Effect of ultrasound on the physicochemical properties of organosolv lignins from wheat straw

The extractability and physicochemical properties of the wheat straw lignins were comparatively studied by using extraction methods with 0.5M NaOH in 60% aqueous methanol with and without application of ultrasonic irradiation. The results showed that applying sonication for 5, 10, 15, 20, 25, 30, and 35 min solubilized 67.4, 68.6, 74.4, 77.3, 77.3, 77.9, and 78.5% of the original lignin, whereas the treatment with 0.5M NaOH in 60% aqueous methanol at 60°C for 2.5 h without ultrasound assistance released 61.0% of the original lignin. The lignin preparations isolated by ultrasound‐assisted extractions showed slightly lower molecular weights, associated polysaccharides, and thermal stabilities during the initial stage of decomposition. More important, there were no significant differences in the primary structural features between the lignin preparations. Ultrasound‐assisted extractions under the alkaline organosolv extractions did not affect the overall structure of the lignin from wheat straw. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2512–2522, 2002     

Comparative study of lignins from ultrasonic irradiated sugar‐cane bagasse

After ultrasonic irradiation of sugar‐cane bagasse (SCB) in distilled water at 55 °C for 40 min and continuing stirring for 80 min, the irradiated SCB was sequentially treated with 0.5 M NaOH, 0.5 %, 1.0 %, 1.5 %, 2.0 % and 3.0 % H₂O₂ at pH 11.5, and 2 M NaOH at 55 °C for 2 h, which solubilized 3.3, 59.7, 15.5, 4.4, 5.5, 1.7, 0.6 and 0.6 % of the original lignin, and 13.4, 38.2, 11.9, 4.5, 9.0, 2.4, 1.2, and 11.3 % of the original hemicelluloses, respectively. In total, the sequential extractions resulted in a release of 91.2 % of the original lignin and 91.9 % of the original hemicelluloses, which were higher than in the case of corresponding extractions without ultrasound pre‐treatment. The eight lignin fractions were comparatively characterized by chemical composition, structural features, molecular weights, and thermal stability using alkaline nitrobenzene oxidation, acid hydrolysis, UV, FT‐IR, ¹H and ¹³CNMR spectroscopy, GPC, and thermal analysis. Compared to the lignins obtained without ultrasound, the lignin fractions prepared with the assistance of ultrasound had the same primary structure, composition, and similar or slightly higher purity. Copyright © 2004 Society of Chemical Industry     

Ultrasonic Convective Drying Kinetics of Clipfish During the Initial Drying Period

A hybrid drying system for high-intensity airborne ultrasound applied in convective drying was investigated for the drying of salted codfish (clipfish). Convective drying with ultrasonic assistance at 10, 20, and 30°C was compared to the same process without ultrasound. The Weibull model was used to model and investigate the drying behavior, and the effective diffusion in Fick's law was determined. The ultrasound decreased the drying time more at lower drying temperatures. The drying time was reduced by over 90% at a drying temperature of 10°C. For an industrial drying process at a temperature of 20°C, the drying time was reduced by 32.2%. The ultrasonic, convective drying of clipfish at a temperature of 20°C was faster than the same process without ultrasound at 30°C. The investigations showed a thermal effect for all products when ultrasound was applied. The specific moisture extraction ratio (SMER) in the investigated system was improved by 0.2 kg_water kWh^?1. The heat transfer coefficient in the system used was increased by 32.6% for a heating process in a separate investigation, whereas for a cooling process no increased heat transfer coefficient was determined. The thermal effect might (at least partially) explain the faster drying of ultrasonic-assisted convective drying. The results obtained demonstrate the potential of airborne ultrasound in convective drying with regard to drying time, energy consumption, and product quality. Documentation of the thermal effect should be included in future R&D on this topic.     

Structure and thermal stability of polysaccharide fractions extracted from the ultrasonic irradiated and cold alkali pretreated bamboo

