The lignocellulosic biomass is composed of 30% hemicelluloses, which are small polysaccharides. They can lead to interesting chemical platforms that can be declined in various products arousing a growing interest.
In a wood based biorefinery, hemicelluloses were solubilized by water pre-hydrolysis under the form of monosaccharides and oligosaccharides. Then, secondary hydrolysis were performed to convert those oligosaccharides to monosaccharides (acid hydrolysis) or xylans to xyloses (enzymatic hydrolysis).
Applications in the field of product security and authentication to prevent counterfeiting rely on abilities of microscale measurements of printed dots. Thus, researches described in this manuscript have been directed toward the development of measurement methods and apparatus to characterize halftone dot at the microscale.
A polarized reflection optical microscope has been adapted with a commercial digital camera. The Bayer matrix was removed from the surface of the camera and raw images were retrieved. The microscope stage, the camera, the photometer and the thermometer were controlled directly in a Python graphic user interface specifically developed. A high dynamic range capture method was proposed and tuned specifically to obtain richer information on the ink and paper regions. The measurement apparatus and methods helped improve the accuracy and automate the measurements of the halftone dots at the microscale.
The physical and optical dot gains were then separated and analyzed. A Gaussian fitting of the ink and paper histogram peaks was proposed to measure automatically the ink and paper region reflectance as a function of the ink coverage. Thresholding algorithms were applied to separate optical and physical dot gain. An objective threshold evaluation method was developed in order to define the best threshold algorithms for halftone images. The method was based on a simulation of the optical dot gain effects and of the microscope distortions to obtain test images and ground truth images.
Thirty threshold algorithms from literature were evaluated and demonstrated dependency on the ink coverage of the halftones. Two novel threshold algorithms were then developed specifically to process halftones. The first threshold algorithm was based on the determination of the amount of ink peak shift. The second threshold algorithm proposed a pretreatment of the images by applying a pseudo-deconvolution strategy, removing the optical dot gain from the halftones. Characterizations of the optical and physical dot gains were then conducted analyzing 2708 different halftones.
Finally, a physical dot gain model and an optical dot gain model were proposed in order to predict the halftone reflectances from raster to print. The physical dot gain model was based on the generation of single ink particles placed according to a probability mask and on a fusion of the ink particles. The model was evaluated with 43269 dot morphologies that were captured automatically on the microscope. A novel halftone reflectance model was proposed based on a double convolution with two different paper point spread functions. It allowed an accurate reproduction of the main effects of the light diffusion with, at the same time, an accurate reproduction of the light entrapment near the edges of the dots.
Today recovered papers and boards are recycled into similar products; in particular old corrugated boards are transformed into new corrugated boxes. Rich in lignocellulosic material, recovered carton boards might replace wood for the production of higher added-value products. The thesis work investigated the potential of existing processes for delignification, bleaching and cellulose purification, applied on fiber mixes simulating the composition of various carton boards, for the production of bleached paper pulp and dissolving pulp grades.
The treatment was composed of a Kraft cook, followed by a conventional D0-Ep-D1 bleaching sequence, and in the case of dissolving pulp production, a CCE stage for cellulose purification was added. Because carton boards exhibit various fiber compositions, all the study has been conducted on model mixes, made of fibers from unbleached Kraft pulp and mechanical pulp. In all cases, fully bleached pulps have been successfully obtained, although pulp viscosity was sometimes below the standards. Moreover bleached pulps were found difficult to purify. Overall, it has been shown that the quality of the final product, the performances of the processes and their environmental impact, depended on the fiber composition of the mix. Finally, the treatment of an industrial carton board revealed that mineral fillers contained in the material limited its upcycling.
Because of the low quality of the bleached pulp produced, another valorization way has been investigated: the production of oxidized cellulose for cellulose nanofibrils (NFC). A new pre-oxidation process for unbleached Kraft pulp has been developed, combining bleaching and oxidation of the substrate in a single stage including the use of TEMPO as a catalyst and oxidative agents commonly applied in fiber production lines. NFC of the same quality as those produced from bleached Kraft pulp by the classical TEMPO/NaClO/NaBr pre-oxidation system have been obtained.
11 february 2019 - Materials, Mechanical, Civil Engineering, Electrochemistry Ph.D. title
Functionalization of cellulose nanofibrils for the development of biobased medical devices.
Julien BRAS, Associate Professor HDR, Grenoble INP-Pagora / LGP2 ♦♦ Naceur BELGACEM, Professor, Grenoble INP-Pagora / LGP2 ♦♦ Elisa ZENO, Research Engineer (CTP)
In line with the ever-increasing academic and industrial interest for wood derived nanocellulose, the present work investigates the chemical surface modification of cellulose nanofibrils (CNFs) for biomedical application.
Drugs and prodrugs of active principle ingredients (APIs) were covalently immobilized or adsorbed onto CNFs films or suspensions. For covalent immobilization, the first strategy selected calls for water-based and single step esterification of CNF films. The resulting materials demonstrated antibacterial activity against both gram-positive and gram-negative bacterial strains, with a prolonged contact-active effect.
In the second strategy, CNFs suspensions were modified through a multistep reaction, involving amidation and click chemistry, still water-based. Highly innovative characterization tools, such as dynamic nuclear polarization (DNP) enhanced nuclear magnetic resonance (NMR), complemented well-established techniques to confirm the success of grafting.
In parallel to covalent immobilization, an adsorption strategy was also adopted, on both CNFs films and suspensions. Then, the CNF films with grafted or adsorbed APIs were used for preparing 100% CNF membrane for potential topical applications. Another component of this work used CNF suspensions with grafted or adsorbed APIs that were embedded in collagen matrices to prepare composites for designing soft tissue repair implants. Antibacterial activity against both aerobic and anaerobic bacteria, together with controlled release properties were assessed confirming that such composites present the expected active properties, and can be used for the design of innovative medical devices.
The CERISE project, conducted under the auspices of the Tec21 Laboratory of Excellence and the Carnot PolyNat Institute, aims to develop a new process for manufacturing cellulose nanofibrils (CNF) with a high dry matter content and low energy consumption. Twin screw extrusion (TSE) – industrially well-known energy-efficient and highly adaptable technique – was optimized to produce CNF at 20 % dry content. By decreasing considerably their water content, this new strategy improves their transport cost, their storage and extends their field of application.
The objectives were to
• Develop new pretreatments of cellulose fibers to facilitate the nanofibrillation and produce high quality functionalized CNF.
• Optimize TSE screw profile and conditions to produce CNF.
• Prepare new materials made of this new type of CNF.
Four chemical pretreatments, identified as easily industrializable, have been optimized. Extrusion nanofibrillation was simulated by software to obtain optimal extrusion conditions. This cost-effective approach was validated at semi-industrial scale. Various applications are considered for these new NFC with a high dry matter content.