Surface modification of lignocellulosic fibers using high-frequency ultrasound

Enzymatic and chemical oxidation of fiber surfaces has been reported in the literature as a method for producing medium density fiberboards without using synthetic adhesives. This work focuses on modifying the surface properties of wood fibers by the generation of free radicals using high-frequency ultrasound. A sonochemical reactor operating at 610 kHz is used to sonicate the aqueous suspensions of thermomechanical pulp fibers (TMP). TMP is analyzed using FTIR-transmission, FTIR-ATR spectroscopy and inverse gas chromatography (IGC). The non-conjugated carbonyl groups in TMP are represented by the peak area ratio A₁₇₃₆/A₁₅₁₁ in the FTIR-transmission spectra and by A₁₇₂₈/A₁₅₀₉ in the FTIR-ATR spectra. The increase in these ratios suggests that there is an increase in the number of non-conjugated carbonyl groups in TMP after sonication. To further investigate, sonication of the hydrolytic lignin was also carried out and analyzed using UV, UV-ionization and FTIR-transmission spectroscopy. The changes in the surface properties of the fibers are analyzed using IGC which showed an increase in the surface free energy of fibers. The effect of operating parameters such as power of ultrasound and sonication time is also studied.     

Surface properties of lignocellulosic fibers bearing carboxylic groups

Fibers with various amounts of carboxylic acid functionalities as determined with FTIR and conductometric titration were prepared by chemical modification of high bleached kraft pulp (CP) and chemical thermomechanical pulp (CTMP) with succinic anhydride. The degree of the modification was dependent on reaction time and the type of fiber used. The modification levelled off after 15h of reaction, and this effect was similar for both fiber substrates. The amount of carboxylic acid attached to CTMP, determined by weight gain, was however less than half of the amount of carboxylic moieties introduced to CP fibers at any reaction time. ESCA characterization of the succinylated fibers indicates that the carboxylic acid functionalities are predominantly introduced at the fiber surface. The wettability in water, measured as contact angle, of the succinylated CTMP fibers was significantly improved by the modification, whereas the wettability of CP fibers was slightly decreased. The differences in wettability are caused by the dispersive and polar characteristics of succinic acid attached to the fiber surface and its interaction with the fiber surface. The character of the linkage group in the anhydride used for modification as well as the composition of the cellulose fiber surface are suggested to play a crucial role in the surface energy of the modified fibers and hence their wetting properties.     

Characterization of several modified jute fibers using zeta-potential measurements

 ζ-potential measurements using the streaming potential method were performed on several differently modified jute fibers. The time dependence of the ζ-potential measured in 1 × 10⁻³ M KCl solution offers the possibility to characterize the water-uptake behavior and the velocity constant of this process for almost all the jute fibers investigated. All the jute fibers contain, as expected, dissociable acidic surface functional groups as could be verified by measuring the pH dependence of the ζ-potential. Remarkably a peak (increase in the negative ζ-potential values) was detected while measuring the ζ–pH dependency. The origin of this peak is still questionable; however, it could be observed that this peak is a function of the degree of surface coverage of additional components, such as fats, waxes or grafted polymers, i.e. the accessibility of ether functions in the jute fiber surface. Received: 26 May 1999/Accepted in revised form: 28 September 1999     

Surface properties of bamboo fiber and a comparison with cotton linter fibers

In order to understand the different touch senses from bamboo and cotton fibers, the surface properties of bamboo fiber, e.g., the surface free energy, the Lifshitz–van der Waals force, and Lewis acid and base components have been determined using the column wicking technique. Taking the traditional cotton linter fiber as a reference, this paper shows that both these fibers have the similar surface free energies. However, a big difference between these two fibers which has been importantly observed is that the bamboo fiber having greater Lewis acid component seems to be double than the cotton linter fiber. Since water has been found to have such surface property, it is suggested that the bamboo fiber touch in the skin of people may like the touch between water and skin of people. Meanwhile, other surface properties of these two fibers are compared.     

