Effect of Chemical Treatments on Physicochemical Properties of Prosopis juliflora Fibers

Incompatibility between hydrophilic natural fibers and hydrophobic matrix is known to affect the adhesion of the fiber and matrix. Therefore, it becomes necessary to modify the surface of natural fibers for improved adhesion between the fiber and matrix. Prosopis juliflora fibers (PJFs) are known to possess desirable properties for use as reinforcement in polymer matrices. Using chemical analysis, the optimal condition for alkali treatment of the PJFs was found to be 5% (w/v) of NaOH concentration with 60 min soaking time. Chemical modifications favorably changed the physiochemical properties of PJFs and undoubtedly diminished the amorphous and wax contents.     

Bending properties and cell wall structure of alkali-treated wood

Bending tests and X-ray diffraction studies were conducted on oven-dried wood samples (Picea jezoensis Carr.) treated with various concentrations of aqueous NaOH solution to investigate the influence of alkali treatment on the longitudinal contraction, bending properties, and cellulose structure. The length of the wood samples decreased and the density increased at NaOH concentrations greater than 10%. The Young’s modulus and the specific Young’s modulus decreased and the strain at yield increased for the same concentration range. However, the stress at yield was almost constant for all concentration ranges. X-ray diffraction analysis showed that lattice transformation from cellulose I to cellulose II did not occur during alkali treatment and the crystallinity index decreased at NaOH concentrations greater than 10%. The crystallinity index was linearly correlated with the changes in longitudinal contraction and the bending properties, which indicates that the increase in the proportion of amorphous components of the cellulose influences the longitudinal contraction and the bending properties of wood samples during alkali treatment.     

Effect of Chemical Treatment and Fiber Loading on Mechanical Properties of Borassus (Toddy Palm) Fiber/Epoxy Composites

The aim of the present study was to investigate and compare the mechanical properties of untreated and chemically modified Borassus fiber–reinforced epoxy composites. Composites were prepared by the hand lay-up process by reinforcing Borassus fibers with epoxy matrix. To improve the fiber-matrix adhesion properties, alkali (NaOH) and alkali combined with silane (3-aminopropyltriethoxysilane) treatment of the fiber surface was carried out. Examinations through Fourier transform-infrared spectroscopy and scanning electron microscopy (SEM) were conducted to investigate the structural and physical properties of the Borassus fibers. Tensile properties such as modulus and strength of the composites made with chemically modified and untreated Borassus fibers were studied using a universal testing machine. Based on the experimental results, it was found that the tensile properties of the Borassus-reinforced epoxy composites were significantly improved as compared with the neat epoxy. It was also found that the fiber treated with a combination of alkali and silane exhibited superior mechanical properties to alkali-treated and untreated fiber composites. The nature of the fiber/matrix interface was examined through SEM of cryo-fractured samples. Chemical resistance of composites was also found to be improved with chemically modified fiber composites.     

Impact of surface adaptation and Acacia nilotica biofiller on static and dynamic properties of sisal fiber composite

Nowadays, the awareness of the public along with strict legitimate forces over the use of polymers, the manufacturing and automotive industries started using the renewable materials. Since, natural fiber reinforced composites play vital role in developing lightweight structural materials, this study focuses on utilizing sisal fiber as reinforcement in polyester matrix along with natural filler. The influence of fiber length and fiber volume fraction on the mechanical properties of sisal fiber was studied initially. Test results revealed that the composite with 20?mm fiber length and 20-volume fraction composite has better mechanical properties. Furthermore, the effect of fiber surface modification has been analyzed using various chemical solutions such as NaOH, KMnO₄, stearic acid, and maleic acid. Of these, NaOH treatment enhances the mechanical properties of composite compared to all other cases. Finally, the influence of Acacia nilotica, a natural filler addition into the alkali-treated sisal fiber composite has been evaluated by mechanical and dynamic mechanical properties. It is found that the addition of natural filler and surface treatment has enhanced the properties of composites due to their synergetic effect. This effect improves the adhesion and uniform stress transfer among the reinforcements. The fiber surface morphology was evaluated using micrographs obtained from scanning electron microscope.     

