Mixed morphology nanocrystalline cellulose from sugarcane bagasse fibers/poly(lactic acid) nanocomposite films: synthesis,fabrication and characterization

Fully green nanocomposite films with excellent mechanical properties were prepared using mixed morphology nanocrystalline cellulose obtained by the dual acid hydrolysis of sugarcane bagasse fibers as the reinforcing and poly(lactic acid) (PLA) as the matrix member. Sugarcane bagasse fibers were subjected to alkaline pretreatment and bleaching for de-lignification and partial acid hydrolysis resulting in the formation of microcrystalline cellulose (MCC). Nanocrystalline cellulose (NCC) was obtained by the dual acid hydrolysis of MCC using sulfuric acid and hydrochloric acid followed by ultrasonication. The nanocomposite films were solution cast from chloroform in varied compositions. Mixed morphology and surface topography characteristics of NCC and PLA/NCC films were established using microscopic studies. Changes in the functionality and molecular chemistry with subsequent treatments in the fibers were evaluated using FTIR. NCC exhibited better dispersion characteristics, increased crystallinity and rendered thermally stable from room temperature to 230 °C. Degradation profiles of samples were obtained from thermogravimetry, while the reinforcing effects of NCC in PLA were established by analyzing crystallization characteristics from X-ray diffraction studies. X-ray diffraction was utilized to estimate the increase in crystalline constituents and their state. The increase in tensile strength of the films confirmed the increased and effective positive interaction at the matrix–filler interfaces.     

纳米纤维素超微结构的表征与分析

采用场发射环境扫描电镜(FEGE-SEM)、场发射透射电镜(FETEM) 和原子力显微镜(AFM)等仪器对硫酸水解法制备的纳米纤维素(NCC)进行超微结构的表征与分析。结果表明: NCC在水分散体系中可形成非常稳定的胶状溶液。由FEGE-SEM观察到微晶纤维素(MCC)呈不规则形状,直径约为15 μm。通过硫酸水解制得形状较规整的短棒状NCC,直径范围在2～50 nm之间。FETEM观察结果与AFM成像基本一致,FETEM观察大多数NCC直径约2～24 nm,长度为50～450 nm。AFM观察样品尺寸与FETEM观察相比所测得的样品尺寸偏大,这与其质地较软有关。X射线衍射(XRD)图谱表明NCC属于纤维素Ⅰ型,与MCC相比,结晶度由72.25%增大到77.29%。     

秸秆中木质素对其超低酸水解过程的影响

以湖北稻草秸秆为研究对象,研究了超低酸水解木质纤维素的适宜条件,测定了适宜条件下的超低酸法水解15种不同种类秸秆的纤维素及半纤维素的转化率、还原糖得率及结晶度的变化。实验结果表明:秸秆投料量3 g、硫酸投料量45 mL(硫酸质量分数0.05%)、搅拌转速500 r/min、反应温度210 ℃、反应时间10 min为适宜的水解条件。对15种不同种类秸秆的水解结果统计得到,随着秸秆中木质素含量的增大,纤维素和半纤维素的转化率都逐渐降低,还原糖得率逐渐降低;通过SEM和X衍射分析水解前后的木质纤维素结构,得到了木质素影响水解过程的方式:1)木质素含量越大,纤维素的结晶度越大,纤维素的非晶化越困难,从而影响了纤维素的水解;2)原木质素不溶于反应体系且在酸性条件下相对稳定,富木质素层的木质素阻碍反应物与产物扩散,使富木质素层内的纤维素、半纤维素水解速率降低;3)木质素含量越高,木质纤维素的富木质素层越厚、强度越大,水解时难以从颗粒表面脱落,进一步降低水解速率。     

纤维素纳米晶体制备工艺优化的研究

以微晶纤维素(MCC)为原料经硫酸水解制备纤维素纳米晶体(CNC)。采用单因素法结合正交试验系统地研究了硫酸质量分数、反应温度和反应时间对纤维素纳米晶体得率以及平均粒径的影响,并通过扫描电镜(SEM)、原子力显微镜(AFM)、X射线衍射仪(XRD)、纳米激光粒度仪对CNC的性能进行了表征,揭示了酸水解制备CNC的机理。结果表明：CNC制备的最佳工艺参数为硫酸质量分数64%、反应温度45 ℃、反应时间90 min,在此条件下CNC的得率为24.6%,粒径为204.8 nm。CNC水悬浮液呈一种稳定的淡蓝色胶体状态,其微观形貌比较规整,呈短棒状,直径约10~20 nm,长度在150~300 nm之间;XRD结果显示CNC的晶型为纤维素Ⅰ型,结晶度为80.2%。     

