Effect of pre‐treatment of sugarcane bagasse on the cellulose solution and application for the cellulose hydrogel films

Sugarcane bagasse was used as a cellulose resource, and the transparent cellulose hydrogel films were obtained from the purified cellulose by phase inversion process without chemical cross‐linking, when the dissolved cellulose in lithium chloride/N,N‐dimethyl acetamide was transformed into the solid film. On these processes, bagasse was pre‐treated by 10 wt% sodium hydroxide in the absence and presence of bleaching of 10 vol% sodium hypochlorite (NaOCl) solution in order to obtain cellulose fibers. Here, the bleaching temperature was varied from 40 to 50°C. The effect of pre‐treatment conditions on the resultant cellulose solution and hydrogel films was investigated. It was seen that strong bleaching removed most of lignin component from the bagasse. However, viscosity and size exclusion chromatogram of the cellulose indicated that this operation decreased average molecular weight of the cellulose fibers from 2.1 × 10⁶ to 4.8 × 10⁵. These property changes of fibers also caused increase of water content and weakening of mechanical strength of the resultant hydrogels. In addition, scanning probe microscopy in wet state revealed that the porous fiber network structure in the hydrogel was greatly influenced by bleaching with NaOCl. The average pore size of fiber network was decreased from 8.1 to 5.9 nm as the NaOCl treatment was at 50°C, because of expanded fibers in the swollen hydrogel. Copyright © 2016 John Wiley & Sons, Ltd.     

Studies on polymers and composites from lignin and fiber derived from sugar cane

Sugarcane fiber (i.e. bagasse) lignin has a larger fraction of aromatics unsubstitution in the ortho position than hardwood or softwood lignin and hence has the greater ability to be derivatized. Furthermore, organosolv lignin has a higher purity than sulfonated and kraft lignins. This work examines the purification of organosolv lignin derived from bagasse and the physico‐chemical properties of the lignin and lignin‐phenol formaldehyde (PF) resin coatings, and composites. The wetability tests have shown that lignin and lignin‐PF resin films are effective water barrier coatings, though the contact angles of lignin‐PF resin films were considerably less than the wax films. The overall mechanical properties (i.e. peak stress, peak strain and modulus) of the bagasse fiber composites were lower than the values obtained with the composites without the inclusion of bagasse fiber. Copyright © 2007 John Wiley & Sons, Ltd.     

Ceriporiopsis subvermispora used in delignification of sugarcane bagasse prior to soda/anthraquinone pulping

Sugarcane bagasse was pretreated with the white-rot fungus Ceriporiopsis subvermispora for 30 d of incubation. The solid-state fermentation of 800 g of bagasse was carried out in 20-L bioreactors with an inoculum charge of 250 mg of fungal mycelium/kg of bagasse. The oxidative enzymes manganese peroxidase (MnP), lignin peroxidase (LiP), and lac-case (Lac) and the hydrolytic enzyme xylanase (Xyl) were measured by standard methods and related to the fungus’s potential for delignification. Among the lignocellulolytic assayed enzymes, Xyl was detected in larger quantity (4478 IU/kg), followed by MnP (236 IU/kg). LiP and Lac were not detected. The results of chemical analysis and mass component loss showed that C. subvermispora was selective to lignin degradation. Pretreated sugarcane bagasse and control pulps were obtained by soda/anthraquinone (AQ) pulping. Pulp yields, kappa number, and viscosity of all pulps were determined by chemical analysis of the samples. Yields of soda/AQ ranged from 46 to 54%, kappa numbers were 15–25, and the viscosity ranged from 3.6 to 7 cP for pulps obtained from pretreated sugarcane bagasse.     

Effects of fiber physical and chemical characteristics on the interaction between endoglucanase and eucalypt fibers

Roles played by fiber physical and chemical characteristics in enzymatic hydrolysis of cellulosic materials were investigated by analyzing the interaction between an endoglucanase complex and eucalypt kraft fibers. PFI refining was employed to create the difference of fiber size distribution and morphology. Oxygen delignification and bleaching were employed to prepare fibers with different lignin and pentosan contents. The enzyme accessibility was monitored by adsorption at 4 °C and during hydrolysis at 40 °C. Molecular weight changes and reducing sugar released were monitored for digestibility of the samples. Greater maximum adsorption capacities of the enzymes were shown for the pulps with shorter and wider fibers and more fine fractions after refining. Highest amount of enzyme was adsorbed onto fibers with the least lignin contents at 4 °C. Fewer desorbed from fibers with higher lignin contents during hydrolysis at 40 °C. For unrefined fibers, less molecular weight reductions were observed for fibers with higher lignin contents. However, extensive fibrillation by refining negated the effects of lignin on the action of endoglucanase, similar molecular weight reductions were observed for fibers with three different lignin contents. Refining could be able to expose more reaction sites on the fiber surface, hence the impacts of lignin and pentosan diminished during hydrolysis for refined fibers.     