Physico-chemical,Tensile, and Thermal Characterization of Napier Grass (Native African) Fiber Strands

This article presents the extraction and effect of alkali treatment on the physical, chemical, tensile, and thermal characteristics of fiber strands obtained from Napier grass, a renewable biomass. In order to improve these properties, the Napier grass fiber strands were treated with sodium hydroxide. The alkali treatment was carried out using NaOH solution at three different concentrations (5, 10, and 15%) for 2 h. Characterization of untreated and alkali-treated Napier grass fiber strands was carried out by studying the chemical composition, surface morphology, functional group variation, crystallinity, and tensile and thermal behavior. It was found that untreated fiber strands have lower cellulose content, crystallinity, tensile properties, and thermal stability than alkali-treated fiber strands. Napier grass fiber strands treated with 10% NaOH showed optimum tensile strength, modulus, and percentage elongation with an improvement of 51.9, 47.3, and 12.1% respectively. Based on the properties determined for alkali-treated Napier grass fiber strands, we expect that these fibers will be suitable for use as a reinforcement in natural fiber composites.     

Mechanical and thermal properties of Acacia leucophloea fiber/epoxy composites: Influence of fiber loading and alkali treatment

In this work, the influence of fiber content and alkali treatment on the mechanical and thermal properties of Acacia leucophloea fiber-reinforced epoxy composites was studied. Ten composite samples were fabricated by varying fiber content (5, 10, 15, 20, and 25 wt%); both untreated and treated fiber were soaked in a 5% NaOH solution for 45 min by using hand-layup method. The composite reinforced with 20 wt% treated fiber content exhibited better mechanical properties and thermal properties. Fourier transform infrared analysis, morphological analysis by atomic force microscope, and scanning electron microscope of composites were also performed.     

Investigation of Physico-Chemical Properties of Alkali-Treated Prosopis juliflora Fibers

There is ever-increasing interest in using natural fibers in polymer composite systems and textile industry. Prosopis juliflora fibers (PJFs) possess ideal characteristics that make them suitable for various applications. Alkali treatment of PJFs was primarily aimed to change their physico-chemical properties; 5% (w/v) NaOH concentration and 60 min of soaking time were found to be optimal. It is intriguing to note that optimally treated PJFs had higher cellulose (72.27 wt.%), lower hemicellulose (4.02 wt.%) and lignin (12.09 wt.%) contents, higher crystallinity index (73%), tensile strength, and thermal stability.     

多级孔HZSM-5分子筛催化剂的制备及低碳烃芳构化应用

采用0.2 mol/L的NaOH溶液对HZSM-5分子筛进行了不同时间的碱改性处理, 并对分子筛的结构和酸性进行表征, 考察了碱改性对HZSM-5催化剂的低碳烃芳构化活性的影响. 结果表明, HZSM-5分子筛经碱改性后会产生少量介孔, 且随改性时间延长, 介孔数量增加, 平均孔径增大, 总酸量降低, B酸/L酸比值降低. 120 min碱改性HZSM-5催化剂的活性、 稳定性以及目标产物苯、 甲苯、 乙苯和二甲苯(统称BTEX)的选择性最高.     

Optimal conditions for alkaline detoxification of dilute-acid lignocellulose hydrolysates

Alkaline detoxification strongly improves the fermentability of dilute-acid hydrolysates in the production of bioethanol from lignocellulose with Saccharomyces cerevisiae. New experiments were performed with NH₄OH and NaOH to define optimal conditions for detoxification and make a comparison with Ca(OH)₂ treatment feasible. As too harsh conditions lead to sugar degradation, the detoxification treatments were evaluated through the balanced ethanol yield, which takes both the ethanol production and the loss of fermentable sugars into account. The optimization treatments were performed as factorial experiments with 3-h duration and varying pH and temperature. Optimal conditions were found roughly in an area around pH 9.0/60°C for NH₄OH treatment and in a narrow area stretching from pH 9.0/80°C to pH 12.0/30°C for NaOH treatment. By optimizing treatment with NH₄OH, NaOH, and Ca(OH)₂, it was possible to find conditions that resulted in a fermentability that was equal or better than that of a reference fermentation of a synthetic sugar solution without inhibitors, regardless of the type of alkali used. The considerable difference in the amount of precipitate generated after treatment with different types of alkali appears critical for industrial implementation.     