Polysaccharide fractions were extracted from partially delignified bamboo (Neosinocalamus affinis) culms pretreated with ultrasonic irradiation for varied times and cold sodium hydroxide/urea solution, and their structure and thermal stability were comparatively characterized. In this case, ball‐milled bamboo culms were treated with ultrasonic irradiation for varied times (0, 5, 15, and 25 min), dissolved with 7% sodium hydroxide/12% urea solution at −12°C, and then extracted with ethanol and dioxane to obtain partially delignified solid fractions. Subsequently, the solid fractions were subjected to be extracted with dimethyl sulfoxide followed by precipitation in ethanol and yielded the polysaccharide fractions. Sugar analysis indicated that the total sugar content increased from 60.63% in the polysaccharide fraction prepared without ultrasonic irradiation to 81.26% in the polysaccharide fraction prepared with an ultrasonic irradiation time of 25 min. Glucose (∼ 50–55%) was the major sugar component, and xylose (∼ 41–44%) was the second major sugar in polysaccharide fractions in all cases. Spectroscopy (FTIR, ¹H‐NMR, ¹³C‐NMR, and HSQC) analysis suggested that the polysaccharide fractions were mainly composed of (1→4)‐linked α‐D ‐glucan from amylose and (1→4)‐linked β‐D ‐xylan attached with minor amounts of branched sugars from hemicelluloses. In addition, thermal analysis showed that the main degradation stage of the polysaccharide fractions occurred between 210 and 320°C. Compared to the polysaccharide fraction prepared without ultrasonic irradiation, the polysaccharide fraction prepared with ultrasonic irradiation had a slightly lower thermal stability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

秸秆醋酸纤维素的制备

农作物秸秆是自然界中数量极大的可再生资源,本研究以农作物秸秆为反应原料,采用无污染蒸汽爆破技术活化预处理,然后进行乙酰化反应,通过溶剂萃取分离并制备出高附加值的醋酸纤维素。实验结果表明：秸秆汽爆后明显增加了反应活性,制备醋酸纤维素的适宜条件是123℃,2 h,催化剂用量为7％,汽爆秸秆中性洗涤剂处理后的乙酰化结果效果最好,不同汽爆秸秆中小麦秸秆乙酰化效果最佳,优化实验条件下,秸秆醋酸纤维素聚合度均在120以上,取代度2.80以上,并且用红外图谱、1H NMR进行了表征。与目前工业上采用α-纤维素含量较高的高级浆为反应原料相比,不仅原料和预处理成本大大降低,而且工艺流程简单。     

Comparative study of cellulose isolated by totally chlorine‐free method from wood and cereal straw

Highly purified cellulose preparations were obtained by pretreatment of dewaxed barley straw, oil palm frond fiber, poplar wood, maize stems, wheat straw, rice straw, and rye straw with 2.0% H₂O₂ at 45°C and pH 11.6 for 16 h, and sequential purification with 80% acetic acid–70% nitric acid (10/1, v/v) at 120°C for 15 min. The purified cellulose obtained was relatively free of bound hemicelluloses (2.3–3.2%) and lignin (0.4–0.6%) and had a yield of 35.5% from barley straw, 39.6% from oil palm frond fiber, 40.8% from poplar wood, 36.0% from maize stems, 34.1% from wheat straw, 23.4% from rice straw, and 35.8% from rye straw. The weight‐average molecular weights of the purified cellulose ranged from 39,030 to 48,380 g/mol. The thermal stability of the purified cellulose was higher than that of the corresponding crude cellulose. In comparison, the isolated crude and purified cellulose samples were also studied by Fourier transform IR and cross‐polarization/magic‐angle spinning ¹³C‐NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 322–335, 2005     

Effect of ultrasonic irradiation on ceric‐salt‐initiated grafting of methyl methacrylate onto regenerated cellulose film

Effect of ultrasonic irradiation on ceric salt (Ce⁴⁺)‐initiated grafting of methyl methacrylate (MMA) on regenerated cellulose film (thickness = 20 μm) was investigated under an air atmosphere in water solvent at 60°C. The grafting system with the ultrasonic irradiation was characterized by higher percentage of grafting and graft efficiency than the system without the irradiation. Reaction of cellulose with Ce⁴⁺ was also accelerated by the ultrasonic irradiation. No accelerating effect of grafting due to the ultrasonic irradiation was observed for the system under reduced pressure of 5 torr. The effect of the ultrasonic irradiation on the average molecular weight of MMA‐grafted chains was also studied. Moreover, the surface layer of the resulting grafted films was examined by attenuated total reflection–infrared (ATR–IR) measurement and scanning electron microscopy (SEM) observation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 251–258, 1999     

Enhancing water resistance of welded dowel wood joints by acetylated lignin

Low molecular mass acetylated organosolv lignin from wheat straw and from depolymerised low sulphur organosolv wood lignin have been shown to markedly improve both the water resistance and the mechanical performance of welded dowel wood joints. The acetylated oligomers distribution and extent of acetylation of the two lignins were determined by Matrix assisted laser desorption ionization-time-of-flight mass spectrometry. Extensive acetylation was confirmed by CP-MAS ¹³C NMR spectrometry. Force–displacement measurements on welded dowel joints to which acetylated wood lignins were added showed a ductile behaviour. This is due to the interpenetration of the elastic acetylated lignin network into the more rigid composite network of the welded interphase.     

