电喷射技术制备微/纳米纤维素及其性能研究

以海南椰子水为主要培养体系,木醋杆菌为菌种,通过添加蔗糖,生物合成了细菌纤维素(BC)。通过添加离子溶剂[BMIM]Cl和助纺剂聚乙烯醇(PVA)考察该纤维素在电喷射技术下的纺丝性能,并采用FT-IR、XRD和SEM对产物的性能进行了表征。结果表明:所制得的BC数均分子量Mn为335673,重均分子量Mw为347662,硫酸水解后的结晶指数为97%。电纺离子溶剂[BMIM]Cl溶解的BC只能得到粒径在150~400nm之间的纳米纤维素颗粒,但是电纺BC/PVA混合溶胶可得到平均直径在250~400nm之间光滑复合纤维。单一的BC不能纺丝,但是它可以以纳米晶体方式分散在PVA纳米纤维中。     

纳米纤维素在功能纳米材料中的应用进展

纳米纤维素分为纤维素纳米纤维(CNF)、纤维素纳米晶体(CNC)、细菌纳米纤维素(BNC)。CNF主要由机械法和2,2,6,6-四甲基哌啶-1-氧基(TEMPO)介导氧化法制备,呈微纤丝状。CNC主要由酸水解法制备,呈棒状或针状颗粒。BNC由细菌合成,呈纳米纤维网络状。文中综述了纳米纤维素在凝胶、仿生复合材料、导电材料、电极材料、导热材料、电磁屏蔽材料、压电材料及传感器材料领域的应用现状,并对其功能纳米材料未来发展的方向进行了展望。     

流变法测定纤维素的分子量标度及分子量分布

探索了流变法测定纤维素分子量标度及分子量分布的方法。该法认为,由Rouse期终(terminal)松弛时间公式计算得到的分子量为纤维素分子量分布中的峰值分子量(Mp),从而实现了将频率的倒数(表示相对分子量)转换为分子量标度(表示真实分子量),获得纤维素分子量标度分布曲线。将得到的结果与凝胶渗透色谱法(GPC)测定纤维素分子量及其分布的结果进行对比,对比表明,流变法与GPC法测得的Mp值非常接近,测得的多分散指数(PDI)趋势一致。因此,用流变法研究纤维素的分子量及其分布是可行的。     

碳化细菌纤维素的理化性质及其在甲醇电催化中的应用

对在实验室发酵制备的细菌纳米纤维素(BC)分别进行烘箱干燥和冷冻干燥,然后对其高温碳化,系统地研究了碳化细菌纤维素(CBC)的微观形貌、元素组成以及晶体结构等理化性质随碳化温度的变化.结果 表明,烘箱干燥的BC失去了纳米纤维结构,而冷冻干燥可防止纳米纤维堆叠而使其保持三维结构.还以CBC碳纳米纤维为导电载体负载金属Pt...     

载钯细菌纤维素纳米纤维的制备及表征

以细菌纤维素为原料载体,硼氢化钾为还原剂,采用水热还原法制得载钯细菌纤维素纳米纤维(Pd/BCF)。通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、原子力显微镜(AFM)、X射线衍射(XRD)、能量色散X射线分析(EDX)、傅里叶变换红外光谱学(FT-IR)和热重分析仪(TGA)表征手段,研究了载钯细菌纤维素纳米纤维材料的微观形态、结晶度、组成成分以及热稳定性,均达到了相对理想的效果。反应3h后,钯纳米颗粒(PdNPs)在纤维上均匀分布,粒径约55nm。纳米纤维上Pd单质载量约19.40%,且Pd/BCF材料热稳定性较高,能承受250℃的高温。     

