细菌纤维素基CNFs/ZnO吸波材料的制备及性能

随着电子信息技术的不断发展,电磁污染问题日益严重,高效吸波材料的研究受到越来越多的关注。该文以生物多孔材料细菌纤维素为碳源,采用碳化改性和水热法两步制备了细菌纤维素基CNFs/ZnO复合材料,研究了二水合醋酸锌的浓度对CNFs/ZnO复合材料吸波性能的影响。通过X射线衍射仪(XRD)、冷场发射扫描电子显微镜(FESEM)、矢量网络分析仪(VNA)对复合材料的结构、形貌和吸波性能进行表征。结果表明:CNFs/ZnO复合材料被成功制备,其中碳纳米纤维(CNFs)没有明显的衍射峰,呈无定形状态;碳化和改性CNFs均保持了细菌纤维素三维网络多孔架构的精细纳米纤维微观形貌,但是CNFs变得卷曲且直径明显减小;CNFs/ZnO复合材料中,ZnO被紧密吸引在CNFs表面或随机插入CNFs的空隙中。通过改变二水合醋酸锌的浓度可以控制ZnO在复合材料中的含量,进而调控复合材料的电磁参数,获得良好的阻抗匹配。当二水合醋酸锌的浓度为0.25 mol/L时,ZnO在CNFs上分散得最为均匀,此时CNFs和ZnO的电阻损耗、介电损耗和界面极化等协同作用于三维多孔网络结构上,增加了复合材料对电磁波的多次反射、散射和长程耗散作用。该条件下制备的CNFs/ZnO复合材料,在涂层厚度为2.8 mm、频率为15.1 GHz附近时,其最佳反射损耗为−57.5 dB,有效吸收带宽为7.1 GHz,是一种可靠的复合吸波材料。

锂硫电池中CNTs-CNFs夹层对多硫化物的捕获和加速转化机理

为有效抑制多硫化锂(LiPSs)的穿梭效应,通过静电纺丝、电化学沉积和化学气相生长技术在碳纳米纤维(CNFs)上垂直生长碳纳米管(CNTs),开发了一种超薄、轻质的多功能三维多层交联碳纳米纤维-碳纳米管(CNTs-CNFs)夹层,并研究CNTs-CNFs对锂硫电池(LSBs)电化学性能的影响。研究结果表明:CNTs-CNFs薄膜优异的导电性和丰富的孔隙结构为LSBs提供了均匀的导电网络和LiPSs的吸附过滤屏障,与无夹层相比,含有CNTs-CNFs夹层的电池具有更优异的容量保持率和循环稳定性,在0.2 C电流密度下具有1296.7 mA·h/g的初始放电比容量,在100次循环后仍能提供了864.7 mA·h/g的放电比容量,容量保持率为66.68%。

CoN_(x)C active sites-rich three-dimensional porous carbon nanofibers network derived from bacterial cellulose and bimetal-ZIFs as efficient multifunctional electrocatalyst for rechargeable Zn–air batteries

In this work, a CoNxC active sites-rich three-dimensional porous carbon nanofibers network derived from bacterial cellulose and bimetal-ZIFs is prepared via a nucleation growth strategy and a pyrolysis process.The material displays excellent electrocatalytic activity for the oxygen reduction reaction, reaching a high limiting diffusion current density of -7.8 mA cm^(-2), outperforming metal–organic frameworks derived multifunctional electrocatalysts, and oxygen evolution reaction and hydrogen evolution reaction with low overpotentials of 380 and 107 mV, respectively. When the electrochemical properties are further evaluated, the electrocatalyst as an air cathode for Zn-air batteries exhibits a high cycling stability for63 h as well as a maximum power density of 308 mW cm^(-2), which is better than those for most Zn-air batteries reported to date. In addition, a power density of 152 mW cm^(-2) is provided by the solid-state Zn-air batteries, and the cycling stability is outstanding for 24 h. The remarkable electrocatalytic properties are attributed to the synergistic effect of the 3 D porous carbon nanofibers network and abundant inserted CoNxC active sites, which enable the fast transmission of ions and mass and simultaneously provide a large contact area for the electrode/electrolyte.