Alkali treatment of lignocellulosic fibers extracted from sugarcane bagasse: Composition,structure, properties

Lignocellulosic fibers extracted from sugarcane bagasse were treated with NaOH solutions of different concentration (0-40 wt%) to study the effect of alkali treatment on the composition, structure and properties of the fibers. Composition was determined by the van Soest method, structure was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), while mechanical properties by tensile testing. Hemicellulose and lignin content decrease, while cellulose content goes through a maximum as a function of alkali concentration. Crystallinity changes only slightly and microfibril angle (MFA) remains constant thus structural effects and especially MFA are not the primary reasons for changing properties. The Young's modulus of the fibers shows a slight maximum at around 2-4 wt% NaOH content, while tensile strength goes through a much more pronounced one at around 5-8 wt%. Direct correlation between structure and mechanical properties was not found indicating that composition is more important in the determination of properties than structure. Regression analysis proved that the combination of several compositional variables determines mechanical properties in a non-linear manner. The improvement in fiber properties was explained with the dissolution of weak amorphous fractions and the relative increase of cellulose content.     

Biological pretreatment of lignocellulose for enzymatic hydrolysis of cellulose

Pretreatment of lignocellulosic materials is considered as the rate-limiting step in an economically feasible process for enzymatic hydrolysis of cellulose. Biological delignification techniques have not been developed as intensively as physical and chemical methods. However, white-rot fungi are effective degraders of lignin, and some of them even preferentially remove lignin from wood compared with carbohydrates, and therefore might be suitable for biological pretreatment of lignocellulose. White-rot fungi were cultivated on wheat straw and the residue was hydrolyzed withTrichoderma reesei cellulase. Of nineteen fungi examined,Pleurotus ostreatus, Pleurotus sp. 535,Pycnoporus cinnabarinus 115,Ischnoderma benzoinum 108,Phanerochaete sordida 37,Phlebia radiata 79, and two unidentified fungi were found suitable for pretreatment of straw: the yields of reducing sugars and glucose based on original straw were markedly better compared with uninoculated straw, and these fungi also gave better results thanPolyporus versicolor, a nonselective reference fungus (Cowling, 1961). In the best cases the efficiency of the biological pretreatment was comparable with that of alkali treatment (2% NaOH, 0.4 g NaOH/g straw, 10 min at 115‡C), but the fungal treatment resulted in a higher proportion of glucose in the hydrolyzates. Combined fungal and (strong) alkali treatment did not give better results than alkali or fungal treatment alone. When culture flasks were periodically flushed with oxygen the treatment time could be reduced by about 1 wk with the two fungi,P. sordida 37 andP. cinnabarinus 115, tested. The effect of oxygen in pretreatment reflected the effect of oxygen in the degradation of¹⁴C-lignin of poplar wood to¹⁴CO₂ by these fungi (Hatakka and Uusi-Rauva, 1983). The economic feasibility of the biological pretreatment process is poor due to the long cultivation times needed. The best results were obtained with the longest treatment time studied, which was 5 wk. However, the rapid progress in the field of biological lignin degradation may help to accelerate the delignification process, and also find factors that favor lignin degradation, but suppress the utilization of carbohydrates.     

Carbazole-functionalized polyfluorenes: synthesis and conformational properties in chloroform solution and β-phase formation in copolyfluorene films

Novel copolyfluorenes (CPFs) containing 2.5 or 10 mol% of carbazole-2,7-diyl (2,7-Cz) or carbazole-3,6-diyl (3,6-Cz) derivatives in the backbone have been synthesized by means of palladium-catalyzed Suzuki polymerization under microwave irradiation. The structure of the CPF polymers was also modified by insertion of additional 2-ethylhexyl or carbazole, diaryloxadiazole, or triphenylamine units via 3,6-Cz or 2,7-Cz comonomer units in the side chains of polymers. The self-organization of molecules in chloroform solutions was investigated using light scattering and within a wide concentration interval. Analysis of the behavior of the CPFs showed that the synthesized copolymers have an increased equilibrium rigidity of molecules with a Kuhn segment length A = (10–15) nm. The A value decreases with the introduction of Cz-units into the macromolecule in the meta-position. It is shown that chemical structure of the CPFs and thermal treatment in the temperature range 60–150 °C have a dominant effect on the optoelectronic properties as well as on microstructures of their films.     