Carboxymethylcellulose obtained by ethanol/water organosolv process under acid conditions

Sugar cane bagasse pulps were obtained by ethanol/water organosolv process under acid and alkaline conditions. The best condition of acid pulping for the sugarcane bagasse was 0.02 mol/L sulfuric acid at 160 degrees C, for 1 h, whereas the best condition for alkaline pulping was 5% sodium hydroxide (base pulp) at 160 degrees C, for 3 h. For the residual lignin removal, the acid and alkaline pulps were submitted to a chemical bleaching using sodium chlorite. Pulps under acid and alkaline conditions bleached with sodium chlorite presented viscosities of 3.6 and 7.8 mPa x s, respectively, and mu-kappa numbers of 1.1 and 2.4, respectively. The pulp under acid condition, bleached with sodium chlorite was used to obtain carboxymethylcellulose (CMC). CMC yield was 35% (pulp based), showing mass gain after the carboxymethylation reaction corresponding to 23.6% of substitution or 0.70 groups -CH(2) COONa per unit of glucose residue. The infrared spectra showed the CMC characteristic bands and by the infrared technique it was possible to obtain a substitution degree (0.63), similar to the substitution degree calculated by mass gain (0.70).     

Deconvolution of lignin fluorescence spectra: A contribution to the comparative structural studies of lignins

In this work, we deconvoluted the fluorescence spectra of lignin and a lignin model compound using a combination of one symmetric (Gaussian) and the most appropriate number of asymmetric (Log-normal) models. We aimed to obtain new data on the structural characteristics of lignin as a complex molecule using fluorescence spectroscopy in combination with FTIR spectra. We analyzed the emission spectra of the lignin model compound, DHP, and isolated lignins from a deciduous tree, poplar, and a coniferous tree, spruce. The number of applied asymmetric components was varied for each sample until the component positions obtained from deconvolution of a series of spectra became constant. The lignin model compound contains fewer components in the emission spectrum. The same components in the spectra of all three samples show that they contain the same fluorophores. The small shift of the peak position can be attributed to the influence of different environments. The FTIR spectra of the three polymers show a small difference between their structures. The main difference among the IR spectra of the three samples is in the intensity of some peaks. The text was submitted by the authors in English.     

Three‐dimensional printing of poly(lactic acid) bio‐based composites with sugarcane bagasse fiber: Effect of printing orientation on tensile performance

The cellulose fiber was extracted from the abandoned crop sugarcane bagasse (SCB) by means of chemical treatment methods. Poly(lactic acid) (PLA) bio‐based composites with SCB were prepared through fused deposition modeling (FDM) 3D‐printing technology, and the morphologies, mechanical properties, crystallization properties, and thermal stability of 3D‐printed composites were investigated. Compared with the neat PLA, the incorporation of SCB into PLA reduces the tensile strength and flexural strength of 3D‐printed samples but increases the flexural modulus. The difference in tensile performance and bending performance is that the tensile strength of 3D‐printed samples is best when the SCB content is 6 wt%, while the flexural modulus continuously decreases as the SCB content increases. Furthermore, the effects of various printing methods on the tensile performance of 3D‐printed samples were explored via modifying G‐code of 3D models. The results indicate that the optimum SCB fiber content is identical for all printing methods except method “vertical.” Due to the fibers and molecular chains are oriented to varying degrees with altering raster angle in 3D‐printed samples, the fully oriented sample printed by method “parallel” has a better tensile strength. Besides, SCB exhibits enough high thermal decomposition temperature to meet requirements for melt extrusion processing of PLA composites, and SCB fiber is capable of promoting the crystallization of PLA.     

