【作者】 颜志勇；

【导师】 江建明；

【作者基本信息】 东华大学 ， 材料学， 2008， 博士

【摘要】 碳纳米管以其特有的力学、电学和化学特性以及独特的准一维纳米管状分子结构,作为增强和导电材料广泛用于高聚物基高性能复合材料的制备。本文以木醋杆菌为菌种,以葡萄糖为碳源,采用静态培养和摇床培养合成高性能纳米细菌纤维素纤维,并通过原位合成、浸泡法和打浆法,与碳纳米管复合,制成细菌纤维素纤维/碳纳米管纳米复合材料,具体内容如下:以木醋杆菌1.1812为发酵菌种,采用Hestrin＆Schramm’s培养液,静态培养细菌纤维素,系统考察接种量、培养温度、培养时间等因素对细菌纤维素产量的影响,确定了高产率和高转化率下的静态培养条件,制备了高品质细菌纤维素纤维。通过元素分析,经4wt%NaOH溶液煮沸1h的初生细菌纤维素膜,可有效除去残留在膜上的细菌体和培养液;通过X射线衍射分析,证明碱处理没有破坏晶体结构。用扫描电镜（SEM）分析,观察到细菌纤维素膜由直径40～100 nm、长数微米的细菌纤维素纤维交织成网状结构的薄膜,有大量微孔,持水量高达98.5%。用红外光谱（FT-IR）、X射线衍射（XRD）和固体核磁共振(solid state ¹³CNMR)分析,得出碱处理的细菌纤维素纤维,结晶指数高达84.3%（XRD分析数据）,纤维素I_α含量达87.4%（NMR分析数据）,比BPR2001静态培养的高。细菌纤维素膜拉伸强度高达56.2 MPa,拉伸模量达831.1 MPa。在30℃下摇床培养HS培养液,生成松散的“雪花状”细菌纤维素,经SEM观察,其形态结构发生显著变化,由静态培养的纤维素束转变为扁平状纤维素带,持水量大幅提高,由98.5%提高到99.34%,能吸收自重150倍的水分;通过FT-IR、XRD和NMR分析,结晶指数、晶粒尺寸和都纤维素I_α含量降低了,结晶指数由84.3%（XRD分析数据）下降到67.1%,纤维素I_α含量由87.4%（NMR分析数据）下降到75.3%。在14℃下摇床培养,其形态结构变化加剧,生成带状纤维素微纤,产生强烈扭曲,形成空心球状,并通过FT-IR、XRD和NMR进一步分析,表明该纤维素由高结晶纤维素转变为完全无定形纤维素。为了增强了碳纳米管的亲水性和表面活性,提高了水相体系的分散性和稳定性,将碳纳米管经浓硫酸/浓硝酸回流处理,FT-IR分析表明,在其表面有羟基、羧基等亲水基团存在。把酸处理后的碳纳米管引入到培养体系,同样能实现细菌纤维素的制备,间接表明了酸处理的碳纳米管有良好的生物相容性;在系统考察培养方式和培养条件的基础上,通过SEM、原子力显微镜（AFM）、FT-IR、XRD和NMR分析,结果表明:在30℃下静态培养条件下,原位合成了细菌纤维素纤维/碳纳米管复合材料,碳纳米管被嵌入细菌纤维素纤维的网络中,形成了碳纳米管网络,与细菌纤维素纤维网络互相贯穿,构建成细菌纤维素纤维一碳纳米管三维网络结构;碳纳米管的加入既影响了细菌纤维素亚微纤组装方式,由纤维素束转变为扁平状纤维素带,宽度达400～900 nm,又影响其结晶形态和结晶度,结晶指数由84.3%降为80.65%,纤维素I_α含量由87.4%降为79.6%。在30℃下摇床培养,原位合成了细菌纤维素纤维/碳纳米管复合材料,细菌纤维素纤维包裹碳纳米管,拧成纤维状绳,纤维素的结晶指数和纤维素I_α含量比静态培养低。在14℃下摇床培养,原位制备了细菌纤维素纤维和碳纳米管复合材料,碳纳米管和细菌纤维素自组装成空心球,沿径向呈放射状排列,分布均匀,经FT-IR、XRD和NMR分析,证明该纤维素是完全无定形纤维素。把细菌纤维素膜浸泡在碳纳米管悬浮液中,利用吸附作用,制备细菌纤维素纤维/碳纳米管复合材料,结果表明,在膜表面均匀沉积了一层碳纳米管,形成导电网络,通过SEM分析和电阻率测试表明,碳纳米管浓度越高,浸泡时间越长,碳纳米管的沉积量越多;在摇床振荡和超声波辅助作用下,碳纳米管沉积量可进一步增加,使得细菌纤维素纤维/碳纳米管纳米复合材料的电阻率降低至0.865Ω·cm。细菌纤维素纤维经匀浆后形成浆液,利用打浆法制备细菌纤维素纤维/碳纳米管纳米复合材料,经AFM分析,细菌纤维素纤维和碳纳米管形成互相穿贯的三维网络。加入碳纳米管提高了复合材料的力学性能、热稳定性和电导率:当碳纳米管含量高于5wt%时,碳纳米管网络可贯穿整个复合材料体系,一方面保持细菌纤维素纤维的韧性,同时大幅提高了复合材料的拉伸强度;另一方面,大幅度降低复合材料电阻率,降低了3个数量级。更多还原

