Cellulose nanowhisker-incorporated poly(lactic acid) composites for high thermal stability

In this study, biodegradable composites were prepared using cellulose nanowhiskers and poly(lactic acid). For processing at high temperature over 200 °C, cellulose nanowhiskers were prepared by ultra-sound treatment, with the high thermal stability of natural cellulose. The nanowhiskers were confirmed using transmission electron microscopy, X-ray diffraction, and thermo-gravimetric analysis. Surface modification of the cellulose nanowhiskers was performed to increase the adhesion between hydrophilic nanofillers and hydrophobic polymer matrix. The dynamic mechanical thermal analysis of the composites showed better reinforcing effect of the modified cellulose nanocrystals. The effects of cellulose nanowhiskers on the biodegradability of poly(lactic acid) were studied using a microbial oxidative degradation analyzer.     

Evaluation of thermomechanical pretreatment for enzymatic hydrolysis of pure microcrystalline cellulose and cellulose from Brewers’ spent grain

Microcrystalline cellulose (Avicel PH102) and Brewers’ spent grain (BSG) were subjected to Détente Instantanée Contrôlée (DIC) thermomechanical pre-treatment before exposure to cellulases (Celluclast 1.5 L). In a first part, we showed that the addition of β-glucosidase (Novozym-188) increased the hydrolysis yield of Avicel. A maximal theoretical yield (100%), was obtained for 5 and 10 g/L of Avicel using a mixture of Celluclast 1.5 L/Novozym-188. After DIC pre-treatments, the initial rate and final yield of hydrolysis decreased in comparison with those from untreated microcrystalline cellulose. This phenomenon may be due to the modification of the crystallinity of pure cellulose and the formation of inhibitors during the pre-treatment. In a second part, BSG was thermomechanically pre-treated and hydrolyzed. The results showed that the hydrolysis yield of BSG treated at pressure levels between 2 and 7 bar during 15 min was strongly improved compared to hydrolysis yield of untreated BSG. The optimized hydrolysis process, under intensive DIC conditions, achieved a glucose yield corresponding to 100% of the theoretical cellulose value. The morphology of BSG samples was studied with Scanning Electronic Microscopy (SEM) and highlighted that the structure of pre-treated BSG showed an important disruption compared to the rigid structure of untreated BSG.     

Conversion of Potato Starch and Peel Waste to High Value Nanocrystals

The present study aimed to convert starch and potato peel waste to nanocrystals. Starch nanocrystals were prepared using two methodologies: direct acid hydrolysis and enzyme pretreatment followed by acid hydrolysis. Direct hydrolysis broke down the starch granules to nanocrystals in 12 days. Enzyme pretreatment with starch hydrolytic enzymes (α-amylase and amyloglucosidase) reduced the time for preparation of starch nanocrystals by 6 days. Starch nanocrystals of optimum size were obtained with both the treatments and the resultant size ranged from 10 to 50 nm. Nanocrystals were disk-like platelets in appearance. Cellulose nanocrystals were derived from cellulosic material in the potato peel. Cellulose was isolated from peel waste with alkali treatment. Further, cellulose nanocrystals from potato peel and cellulose microcrystalline were prepared by acid hydrolysis. Microscopic images revealed that the aqueous suspension of cellulose nanocrystals derived from potato peel were single rod shaped, whereas those derived from cellulose microcrystalline were rod-like nanoparticles, agglomerated in the form of bundles including some of the rods in single units (well separated). The size of potato peel nanocrystals ranged from 40 to 100 nm (length) and cellulose microcrystalline ranged from 4 to 20 nm (diameter) by 110 to 250, given 4 to 20 nm (length), respectively. As starch nanocrystals as well as cellulose nanocrystals are derived from biopolymer, both can be considered safe for humans and the environment. Moreover, the biodegradable nature of these nanocrystals makes them superior over metallic nanoparticles, particularly in the field of nanocomposites.     

