Characterisation of macrogel composition from industrial natural rubber samples: Influence of proteins on the macrogel crosslink density

The insoluble (macrogel) and soluble fractions of 11 commercial natural rubber (NR) samples (Technically specified rubber) were separated. Nitrogen titrations and lipid extractions enabled a quantitative assessment of the proteins and extractable lipids in each fraction. Swelling was measured in tetrahydrofuran in order to evaluate the crosslink density (Mc –1) of each macrogel. While the soluble fraction had a high lipid concentration, the majority of non-isoprene compounds of the macrogel were found to be proteins, which accounted for 4.6 to 50.8% (w/w) of the macrogel. Indeed, the macrogels contained less than 0.5% (w/w) extractable lipids. However, our results showed that the soluble fraction contained large quantities of proteins (16–66% of the nitrogen content of the raw NR sample), probably structuring microaggregates. An exponential correlation (R2 > 0.96) was found between the crosslink density and the protein concentration of macrogel, suggesting that proteins are involved in the majority of crosslinks in macrogel. (Résumé d'auteur

Étude des interactions à l'origine de la structure associative du caoutchouc naturel et de leurs influences sur les propriétés rhéologiques

Le caoutchouc naturel (CN) est un élastomère produit à partir du latex d'Hevea brasiliensis. Ce matériau est constitué en moyenne de 94% (m/m) de poly(cis-1,4-isoprène) et de 6% (m/m) de composés non-isoprènes avec notamment des lipides (1,5-3,0%), des protéines (~ 2,0%) et des éléments minéraux (0,2%). Ces composés non-isoprènes seraient responsables de la structure associative ainsi que des propriétés remarquables du CN. Ce matériau présente une grande variabilité de ses propriétés de mise en oeuvre, liée aux conditions agronomiques (saison, clones, système d'exploitation) et aux différents procédés de fabrication existants. Le projet CANAOPT, dans lequel s'inscrit cette thèse, vise à identifier et à quantifier les sources de variabilité, ainsi qu'à développer de nouveaux grades de CN à variabilité réduite et contrôlée pour les applications antivibratoires. Ces travaux de thèse visent à mieux comprendre l'origine du gel du CN et son influence sur les propriétés rhéologiques du matériau. Cette phase gel (ou gel total) est constituée d'une fraction insoluble en solvant organique appelée le macrogel, et d'une fraction de microagrégats dispersés dans la fraction soluble, appelée le microgel. Le premier axe de recherche de cette thèse vise à identifier l'effet du gel sur les propriétés rhéologiques du CN. Dans ce but, des méthodes ont été développées afin de quantifier les différents taux de gels du CN, de caractériser la structure des chaînes de poly(cis-1,4-isoprène) et des microagrégats (SEC-MALS en mode TBABr), mais également de mesurer les propriétés rhéologiques en double cisaillement (DMTA). Une méthode permettant de caractériser rapidement le taux de composés non-isoprènes des échantillons par spectroscopie FT-IR a également été mise au point. Des corrélations ont d'abord été mises en évidence entre les masses molaires moyennes des macromolécules et les propriétés rhéologiques d'une sélection de 25 échantillons différents. Enfin, une corrélation a également été mise en évidence entre le taux de gel total et le paramètre K' décrit par le modèle de Perez. Ce paramètre est déterminé graphiquement par la représentation Cole-Cole. En parallèle, ces travaux se sont portés sur une caractérisation physico-chimique du microgel et du macrogel du CN. Une méthodologie d'extraction du microgel a été mise en place, et a permis la caractérisation des microagrégats du CN. La composition, le degré de réticulation, et les propriétés rhéologiques des macrogels issus d'une sélection de 11 échantillons de CN ont également été étudiés. Il a été montré que le taux de protéines contenues dans le macrogel (5-51% m/m) est directement lié à son degré de réticulation et impacte ses propriétés rhéologiques, très supérieures à celles du CN brut et de la fraction soluble correspondants. (Résumé d'auteur

Study of the interactions underlying the associative structure of Natural Rubber and its effects on rheological properties

