Luc Avérous

Cellulose-Based Bio- and Nanocomposites: A Review

Cellulose macro- and nanofibers have gained increasing attention due to the high strength and stiffness, biodegradability and renewability, and their production and application in development of composites. Application of cellulose nanofibers for the development of composites is a relatively new research area. Cellulose macro- and nanofibers can be used as reinforcement in composite materials because of enhanced mechanical, thermal, and biodegradation properties of composites. Cellulose fibers are hydrophilic in nature, so it becomes necessary to increase their surface roughness for the development of composites with enhanced properties. In the present paper, we have reviewed the surface modification of cellulose fibers by various methods. Processing methods, properties, and various applications of nanocellulose and cellulosic composites are also discussed in this paper.

Mixed culture polyhydroxyalkanoate (PHA) production from volatile fatty acid (VFA)-rich streams: effect of substrate composition and feeding regime on PHA productivity, composition and properties.

In this study, the possibility of manipulating biopolymer composition in mixed culture polyhydroxyalkanoate (PHA) production from fermented molasses was assessed by studying the effects of substrate volatile fatty acid (VFA) composition and feeding regime (pulse wise versus continuous). It was found that the use of a continuous feeding strategy rather than a pulse feeding strategy can not only help mitigate the process constraints of the pulse-feeding strategy (resulting in higher specific and volumetric productivities) but also be used as means to broaden the range of polymer structures. Continuous feeding increased the hydroxyvalerate content by 8% relatively to that obtained from the same feedstock using pulse wise feeding. Therefore, the feeding strategy can be used to manipulate polymer composition. Furthermore, the range of PHA compositions, copolymers of P(HB-co-HV) with HV fraction ranging from 15 to 39%, obtained subsequently resulted in different polymer properties. Increasing HV content resulted in a decrease of the average molecular weight, the glass transition and melting temperatures and also in a reduction in the crystallinity degree from a semi-crystalline material to an amorphous matrix.

New approach to elaborate exfoliated starch-based nanobiocomposites.

The present paper reports the successful elaboration of exfoliated plasticized starch-based nanobiocomposites. This was made possible by using cationic starch as a new clay organomodifier to better match the polarity of the matrix and thus to facilitate the clay exfoliation process. To demonstrate the efficiency of this new approach, either natural (MMT-Na) or organomodified (OMMT-CS) montmorillonite were incorporated into the starch nanobiocomposites by a melt blending process. The morphological analyses (SAXD and TEM) showed that MMT-Na leads to the formation of intercalated nanobiocomposites. On the contrary, OMMT-CS allowed the elaboration of well-exfoliated nanobiocomposites. Tensile tests performed on the obtained nanobiocomposites showed that exfoliated nanobiocomposites display enhanced mechanical properties compared to those of the intercalated nanobiocomposites and neat matrix. These results clearly highlight the great interest in using OMMT-CS to obtain starch-based nanobiocomposites with improved properties.

Original biobased nonisocyanate polyurethanes: solvent- and catalyst-free synthesis, thermal properties and rheological behaviour†

Novel biobased NonIsocyanate PolyUrethanes (NIPUs) were synthesized from dimer-based diamines and sebacic biscyclocarbonate in bulk, and without catalyst. All synthesized NIPUs present biobased contents around 80%. Biscyclocarbonates and final NIPUs were characterized by FTIR and NMR spectroscopy. A specific study was conducted to determine the best carbonate to amine ratio. The influence on the structures and properties of NIPUs with different average amine functionalities, varying from 2.0 to 2.2, was investigated by DSC, SEC and dynamic rheological analyses. Based on FTIR analyses, it was found that the stoichiometric ratio is optimal for the NIPU synthesis to obtain the highest molar masses with appropriate kinetics. However, the results show that the molar masses (up to 22000 g mol−1) were lower than conventional polyurethanes. A specific structuration due to a higher crosslink degree was observed when the average functionality of the diamine dimer increased. As expected, the glass transition temperature rises in this case. Crosslinked samples were synthesized with an average amine functionality of 2.15 and 2.2. A promising elastomer sample with elongation higher than 600% was then obtained.

Chemical modification of tannins to elaborate aromatic biobased macromolecular architectures

Tannins are, after lignins, the most abundant source of natural aromatic biomolecules and can be an alternative feedstock for the elaboration of chemicals, building blocks to develop polymers and materials. Tannins are present in all vascular and some non-vascular plants. One of their major issues is the versatility according to their botanical origin, extraction and purification processes. During the last few decades, tannins have been exploited and chemically modified for the development of new biobased polymers, thanks to their functionality brought by phenolic and aliphatic hydroxyl groups. After a historical overview, this review summarizes the different classes of tannins. Some generalities concerning the extraction techniques of tannins and the corresponding properties are also described. This review provides in detail the different chemical modifications of tannins which have been previously reported, with corresponding pathways and applications. Finally, the main chemical pathways to obtain polymeric materials are especially presented.