In Situ Synthesis of Cuprous Oxide/Cellulose Nanofibers Gel and Antibacterial Properties

Cellulose nanofibers were synthesized by acetobacter xylinum(xylinum 1.1812).The cellulose nanofibers with 30-90 nm width constructed three-dimension network gel,which could be used as a wound dressing since it can provide moist environment to a wound.However,cellulose nanofibers have no antimicrobial activity to prevent wound infection.To achieve antimicrobial activity,the cellulose nanofibers can load cuprous oxide(Cu2O)particles on the surface.The cuprous oxide is a kind of safe antibacterial material.The copper ions can be reduced into cuprous oxides by reducing agents such as glucose,N2H4 and sodium hypophosphite.The cellulose nanofibers network gel was soaked in CuSO4 solution and filled with copper ions.The cuprous oxide nanoparticles were in situ synthesized by glucose and embedded in cellulose nanofibers network.The morphologies and structure of the composite gel were analyzed by FESEM,FTIR,WAXRD and inductively coupled plasma(ICP).The sizes of Cu2O embedded in cellulose nanofibers network are 200-500 nm wide.The peak at 605 cm−1 attributed to Cu(I)-O vibration of Cu2O shits to 611 cm−1 in the Cu2O/cellulose composite.The Cu2O/cellulose nanofibers composite reveals the obvious characteristic XRD pattern of Cu2O and the results of ICP show that the content of Cu2O in the composite is 13.1%.The antibacterial tests prove that the Cu2O/cellulose nanofibers composite has the high antibacterial activities which is higher against S.aureus than against E.coli.

Effect of High Pressure Homogenization Treatment on Structure and Properties of Soybean Residue Cellulose Nanofibers

To reduce the adverse effects of non-cellulose materials on subsequent homogenization,the effects of a high-pressure homogenization treatment on the structure and properties of cellulose nanofibers(CNF)prepared by acid treatment of soybean residue were studied.The effects of the number of homogenization step on the microfibrillation degree,crystalline structure and mechanical properties of the soybean residue were analyzed by SEM,FT-IR,XRD,TG and DTG.The results showed that an increase in the number of homogenization steps led to an increase in the degree of microfibrillation,a more uniform distribution of the CNF diameter,and an increase in the crystallinity of CNF.However,but when the number of homogenization steps exceeded 15,the rate of change decreased,and the crystallinity of CNF decreased.As the number of homogenization steps increased,the average degree of polymerization and average molecular weight of CNF decreased continuously,and after 15 homogenization steps,their rate of change also decreased.Therefore,15 steps of high-pressure homogenization represented a suitable number of steps to prepare the soybean residue CNF with an average diameter of 15 nm.

Bacterial Cellulose Nanofibers as Reinforcement for Preparation of Bamboo Pulp Based Composite Paper

Bamboo fibers(BFs),with features of renewability and biodegradability,have been widely used in paper-making products.In order to improve the mechanical properties and water absorption behaviors of the BF paper,bacterial cellulose nanofibers(BCNFs)as environmentally friendly nano-fibrillated cellulose(NFC)were combined with BFs.The structures and properties of the BF/BCNF composite paper were characterized by field emission scanning electron microscopy(FE-SEM),X-ray diffraction(XRD),Fourier transforms infrared(FTIR)spectroscopy,mechanical tests,pore size tests,and water absorption tests.The results indicated that the addition of BCNFs could significantly improve the water absorption capacity and mechanical properties.The water absorption ratio of the BF/BCNF composite paper with a BCNF mass fraction of 9%comes to 443%,about 1.33 times that of the pure BF paper.At the same BCNF content,the tensile strength of the BF/BCNF composite paper in dry and wet states was 12.37 MPa and 200.9 kPa,respectively,increasing by 98.24%and 136.91%as compared with that of the BF paper.

Application of Cellulose and Cellulose Nanofibers in Oil Exploration

In this article, the application of cellulose and cellulose nanofibers in oil exploration was discussed, and the research status of using cellulose and cellulose nanofibers as oil displacement agents, oil-well cementing additives, and foam stabilizers were summarized.

高性能柔性自支撑CNFs@UIO-66@PANI复合膜电极材料的制备及应用

以纳米纤维素(CNFs)为柔性基体,在其表面通过溶剂热反应原位生长UIO-66纳米层,随后通过原位聚合将聚苯胺(PANI)沉积在CNFs@UIO-66表面,真空抽滤得到柔性纳米膜,并组装成柔性固态超级电容器。考察了CNFs/UIO-66比例以及苯胺(ANI)浓度对CNFs@UIO-66@PANI复合膜电化学性能的影响。结果表明,CNFs/UIO-66的比例对复合膜的电化学性能有关键影响,当CNF/UIO-66比例为1∶1电流密度在1 A·g^(-1)时,复合膜比容量高达1287 F·g^(-1),随着CNF/UIO-66中UIO-66比例的增加,复合膜的比电容下降;当CNF/UIO-66比例为1∶3时,复合膜的比电容降至554 F·g^(-1)。将复合膜组装成柔性对称固态超级电容器,当功率密度为200 W·kg^(-1)时,能量密度为47.39 Wh·kg^(-1),在10 A·g^(-1)的电流密度下循环5000次后,循环稳定性高达100%,表现出极佳的稳定性,亦证实了CNFs@UIO-66@PANI复合膜在柔性储能领域的巨大应用潜力。

