TEMPO-Mediated Oxidation of Norway Spruce and Eucalyptus Pulps: Preparation and Characterization of Nanofibers and Nanofiber Dispersions

This study deals with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose. Softwood and hardwood pulp fibers were suspended in water and oxidized to various extents at pH 10 and 22 °C using sodium hypochlorite in the presence of TEMPO radical and sodium bromide. This reaction system is known to be the most efficient one for the introduction of both surface carboxyl and aldehyde groups. Important relationships between formation of these functional groups and the fibrillation yield, light transmittance of the water dispersions and degree of polymerization of the oxidized softwood and hardwood pulps were established in the present study. A birefringence test confirmed the presence of nanofibers which according to atomic force microscopy analyses had diameters in the 1.6–3.8 nm range.     

Bacterial Cellulose from Simple and Low Cost Production Media by Gluconacetobacter xylinus

Bacterial cellulose pellicles were produced by Gluconacetobacter xylinus using non conventional low-cost carbon sources, such as glycerol remaining from biodiesel production and grape bagasse, a residue of wine production. The carbon sources assayed showed their suitability for microbial cellulose production, with relatively high production values such as 10.0 g/l for the culture medium with glycerol from biodiesel as carbon source and corn steep liquor as nitrogen source; and 8.0 g/l for the culture medium containing grape bagasse and corn steep liquor. Glucose, commercial glycerol and cane molasses were also assayed as carbon sources for comparison. The bacterial celluloses produced were characterized by means of scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. Morphological analysis showed that bacterial cellulose microfibrils produced from the non-conventional media used were several micrometers long and had rectangular cross-sections with widths and thicknesses in the range of 35–70 and 13–24 nm, respectively. X-ray patterns showed crystallinity levels in the range of 74–79 % (area method), whereas both X-ray patterns and infrared spectroscopy evidenced the presence of peaks characteristic of Cellulose I polymorph. Besides thermal properties were similar to those found for the pellicle obtained from glucose. The study performed showed the suitability of using wine residues or glycerol remaining from increasing biodiesel production as cheap carbon sources for production of bacterial cellulose microfibrils, with similar characteristics as those obtained by use of more expensive carbon sources such as glucose or commercial glycerol. On the other hand, the low cost nitrogen sources used (corn steep liquor or diammonium phosphate) also contributed to the economy of the bioprocess.     

Cellulose Fiber Isolation and Characterization from Sweet Blue Lupin Hull and Canola Straw

In this study, cellulose fibers were removed from crop by-products using a combination of sodium hydroxide treatment followed by acidified sodium chlorite treatment. The objective was to obtain high recovery of cellulose by optimizing treatment conditions with sodium hydroxide (5–20%, 25–75 °C and 2–10 h) followed by acidified sodium chlorite (1.7%, 75 °C for 2–6 h) to remove maximum lignin and hemicellulose, as well as to investigate the effect of lignin content of the starting materials on the treatment efficiency. Samples were characterized for their chemical composition, crystallinity, thermal behavior and morphology to evaluate the effects of treatments on the fibers’ structure. The optimum sodium hydroxide treatment conditions for maximum cellulose recovery was at 15% NaOH concentration, 99 °C and 6 h. Subsequent acidified sodium chlorite treatment at 75 °C was found to be effective in removing both hemicellulose and lignin, resulting in higher recovery of cellulose in lupin hull (~?95%) and canola straw (~?93%). The resultant cellulose fibers of both crop by-products had increased crystallinity without changing cellulose I structure (~?68–73%). Improved thermal stabilities were observed with increased onset of degradation temperatures up to 307–318 °C. Morphological investigations validated the effectiveness of treatments, revealing disrupted cell wall matrix and increased surface area due to the removal of non-cellulosics. The results suggest that the optimized combination of sodium hydroxide and acidified sodium chlorite treatments could be effectively used for the isolation of cellulose fibers from sweet blue lupin hull and canola straw, which find a great number of uses in a wide range of industrial applications.     