Surface structural analysis of fine silica powder modified with butyl alcohol

The surface structure of modified silica powder has been studied by various experiments and simulations. In addition, the effect of surface structure on wettability has also been investigated. Nonporous silica powder was modified with n-and t-butyl alcohol. Two series of the modified silica surfaces were characterized by fractal dimension analysis from isotherms with some kinds of adsorptives. The fractal dimensions of the two series of modified surfaces were different from each other with an increase in modified ratio. The fractal dimension of the surface modified with t-butyl alcohol (t-modified surface) increased monotonously with butoxy group density. It is thought that the structure of the t-butoxy group is rigid and that the t-butoxy group cannot change its conformation. On the other hand, the variation of the surface fractal dimension value for the surface modified with n-butyl alcohol (n-modified surface), whose structure is flexible, was unique compared with the t-modified surface. Such discrepancy was assumed to be caused by the difference in the structure of the modifier and the assembled state of modifiers between the t- and n-modified surfaces. In order to investigate the variation of surface structure of the surface modified by the butoxy group with an increase in modified ratio, molecular dynamics simulations were performed. By comparing the results of these simulations with experimental results, it has been clarified that the variation in the mobility of the methyl group in the n-butoxy groups was closely related to the change in the surface fractal dimension value for the n-modified surface. It was then elucidated that this mobility change was caused by steric hindrance among the groups. Furthermore, the variation of conformation in the n-butoxy groups, which was obtained from molecular dynamics simulations, was in good agreement with the change in the wettability of the n-modified surface. It is suggested that the surface density of the modifier, the covering structure and the bulkiness significantly influence the wettability of the modified surface. Received: 6 April 1999 /Accepted in revised form: 24 August 1999     

Wettability of carbon fibers modified by acrylic acid and interface properties of carbon fiber/epoxy

The oxidation-reduction and pre-irradiation induced methods were employed to study the effect of acrylic acid modification on the wetting and adsorption ability of carbon fiber (CF) in epoxy solution and the interfacial properties of CF/epoxy. Systematic experimental work was conducted to determine the surface topography, surface energy, surface chemical composition, absorbability and tensile strength of carbon fibers and interfacial adhesion of CF/epoxy before and after modification. The roughness, surface energy, amount of containing-oxygen functional groups and wetting ability were all found to increase significantly after modifications. The tensile strength of carbon fibers was improved marginally by γ-ray pre-irradiation while was decreased little by oxidation-reduction modification. Consequently, the surface modifications of carbon fibers via both oxidation-reduction and pre-irradiation led to an improvement (more than 15%) of the interlaminar shear strength of CF/epoxy composites. The mechanisms of interfacial improvement of modified CF/epoxy composites are proposed.     

Upgrading of paper-grade pulps to dissolving pulps by nitren extraction: properties of nitren extracted xylans in comparison to NaOH and KOH extracted xylans

Different paper-grade pulps were extracted with nitren, NaOH and KOH in order to produce dissolving pulps and polymeric xylan. The yield and structure of the isolated nitren and alkali xylans were investigated by carbohydrate analysis, HPSEC and ¹H-NMR spectroscopy. In addition the effect of washing stages on the residual nickel content of the nitren xylans was investigated. By nitren extraction up to 98% of the xylan could be extracted out of the fully bleached eucalyptus and birch kraft pulps. The nitren extracted kraft xylans had DP values between 95 (birch) and 111 (eucalyptus). At most 5 mol% of the xylose units were substituted. In the case of pulps with low mannan content only marginally differences between the nitren and alkaline (KOH, NaOH) extractions occurred. The extraction of the relatively “mannnan rich” pulps of this study like softwood kraft and beech sulfite pulps revealed that the dissolution effect regarding mannans increased in the following order: nitren < KOH < NaOH. In general the nitren extractions required a lower chemical charge compared to the alkaline extractions, in order to yield similar amounts of xylans. On the other side the necessity of an effective nickel removal is a disadvantage of the nitren extractions.     

Surface characterization and electrical property of carbon fibers modified by air oxidation

Polyacrylonitrile‐based carbon fibers were modified by oxidation in air, and a systematic study of surface groups and surface resistance at different treated temperatures was made. Progressive fiber weight loss occurred with increasing extents of air oxidation, and it was approximately proportional to the extent of air oxidation from the onset of oxidation up to 400 °C. At this point 4.4% of the initial fiber weight had been lost. A faster loss of weight occurred as the extent of air oxidation increased from 400 °C to 700 °C. X‐ray photoelectron spectroscopy studies (C 1s and O 1s) indicated that the oxygen/carbon atomic ratio rose rapidly from 2.64% (as‐received carbon fiber) to 42.83% as the oxidation temperature was increased to 400 °C. Fourier transform infrared spectra showed the relative intensity of the peaks at about 3440 cm^?1 from ―OH stretching vibrations and at 1634 cm^?1 from ―C?O stretching vibrations increased significantly at 400 °C. FESEM micrographs showed that as‐received fibers show relatively smooth surface. With oxidation temperature increasing, the fiber surface was rougher. The surface resistance of treated carbon fibers decreased obviously with increasing oxidation temperatures. The most decrease was about 100% at 400 °C. Copyright © 2014 John Wiley & Sons, Ltd.     

