Nathanael Guigo

Nonisothermal crystallization of polytetrafluoroethylene in a wide range of cooling rates.

Compared to other semicrystalline polymers, PTFE demonstrates a very fast crystallization process on cooling. This study explores for the first time the nonisothermal PTFE ultrafast crystallization under tremendously fast cooling rates (up to 800,000 K·s(-1)) achieved by using fast scanning calorimetry (FSC) and ultra-fast scanning calorimetry (UFSC). Regular DSC was also used to get crystallization at slower rates. The data obtained on a wide range of cooling rates (over 8 orders of magnitudes) help to get new knowledge about crystallization kinetics of PTFE. Both FSC and UFSC data show that it is impossible to bypass the crystallization and thus to reach a metastable glassy state even for the fastest cooling rate employed (800,000 K·s(-1)). The crystals formed under such conditions are slightly less stable than those produced under slower cooling rates, as reflected by a shift of the melting peak to lower temperature. The difference in crystal morphologies was confirmed by SEM observations. The variation of the effective activation energy (Eα) with the relative extent of crystallization reveals that PTFE crystallization follows a transition from regime II to regime III around 315-312 °C. Corroborated temperature dependences of Eα obtained respectively for crystallizations under slow and fast cooling rates were combined and fitted to the theoretical dependence of the growth rate derived from the Hoffman-Lauritzen theory.

Surface modification of cellulose microfibrils by periodate oxidation and subsequent reductive amination with benzylamine: a topochemical study

Never-dried sulfite wood pulp was beaten and subsequently microfibrillated before being submitted to periodate oxidation for various times. The oxidation progress, which was followed by 13C solid-state NMR spectroscopy in conjunction with degree of oxidation (DO) measurements together with ultrastructural observations, revealed that the cellulose crystallinity and microfibrillar integrity were kept intact until a DO of 0.3/0.4, indicating that at that level, the cellulose microfibrils had been oxidized exclusively at their surface. Beyond this DO value, the sample crystallinity started to deteriorate, as the oxidation progressed toward the core of the microfibrils. Remarkably, throughout the oxidation, the created carbonyl moieties were never observed, as they were readily recombined into hemiacetals by cyclization either within the same anhydro glucose unit (AGU) or with the adjacent un-oxidized AGUs of the same cellulose chain. At DO below 0.3/0.4, hemiacetal coupling with adjacent cellulose chains was also considered, but it appeared unlikely in view of the interchain distance imposed by the crystalline lattice. The oxidized samples were subjected to a reductive amination with benzylamine in order to convert their hydrophilic surfaces into hydrophobic ones. Despite the ease of this derivatization, the analysis of the 13C solid-state NMR spectra of the aminated products showed that, below a DO of 0.3, only half of the hemiacetal moieties could be converted into secondary amine products, whereas the other half remained untouched, likely for steric reasons.

Synthesis, properties and thermal behavior of poly(decylene-2,5-furanoate): a biobased polyester from 2,5-furan dicarboxylic acid

In the present study, an interesting, eco-friendly polyester, poly(decylene-2,5-furanoate) (PDeF) was synthesized from 2,5-furan dicarboxylic acid with a variation of the well-known two-step melt polycondensation method. The crystallization and melting behavior of PDeF, was evaluated with different calorimetric methods; conventional, fast and temperature modulated scanning calorimetry. The results showed that PDeF is a fast crystallizing polyester, with a glass transition close to 1 °C and an equilibrium melting temperature equal to 129.8 °C. Various crystallization temperatures and rates were employed in order to evaluate in detail the thermal characteristics of PDeF. Isothermal and non-isothermal crystallization kinetics were also investigated by means of Avrami, Lauritzen–Hoffman theories and model-free kinetics. The structural features of PDeF were also studied by X-ray diffraction (XRD) and nuclear magnetic resonance (1H-NMR) while the size and density of spherulites was observed by polarized optical microscopy (POM) after crystallization in a wide range of temperatures. Finally, from tensile testing it was realized that PDeF has similar mechanical properties like tensile strength and Youngs modulus to that of low density polyethylene (LDPE).

Complex Kinetic Pathway of Furfuryl Alcohol Polymerization Catalyzed by Green Montmorillonite Clays

Furfuryl alcohol (FA) which is derived from lignocellulosic biomass polymerizes into poly(furfuryl alcohol) (PFA) under acidic catalysis. A greener and more sustainable catalytic route was proposed in order to replace hazardous acidic catalysts. Organically modified montmorillonite (Org-MMT) and, in comparison, sodium MMT (Na-MMT) are used to evaluate the catalytic effect on the FA polymerization. X-ray diffraction (XRD) and transmission electronic microscopy (TEM) show that clay layers have been exfoliated during polymerization. Additional FTIR spectroscopy measurements confirm that furanic oligomers have intercalated between clay layers by cation exchange. An original combination between chemorheological and model-free kinetic analysis allows highlighting the influence of MMT on the overall polymerization pathway. The octadecyl ammonium cation (ODA) was also used as homogeneous acidic catalyst to highlight the specific role of this interlayer cation present in Org-MMT. Interestingly, FA/Org-MMT polymerizes more rapidly than FA/ODA but initiation of polymerization is slightly shifted to higher temperature due to initial intercalation between MMT layers. Then, the dual acidic character (Lewis + Brönsted) of Org-MMT leads to gelation at early stage of polymerization. The results clearly show that exfoliation of MMT layers increases the efficiency of collisions.