Mechanical Properties of Poly (Lactic Acid)/Hemp Fiber Composites Prepared with a Novel Method

This research dealt with a novel method of fabricating green composites with biodegradable poly (lactic acid) (PLA) and natural hemp fiber. The new preparation method was that hemp fibers were firstly blending-spun with a small amount of PLA fibers to form compound fiber pellets, and then the traditional twin-screw extruding and injection-molding method were applied for preparing the composites containing 10–40 wt% hemp fibers with PLA pellets and compound fiber pellets. This method was very effective to control the feeding and dispersing of fibers uniformly in the matrix thus much powerful for improving the mechanical properties. The tensile strength and modulus were improved by 39 and 92 %, respectively without a significant decrease in elongation at break, and the corresponding flexural strength and modulus of composites were also improved by 62 and 90 %, respectively, when the hemp fiber content was 40 wt%. The impact strength of composite with 20 wt% hemp fiber was improved nearly 68 % compared with the neat PLA. The application of the silane coupling agent promoted further the mechanical properties of composites attributed to the improvement of interaction between fiber and resin matrix.     

Oxygen Permeability and Biodegradability of Polyuronic Acids Prepared from Polysaccharides by TEMPO-Mediated Oxidation

Polyuronic acids, i.e., amylouronic acid, cellouronic acid and chitouronic acid, were prepared from starch, cellulose and chitin, respectively, by the 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO)-mediated oxidation, and their gas-barrier properties and biodegradability were studied in consideration to use the polyuronic acids as flexible packaging films or coating materials. Cellouronic acid and amylouronic acid had excellent oxygen-barrier properties similar to that of poly(vinyl alcohol) (PVA), while chitouronic acid did not. The regular chemical structures of the former two polyuronic acids with no bulky substituents or adducts may have brought about such high oxygen-barrier levels. An oxidized product prepared form fine microcrystalline cellulose by the TEMPO-mediated oxidation was not completely dissolved in water, but became a paste. However, this paste also formed sufficiently smooth films by coating, and had good gas-barrier property. All polyuronic acids prepared were biodegradable; cellouronic acid and chitouronic acid had high degrees of biodegradability, while amylouronic acid had quite low value. These various characteristics are significant for end use of these new polyuronic acids as gas-barrier materials for biodegradable packaging.     

Extraction of Cellulose Nanocrystals from Phormium tenax Fibres

Cellulose nanocrystals with an acicular structure ranged from 100 to 200 nm in length and 15 nm in width were extracted from Phormium tenax leaf fibres by acid hydrolysis. A two-step procedure for the extraction of nano-sized cellulose was studied and the obtained nanocrystals were characterized using morphological investigations (optical, scanning electron and atomic force microscopy), as well as physico-chemical characterization by Wide Angle X-ray Scattering, infrared spectroscopy and thermogravimetric analysis. A study of birefringence properties was also performed. The first chemical treatment leads to the production of holocellulose by the gradual removal of lignin, while the subsequent sulphuric acid hydrolysis process allows obtaining cellulose nanocrystals in an aqueous suspension. The results reported support the repeatability and the effectiveness of the procedure performed. Moreover, the high cellulose content of P. tenax fibre and their declining market interest, suggest the interest of this investigation and the possibility to use natural fibres for the production of a reinforcement phase to involve in the nanocomposite approach for industrial applications.     

Preparation of biochar catalyst with saccharide and lignocellulose residues of corncob degradation for corncob hydrolysis into furfural

This paper presented a novel process for production of furfural by hydrothermal degradation of corncob over biochar catalyst, in which it was prepared with the recycling degradation solution and lignocellulosic solid residues. The biochar catalyst was papered by lignocellulose residues and concentrated saccharide solution, and then impregnated in 0.5 mol/L sulphuric acid at room temperature for 24 h assisted by the ultrasonic vibration. In the system of recycling, 8.8 % lignocellulose residues and 100 % concentrated saccharide solution from corncob hydrolysis have been recycled. Hydrolysis of corncob was carried out at 180 °C for duration of 170 min over the biochar catalyst. The experimental results have shown that the furfural yield of up to 37.75 % and overall corncob conversion rate of 62.00 % could be achieved under optimum operating conditions for the catalysts preparation and the corncob hydrolysis. It is believed that the acid density of 4.27 mmol/g of biochar catalyst makes the SO₃H groups cleave β-1,4 glycosidic linkages effectively and hydrolyze the cellulose and hemicellulose to water-soluble sugars, as well as to facilitate dehydration of xylose to give the product of furfural.     

