共查询到20条相似文献,搜索用时 31 毫秒
1.
Thi Thu Thao Ho Tanja Zimmermann Walter Remo Caseri Paul Smith 《Journal of Polymer Science.Polymer Physics》2013,51(8):638-648
Liquid ammonia was used to treat films of nanofibrillated cellulose (NFC), trimethylammonium-modified NFC (TMA-NFC), and their composites with vermiculite. Crystal structure, mechanical properties, water vapor permeation and water vapor adsorption of the resulting materials were investigated. Upon treatment, the crystal structure of (TMA-)NFC both in presence and absence of vermiculite changed from cellulose I to III. With the exception of TMA-NFC/vermiculite composites, pronounced effects on the addressed mechanical properties arose after exposure of the materials to ammonia. Furthermore, treatment of composite films with ammonia led to a distinct decrease in water vapor permeation. Remarkably, TMA-NFC/vermiculite composites films show the best water vapor barrier properties, highest tensile strength and highest elastic modulus after treatment with liquid ammonia. This is regarded to be at least partially a consequence of electrostatic attraction between the positively charged ammonium groups in TMA-NFC and the anionic silicate layers of vermiculite. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 相似文献
2.
Mohammad Shateri Khalil-Abad Mohammad Esmail Yazdanshenas Mohammad Reza Nateghi 《Cellulose (London, England)》2009,16(6):1147-1157
Cotton was cationized by exhaustion method using 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) as a cation-generating
agent. Adsorption of silver nanoparticles on normal and cationized cotton was studied by exhaustion method at temperatures
of 80°C and 100°C. Two exhaustion baths were used, containing nanosilver colloidal solutions stabilized by two different stabilizers
and various concentrations of silver nanoparticles. Fourier-transform infrared (FT-IR) spectra of normal and cationized samples
confirmed the existence of quaternary ammonium groups on cationized cellulose fibers. X-ray diffraction (XRD) patterns showed
that crystallinity of the modified cellulose fibers was decreased. Scanning electron microscope (SEM) images revealed that
the surface of the modified cotton was rougher than that of normal cotton. In addition, SEM images showed the presence of
silver nanoparticles on the surface of treated fabric samples. The amount of silver particles adsorbed on the fabric samples
was determined using inductively coupled plasma-optical emission spectrometer. Antibacterial tests were performed against
Escherichia coli bacteria as an indication of antibacterial effect of samples. Cationized cotton samples adsorbed more silver nanoparticles
and then had greater ability to inhibit bacteria. 相似文献
3.
Assessing the combined benefits of clay and nanofibrillated cellulose in layered TMP-based sheets 总被引:1,自引:0,他引:1
A new concept for both furnish composition and z-directional furnish arrangement involving the interaction between specific thermo-mechanical pulp fractions (TMP), nanofibrillated
cellulose (NFC) and clay in oriented layered laboratory sheets is presented. Used separately, NFC improves the strength properties
of paper while fillers enhance the optical properties. Synergy effects of clay–NFC interactions are assessed. The study comprises
a structural assessment, including laser profilometry, scanning electron microscopy (SEM) and field-emission (FE)-SEM analyses.
In addition, optical and strength properties are assessed. It is demonstrated that a potential reduction of strength properties
caused by filler addition may be counteracted by appropriate NFC addition to specific layers in the z-direction. Based on an estimation of an overall quality index considering five variables, it is concluded that the best sheet
construction is obtained when placing the fillers in surface layers with the TMP accept fraction and the NFC in the centre
of the sheets together with the refined TMP reject fraction. 相似文献
4.