Copolymerization as a Strategy to Combine Epoxidized Linseed Oil and Furfuryl Alcohol: The Design of a Fully Bio-Based Thermoset

Epoxidized linseed oil and furfuryl alcohol are bio-sourced monomers known for their high-potential applications in materials science. In this work, we propose the association of these monomers through copolymerization reactions with the target to design fully bio-based thermosets. Herein, investigations on cationic polymerization reactivity have been explored using differential scanning calorimetry. The obtained structures have been confirmed by IR spectroscopy and 2 D NMR spectroscopy, which revealed the principal chain connections. In spite of the multiple capabilities of chemical connections, which include copolymerization and cross-linking, the obtained networks are homogeneous as confirmed by dynamic mechanical analysis and SEM. Furthermore, the copolymer demonstrates a semiductile behavior if subjected to tensile measurements (tensile strain at break ≈40 %), which is a significant advance in terms of its applications as a furanic bio-based thermoset material.

Gelation on heating of supercooled gelatin solutions

Diluted (1.0-1.5 wt%) aqueous gelatin solutions have been cooled to -10 °C at a cooling rate 20 °C min(-1) without freezing and detectable gelation. When heated at a constant heating rate (0.5 -2 °C min(-1)), the obtained supercooled solutions demonstrate an atypical process of gelation that has been characterized by regular and stochastically modulated differential scanning calorimetry (DSC) as well as by isoconversional kinetic analysis. The process is detectable as an exothermic peak in the total heat flow of regular DSC and in the nonreversing heat flow of stochastically modulated DSC. Isoconversional kinetic analysis applied to DSC data reveals that the effective activation energy of the process increases from approximately 75 to 200 kJ mol(-1) as a supercooled solution transforms to gel on continuous heating.

Preparation and crystallization behavior of poly(ethylene 2,5-furandicarboxylate)/cellulose composites by twin screw extrusion

Poly(ethylene 2,5-furandicarboxylate) (PEF), an emerging biobased polyester, was compounded with cellulose via twin-screw extrusion. Different extrusion parameters such as mixing time, screw speed and temperature were employed. Composite thin films containing 1, 2 and 4% cellulose w/w were prepared and compared with neat PEF films. The morphology of PEF/cellulose composites was examined by scanning electron microscopy (SEM) and the molecular weight after extrusion was controlled by means of size exclusion chromatography (SEC). The influence of the cellulose on both isothermal and non-isothermal crystallizations of PEF was investigated by differential scanning calorimetry (DSC). Crystallization is faster in presence of cellulose and the nucleating effect increases with the cellulose concentration.

Tailored design of renewable copolymers based on poly(1,4-butylene 2,5-furandicarboxylate) and poly(ethylene glycol) with refined thermal properties

In the recent years, search for innovative polymers derived from renewable resources resulted in an intense research and development of 2,5-furandicarboxylic acid-based polyesters. Special emphasis has been placed in high-performance polyesters, such as the poly(1,4-butylene 2,5-furandicarboxylate) (PBF)-based structures. In this study, both thermal and crystallisation-thermal properties of PBF have been enlarged simply by the incorporation of other renewable soft moieties in the polymer structure, namely, poly(ethylene glycol) (PEG) moieties. In particular, these novel copolymers can be designed to show some advantageous processing features as revealed by the lower melting temperature (in particular, it could be 107 °C) and higher thermal stability (up to 352–380 °C) as compared with PBF. Moreover, fast scanning calorimetric (FSC) studies of these novel copolymers indicated that crystallisation could be prevented even using relatively slow cooling rates (e.g., 0.1 °C s−1). The judicious selection and balance between hard PBF and soft PEG units enabled a segmented copolymer behaviour.

Preparation and characterization of poly(ethylene 2,5-furandicarboxylate/nanocrystalline cellulose composites via solvent casting

Abstract The effect of nanocrystalline cellulose dispersion on the nonisothermal crystallization of poly(ethylene 2,5-furandicarboxylate) (PEF) has been investigated by means of solvent casting. The cellulose dispersion plays a significant role on the crystallization temperature, thus dispersive equipments of increasing energies were employed to improve the cellulose particles disaggregation. Therefore, ultra-sonic bath, ultra-sonication, and ultra-turrax were used to disperse cellulose nanocrystals in 1,1,1,3,3,3-hexafluoro-2-propanol. Dissolved separately in the same solvent, PEF was then poured into the cellulose suspension before casting. The cellulose whiskers were inspected by transmission electron microscopy. Differential scanning calorimetry was used to measure the crystallization temperature, while scanning electron microscopy visualized the cellulose dispersion at the fracture surface. After investigation on the interaction of cellulose/PEF via Fourier transform infrared spectroscopy, the thermal stability of the blends was measured by means of thermogravimetric analysis.

FA Polymerization Disruption by Protic Polar Solvents

Furfuryl alcohol (FA) is a biobased monomer derived from lignocellulosic biomass. The present work describes its polymerization in the presence of protic polar solvents, i.e., water or isopropyl alcohol (IPA), using maleic anhydride (MA) as an acidic initiator. The polymerization was followed from the liquid to the rubbery state by combining DSC and DMA data. In the liquid state, IPA disrupts the expected reactions during the FA polymerization due to a stabilization of the furfuryl carbenium center. This causes the initiation of the polymerization at a higher temperature, which is also reflected by a higher activation energy. In the water system, the MA opening allows the reaction to start at a lower temperature. A higher pre-exponential factor value is obtained in that case. The DMA study of the final branching reaction occurring in the rubbery state has highlighted a continuous increase of elastic modulus until 290 °C. This increasing tendency of modulus was exploited to obtain activation energy dependences (Eα) of FA polymerization in the rubbery state.