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纳米纤维素因其独特的结构及优越的性能引起了学术和企业界的广泛关注与重视,日渐成为新材料和纤维素科学领域的研究热点。以木质纤维资源为原料,可分离出两种主要类型的纳米纤维素:纤维素纳米晶体(CNC)和纤维素纳米纤丝(CNF)。本文详细综述了CNC和CNF的制备方法,着重介绍了近几年新兴的制备方法,包括可回收的有机酸水解法综合制备CNC和CNF,美国高附加值制浆(AVAP)法制备木质素包覆的CNC和CNF,低共熔溶剂预处理结合机械剪切高效制备CNC和CNF,以及微极性环境下可调控机械剥离制备亲疏水性CNF等。同时,讨论了各种制备方法的优缺点,并介绍了国内外纳米纤维素的产业化研究进展。最后,我们提出纳米纤维素的制备方法未来将朝着绿色、高效和可持续的方向发展。 相似文献
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纳米纤维素的制备* 总被引:22,自引:0,他引:22
在纳米尺寸范围操控纤维素分子及其超分子聚集体,结构设计并组装出稳定的多重花样,由此创制出具有优异功能的新纳米精细化工品、新纳米材料,是纤维素科学的前沿领域和热点。为了研究当前制备纳米纤维素的现状和发展方向,简述了纳米纤维素化学基础,介绍了三类纳米纤维素:纳米纤维素晶体(晶须)、纳米纤维素复合物和纳米纤维素纤维,重点综述了纳米纤维素的五种制备方法:化学法制备纳米纤维素晶体和晶须、生物法制备细菌纤维素、物理法制备微纤化纳米纤维素、人工合成纳米纤维素和静电纺丝制备纤维素纤维,讨论了各种制备方法的优点和缺点,指出开展纳米纤维素超分子的可控结构设计、立体与位向选择性控制与制备、分子识别与位点识别等自组装过程机理、多尺度结构效应的形成机理等基础理论性研究是主要研究基础,新型的、绿色、低能耗、快速、高效的制备方法是纳米纤维素制备方法的发展方向。 相似文献
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本文通过氨水扩散共沉淀法,在可溶纤维素的调控作用下制备得到了纳米带状羟基磷灰石。在120℃下加热回流高浓度氯化钙溶液和纤维素,作为后续合成羟基磷灰石的原料溶液。随后将磷酸二氢钠溶液加入到含有溶解纤维素和Ca2+离子原料溶液中,通过氨水扩散来提高溶液的pH值,从而引发羟基磷灰石从溶液中析出,反应一段时间后,收集析出样品。对照实验样品在不加纤维素条件下反应收集得到。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)、傅立叶变换红外仪(FT-IR)和X射线衍射仪(XRD)分析了纤维素对HA晶体形貌和晶体结构的影响。结果显示,实验合成了超薄纳米带状羟基磷灰石晶体,该晶体的合成可能是因为纤维素分子杂化到了HA的晶体中。 相似文献
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用示差扫描量热(DSC)、偏光显微镜(POM)及X射线衍射(XRD)分析考察了具有纳米结构的聚偏氟乙烯(PVDF)/1-乙烯基-3-丁基咪唑氯盐离子液体([VBIM][Cl])复合材料(PVDF/[VBIM][Cl])中经[VBIM][Cl]接枝的PVDF(PVDF-g-[VBIM][Cl])纳米微区对PVDF结晶行为的影响.研究结果表明,[VBIM][Cl]化学接枝在PVDF的分子链上,在PVDF/[VBIM][Cl]复合材料中,PVDF-g-[VBIM][Cl]嵌段形成大量纳米微区,分散在PVDF基体中.PVDF-g-[VBIM][Cl]纳米微区能够显著提高PVDF熔体结晶温度(Tc)并显著降低PVDF晶体的等温结晶时间.与纯PVDF相比,在纳米结构的PVDF/[VBIM][Cl]复合材料中,PVDF-g-[VBIM][Cl]纳米微区大大提高了PVDF晶体的成核速率,PVDF的球晶尺寸明显减小.由于[VBIM][Cl]完全"受限"于PVDF-g-[VBIM][Cl]纳米微区中,无法与PVDF分子链发生相互作用,因此纳米结构的PVDF/[VBIM][Cl]复合材料最终以非极性的α晶体为主.由于PVDF-g-[VBIM][Cl]纳米微区与PVDF基体具有热力学不相容性,因此其界面处的PVDF分子链处于部分有序的状态,有助于PVDF晶体的成核,加速了PVDF晶体的结晶速率. 相似文献
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纤维素纳米晶体是纤维素原料经加工而得到的纳米级棒状或球状晶体。由于其具有高强度、大比表面积、生物相容性、可再生性和可降解性等优良性能,可应用于复合材料、生物医药和环境等多个领域。本文详细综述了近年来制备纤维素纳米晶体的常用方法,包括酸水解法、氧化法、酶水解法、机械法、溶剂法以及组合法。同时,讨论了各种制备方法的优缺点。在应用研究方面,本文总结了其在增强复合材料、膜过滤复合材料、导电复合材料和无机纳米复合材料等热门领域的研究情况。最后,对纤维素纳米晶体的未来发展方向进行了展望。 相似文献
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利用硼氢化钠还原法制备了金纳米粒子, 通过在其表面修饰链长不同的巯基羧酸, 得到了功能化纳米粒子. 利用荧光发射、紫外吸收和圆二色谱等手段研究了功能化金纳米粒子与蜂毒素分子之间的相互作用及其所诱导的蛋白质分子的构象变化. 研究结果表明, 功能化修饰的金纳米粒子可通过静电相互作用吸附蜂毒素(Melittin)并诱导其α-螺旋结构的形成, 且这种效应与巯基羧酸分子的链长直接相关. 相似文献
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合成了一系列烷基取代的间苯三酚衍生物,并在大气条件下用扫描隧道显微镜研究了它们在高定向裂解石墨表面的吸附和组装行为.实验结果表明,这些自组装分子具有条状结构特征.在链长较短的分子图像中,两条平行的烷氧基链肩并肩地排列在苯环的一侧,另一条烷氧基链则排列在苯环的另一侧,链与链之间彼此相互交错排列形成均一的烷基条带.当链长增加时,这种高稳定性和密排结构遭到破坏,出现单个分子和分子对共存的组装结构.这是由于烷基链与烷基链之间以及烷基链与基底之间的作用力共同决定的.通过调控分子烷基链的长度可以得到不同的表面二维纳米结构. 相似文献
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Mengmeng Zhao Shigenori Kuga Shidong Jiang Min Wu Yong Huang 《Cellulose (London, England)》2016,23(5):2809-2818
