Hamid Kaddami

Control of size and viscoelastic properties of nanofibrillated cellulose from palm tree by varying the TEMPO-mediated oxidation time.

The main objective of the present study was to control and optimize the preparation of nanofibrillated cellulose (NFC) from the date palm tree by monitoring the oxidation time (degree of oxidation) of the pristine cellulose and the number of cycles through the homogenizer. The oxidation was monitored by TEMPO (1-oxo-2,2,6,6-tétraméthylpipyridine 1-oxyle) mediated oxidation. Evidence of the successful isolation of NFC was given by FE-SEM observation revealing fibrils with a width in the range 20-30nm, depending of the oxidation time. The evolution of the transparency of the aqueous NFC suspension and carboxylic content according to the degree of oxidation and number of cycles were also analyzed by UV-vis transmittance, Fourier-transform infrared spectroscopy (FT-IR), conductimetry, and X-ray diffraction analysis. A significant NFC length reduction occurred during the TEMPO-mediated oxidation. The rheological properties of NFC suspensions were characterized as function of the oxidation time. Dynamic rheology showed that the aqueous suspension behavior changed from liquid to gel depending on the concentration. The highest concentration studied was 1wt% and the modulus reached 1MPa which was higher than for non-oxidized NFC. An explanation of the gel structure evolution with the oxidation time applied to the NFC (NFC length) was proposed. The gel structure evolves from an entanglement-governed gel structure to an immobilized water molecule-governed one.

Bio-based polyurethane reinforced with cellulose nanofibers: A comprehensive investigation on the effect of interface

Novel bio-based polyurethane (PU) nanocomposites composed of cellulose nanofiller extracted from the rachis of date palm tree and polycaprolactone (PCL) diol based PU were prepared by casting/evaporation. Two types of nanofiber were used: cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs). The mechanical and thermal properties of the nanocomposite films were studied by DMA, DSC, and tensile tests and the morphology was investigated by SEM. Bionanocomposites presented good mechanical properties in comparison to neat PU. While comparing both nanofillers, the improvement in mechanical and thermal properties was more pronounced for the nanocomposites based on CNF which could be explained, not only by the higher aspect ratio of CNF, but also by their better dispersion in the PU matrix. Calculation of the solubility parameters of the nanofiller surface polymers and of the PU segments portend a better interfacial adhesion for CNF based nanocomposites compared to CNC.

Multi-scale cellulose based new bio-aerogel composites with thermal super-insulating and tunable mechanical properties

Bio-composite aerogels based on bleached cellulose fibers (BCF) and cellulose nanoparticles having various morphological and physico-chemical characteristics are prepared by a freeze-drying technique and characterized. The various composite aerogels obtained were compared to a BCF aerogel used as the reference. Severe changes in the material morphology were observed by SEM and AFM due to a variation of the cellulose nanoparticle properties such as the aspect ratio, the crystalline index and the surface charge density. BCF fibers form a 3D network and they are surrounded by the cellulose nanoparticle thin films inducing a significant reduction of the size of the pores in comparison with a neat BCF based aerogel. BET analyses confirm the appearance of a new organization structure with pores of nanometric sizes. As a consequence, a decrease of the thermal conductivities is observed from 28mWm(-1)K(-1) (BCF aerogel) to 23mWm(-1)K(-1) (bio-composite aerogel), which is below the air conductivity (25mWm(-1)K(-1)). This improvement of the insulation properties for composite materials is more pronounced for aerogels based on cellulose nanoparticles having a low crystalline index and high surface charge (NFC-2h). The significant improvement of their insulation properties allows the bio-composite aerogels to enter the super-insulating materials family. The characteristics of cellulose nanoparticles also influence the mechanical properties of the bio-composite aerogels. A significant improvement of the mechanical properties under compression is obtained by self-organization, yielding a multi-scale architecture of the cellulose nanoparticles in the bio-composite aerogels. In this case, the mechanical property is more dependent on the morphology of the composite aerogel rather than the intrinsic characteristics of the cellulose nanoparticles.

Elucidating the crystal-chemistry of Jbel Rhassoul stevensite (Morocco) by advanced analytical techniques

Abstract The composition of Rhassoul clay is controversial regarding the nature of the puremineral clay fraction which is claimed to be stevensite rather than saponite. In this study, the raw and mineral fractions were characterized using various techniques including Fourier transform infrared spectroscopy and magic angle spinning nuclear magnetic resonance (MAS NMR). The isolated fine clay mineral fraction contained a larger amount of Al (>1 wt.%) than that reported for other stevensite occurrences. The 27Al MAS NMR technique confirmed that the mineral is stevensite in which the Al is equally split between the tetrahedral and octahedral coordination sites. The 29Si NMR spectrum showed a single unresolved resonance indicating little or no short-range ordering of silicon. The chemical composition of the stevensite from Jbel Rhassoul was determined to be ((Na0.25K0.20)(Mg5.04Al0.37Fe0.20⃞0.21)5.61(Si7.76Al0.24)8O20(OH)4). This formula differs from previous compositions described from this locality and shows it to be an Al-bearing lacustrine clay mineral.

