsions increases and the stability of the emulsions also improves. With the increase of NaCl concentration, thestabilityoftheemulsionsreducesandthevolumefractionoftheemulsionsdecreases.Inaddition,fromthe SEM observation,the BCN reveal two kinds of morphologies as fiber line and aggregated particles in the stabilizing process of Pickering emulsions.%采用生物法合成了高纯度的细菌纤维素（BC），通过浓硫酸水解制得细菌纤维素纳米晶（BCN）。以液体石蜡为油相，BCN为固体乳化剂，在超声作用下制得O／W型Pickering乳液。通过SEM，TEM，FT－IR，XRD，接触角测量仪及激光粒度和Zeta电位分析仪对BC及BCN进行了表征。考察了BCN质量浓度、水相pH和离子强度对Pickering乳液稳定性的影响。结果表明，BC在浓硫酸水解过程中发生了氧化反应，其水解主要发生在无定型区，使所得BCN的结晶指数高达97％。BCN悬浮液的粒径和Zeta电位值分别为462.5 nm和－40.8 mV，其三相接触角为95.7°，具有良好的乳化性能。在超声乳化作用下制得的乳液粒径大小为8.6～17.3μm。通过调控水相pH能够改变BCN表面电荷密度，从而改变乳液的稳定性，随着水相pH的增大，乳液相体积分数增大，乳液稳定性增强。随着NaCl浓度的增大，乳液的稳定性降低，乳液相体积分数减小。此外，SEM的观测结果表明，BCN在稳定Pickering乳液过程中呈现纤维线条和聚集体颗粒2种形态。