The nanoscale structural changes of crystalline cellulose by mechanical milling was studied by high-resolution microscopy (AFM, SEM, TEM). We examined influence of environment [dry, water, silicone oil (PDMS)] on cellulose milling, finding their characteristic effects on microscopic morphology of the products. Dry milling of cellulose gave aggregated globular particles with fast decrystallization. Milling with water or PDMS caused partial dispersion of nanofibers. Milling with PDMS formed micro-platelets <1 µm thick with slight decrystallization. Remarkably, nanoscale particles isolated from PDMS-milled cellulose by sonication in ethanol contained cellulose nanosheets, typically 0.1–10 µm wide and 4.2 nm thick, apparently formed by monolayer association of elementary fibrils. TEM and electron diffraction revealed crystalline nature of nanosheets, with specific orientation of (110) plane or (200) plane perpendicular to the sheet plane. A possible mechanism of the nanosheets formation is proposed, in which the elementary fibrils are aligned parallel by mechanical impacts. 相似文献
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通过不同TEMPO氧化体系对商品竹浆进行氧化处理,经高频超声纳米纤丝化后,可以制得长度在数百纳米,宽度小于5.0 nm,厚度仅为几个埃的纤维素纳米纤丝(TEMPO-oxided cellulose nanofibrils,TOCNs).这种纳米带状(nanostrip)的TOCNs是由纤维素片层构成的.本文通过场发射扫描电子显微镜(FE-SEM)探究了原料和2组TOCNs样品的形貌变化,利用透射电子显微镜(TEM)和原子力显微镜(AFM)对2组TOCNs样品的三维尺寸(长、宽、厚)进行测量统计.通过不同氧化体系产物的TOCNs三维尺寸差异,并结合傅里叶红外吸收光谱(FTIR)、X射线衍射(XRD)及交叉极化和魔角旋转13C固态核磁共振光谱(CP/MAS 13C-NMR)揭示了不同氧化体系对纤维素Iβ层内氢键及长轴方向的作用机理. 相似文献
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Manna L Wang LW Cingolani R Alivisatos AP 《The journal of physical chemistry. B》2005,109(13):6183-6192
Equilibrium geometries, surface energies, and surfactant binding energies are calculated for selected bulk facets of wurtzite CdSe with a first-principles approach. Passivation of the surface Cd atoms with alkyl phosphonic acids or amines lowers the surface energy of all facets, except for the polar 000 facet. On the nonpolar facets, the most stable configuration corresponds to full coverage of surface Cd atoms with surfactants, while on the polar 0001 facet it corresponds only to a partial coverage. In addition, the passivated surface energies of the nonpolar facets are in general lower than the passivated polar 0001 facet. Therefore, the polar facets are less stable and less efficiently passivated than the nonpolar facets, and this can rationalize the observed anisotropic growth mechanism of wurtzite nanocrystals in the presence of suitable surfactants. 相似文献
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Mohammad Ghasemi Paschalis Alexandridis Marina Tsianou 《Cellulose (London, England)》2017,24(2):571-590
The dissolution of cellulose is a critical step for the efficient utilization of this renewable resource as a starting material for the synthesis of high value-added functional polymers and chemicals and also for biofuel production. The recalcitrance of semicrystalline cellulose microfibrils presents a major barrier to cellulose dissolution. Despite research efforts, important aspects of cellulose dissolution such as solvent-induced decrystallization and chain disentanglement are not well-understood. Here we address these fundamental issues with the practical goal of gaining insights into the swelling and dissolution of cellulose that cannot be obtained from macroscopic experimental data. To this end, we have used a newly-developed phenomenological model that captures the phenomena governing the dissolution of semicrystalline polymers as well as the thermodynamics and kinetics of dissolution. This model fits well experimental data for swelling and dissolution of cotton fibers in the ionic liquid [bmim]Cl, and allows the quantification