Structural Variations in Biobased Polyfurfuryl Alcohol Induced by Polymerization in Water.

Poly(furfuryl alcohol) is a thermostable biobased thermoset. The polymerization of furfuryl alcohol (FA) is sensitive to a number of side reactions, mainly the opening of the furan ring into carbonyl species. Such carbonyls can be used to introduce new properties into the PFA materials through derivatization. Hence, better understanding of the furan ring opening is required to develop new applications for PFA. This article studies the structural discrepancies between a PFA prepared in neat conditions versus a PFA prepared in aqueous conditions, i.e., with more carbonyls, through NMR and MALDI ToF. Overall, the PFA prepared in water exhibited a structure more heterogeneous than the PFA prepared in neat conditions. The presence of ketonic derivatives such as enols and ketals were highlighted in the case of the aqueous PFA. In this line, the addition of water at the beginning of the polymerization stimulated the production of aldehydes by a factor two. Finally, the PFA prepared in neat conditions showed terminal lactones instead of aldehydes.

Mechanical Behaviour and Induced Microstructural Development upon Simultaneous and Balanced Biaxial Stretching of Poly(ethylene furandicarboxylate), PEF.

The biaxial behavior of PEF has been analyzed for equilibrated and simultaneous biaxial stretching. The ability of PEF to develop an organized microstructure through strain induced crystallization (SIC) has been described. Upon biaxial stretching, SIC can be difficult to perform because the stretching is performed in two perpendicular directions. However, thanks to the time/temperature superposition principle and an accurate heating protocol, relevant stretching settings have been chosen to stretch the material in its rubbery-like state and to reach high levels of deformation. By the protocol applied, the mechanical behavior is easily transposable to the industry. This work has shown that PEF can, as in uniaxial stretching, develop well-organized crystals and a defined microstructure upon biaxial stretching. This microstructure allows the obtention of improved mechanical properties and thermal stability of the biaxially stretched samples. The crystals induced upon biaxial stretching are similar to the one that has been developed and observed after uniaxial stretching and upon static crystallization. Moreover, the furan cycles seem to appear in a state similar to the one of a sample crystallized upon quiescent condition. The rigidity is increased, and the α-relaxation temperature is increased by 15 °C.

Exploring New Horizons for Bio-Based Poly(furfuryl alcohol) by Exploiting Functionalities Offered by Side Reactions.

Poly(furfuryl alcohol) is a bio-based thermoset resin with a limited application portfolio due to its brittleness. Side ring-opening reactions that occur during polymerization lead to carbonyl moieties. Such unique self-generated functionality was exploited to generate tough and ductile materials via the creation of Schiff-based macromolecular architectures.

Conditions to Control Furan Ring Opening during Furfuryl Alcohol Polymerization.

The chemistry of biomass-derived furans is particularly sensitive to ring openings. These side reactions occur during furfuryl alcohol polymerization. In this work, the furan ring-opening was controlled by changing polymerization conditions, such as varying the type of acidic initiator or the water content. The degree of open structures (DOS) was determined by quantifying the formed carbonyl species by means of quantitative 19F NMR and potentiometric titration. The progress of polymerization and ring opening were monitored by DSC and FT-IR spectroscopy. The presence of additional water is more determining on ring opening than the nature of the acidic initiator. Qualitative structural assessment by means of 13C NMR and FT-IR shows that, depending on the employed conditions, poly(furfuryl alcohol) samples can be classified in two groups. Indeed, either more ester or more ketone side groups are formed as a result of side ring opening reactions. The absence of additional water during FA polymerization preferentially leads to opened structures in the PFA bearing more ester moieties.

Furanic Humins from Biorefinery as Biobased Binder for Bitumen.

To decrease the environmental impact of bitumen, more sustainable binders should be proposed. This study emphasizes how industrial humins co-produced during the biorefining of carbohydrates can be employed as a macromolecular binder for bitumen. Humins are heterogeneous polyfuranic compounds, and they were mixed at 50 wt% with bitumen. When the non-water-soluble fractions of humins were employed (Hns), no variation of the chemical structure was observed in FTIR spectra after the mixing. The DSC investigations showed that the crystallization of aromatic fractions in bitumen shifted to higher temperature for humins' modified bitumen. The thermogravimetric data highlighted that the presence of humins or Hns in bitumen can lead to mass loss below 200 °C. The rheological investigations highlighted some key advantages of using humins or Hns with bitumen. At high temperatures, the storage modulus of the modified bitumen is increased and shows lower susceptibility to variations in frequency. At low temperatures, the phase angle of Hns-modified bitumen is lower than that of bitumen, suggesting less temperature susceptibility as a consequence of a cross-linked network formation.

