Dwarf cavendish as a source of natural fibers in poly(propylene)-based composites

Composite materials were prepared by com pounding and hot-pressing PP or MAPP and lignocellulosic fibers extracted from the rachis of Musa acuminate Colla var. Dwarf Cavendish banana tree. The fibers were used as raw filler or after a chemical treatment expected to remove most of the extractible compounds. The resulting materials were characterized using SEM, DSC, DMA, tensile tests and water sorption experiments. All results show that the main aspect involved in the interfacial adhesion between the polar filler and the non-polar matrix is the extraction of lignin and fatty substances. This results in higher values of the degree of crystallinity and crystallization temperature of the matrix, higher mechanical properties and lower water sensitivity. Scanning electron micrograph showing the cross section of the lignocellulosic filler obtained from rachis of banana tree: (a) raw, and (b) extracted fibers.info:eu-repo/semantics/publishedVersio

Cellulose Nanocrystals: From Classical Hydrolysis to the Use of Deep Eutectic Solvents

During the last two decades, interest in cellulosic nanomaterials has greatly increased. Among these nanocelluloses, cellulose nanocrystals (CNC) exhibit outstanding properties. Indeed, besides their high crystallinity, cellulose nanocrystals are interesting in terms of morphology with high aspect ratio (length 100–1000 nm, width 2–15 nm), high specific area, and high mechanical properties. Moreover, they can be used as rheological modifier, emulsifier, or for barrier properties, and their surface chemistry opens the door to numerous feasible chemical modifications, leading to a large panel of applications in medical, electronic, composites, or packaging, for example. Traditionally, their extraction is performed via monitored sulfuric acid hydrolysis, leading to well-dispersed aqueous CNC suspensions; these last bearing negative charges (half-sulfate ester groups) at their surface. More recently, natural chemicals called deep eutectic solvents (DESs) have been used for the production of CNC in a way of green chemistry, and characterization of recovered CNC is encouraging

Urethanes and polyurethanes from suberin: 1. Kinetic study

Within the context of a study on the preparation and the characterization of polyurethanes based on suberin, as a polyol, and conventional polyisocyanates, it was deemed necessary to carry out a preliminary study on the reactivity of the hydroxy functions of suberin. Aliphatic and aromatic mono- and di-isocyanates were tested and the kinetics of this system followed the classical second order up to conversions of about 85%. The influence of the steric hindrance and the electronic factors, linked to the specific structures of both types of isocyanates, was established.info:eu-repo/semantics/publishedVersio

Surface properties of suberin

The surface energy of suberin was determined by four different methods, namely, (i) contact angle measurements, (ii) Wilhelmy plate measurements, (iii) maximum bubble pressure, and (iv) inverse gas chromatography (IGC). The first three methods gave a gammasub value in the range 40-50 mN m-1 at room temperature. The major component of this value reflects the dispersive contribution. The IGC measurements showed a higher dispersive term, which is common with this method of characterization. The surface acid (A)/base (B) properties were also evaluated, and the results indicated that suberin has an acidic character.info:eu-repo/semantics/publishedVersio

Surface modification of banana-based lignocellulose fibres

Lignocellulosic raw materials were isolated from rachis of Musa acuminata Colla var. cavendish and characterised before and after chemical modification. The rachis was submitted to different mechanical treatments, milling and defibration, resulting in rachis powder and rachis fi bers, respectively. The chemical composition of these two samples was established and it was shown that rachis fibres exhibited higher polysaccharide and lignin contents and lower amounts of ash and extractives components, as compared with the rachis powder. The effects of solvent extrac tion, alkali treatment and chemical modification using phenyl isocyanate, maleic anhydride, alkenyl succinic anhydride and alkyl ketone dimer as grafting agents were studied. The materials were characterized in terms of chemical structure by ATR–FT-IR and 13C-CP-MAS-NMR spectroscopy, morphology by scanning electron microscopy and surface energies by inverse gas chromatography and contact angle measurements. The surface energy of these materials was found to be very close to other similar lignocellulosic materials. Finally, the water absorption of these materials before and after treatment was ascertained. The modified fibres showed considerable changes in ATR–FT-IR and 13C-CP-MAS-NMR spectra and surface properties, providing very convincing evidence that chemical grafting had occurred.info:eu-repo/semantics/publishedVersio

POLYPYRROLE SYNTHESIS VIA CARBOXYMETHYLCELLULOSE-IRON COMPLEXES

Polypyrrole (PPy) was chemically synthesised at two pH levels (pH = 2 and unadjusted pH, i.e. 6.6) using pre-formed carboxymethylcellulose-iron (CMC-Fe) complexes. The CMC-Fe complexes were prepared at a fixed CMC concentration, i.e. 5.5x10-5 mol/L, and with an increasing FeCl3 amount (from 4x10-3 to 5x10-2 mol/L). The quantity of iron bound to CMC was determined by the inductively coupled plasma (ICP-MS) method. In order to understand the interactions between CMC and iron, speciation of the systems was simulated by Phreeqc software. SEM analysis showed that, in some conditions (particularly at pH = 2), Py polymerised within the CMC-Fe complexes, forming particles with size ranging between 300 and 600 nm. In order to evaluate polymer electric conductivity, films were prepared by direct casting of the PPy-CMC-Fe dispersions with and without addition of film-forming CMC, and bulky PPy-CMC-Fe pellets were obtained by compression. Despite the different arrangement PPy-CMC-Fe particles in dry films, the amount of iron bound to CMC during the formation of CMC-Fe complexes was found to be the dominant parameter affecting polymer conductivity