Synthesis and characterization of poly(o‐toluidine) doped with organic sulfonic acid by solid‐state polymerization

Poly (o‐toluidine) (POT) salts doped with organic sulfonic acids (β‐naphthalene sulfonic acid, camphor sulfonic acid, and p‐toluene sulfonic acid) were directly synthesized by using a new solid‐state polymerization method. The FTIR spectra, ultraviolet visibility (UV–vis) absorption spectra, and X‐ray diffraction patterns were used to characterize the molecular structures of the POT salts. Voltammetric study was done to investigate the electrochemical behaviors of all these POT salts. The FTIR and UV–vis absorption spectra revealed that the POT salts were composed of mixed oxidation state phases. All POT salts contained the conducting emeraldine salt (half‐oxidized and protonated form) phase; the pernigraniline (fully oxidized form) phase is predominant in POT doped with β‐naphthalene sulfonic acid, and POT doped with p‐toluene sulfonic acid had the highest doping level. The X‐ray diffraction patterns showed that the obtained POT doped with organic sulfonic acids were lower at crystallinity. The conductivity of the POT salts were found to be of the order 10^?3‐10^?4 S/cm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1630–1634, 2005     

磷酸锆辅助催化水解菌糠制备纳米纤维素晶体的性能

以食用菌产业的副产品菌糠为原料,采用磷酸锆催化剂辅助稀硫酸水解制备纳米纤维素晶体(cellulose nanocrystals,CNCs).与传统酸水解方法相比,该方法简化了工艺流程,制备过程环境友好。考察了超声时间、超声温度以及稀硫酸浓度等因素对CNCs得率的影响。结果表明当超声时间为5h、超声温度为75℃及稀硫酸浓度为12.3%时,CNCs得率为42.80%.采用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、傅里叶变换红外光谱(FTIR)以及X射线衍射仪(XRD)对样品的微观形貌、谱学性能和晶体结构进行了研究分析,结果表明所制得的CNCs呈棒状,直径介于10～30nm之间;CNCs属于纤维素I型,与原料菌糠相比,结晶度由63.79%增大到81.04%;且CNCs仍具有天然纤维素的基本化学结构。论文研究为菌糠的资源化高效利用开辟了新途径。     

桉木浆纳米纤维素响应面法优化制备及表征

采用响应面法优化桉木浆纳米纤维素(NCC)制备工艺条件并利用傅里叶变换红外(FTIR)、X射线衍射(XRD)、激光粒度分析法和透射电子显微镜(TEM)观察法对NCC进行性能表征。结果表明NCC最优制备工艺条件为硫酸浓度55%,反应温度52℃,水解时间4 h,NCC得率为65.80%,与响应面法预测值66.23%相接近;模型的决定系数为94.63%,说明模型拟合有效;制备的NCC为纤维素Ⅰ型,平均粒径365.7 nm,呈棒状。     

Reaction mechanisms and kinetics of xylo‐oligosaccharide hydrolysis by dicarboxylic acids

Hydrothermal pretreatment of lignocellulosic materials generates a liquid stream rich in pentose sugar oligomers. Cost‐effective hydrolysis and utilization of these soluble sugar oligomers is an integral process of biofuel production. We report integrated rate equations for hydrolysis of xylo‐oligomers derived from pretreated hardwood by dicarboxylic maleic and oxalic acids. The highest xylose yield observed with dicarboxylic acids was 96%, and compared to sulfuric acid, was 5–15% higher with less xylose degradation. Dicarboxylic acids showed an inverse correlation between xylose degradation rates and acid loadings unlike sulfuric acid for which less acid results in less xylose degradation to aldehydes and humic substances. A combination of high acid and low‐temperature leads to xylose yield improvement. Hydrolysis time course data at three different acid concentrations and three temperatures between 140 and 180°C were used to develop a reaction model for the hydrolysis of xylo‐oligosaccharides to xylose by dicarboxylic acids. © 2012 American Institute of Chemical Engineers AIChE J, 59: 188–199, 2013     

