【作者】 王勇；

【导师】 苗伟俊； 张立生；

【作者基本信息】 宁波大学 ， 工程硕士（专业学位）， 2022， 硕士

【摘要】 聚偏氟乙烯(PVDF)是一种半结晶型高分子聚合物,C-F键能很强,具有优异的机械性能、化学稳定性和热稳定性,此外,还具有良好的成膜能力,因此经常被用于制备分离膜。然而,PVDF膜的高疏水性不仅导致其渗透通量低,而且在过滤过程中容易受到有机污染物(例如蛋白质)和生物污染物(例如细菌)的影响,导致过滤效率下降、清洗频率增加、使用寿命缩短和增加使用成本。为了解决PVDF膜亲水性差、抗污能力弱、功能性单一等问题,本论文采用酶催化合成的纤维素低聚物对PVDF膜进行表面涂覆改性,制备了具有多种复合功能的PVDF膜。相应的研究结果如下:1.使用纤维糊精磷酸化酶(Ct CDP)催化葡萄糖1-磷酸(G1P)与引物(纤维二糖/熊果苷)之间的反应成功的合成了纳米纤维素(EC)和功能化纳米纤维素(ECP)。EC/ECP分子链的聚合度约为10,由EC/ECP分子链自组装形成二维矩形纳米片,片中的纤维素分子链反向排列,形成热稳定性较好的纤维素Ⅱ型晶体。2.将上述合成的EC溶解于三氟乙酸(TFA)中制备均相溶液以用于PVDF膜表面涂覆,通过调控实验条件,制备了非晶EC改性的PVDF膜(表面光滑)、部分结晶EC改性的PVDF膜(表面粗糙)和完全结晶EC改性的PVDF膜。EC分子涂层使PVDF膜的亲水性和渗透性大大提高,最大水通量达到9 591 L/(m~2·h),是未改性膜的14倍(652 L/(m~2·h))。此外,由于衍生化反应导致涂层带有负电荷和与生俱来的亲水性,EC涂层有效地阻止了BSA在膜表面的沉积,表现出优异的抗污性能。与非晶EC改性的PVDF膜相比,部分结晶EC改性的PVDF膜由于粗糙度较高导致比表面积较大,因而具有更强的亲水性和渗透性。3.将合成的ECP溶解于TFA中,通过调控实验条件,在PVDF膜上制备了光滑的且具有抗菌、抗黏附功能的纤维素分子涂层。由于ECP分子涂层在膜表面和孔壁的均匀分布,大大改善了PVDF膜的润湿性和渗透性。水接触角从134.2°(M0)降至44.3°(M@ECP5),纯水通量从652 L/(m~2·h)(M0)增加到10 165 L/(m~2·h)(M@ECP3),提高了近16倍。此外,ECP末端的苯酚基团均匀分布在膜的表面,使膜具有优异的抗菌性能,ECP涂层优异的亲水性赋予了PVDF膜抗污染和抗细菌黏附性能。4.对比研究了两种纤维素分子涂层的染料吸附能力。部分结晶的EC/ECP增加了膜的比表面积,而且涂层带有负电荷,这两者的协同作用使得膜具有优异的染料去除能力。实验结果表明,M@r EC3和M@r ECP3对结晶紫(CV)的吸附过程均符合准二级动力学方程和Langmuir等温方程。吸附动力学实验表明约7 h达到吸附平衡,M@r EC3和M@r ECP3对CV的最大吸附量分别为2.839 mg/g和3.152mg/g。通过吸附等温线实验计算得到M@r EC3和M@r ECP3对CV的最大吸附量分别为9.650 mg/g和11.309 mg/g。此外,改性膜还具有优秀的重复使用性能。更多还原