Le caoutchouc naturel (CN) est un élastomère produit à partir du latex d'Hevea brasiliensis. Ce matériau est constitué en moyenne de 94% (m/m) de poly(cis-1,4-isoprène) et de 6% (m/m) de composés non-isoprènes avec notamment des lipides (1,5-3,0%), des protéines (~ 2,0%) et des éléments minéraux (0,2%). Ces composés non-isoprènes seraient responsables de la structure associative ainsi que des propriétés remarquables du CN. Ce matériau présente une grande variabilité de ses propriétés de mise en œuvre, liée aux conditions agronomiques (saison, clones, système d'exploitation) et aux différents procédés de fabrication existants. Le projet CANAOPT, dans lequel s'inscrit cette thèse, vise à identifier et à quantifier les sources de variabilité, ainsi qu'à développer de nouveaux grades de CN à variabilité réduite et contrôlée pour les applications antivibratoires. Ces travaux de thèse visent à mieux comprendre l'origine du gel du CN et son influence sur les propriétés rhéologiques du matériau. Cette phase gel (ou gel total) est constituée d'une fraction insoluble en solvant organique appelée le macrogel, et d'une fraction de microagrégats dispersés dans la fraction soluble et appelée le microgel. Le premier axe de recherche de cette thèse vise à identifier l'effet du gel sur les propriétés rhéologiques du CN. Dans ce but, des méthodes ont été développées afin de quantifier les différents taux de gels du CN, de caractériser la structure des chaînes de poly(cis-1,4-isoprène) et des microagrégats (SEC-MALS en mode TBABr), mais également de mesurer les propriétés rhéologiques en double cisaillement (DMTA). Une méthode permettant de caractériser rapidement le taux de composés non-isoprènes des échantillons par spectroscopie FT-IR a également été mise au point. Des corrélations ont d'abord été mises en évidence entre les masses molaires moyennes des macromolécules et les propriétés rhéologiques d'une sélection de 25 échantillons différents. Enfin, une corrélation a également été mise en évidence entre le taux de gel total et le paramètre K' décrit par le modèle de Perez. Ce paramètre est déterminé graphiquement par la représentation Cole-Cole. En parallèle, ces travaux se sont portés sur une caractérisation physico-chimique du microgel et du macrogel du CN. Une méthodologie d'extraction du microgel a été mise en place, et a permis la caractérisation des microagrégats du CN. La composition, le degré de réticulation, et les propriétés rhéologiques des macrogels issus d'une sélection de 11 échantillons de CN ont également été étudiés. Il a été montré que le taux de protéines contenus dans le macrogel (5-51% m/m) est directement lié à son degré de réticulation et impacte ses propriétés rhéologiques, très supérieures à celles du CN brut et de la fraction soluble correspondants.Natural Rubber (NR) is an elastomer made from Hevea brasiliensis latex. It contains about 94% (w/w) of cis-1,4-polyisoprene and 6% (w/w) of non-isoprene compounds, such as lipids (1.5-3.0%), proteins (~ 2.0%) and minerals (0.2%). These non-isoprene compounds are assumed to be responsible for the associative structure and the outstanding properties of NR. However, substantial variability in NR properties is caused by diverse agronomic conditions (season, clones and tapping system) and by the different manufacturing processes. This PhD thesis is part of the French CANAOPT project, which aims to create new NR grades with reduced and controlled variability for antivibratory applications. This PhD work aims for a better understanding of the origin of the NR gel phase and its influence on rheological properties. The gel phase of NR (or total gel) is composed of a fraction that is insoluble in organic solvent (macrogel), and of microaggregates dispersed in the soluble fraction (microgel). The first component of this PhD research set out to identify the impact of the gel phase on NR properties. To that end, characterization methods were developed in order to investigate the different gel contents, the structures of cis-1,4-polyisoprene chains and microaggregates (SEC-MALS in TBABr mode), and also rheological properties in double-shear solicitation (DMTA) of NR samples. The non-isoprene contents (lipids and proteins) were also investigated using a new characterization method in FT-IR spectroscopy, developed during this PhD work. Correlations between the average molar masses of the macromolecules and the rheological properties of 25 NR samples were highlighted. Finally, a correlation was found between the total gel content and a K' parameter, introduced by the Perez model and graphically determined by the Cole-Cole representation.At the same time, physicochemical characterization of the microgel and the macrogel of NR samples was undertaken. First, a new method was developed in order to extract and study NR microaggregates. The composition, the degree of crosslinking and the rheological properties of macrogels extracted from 11 NR samples were also investigated. It was found that the protein content (5-51% w/w) of the macrogel was clearly correlated to its degree of crosslinking. The macrogel protein content also influenced its rheological properties, which were much greater than those of the corresponding NR and soluble fraction