Karoliina Junka Ilari Filpponen Tom Lindström Janne Laine 《Cellulose (London, England)》2013,20(6):2887-2895
Total and surface charge of three different carboxymethylated nanofibrillated/microfibrillated cellulose (NFC/MFC) samples were investigated by using titrimetric methods (conductometric and polyelectrolyte (PE) titrations). Conductometric titration was found to be suitable method for the NFC total charge measurements when the back titration with HCl was applied. Surface charge measurements of NFC/MFC were conducted by using both indirect and direct PE titrations. The direct PE titration was found to be a more suitable method for the surface charge determination of NFC/MFC whereas the indirect PE titration produced too high surface charge values. This is presumably due to kinetically locked polyelectrolyte conformations on the NFC/MFC surfaces or entrapment of residual polymer after adsorption onto the NFC/MFC gel network. Finally, NFC was propargyl-functionalized and the changes in surface and total charge were successfully monitored and compared to those of propargyl-functionalized pulp. A good correlation between the titrimetric methods and elemental analysis was observed. 相似文献
5.
Nikolaos Pahimanolis Ulla Hippi Leena-Sisko Johansson Tapio Saarinen Nikolay Houbenov Janne Ruokolainen Jukka Seppälä 《Cellulose (London, England)》2011,18(5):1201-1212
In the present work, amino functionalized nanofibrillated cellulose (NFC) was prepared using click-chemistry in aqueous reaction
conditions. First, reactive azide groups were introduced on the surface of NFC by the etherification of 1-azido-2,3-epoxypropane
in alkaline water/isopropanol-mixture at ambient temperature. Then the azide groups were reacted with propargyl amine utilizing
copper catalyzed azide-alkyne cycloaddition (CuAAC), leading to pH-responsive 1,2,3-triazole-4-methanamine decorated NFC.
The reaction products were characterized using Fourier transform infrared spectroscopy, elemental analysis and X-ray photoelectron
spectroscopy. The presence of the attached azide groups was also confirmed by reacting them with 5-(dimethylamino)-N-(2-propyl)-1-naphthalenesulfonamide
by CuAAC, yielding highly fluorescent NFC. In addition, atom force microscopy and rheology studies confirmed that the original
NFC nanostructure was maintained during the synthesis. 相似文献
6.
Ch. Eyholzer F. Lopez-Suevos P. Tingaut T. Zimmermann K. Oksman 《Cellulose (London, England)》2010,17(4):793-802
Bionanocomposites of hydroxypropyl cellulose (HPC) and nanofibrillated cellulose (NFC) were prepared by solution casting. The various NFC were in form of powders and were prepared from refined, bleached beech pulp (RBP) by mechanical disintegration, optionally combined with a pre- or post mechanical carboxymethylation. Dynamic mechanical analysis (DMA) and tensile tests were performed to compare the reinforcing effects of the NFC powders to those of their never-dried analogues. For unmodified NFC powders an inferior reinforcing potential in HPC was observed that was ascribed to severe hornification and reagglomeration of NFC. In contrast, the composites with carboxymethylated NFC showed similar behaviors, regardless of the NFC suspensions being dried or not prior to composite preparation. SEM characterization confirmed a homogeneous dispersion of dried, carboxymethylated NFC within the HPC matrix. These results clearly demonstrate that drying of carboxymethylated NFC to a powder does not decrease its reinforcing potential in (bio)nanocomposites. 相似文献
7.
Cellulose carbamate, an environmentally friendly material presents an interesting alternative to petroleum-based polymers because of its renewable, biodegradable, biocompatible nature and its solubility in conventional solvents. In synthesis process of cellulose carbamate, urea was firstly impregnated into the cellulose pulp by supercritical CO2(scCO2), followed by the esterification of cellulose. The structure of cellulose carbamate was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The rheological properties of these cellulose carbamates in 9% sodium hydroxide solution were investigated, using a range of the nitrogen content, concentrations and shear rates. 相似文献
8.