【Abstract】 Polyvinylidene fluoride(PVDF)is a semi-crystalline polymer with strong C-F bond energy and excellent mechanical properties,chemical stability,and thermal stability.In addition,it also has a good film-forming ability,so it is often used as a material for membrane separation.However,the high hydrophobicity of PVDF membrane not only leads to low permeation flux,but also makes it vulnerable to organic pollutants(such as proteins)and biological pollutants(such as bacteria)in the filtration process,resulting in decreased filtration efficiency,increased cleaning frequency,shortened service life,and increased practical application costs.In order to solve the problems of poor hydrophilicity,weak anti-fouling ability and single function of PVDF membrane,the surface of PVDF membrane was modified by nano-cellulose synthesized by enzymatic synthesis,and PVDF membrane with multiple composite functions was prepared.The main findings of this thesis are as follows:1.Nanocellulose(EC)and functionalized nanocellulose(ECP)were successfully synthesized by the reaction between glucose 1-phosphate(G1P)and primers(cellobiose/arbutin)catalyzed by cellodextrin phosphorylase(Ct CDP).The degree of polymerization of EC/ECP molecular chain is about 10.The final two-dimensional rectangular nanowires are self-assembled from EC/ECP molecular chains.The cellulose molecular chains in the nanosheets are arranged in the opposite direction to form cellulose Ⅱ allomorph with good thermal stability.2.The EC synthesized by enzymatic reaction was lyophilized and dissolved in trifluoroacetic acid(TFA).By adjusting the experimental conditions,amorphous EC-modified PVDF membranes(smooth surface),partially crystalline EC-modified PVDF membranes(rough surface)and fully crystalline EC-modified PVDF membranes were prepared.EC molecular coating greatly improved the hydrophilicity and permeability of PVDF membranes,and the maximum water flux reached 9591 L/(m~2·h),which was 14 times higher than that of unmodified membrane(652 L/(m~2·h)).In addition,due to the negative charge(derivatization reaction)and inherent hydrophilicity of the coating,the EC coating effectively prevented the deposition of BSA on the surface of the membrane and showed excellent anti-fouling performance.Partially crystalline EC-modified PVDF membranes have higher hydrophilicity and permeability due to higher specific surface area due to higher roughness.3.The ECP synthesized by enzymatic reaction was lyophilized and dissolved in TFA.By adjusting the experimental conditions,a smooth cellulose molecular coating with antibacterial and anti-adhesion function was prepared on PVDF membranes.Due to the uniform distribution of ECP molecular coating on the membrane surface and pore wall,the wettability and permeability of PVDF membrane were greatly improved.The water contact angle decreased from 134.2°(M0)to44.3°(M@ECP5),and the pure water flux increased from 652 L/(m~2·h)(M0)to 10 165 L/(m~2·h)(M@ECP3),which increased by nearly 16 times.In addition,the phenol groups at the end of ECP are uniformly distributed on the surface of the membrane,which makes the membrane have excellent antibacterial properties.The excellent hydrophilicity of ECP coating gives the PVDF membrane anti-fouling and anti-bacterial adhesion properties.4.The EC/ECP synthesized by enzymatic reaction was lyophilized and dissolved in TFA.By adjusting the experimental conditions,a molecular coating with a rough surface was constructed on the PVDF membrane.Partially crystallized EC/ECP increases the specific surface area of the membrane,and the coating has a negative charge,which makes the membrane have excellent dye removal ability.The experimental results show that the adsorption process of CV by M@r EC3 and M@r ECP3 accords with the pseudo-second-order rate equation and Langmuir isotherm equation.In the adsorption kinetics experiment,the adsorption equilibrium was reached in about 7 hours.The maximum adsorption amounts of CV by M@r EC3 and M@r ECP3 were 2.839 mg/g and 3.152 mg/g,respectively.In the adsorption isotherm experiment,the maximum adsorption amounts of M@r EC3and M@r ECP3 for CV were calculated to be 9.650 mg/g and 11.309 mg/g,respectively.In addition,the modified membrane also has excellent reuse performance.更多还原