Ketoprofen/ethyl Cellulose Nanofibers Fabricated Using an Epoxy-coated Spinneret

The present study investigates the preparation of sustained release drug-loaded nanofibers using a novel epoxy-coated spinneret. With ethyl cellulose (EC) and ketoprofen (KET) as the filament-forming matrix and the active pharmaceutical ingredient, Drug-loaded composite nanofibers are generated smoothly and continuously with few user interventions. Field-emission scanning electron microscopic observations demonstrated that the composite nanofibers prepared using the epoxy-coated spinneret have better quality than those from a traditional stainless steel spinneret in terms of diameter and its distribution. Both of the composite nanofibers are in essential a molecular solid dispersion of EC and KET based on the hydrogen bonding between them, as verified by XRD and ATR-FTIR results. In vitro dissolution tests show that the nanofibers resulted from the new spinneret provide a finer sustained KET release profile than their counter-parts. Epoxy-coated spinneret is a useful tool to facilitate the electrospinning process through the prevention of clogging for generating high quality nanofibers.

Isolation and Characterization of Cellulose Nanofibers from Argentine Tacuara Cane(Guadua Angustifolia Kunth)

New trends in the area of material improvement are the use of natural nano-charges from renewable biomass,improving the value and sustainability of our country’s natural products.Bamboo is widely used in many countries of the world,although in Argentina,despite being commercialized and exported for the manufacture of wood floors,it goes unnoticed despite having native species.Therefore,researchers identified the native and exotic species present in our country and are working on novel uses.In this context,it is proposed the Argentine Tacuara Cane(Guadua Angustifolia Kunth),endemic plant as a new source of nanocellulosic materials,where stem fibers have been isolated using a green method achieving with yield of 45.9%of cellulose.The cellulose nanofibrils(CNF)were obtained using a green homogenization method.The CNF exhibited web-like long fibrous structure with the diameter of 10-20 nm.The crystallinity was 65.5%,as for the onset temperature of thermal decomposition was 212°C.The nanocellulose isolated from the Tacuara Cane seed fibers has a high potential to be used as a new source of cellulose-based nanofiller for the reinforcement of bionanocomposite films.

The Influence of Sheath Solvent’s Flow Rate on the Quality of Electrospun Ethyl Cellulose Nanofibers

The present research investigates the influence of sheath solvent’s flow rate on the quality of electrospun ethyl cellulose (EC) nanofibers using a modified coaxial process. With 24 w/v % EC in ethanol as electrospinnable core fluid and ethanol as sheath fluid, EC nanofibers generated under different sheath flow rates were generated from the modified processes. FESEM observations demonstrate that the modified process is effective in preventing the clogging of spinneret for a smooth electrospinning. The key for the modified coaxial process is the reasonable selection of a sheath flow rate matching the drawing process of core EC fluid during the electrpospinning. The EC nanofibers’ diameters (D, nm) could be manipulated through the sheath-to-core flow rate ratio (f) as D = 819-1651f (R= 0.9754) within a suitable range of 0 to 0.25. The present paper provides useful data for the implementation of the modified coaxial process controllably to obtain polymer nanofibers with high quality.

Molecular Dynamics Study on Transmission Mechanism of Torsional Deformation in Cellulose Nanofibers with Hierarchical Structure

Cellulose nanofiber (CNF) is a fibrous and nano-sized substance produced by decomposition of bulk-type cellulose which is a main component of plants. It has high strength comparable to steel, and it shows low environmental load during a cycle of production and disposal. Besides it has many excellent properties and functions such as high rigidity, light-weight, flexibility and shape memory effect, so it is expected as a next-generation new material. Usually it is composed of many cellulose micro fibrils (CMFs) in which molecular chains of cellulose are aggregated in a crystal structure, the knowledge of mechanical properties for each CMF unit is important. Since actual fibrils are complicatedly intertwined, it is also crucial to elucidate the transmission mechanism of force and deformation not only in one fibril but also in between fibrils. How the dynamic and hierarchical structure composed of CMFs responds to bending or torsion is an interesting issue. However, little is known on torsional characteristics (shear modulus, torsional rigidity, etc.) concerning CMF. In general, in a wire-like structure, it is difficult to enhance torsional rigidity and strength, compared with tensile ones. Therefore, in this study, we try to build a hierarchical model of CNF by multiplying CMF fibers and to conduct molecular dynamics simulation for torsional deformation, by using hybrid model between all-atom and united-atoms model. First, shear modulus was estimated for one CMF fibril and it showed a value close to the experimental values. Also, we assume a state in which two CMFs are ideally arranged in parallel, and create a hierarchical structure. We evaluate the dependence on the temperature for the bond strength and toughness in the hierarchical structures. Furthermore, we mentioned the transmission mechanism between components of a hierarchical structure.