Impact of Cathode Conditions on Coupled Electrochemical Treatment of Nitrate Brine Concentrates

Simulated concentrated nitrate brine waste was treated in a two-stage electrolysis process, where reduction of nitrate in a cathodic chamber was coupled with oxidation of ammonium (produced in the previous stage) in an anodic chamber. The influence of operating conditions such as applied potential, electrolyte composition, and initial concentration on conversion of nitrate to ammonium in the cathodic chamber was investigated. The effects of chloride and current density on the two-stage treatment process were also examined. More negative potential at the cathode (?2.0 vs. ?1.7 and ?1.5 V) and higher current density (33 vs. 22 and 13.9 mA/cm²) favored ammonium as the product of nitrate reduction at a copper cathode and increased the overall amount of nitrate conversion. Faster reduction was seen when nitrate concentration was lower (0.01 vs. 0.02 N), but total mass conversion of nitrate in the same time period was higher for 0.02 N. The reduction of nitrate was not sensitive to sulfate or chloride concentration in the ranges studied (0–2 and 1–1.5 mg/L, respectively), but the oxidation of ammonium was noticeably higher when chloride was present. Only small amounts of ammonium and nitrate remained in the second-stage effluent after coupled treatment.     

Preparation and Fundamental Characterization of Cellulose Nanocrystal from Oil Palm Fronds Biomass

The objective of this work was to isolate cellulose nanocrystal (CNC) from oil palm fronds (Elaeis guineensis) and its subsequent characterization. Isolation involves sodium hydroxide/anthraquinone pulping with mechanical refining followed by total chlorine free bleaching (includes oxygen delignification, hydrogen peroxide oxidation and peracetic acid treatment) before acid hydrolysis. Bleaching significantly decreased kappa number and increased α-cellulose percentage of fibers as confirmed by Technical Association of the Pulp and Paper Industry standards. Transmission electron microscopy (TEM), X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis revealed that acid hydrolysis along with bleaching improved crystallinity index and thermal stability of the extracted nanocrystals. It was observed that CNC maintained its cellulose 1 polymorph despite hydrolysis treatment. Mean diameter as observed by TEM and average fiber aspect ratio of obtained CNC was 7.44 ± 0.17 nm and 16.53 ± 3.52, respectively making it suitable as a reinforcing material for nanocomposite.     

PCBs,PBDEs and dioxin-related compounds in floor dust from an informal end-of-life vehicle recycling site in northern Vietnam: contamination levels and implications for human exposure

Floor dusts from Vietnamese end-of-life vehicle (ELV)-processing households were investigated to elucidate the contamination levels and exposure risk of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and dioxin-related compounds (DRCs). The concentrations were in order of PBDEs (260–11,000, median 280 ng/g overall) > PCBs (19–2200, median 140 ng/g) > dioxin-like PCBs (8.8–450, median 22 ng/g) ? polybrominated dibenzo-p-dioxin/dibenzofurans (PBDD/Fs, 2000–28,000, median 8500 pg/g) > polychlorinated dibenzo-p-dioxin/dibenzofurans (PCDD/Fs, 440–4100, median 1800 pg/g) > MoBPCDD/Fs (1.9–1200, median 250 pg/g). Concentrations of PCBs and DRCs were higher than those reported for Vietnamese urban houses, indicating ELV processing as a significant source of these contaminants. Higher concentrations of PCBs relative to PBDEs suggest the abundance of old electrical capacitors/transformers in ELVs. The PBDD/F and PCDD/F profiles were indicative of DecaBDE-containing materials and combustion sources, respectively. PBDFs, PCDFs and DL-PCBs were the most important dioxin-like toxic equivalent (TEQ) contributors. The estimated PCB and TEQ intake doses from dust ingestion approached or exceeded the reference doses for children living in some ELV-processing households, indicating potential health risk. More comprehensive risk assessment of the exposure to PCBs and DRCs is required for residents of informal ELV recycling sites.     

