Ramzi Khiari

Chemical composition and pulping of date palm rachis and Posidonia oceanica--a comparison with other wood and non-wood fibre sources.

In the present paper, the valorisation of two residues: Posidonia oceanica and date palm rachis was investigated. First, their chemical composition was studied and showed that they present amounts of holocellulose, lignin and cellulose similar to those encountered in softwood and hardwood. Extractives in different solvents and ash contents are relatively high. Moreover, ash composition assessment showed that silicon is the major component (17.7%) for P. oceanica. The high ash quantity and the low DP (about 370) may be considered as serious disadvantages of P. oceanica, in the pulping and papermaking context. Oppositely, the properties of rachis date palm and those of the ensuing pulp, obtained from a classical soda-anthraquinone cooking, demonstrated the suitability of this agricultural by-product for papermaking. Preliminary tests conducted on unrefined pulp suspensions and handsheets from date palm rachis in terms of freeness, Water Retention Value and mechanical properties allowed confirming the good quality of date palm rachis fibres.

Mechanical and thermal properties of Posidonia oceanica cellulose nanocrystal reinforced polymer

In the present study, cellulose nanocrystals (CNC) were isolated from Posidonia oceanica balls and leaves. CNC was prepared from this marine biomass by sulfuric acid hydrolysis (H2SO4) treatment. The raw fibers were firstly isolated by a delignification-bleaching process then the acid hydrolysis treatment was performed at 55°C during 40min under mechanical stirring. The ensuing CNCs were characterized by their morphological and thermal properties using transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA), respectively. Nanocomposite materials using the CNC extracted from marine biomass were obtained by casting and evaporating a mixture of this suspension with poly(styrene-co-butyl acrylate). The effect of CNC loading on mechanical and thermal properties was studied. Dynamic mechanical analysis (DMA) results showed a strong reinforcing effect of CNC that depends on their origin (balls or leaves). The difference was attributed not only to differences in the aspect ratio of CNC but also to the stiffness of the percolating network of nanoparticles.

Experimental evaluation of eco-friendly flocculants prepared from date palm rachis

Sodium carboxymethylcellulose (CMCNa) is an anionic water soluble polyelectrolyte widely used in many industrial sectors including food, textiles, papers, adhesives, paints, pharmaceuticals, cosmetics and mineral processing. CMCNa was produced by chemical modification of cellulose, and represents many advantages: natural, renewable, non-toxic and biodegradable. In this study, different kinds of CMCNa, prepared from an agricultural waste date palm rachis, were tested as eco-friendly flocculants for drinking water treatment and their performances as flocculants in turbidity removal enhancement were assessed. The prepared materials were characterized by the degree of substitution (DS) and polymerisation (DP). The study of the effect of some experimental parameters on the coagulation-flocculation performance, using the prepared materials combined with aluminium sulphate (as coagulant), showed that the best conditions for turbidity treatment were given for pH 8, coagulant dose 20 mg/L, flocculant concentration of 100 mg/L and stirring velocity (during the flocculation step) of 30 r/min. Under the optimum conditions, the turbidity removal using CMCNa, prepared from raw material, was about 95%. A comparison study between the flocculation performance of a commercial anionic flocculant (A100PWG: polyacrylamide) and that of the prepared CMCNa showed that the performance of the waste-based flocculant with a DS of 1.17 and a DP of 480 was 10% better than that achieved by the commercial one.

Effect of the oxidation treatment on the production of cellulose nanofiber suspensions from Posidonia oceanica: The rheological aspect

Different grades of cellulose nanofibrils (CNF) were prepared from Posidonia oceanica balls and leaves (POB and POL). Pretreatment using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation was performed to facilitate the fibrillation during ultrafine friction grinding process. The ensuing CNF batches were compared in terms of morphology and degree of fibrillation. The rheological properties of the produced CNF suspensions were also analyzed for varying doses of sodium hypochlorite used during the TEMPO- mediated oxidation procedure. The stronger fibrous network structures were formed when increasing the oxidant concentration, which was confirmed by the increase of the storage moduli value. P. oceanica balls were found to undergo stronger fibrillation and, consequently, to form stronger networks, compared to P. oceanica leaves, when using equivalent concentration of the oxidizing agent.