形状记忆聚合物表面微结构及黏附性能的可逆调控

采用模板法在形状记忆聚合物表面构筑了微纳米等级结构,获得了一种具有低黏附性的超疏水表面.在外压作用下,表面微结构发生坍塌,失去超疏水性,同时呈高黏附性.在120℃热处理后,表面微结构恢复到原始状态,同时表面恢复到低黏附状态.通过外压及热处理过程可实现对表面微结构及其黏附性能的可逆调控.研究结果表明,表面不同的微结构状态赋予了表面不同的黏附性能,即在原始表面上,液滴处于低黏附的Cassie态,而在坍塌结构表面上水滴处于高黏附的Wenzel态.     

Highly hydrophobic sisal chemithermomechanical pulp (CTMP) paper by fluorotrimethylsilane plasma treatment

Fluorinated thin layers were created on chemithermomechanical pulp (CTMP) sisal paper surfaces with fluorotrimethylsilane (FTMS) radio frequency-plasma conditions. It was found that the FTMS-discharge environments caused implantation of fluorine and –Si(CH₃) _x groups into the surface layers of the paper substrates. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy and Electron Spectroscopy for Chemical Analysis, as well as Atomic Force Microscopy and Scanning Electron Microscopy analyses revealed a smooth surface for the FTMS plasma-treated paper, apparently covered completely with a cross-linked polymerized network. Although the plasma reaction takes place with the cellulose, hemicelluloses and lignin, it appears that the chemical linkage is mainly to the lignin component on the CTMP paper surface by means of mainly C–O–Si–F, with some C–Si–F structures. The CTMP fibers apparently have a high lignin surface concentration. The water absorption for the plasma-treated CTMP paper was reduced from greater than 300 to 17 g of water/m² and the contact angle increased from less than 15° to greater than 120° the strength properties were only slightly reduced and the brightness was essentially unaffected with the FTMS plasma treatment.     

纳米结构表面浸润性质的分子动力学研究

采用分子动力学方法研究了氩纳米液滴在铂金属及其模型固体表面的浸润现象,获得了液滴在平滑表面和三角纳米结构阵列表面的接触角和展布特性.研究表明,液滴与壁面的势能作用较强时,液滴与纳米结构表面为均匀浸润,但是由于迟滞效应,接触角受表面纳米结构的影响不明显;势能作用较弱时,纳米结构间隙中存在类似蒸汽的低密度相,液滴与纳米结构表面为非均匀浸润,接触角受纳米结构的影响而增大;表面纳米结构可以使表面具有超疏水性.     

Surface properties of cellulose modified by imidazolidinone

The influence of the modification of cellulose fibres by the imidazolidinone derivative 1,3-dimethyl-4,5-dihydroxyethylene urea (DMeDHEU) on fibre surface free energy and electrochemical potential was studied. The presence of DMeDHEU in the cellulose structure was confirmed by infrared spectral analysis. The surface free energy of untreated and treated cellulose fibres was determined from the results of thin-layer wicking, where the rate of liquid penetration into the cellulose fabric was measured. Using the van Oss-Chaudhury-Good theoretical approach, apolar, γ _S ^LW , polar electron-acceptor, γ _S ⁺, and electron-donor, γ _S ⁻, components of the surface free energy were calculated. The electrokinetic potential was determined from the results of steaming potential measurements. The results revealed that the incorporation of DMeDHEU into the cellulose structure lead to a decrease in the value of γ _S ⁻, whereas the values of γ _S ^LW and γ _S ⁺ remained almost unchanged. Despite their decreased γ _S ⁻ value, the treated cellulose fibres still represent a monopolar solid with a strongly expressed electron-donor component. The values of ΔG _iw and ΔG _iwi suggested that both untreated and treated cellulose samples could be considered hydrophilic substrates. The results of the electrokinetic potential measurements showed that the consumption of cellulose hydroxyl groups in the crosslinking reaction with DMeDHEU did not decrease the electrokinetic properties of the cellulose surface.     