N. Neibolts O. Platnieks S. Gaidukovs A. Barkane V.K. Thakur I. Filipova G. Mihai Z. Zelca K. Yamaguchi M. Enachescu 《Materials Today Chemistry》2020
Sustainable materials have slowly overtaken the nanofiber research field while the tailoring of their properties and the upscaling for industrial production are some of the major challenges. We report preparation of nanofibers that are bio-based and biodegradable prepared from poly (butylene succinate) (PBS) with the incorporation of nanofibrillated cellulose (NFC) and graphene nanoplatelets (GN). NFC and GN were combined as hybrid filler, which led to the improved morphological structure for electrospun nanofibers. A needleless approach was used for solution electrospinning fabrication of nanofiber mesh structures to promote application scalability. The polymer crystallization process was examined by differential scanning calorimetry (DSC), the thermal stability was evaluated by thermal gravimetric analysis (TGA), while the extensive investigation of the nanofibers structure was carried out with scanning electron microscopy (SEM) and atomic force microscopy (AFM). NFC and GN loadings were 0.5 and 1.0 wt %; while poly (ethylene glycol) (PEG) was employed as a compatibilizer to enhance fillers’ interaction within the polymer matrix. The interactions in the interface of the fillers and matrix components were studied by FTIR and Raman spectroscopies. The hybrid filler approach proved to be most suitable for consistent and high-quality nanofiber production. The obtained dense mesh-based structures could have foreseeable potential application in biomedical field like scaffolds for the tissue and bone recovery, while other applications could focus on filtration technologies and smart sensors. 相似文献
9.
磁性碳基磺酸化固体酸催化剂的制备及其催化水解纤维素 总被引:6,自引:0,他引:6
以纤维素和硝酸铁为原料,发烟硫酸为磺酸化试剂,采用热解法合成了磁性碳基磺酸化固体酸催化剂(Fe/C-SO3H).利用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、傅里叶变换红外(FT-IR)光谱仪和振动样品磁强计(VSM)等手段对催化剂进行了表征,评价了催化剂在纤维素水解反应中的催化活性.结果表明,Fe是以γ-Fe2O3的形式存在于碳本体中,催化剂呈现超顺磁性.对于纤维素的水解反应,在优化条件下,纤维素的转化率可达40.6%.此外,催化剂可稳定分散于反应体系中,并在外加磁场作用下可快速与反应体系分离.但催化剂重复使用时催化活性有所下降,其失活原因经初步认定是由于表面部分磺酸基团在反应过程中脱落. 相似文献
10.
Alina I. Chiriac Francisco I. Javier Pastor Valentin I. Popa Magdalena Aflori Diana Ciolacu 《Cellulose (London, England)》2014,21(1):203-219
A newly identified cellulase with a high polysaccharide degrading potential and a processive mode of action, has been evaluated on cellulose fibers. Cellulase Cel9B from Paenibacillus barcinonensis is a modular endoglucanase with the domain structure GH9-CBM3c-Fn3-CBM3b, consisting of a family nine catalytic module GH9, an auxiliary module CBM3c, a fibronectin-like module Fn3, and a functional cellulose binding module CBM3b. The whole cellulase Cel9B (E1) and two truncated forms of the enzyme that consist of the catalytic module linked to the auxiliary module, GH9-CBM3c (E2), and of the cellulose binding module of the enzyme, CBM3b (CBD), were applied to softwood dissolving pulp. The changes in the supramolecular structure and morphology of the fibres after the enzymatic treatment were evaluated by viscosimetry, X-ray diffraction (XRD), thermogravimetric analysis, differential scanning calorimetry and scanning electron microscopy (SEM). XRD studies provided the crystallite size, interplanar distances and crystallinity index of the samples before and after the enzymatic treatment. The treatment with cellulases E1 and E2 decreased the degree of polymerization and increased the crystallinity index of the pulp. Both E1 and E2 had a pronounced capacity for removing fuzz and improved the smoothness and surface appearance of the fibers, as shown by SEM. On the other hand, CBD proved to be less effective under the tested conditions. Moreover, the solubility of dissolving pulp in alkaline solutions has been evaluated as an indirect measure of cellulose accessibility. A notable enhancement in alkaline solubility of the samples treated with the cellulases was observed. 相似文献
11.