Chitin and Chitosan Extracted from Shrimp Waste Using Fish Proteases Aided Process: Efficiency of Chitosan in the Treatment of Unhairing Effluents

Extraction and depolymerisation of chitin and chitosan from shrimp waste material was carried out using fish proteases aided process. A high deproteinization level (80 %) was recorded with an Enzyme/Substrate ratio of 10 U/mg. The demineralization of shrimp waste was completely achieved within 6 h at room temperature in HCl 1.25 M, and the residual content of calcium in chitin was below 0.01 %. The degree of N-acetylation, calculated from the ¹³C CP/MAS-NMR spectrum, was 85 %. The chitin obtained was converted to chitosan by N-deacetylation. X-ray diffraction patterns also indicated two characteristics crystalline peaks approximately at 10° and 20° (2θ). Chitosan was then evaluated in the treatment of unhairing effluents from the tanning industry. A result showed that chitosan as a coagulant has good performance in alkaline pH and at concentration of 0.5 g/L. Within these conditions, chitosan could decrease turbidity value, total suspended solids (89 % at 1.5 g/L), biological oxygen demand (33.3 % at 1.5 g/L) and chemical oxygen demand (58.7 % at 1.5 g/L).     

Dechlorination and decomposition of Aroclor 1242 in real waste transformer oil using a nucleophilic material with a modified domestic microwave oven

This research was done to assess the dechlorination and decomposition of polychlorinated biphenyls (PCBs) in real waste transformer oil through a modified domestic microwave oven (MDMW). The influence of microwave power (200–1000 W), reaction time (30–600 s), polyethylene glycol (PEG) (1.5–7.5 g), iron powder (0.3–1.5 g), NaOH (0.3–1.5 g), and H₂O (0.4–2 ml) were investigated on the decomposition efficiency of PCBs existing in real waste transformer oil with MDMW. Obtained data indicate that PEG and NaOH have the greatest influence on decomposition of PCBs; while, iron did not influence, and H₂O decreased, the decomposition efficiency of PCBs. Experimental data also indicated that with the optimum amount of variables through a central composites design method (PEG = 5.34 g, NaOH = 1.17 g, Fe = 0.6 g, H₂O = 0.8 ml and microwave power 800 W), 78 % of PCBs was degraded at a reaction time of about 6 min. In addition, the PCBs decomposition without using water increased up to 100 % in the reactor with the MDMW at 6 min. Accordingly, results showed that MDMW was a very efficient factor for PCBs decomposition from waste transformer oil. Also, using microwave irradiation, availability and inexpensive materials (PEG, NaOH), and iron suggest this method as a fast, effective, and cheap method for PCB decomposition of waste oils.     

Optimal Design of Ozone Bleaching Parameters to Approach Cellulose Nanofibers Extraction from Sugarcane Bagasse Fibers

Cellulose nanofibers (CNFs) were isolated from sugarcane bagasse (SCB) through the combination of bio-refinery, sulfur-free, and totally chlorine free (TCF) chemo-mechanical pretreatments, with a focus on the optimal design of ozone bleaching parameters based on a response surface methodology (RSM). For this purpose, the most effective parameters in ozone bleaching (temperature, time, and pulp consistency) were set between 40 and 85 °C, 60 and 360 min, and 1–5 wt%, respectively. High-performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR), Kappa number, and scanning electron microscopy (SEM) were used to chemically and morphologically characterize the SCB fibers. The size distribution and morphology of CNFs were also evaluated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). HPLC analysis revealed that percentage of cellulose increased from 41.5 to 91.39% after chemical pretreatments. FTIR and Kappa number analyses also confirmed the successful isolation of cellulose fibers from the SCB fibers after chemical pretreatments. Furthermore, DLS results showed that the hydrodynamic diameter of the isolated cellulose fibers reduced to 268 nm by dint of ultrasonication. Additionally, TEM images confirmed the isolation of CNFs: the average diameter of cellulose fibers decreased to about 28 nm after mechanical steps and the yield of fibrillation was found to be around 99%. According to the obtained results, the applied chemo-mechanical treatment appears to be promising for green and facile isolation of CNFs.     