Mechanical properties of silk fibroin–microcrystalline cellulose composite films

Silk fibroin–microcrystalline cellulose (cellulose whisker) composite films with varied compositions were prepared by casting mixed aqueous solution/suspensions of the two components. Silk fibroin was dissolved in 10M LiSCN followed by dialysis; a cellulose whisker suspension was prepared by sulfuric acid hydrolysis of tunicate cellulose. Macroscopically homogeneous films were obtained at all mixing ratios. While the Young's modulus of the composite films showed a linear, additive dependence on the mixing ratio, the tensile strength and ultimate strain showed a maximum at a 70–80% cellulose content, reaching five times those of fibroin‐alone or cellulose‐alone films. At the same mixing ratio, infrared spectra of the composite films showed a shift of the amide I peak from 1654 to 1625 cm^?1, indicating the conformational change of fibroin from a random coil to a β structure (silk II) at the whisker–matrix interface. This change seems to be induced by contact of fibroin molecules with a highly ordered surface of cellulose whisker. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3425–3429, 2002     

Characteristics of cellulose isolated by a totally chlorine‐free method from Caragana korshinskii

The chemical composition and fiber morphology of Caragana korshinskii were investigated in this study. Isolation of cellulose was performed in a nonsulfur acetic acid/nitric acid system under various conditions. The influence of three factors, i.e., nitric acid concentration (0, 2, 4, 6, 8, or 10%), temperature (95, 100, 110, 115, 120, or 130°C), and reaction time (30, 40, 50, 60, or 90 min) on the cellulose properties (viscosity, yield, and molecular weight) was studied. The cellulose isolated was characterized by using Fourier transform infrared, gas chromatography, high performance liquid chromatography, solid‐state cross‐polarization magic angle spinning carbon‐13 nuclear magnetic resonance, wide‐angle X‐ray diffraction, and thermogravimetric analysis/differential scanning calorimetry techniques. The results showed that the treatment using 80% acetic acid and nitric acid as a catalyst under the given conditions resulted in slight acetylation of the cellulose and increased the degree of crystallinity of cellulose except for significant degradation of lignin and hemicellulosic polymers. The thermal stability of the cellulose declined with an increase in nitric acid concentration. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3251–3263, 2006     

Development and material properties of poly(lactic acid)/poly(3‐hydroxybutyrate‐co−3‐hydroxyvalerate)‐based nanocrystalline cellulose nanocomposites

This study is focused on the development and analysis of the thermal and structural behavior of nanocrystalline cellulose (NCC)‐based bionanocomposites (BCs). Nanocrystalline cellulose was prepared by controlled acid hydrolysis of oil palm empty fruit bunch fibers. The resulting NCC was surface modified using TEMPO‐mediated oxidation and solvent exchange methods for surface functionalization and also to improve dispersion of fillers. Solvent exchange NCC reinforced polymer blend containing poly(lactic acid)/poly‐(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) was prepared by using solution casting technique at various NCC loading percentages. The addition of NCC resulted in the improvement of structural, thermal, and mechanical properties of BCs as compared to that of the polymer blend. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44328.     

Study on the poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)‐based nanocomposites reinforced by surface modified nanocrystalline cellulose

As a kind of reinforcing agent, the application of nanocrystalline cellulose (NCC) is widely limited in hydrophobic polymers owing to its rich hydroxyl surface. In this study, NCC was modified with lauric acid/p‐toluensulfonyl chloride mixture, then the modified nanocrystalline cellulose (mNCC) was incorporated into biopolyester poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P(3,4)HB) by solution casting to prepare P(3,4)HB/mNCC nanocomposites. The prepared mNCC and P(3,4)HB/mNCC nanocomposites were characterized by Fourier transform‐infrared, X‐ray diffraction, contact angle test, transmission electron microscopy, scanning electron microscopy, differential scanning calorimetric, polarized optical microscope, dynamic mechanical analysis, and thermogravimetric analysis. The results show that the crystallinity and mechanical properties of P(3,4)HB are greatly improved due to the fact that NCC can be modified successfully and the mNCC can distribute uniformly in nanoscale in the matrix with good compatibility along the interface. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2015–2022, 2013     