Preparation of organic vermiculite/polymethylmethacrylate nanocomposite featuring excellent mechanical and thermal properties via ultrasonic in situ polymerisation

To improve the dispersion of organically modified vermiculite (OVMT) in polymethylmethacrylate (PMMA), the method of ultrasonic in situ polymerization was introduced, and a series of OVMT/PMMA nanocomposites were successfully prepared. The structure, morphology, and mechanical and thermal properties of as-prepared sample had been investigated. Results showed that the assistance of ultrasonic irradiation could be beneficial for the good homogeneous dispersion and strong interfacial interaction of OVMT in PMMA. Consequently, the obtained nanocomposites showed better mechanical and thermal properties than those prepared without the assistance of ultrasonic irradiation. When the OVMT content was 3 wt.%, the nanocomposite prepared by ultrasonic in situ polymerization exhibited the Young's modulus, tensile strength, elongation at break and degradation temperatures for 5% and 50% weight loss of 1177 MPa, 65 MPa, 14%, 219.82ºC and 373.91ºC, respectively. These results suggested the great potential application of ultrasonic in situ polymerization for the synthesis of polymer/clay nanocomposite.     

Succinoylation of wheat straw hemicelluloses with a low degree of substitution in aqueous systems

The reaction of wheat straw hemicelluloses with succinic anhydride in aqueous alkaline systems was studied. The products showed a rather low degree of substitution, ranging from 0.017 to 0.21. The effects of reaction times of 0.5–16 h, temperatures of 25–45°C, and molar ratios of succinic anhydride to anhydroxylose units in hemicelluloses of 1:5–1:1 on the succinoylation yield and degree of substitution were examined. With the reaction kept within a pH range of 8.5–9.0, a temperature range of 25–28°C, a reaction duration of 1–2 h, and a 1:1 molar ratio of succinic anhydride to hemicelluloses were preferred. The structure of the resulting polymers was determined with Fourier transform infrared and ¹H‐ and ¹³C‐NMR spectroscopy, which indicated monoester substitution. The thermal stability of the esterified polymer increased with chemical modification. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 757–766, 2002     

Studies of acetylation of jute using simplified procedure and its characterization

Dried and defatted jute fibers were acetylated for different time and temperature in the absence of catalyst and solvent. Extent of acetylation were measured by weight percent gain (WPG). These values were compared with the standard method of acetylation using a cosolvent (pyridine) system. The characterization of acetylated fibers was performed by FTIR, DSC, TGA, and SEM studies. The maximum WPG was 18.0 for an acetic anhydride-pyridine system at 120°C for 4 h whereas using only acetic anhydride WPG was 12.3 at the same reaction condition. Thermal stability of acetylated jute was found to be higher than the untreated jute. SEM studies were carried out to investigate the fiber surface morphology. FTIR studies also produced evidence for acetylation. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1517–1523, 1997     

Behavior of polyolefin blends with acetylated sisal fibers

The influence of acetylation on the mechanical, thermal and thermodegradative behavior of sisal fiber‐reinforced PP, PP/HDPE and PP/HDPE with functionalized and non‐functionalized EPR composites was studied. Acetylation of the fiber improves adhesion of the fiber to the polyolefin matrix. In general, acetylation of the sisal fiber was found to enhance the tensile strength and modulus of the resulting composites, except in some cases. Thermal properties suggest that the mixing and molding temperatures are between 160 and 230 °C and that when acetylated fiber is mixed with polyolefins, greater polymer‐fiber interactions takes place, which slightly favor stability of these composite materials. The results allow us to suggest that a satisfactory profit/cost relation justifies the addition of acetylated fiber to PP, PP/HDPE, and PP/HDPE/EPR. © 2000 Society of Chemical Industry     

H3PW12O40·4H2O as an efficient catalyst for the conversion of cellulose into partially substituted cellulose acetate

The preparation of partial acetylation of cellulose derived from rice straw was catalyzed by phosphotungstic acid with various numbers of crystal water, and H₃PW₁₂O₄₀·4H₂O was found to be as effective catalyst. The yield of the cellulose acetate was significantly enhanced by converting cellulose directly isolated from rice straw into microcrystalline cellulose before acetylation. The optimization of the acetylation was investigated by varying the amount of catalyst and acetic anhydride as well as reaction conditions including reaction time and medium, and a degree of substitution (DS) value of 2.29 and yield of 62.9% were obtained under the optimized conditions. The structure and the formation of the acetylated product were confirmed by Fourier transform infrared spectroscopy (FTIR) and powder X‐ray diffraction (XRD) technique, the thermal properties were determined by thermal analysis including thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC), and the morphology was observed by scanning electron microscope (SEM). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41212.     