K.K. Kesari M. Leppänen S. Ceccherini J. Seitsonen S. Väisänen M. Altgen L.-S. Johansson T. Maloney J. Ruokolainen T. Vuorinen 《Materials Today Chemistry》2020
Understanding the ultrastructure and chemical characterization of pulp fibers is highly important in utilizing wood as a raw material in a wide scope of applications, such as forest biomass-based biorefineries and low-cost renewable materials. The observation of the ultrastructure is not possible without advanced microscopy and spectroscopy techniques. Therefore, this study focuses on exploring the ultrastructure of pulp fibers with helium ion microscopy (HIM) and scanning electron microscopy (SEM). For the analysis of chemical characterization in the pulp fibers, Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) were performed. For these studies, the pulp fiber samples were obtained mainly from three different wood species, i.e. spruce, birch and eucalyptus. They were received in the never dried state and dried with a critical point drier (CPD) to minimize pore collapse. The spectroscopy results showed a strong signal from crystalline cellulose and confirmed the absence of lignin after Kraft pulping and bleaching. However, with XPS about 2% of lignin was detected in eucalyptus pulp. The results obtained with the microscopy techniques are compared and indicating the nanofibril size, shape, surface roughness as well as their orientation in pulp fibers. To our knowledge, this is the first time that HIM is applied to study the ultrastructure of pulp fibers and compared against more conventional microscopy and spectroscopy techniques. The main differences between HIM and SEM were found to be related to the focusing and magnification. The individual nano- and microfibrils as well as their bundles were more easily visible with HIM than with SEM. Also, with HIM it was possible to get the total area in focus at once which was not the case with SEM. The increased understanding of the ultrastructure and chemical composition of wood pulp enhance the development of novel wood-based products and processes for their manufacture. 相似文献
12.
Timo Pääkkönen Katarina Dimic-Misic Hannes Orelma Raili Pönni Tapani Vuorinen Thad Maloney 《Cellulose (London, England)》2016,23(1):277-293
alkali-washed nanofibrillated cellulose (NFC) samples, obtained from hardwood kraft pulp, with different amounts of retained xylan were prepared to study the influence of xylan on the water-retention properties of NFC suspensions. In this study, NFC was produced using an oxoammonium-catalyzed oxidation reaction that converts the cellulosic substrate to a more highly oxidized material via the action of the nitroxide radical species 2,2,6,6-tetramethylpiperidine-1-oxyl. Reduction of the xylan content in NFC was achieved by cold alkali extraction of kraft pulp. The pulps were then oxidized to a set charge under constant chemical conditions, and the reaction time was determined. The xylan content of the feed pulp was found to have a large negative influence on the oxidation rate of the pulp, as the oxidation time shortened when xylan was removed, from 220 min (for 25.2 % xylan content) to 28 min (for 7.3 % xylan content). Following fibrillation by homogenization, the swelling of the NFC was determined by a two-point solute exclusion method. The distribution of hemicellulose over the fibril surface was observed by atomic force microscopy. Xylan was found to be distributed unevenly over the surface, and its presence increased the water immobilized within flocs of NFC, i.e., so-called network swelling. The swelling of the NFC had a large impact on its rheology and dewatering. Comparison of the morphological and swelling properties of the suspensions with their rheological and dynamic dewatering behavior showed that reducing the xylan content in NFC results in a weaker gel structure of the nanocellulose suspension. The results indicate that most of the water is held by the swollen structure by means of xylan particles trapped within the hemicellulose layer covering the fibril surface. Samples with high xylan content had high shear modulus and viscosity and were difficult to dewater. 相似文献
13.
采用硫酸水解法制备纳米纤维素晶须, 再以冰醋酸为分散介质, 浓硫酸为催化剂, 醋酸酐为酯化剂对纳米纤维素晶须进行不同程度醋酸酯化改性, 得到醋酸酯化的纳米纤维素. 采用红外光谱(FTIR)、 X射线光衍射(XRD)、 透射电子显微镜(TEM)和X射线光电子能谱(XPS)等手段对改性产物进行分析和表征. 结果表明, 改性纳米纤维素晶须中醋酸酯基的平均取代度过小或过大时均不适宜用作复合材料的增强相. 当改性纳米纤维素晶须中醋酸酯基的平均取代度为0.05时, 醋酸酯化反应只发生在纳米纤维素晶须的表面. 此时, 晶须能在丙酮中稳定悬浮, 表现出流动双折射现象, 并保持了改性前纳米纤维素晶须的棒状形态和高结晶度. 将这种改性后的纳米纤维素晶须作为增强相与醋酸纤维素通过溶液浇铸法制成纳米复合膜, 结果显示, 与空白醋酸纤维素膜相比, 添加改性纳米纤维素晶须后, 纳米复合膜的拉伸强度、 杨氏模量和断裂伸长率都得到了提高. 在玻璃化转变区间纳米复合膜储能模量的降低幅度小于空白膜. 相似文献
14.