A comparative study on properties of multi-walled carbon nanotubes (MWCNTs) modified with acids and oxyfluorination

In this study, the surface modification of multi-walled carbon nanotubes (MWCNTs) with acid and oxyfluorination has been examined. Acid treatment of multi-walled CNTs produces many functionalized groups on the surface of MWCNTs, such as C-N stretching and the asymmetric carboxylate group (-COO-). It can be concluded that nitrogen doping of the graphite sheets may take place and a C-N bond identical to the sp³-bonded carbon nitride may form during the acid treatment process. In addition, oxyfluorinated MWCNTs exhibit higher BET specific surface area and mesopore volume than those of the as-received and acid treated MWCNTs. Therefore, acid and oxyfluorination treatments are more effective methods for enhancing the chemical and textural properties of MWCNTs.     

Improved surface properties of CTMP fibers with enzymatic pretreatment of wood chips prior to refining

Surface properties of chemithermomechanical pulp (CTMP) fibers produced from enzymatically pretreated eucalyptus wood chips prior to refining were investigated by Field Emission Scanning Electron Microscope (FE-SEM), Transmission Electron Microscope (TEM) and X-ray Photoelectron Spectroscopy (XPS). The results showed that in a traditional CTMP refining process most fiber disruptions occur in the middle lamella (ML) leaving behind a significant amount of hydrophobic materials on the resulting fiber surface. However, in a Bio-CTMP refining process, fiber fractures preferentially take place in the primary (P) and secondary 1 (S1) layers or the S1 and secondary 2 (S2) layers, which results in more fibrillation being generated in the subsequent refining thus improving inter-fiber bonding strength and paper strength. XPS chemical composition analysis together with pulp physical strength property showed that the surfaces of Bio-CTMP fibers become enriched with a greater proportion of carbohydrates in comparison with CTMP fiber surface, which supports FE-SEM and TEM observations.     

Properties and treatments of pulps from recycled paper. Part II. Surface properties and crystallinity of fibers and fines

Surface properties of bleached kraft pulps were evaluated before and after recycling, and after a series of chemical treatments designed to improve and/or modify the pulp characteristics. The surface free energy characteristics of the pulps were determined using the Wilhelmy technique, and ESCA and ATR-FTIR methods were used to evaluate the chemical composition of the surfaces of the pulp fibers. In general rather small changes were noted at the fiber surfaces with recycling and chemical treatment. Recycling tended to increase the acid component and decrease the base component of the surface free energy of the pulps. This could result from exposure of carboxyl groups from hemicelluloses and/or from oxidized layers from the bleaching process. ESCA analyses also indicated increased carboxyl concentration at the surfaces of the recycled fibers. Although treatment with aqueous bases and organic solvents tended to increase the hydroxyl content on the surface of recycled pulps, the chemical treatments were not beneficial to pulp quality. AFM and SEM of fiber and fine surfaces of kraft pulps revealed that the fines fraction was altered to a much greater extent with recycling. Although recycled fibers appeared to have improved wettability, these small changes in the surface characteristics do not appear to play the dominant role in the characteristics of recycled pulps. Recycling did not change the crystallinity of whole pulps, but it increased the crystallinity of the fines fraction. The increase in the crystallinity of the fines fraction and the reduction in the water retention value (WRV) and the bulk carboxyl content (xylan) of the recycled pulps, as noted in Part I of this paper, appear to play the predominant role in determining the characteristics of recycled pulps. It appears that the loss of the hemicelluloses in the bulk of the fiber with recycling is much more important for internal fibrillation than the apparent small increase of hemicelluloses at the surface of recycled fibers.     

十八烷基三氯硅烷表面改性钛酸钾晶须

利用十八烷基三氯硅烷(OTS)的自组装对钛酸钾晶须(PTW)进行表面改性. 通过测定苯、乙二醇、水在OTS改性的PTW压片上的接触角, 计算了OTS改性PTW后的表面能和极性分量, 并与传统方法(PMMA包裹和KH560表面改性)改性的PTW进行比较, 结果表明, OTS改性的PTW具有更低的表面能和极性分量, 以及更好的亲油疏水性能. IR分析和色散分量测定表明, 改性后OTS的烷基链倾斜在PTW表面.     