Emulsion Graft Polymerization of Methyl Methacrylate onto Cellulose Nanofibers

Methyl methacrylate (MMA) was successfully grafted onto cellulose nanofibers (CNFs) at room temperature in an emulsion system using a diethyl(1,10-phenanthroline N1,N10)zinc(II) complex (Phen-DEZ) with oxygen as the radical initiator. The effects of reaction temperature, initiator concentration, and monomer content on the grafting reaction were investigated. The molecular weight of the non-grafted PMMA, which was produced during graft polymerization, was more than 1 million, as determined by size exclusion chromatography. The PMMA-grafted CNFs were analyzed by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy, which confirmed the grafting of PMMA on the nanofiber surface. The study presents a strategy for the grafting of high-molecular weight PMMA onto CNFs in an emulsion system using Phen-DEZ and O2.

液相共沉淀法制备MnO_2/CNFs催化剂及其低温脱硝性能

以碳纳米纤维为载体,采用液相共沉淀法制备MnO_2/CNFs催化剂并将其应用于低温选择性催化还原(SCR)NO,利用BET,XRD,FESEM,EDS,TEM及XPS对催化剂的微观形貌、结构特征、元素组成以及价态分布进行表征。结果表明:催化剂的活性组分是MnO_2,且以无定型态负载于CNFs表面。在80~180℃下进行低温脱硝活性的测试。当负载量为6%时,MnO_2/CNFs催化剂的脱硝性能最为优异,在80℃时脱硝率就达到了65.25%,当温度升高至180℃时脱硝率达95.25%。无定型结构、良好的分散性以及较高的表面吸附氧含量是MnO_2/CNFs催化剂具有优异低温脱硝催化活性的主要原因。本研究在未经过任何酸处理的情况下使MnO_2负载在CNFs上,很大程度上减小了对环境的污染。

CNFs/SA复合水凝胶球对IBU释放性能的影响

为了提高疏水性药物的缓释性能,采用离子交联的方法制备复合水凝胶球并进行改性研究。以海藻酸钠(Sodium alginate,SA)和纤维素纳米纤维(Cellulose nanofibers,CNFs)为原料,制备不同CNFs含量的CNFs/SA复合水凝胶球。通过形貌表征和吸水率测试,探讨了CNFs对凝胶球的结构、成型性和溶胀率的影响。以布洛芬(Ibuprofen,IBU)作为药物模型,研究水凝胶球载体对IBU释放性能的影响。实验表明,随着CNFs含量增加,复合水凝胶球的成型性及在生理盐水中的稳定性提高。水凝胶载体对疏水性药物IBU有明显缓释作用,加入CNFs后,IBU在相同时间内的释放量高于纯SA水凝胶球载体。当CNFs含量为21%时,所得复合水凝胶球网络结构规整,在生理盐水中的稳定性最好,IBU释放时间长。

多孔PVA/CNFs复合水凝胶的制备与性能

目的研究聚乙二醇(PEG)的加入对复合凝胶微观结构、溶胀性能和热稳定性的影响,扩大复合凝胶在包装领域的应用。方法以PEG为致孔剂,纳米纤维素(CNFs)为增强相,利用物理交联法制备出多孔聚乙烯醇/纳米纤维素复合水凝胶。结果 PEG作为致孔剂时可制得网络互穿结构的多孔水凝胶,复合凝胶的溶胀度可达到1000,相比于纯PVA水凝胶有极大的提高,同时加入CNFs的聚乙烯醇凝胶与纯的聚乙烯醇凝胶相比具有更好的热稳定性。结论这种有着高溶胀性和良好热稳定性的多孔复合凝胶可用于包装产品的保鲜与物流防护。