Optimization of lignin recovery from sugarcane bagasse using ionic liquid aided pretreatment

Ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM]oAc) was employed for the pretreatment of sugarcane bagasse (SCB) and extraction of lignin, a potentially valuable by-product of the biofuel industry. Response surface methodology based on central composite design was exploited and thereby an empirical model, exhibiting a coefficient of determination, R², of 0.9890, was established to optimize lignin recovery. In particular, a maximum lignin yield, equal to 90.1%, was calculated at the optimal pretreatment conditions, namely time: 120 min, temperature: 140 °C, and ionic liquid to bagasse ratio equal to 20:1 (wt/wt). The presence of guaiacyl and syringyl rings in lignin was confirmed by Fourier transform infrared spectroscopy (FTIR); whereas UV–Vis spectrophotometry showed that both p-coumaric acid and ferulic acid were contained in the lignin. Thermal analysis indicated a maximum decomposition rate of 2%/°C at 265 °C while Gel permeation chromatography analysis revealed that the molecular weight (M_w) of recovered lignin was equal to 1769 g/mol. Comparison of FTIR spectra of pretreated and untreated bagasse showed a negligible presence of lignin in the pretreated samples. Maximum delignification of bagasse after pretreatment was thus ensured. Thermal stability of the ionic liquid towards recyclability was proven by thermogravimetric analysis. The present study established adequate performance of neat and recycled ([EMIM]oAc) with regard to lignin recovery from SCB.     

Direct analysis of lignin and lignin-like components from softwood kraft pulp by Py-GC/MS techniques

Analytical pyrolysis combined with gas chromatography/mass spectrometry was used to analyse the structure and quantity of aromatic components, mainly guaiacyl and hydroxyphenyl derivatives, directly from chemical pulps. The quantity of aromatic degradation products was determined using a new external calibration method. The external standard was analyzed similarly to the pulp sample, and the combined area of the degradation products formed, normalized to the sample amount, was used for calibration. The method was sensitive enough to detect aromatics from fully bleached softwood pulps at a concentration level of 0.4 wt.%.The effect of bleaching on lignin structures in softwood pulps was studied by following the changes in guaiacyl-type degradation product distribution. The residual lignin structures that had been modified during cooking were removed during the course of bleaching. The residual lignin in fully bleached pulps therefore was found to bear features characteristic of native lignin in addition to increased oxidation. A striking enrichment of hydroxyphenyl-type aromatic pyrolysis products was observed during bleaching. It is suggested that they are derived not only from lignin but also from other pulp components.     

Reactions of lignin in chlorine dioxide bleaching of kraft pulps

The reactions between chlorine dioxide and the residual lignin in oxygen-bleached softwood kraft pulps have been studied. In a first series, isolated lignin samples have been subjected to chlorine dioxide oxidation at different pH values and subsequently analysed by oxidative degradation and elemental analysis. Different analytical techniques have also been employed to follow the gradual chemical changes in lignins isolated from kraft pulps after each of the bleaching stages in the OD(EOP)DD sequence. The results demonstrate that, in order to minimize chlorination of the lignin, the first chlorine dioxide stage should be carried out at a pH around or above three. At this pH level, a high degree of lignin oxidation is also achieved. A certain (mono)-chlorination of the lignin in the first D stage cannot be avoided, but this chlorine is to a large extent removed in the later bleaching stages. The efficient and non-selective oxidation of the various phenolic lignin end groups by chlorine dioxide is clearly illustrated by the analytical data. Moreover,¹³C NMR reveals that reduced lignin structures formed during the kraft cook survive the oxidative bleaching stages to a large extent.     

Characterization of sugarcane and coconut fibers by thermal analysis and FTIR

Pyrolysis of sugarcane bagasse and coconut fiber was studied by thermal analysis in order to characterize their thermal behavior and to identify their constituents by the aid of their thermogravimetric curves and to determine their heat capacity by means of DSC. The Fourier Transform Infrared Spectrum (FTIR) was used to determine the main constituents present in both residues. The thermal degradation of sugarcane bagasse and coconut fiber presents two mass loss steps attributed to the release of humidity and to the decomposition of organic material (hemicellulose, cellulose and lignin). It was expected that the results of DSC analysis were almost the same for both types of biomasses.     