Experimental Investigation of Cellulose/Silver Nanocomposites Using In Situ Generation Method

Cellulose gel films were prepared by regeneration process using pre-cooled aq.(8 wt% LiOH + 15 wt% urea) mixture as solvent and ethyl alcohol as non solvent. The Terminus cattapa leaf extract diffused wet cellulose films were then dipped in 1–5 mM aq.AgNO₃ solutions to allow in situ generation of silver nanoparticles (AgNPs). Besides the in situ generation, some AgNPs were also formed outside the wet films in the solution. The AgNPs formed outside the films were observed under transmission electron microscope and scanning electron microscope. The nanocomposite films were also characterized by Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis and tensile test. The thermal stability of the composite films was lower than that of the matrix up to a temperature of ~300 °C and afterwards showed a reverse trend. The tensile strength of the nanocomposite films was found to be higher than the matrix but decreased with increasing concentration of aq.AgNO₃. The cellulose/AgNPs composite films showed good antibacterial activity against E. coli (gram positive) and Bacillus sp. (gram negative). Based on the aforementioned properties, the cellulose/AgNPs composite films can be considered for antibacterial packaging and medical applications.     

Polyhydroxybutyrate-Based Nanocomposites with Cellulose Nanocrystals and Bacterial Cellulose

Polyhydroxybutyrate (PHB) films nanoreinforced with hydrolyzed cellulose nanocrystals (CNC) and bacterial cellulose (BC) were prepared by solvent casting. The influence of different cellulose nanoparticles content (2, 4 and 6 wt% of CNC and 2 wt% of BC) on the PHB properties was studied. CNC nanocomposites presented good dispersion of the nanocrystals, improving transparency, mechanical and barrier properties of the PHB films. On the other hand, reduced thermal stability and mechanical properties were yielded by BC addition due to the intrinsic lower degradation temperature and higher length of the BC nanofibrils compared to CNC. Nanocomposites performance variation is mainly caused by the marked difference in nanoparticles structure. It was demonstrated that PHB–CNC films exhibited higher performance enhancement without detrimental effect of the pristine PHB properties.     

Hydrolysis of organic matter during autoclaving of commingled household waste

Commingled household waste (HW) that had a controlled composition was autoclaved at elevated pressures in the presence of saturated steam for one hour at the nominal temperature levels of 130 °C, 160 °C and 200 °C. The focus of this study was the impact of temperature/pressure on hydrolysis of organic matter during autoclaving and the extent of its hydrolysis. The pH decreased with autoclaving temperature with which it had a linear relationship, and ranged from 7.4 and 6 in floc, and 6.7 and 3.6 in steam condensate. Overall, organic matter solubilisation, as indicated by dissolved organic carbon, biological and chemical oxygen demands, and total dissolved solids, increased with temperature. Lignin did not appear to hydrolyse. Hemicellulose hydrolysed and degraded the most, followed by cellulose. The highest recoveries of hemicellulose and cellulose in solution were achieved at 160 °C, although the latter could be due to experimental error. The largest losses of hemicellulose and cellulose were recorded at 200 °C. The performance of the system in respect to hydrolysis was inferior compared to other hydrothermal systems, particularly those employing wet oxidation.     

Stiff Biodegradable Polylactide Composites with Ultrafine Cellulose Filler

Polylactide (PLA) composites with 10–30 wt% of commercial fine grain filler of native cellulose were prepared by melt-mixing, and examined. The composite films had esthetic appearance, glossy surface, creamy color and density close to that of neat PLA. Good dispersion of the filler in PLA matrix was achieved. The composites were stiffer than neat PLA; in the glassy region the storage modulus increased by approx. 30 %. The tensile strength of the composite materials in the temperature range from 25 to 45 °C was similar to that of neat PLA. No marked decrease in molar mass of PLA in the composites occurred during processing in comparison to neat PLA. Moreover, thermogravimetry experiments demonstrated good thermal stability of the composites; 5 % weight loss occurred well above 300 °C.     

