Cellulose consolidation under high-pressure and high-temperature uniaxial compression

Materials based on cellulose cannot be obtained from thermoplastic processes. Our aim is to prepare all-cellulose materials by uniaxial high pressure thermocompression of cellulose. The effect of moisture content (0–8 w/w%) and temperature (175–250 °C) was characterized through the mechanical properties (bending and tensile), morphology (scanning electron microscopy, X-ray tomography) and microstructure (viscometric degree of polymerization, Raman spectroscopy, X-ray diffraction, solid-state NMR) of the specimens. The specimens were mechanically stronger in bending than in tension. They exhibited a more porous heart, a dense but very thin skin on the faces (orthogonal to the compression axis) and thick and extremely dense sides. During thermocompression severe friction between fibers caused a decrease in molecular weight while heating above the glass transition temperature was responsible for water migration towards the specimen heart. Most of the cohesion came from the small sides of the test samples (parallel to the compression axis) and seemed mainly related to the entanglement of amorphized cellulose at the interface between particles. Around 200 °C water accumulated and provoked delamination upon pressure release, but at higher temperatures water, in a subcritical state, may have been consumed during the hydrolysis of amorphous cellulose regions. The all-cellulose material with the best mechanical properties was obtained at 2% moisture and 250 °C. This work shows that thermocompression at high temperature with limited moisture may be viable to produce renewable, sustainable all-cellulose materials for application in biobased plastic substitutes including binderless boards

Interplay between Structure and Dynamics in Chitosan Films Investigated with Solid-State NMR, Dynamic Mechanical Analysis, and X-ray Diffraction

Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films. Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Cl⁻) was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Cl⁻ counterions act as a defect and impair the long-range organization by immobilizing hydration water. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content

Etude par RMN du solide de l'hétérogénéité spatiale et dynamique dans des ahdésifs sensibles à la pression (PSAs) acryliques comparés à des poly(acrylates de n-alkyles) et des poly(méthacrylates de n-alkyles) modèles

Des adhésifs sensibles à la pression (PSAs) acryliques industriels, des polyacrylates et polyméthacrylates de n-alkyles modèles, ont été étudiés principalement par RMN (résonance magnétique nucléaire) du solide. Le but à long terme est de comprendre l'infIndustrial acrylic pressure sensitive adhesives (PSAs), poly(n-alkyl acrylate) and poly(n-alkyl methacrylate) model samples were investigated using predominantly solid-state NMR (nuclear magnetic resonance). The long term goal is to understand the influe

Solid-state NMR investigation of spatial and dynamic heterogeneity in acrylic pressure sensitive adhesives (PSAs) compared to model poly(n-alkyl acrylates) and poly(n-alkyl methacrylates)