Nanocellulose reinforced PVA composite films: Effects of acid treatment and filler loading

Nanocellulose was prepared by acid hydrolysis of microcrystalline cellulose (MCC) at different hydrobromic acid (HBr) concentrations. Polyvinyl alcohol (PVA) composite films were prepared by the reinforcement of nanocellulose into a PVA matrix at different filler loading levels and subsequent film casting. Chemical characterization of nanocelluloses was performed for the analysis of crystallinity (X_c), degree of polymerization (DP), and molecular weight (M_w). The mechanical and thermal properties of the nanocellulose reinforced PVA films were also measured for tensile strength and thermogravimetric analysis (TGA). The acid hydrolysis decreased steadily the DP and M_w of MCC. The crystallinity of MCC with 1.5 M and 2.5 M HBr showed a significant increase due to the degradation of amorphous domains in cellulose. Higher crystalline cellulose showed the higher thermal stability than MCC. From X-ray diffraction (XRD) analysis, nanocellulose samples showed the higher peak intensity than MCC cases. Reduction of MCC particle by acid hydrolysis was clearly observed from scanning electron microscope (SEM) images. The tensile and thermal properties of PVA composite films were significantly improved with the increase of the nanocellulose loading.     

Electrospinning of cellulose nanofibers mat for laminated epoxy composite production

In this study, a new approach consisting of chemical treatment steps followed by electrospinning process was applied to produce cellulose nanofibers from wheat straws. Wheat straws were initially pretreated by NaOH solution to open the complex structure of raw materials and remove non-cellulosic materials. Then, acid and alkali hydrolysis was separately performed to eliminate hemicellulose and soluble lignin. Also, bleaching processes were implemented to remove the insoluble lignin. Cellulose nanofibers were produced by electrospinning of various concentrations of cellulose in different solvents including sodium hydroxide/urea/thiourea, pure trifluoroacetic acid (TFA), and TFA/methylene chloride. Images obtained by Scanning Electron Microscope (SEM) showed long and uniform nanofibers produced from electrospinning of cellulose/TFA/methylene chloride solution. An epoxy based laminated composite was prepared by a lamina of cellulose microfiber and electrospun nanofiber mat using hand lay-up composite manufacturing method. The fracture surface of the epoxy nanocomposite was analyzed by SEM images. In addition, the mechanical properties of laminated epoxy composites were compared with pure epoxy by conducting tensile and impact tests. Tensile test results showed that the ultimate tensile strength, elongation, and modulus of laminated epoxy nanocomposites were significantly increased. Moreover, it was found that by adding a nanofiber lamina in the epoxy composite, the impact resistance was significantly improved as a result of crack growth prevention.     

Thermal and structure properties of biobased cellulose nanowhiskers/poly (lactic acid) nanocomposites

Cellulose nanowhiskers were used to improve the performance of poly (lactic acid) (PLA). The nanocomposites mixed with three different molecular weight of poly (ethylene glycol) (PEG) were characterized by mechanical testing, thermal gravimetry and differential scanning calorimetry. The tensile test showed an increase in tensile strength and elongation at break with the addition of PEG to PLA/CNW nanocomposites, the thermal analysis results showed an increase of crystallization temperature (T _c) and crystallization compatibility (larger crystallization and melting areas), which indicated that the cellulose nanowhiskers (CNW) and PEG or CNW alone should not be considered as nucleating agents for the PLA matrix; The CNW was homo-dispersed which contributed to decreasing mobility of polymer chain segments. The compatibility between hydrophobic PLA matrix and the hydrophilic CNW was improved by the addition of different molecular weight polymeric-PEG. The thermo gravimetric analysis indicated that the thermal stability of the different composites were reflected well in the region between 25 °C and 245 oC. The structure of the PLA/CNW/PEG composites was characterized by AFM, which showed that the CNW dispersed in the PLA matrix evenly.     

Carbohydrate analysis of plant materials with uronic acid-containing polysaccharides–A comparison between different hydrolysis and subsequent chromatographic analytical techniques

Acid hydrolysis, acid methanolysis, and enzymatic hydrolysis were compared for depolymerization of five different plant materials containing uronic acids. The analyzed plant materials were oat spelt, wheat straw, spruce thermomechanical pulp, aspen stemwood, and totally chlorine-free (TCF) bleached hardwood kraft pulp. Furthermore, GC (using both HP-1 and HP-5 capillary columns and FID and MSD detectors), HPAEC-PAD, and HPAEC-Borate techniques were compared for subsequent analysis of the released monosaccharides. It was shown that acid methanolysis combined with GC analysis is a convenient method for obtaining the sugar unit composition and amount of non-crystalline polysaccharides in different plant materials. The methanolysis method was generally superior to the hydrolysis method for xylan- and uronic acid-containing samples. However, acid and enzymatic hydrolysis showed the highest recoveries for bleached chemical pulp samples. Acid hydrolysis is also required for crystalline polysaccharides, but the strong acid conditions evidently lead to degradation of labile sugars. The plant methanolysates were not suitable as such for analysis on an HPAEC-PAD system. For analysis of the total amount of sugar units, hence including cellulose, other non-crystalline hemicelluloses, and pectins, a combination of the methanolysis and hydrolysis methods is recommended.     