【Abstract】 Owning to their unique and superior physical properties,including mechanical, electrical,chemical properties and high aspect ratio,carbon nanotubes（CNTs） have been uesd to fabricate performanced composite materials by embedded into the polymer matrix as reinforcing and electric materials.In this study,the bacterial cellulose（BC） nanofibers with unique properties were synthesized by Acetobacter xylinum（A.xylinum） which consumed the glucose in static and agitated culture.The BC/CNTs nanocomposites were manufactured using BC microfibrils and carbon nanotubes via in situ synthesis in CNTs-containing culture medium,immersing BC membrane in CNTs suspension and homogenizing BC membranes into slurry to mix the CNTs suspension.The fabricating methods, structure and properties ofnanocomposites were investigated as follows:The Acetobacter xylinum 1.1812 strains were cultivated in Hestrin & Schramm’s static medium.The effects of inoculum amount,cultivation temperature and time on the BC yield were systematically studied.The optimization cultivation conditions for the greatest BC productivity and transfer efficiency were ascertained. The high quality and properties BC was obtained.The elemental analysis data showed that the residual culture medium and bacterial cell debris in the nascent BC membrane were removed efficiently by boiling in a 4w/v%aqueous solution of NaOH for 1 h.The alkali treatment did not destroy the crystal microstructure of the BC ribbons from the X-ray Diffraction（XRD） analysis.The scanning electron microscopy（SEM） analysis showed that the BC membrane was fabricated into layer-by-layer network pellicles by microfibrils with about 40～100 nm width and several microns length.The porous BC membrane had high water holding capacity（WHC） with 98.5%.The data from by Fourier transform infrared spectroscopy（FT-IR）,CP/MAS ¹³C NMR and XRD analysis indicated the alkali treatment BC had a high crystalline index with 84.3%(CrI^XRD) and high cellulose I_αcontent with 87.4%(f_α^NMR),higher than that synthesized by BRP2001.The dried BC membranes had great tensile strength with 56.2 MPa and tensile modulus with 831.1 MPa.The morphology and microstructure of BC strictly depended on the culture conditions.The snow-like assemblies consisting of loose microfibrils were synthesized in agitated medium at 30℃and could absorb the 150 times water than its dried weight,which WHC was changed from 98.5%into 99.34%.The SEM images showed that the microfibrils assemblies changed from cellulose ribbons into flat cellulose bands.Comparing with the cellulose synthesized in static culture,the snow-like assemblies decreased the crystalline index,crystallite size and cellulose l_αcontent determined by FT-IR,NMR and XRD analysis,which may be ascribed that the agitated stress influenced the secretion,assembly and crystallization of BC microfibrils.While cultivation in agitated culture at 14℃,the BC microfibrils twisted intensively and assembled a hollow spheres,which was amorphous cellulose determined by FT-IR,NMR and XRD analysis.The CNTs were fluxed by concentrated H₂SO4 and HNO₃ and the chemical structure was analyzed by FT-IR.As a result,amount of functional aqueous groups such as carbonyl,carboxyl and hydroxyl groups were introduced onto the surface of CNTs,which increased their surface activities and adsorbability and improved their dispersibility and stabilizability in water.The acid-treated CNTs were dispersed uniformly in the culture medium and the A.xylinum strains could grow and synthesize cellulose continuously,which indicated that the acid-treated CNTs had good biocompatibility.On the basis of systematic research on the culture methods and conditions,black composite membranes could be in situ synthesized in static medium containing CNTs at 30℃.The SEM images showed that the CNTs were incorporated into the BC microfibrils network and formed nano-network.The BC microfibrils interwound with the MWNTs,and constructed the three-dimensional reticular tissue. By SEM,AFM,FT-IR,XRD and NMR analysis,the results showed that the CNTs in the medium influenced the assembly and crystallization of microfibrils,changed the morphology,resulting in flat BC bands with 400～900 nm width and the crystalline index changed from 84.3%into 80.65%,and the cellulose I_αcontent changed from 87.4%into 79.6%.In agitated medium containing CNTs at 30℃,the BC/CNTs composites could also be in situ synthesized.However,the BC microfibrils packed the CNTs and formed fibrous assemblies.Comparing with the static culture,the fibrous assemblies synthesized in agitated CNTs medium had lower crystalline index and cellulose I_αcontent.Interestingly,the BC microfibrils and CNTs could assemble a hollow sphere in agitated medium at 14℃.The BC microfibrils and CNTs arranged uniformly along the radial direction.The spherical BC microfibrils were amorphous cellulose determined by FT-IR,XRD and NMR analysis.The purified BC membranes were immersed into the CNTs suspension and a layer of MWNTs were adsorbed onto the surface of BC membrane,resulting in the BC/CNTs composites.The higher the CNTs content was and the more time BC membrane was immersed,the more CNTs were adsorded.The agitating or ultrasonic treatment could help the CNTs adhere to the BC membrane.The CNTs on the surface of BC could construct electrical conductive networks,and formed the low electrical resistivity composites with 0.865Ω·cm.The electric conductive mechanism of composite membranes was also investigated.The BC microfibrils were disintegrated by a double-cylinder type homogenizer and formed the suspension,which was rapidly blended with the CNTs suspension. The mixed suspension was filtered using a Buckner funnel and a composite film was obtained.The BC microfibrils and CNTs impenetrated each other and built a new 3-dimensional reticulate structure by SEM and AFM analysis.The CNTs could enhance the mechanical properties,thermal stability and the conductivity of composites.When the CNTs content in the composites was above 5wt%,the CNTs could construct a continuous network and enhance sharply the tensile strength and modulus,and reduce the electrical resistance.更多还原