Comparative Analysis of the Mechanical Behaviour of PEF and PET Uniaxial Stretching Based on the Time/Temperature Superposition Principle.

Poly(ethylene 2,5-furandicarboxylate), PEF and poly(ethylene terephthalate), PET, are two polyesters with close chemical structures. It leads to similar thermal, mechanical and barrier properties. In order to optimize their stretching, a strategy based on the time/temperature principle is used. The building of master curves, in the linear visco-elastic domain, allows the identification of the experimental conditions for which the two materials are in the same physical state. The initial physical state of the materials is important as, to fit with the industrial constrains, the polymers must reach high level of deformation, and develop strain induced crystallization (SIC). In this paper, the screening of the forming range is described, as well as the mechanical response depending on the stretching settings. Moreover, the same mechanical response can exist for PEF and PET if the same gap from the α-relaxation exists.

Non-Furanic Humins-Based Non-Isocyanate Polyurethane (NIPU) Thermoset Wood Adhesives.

Predominantly non-furanic commercial humins were used to prepare humin-based non-isocyanate polyurethane (NIPU) resins for wood panel adhesives. Pure humin-based NIPU resins and tannin-humin NIPU resins were prepared, the latter to upgrade the humins' performance. Species in the raw humins and species formed in the NIPU resins were identified by Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI ToF) spectrometry and Fourier Transform Infrared (FTIR). Humins, fulvic acid and derivatives, humic acid and its fragments, some lignans present and furanic oligomers present formed NIPU linkages. Thermomechanical analysis (TMA) showed that as with other biomaterials-based NIPU resins, all these resins also showed two temperature peaks of curing, the first around 130 °C and the second around 220 °C. A decrease in the Modulus of Elasticity (MOE) between the two indicated that the first curing period corresponded to linear growth of the oligomers forming a physical entanglement network. This then disentangled, and the second corresponded to the formation of a chemical cross-linked network. This second peak was more evident for the tannin-humin NIPU resins. All the laboratory particleboard made and tested either bonded with pure humins or with tannin-humin NIPU adhesives satisfied well the internal bond strength requirements of the relevant standard for interior grade panels. The tannin-humin adhesives performed clearly better than the pure humins one.

Ambient Temperature Self-Blowing Tannin-Humins Biofoams.

Ambient temperature self-blowing tannin-furanic foams have been prepared by substituting a great part-even a majority-of furfuryl alcohol with humins, a polyfuranic material derived from the acid treatment at high temperature of fructose. Closed-cell foams were prepared at room temperature and curing, while interconnected-cell foams were prepared at 80 °C and curing, this being due to the more vigorous evaporation of the solvent. These foams appear to present similar characteristics as other tannin-furanic foams based only on furfuryl alcohol. A series of tannin-humins-furfuryl alcohol oligomer structures have been defined indicating that all three reagents co-react. Humins appeared to react well with condensed tannins, even higher molecular weight humins species, and even at ambient temperature, but they react slower than furfuryl alcohol. This is due to their high average molecular weight and high viscosity, causing their reaction with other species to be diffusion controlled. Thus, small increases in solvent led to foams with less cracks and open structures. It showed that furfuryl alcohol appears to also have a role as a humins solvent, and not just as a co-reagent and self-polymerization heat generator for foam expansion and hardening. Stress-strain for the different foams showed a higher compressive strength for both the foam with the lowest and the highest proportion of humins, thus in the dominant proportions of either furfuryl alcohol or the humins. Thus, due to their slower reactivity as their proportion increases to a certain critical level, more of them do proportionally participate within the expansion/curing time of the foam to the reaction.

A Perspective on PEF Synthesis, Properties, and End-Life.

This critical review considers the extensive research and development dedicated, in the last years, to a single polymer, the poly(ethylene 2,5-furandicarboxylate), usually simply referred to as PEF. PEF importance stems from the fact that it is based on renewable resources, typically prepared from C6 sugars present in biomass feedstocks, for its resemblance to the high-performance poly(ethylene terephthalate) (PET) and in terms of barrier properties even outperforming PET. For the first time synthesis, properties, and end-life targeting-a more sustainable PEF-are critically reviewed. The emphasis is placed on how synthetic roots to PEF evolved toward the development of greener processes based on ring open polymerization, enzymatic synthesis, or the use of ionic liquids; together with a broader perspective on PEF end-life, highlighting recycling and (bio)degradation solutions.