Biodegradation and Ecotoxicity of Polyethylene Films Containing Pro-Oxidant Additive

The worldwide accumulation of non-degradable plastic materials, such as plastic bags, is one of the most important environmental concerns nowadays. The use of degradable materials is an option to mitigate the environmental impact generated by the consumption of plastics. One of the technologies used for the manufacture and use of degradable plastics is the use of pro-degradant additives that are incorporated in conventional plastics to promote their degradation under certain conditions. The aim of this study is to evaluate the process of oxidation, biodegradation and potential ecotoxicity of polyethylene films containing an oxo-degradable additive, according to the standard ASTM D-6954. This method establishes a procedure in which the samples are subjected to consecutive steps of accelerated oxidation, biodegradation by composting and ecotoxicity assessment. Furthermore, the effect of the presence of printing ink in the polyethylene samples with oxo-degradable additive was evaluated, and the results were compared with those obtained for samples of conventional polyethylene and polylactic acid. After 180 days of laboratory controlled composting, the samples reached the following percentages of biodegradation: polylactic acid, 41 %; printed oxo-degradable polyethylene, 32.24 %; oxo-degradable polyethylene, 25.84 %; printed polyethylene, 18.23 % and polyethylene, 13.48 %. The cellulose sample used as a control was mineralized in 58.45 %. Ecotoxicity assessment showed that the products of biodegradation of the samples tested, did not generate a negative effect on germination or development of the vegetal species studied. Under proper waste management conditions, these plastics can be used as an option to decrease the environmental impact of plastic films.     

Thermal,Rheological, Mechanical and Morphological Behavior of High Density Polyethylene and Carboxymethyl Cellulose Blend

In this study water soluble sodium carboxymethyl cellulose (CMC) was blended with high density polyethylene (HDPE) by peroxide-initiated melt compounding technique. The compatibility of the blended polymers were carried out by silane crosslinking agent. A series of blends were prepared by varying the CMC contents up to a maximum of 50 phr. The physical properties of non-crosslinked and crosslinked blends were investigated in detail. FTIR analysis of crosslinked blend confirmed the presence of Si–O–Si and Si–O–C absorption peaks at 1050 and 1159 cm^?1. Thermal stability of crosslinked blends improved as compared to its non-crosslinked congener. Rheological study of crosslinked blends illustrated high complex viscosity and dynamic shear storage modulus. The tensile strength of virgin polyethylene was 8.1 MPa whereas the maximum tensile strength of 19.6 MPa was observed in crosslinked blend. Similarly lower deformation was observed in crosslinked blends under static load. Scanning electron microscopy of crosslinked formulations also showed strong adhesion between the polymers interface. The compatibility of HDPE and CMC is attributed to both free radical and condensation reactions.     

Chitosan Functionalization with Amino Acids Yields to Higher Copper Ions Adsorption Capacity

Chitosan (Chi) beads were conjugated with three different amino acids [namely, glutamic acid (GLU), methionine (MET), and taurine (TAU)] aiming to increase the divalent copper ions uptake in aqueous media. Scanning Electron Microscopy evidenced the development of a large porous structure after amino acid functionalization, associated with the increase in a number of amino groups in the polymer backbone. X-Ray Photoelectron Spectroscopy and Fourier-Transform Infrared Spectra analyses were also employed to assess the conjugation of these three different amino acids in chitosan backbone. Adsorption experiments were conducted in a batch process, at 298 K, and kinetic data indicated a slightly better fitting for the pseudo-first-order model when compared to pseudo-second order. Intraparticle diffusion model suggested a three-step mechanism for Cu(II) adsorption kinetics, limited by the third step, the intraparticle diffusion. The isotherm data fitting to the traditional Langmuir and Freundlich models indicated a better fit for the former case. The amino acid conjugation resulted in the increase of the maximum adsorption capacity for Cu(II) from 1.30 mmol g^?1 prior to amino acid conjugation to values as high as 2.31 mmol g^?1, 2.40 mmol g^?1 and 2.68 mmol g^?1 for Chi–TAU, Chi–GLU, and Chi–MET, respectively. These results are attributed to the introduction of additional amino groups and new carboxylate and amino acid residues into the chitosan backbone, which might also be explored for amino acid demanding applications.