细菌纤维素/碳纳米管柔性纳米复合膜的制备及其导电性能研究

以细菌培养生成的细菌纤维素(BC)为基材,碳纳米管(CNTs)为导电填充物,通过简单的物理吸附法制备出了BC/CNTs纳米复合膜。利用扫描电子显微镜(SEM)、傅里叶红外变换光谱仪(FT-IR)、热重分析仪(TG)和四探针测试仪(FPT)对其形貌、结构、热学以及导电性能进行了表征。结果表明:CNTs均匀负载在BC膜上,CNTs的掺入使BC膜的热学性能得到很大改善;同时制备出的柔性纳米复合膜在不同弯曲角度下均具有很好的导电性能,导电率为0.32±0.003S/cm,且性能稳定。这表明合成的纳米复合膜可作为柔性基材在生物传感器、超级电容器及其锂电材料等领域得到很好应用。     

花生壳纳米纤维素超疏水气凝胶的制备及在棉织物上的应用

以花生壳粉为原料,通过化学机械法从中提取纳米纤维素,采用溶胶-凝胶法,在花生壳纳米纤维素悬浮液中加入甲基三甲氧基硅烷以对其进行改性,并采用冷冻干燥法最终制备了纳米纤维素超疏水气凝胶.将通过喷涂的方法使纳米纤维素超疏水气凝胶和聚二甲基硅氧烷(PDMS)整理到棉织物上,分别对超疏水气凝胶和超疏水棉织物进行分析和表征.结果表...     

纳米纤维素修饰的碳纳米纤维制备及其疏水性研究

为拓展碳纳米纤维在环境清洁领域的应用，提高碳纳米纤维的水接触角，改善膜表面的疏水性能，获得疏水性较好的碳纳米纤维薄膜，利用静电纺丝法将纳米纤维素(CNFs)与碳纳米纤维前驱体复合，获得具有低表面能和良好疏水性能的纳米碳纤维/纳米纤维素复合纤维膜。通过对纳米纤维素含量进行调控，经预氧化和碳化处理后得到一系列具有规则三维空间网络结构的复合纤维膜，并探究不同纳米纤维素含量对复合纤维膜疏水性能的影响。结果表明：纳米纤维素修饰复合纤维膜随着碳化程度的提高其表面能呈现逐渐降低的趋势，其对水的接触角也逐渐增大，疏水效果得到较大幅度提升。随着纳米纤维素含量继续增加，复合纤维膜的水接触角呈上升趋势，未添加前接触角为36.13°,当纳米纤维素添加质量为20%时，水接触角最大为132.14°,提高了366%。     

表面沉积铜纳米颗粒的细菌纤维素/壳聚糖交联复合膜的制备及其抗菌性能研究

通过戊二醛交联制备了细菌纤维素/壳聚糖复合材料,并采用磁控溅射技术在交联复合膜表面沉积铜(Cu)纳米颗粒。利用扫描电子显微镜观察纳米纤维膜表面形貌,采用傅里叶红外光谱仪、热重分析仪和X射线衍射仪比较交联复合前后以及镀铜前后复合膜基本化学结构、热稳定性和晶面结构的变化。通过能量色散X射线光谱对壳聚糖和铜在复合膜表面的分布情况进行表征。同时借助抗菌实验探究复合膜对金黄色葡萄球菌和大肠杆菌的抗菌能力。结果表明:壳聚糖与细菌纤维素发生了有效交联,改变了细菌纤维素的基本形貌、化学结构、晶体形态以及热学性能,并且镀铜后交联复合膜的抗菌性能得到了明显的提升(膜与细菌接触20min,对金黄色葡萄球菌和大肠杆菌的抗菌效果均达到了99.999%)。     

细菌纤维素基电磁功能复合膜的制备与性能研究

以细菌纤维素(BC)基体材料,通过共沉淀原位复合法制备纳米钴铁氧体(CoFe2O4)/细菌纤维素磁性复合膜;并在此基础上,通过原位化学氧化聚合法,制备了聚吡咯/钴铁氧体/细菌纤维素(PPy/CoFe2O4/BC)复合膜,对其结构性能及应用进行研究。结果表明,PPy/CoFe2O4/BC复合膜仍然保持了BC的三维网状结构。当吡咯单体浓度为0.07mol/L时,复合膜由连续的核壳结构构成,电导率稳定在0.4S/cm左右,其电磁屏蔽效能在25dB左右,是一种良好的民用或商用电磁屏蔽材料。     