Kinetics and Chemorheological Analysis of Cross-Linking Reactions in Humins.

Humins is a biomass-derived material, co-product of the acid-catalyzed conversion of cellulose and hemicellulose to platform chemicals. This work presents a thorough study concerning the crosslinking kinetics of humins by chemorheological analysis and model-free kinetics under isothermal and non-isothermal curing. Humins can auto-crosslink under the effect of temperature, and the reaction can be fastener when adding an acidic initiator. Thus, the effect of P-Toluenesulfonic acid monohydrate (pTSA) on the crosslinking kinetics was also studied. The dependencies of the effective activation energy (Eα-dependencies) were determined by an advanced isoconversional method and correlated with the variation of complex viscosity during curing. It is shown that humins curing involves multi-step complex reactions and that the use of an acidic initiator allows faster crosslinking at lower temperatures, involving lower Eα. The shift from chemical to diffusion control was also estimated.

Crystallization of Polytetrafluoroethylene in a Wide Range of Cooling Rates: Nucleation and Diffusion in the Presence of Nanosilica Clusters.

Polytetrafluoroethylene (PTFE) is a polymer that displays exceptional properties. This synthetic fluoropolymer is also known to crystallize very fast upon cooling. The present work highlights for the first time the influence of nanosilica clusters on PTFE crystallization at fast cooling rates (up to 5000 K·s-1). The silica was synthesized from aqueous silicate solution and the surface modification was performed using TriEthoxyFluoroSilane (TEFS). In order to understand the crystallization behavior of PTFE/silica nanocomposite at a fast cooling rate, the measurements were carried out by Fast Scanning Calorimetry (FSC). The data were consequently combined with the measurements performed by conventional Differential Scanning Calorimetry (DSC). Interestingly, the results displayed variation of the crystallization behavior for the nanocomposite at fast cooling rates compared to slow cooling rates. The differences in crystal morphologies were then observed by Scanning Electron Microscopy (SEM) after slow and fast cooling rates. Finally, the effective activation energies (Eα) obtained from the crystallization under various cooling rates were combined in order to obtain one set of Hoffman-Lauritzen parameters. This procedure allowed us to show that the crystallization of PTFE in the presence of silica is promoted or hampered according to the cooling rates employed.

Suberin/trans-Cinnamaldehyde Oil Nanoparticles with Antimicrobial Activity and Anticancer Properties When Loaded with Paclitaxel.

Suberin is a biopolyester that can be extracted from bioresources such as cork trees and may find many applications in food packaging, sealing, and biomedical fields. In this work, we describe for the first time the preparation of suberin nanoparticles using the solvent/antisolvent method. Three different suberin extraction methods from cork trees were used to reveal any differences in the production and properties of the nanoparticles. trans-Cinnamaldehyde, a component of cinnamon essential oil, was added to suberin nanoparticles due to its antimicrobial and/or anticancer properties, and its synergistic effect was studied with the inherent biological properties of suberin. Interestingly, both suberin and suberin/trans-cinnamaldehyde nanoparticles showed very good antimicrobial properties against Staphylococcus aureus and Pseudomonas aeruginosa bacteria, and also against Candida albicans (yeast). Suberin nanoparticles containing trans-cinnamaldehyde loaded with 0.1% w/w paclitaxel provided significant anticancer properties against human hepatocellular carcinoma HepG2 cancer cell lines. This study can be used to explore novel biobased polymers as efficient carriers of essential oils and drugs for infection and cancer therapy, by using minimum amount of drugs and therefore reducing their cytotoxicity and side effects.

Humins from Biorefineries as Thermoreactive Macromolecular Systems.

Conversion of lignocellulosic biomass often brings about the formation of several side products. Among these, a black and viscous coproduct known as humins is formed on acidic treatment of polysaccharides. To improve the efficiency of this process from an economical and environmental perspective, new solutions for humins valorization are urgently needed. This work focuses on the comprehensive understanding of humins with special emphasis on their structure/properties relationships. Humins were subjected to different thermal treatments and characterized by means of structural, thermoanalytical, and rheological investigations. The structure and composition of humins are very diverse and depend on the thermochemical conditions. On sufficient heating, humins change into a nonreversible and more branched furanic structure with a relatively high glass-transition temperature (Tg >65 °C). Thus, humins can be easily processed for preparing thermoset-like resins.