Des adhésifs sensibles à la pression (PSAs) acryliques industriels, des polyacrylates et polyméthacrylates de n-alkyles modèles, ont été étudiés principalement par RMN (résonance magnétique nucléaire) du solide. Le but à long terme est de comprendre l’influence des propriétés microscopiques sur l’adhésion. Notre contribution est l’apport d’outils analytiques pour la caractérisation du branchement, de la dynamique locale et de l’hétérogénéité dynamique. Après comparaison de plusieurs techniques de RMN 13C, une méthode de quantification du branchement dans les poly(acrylates d’alkyles) par irradiation simple de l’échantillon fondu sous rotation à l’angle magique (MAS) a été proposée. Cela a permis la première estimation fiable du branchement dans les poly(acrylates d’alkyles) et est applicable directement aux échantillons industriels réticulés et multi-composants. Cela facilitera la compréhension du procédé de polymérisation. Dans le cadre d’une meilleure compréhension du mécanisme d’adhésion, une méthode de chromatographie d’exclusion stérique (SEC) multi-détection a été proposée pour la détection des longues branches (LCB) dans les poly(acrylates d’alkyles) solubles. L’utilisation de la RMN du solide pour la quantification sélective de mouvements locaux dans des polymères fondus sans marquage isotopique a été étudiée. La technique expérimentale est la même que celle de la diffusion de spin 1H conventionnelle avec filtre dipolaire, beaucoup utilisée antérieurement pour quantifier la taille d’hétérogénéités dynamiques dans des polymères ayant un fort contraste dynamique. Dans les poly(acrylates d’alkyles) et les poly(méthacrylates de n-alkyles), qui présentent un contraste dynamique faible au sein de l’unité monomère, la dynamique entravée des chaînes latérales dans les nanodomaines alkyles a été quantifiée via une analyse de relaxation croisée. Industrial acrylic pressure sensitive adhesives (PSAs), poly(n-alkyl acrylate) and poly(n-alkyl methacrylate) model samples were investigated using predominantly solid-state NMR (nuclear magnetic resonance). The long term goal is to understand the influence of their microscopic properties on adhesion. Our contribution was to provide analytical tools to characterize branching, local dynamics and dynamic heterogeneity of poly(alkyl acrylates). Several 13C NMR techniques were compared for branching quantification in poly(alkyl acrylates) and single pulse excitation of the molten sample under magic angle spinning (MAS) was proved to be the most accurate. This provided the first reliable estimate of branching in poly(alkyl acrylates) and is directly applicable to crosslinked and multi-component industrial samples. This will help the understanding of the polymerization process for these samples. In the context of a better understanding of the adhesion mechanism, an alternative method of multiple detection size exclusion chromatography (SEC) was presented to detect long branches (LCB) in soluble poly(alkyl acrylates). Extensive experimental and theoretical work will be necessary to obtain quantitative results. The use of solid-state NMR to quantify local motion of specific chemical sites in non isotopically labeled polymeric samples in the melt was investigated. The experimental scheme is the same as conventional 1H spin diffusion with dipolar filter, previously widely used to quantify the size of dynamic heterogeneities in polymeric samples exhibiting a strong dynamic contrast. In poly(alkyl acrylates) and poly(alkyl methacrylates) with a weak dynamic contrast within the monomeric unit, the hindered dynamics of the side chains in alkyl nanodomains was quantified via cross-relaxation analysis

Etude par RMN du solide de l'hétérogénéité spatiale et dynamique dans des ahdésifs sensibles à la pression (PSAs) acryliques comparés à des poly(acrylates de n-alkyles) et des poly(méthacrylates de n-alkyles) modèles

Des adhésifs sensibles à la pression (PSAs) acryliques industriels, des polyacrylates et polyméthacrylates de n-alkyles modèles, ont été étudiés principalement par RMN (résonance magnétique nucléaire) du solide. Le but à long terme est de comprendre l'influence des propriétés microscopiques sur l'adhésion. Notre contribution est l'apport d'outils analytiques pour la caractérisation du branchement, de la dynamique locale et de l'hétérogénéité dynamique.Après comparaison de plusieurs techniques de RMN 13C, une méthode de quantification du branchement dans les poly(acrylates d'alkyles) par irradiation simple de l'échantillon fondu sous rotation à l'angle magique (MAS) a été proposée. Cela a permis la première estimation fiable du branchement dans les poly(acrylates d'alkyles) et est applicable directement aux échantillons industriels réticulés et multi-composants. Cela facilitera la compréhension du procédé de polymérisation.Dans le cadre d'une meilleure compréhension du mécanisme d'adhésion, une méthode de chromatographie d'exclusion stérique (SEC) multi-détection a été proposée pour la détection des longues branches (LCB) dans les poly(acrylates d'alkyles) solubles. L'utilisation de la RMN du solide pour la quantification sélective de mouvements locaux dans des polymères fondus sans marquage isotopique a été étudiée. La technique expérimentale est la même que celle de la diffusion de spin 1H conventionnelle avec filtre dipolaire, beaucoup utilisée antérieurement pour quantifier la taille d'hétérogénéités dynamiques dans des polymères ayant un fort contraste dynamique. Dans les poly(acrylates d'alkyles) et les poly(méthacrylates de n-alkyles), qui présentent un contraste dynamique faible au sein de l'unité monomère, la dynamique entravée des chaînes latérales dans les nanodomaines alkyles a été quantifiée via une analyse de relaxation croisée.Industrial acrylic pressure sensitive adhesives (PSAs), poly(n-alkyl acrylate) and poly(n-alkyl methacrylate) model samples were investigated using predominantly solid-state NMR (nuclear magnetic resonance). The long term goal is to understand the influence of their microscopic properties on adhesion. Our contribution was to provide analytical tools to characterize branching, local dynamics and dynamic heterogeneity of poly(alkyl acrylates).Several 13C NMR techniques were compared for branching quantification in poly(alkyl acrylates) and single pulse excitation of the molten sample under magic angle spinning (MAS) was proved to be the most accurate. This provided the first reliable estimate of branching in poly(alkyl acrylates) and is directly applicable to crosslinked and multi-component industrial samples. This will help the understanding of the polymerization process for these samples.In the context of a better understanding of the adhesion mechanism, an alternative method of multiple detection size exclusion chromatography (SEC) was presented to detect long branches (LCB) in soluble poly(alkyl acrylates). Extensive experimental and theoretical work will be necessary to obtain quantitative results. The use of solid-state NMR to quantify local motion of specific chemical sites in non isotopically labeled polymeric samples in the melt was investigated. The experimental scheme is the same as conventional 1H spin diffusion with dipolar filter, previously widely used to quantify the size of dynamic heterogeneities in polymeric samples exhibiting a strong dynamic contrast. In poly(alkyl acrylates) and poly(alkyl methacrylates) with a weak dynamic contrast within the monomeric unit, the hindered dynamics of the side chains in alkyl nanodomains was quantified via cross-relaxation analysis