纳米细菌纤维素的生物合成

采用木醋杆茵茵株A.xylinumHN001,以椰子水为培养基,生物合成了纳米细茵纤维素(NBC).研究了影响纳米细菌纤维素合成的几个主要因素:培养时间、培养基初始pH值和培养方式.实验所得NBC的产率为1.2g/L.采用凝胶渗透色谱仪(GFC)测定了相对分子质量及其分布,其相对分子质量分布指数(MMD)约为1.0,说明相对分子质量均匀.采用透射电镜测试了形貌,证明NBC分子近似球形,直径约100nm.NBC冷冻干燥后采用红外光谱确证了结构.     

Amino-Functionalized Interfacial Layer Enables an Ultra-Uniform Amorphous Solid Electrolyte Interphase for High-Performance Aqueous Zinc-Based Batteries

Aqueous rechargeable zinc-based batteries (ZBBs) are emerging as desirable energy storage systems because of their high capacity, low cost, and inherent safety. However, the further application of ZBBs still faces many challenges, such as the issues of uncontrolled dendrite growth and severe parasitic reactions occurring at the Zn anode. Herein, an amino-grafted bacterial cellulose (NBC) film is prepared as artificial solid electrolyte interphase (SEI) for the Zn metal anodes, which can significantly reduce zinc nucleation overpotential and lead to the dendrite-free deposition of Zn metal along the (002) crystal plane more easily without any external stimulus. More importantly, the chelation between the modified amino groups and zinc ions can promote the formation of an ultra-even amorphous SEI upon cycling, reducing the activity of hydrate ions, and inhibiting the water-induced side reactions. As a result, the Zn||Zn symmetric cell with NBC film exhibits lower overpotential and higher cyclic stability. When coupled with the V₂O₅ cathode, the practical pouch cell achieves superior electrochemical performance over 1000 cycles.     

Haemocompatibility and ion exchange capability of nanocellulose polypyrrole membranes intended for blood purification

Composites of nanocellulose and the conductive polymer polypyrrole (PPy) are presented as candidates for a new generation of haemodialysis membranes. The composites may combine active ion exchange with passive ultrafiltration, and the large surface area (about 80 m² g⁻¹) could potentially provide compact dialysers. Herein, the haemocompatibility of the novel membranes and the feasibility of effectively removing small uraemic toxins by potential-controlled ion exchange were studied. The thrombogenic properties of the composites were improved by applying a stable heparin coating. In terms of platelet adhesion and thrombin generation, the composites were comparable with haemocompatible polymer polysulphone, and regarding complement activation, the composites were more biocompatible than commercially available membranes. It was possible to extract phosphate and oxalate ions from solutions with physiological pH and the same tonicity as that of the blood. The exchange capacity of the materials was found to be 600 ± 26 and 706 ± 31 μmol g⁻¹ in a 0.1 M solution (pH 7.4) and in an isotonic solution of phosphate, respectively. The corresponding values with oxalate were 523 ± 5 in a 0.1 M solution (pH 7.4) and 610 ± 1 μmol g⁻¹ in an isotonic solution. The heparinized PPy–cellulose composite is consequently a promising haemodialysis material, with respect to both potential-controlled extraction of small uraemic toxins and haemocompatibility.     

New CUSUM and dual CUSUM mean charts

The CUSUM (C) charts are well recognized as a potentially advanced process monitoring tools because of their sensitivity against small and moderate shifts. In this paper, we first improve the sensitivity of the Brownian motion–based C (BC) chart with an appropriate transformation, named new BC (NBC) chart, for monitoring moderate and large shifts in the mean of a normal process. Then, using the control charting structure of the Crosier C (CC) chart, we propose the NBCC (NBC with CC structure) chart. In addition, for efficiently detecting a mean shift within an interval, dual version of these control charts are also proposed, named the dual NBC (DNBC) and dual NBCC (DNBCC) charts. Moreover, the fast initial response feature is also incorporated into the proposed charts. Using the Monte Carlo simulation, the run length properties of the proposed charts are computed. The run length performances of the existing and proposed charts are compared using the extra quadratic loss and integral relative average run length as performance criterion. It turns out that the NBC and NBCC (DNBC and DNBCC) charts are uniformly more sensitive than the C, CC, and NBC (dual C and dual CC) charts when detecting the mean shifts in small, moderate, and large intervals, where the DNBCC chart outperforms all considered charts. The proposed charts are also applied on real data sets to support the proposed theory.     