Isolation of Nanocellulose from Water Hyacinth Fiber (WHF) Produced via Digester-Sonication and Its Characterization

The successful isolation and characterization of water hyacinth fiber (Eichornia crassipes) (WHF) nanocellulose is presented in this study. The novelty was in exploring a wider range of properties of highly purified samples of WHF after each stage of production in more depth. The isolation was accomplished by pulping in a digester and sonication. Morphological changes before and after treatment were demonstrated by scanning electron microscopy (SEM). The lignin and hemicellulose content decreased during chemical treatment. Transmission electron microscopy (TEM) and particle size analyzer (PSA) were used to determine the morphology of WHF after sonication for 1 h. TEM shows that the diameter and length of nanocellulose WHF were 15.61 and 147.4 nm, respectively. The crystallinity index and crystalline domain area significantly increased after chemical treatment. The highest crystallinity index was 84.87 % after an acid hydrolysis process. The increase in crystallinity leads to good thermal stability. Moisture absorption tests of WHF were carried out before and after treatment. The lowest moisture absorption was in the cellulose fiber after sonication (nanocellulose).     

Characterization of depolymerized residues from extremely low acid hydrolysis (ELA) of sugarcane bagasse cellulose: Effects of degree of polymerization, crystallinity and crystallite size on thermal decomposition

Sugarcane bagasse cellulose was subjected to the extremely low acid (ELA) hydrolysis in 0.07% H₂SO₄ at 190, 210 and 225 °C for various times. The cellulose residues from this process were characterized by TGA, XRD, GPC, FTIR and SEM. A kinetic study of thermal decomposition of the residues was also carried out, using the ASTM and Kissinger methods. The thermal studies revealed that residues of cellulose hydrolyzed at 190, 210 and 225 °C for 80, 40 and 8 min have initial decomposition temperature and activation energy for the main decomposition step similar to those of Avicel PH-101. XRD studies confirmed this finding by showing that these cellulose residues are similar to Avicel in crystallinity index and crystallite size in relation to the 110 and 200 planes. FTIR spectra revealed no significant changes in the cellulose chemical structure and analysis of SEM micrographs demonstrated that the particle size of the cellulose residues hydrolyzed at 190 and 210 °C were similar to that of Avicel.     

Mechanical,Thermal, and Swelling Properties of Cross-linked Hydrogels Based on Oxidized Cellulose Nanowhiskers and Chitosan/poly(vinyl alcohol) Blends

Cross-linked hydrogels of chitosan/poly(vinyl alcohol) (PVA)/oxidized cellulose nanowhiskers (CNWs) were prepared by using oxidized CNWs as a cross-linker. The effects of the oxidation level of CNWs on the swelling behavior, thermal stability, viscoelastic properties and compressive strength of the hydrogels were studied. Chemical cross-links, hydrogen bonds, as well as nanofiller reinforcement between the three materials played a major role in determining the properties of the hydrogels. Swelling test results showed that the incorporation of oxidized CNWs decreased the water absorbability of the hydrogels due to the increase in cross-linking degree. Viscoelastic properties of the hydrogels with oxidized CNWs was increased by 537 % in storage modulus, from 4.65 kPa to 29.6 kPa. Compressive strength of 181.5 kPa at 50 % strain was observed from the cross-linked hydrogels, compared with 21.2 kPa of the non-cross-linked hydrogels. The thermal experiments showed that the chemical cross-linking slightly increase the resistance toward thermal degradation of the hydrogels.     

Extraction, preparation and characterization of cellulose fibres and nanocrystals from rice husk

Cellulose fibres and cellulose nanocrystals were extracted from rice husk. Fibres were obtained by submitting the industrial rice crop to alkali (NaOH) and bleaching treatments. Nanocrystals were extracted from these fibres using sulphuric acid (H₂SO₄) hydrolysis treatment. The material obtained after each stage of the treatments was carefully characterized and its chemical composition was determined. Morphological investigation was performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectroscopy showed the progressive removal of non-cellulosic constituents. X-ray diffraction (XRD) analysis revealed that the crystallinity increased with successive treatments. The thermal stability of the rice husk fibres and cellulose nanocrystals was also investigated using thermogravimetric analysis (TGA).     