Cellulose nanocrystals and carboxymethyl cellulose from olive stones and their use to improve paper sheets properties

Olive stones wastes were used to prepare cellulose nanocrystals (CNC) and carboxymethyl cellulose (CMC). Transmission electron microscopy images showed that the prepared nanocrystals had width and length of about 5–7 nm and 174–234 nm, respectively. Mixtures containing CMC and CNC in water were prepared and the effect of CNC ratio (from 2.5–10 wt.% based on CMC) on viscosity of CMC solution was studied. Films casted from CMC/CNC mixtures were characterised regarding their crystallinity, tensile strength, and dynamic mechanical thermal properties. In addition, the prepared mixtures were used for coating of paper sheets and the effect of coating on mechanical properties (breaking length and tear factor), water absorption, and air permeability of paper sheets was studied. Presence of CNC in the coating mixtures resulted in improving mechanical properties and decreasing water absorption and air permeability of paper sheets as compared to paper sheets coated with neat CMC coating mixture.

Synthesis and characterization of cellulose carbonate using greenchemistry: Surface modification of Avicel

The development of new derivatives based on renewable natural resources using green chemistry is a concept gaining recognition in several industries. This work focused on the preparation and characterization of cellulose carbonate using dimethyl carbonate as the green reagent in ethanoic KOH solution. The effect of several reaction parameters were evaluated, i.e., temperature (25°C, 50°C, 90°C, 120°C, 150°C, and 180°C), time (6, 24, 48, and 72h), KOH concentration (15% and 30%), and the use of a catalyst (DBU). The degree of substitution (DS) of the resulting materials was evaluated by 13C CP/MAS NMR. The spectra of the prepared cellulose carbonate exhibited the main peaks associated with cellulose macromolecules (C1-C6) and those corresponding to carbonate functions at approximately 162ppm. Moreover, XPS was performed and confirmed the reaction modifications. Nevertheless, it is worth noting that 13C NMR and XPS spectra showed a significant difference in DS value, due to the difference between both techniques. However, our results from NMR and XPS experiments confirm that the major modifications during all the reactions occurred mainly at the surface. This green process opens the way for the easy production of a new class of cellulose derivatives.

Biomimetic Mineralization of Three-Dimensional Printed Alginate/TEMPO-Oxidized Cellulose Nanofibril Scaffolds for Bone Tissue Engineering

The three-dimensional (3D) printed scaffolds were prepared by partial cross-linking of TEMPO-oxidized cellulose nanofibril/alginate hydrogel using calcium ions for printing the hydrogel while maintaining its shape, fidelity, and preventing the collapse of the filaments. The prepared scaffolds were fully cross-linked using calcium ions immediately after printing to provide the rigidity of the hydrogel and give it long-term stability. The composition of the prepared pastes was adjusted in view of the description of the hydrogel and 3D printing parameters. The rheological properties in terms of thixotropic behavior and viscosity recovery of hydrogels were investigated by performing steady shear rate experiments. The results show that the viscosity recovery for pure alginate hydrogel was only about 16% of the initial value, whereas it was 66% when adding cellulose nanofibrils to alginate. Consequently, the shape of the pure alginate scaffold was soft and easy to collapse contrarily to the composite scaffold. The biomimetic mineralization process of printed scaffolds using simulated body fluid, mimicking the inorganic composition of human blood plasma, was performed and the hydroxyapatite nucleation on the hydrogel was confirmed. The strength properties of the fabricated scaffolds in terms of compressive strength analysis were also investigated and discussed. The results show that the alginate/TEMPO-oxidized cellulose nanofibril system may be a promising 3D printing scaffold for bone tissue engineering.

Current State and New Trends in the Use of Cellulose Nanomaterials for Wastewater Treatment

Nanotechnology has been identified as having great potential for improving the efficiency of water prevention and purification while reducing costs. In this field, two applications of nanocellulose have generated attention and have proven to be a sound strategy as an adsorbent and as a membrane for the removal of contaminants. This potential is attributed to its high aspect ratio, high specific surface area, high capacity retention, and environmental inertness. In addition to the aforementioned advantages, the presence of active sites allows the incorporation of chemical moieties that may enhance the binding efficiency of pollutants to the surface. This review paper intends to understand how nanocellulose affects the adsorption behavior of water pollutants, e.g., heavy metal ions, microbes, dyes, and organic molecules, and is divided in two parts. First, a general overview of the different strategies for the preparation of nanocellulose is described, and its specific properties are reported. The second section reports some of its application as adsorbent nanomaterial or separation membrane. It appears that the use of nanocellulose for these applications is very promising for wastewater treatment industries.