Acetylation of sugarcane bagasse hemicelluloses under mild reaction conditions by using NBS as a catalyst

Sugarcane bagasse hemicelluloses were partially acetylated with acetic anhydride using N‐bromosuccinimide (NBS) as a catalyst under mild conditions in an almost solvent‐free system. The overall yield and degree of substitution (DS) were varied from 66.2 and 83.5% and between 0.27 and 1.15, respectively, by changing the reaction temperature and duration. It was found that the yield and DS increased with reaction temperature from 18 to 80°C and reaction time between 0.5 and 5.0 h. The results showed that treatment of the native hemicelluloses with acetic anhydride using NBS as a catalyst conveniently provided the corresponding biopolymer esters. The products were characterized by FTIR, ¹³C‐NMR spectroscopy, and thermal analysis. The new biopolymer acetates were thermally stable to over 200°C but underwent significant and rapid thermal degradation when heated above the onset of thermal degradation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 53–61, 2004     

Succinoylation of wheat straw hemicelluloses in N,N‐dimethylformamide/lithium chloride systems

The chemical modification of native wheat straw hemicelluloses with succinic anhydride using N,N‐dimethylformamide/lithium chloride system as solvent and pyridine and/or 4‐dimethyaminopyridine as catalyst has been examined. In particular, the progress of the succinoylation reaction is studied as a function of the molar ratio of succinic anhydride/anhydroxylose unit in native hemicelluloses from 1:1 to 5:1, DMAP concentration 0.025–0.20 g, reaction temperature 40–140 °C, and reaction time 2–12 h with succinic anhydride. The degree of substitution of succinylated hemicelluloses ranges between 0.4 and 1.5 depending on the experimental conditions. FTIR and ¹H NMR spectroscopic characterization of the esterified polymers indicates a monoester substitution. The thermal stability of the esterified polymer decreases slightly upon chemical modification, but no significant further decrease in thermal stability is observed for DS ≥ 0.7. © 2001 Society of Chemical Industry     

ACETYLATED PLANT-FIBER-REINFORCED POLYESTER COMPOSITES: A STUDY OF MECHANICAL,HYGROTHERMAL, AND AGING CHARACTERISTICS

The potential of acetylation of plant fibers to improve the properties of composites was studied. The chemical modification of oil palm empty fruit bunch (EFB), coconut fiber (Coir), oil palm frond (OPF), jute, and flax using noncatalyzed acetic anhydride were investigated. Proof of acetylation was indicated by the increase in weight percent gain (WPG). Acetylation at a reaction temperature of 120°C had resulted in the reduction in the tensile properties (stress, modulus, and elongation at break) of EFB and Coir composites. However, at 100°C, the acetylated samples exhibited improved properties. The mechanical properties of acetylated EFB- and Coir-fiber-reinforced polyester composites was evaluated at different fiber loadings. The tensile strength and modulus were improved, but elongation at break was slightly reduced upon acetylation, particularly at high fiber loading. Impact properties were moderately increased for those composites with fiber loadings up to 45%. Acetylation exhibited a low moisture absorption, comparable with glass-fiber composites. Acetylated EFB and Coir composites showed superior retention of tensile and impact properties after aging in water up to 12 months.     

Preparation and properties of polyimide solvent‐resistant nanofiltration membrane obtained by a two‐step method

This study investigated the preparation of polyimide solvent‐resistant nanofiltration membranes by a two‐step method (casting the membrane first and then crosslinking by the thermal imidization method). The influences of polymer concentration, thickness of membranes, temperature of the imidization, phase inversion time and thermal imidization procedure were studied. The membranes with the highest rejection rate of Fast Green FCF (molecular weight 808.86 g mol^?1) were prepared in the following conditions: polymer concentration 13 wt%, phase inversion time 1 h, membrane thickness 150 µm and thermal imidization procedure 200 °C for 2.5 h, 250 °C for 2 h and 300 °C for 2 h in a vacuum environment; the heating rate was 5 °C min^?1. The membrane was stable in most of the solvents tested and the fluxes of some common solvents were equal to or higher than a number of commercial solvent‐resistant nanofiltration membranes. A much higher rejection of dyes in water than in methanol was observed in the filtration experiments and a new way to explain it was developed. Copyright © 2011 Society of Chemical Industry     