Influence of the curing temperature on the diffusion rate of the perfluorinated alkyl chains of a modified epoxy resin

International audiencePerfluorononanoic acid (F17) was grafted to an epoxy resin. The virgin epoxy resin and the fluorinated epoxy resin were cured at various temperatures. Both air-resin and substrate-resin interfaces of the cured materials were characterized in terms of: (i) free surface energy, (ii) surface composition, evaluated using angle-resolved X-ray photoelectron spectroscopy (AR-XPS). Fluorine proportion was quantified at probing depths of about 4.5 and 9 nm. The curing temperature highly influenced the diffusion of the perfluorinated chains towards both interfaces. Depending on the curing conditions, very low free surface energies (17 mJ/m2) due to high fluorine concentrations (fluorine/carbon ratio = 0.6) were measured at the air-resin interface. However, the F17 diffusion towards the substrate was also observed and led to important fluorine concentrations (F/C up to 0.4). Finally, a two-step curing procedure was used for monitoring the F17 diffusion during the curing, illustrated by an accumulation of fluorine atoms at both interfaces. A non-linear relation was highlighted between the surface energy drop and the fluorine content measured by AR-XPS

Development of bio-based Non-Isocyanate PolyUrethane (NIPU) foams with optimized reactivity

International audienceThe substitution of polyurethane foams (PUF) with Non-Isocyanate Polyurethanes (NIPU) from CO2-derived cyclocarbonates is of great interest to avoid toxic isocyanates, but this requires optimizing the crosslinking kinetics. New bi-component resins with high biobased content (70-90 wt%) were synthesised from carbonated vegetable oil with diamines for the production of NIPU foams with a wide range of properties. Curing cycles shorter than 10 min at 60 °C, were optimized using an in situ NMR spectroscopy method and by adjusting the rates of catalysts and residual epoxides, allowing for the industrial deployment of these materials. Modulation of the mechanical and thermal properties was studied by varying the nature and functionality of the monomers. NIPU foams with Tg around -40°C, density lower than 150 kg/m3, and compression set lower than 6%, were obtained, in good agreement with automotive seat specification

Development of bio-based Non-Isocyanate PolyUrethane (NIPU) foams with optimized reactivity

International audienceThe substitution of polyurethane foams (PUF) with Non-Isocyanate Polyurethanes (NIPU) from CO2-derived cyclocarbonates is of great interest to avoid toxic isocyanates, but this requires optimizing the crosslinking kinetics. New bi-component resins with high biobased content (70-90 wt%) were synthesised from carbonated vegetable oil with diamines for the production of NIPU foams with a wide range of properties. Curing cycles shorter than 10 min at 60 °C, were optimized using an in situ NMR spectroscopy method and by adjusting the rates of catalysts and residual epoxides, allowing for the industrial deployment of these materials. Modulation of the mechanical and thermal properties was studied by varying the nature and functionality of the monomers. NIPU foams with Tg around -40°C, density lower than 150 kg/m3, and compression set lower than 6%, were obtained, in good agreement with automotive seat specification

A rheological method exploiting Cole-Cole plot allows gel quantification in Natural Rubber