Ch. Eyholzer N. Bordeanu F. Lopez-Suevos D. Rentsch T. Zimmermann K. Oksman 《Cellulose (London, England)》2010,17(1):19-30
Water-redispersible, nanofibrillated cellulose (NFC) in powder form was prepared from refined, bleached beech pulp (RBP) by
carboxymethylation (c) and mechanical disintegration (m). Two routes were examined by altering the sequence of the chemical
and mechanical treatment, leading to four different products: RBP-m and RBP-mc (route 1), and RBP-c and RBP-cm (route 2).
The occurrence of the carboxymethylation reaction was confirmed by FT-IR spectrometry and 13C solid state NMR (13C CP-MAS) spectroscopy with the appearance of characteristic signals for the carboxylate group at 1,595 cm−1 and 180 ppm, respectively. The chemical modification reduced the crystallinity of the products, especially for those of route
2, as shown by XRD experiments. Also, TGA showed a decrease in the thermal stability of the carboxymethylated products. However,
sedimentation tests revealed that carboxymethylation was critical to obtain water-redispersible powders: the products of route
2 were easier to redisperse in water and their aqueous suspensions were more stable and transparent than those from route
1. SEM images of freeze-dried suspensions from redispersed RBP powders confirmed that carboxymethylation prevented irreversible
agglomeration of cellulose fibrils during drying. These results suggest that carboxymethylated and mechanically disintegrated
RBP in dry form is a very attractive alternative to conventional NFC aqueous suspensions as starting material for derivatization
and compounding with (bio)polymers. 相似文献
15.
Han-Seung Yang Douglas J. Gardner Jacques W. Nader 《Journal of Thermal Analysis and Calorimetry》2011,103(3):1007-1015
Microcrystalline cellulose-filled polypropylene (PP) composites and cellulose nanofiber-filled composites were prepared by
melt blending. The compounded material was used to evaluate dispersion of cellulose fillers in the polypropylene matrix. Thermogravimetric
analysis (TG) and mechanical testing were conducted on composites blended multiple times and the results were compared with
single batch melt blended composites. The residual mass, tensile strength, and coefficient of variance values were used to
evaluate dispersion of the microcrystalline cellulose fillers in the PP matrix. The potential of using TG to evaluate cellulose
nanofiber-filled thermoplastic polymers was also investigated and it was found that the value and variability of residual
mass after TG measurements can be a criterion for describing filler dispersion. A probabilistic approach is presented to evaluate
the residual mass and tensile strength distribution, and the correlation between those two properties. Both the multiple melt
blending and single batch composites manufactured with increased blending times showed improved filler dispersion in terms
of variation and reliability of mechanical properties. The relationship between cellulose nanofiber loading and residual mass
was in good agreement with the rule of mixtures. In this article, the authors propose to use a novel method for dispersion
evaluation of natural fillers in a polymer matrix using TG residual mass analysis. This method can be used along with other
techniques such as scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD)
for filler dispersion evaluation in thermoplastic composites. 相似文献
16.
高碘酸钠催化微晶纤维素的氧化 总被引:1,自引:0,他引:1
主要讨论了使用高碘酸钠(NaIO4)溶液氧化微晶纤维素的过程及性能,用红外光谱(IR)验证了氧化纤维素的生成;通过扫描电镜(SEM)、热重分析(TG-DSC)以及X射线衍射(XRD)对比了反应前后纤维素的变化;考察了氧化时间、氧化温度、氧化剂的浓度以及溶液的pH值对氧化纤维素的产率及醛基含量的影响;结果表明,反应前后纤维素的晶型和形貌基本没有变化,随着氧化程度的加深,氧化纤维素的热稳定性越来越差;并且随着氧化温度的提高和氧化剂浓度的增大,醛基含量相应提高,而氧化时间和pH值对醛基含量存在相对最高值。 相似文献
17.