Effect of Palm Tree Fiber Orientation on Electrical Properties of Palm Tree Fiber-reinforced Polyester Composites

The dynamic dielectrical analysis of short palm tree lignocellulosic fiber-reinforced polyester composites was carried out with special reference to the effect of fiber orientation, frequency, and temperature. Measurements were performed in the temperature range 40—200°C and in the frequency range 1—100 kHz. Three relaxations processes were identified, namely the orientation polarization imputed to the presence of polar water molecules in palm fiber, the relaxation process associated with conductivity occurring as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies, and the interfacial or Maxwell—Wagner—Sillars relaxation that is attributable to the accumulation of charges at the palm fibers/polyester interfaces. The orientation of the fiber can strongly influence the dielectrical properties and interfacial polarization processes in composites.

Esterification and amidation for grafting long aliphatic chains on to cellulose nanocrystals: a comparative study

Heterogeneous modification of cellulose nanocrystals (CNC) has been achieved by using esterification and amidification to attach long aliphatic chains. Long-chain aliphatic acid chlorides and amines were used as grafting reagents. Surface grafting with acyl chains was confirmed by Fourier-transform infrared spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy. It was found that the degree of substitution (DS) of the surface is highly dependent on the method of modification. Irrespective of grafting approach, the modified CNC was found to be hydrophobic after modification, as attested by contact angle measurement. The main emphasis was on the correlation between DS and the extent of surface grafting.

Electric field alignment of nanofibrillated cellulose (NFC) in silicone oil: impact on electrical properties.

This work aims to study how the magnitude, frequency, and duration of an AC electric field affect the orientation of two kinds of nanofibrillated cellulose (NFC) dispersed in silicone oil that differ by their surface charge density and aspect ratio. In both cases, the electric field alignment occurs in two steps: first, the NFC makes a gyratory motion oriented by the electric field; second, NFC interacts with itself to form chains parallel to the electric field lines. It was also observed that NFC chains become thicker and longer when the duration of application of the electric field is increased. In-situ dielectric properties have shown that the dielectric constant of the medium increases in comparison to the randomly dispersed NFC (when no electric field is applied). The optimal parameters of alignment were found to be 5000 Vpp/mm and 10 kHz for a duration of 20 min for both kinds of NFC. The highest increase in dielectric constant was achieved with NFC oxidized for 5 min (NFC-O-5 min) at the optimum conditions mentioned above.

Design and characterization of cellulose fibers with hierarchical structure for polymer reinforcement

This paper describes an approach to manufacture hierarchical composites from environmentally friendly materials by grafting cellulose whiskers onto regenerated cellulose fibers (Cordenka 700). Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy and X-ray diffraction analysis were performed to verify the degree of modification. The mechanical properties of the unmodified and modified fibers were analyzed using fiber bundle tensile static and loading–unloading tests. To show the effect of cellulose whiskers grafting on the Cordenka fibers, epoxy based composites were manufactured and tensile tests done on transverse uni-directional specimens. The mechanical properties were significantly increased by fiber modification and addition of the nano-phase into composite reinforced with micro-sized fibers.

Investigation of Relaxation Properties and Potentiality of the Thermoformability of HDPE Charged by Wood Flours

The processability of the composites made up of wood and a matrix of thermoplastic materials was experimentally and numerically investigated for six different proportions of wood flours. To take account of the enclosed gas volume responsible for inflation of the thermoplastic composite membrane, which contributes significantly to the strength and stiffness of a thermoplastic composite structure, we considered a thermodynamical approach to express external work in terms of a closed volume. The pressure load is thus deduced from the thermodynamic law of the Redlich-Kwong real gas. The viscoelastic behavior of the Lodge model is considered. The Lagrangian formulation together with the assumption of the membrane theory is used in the finite element implementation. Moreover, the air flow influence on the inflation of bubble is analyzed for six different proportions of wood flours in the HDPE material.

Impact of TEMPO-oxidization strength on the properties of cellulose nanofibril reinforced polyvinyl acetate nanocomposites

Nanocomposites of polyvinyl acetate (PVAc) reinforced with two different TEMPO-oxidized cellulose nanofibrils (CNF) were prepared by casting/evaporation method. These two sets of CNF, designed as CNF-O-5min (5min of oxidation) and CNF-O-120min (120min of oxidation), are different by their surface charge, geometrical characteristics and crystallinity index. The weight fraction of CNF was changed from 1 to 10wt%. The mechanical and thermal properties of the nanocomposite films were studied by dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests, and their morphology was investigated by scanning electron microscopy (SEM). For all nanocomposites, increasing amounts of CNF led to a significant increase in the mechanical properties (increase in Youngs modulus and tensile strength) and in the water uptake. On the other hand, the lost of transparency became very significant when the weight fraction of CNF exceeded 3wt%. The comparison between the two sets of CNF showed that PVAc/CNF-O-5min nanocomposite films had a tendency to display higher tensile strength and elastic modulus than those of PVAc/CNF-O-120min films. In addition, the water uptake is higher for PVAc/CNF-O-120min. Finally, the thermal stability analyses for PVAc/CNF films show that shorter and more charged fibrils (CNF-O-120min) appear to slightly increase the thermal stability compared to other larger and less charged fibrils (CNF-O-5min). All these results are discussed in connection with the CNFs characteristics.