Patterns on growing square domains via mode interactions

Numerical simulations of reaction-diffusion systems with Neumann boundary conditions (NBC) on growing square domains by Maini et al. exhibit square and stripe (or roll) patterns that are usually associated with bifurcations from a trivial equilibrium on a square lattice. However, these patterns change as the domain grows. In this article we discuss several of these transitions; namely, transitions between different types of squares and between squares and stripes (or rolls). We show that these transitions can be understood by tracing paths through the unfoldings of certain co-dimension two mode interactions. To understand these transitions, we need to discuss two issues: the speed at which the domain size changes and the relations between NBC and periodic boundary conditions (PBC) on a square. First, in the simulations, the domain growth takes place on a time scale that is longer than the one needed for pattern formation. Therefore, we can assume that the domain growth is identified with quasistatic variation of time; that is, the domain grows slowly enough that the PDE solution of the time-dependent system tracks equilibria of the reaction-diffusion systems posed on a fixed size domain. Second, as is well-known, NBC problems on a square of side length l can be embedded in PBC problems on a square with side length 2l. The PBC problem has translation symmetries that are not present in the NBC problem. These additional symmetries are called hidden symmetries in the literature. Moreover, solutions to PBC that restrict to the smaller square and satisfy NBC are just those solutions that satisfy certain symmetry constraints. We show further that the transitions between different patterns can be understood by considering relevant mode interaction bifurcation problems on the larger square and then restricting to the smaller square. We have found that a generic continuous transition can occur between two types of squares. Also, the transition between squares and stripes can generically occur either via steady states and time-periodic states (standing waves) or via a jump. Interestingly, in mode interactions, the symmetry constraints induced by NBC are important in understanding which solutions exist and which solutions are stable. For example, diagonal stripes cannot occur as a primary branch in the NBC problem but do in the PBC problem. Also, patterns can be stable in the NBC problem that are not stable in the PBC problem. As a consequence, in the NBC problem we see standing wave time-periodic solutions as stable patterns leading to stable stripes, whereas in the PBC problem we see wavy rolls steady states as stable patterns leading to stable stripes. In principle, a classification of all transitions in NBC mode interactions is possible. However, we concentrate only on those transitions that are relevant to the numerically observed transitions.     

Processing of cellulose nanowhiskers/cellulose acetate butyrate nanocomposites using sol-gel process to facilitate dispersion

Biobased nanocomposites based on cellulose nanowhiskers (CNWs) and cellulose acetate butyrate (CAB) were prepared using solvent exchange of CNWs to ethanol by sol-gel method followed by casting. The strong flow birefringence of the solutions indicated evenly dispersed cellulose nanowhiskers in the dissolved polymer CAB. Scanning electron microscopy of the nanocomposites confirmed well dispersed CNWs in the CAB matrix, which was further supported by the high transparency exhibited by the nanocomposites. The results of tensile tests indicated significant improvements in the mechanical properties of nanocomposites by increasing the CNWs contents. The Young’s modulus and strength increased 83% and 70%, respectively, for nanocomposites with 12 wt% of CNW, and the strain was not suppressed compared to the neat CAB. The dynamic mechanical thermal analysis demonstrated significant improvement in storage modulus with increasing CNW contents, and the tan δ peak position was moved towards higher temperature when CNW was added. It is expected that solvent exchange by the sol-gel route followed by casting of nanocomposites from the same solvent will provide a promising route for obtaining cellulose nanocomposites with well dispersed CNW, leading to improved mechanical properties, even with low nanowhisker contents.     