Separation and Characterization of Waste Cotton/polyester Blend Fabric with Hydrothermal Method

In the study, a good separation efficiency of waste cotton/polyester blended fabrics (WBFs) was achieved, with dilute hydrochloric acid as the catalyst under hydrothermal conditions. The morphology and structure of the hydrothermal products including solid and liquid products were characterized by scanning electron microscopy, Fourier transform Infrared spectroscopy, X-ray diffraction, and high-performance liquid chromatography techniques and compared to the untreated polyester and cotton. The results show that the cotton fiber decomposed completely while polyester still retained its fiber characteristics after 3 h of reaction time at 150 oC and 1.5 wt% dilute hydrochloric acid. The hydrolysis of cellulose resulted in a recovery of 96.24 % of the polyester without significant change in its properties; 48.21 % of cellulose powder can be further used as the raw material of microcrystalline cellulose (MCC) and 15.57 % of glucose.     

The influence of supermasscolloider on the morphology of sugarcane bagasse and bagasse cellulose

Sugarcane bagasse (SB) was subjected to mechanical and chemical treatments in order to investigate the influence of both treatments on the morphology of cellulose extracted from SB. Samples treated with supermasscolloider (SMC) showed a slight increase in the cellulose content and a highest content after chemical treatment. Furthermore, SEM and XRD results revealed a decline in the fibre average diameter (10-2 μm) and sheet-like fibrils from mechanically treated samples, while the crystallinity index values increased for both mechanical and chemical treatment. FTIR and chemical composition analysis confirmed a partial removal of hemicellulose and lignin by supermasscolloider, whereas the chemical treatments removed a significant amount and this was effectively reflected on the improved thermal stability of cellulose mechanically and chemically treated respectively.     

Probing of an environmentally friendly regenerated cellulose material having bimorphic behavior

Novel regenerated cellulose material which was prepared from cellulose acetate fiber through the hydrolysis of acetyl groups have been developed by an environmentally friendly process without emitting toxic substances in addition to be at low production cost. They have composite crystalline structure constituted of cellulose II and cellulose IV. Also, they show a lamellar morphology with an increased amorphous region, as compared to conventional regenerated cellulose such as viscose rayon and cupra rayon. Our data obtained by several independent methods demonstrated that the adsorption properties of cellulose fibers depend predominantly on the amorphous region.     

Sugarcane bagasse whiskers: Extraction and characterizations

This work evaluates the use of sugarcane bagasse (SCB) as a source of cellulose to obtain whiskers. These fibers were extracted after SCB underwent alkaline peroxide pre-treatment followed by acid hydrolysis at 45 °C. The influence of extraction time (30 and 75 min) on the properties of the nanofibers was investigated. Sugarcane bagasse whiskers (SCBW) were analyzed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) in air atmosphere. The results showed that SCB could be used as source to obtain cellulose whiskers and they had needle-like structures with an average length (L) of 255 ± 55 nm and diameter (D) of 4 ± 2 nm, giving an aspect ratio (L/D) around 64. More drastic hydrolysis conditions (75 min) resulted in less thermally stable whiskers and caused some damage on the crystal structure of the cellulose as observed by XRD analysis.     

Macro-micro structure,antibacterial activity,and physico-mechanical properties of the mulberry bast fibers

In this paper, the mulberry fibers were successfully obtained by a new pretreatment named alkali-assisted microwave plus biological enzymatic technique (AMBET). The morphology, microstructure, physico-mechanical and antibacterial properties of the mulberry bast fibers were investigated by means of scanning electron microscope (SEM), Fourier Transform-Infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), instron tensile tester and antibacterial testing. The results showed that impurities of the bast fibers could be removed by AMBET treatment. AMBET treated mulberry fiber was even, smooth and fine, and typical cellulose I in the mulberry fibers was confirmed by FTIR and XRD analysis. The crystallinity of the AMBET treated fibers was higher than that of the raw mulberry and chemical treated mulberry fibers. Thermal analysis indicated that the mulberry fibers had a good thermal stability. Moreover, the AMBET treated mulberry fibers showed excellent antimicrobial activities against S.aureus. The physical properties of the mulberry fibers indicated the AMBET treated mulberry fibers were ideal candidates for new textile materials.     