Micromechanical modeling and characterization of the effective properties in starch-based nano-biocomposites

The aim of this work was to predict the effective elastic properties of starch-based nano-biocomposites. Experiments (materials elaboration, morphological characterization and determination of mechanical properties) were conducted on both the pristine matrix (plasticized starch) and the matrix filled with montmorillonite nanoclay. Aggregated/intercalated and exfoliated nano-biocomposites were produced and mechanically tested under uniaxial tension to understand the effect of montmorillonite morphology/dispersion on the stiffness properties of starch-based nano-biocomposites. Micromechanical models, based on the classical bounds and the Mori-Tanaka approaches, were developed taking into consideration the influence of the clay concentration, the exfoliation ratio, the relative humidity and the storage time (ageing). Predicted results are in a good agreement with our experiments and show that the micromechanical model can be used as an indirect characterization technique to quantify the exfoliation/aggregation degree in the plasticized starch/clay nano-biocomposites.

Original polyols based on organosolv lignin and fatty acids: new bio-based building blocks for segmented polyurethane synthesis

A macropolyol was successfully prepared by combining two different biomolecules from biomass, i.e. lignin and oleic acid, using a solvent-free and catalyst-free method. The chemical structures of this original lignin–fatty acid based polyol and its intermediates were determined by 1H NMR and FT-IR analyses. A series of polyurethanes (PUs) were then prepared by a two-step procedure. Three linear isocyanate prepolymers were first synthesized from 4,4′-methylenebis(phenyl isocyanate) and poly(propylene)glycol of different molecular weights (PPG – 425, 1000 and 2000 g mol−1). These intermediates were used to obtain different PU macromolecular architectures by varying reaction parameters in the presence of the lignin–fatty acid based macropolyol. The final lignin-based polyurethanes were thoroughly chemically characterized by FT-IR studies, whereas the properties of these polymers were assessed by DSC, TGA, DMTA, and tensile test experiments. All these were performed in order to evaluate the influence of the NCO : OH molar ratio (from 0.2 to 1.0) as well as the influence of the PPG chain length. These new polymers with controlled architectures presented advanced properties. Their high biobased content (until 89%) depicts an important output for the valorisation of lignin and they may be an optimal alternative to conventional PUs.

Disruption of β-oxidation pathway in Pseudomonas putida KT2442 to produce new functionalized PHAs with thioester groups

This work describes the generation of novel PHAs (named PHACOS) with a new monomer composition containing thioester groups in the side chain, which confers new properties and made them suitable for chemical modifications after their biosynthesis. We have analyzed the PHACOS production abilities of the wild-type strain Pseudomonas putida KT2442 vs. its derived strain P. putida KT42FadB, mutated in the fadB gene from the central metabolic β-oxidation pathway involved in the synthesis of medium-chain-length PHA (mcl-PHA). Different fermentation strategies based on one- or two-stage cultures have been tested resulting in PHACOS with different monomer composition. Using decanoic acid as inducer of the growth and polymer synthesis and 6-acetylthiohexanoic acid as PHA precursor in a two-stage strategy, the maximum yield was obtained by culturing the strain KT42FadB. Nuclear magnetic resonance and gas chromatography coupled to mass spectrometry showed that polymers obtained from the wild-type and KT42FadB strains, included 6-acetylthio-3-hydroxyhexanoic acid (OH-6ATH) and the shorter derivative 4-acetylthio-3-hydroxybutanoic acid (OH-4ATB) in their composition, although in different ratios. While the polymer obtained from KT42FadB strain contained mainly OH-6ATH monomer units, mcl-PHA produced by the wild-type strain contained OH-6ATH and OH-4ATB. Furthermore, polyesters showed differences in the OH-alkyl derivates moiety. The strain KT42FadB overproduced PHACOS when compared to the production rate of the control strain in one- and two-stage cultures. Thermal properties obtained by differential scanning calorimetry indicated that both polymers have different glass transition temperatures related to their composition.

Innovative thermoplastic chitosan obtained by thermo-mechanical mixing with polyol plasticizers

Chitosan shows a degradation temperature lower than its melting point, which prevents its development in several applications. One way to overcome this issue is the plasticization of the carbohydrate. In this work plasticized chitosan was prepared by a thermo-mechanical kneading approach. The effects of different non-volatile polyol plasticizers (glycerol, xylitol and sorbitol) were investigated. The microstructure and morphology were determined using FTIR, XRD, TEM and SEM in order to understand the plasticization mechanism. Sorbitol, which is the highest molecular weight polyol used, resulted in plasticized chitosan with the highest thermal, mechanical and rheological properties. On the other hand, the sample plasticized with glycerol, the lowest molecular weight polyol, had the most important amorphous phase content and the lowest thermal, mechanical and rheological properties. Also, when the polyol content increased in the formulation, the plasticized chitosan was more amorphous and consequently its processability easier, while its properties decreased.

Elaboration, morphology and properties of starch/polyester nano-biocomposites based on sepiolite clay

The incorporation of nano-sized sepiolite clays into thermoplastic starch/poly(butylene adipate-co-terephthalate) (TPS/PBAT) blends has been investigated with the goal of improving the matrix properties. TPS/PBAT nano-biocomposites were elaborated with two different proportions of the polymeric phases. The influence of the sepiolite nanoclays on the mechanical, thermal and structural properties of the corresponding blends was evaluated. SEM images confirmed the good dispersion of the sepiolite clay, with a low occurrence of small aggregates in the polymeric matrix. Wide-angle X-ray diffraction showed no significant alteration of the crystalline structures of PBAT and starch induced by the sepiolite clay. The addition of sepiolite slightly affected the thermal degradation of the nano-biocomposites; however, the mechanical tests revealed an increase in some mechanical properties, demonstrating that sepiolite is a promising nanofiller for TPS-based materials.