Mohamed Naceur Belgacem

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.

Lignins as Macromonomers for Polyesters and Polyurethanes

Lignins from different sources, namely papermaking processes or biomass refineries vary widely in terms of structure, average molecular weight and polydispersity as a function of both the actual species used and their mode of isolation. However, they all share two common features; they are always in the form of solid particles and they all bear phenolic and aliphatic hydroxy groups, albeit in different proportions. Hence, the utilization of lignins in polymeric materials either as fillers, blends or as macromonomers can be applied in principle to all samples, provided that their specific characteristics have been carefully assessed.1-6

Surface cationized cellulose nanofibrils for the production of contact active antimicrobial surfaces

In the last decade, a new fiber pretreatment has been proposed to make easy cellulose fibrillation into microfibrils. In this context, different surface cationized MFC was prepared by optimizing the experimental parameters for cellulose fibers pretreatment before fibrillation. All MFCs were characterized by conductometric titration to establish degree of substitution, field emission gun scanning electron microscopy (FEG-SEM), atomic force microscopy (AFM) and optical microscopy assessed the effect of pretreatment on the morphology of the ensuing MFCs. Antibacterial activities of neat and cationized MFC samples were investigated against Gram positive bacteria (Bacillus subtilis, Staphylococcus aureus) and Gram negative bacteria (Escherichia coli). The CATMFC sample at DS greater than 0.18 displayed promising results with antibacterial properties without any leaching of quaternary ammonium into the environment. This work proved the potential of cationic MFCs with specific DS for contact active antimicrobial surface applications in active food packaging, medical packaging or in health and cosmetic field.

Lignin-based rigid polyurethane foams with improved biodegradation

Rigid polyurethane (RPU) foams have been synthesized using lignin-based polyols obtained by oxypropylation of four distinct lignins (Alcell, Indulin AT, Curan 27-11P, and Sarkanda). Polyol formulations with two lignin/propylene oxide/catalyst content (L/PO/C) ratios were chosen (30/70/2 and 20/80/5). RPU foams have been prepared with a polyol component that incorporates the lignin-based one at contents ranging from 25 to 100%. A 100% commercial polyol-based (Lupranol® 3323) RPU foam was also prepared and used as the reference. RPU foams were characterized in terms of density, compressive modulus, and conductivity. Cell morphology and size estimation were accessed by scanning electron microscopy. Moreover, biodegradation of the Alcell- and Indulin AT-based foams was evaluated using respirometry tests in liquid and solid media. The Alcell- and Indulin AT-based polyols together with the 20/80/5 Curan 27-11P-based one led to RPU foams with properties quite similar to those of the reference homolog. Biodegradation seems to be, particularly, favored if using Indulin AT-based polyols mixed with Lupranol® 3323.

Chapter 11 – Lignins as Components of Macromolecular Materials

Publisher Summary This chapter provides the information on usage of lignin, as such or after modification, as an additive to other polymers, a blend component, and a macromonomer. After a brief description of the use of lignin as a filler in different polymeric vehicles, such as inks and paints, the use of this renewable macromolecule as a co-reactant in phenol–formaldehyde, and urea–formaldehyde resins, is described. Then, different systems aiming at preparing poly(urethane)s, polyesters, epoxy resins, and resins based on lignins and furans are reviewed, and those giving the most interesting materials discussed in some depth. The modification of lignin with alkenyl groups and the polymerization of the ensuing macromonomers are also critically assessed. The following topic is the preparation of lignin-based carbon fibers and activated carbons and their use as reinforcing elements in composites and selective adsorbents, respectively. Finally, the preparation of aromatic monomers from lignin and the interest of their polymers is discussed.

Chapter 6 – Furan Derivatives and Furan Chemistry at the Service of Macromolecular Materials

Publisher Summary This chapter reports the most relevant aspects related to the preparation and the characterization of macromolecular structures incorporating furan heterocycles or moieties arising from them. It discusses the major chemical features of furans and the synthesis of furfural and hydroxymethyl furfural, which constitute the basic precursors to monomers suitable for both chain- and step growth polymerizations. It then deals with the free radical, cationic, anionic, and stereospecific polymerization and copolymerizations and with step-growth systems of suitable furan monomers. Particular emphasis is placed on furan polyesters, polyamides, polyurethanes, and conjugated oligomers as the most promising macromolecular architectures. This chapter discusses the application of the Diels–Alder reaction to the synthesis and properties of linear, crosslinked and dendritic macromolecules, with a strong accent on the reversible nature of these constructions. Finally, the aging of furan polymers is briefly discussed.

Synthesis and characterization of cellulose whiskers/polymer nanocomposite dispersion by mini-emulsion polymerization

Stable film-forming nanocomposite particles with diameters ranging from 120 to 300 nm, based on polybutylmethacrylate (PBMA) and cellulose whiskers in water dispersions, were successfully synthesized in one step through mini-emulsion polymerization. The nanocomposite dispersion with a solid content of 25 wt.% and up to 5 wt.% of nanofiller loading was prepared by in situ polymerization, in the presence of the whiskers using dodecylpyridinium chloride (DPC), as a cationic surfactant, and 2,2-azobis(isobutyronitrile) (AIBN), as initiator. The electrostatic interaction between the positively charged droplets and negatively charged whiskers ensured the anchoring of the nanofiller around the polymer particles. The ensuing dispersions were characterized by Dynamic Light Scattering (DLS), ζ-Potential Measurements, and Field-Emission Scanning Electron Microscopy (FE-SEM). After the film formation process, the nanocomposite film exhibits a high transparency, denoting the good dispersion of the whiskers throughout the matrix.

Recent Advances in Surface Chemical Modification of Cellulose Fibres

Over the last two decades, our research group has been involved in several approaches for chemical modification of cellulose fibre surfaces, with the aim to reduce their hydrophilic character and/or improve their adhesion strength to matrices in composite materials. Relevant advances were achieved recently by different modification strategies, namely (i) physical treatments, such as plasma; (ii) chemical grafting by click chemistry or by using polyether and polyester grafts and (iii) direct silanol-cellulose condensation with a prior hydrolysis treatment. The characterisation of the modified surfaces was performed using different characterisation techniques. The grafted materials were evaluated by elemental analysis, contact angle measurements, scanning electron microscopy, 13C-NMR CP-MAS, FTIR and X-ray photoelectron spectroscopy. The present paper reports the most relevant advances in the field of surface chemical modification of cellulose fibres achieved by our group over the last two years.

Impact of bleaching pine fibre on the fibre/cement interface

The goal of this article was to evaluate the surface characteristics of the pine fibres and its impact on the performance of fibre–cement composites. Lower polar contribution of the surface energy indicates that unbleached fibres have less hydrophilic nature than the bleached fibres. Bleaching the pulp makes the fibres less stronger, more fibrillated and permeable to liquids due to removal the amorphous lignin and its extraction from the fibre surface. Atomic force microscopy reveals these changes occurring on the fibre surface and contributes to understanding the mechanism of adhesion of the resulting fibre to cement interface. Scanning electron microscopy shows that pulp bleaching increased fibre/cement interfacial bonding, whilst unbleached fibres were less susceptible to cement precipitation into the fibre cavities (lumens) in the prepared composites. Consequently, bleached fibre-reinforced composites had lower ductility due to the high interfacial adhesion between the fibre and the cement and elevated rates of fibre mineralization.