Etude par RMN du solide de l'hétérogénéité spatiale et dynamique dans des ahdésifs sensibles à la pression (PSAs) acryliques comparés à des poly(acrylates de n-alkyles) et des poly(méthacrylates de n-alkyles) modèles

Des adhésifs sensibles à la pression (PSAs) acryliques industriels, des polyacrylates et polyméthacrylates de n-alkyles modèles, ont été étudiés principalement par RMN (résonance magnétique nucléaire) du solide. Le but à long terme est de comprendre l'influence des propriétés microscopiques sur l'adhésion. Notre contribution est l'apport d'outils analytiques pour la caractérisation du branchement, de la dynamique locale et de l'hétérogénéité dynamique.Après comparaison de plusieurs techniques de RMN 13C, une méthode de quantification du branchement dans les poly(acrylates d'alkyles) par irradiation simple de l'échantillon fondu sous rotation à l'angle magique (MAS) a été proposée. Cela a permis la première estimation fiable du branchement dans les poly(acrylates d'alkyles) et est applicable directement aux échantillons industriels réticulés et multi-composants. Cela facilitera la compréhension du procédé de polymérisation.Dans le cadre d'une meilleure compréhension du mécanisme d'adhésion, une méthode de chromatographie d'exclusion stérique (SEC) multi-détection a été proposée pour la détection des longues branches (LCB) dans les poly(acrylates d'alkyles) solubles. L'utilisation de la RMN du solide pour la quantification sélective de mouvements locaux dans des polymères fondus sans marquage isotopique a été étudiée. La technique expérimentale est la même que celle de la diffusion de spin 1H conventionnelle avec filtre dipolaire, beaucoup utilisée antérieurement pour quantifier la taille d'hétérogénéités dynamiques dans des polymères ayant un fort contraste dynamique. Dans les poly(acrylates d'alkyles) et les poly(méthacrylates de n-alkyles), qui présentent un contraste dynamique faible au sein de l'unité monomère, la dynamique entravée des chaînes latérales dans les nanodomaines alkyles a été quantifiée via une analyse de relaxation croisée.Industrial acrylic pressure sensitive adhesives (PSAs), poly(n-alkyl acrylate) and poly(n-alkyl methacrylate) model samples were investigated using predominantly solid-state NMR (nuclear magnetic resonance). The long term goal is to understand the influence of their microscopic properties on adhesion. Our contribution was to provide analytical tools to characterize branching, local dynamics and dynamic heterogeneity of poly(alkyl acrylates).Several 13C NMR techniques were compared for branching quantification in poly(alkyl acrylates) and single pulse excitation of the molten sample under magic angle spinning (MAS) was proved to be the most accurate. This provided the first reliable estimate of branching in poly(alkyl acrylates) and is directly applicable to crosslinked and multi-component industrial samples. This will help the understanding of the polymerization process for these samples.In the context of a better understanding of the adhesion mechanism, an alternative method of multiple detection size exclusion chromatography (SEC) was presented to detect long branches (LCB) in soluble poly(alkyl acrylates). Extensive experimental and theoretical work will be necessary to obtain quantitative results. The use of solid-state NMR to quantify local motion of specific chemical sites in non isotopically labeled polymeric samples in the melt was investigated. The experimental scheme is the same as conventional 1H spin diffusion with dipolar filter, previously widely used to quantify the size of dynamic heterogeneities in polymeric samples exhibiting a strong dynamic contrast. In poly(alkyl acrylates) and poly(alkyl methacrylates) with a weak dynamic contrast within the monomeric unit, the hindered dynamics of the side chains in alkyl nanodomains was quantified via cross-relaxation analysis.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Size-exclusion chromatography (SEC) of branched polymers and polysaccharides