of two important aspects, i.e., solvent effectiveness in cellulose (1) decrystallization and (2) chain disentanglement, the balance of which controls the mechanism and kinetics of cellulose dissolution. The activation parameters of cellulose decrystallization, estimated using the obtained decrystallization constant values, reveal that the decrystallization of cellulose in [bmim]Cl is associated with positive enthalpy and entropy and it is also very sensitive to temperature. When the solvent effectiveness in the disruption of cellulose crystals is relatively lower than its ability to disentangle the chains, the kinetics of dissolution are controlled by decrystallization. Furthermore, conditions that facilitate cellulose chain disentanglement, in addition to increasing the rate of dissolution, can result in faster decrystallization. The solvent effectiveness in chain disentanglement is the only factor that determines the decrease of the cellulose fiber radius. In cases where the fiber dissolution rate is lower than the decrystallization rate, the dissolution of cellulose is mostly controlled by the solvent ability to disentangle the chains. The insights obtained from this study improve the understanding of cellulose–solvent interactions underlying decrystallization and disentanglement and their contributions in controlling the kinetics of cellulose swelling and dissolution. 相似文献
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The wettabilities of fluorinated polymers were evaluated using a series of contacting probe liquids ranging in nature from nonpolar aprotic to polar aprotic to polar protic. Fully fluorinated polymers were wet less than partially fluorinated polymers, highlighting the weak dispersive interactions of fluorocarbons. For partially fluorinated polymers, the interactions between the distributed dipoles along the polymer backbone and the dipoles of the contacting liquids were evaluated using both polar and nonpolar probe liquids. The results demonstrate that the surface dipoles of the fluoropolymers generated by substituting fluorine atoms with hydrogen or chlorine atoms can strongly interact with polar contacting liquids. The wettabilities of the partially fluorinated polymers were enhanced by increasing the density of dipoles across the surfaces and by introducing differentially distributed dipoles. 相似文献
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Canongia Lopes JN Costa Gomes MF Pádua AA 《The journal of physical chemistry. B》2006,110(34):16816-16818
The existence of microphase segregation between polar and nonpolar domains in ionic liquids changes the way in which solvation can be understood in these media. Here, we perform a structural analysis on the solvation of nonpolar, polar, and associating solutes in imidazolium-based ionic liquids, where this novel way of understanding their nature as microsegregated solvents is correlated with their ability to interact with different species in diverse and complex ways. 相似文献
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Benjamin I 《The journal of physical chemistry. B》2005,109(28):13711-13715