Study of ultrasound-promoted, lipase-catalyzed synthesis of fructose ester

The effect of low energy ultrasound in biochemistry and biotechnology has attracted great attention in recent years. It can enhance substrate dissolution and improve mass transfer within and outside of a cell, both of which are beneficial to the synthesis of fructose ester. Here we describe the experimental study of the effect of ultrasounds of different intensity on the lipase-catalyzed synthesis of fructose ester in the solvent butanone. The results were compared with control reactions performed with no ultrasound. High performance liquid chromatography (HPLC) and thin layer chromatography (TLC) were used for qualitative and quantitative analyses. The results show the following: 1) the concentration of mono-ester and diester increased with the reaction time, either with or without ultrasonic irradiation. Low energy ultrasound accelerated the reaction due to the effect of ultrasonic steady cavitations, and high energy ultrasound was not beneficial to the reaction. 2) The application of ultrasound played an important role in our lipase-catalyzed reaction. It decreased reaction time as compared to a reaction without ultrasound that resulted in the same yield, increased reaction rate, and enhanced the amount of fructose ester produced. When the frequency was 10 kHz and sound intensity was 0.16 W·m⁻², the concentration of ester was twofold more than without ultrasonic irradiation after a reaction time of up to 12 h. With the proper ultrasonic parameters, the overall concentration of production appeared to increase exponentially with the reaction time. 3) Ultrasound had little effect on the initial reaction rate, and continuous ultrasonic irradiation was favorable for the reaction. The longer the reaction continued, the more obvious the effects of the ultrasound became in our experiments.     

Enzymatic hydrolysis and fermentation of lime pretreated wheat straw to ethanol

BACKGROUND: The objective of this work is to develop an efficient pretreatment method that can help enzymes break down the complex carbohydrates present in wheat straw to sugars, and to then ferment of all these sugars to ethanol. RESULTS: The yield of sugars from wheat straw (8.6%, w/v) by lime pretreatment (100 mg g^?1 straw, 121 °C, 1 h) and enzymatic hydrolysis (45 °C, pH 5.0, 120 h) using a cocktail of three commercial enzyme preparations (cellulase, β‐glucosidase, and xylanase) at the dose level of 0.15 mL of each enzyme preparation g^?1 straw was 568 ± 13 mg g^?1 (82% yield). The concentration of ethanol from lime pretreated enzyme saccharified wheat straw (78 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 °C in 24 h was 22.5 ± 0.6 g L^?1 with a yield of 0.50 g g^?1 available sugars (0.29 g g^?1 straw). The ethanol concentration was 20.6 ± 0.4 g L^?1 with a yield of 0.26 g g^?1 straw in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 °C in 72 h. CONCLUSION: The results are important in choosing a suitable pretreatment option for developing bioprocess technologies for conversion of wheat straw to fuel ethanol. Copyright © 2007 Society of Chemical Industry     

Effect of acetylation on dimensional stability,mechanical, and dynamic properties of jute board

Jute slivers were acetylated in pilot scale following a no catalyst‐no solvent method at 120°C for 2 h. The weight % gain was found to be 11.37. Different jute boards were pressed under heat and pressure using acetylated jute sliver and urea formaldehyde resin. Neutral salt (NaCl), acid salt (NH₄Cl), and melamine powder were used separately for curing urea formaldehyde. For comparison purposes, control boards were also prepared using nonacetylated slivers. The boards were tested for water soaking, cyclic water soaking, and cyclic humidity to see the effect of acetylation on dimensional stabilization. This chemical modification was found to improve the dimensional stability to a great extent for NaCl and NH₄Cl cured boards and to a less extent for a melamine‐cured one. Tensile and flexural strengths were tested by Instron before and after the cyclic tests. Retention values were found to be as high as 60% after cyclic water tests for acetylated boards and the same was as low as 24% for control boards. Dynamic parameters, such as storage flexural modulus (E′), loss flexural modulus (E"), and loss factor or damping efficiency (tan δ) were determined in a fixed‐frequency mode. Dynamic mechanical study revealed that tan δ peaks were lowered due to increased bulkiness of the fiber after acetylation and thus restricted mobility. A tiny additional peak was also visible at ∼90°C beside the main peak at ∼125°C for boards with modified slivers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 935–944, 1999