Branched polymers are among the most important polymers, ranging from polyolefins to polysaccharides. Branching plays a key role in the chain dynamics. It is thus very important for application properties such as mechanical and adhesive properties and digestibility. It also plays a key role in viscous properties, and thus in the mechanism of the separation of these polymers in size-exclusion chromatography (SEC). Critically reviewing the literature, particularly on SEC of polyolefins, polyacrylates and starch, we discuss common pitfalls but also highlight some unexplored possibilities to characterize branched polymers. The presence of a few long-chain branches has been shown to lead to a poor separation in SEC, as evidenced by multiple-detection SEC or multidimensional liquid chromatography. The local dispersity can be large in that case, and the accuracy of molecular weight determination achieved by current methods is poor, although hydrodynamic volume distributions offer alternatives. In contrast, highly branched polymers do not suffer from this extensive incomplete separation in terms of molecular weight

Versatility of the dipolar filter selection: From 1H nuclear spin diffusion experiment to the measurement of nuclear Overhauser effect in homopolymer melts

Dipolar filters select 1H magnetization according to local dipolar dephasing, which corresponds to site mobility in systems with heterogeneous molecular mobility. Combined with a conventional exchange experiment, it is usually applied to polymeric samples exhibiting structures on the nanometer length scale associated with a strong dynamic contrast. There, the resulting 1H nuclear spin diffusion experiment yields the size of the structure. When the same experiment is applied to homopolymer melts exhibiting a weak dynamic contrast and dynamic heterogeneities on significant shorter length scales, the recorded magnetization decay is in agreement with decays expected from a heterogeneous nanostructure. However, dipolar filters actually can also select mobile parts of the repeat unit, e.g. the end of the alkyl side chains and the subsequent magnetization transfer then can occur via cross relaxation due to non coherent zero-quantum transitions (nuclear Overhauser effect, NOE). The difficulties of distinguishing these two cases are examined and it is demonstrated that NOE experiments exploiting magnetization selection via the dipolar filter allow quantifying the local dynamics of the side chains. This opens new possibilities for measurements of local dynamics in non isotopically labeled homopolymer melts

Investigation of chain dynamics in poly(n-alkyl methacrylate)s by solid-state NMR : comparison with poly(n-alkyl acrylate)s

PnAMAs exhibit a local nanophase separation associated with intriguing chain dynamics (Macromol. Chem. Phys. 2005, 206, 142). PnAMAs of high molar mass, as determined by SEC and MHKS parameters, were investigated in the melt with a recently-developed solid-state NMR method (NOE with dipolar filter; Solid State Nucl. Magn. Res. 2005, 28, 160). The correlation times are assigned to the relaxation of the alkyl nanodomains, as coupled motions of the main chain and hindered local modes in the side chain. Comparison with poly(n-alkyl acrylates) shows a higher anisotropy of the main chain motions and a better organized local nanophase separation in PnAMAs