Preparation and characterization of biodegradable sugarcane bagasse nano reinforcement for polymer composites using ball milling operation

The present work includes the processing and characterization of nano-based natural reinforcement for polymer composite materials. Sugarcane bagasse has been collected and the fibers were extracted using manual striping process. Undesirable materials present in the extracted fibers were removed by 1% NaOH-based chemical treatment. The macrofibers were reduced to nano scale by using high-energy ball milling process. Nanoparticles from bagasse fibers were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The degree of crystallinity of nano bagasse is 55.2% and it was reported by using XRD. A FTIR spectrum confirms the presence of cellulose functional groups in nano bagasse. The nano bagasse dimensions and morphology were investigated using SEM. The average length and diameter of the nano bagasse is 51.2 and 46.1 nm, respectively. Thermal stability of the nano bagasse was revealed by TGA analysis. The chemical composition of cellulose, lignin, and hemicellulose contents was also investigated.     

Oxidation in Acidic Medium of Lignins from Agricultural Residues

Agricultural residues as sugarcane straw and bagasse are burned in boilers for generation of energy in sugar and alcohol industries. However, excess of those by-products could be used to obtain products with higher value. Pulping process generates cellulosic pulps and lignin. The lignin could be oxidized and applied in effluent treatments for heavy metal removal. Oxidized lignin presents very strong chelating properties. Lignins from sugarcane straw and bagasse were obtained by ethanol–water pulping. Oxidation of lignins was carried out using acetic acid and Co/Mn/Br catalytical system at 50, 80, and 115 °C for 5 h. Kinetics of the reaction was accomplished by measuring the UV-visible region. Activation energy was calculated for lignins from sugarcane straw and bagasse (34.2 and 23.4 kJ mol⁻¹, respectively). The first value indicates higher cross-linked formation. Fourier-transformed infrared spectroscopy data of samples collected during oxidation are very similar. Principal component analysis applied to spectra shows only slight structure modifications in lignins after oxidation reaction.     

Effect of tissue-processing techniques on the sensitivity of microfluorimetric determinations of tracers in tissue sections

The measurement of low concentrations of fluorescent tracers in sections of tissue is theoretically possible using several microfluorimetric techniques but the sensitivity attainable can be greatly decreased if high levels of autofluorescence are emitted by tissue components. The effects of tissue-processing techniques on autofluorescence and tracer fluorescence intensities were investigated. Autofluorescence in sections of rabbit carotid artery and fluorescence from lissamine rhodamine B-labelled albumin in a model system were measured by densitometry. Autofluorescence intensities appeared to be related to the degree of cross-linking resulting from fixation of the tissue. Tissue fixed with formaldehyde or mercury (II) chloride had the lowest emission. Fluorescence from the labelled albumin was not quenched by prolonged fixation with mercury (II) chloride and formaldehyde but extracting the “mercury pigment” from sections with alcoholic iodine resulted in a 34% decrease in intensity.     

Isolation of cellulose fibers from kenaf using electron beam

Cellulose fibers were isolated from a kenaf bast fiber using a electron beam irradiation (EBI) treatment. The methods of isolation were based on a hot water treatment after EBI and two-step bleaching processes. FT-IR spectroscopy demonstrated that the content of lignin and hemicellulose in the bleached cellulose fibers treated with various EBI doses decreased with increasing doses of EBI. Specifically, the lignin in the bleached cellulose fibers treated at 300 kGy, was almost completely removed. Moreover, XRD analyses showed that the bleached cellulose fibers treated at 300 kGy presented the highest crystallinity of all the samples treated with EBI. Finally, the morphology of the bleached fiber was characterized by SEM imagery, and the studies showed that the separated degree of bleached cellulose fibers treated with various EBI doses increased with an increase of EBI dose, and the bleached cellulose fibers obtained by EBI treatment at 300 kGy was separated more uniformly than the bleached cellulose fiber obtained by alkali cooking with non-irradiated kenaf fiber.     

Coumarins in Phormium (New Zealand flax) fibers: their role in fluorescence and photodegradation

The genus Phormium (New Zealand flax) has fiber possessing a high content of lignin and, like other lignocellulosic materials, it is subject to photodegradation. Photoproducts in the fiber absorbing over a broad spectral region from ～370 to 600 nm are observed as a result of exposure to near‐UV radiation from 350 to 400 nm. Irradiation was shown to produce hydrogen peroxide and this can account, at least in part, for the photo‐oxidation manifested in changes in the reflectance spectra of the fibers. Unirradiated solid fibers and their aqueous extracts exhibit fluorescence with excitation maxima at 350–360 nm and emission maxima at 440 nm. The fluorescence spectra of the fibers change following exposure to near‐UV radiation with the major fluorophore being substantially photodegraded, evidenced by a substantial loss of emission between 410 and 480 nm, which is largely responsible for the yellow and duller appearance of the fiber. Analysis of the aqueous extracts of the fibers, using electron‐spray ionization mass spectroscopy of aqueous extracts, showed the presence of coumarin, hydroxycoumarin and a number of substituted hydroxycoumarins. The spectral distributions of the fluorescence associated with the unirradiated fibers and their aqueous extracts are consistent with them originating from a number of 7‐hydroxycoumarins present.     