Raw Natural Rubber (NR) quality, rather variable, is controlled according to international standards (ISO2000, etc.). Despite these standards, better characterization of this complex material is still needed to reduce feedstock waste and energy losses in the manufacturing processes. Twenty-four NR samples were studied. Their gel contents were quantified after dissolution in tetrahydrofuran. The rheological properties of the raw NR samples were measured in double-shear geometry. The Cole-Cole plot of the shear moduli (G″ = f(G′)) was used to graphically calculate an h parameter, described as an indicator of the crosslink density of a polymer. The total gel of NR was found to clearly influence the rheological properties of the material at low frequency. This study also showed that the microgel of NR accounted for 46–92% of the total gel, and cannot be neglected when investigating the influence of gel on NR properties. (Résumé d'auteur

New insights on Natural Rubber microgel structure thanks to a new method for microaggregates extraction

Size exclusion chromatography (SEC) columns pre-treated with a tetrabutylammonium bromide (TBABr) solution were used to develop a new method for extracting the microgel of Natural Rubber (NR). A solution of microaggregates smaller than 1 μm (Microgel<1μ) was obtained by collecting the corresponding elution volume after injecting the soluble fraction of the studied sample. The Microgel<1μ solution was then characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Direct imaging of two populations of isolated microaggregates with different sizes and structures was carried out. Spherical microaggregates with a hydrodynamic diameter (dh) of 500 nm were found to account for the majority of the isolated microaggregates. Larger microaggregates, with a dh of 1000 nm, were also observed and may have been formed by aggregation of the former. An “apparent molecular density” parameter was used to compare their compactness: the larger microaggregates were found to be 66% denser than the smaller ones. (Résumé d'auteur

Effect of mastication on the structure of microgel present in natural rubber

Mechanical or thermal mastication experiments were performed on three commercial natural rubber (NR) samples of TSR10 grade made from latex of three different clones (GT1, PB235, and RRIM600). The mesostructure (different gel or aggregate fractions, structure of random coils of cis-1,4-polyisoprene) of all the NR samples was fully characterized by size exclusion chromatography coupled with multiangle light scattering (SEC-MALS), using pretreated SEC columns. This method was used to quantify and investigate the structure of the little-studied smaller microaggregates, constituting the microgel fraction smaller than 1 μm (Microgel<1μ) of NR. The three unmasticated NR samples showed no difference in terms of microaggregate structure. Conversely, microaggregates appeared denser after mastication. This phenomenon was found to depend on the mastication conditions, as mechanically masticated NR samples had smaller (lower radius of gyration) and more compact microaggregates than thermally masticated samples. Macrogel also behaved differently depending on the mastication conditions. Mechanical mastication conditions allowed a higher degradation of the macrogel compared with thermal mastication conditions. (Résumé d'auteur

Flexible polyhydroxyurethane foams from highly reactive formulations based on carbonated hemp oil

International audiencePolyurethanes (PUs) are thermosetting materials mainly used in the form of rigid or flexible foams, with a prominent place in construction, transport, and consumer goods industries. Due to their negative health and environmental impacts, conventional PUs are subject to severe regulatory restrictions under the REACH regulation. The substitution of PUs with more sustainable non-isocyanate polyurethanes (NIPUs) is therefore of great interest. Nevertheless, because of their lower reactivity, the curing times of NIPU foams are currently incompatible with the industrial production rates of PU foams, and therefore must be optimised. In this context, the present work aims at developing new flexible biobased NIPU foams with optimised reactivity, and with equivalent thermal and mechanical properties to standard PU foams. New two-component resins with a high content of renewable materials (>90 wt%) were synthesised from biobased diamines and modified hemp oil, for the production of a wide range of polyhydroxyurethane (PHU) foams. Using an in situ NMR spectroscopy methodology, the influence of the catalyst concentration and nature, and of the reaction temperature, was first highlighted [1]. Using rheometry, very interesting curing times (5 min at 80 °C) were obtained by adjusting the residual epoxy content in the carbonated oil, the amine nature and concentrations, as well as the catalysis conditions. After optimising the expansion method, PHU foams with a glass transition temperature of -25 °C, a density lower than 150 kg.m-3, and a compression set lower than 1 %, were developed, in line with industrial PU specifications