Diverse nanocelluloses prepared from TEMPO-oxidized wood cellulose fibers: Nanonetworks,nanofibers, and nanocrystals

When wood cellulose fibers are oxidized with NaClO and catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and NaBr in water at pH 10, significant amounts of sodium carboxylate groups (≤1.7 mmol/g) are introduced into the oxidized celluloses. The original fibrous morphologies and cellulose I crystal structures are unchanged by oxidation. The TEMPO-oxidized cellulose fibers can be converted to partially fibrillated nanonetworks, completely individualized cellulose nanofibers with high aspect ratios, and needle-like cellulose nanocrystals with low aspect ratios by controlling the conditions of mechanical disintegration in water. It is therefore possible to prepare diverse nanocelluloses with different morphologies and properties from the same TEMPO-oxidized cellulose fibers, for various end uses and applications. All TEMPO-oxidized nanocelluloses contain large amounts of carboxylate groups. These provide scaffolds for versatile surface modification of nanocelluloses by simple ion exchange of sodium for other metal ions and alkylammonium ions.     

非均相超声法制备纤维素-聚苯胺导电复合材料及其导电性能研究

用非均相超声法制备了纤维素-聚苯胺导电复合材料,通过红外光谱(FT-IR)、扫描电镜(SEM)、和热重(TG)以及四探针仪(SDY-4)对其结构及导电性能进行了表征。经过超声处理的纤维素表面部分细胞初生壁(P)和次生壁外层(S1)脱除,次生壁中层(S2)裸露,表面粗糙。苯胺单体均匀地附着于其表面,并进一步聚合得到颗粒状聚苯胺,有效地抑制了团聚现象的产生。复合材料的热稳定性和导电性都有相应的提高。     

Sensitive Humidity‐Driven Reversible and Bidirectional Bending of Nanocellulose Thin Films as Bio‐Inspired Actuation

Inspired by plant movements caused by water swelling and deswelling within nano‐ and mesoscale cellulose fibrillar structures, asymmetric exposure of water vapors to thin films of nanofibrillated cellulose, NFC (also denoted as microfibrillated cellulose, MFC, or native cellulose nanofibers, CNF) is here shown to induce humidity‐controlled reversible actuation. The extent of the bending depends on the humidity difference across the film. A steady‐state bending is reached within a fraction of minute upon continued humidity exposure, and the film relaxes back upon removing the imposed humidity. The bending curvature becomes reduced when the film thickness increases, thus explaining that the effect is not observable in classic paper sheets, which are much thicker due to their constituent macroscopic thicker cellulose fibers. The bending is highly sensitive to humidity, as demonstrated by the observation that the film bends even based on the small humidity of human hand from a distance of several millimeters. Such a bending of a cellulose nanofiber film offers a particularly simple route toward biomimetic actuation and novel types of active material.     

Ultrahigh molar mass component detected in ethylhydroxyethyl cellulose by asymmetrical flow field-flow fractionation coupled to multiangle light scattering.

Asymmetrical flow field-flow fractionation (flow FFF) was connected to multiangle light scattering (MALS) and refractive index (RI) detectors for characterization of the molar mass distribution and molecular radius of a cellulose derivative, ethylhydroxyethyl cellulose (EHEC). Experimental conditions were optimized to allow study of a wide range of molar mass including even ultrahigh molar mass (UHM) components. The weight-average molar mass was 3.1 x 10(5) g x mol(-1) representing a very broad range (of molar mass) from 4.0 x 10(4) to 10(7) g x mol(-1), which corresponds to from <20 to 200 nm rms radius. The light scattering signal showed the presence of an UHM component, possibly an aggregate of extreme size, i.e., approximately 10(8) g x mol(-1) with a hydrodynamic diameter of 0.35 microm. Careful choice of the pore size in in-line filters is necessary in order to minimize MALS detector noise without removing the UHM component. Flow FFF-MALS-RI was demonstrated to be uniquely suited to detect the presence of UHM components.