不同磺化及碱处理聚醚醚酮的表面化学组成及体外生物活性评价

提出一种酸碱结合改性聚醚醚酮（PEEK）方法,并评价其对PEEK表面类骨磷灰石形成的影响.结果表明,通过磺化处理引入-SO₃H,显著改善了样品的亲水性,且磺化程度与H₂SO₄浓度和磺化反应时间成正比,并影响样品的表面形貌.质量分数为85% H₂SO₄处理30 min的PEEK-S具有较好的改性效果.将PEEK-S进一步用NaOH处理,可继续引入Na元素并提高样品的亲水性,但会受处理时间的影响.模拟体液（SBF）浸泡的生物活性评价结果表明,磺化后碱处理24 h的PEEK-Na具有快速的类骨磷灰石沉积能力,浸泡3 d的样品表面即可完全被沉积的类骨磷灰石覆盖,表现出较佳的生物活性.此酸碱双重改性方法操作简单,可大幅度提升PEEK的生物活性,具有较好的应用前景.     

Biomimetic apatite formation and biocompatibility on chemically treated Ti‐6Al‐7Nb alloy

Alkali treatment of the Ti‐6Al‐7Nb alloys with subsequent heat treatment has been adopted as an important surface treatment procedure for apatite formation in dental implants. This study examined the effects of alkali treatment on the precipitation of apatite on a Ti‐6Al‐7Nb alloy. All samples were immersed in a Hanks' Balanced Salts Solution [simulated body fluid (SBF)] at pH 7.4 and 36.5 °C for 15 days. The surface structural changes of samples due to the alkali treatment and immersing in SBF were analyzed by XRD, SEM and XPS. The cell toxicity was evaluated based on the optical density of the surviving cells. The samples were implanted into the abdominal connective tissue of mice for 4 weeks. A sodium titanate hydrogel layer was formed after immersion in an NaOH solution. A dense and uniform bone‐like apatite layer precipitated on the alkali and heat‐treated Ti‐6Al‐7Nb alloy in the SBF. There was a significant difference in cell toxicity between the treated and untreated Ti‐6Al‐7Nb (P < 0.05). The thickness of the fibrous capsule formed around the implant body was decreased significantly by the alkali and heat treatment (P < 0.05). The alkali treatment samples showed a better biocompatibility than the commercial metal samples. Copyright © 2008 John Wiley & Sons, Ltd.     

A SEM/EDXA study on the chemical attack of aqueous NaOH/KOH solutions on the surface of the metal-metalloid glass (Fe, Cr)80 (P, C, Si)20 and Fe75Cr5P8C10Si2, respectively

After a treatment of the metal-metalloid glassy alloy (Fe, Cr)₈₀ (P, C, Si)₂₀ and Fe₇₅Cr₅P₈C₁₀Si₂, respectively, by aqueous alkaline solutions of 1.0M NaOH + 1.0M KOH and 2.5M NaOH + 2.5M KOH, respectively, a SEM/EDXA study of the glass surface was performed.The results of the accelerated ageing procedure demonstrate that the glass treated with the 1.0M NaOH + 1.0M KOH solution at room temperature (20 °C) is characterized by a surface state like that of the initial material.For the glass treatment with the 2.5M NaOH + 2.5M KOH solution at 20 °C the surface layer shows a different morphology and is thicker. It can be supposed that the reinforcing property is reduced.The glass treatment at 80 °C with the aqueous solutions 1.0M and 2.5M (NaOH + KOH), respectively, leads to surface layers of different morphology and such a layer is about 5 m thick. The strength of solid residue of such a treated glass is very low.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Butene catalytic cracking to ethylene and propylene on mesoporous ZSM-5 by desilication

Mesopore ZSM-5 was prepared by alkali treatment of parent ZSM-5 zeolite and applied for butene catalytic cracking. The zeolite was treated in the NaOH solutions with different concentrations at 85 °C. XRD showed that the intrinsic MFI structure of ZSM-5 zeolite was preserved and corresponding crystallinity remained unchangeableness when ZSM-5 was treated with low concentration NaOH solutions. However, excessive NaOH led to the destruction of zeolite structure. The BET surface area increased obviously after desilication, and the N₂ adsorption/desorption curves indicated a number of mesopores generation. The experiment of butene catalytic cracking was carried out in a fixed-bed to investigate the influence of mesopores. The results showed that catalytic performances can be greatly improved through introducing the mesopores into parent ZSM-5 by alkali treatment. Highest yield of ethylene plus propylene were obtained when the treated concentration of NaOH solution is 0.1–0.2 M.     