芦苇浆纳米纤维素的制备及其尺寸均一性制备方法初探

采用硫酸水解芦苇浆和乙酸预处理芦苇浆制备纳米纤维素（NCC）,并对NCC尺寸和形貌进行测定和分析,探究均一纳米纤维素的制备方法。结果表明芦苇浆NCC得率为61．50％,3次重复实验的乙酸预处理芦苇浆NCC得率分别为63．13％（NCC-1）、62．30％（NCC-2）和62．15％（NCC-3）;乙酸预处理芦苇浆NCC乙酸回收率分别为75．00％（NCC-1）、78．15％（NCC-2）和77．56％（NCC-3）。NCC尺寸分析表明芦苇浆NCC和3次重复实验的乙酸预处理芦苇浆NCC平均尺寸均有差异,其中只有乙酸预处理芦苇浆NCC-1尺寸分布较均匀,平均尺寸185．3nm。透射电子显微镜（TEM）下观察所制备的芦苇浆NCC和乙酸预处理芦苇浆NCC-1均呈棒状。     

Influence of the polymorphism of cellulose on the formation of nanocrystals and their application in chitosan/nanocellulose composites

In this study, we evaluated the physicochemical properties of the chitosan/nanocellulose composites. Wide‐angle X‐ray scattering was applied to define the supermolecular structure of the materials, the laser diffracting technique was used to characterize the particle sizes, and scanning electron microscopy was used to evaluate the morphologies of the samples. The tensile properties of the composite films were also determined. Cellulose pulp was mercerized with 16% sodium hydroxide to give only cellulose II. Cellulose I and cellulose II were subsequently hydrolyzed with 64% sulfuric acid. As a result, nanocellulose I (NCC I) from cellulose I and nanocellulose II (NCC II) from cellulose II were produced. The mercerization of cellulose pulp contributed to a significant particle size reduction; more than 50% of the particles of the NCC II sample and only 36% of the particles of the NCC I sample were smaller than 100 nm. Chitosan composite films containing 5, 10, and 20% w/w of nanocelluloses were prepared by a solvent casting method. This was the first study investigating the influence of the crystallographic forms of cellulose on the formation of nanocrystals. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42864.     

Extraction and characterization of rice straw cellulose nanofibers by an optimized chemomechanical method

In this study, a chemomechanical method was performed to extract nanofibers from rice straw. This procedure included swelling, acid hydrolysis, alkali treatment, bleaching, and sonication. X‐ray diffractometer was employed to investigate the effect of acid hydrolysis conditions and other chemical treatments on the chemical structure of the extracted cellulose fibers. It was concluded that by increasing the acid concentration and hydrolysis time, the crystallinity of the extracted fibers was increased. The optimum acid hydrolysis conditions were found to be 2M and 2 h for the acid concentration and hydrolysis time, respectively. The chemical compositions of fibers including cellulose, hemicelluloses, lignin, and silica were determined by different examinations. It was noticed that almost all the silica content of fibers was solubilized in the swelling step. Moreover, the achieved results showed that the cellulose content of the alkali treated fibers was increased around 71% compared to the raw materials. ATR‐FTIR was applied out to compare the chemical structure of untreated and bleached fibers. The dimensions and morphology of the chemically and mechanically extracted nanofibers were investigated by scanning electron microscopy, field emission scanning electron microscopy, and transmission electron microscopy. The results of the image analyzer showed that almost 50% of fibers have a diameter within a range of 70–90 nm and length of several micrometers. The thermal gravimetric analyses were performed on the untreated and bleached fibers. It was demonstrated that the degradation temperature was increased around 19% for the purified fibers compared to raw materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40063.     