CMC-CNCs和CMC-CNFs阳离子交换膜的制备与性能研究

为了提升羧甲基纤维素钠(CMC)阳离子交换膜(CEMs)的污染物迁移性能,以纤维素纳米晶须(CNCs)和纤维素纳米纤维(CNFs)为掺杂材料,通过流延法制备复合阳离子交换膜.表征了复合膜的形貌、溶胀度、亲水性、J-V曲线,并以氨氮为目标污染物,测试了纯CMC及复合膜在电渗析过程中的氨氮迁移性能.结果表明,CMC-CNCs和CMC-CNFs复合膜较纯CMC膜表面光滑,亲水性提升,膜阻抗及工作电压均减少,在酸性溶液中能保持较好的结构稳定性.同时,以m(CMC)∶m(CNCs)=1.0∶2.0及m(CMC)∶m(CNFs)=1.5∶1.5为例,适量掺杂CNCs和CNFs均可以降低复合膜在工作过程中的槽电压,提升电流密度,3 h内对氨氮的迁移能力分别从86.6%提升到93.2%及94.5%.

Morphological, Mechanical and Thermal Properties of Poly(lactic acid)(PLA)/Cellulose Nanofibrils(CNF) Composites Nanofiber for Tissue Engineering

Composite nanofiber membranes based on biodegradable poly(lactic acid)(PLA) and cellulose nanofibrils(CNF) were produced via electrospinning. The influence of CNF content on the morphology, thermal properties, and mechanical properties of PLA/CNF composite nanofiber membranes were characterized by field scanning electron microscopy(FE-SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), and dynamic mechanical analysis(DMA), respectively. The results show that the PLA/CNF composite nanofibers with smooth, free-bead surface can be successfully fabricated with various CNF contents. The introduction of CNF is an effective approach to improve the crystalline ability, thermal stability and mechanical properties for PLA/CNF composite fibers. The Young's moduli and tensile strength of the PLA/CNF composite nanofiber reach 106.6 MPa and 2.7 MPa when the CNF content is 3%, respectively, which are one times higher and 1.5 times than those of pure PLA nanofiber. Additionally, the water contact angle of PLA/CNF composite nanofiber membranes decreases with the increase of the CNF loading, resulting in the enhancement of their hydrophilicity.

Tensile Properties of Mechanically-Defibrated Cellulose Nanofiber-Reinforced Polylactic Acid Matrix Composites Fabricated by Fused Deposition Modeling

Biodegradable polymers are highly attractive as potential alternatives to petroleum-based polymers in an attempt to achieve carbon neutrality whilst maintaining the mechanical properties of the structures.Among these polymers,polylactic acid(PLA)is particularly promising due to its good mechanical properties,biocompatibility and thermoplasticity.In this work,we aim to enhance the mechanical properties of PLA using mechanically-defibrated cellulose nanofibers(CNFs)that exhibit remarkable mechanical properties and biodegradability.We also employ fused deposition modeling(FDM),one of the three-dimensional printing methods for thermoplastic polymers,for the low-cost fabrication of the products.Mechanically-defibrated CNF-reinforced PLA matrix composites are fabricated by FDM.Their tensile properties are investigated in two printing directions(0°/90°and+45°/-45°).The discussion about the relationship between printing direction and tensile behavoir of mechanically-defibrated CNF-reinforced PLA matrix composite is the unique point of this study.We further discuss the microstructure and fracture surface of mechanically-defibrated CNF-reinforced PLA matrix composite by scanning electron microscope.

ZIF-67@Cellulose nanofiber hybrid membrane with controlled porosity for use as Li-ion battery separator

Zeolitic imidazolate framework-67(ZIF-67) was synthesized on the surface of cellulose nanofibers(CNFs)in methonal to address the problems of unhomogeneous pore size and pore distribution of pure CNF membrane.A combination of Energy Dispersive X-Ray Spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS) and X-ray powder diffraction(XRD) patterns were used to determine the successful synthesis of ZIF-67@CNFs.The size of the ZIF-67 particles and pore size of the ZIF-67@CNF membrane were50-200 nm and 150-350 nm, respectively.The prepared ZIF-67@CNF membrane exhibited excellent thermal stability,lower thermal shrinkage and high surface wettability.The discharge capacity retention of the Li-ion batteries(LIBs) made with ZIF-67@CNF,glass fiber(GF),CNF and commercial polymer membranes after 100 th cycle at 0.5 C rate were 88.41%,86.22%,83.27%,and 81.03%,respectively.LIBs with ZIF-67@CNF membrane exhibited a better rate capability than these with other membranes.No damage of porous structure or peel-off of ZIF-67 was observed in the SEM images of ZIF-67@CNF membrane after100 th cycle.The improved cycling performance,rate capability,and good electrochemical stability implied that ZIF-67@CNFs membrane can be considered as a good alternative LIB separator.