Guayule as a feedstock for lignocellulosic biorefineries using ammonia fiber expansion (AFEX) pretreatment

Natural rubber latex extraction from guayule leaves behind greater than 90% (by weight) of agricultural residue as a feedstock suitable for conversion to biofuels via a thermochemical or biochemical route. Untreated guayule shrub and bagasse (after latex extraction) has shown to be very recalcitrant to enzymatic hydrolysis, necessitating application of a chemical pretreatment to enhance cellulase accessibility. The objective of this work was to carry out detailed compositional analysis, ammonia fiber expansion (AFEX¹) pretreatment, enzymatic hydrolysis and ethanol fermentation for various guayule-derived biomass fractions. Plant feedstocks tested were derived from two sources; (a) a mature 2007 AZ-2 whole guayule shrub plant obtained from USDA/ARS² research fields, and (b) the guayule latex-extracted commercial grade bagasse (62505) from Yulex Corporation. Compositional analysis and enzymatic hydrolysis were carried out using standard NREL³ protocols (www.nrel.gov/biomass/analytical_procedures.html). AFEX pretreatment was carried out using concentrated ammonium hydroxide at elevated temperatures for desired residence times in a pressurized reactor. Yeast fermentations on biomass hydrolyzates were carried out micro-aerobically using Saccharomyces cerevisiae (424A strain) in shake flasks.AFEX pretreatment was found to substantially improve overall enzymatic digestibility by 4-20 fold for both untreated guayule shrub and latex-extracted bagasse. Maximum glucan and xylan conversion achieved for the latex-extracted bagasse was 40% and 50%, respectively. The yeast was readily able to ferment both glucose and xylose to ethanol from the guayule bagasse hydrolyzate with or without external nutrient supplementation (i.e., yeast extract and tryptone). Our results highlight the possible utilization of guayule as a feedstock for lignocellulosic refineries co-producing natural rubber latex and biofuels. However, further process improvements (e.g., lignin/resin extraction and cellulose decrystallization using a modified AFEX process) are necessary to increase the effectiveness of ammonia-based pretreatments for further enhancing enzymatic digestibility of guayule-derived hardwood biomass.     

Pod Dehiscence in Relation to Chemical Components of Pod Shell in Soybean

Abstract

The relationship between chemical components of pod shell and pod dehiscence was investigated using 25 soybean cultivars; 16 with easily dehiscing pods (susceptible cultivars) and 9 with hardly dehiscing pods (resistant cultivars). After air-drying for about three weeks, the pod shells were ground and analyzed for the contents of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), hemi-cellulose (HCe), cellulose (Ce), uronic acid and calcium. The correlation of the contents of chemical components with the percentage of pod dehiscence (%PD) was examined by principal component analysis. The first principal ingredient score was given by the formula; score = – 0.421[ADF] – 0.038[ADL] + 0.821[HCe] – 0.382[Ce] + 20.556, where, [ADF], [ADL], [HCe] and [Ce] are percentage of each component in dried pod shell. This score gave an eigenvalue of 30.2 and contribution rate of 97.1%, and the score was higher in the susceptible cultivars than in the resistant cultivars on the average. The multiple regression analysis of the relationship between %PD and the content of chemical components also showed that %PD was best predicted by the regression equation with two chemical components, [HCe] and [Ce]. Water retention capacity and cellulose crystallinity of the pod shell were less different between the susceptible and resistant cultivars. The results in this study suggested that the chemical analysis of dry pod shell may provide useful information on breeding and selection of the resistant cultivars.     

Effects of Structural and Compositional Changes of Nanochloropsis oceania after Enzyme Treatment on EPA-Rich Lipids Extraction

Improved methods for the extraction of eicosapentaenoic acid (EPA), an essential and economically important polyunsaturated fatty acid, are urgently required. However, lipid extraction rates using food-grade solvents such as ethanol are usually low. To improve the ethanol-based extraction rate, and to elucidate the relevant mechanisms, we used cellulase and laccase to treat powdered Nannochloropsis, one of the most promising microalgal sources of EPA. Cellulase and laccase synergistically increased lipid yields by 69.31% and lipid EPA content by 42.63%, by degrading the amorphous hemicellulose and cellulose, improving crystallinity, and promoting the release and extraction of lysodiacylglyceryltrimethylhomoserine. Scanning electron microscopy showed that cell morphology was substantially altered, with cell-wall rupture, loss of cell boundaries, and the release of intracellular substances. In conclusion, Nannochloropsis lipid yields may be directly linked to cell-wall hemicellulose structure, and enzymatic treatment to alter this may improve lipid yields.