以石墨、沥青和纳米硅粉为原料制备了锂离子电池Si/C负极材料,使用SEM/ BSE 、Raman、XRD、XPS及XPS氩离子刻蚀等方法对其硅活性物质进行了具体分析。结果表明,XRD和Raman仅判断出负极材料中含有活性物质单质Si;常规XPS结果发现近一半的Si已被氧化为惰性物质SiO2;而使用XPS氩离子刻蚀方法发现负极材料中Si存在5种化学态,包括活性物质单质Si、Si2O、SiO、Si2O3,及惰性物质SiO2;定量结果表明,复合材料的硅活性物质高于96.56%,且主要结构是低价态硅氧化物,而非单质Si。XPS氩离子刻蚀的分析方法为锂离子电池负极材料中硅活性物质的研究提供了新思路。 相似文献
18.
Preparation and characterization of cellulose nanocrystals via ultrasonication-assisted FeCl3-catalyzed hydrolysis 总被引:2,自引:0,他引:2
Qilin Lu Lirong Tang Fengcai Lin Siqun Wang Yandan Chen Xuerong Chen Biao Huang 《Cellulose (London, England)》2014,21(5):3497-3506
Cellulose nanocrystals (CNC) was obtained from bamboo pulp via ultrasonication-assisted FeCl3-catalyzed hydrolysis process, with parameters optimized by response surface methodology. The optimal parameters were reaction temperature: 107 °C, reaction time: 58 min, ultrasonication time: 186 min. The morphological, crystal structural, chemical structural and thermal features of the prepared cellulose nanocrystals were analyzed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), Fourier transfer infrared (FTIR) and thermogravimetric analysis. The results showed that the cellulose nanocrystals formed an interconnected network structure and CNC was rod-like with the length of 100–200 nm and the width of 10–20 nm. XRD result revealed that, compared with cellulose pulp, the crystallinity index of CNC increased from 69.5 to 79.4 %, while the cellulose I crystal structure remained. FTIR analysis demonstrated that CNC had the similar chemical structures to that of cellulose pulp, which indicated that the chemical structures of CNC remained unchanged in the presence of FeCl3-catalyzed hydrolysis process and ultrasonication treatment. Thermogravimetric analysis revealed that the resulting CNC exhibited relatively high thermal stability. The research shows that ultrasonication-assisted FeCl3-catalyzed hydrolysis could be a highly efficient method for preparing CNC. 相似文献
19.
Yangbing Wen Bing Wei Dong Cheng Xinye An Yonghao Ni 《Cellulose (London, England)》2017,24(2):731-738
This study aimed to improve the stability of nanofibrillated cellulose (NFC) in an electrolyte containing system, which was achieved by the grafting of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) via the ceric ammonium nitrate-induced polymerization process. The results indicated that upon grafting the salt resistance and thermal stability of NFC were significantly improved. Moreover, the stability of the modified NFC increased with the AMPS loading. Compared to the control (the original NFC), the poly-AMPS/NFC (357.5 mg/g AMPS) exhibited much improved stability in a 400 mmol/L NaCl solution, and its viscosity was 350 mPa s. The thermogravimetric analysis results showed that the initial decomposition temperature of the modified NFC increased from 265 to 330 °C. Transmission electron microscopy (TEM) observations showed that the main morphologic features of NFC were not altered, suggesting that the grafting reaction occurred on the fiber surface. The modified NFC can have promising industrial applications, such as oil recovery. 相似文献
20.
Composite microtubes of Mo(2)C/MoCO have been synthesized for the first time under well-controlled conditions by thermal decomposition of Mo(CO)(6) at about 600 degrees C. Here, thermal stability and phase transition of the products, as well as the influence of reaction temperature and argon flow rate, have been carefully investigated. All samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The reaction model and rolling mechanism were proposed on the basis of the experimental facts. 相似文献