Changes in the Inter- and Intra- Fibrillar Structure of Lyocell (TENCEL®) Fibers after KOH Treatment

Lyocell fibers were treated with KOH up to 8 M which was demonstrated to distribute homogeneously at the outer zones of fiber cross section compared to NaOH which accesses more deeply but less homogenously. Both NaOH and KOH solutions can be used to lower significantly the fibrillation of lyocell fibers. However, due to intrafibrillar swelling together with deep penetration ability of alkali seen for NaOH treatments results in great fiber tensile strength loss which is not observed for KOH treatments due to its inability to penetrate the fiber completely. The porous structure of fibers was studied by inverse size exclusion chromatography (ISEC) to identify mean pore diameter, total pore area and accessible pore volume (APV). Mean pore diameter of fibers decreased after KOH treatments which did not change after NaOH treatments. Wide angle X-ray diffraction analyses (WAXD) were applied to identify the crystallinity index and crystallite size. In general, fiber properties such as water retention value, carboxyl content using methylene blue sorption method, depth of color measured after dyeing with C.I. Direct Red 81 and weight loss were distinctly different in the ranges up to 2 M, 2-5 M and 5 to 8 M KOH. KOH treatment suggests new possibilities for the pretreatment of lyocell fibers to lower fibrillation while slightly lowering elongation at break without a distinct loss in tensile strength and with less decrease in carboxyl content and weight loss without changing dyeing properties of fibers compared to NaOH treatment.     

Characterization of the surface hydrolysis of kevlar-49 fibers by diffuse reflectance FTIR spectroscopy

A modified diffuse reflectance technique is used to characterize the surface hydrolysis of Kevlar-49 fibers. Treatment with 10 wt% NaOH solution produces carboxylate groups on the surface which increase rapidly up to treatment times of about 20 min at room temperature or 50 min in boiling solution. After this maximum the carboxylate groups decrease and then level out. This behavior can be explained by considering the increase as due to hydrolysis of the surface amide groups, competing with the decrease due to removal of the extensively hydrolyzed, fragmented molecules into the treatment solution. Our results shows that mild conditions (10 wt% NaOH and room temperature) as well as relatively small treatment times (less than 20 min) can be used for modifying the surface of the Kevlar-49 fiber without destroying the skin and thus deteriorating the mechanical properties of the fiber.     

甘油脱水合成丙烯醛ZSM-5催化剂的孔结构和酸性调控

研究了ZSM-5 孔结构和表面酸性对甘油脱水合成丙烯醛反应性能的影响. 在碱浓度为0.2 mol·L^-1的NaOH溶液中, 分别在65和85 ℃条件下对ZSM-5进行化学刻蚀, 成功地制备了含微介孔的ZSM-5催化剂, 提高了催化剂的表面强酸密度. 碱处理后的ZSM-5催化剂在甘油脱水反应中的稳定性得到显著提高, 在ZSM-5-at85 (经85 ℃碱处理的ZSM-5)催化剂上甘油转化率在反应10 h 后仍可保持95%以上, 丙烯醛选择性达到78%. 采用N₂吸附-脱附等温线、X射线粉末衍射(XRD)、²⁷Al 固体核磁共振(²⁷Al MAS-NMR)和透射电子显微镜(TEM)等手段对ZSM-5 结构和表面性质进行了表征, 实验结果表明在碱处理过程中骨架中的硅发生了溶脱现象, 在分子筛表面上形成了大量介孔, 但是ZSM-5 的MFI 拓扑结构没有发生变化, 骨架中的大部分铝得到保持. X射线光电子能谱(XPS)、X射线荧光光谱(XRF)和氨气程序升温脱附(NH₃-TPD)证实了在碱处理后ZSM-5分子筛外表面的Si/Al 摩尔比低于其骨架中的比例, 由此表明脱硅现象主要发生在ZSM-5 的外表面, 在新产生的介孔区域由于Si/Al 摩尔比的降低使得强酸密度得到提高. 具有微介孔结构和较高酸密度的ZSM-5催化剂增强了反应物扩散性能和容碳能力, 这对于提高甘油脱水合成丙烯醛催化剂的活性和稳定性起到了关键作用.     

Physicochemical properties of alkali-treated new cellulosic fiber from cotton shell

The aim of this present investigation was to identify a new natural fiber from one of the cotton plant’s byproducts, which is chemically modified by alkaline treatment. Its characteristics were examined for the preparation of natural fiber–reinforced polymer composites. The cotton shell fibers (CSFs) were extracted from the cotton shell and its degree of crystallinity, crystallite size, chemical constituents group, and thermal stability were determined by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis. The alkali treatment of CSFs is optimized at 5% (w/v) NaOH aqueous solution with 45 min soaking time.