Synthesis and characterization of biodegradable polyethylene by graft copolymerization of starch using glucose–Ce(IV) redox system

Graft copolymerization of low‐density polyethylene (LDPE) onto starch was carried out with glucose–cerium(IV) redox initiator in an aqueous sulfuric acid medium under nitrogen atmosphere. The graft yield was influenced by various parameters like reaction time, temperature, and concentrations of acid, glucose, polyethylene (PE), starch, and initiator. A maximum graft yield of 85.66% was obtained at a temperature of 50°C and at higher concentration of starch. Effect of grafting on crystallinity, morphology, and thermal properties of modified PE has been evaluated using X‐ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA/DTA). Biodegradability of starch‐grafted PE has been tested applying soil‐burial test. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3229–3239, 2006     

超声波辅助纤维素酶水解制备纳米纤维素

以人纤浆为原料,利用超声波辅助纤维素酶水解制备纳米纤维素（NCC）,在单因素试验基础上,采用正交试验优化NCC的制备条件,并通过透射电镜（TEM）、X射线衍射（XRD）、红外光谱（FT-IR）、热重（TG）和Zeta电位测定对NCC的结构和性能进行了分析与表征。研究结果表明：NCC的最佳制备条件为酶用量为人纤浆质量的7%、50℃条件下酶解反应10 h,此时纳米纤维素的得率可达62.3%。TEM表征显示制备的纳米纤维素呈短棒状,纳米纤维素之间相互交织形成网络结构;XRD分析表明纳米纤维素的晶体结构并未发生改变,仍为纤维素Ⅰ型,结晶度由人纤浆的54.2%增大到73%;FT-IR分析显示纳米纤维素仍保持天然纤维素的化学结构;热重分析表明纳米纤维素的热稳定性较纤维素原料显著提高;Zeta电位测试结果表明纳米纤维素在水介质中具有良好的分散稳定性。     

［Bmim］Cl离子液体中微波辐射加热促进稻草秸秆酸水解制备还原糖

以［Bmim］Cl离子液体为介质,研究了微波辐射加热对硫酸催化稻草秸秆水解的促进作用,并对水解产物中的还原糖进行了测定。着重考察了［Bmim］Cl离子液体用量、硫酸浓度、反应温度和反应时间等因素对还原糖收率的影响,并采用正交试验法对微波辐射下稻草酸水解条件进行了优化。结果表明,在［Bmim］Cl离子液体介质中,用微波辐射加热促进稻草酸水解制备还原糖的最佳条件是：［Bmim］Cl用量10.0ml,硫酸浓度10.0%,微波加热温度85℃,反应时间60 min。在此条件下还原糖的收率可达到23. 22%,而常规酸水解得到的还原糖收率仅为18.74%。通过显微镜和红外光谱对水解残余物与稻草原料进行分析后发现：水解后的稻草残渣变细、变薄,并且与稻草原料的结构基本一致,保留了较好的纤维素特征。     

Microwave irradiation promoting acid hydrolysis of straw pole into reducing sugar in ionic liquid ［Bmim］Cl

以［Bmim］Cl离子液体为介质,研究了微波辐射加热对硫酸催化稻草秸秆水解的促进作用,并对水解产物中的还原糖进行了测定。着重考察了［Bmim］Cl离子液体用量、硫酸浓度、反应温度和反应时间等因素对还原糖收率的影响,并采用正交试验法对微波辐射下稻草酸水解条件进行了优化。结果表明,在［Bmim］Cl离子液体介质中,用微波辐射加热促进稻草酸水解制备还原糖的最佳条件是：［Bmim］Cl用量10.0ml,硫酸浓度10.0%,微波加热温度85℃,反应时间60 min。在此条件下还原糖的收率可达到23. 22%,而常规酸水解得到的还原糖收率仅为18.74%。通过显微镜和红外光谱对水解残余物与稻草原料进行分析后发现：水解后的稻草残渣变细、变薄,并且与稻草原料的结构基本一致,保留了较好的纤维素特征。     

竹纳米纤维素晶须的制备

利用硫酸水解竹浆纤维制备纳米纤维素晶须。通过原子力显微镜(AFM)和X射线衍射对纳米纤维素晶须的形貌、结构进行分析和表征,研究不同酸水解时间对纳米纤维素晶须结构的影响。结果表明,用竹浆制备的纳米纤维素晶须为长棒状结构。随着酸水解时间的延长,其长度和直径逐渐减小;在酸水解时间为20 min时无定形区逐渐被降解,其长径比最大,结晶度最高。