Opening Furan for Tailoring Properties of Bio-based Poly(Furfuryl Alcohol) Thermoset.

This work shows how furan ring-opening reactions were controlled by polymerization conditions to tune the cross-link density in bio-based poly(furfuryl alcohol) (PFA). The influence of water and isopropyl alcohol (IPA) on the polymerization of furfuryl alcohol, and particularly on furan ring-opening, was investigated by means of 13 C NMR and FT-IR spectroscopy. Results indicated that formation of open structures were favored in the presence of solvents, thus leading to modification of the thermo-mechanical properties compared to PFA cross-linked without solvent. Dynamic mechanical analyses showed that when slightly more open structures were present in PFA it resulted in an important decrease of the cross-link density. Despite lower glass-transition temperature and lower elastic modulus for PFA polymerized with solvent, the thermal stability remains very high (>350 °C) even with more open structures in PFA.

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.

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.

Further insights into the kinetics of thermal decomposition during continuous cooling.

Following the previous work (Phys. Chem. Chem. Phys., 2016, 18, 32021), this study continues to investigate the intriguing phenomenon of thermal decomposition during continuous cooling. The phenomenon can be detected and its kinetics can be measured by means of thermogravimetric analysis (TGA). The kinetics of the thermal decomposition of ammonium nitrate (NH4NO3), nickel oxalate (NiC2O4), and lithium sulfate monohydrate (Li2SO4·H2O) have been measured upon heating and cooling and analyzed by means of the isoconversional methodology. The results have confirmed the hypothesis that the respective kinetics should be similar for single-step processes (NH4NO3 decomposition) but different for multi-step ones (NiC2O4 decomposition and Li2SO4·H2O dehydration). It has been discovered that the differences in the kinetics can be either quantitative or qualitative. Physical insights into the nature of the differences have been proposed.

Glass transition dynamics and cooperativity length of poly(ethylene 2,5-furandicarboxylate) compared to poly(ethylene terephthalate).

The glass transition of poly(ethylene 2,5-furandicarboxylate) (PEF), an emergent bio-based polyester, was investigated in comparison to one of its chemical analogues: poly(ethylene terephthalate) (PET). These investigations were conducted at different crystallinities by means of stochastic modulated differential scanning calorimetry (stochastic TMDSC) and dynamic mechanical analysis (DMA). Amorphous PEF presents a higher ΔCp at the glass transition and a broader relaxation spectrum attributed to a higher free volume. The higher Tg of PEF is then purely related to segmental mobility and specific interactions in PEF. The length of cooperative rearranging regions (CRR) was similar for both materials. Additionally, the variations of the effective activation energy E of PEF and PET at glass transitions were determined by isoconversional kinetic analysis. The rate of decrease in E was similar for the two amorphous polyesters. Upon crystallization, the glass transition of PEF is broadened but its temperature range is not increased as with PET. The creation of the rigid amorphous fraction (RAF) with crystallinity is lower in PEF than in PET. The difference in free volume also explains the lower coupling between the crystalline phase and the amorphous phase in PEF.

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.

Melt and glass crystallization of PDMS and PDMS silica nanocomposites.

Silica nanoclusters were homogeneously dispersed into an end-linked PolyDiMethylSiloxane (PDMS) matrix. Dynamic relaxation, glass and melt crystallization of end-linked PDMS-silica nanocomposites (PDMSnanoSi) were compared to those of PDMS. A particular emphasis is made on the kinetic aspects of these transitions by corroborating investigations conducted by means of Dynamic Mechanical Analysis (DMA) and Differential Scanning Calorimetry (DSC). Addition of silica nanoclusters does not modify the relaxation behavior of the amorphous phase and the glass transition kinetics. However, melt and glass crystallizations are significantly promoted in the presence of silica nanoclusters. The secondary crystallization process is more pronounced for PDMSnanoSi and higher crystal perfection due to structuring effects of silica nanoclusters is also highlighted. For the two systems, one set of Hoffman-Lauritzen parameters have been evaluated by combining melt and glass crystallization kinetic data.