Physicochemical characterisation of sugar cane bagasse lignin oxidized by hydrogen peroxide

The oxidation of soda lignin extracted from sugar cane bagasse was studied in acid medium. Soda lignin was precipitated from black liquor by adding (36N) sulphuric acid until the pH of the resultant solution was close to 2. The resultant, dried, material was oxidized using hydrogen peroxide. Soda lignin oxidized at different times was investigated by CHNS and EDX chemical analysis, GPC, FTIR and solid state CP-MAS ¹³C NMR spectroscopy. Oxidation increased the amount of carboxylic groups, while that of associated carbohydrates decreased. In addition, self-condensation with increase of molecular weight was observed.     

Physico-chemical and anatomical characterization of residual lignocellulosic fibers

Anatomical and physico-chemical properties of residual natural fibers (sugarcane bagasse, coconut fibers and peanut hulls) were characterized in order to evaluate their potential for use in the production of particleboard. The bulk density was determined by helium pycnometer and the chemical characteristics by using an electronic pH meter (for pH determination) on fibers dissolved in acidic and neutral detergents (to determine the levels of cellulose, hemicellulose and lignin). The anatomical characteristics were established using scanning electron microscopy coupled with an X-ray detector system, as well as energy dispersive X-ray spectroscopy. Results indicated similarities and differences between physico-chemical and anatomical characteristics of the residual lignocellulosic fibers when compared with the Pinus sp. wood commercially employed in particleboard production. Bulk density and pH for residual lignocellulosic fibers and Pinus sp. wood presented analogous values. Similar amounts of cellulose and lignin were identified between waste fibers and Pinus sp. wood. The presence of silica was identified in coconut fiber, peanut hull and sugarcane bagasse waste fibers, and may affect the mechanical characteristics of panels. Coconut and sugarcane bagasse fibers show surface pores with diameters ranging from 1.2 to 2.1 μm, below the 5 μm identified for Pinus sp. wood. Both fibers present pores distributed over their entire surface, whereas peanut hull fibers have no pores on their surface. This characteristic contributes to resin dispersion among particles, reflecting positively on the physical–mechanical properties of the panels. Particleboards produced with residual lignocellulosic fibers present similar physical–mechanical properties to those of Pinus sp. wood panels.     

Cellulose nanocrystal extraction from rice straw using a chlorine-free bleaching process

Cellulose nanocrystals (CNCs) have attracted tremendous attention because of their excellent chemical and physical properties and due to their renewability and sustainability. This material can be extracted from agricultural by-products such as rice straw, banana tree, or bagasse. Rice straw was selected as the raw material in this study. Initially, a large amount of lignin must be removed by an alkaline process to obtain a slurry. Thereafter, a green bleaching process can be used to remove the remaining lignin in the slurry. An UV-emitting diode with 365 nm wavelength assisted the oxidation reaction of the H₂O₂ solution without the use of chlorine-containing chemical bleach. The reaction required only 2.5 h to obtain high-purity cellulose and successfully enhanced the yield. Transmission electron microscopy images showed that the CNCs from rice straw were?~?100 nm long and 10–15 nm wide. The crystalline index and degradation temperature of CNCs were 83.8% and 257 °C, respectively.

     

Analysis of precipitated lignin on kraft pulp fibers using atomic force microscopy

A method is presented which enables analysis of lignin precipitated on the surface of kraft pulp fibers. As experimental input, high-resolution atomic force microscopy phase images of the fiber surfaces have been recorded in tapping mode. A digital image analysis procedure—based on the watershed algorithm—is applied to distinguish between cellulose fibrils and the precipitated lignin. In this way, size distributions for the diameter of lignin precipitates on pulp fiber surfaces can be obtained. In an initial application of the method, three softwood kraft pulps were analyzed: a black liquor cook with a very high content of precipitated lignin, a bleached pulp where nearly no precipitated lignin is visible and an unbleached industrial pulp. The proposed method is suggested as an appropriate tool to investigate the kinetics of lignin precipitation and the structure of lignin precipitates in pulping and bleaching.