Hydrogen bond dynamics at the neat interface between water and a series of organic liquids are studied with molecular dynamics computer simulation. The organic liquids are nonpolar (carbon tetrachloride), weakly polar (1,2-dichloroethane), and polar (nitrobenzene). The effect of surface polarity and surface roughness is examined. The dynamics are expressed in terms of the hydrogen bond population autocorrelation functions and are found to be nonexponential and strongly dependent on the nature of the organic phase. In particular, at all interfaces, the dynamics are slower at the interface than in the bulk and sensitive to the location of the water molecules along the interface normal. 相似文献
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The goal of this study is to investigate the hydration and dehydration induced structural changes of native cellulose. Never dried cotton, and never dried bacterial cellulose with and without added matrix polymer xyloglucan, are examined under the influence of dehydration and rehydration. Significant crystal structure changes were observed in the later stage of drying for both cotton and bacterial cellulose (BC). The 1 % lateral expansion in glucan chain spacing and 17 % decrease of calculated Scherrer dimension were detected for cotton due to the distortion of the structure possibly caused by mechanical stresses associated with drying. No detectable changes on average glucan chain spacings were observed for large BC crystals. However, an average width decrease by 4.4 nm was discovered in the (010) direction, which was more significant than that observed in the (100) and (110) directions. It is hypothesized that co-crystallized elementary fibrils preferentially disassociate along the (010) plane resulting in a significant reduction of crystal width. In the BC-xyloglucan model composite, the presence of xyloglucan does not interfere with the dehydration behavior. Rehydration leads to some structural changes but to a lesser extent than the initial drying. High temperature dehydration induced deformation and crystal size changes are found to be non-reversible due to the removal of the last hydration layer on the cellulose surface. 相似文献
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L. V. Zherenkova P. G. Khalatur 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(6):987-993
The theory of integral equations was applied to investigate the formation of structures in ionic liquids (ILs). The effect
of temperature and the length of the cation tails on the structural properties of a system was studied. An intermediate type
of ordering in ILs as compared with common liquids was observed. The formation of polar and nonpolar domains was revealed,
with the distribution of the polar domains having the shape of a three-dimensional net coexisting with nonpolar domains. The
characteristic scale of intermediate ordering was shown to increase as a power function without disturbing the shape of the
distribution of polar domains as the length of the cation tails grew. 相似文献
20.
The effect of polyketone (PK) γ-irradiation dose on the energy characteristics of the PK surface, the specific free surface energy, and the interfacial energy at the boundary between polar (water) and nonpolar (octane) liquids has been studied for the first time. The most significant changes in the energy characteristics of the surface occur at doses up to 100 kGy, and improvement in PK adhesion to the polar and nonpolar phases is observed at doses above 75 and 200 kGy, respectively. 相似文献