Modification of one side of mulberry silk fabric by monochromatic VUV excimer lamp

One side of mulberry silk fabric surface was irradiated with monochromatic VUV excimer lamp (172 nm). Change in surface morphology due to one side (I) and two side (II) irradiation was analyzed using high resolution scanning electron microscope (SEM) and atomic force microscope (AFM). The irradiated samples were further characterized through measurement of wetting time, vertical and horizontal wicking. Surface nanopores of 100 nm × 10 nm were formed on the irradiated side, however, on back side change in morphology was not observed. Upon one side irradiation the wettability and wickability improved significantly. One side irradiated silk surface (I) showed average wetting time of 14.7 s and 7.2 s while the two side irradiated silk surface (II) showed a wetting time of 9.3 s and 3.1 s for irradiation period of 1 min and 5 min, respectively. Beyond 5 min of irradiation the wettability of both the surfaces stabilized. Mechanism responsible for wetting behaviour of one side irradiated sample has been proposed. The influence of lamp geometry on irradiation effect was found to be noticeable for irradiation timings <5 min.     

Nanocomposite-based lignocellulosic fibers 1. Thermal stability of modified fibers with clay-polyelectrolyte multilayers

The layer-by-layer (LbL) assembly process of creating highly structured thin films derived from layers of polyelectrolytes and nanoparticles was adopted in this study to modify the surface of lignocellulosic fibers. Aqueous dispersions of clay nanoplatelets were created with ultrasonication and characterized with dynamic light scattering and atomic force microscopy in which confirmed the presence of individual clay nanoplatelets. Film thickness of never-dried clay and poly(diallyldimethylammonium chloride) (PDDA) multilayers was studied with a quartz crystal microbalance with dissipation monitoring (QCM-D). Using identical LbL deposition parameters, a slurry of steam-exploded wood fibers was modified by alternate adsorption of PDDA and clay with multiple rinsing steps after each adsorption cycle. Zeta potential measurements were used to characterize the fiber surface charges after each adsorption step while SEM images revealed that the LbL film masked the cellulose microfibril structure. Using a thermogravimetric analyzer, LbL modified steam-exploded wood fibers were observed to attain increased thermal stability relative to the unmodified material tested in both air and nitrogen atmospheres. Significant char for the LbL clay coated steam-exploded wood suggests the multilayer film serves as a barrier creating an insulating layer to prevent further decomposition of the material. This nanotechnology may have a positive impact on the processing of lignocellulosic fibers in thermoplastic matrices, designing of paper-based overlays for building products, and modification of cellulosic fibers for textiles.     

Surface properties of oxidized LDPE by scanning force microscopy with chemically modified probes

In this article, we present the results of a study on the surface properties of chromic acid-oxidized low-density polyethylene (LDPE) by scanning force microscopy (SFM) and contact angle measurements. LDPE films were surface modified by a chromic acid treatment with subsequent annealing in argon and reconstruction in boiling water as described by Rasmussen, Stedronsky, and Whitesides [J. Am. Chem. Soc., 99 , 4736 (1977)]. The LDPE oxidation in chromic acid was monitored in situ by contact mode SFM. Initially stacks of lamellae became exposed, and at later stages a granular morphology was observed. By tapping mode SFM, the sample roughness was shown to increase during the first 10 min of oxidation from initially ca. 20 nm to ca. 50 nm. Gold-coated SFM probes (tips) functionalized with self-assembled monolayers were used to determine the pull-off force characteristics in ethanol. Variations in the contact area between SFM tips and polymer surfaces that exposed sharp crystalline features were shown to obscure the results of pull-off force measurements. However, on annealed and subsequently reconstructed samples with lower roughness, the results of force measurements correlated well with the measured contact angles. Over the range of surface energies studied, the normalized pull-off force between carboxylic acid-modified tips and these smooth samples was shown to depend approximately linearly on the cosine of the contact angle. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2483–2492, 1998     

半导体光催化剂的表面修饰

从半导体光催化剂表面修饰的类型、机理及效果出发,对其研究进展作了综合评述.