Multilayers of Renewable Nanostructured Materials with High Oxygen and Water Vapor Barriers for Food Packaging

Natural biopolymers have become key players in the preparation of biodegradable food packaging. However, biopolymers are typically highly hydrophilic, which imposes limitations in terms of barrier properties that are associated with water interactions. Here, we enhance the barrier properties of biobased packaging using multilayer designs, in which each layer displays a complementary barrier function. Oxygen, water vapor, and UV barriers were achieved using a stepwise assembly of cellulose nanofibers, biobased wax, and lignin particles supported by chitin nanofibers. We first engineered several designs containing CNFs and carnauba wax. Among them, we obtained low water vapor permeabilities in an assembly containing three layers, i.e., CNF/wax/CNF, in which wax was present as a continuous layer. We then incorporated a layer of lignin nanoparticles nucleated on chitin nanofibrils (LPChNF) to introduce a complete barrier against UV light, while maintaining film translucency. Our multilayer design which comprised CNF/wax/LPChNF enabled high oxygen (OTR of 3 +/- 1 cm(3)/m(2).day) and water vapor (WVTR of 6 +/- 1 g/m(2).day) barriers at 50% relative humidity. It was also effective against oil penetration. Oxygen permeability was controlled by the presence of tight networks of cellulose and chitin nanofibers, while water vapor diffusion through the assembly was regulated by the continuous wax layer. Lastly, we showcased our fully renewable packaging material for preservation of the texture of a commercial cracker (dry food). Our material showed functionality similar to that of the original packaging, which was composed of synthetic polymers.Peer reviewe

Impact de l’apprentissage systémique sur la motivation à apprendre des étudiants dans un contexte d’apprentissage en milieu clinique

L’environnement, les approches et les méthodes pédagogiques sont des facteurs déterminants pour la motivation à apprendre des étudiants. Dans l’enseignement supérieur des sciences de la santé, l’investigation de la dynamique motivationnelle demeure un sujet peu documenté surtout dans un contexte d’apprentissage en milieu clinique. En réponse à ce manque, une étude mixte a été menée auprès des étudiants de troisième année d’études inscrits à l’école supérieure des sciences et techniques de la santé de Tunis dans le but de comparer les effets de l’apprentissage par objectif et de l’apprentissage systémique sur leur motivation. La collecte des données a concerné 172 étudiants en pré-test et 165 étudiants en post-test, réalisée à l’aide du «  Motived Strategies Learning Questionnaire  » dans sa version traduite et validée selon la méthode de Vallerand (1989). Douze étudiants ont fait l’objet d’un entretien de groupe. Les scores moyens des six échelles de la motivation ont enregistré une nette amélioration en faveur du modèle d’apprentissage systémique à l’exception de l’échelle de l’anxiété aux tests. Le score moyen global a été de 3,93 (é-t = 0,81) pour l’approche par objectif et de 4,94 (é-t = 0,53) pour l’apprentissage systémique. Ces résultats ont révélé une différence statistique significative, montrant un avantage appréciable au profit de l’apprentissage systémique. Les propos des étudiants ont confirmé les résultats statistiques donnant beaucoup plus d’arguments.The environment, pedagogical approaches and methods are determining factors for students’ motivation to learn. In higher education in health sciences, the pursuit of motivational dynamics remains a subject that has been poorly documented, especially in the context of clinical learning. In response to this lack, a mixed-method study was conducted with third-year students enrolled at the Higher School of Health Sciences and Techniques in Tunis in order to compare the effects of learning by objective and systemic learning on their motivation. The data collection concerned 172 students in pre-test and 165 students in post-test, carried out using the “Motived Strategies Learning Questionnaire” in its translated and validated version according to the Vallerand method (1989). Twelve students were the subject of a group interview. The overall average on the six motivation scales showed a marked improvement in favour of the systemic learning model with the exception of the test anxiety scale. The overall average score was 3.93 (S-D = 0.81) for the objective approach and 4.94 (S-D = 0:53) for systemic learning. These results revealed a significant statistical difference, showing an appreciable advantage in favour of systemic learning. The students’ comments confirmed the statistical results giving a lot more arguments

Simulation basis for a techno-economic evaluation of chitin nanomaterials production process using Aspen Plus® software

Process simulation is a useful tool that has been widely used to analyze, design and optimize energy balances in chemical technologies including those related to biomass processing, biorefinery processes and chemical engineering. The presented data set serves as basis for the simulation of chitin purification, nanofibers and nanocrystals production processes, considering laboratory experimental procedures described in previous experimental articles.Peer ReviewedPostprint (published version