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The aim of this study was to develop a novel approach allowing simultaneous enrichment as well as specific and fast detection of Escherichia coli O157:H7 by indirect ELISA using optimized support membrane based on chitosan (CHI), cellulose nanocrystals (CNCs), and glycerol (GLY). Therefore, combining the step of the capture of the pathogen and enrichment steps for the microbial growth led to a high detection signal at a low inoculation level without cross-reaction with Pseudomonas and Salmonella strains. The detection was performed by varying incubation periods and different level of inoculations. The signal of detection in samples incubated with the chitosan-based support reinforced with CNCs and directly from E. coli O157:H7 bacterial culture was much higher as compared to CNCs-free support with cell-free supernatant samples. The CCG support reinforced with 0.6% CNCs improved the detection signal of E. coli O157: H7 by 25% compared to control. The whole bacterial culture showed a higher immobilization signal than unfiltered and cell-free supernatant. The spider web trap approach (SWTA) detect E. coli O157:H7 after only 4 h of enrichment compared to 24 h with conventional methods. The adjustment of this innovative SWTA could minimize the risks of cross-contamination and consequently, food product recalls by facilitating significantly the detection of foodborne pathogens in samples collected from food surface, tools and work surfaces in food processing industries. Crown Copyright (C) 2019 Published by Elsevier B.V. All rights reserved.

Cellulose nanocrystals (CNCs) are naturally-sourced nanoparticles that can be used to modify polymers and provide exceptional mechanical properties to nanocomposite materials. In this study, CNCs were incorporated into water-based pressure sensitive adhesives (PSAs) via in situ semi-batch emulsion polymerization to improve PSA properties. A sequential design approach was used to improve CNC/poly(n-butyl acrylate/vinyl acetate) nanocomposite PSAs. In the first part of the design, the effects of acrylic acid (AA) and anionic surfactant sodium dodecyl sulfate (SDS) were examined in the presence of 0.5 wt% CNCs (based on polymer mass). While the SDS was crucial to maintaining latex stability, its excessive addition led to a decrease in PSA performance, namely tack and peel strength. The AA comonomer was pivotal in improving the shear strength of the PSAs, especially in the presence of CNCs. In all cases, the addition of CNCs led to improved PSA shear strength. In the second part of the design, the addition of 1-dodecanethiol (NDM) as a chain transfer agent (CTA) with CNC levels up to 1 wt% led to an improvement in tack and peel strength but at the cost of diminishing the shear strength. Generally, the addition of CNCs improved PSA performance. Thus, to maximize the impact of CNCs on PSA properties, a careful balance of SDS (for latex stability), AA (to improve shear strength) and NDM (to improve tack and peel strength) are needed.

Emulsion polymerized latex-based pressure-sensitive adhesives (PSAs) are more environmentally benign because they are synthesized in water but often underperform compared to their solution polymerized counterparts. Studies have shown a simultaneous improvement in the tack, and peel and shear strength of various acrylic PSAs upon the addition of cellulose nanocrystals (CNCs). This work uses atomic force microscopy (AFM) to examine the role of CNCs in (i) the coalescence of hydrophobic 2-ethyl hexyl acrylate/ n -butyl acrylate/methyl methacrylate (EHA/BA/MMA) latex films and (ii) as adhesion modifiers over multiple length scales. Thin films with varying solids content and CNC loading were prepared by spin coating. AFM revealed that CNCs lowered the solids content threshold for latex particle coalescence during film formation. This improved the cohesive strength of the films, which was directly reflected in the increased shear strength of the EHA/BA/MMA PSAs with increasing CNC loading. Colloidal probe AFM indicated that the nano-adhesion of thicker continuous latex films increased with CNC loading when measured over small contact areas where the effect of surface roughness was negligible. Conversely, the beneficial effects of the CNCs on macroscopic PSA tack and peel strength were outweighed by the effects of increased surface roughness with increasing CNC loading over larger surface areas. This highlights that CNCs can improve both cohesive and adhesive PSA properties; however, the effects are most pronounced when the CNCs interact favourably with the latex polymer and are uniformly dispersed throughout the adhesive film. This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)’.

Spray drying is the most cost-efficient technology to produce bulk quantities of dry cellulose nanocrystals (CNCs) from acid hydrolyzed CNC suspensions. Spray drying results in the aggregation of CNC particles in granular material which is difficult to redisperse in water to individual particles. In this research, we investigated cospray drying of CNC suspensions with nonionic surfactant (10-mol ethoxylated octylphenol) at different concentrations and the role of this nonionic surfactant on the redispersion of spray-dried granular CNC particles. Dispersions of spray-dried CNC powder samples in water were investigated under static, mechanically stirred, and ultrasound-assisted mixing conditions. The granular morphology of spray-dried CNCs was affected by the concentration of nonionic surfactant. Overall, the formations of hollow and blistered particles in the presence of 5 and 10 mM OPE-100 were attributed to interactions between nonionic surfactant and CNCs which cause a reduction in the repulsion of nanoparticles during the shrinking of spray drying droplets. Higher light transmission properties, improved dispersion stability, and narrower particle size distribution of spray-dried CNC suspensions were achieved with the incorporation of nonionic surfactant at 5 and 10 mM prior to spray drying. These results are explained by the presence of hollow particles and by the increased interparticle interaction distance of CNCs due to weak and reversible adsorption of nonionic surfactant. Therefore, the addition of a nonionic surfactant is an attractive approach to control granular particle morphology and aqueous redispersion of CNC granular powder. Such results are of particular significance in the commercialization and process optimization for the manufacture of CNCs.

Cellulose nanocrystals (CNCs) are inherently hydrophilic; even so, their dispersions in water based applications such as rheology modifiers, coatings, and emulsion systems do not often produce perfect dispersions with a minimum energy input. Supplying the CNCs in dry granular powder form is needed in the industrial scale of production because of its easier handling, storage and transportation characteristics. Spray drying is the preferred industrial method for drying acid hydrolyzed CNC suspensions. However, spray drying often causes poor dispersion of dried CNC granules into individual nanoparticles in aqueous solutions if not mixed with high energy input. This study investigates foam-spray drying of CNC particles to enhance their dispersibility in water. Non-ionic 10-mole ethoxylated octylphenol surfactant (OPE-100) and methyl cellulose polymer (MC) were used as additives to assist the foaming of CNC suspensions. Foam-spray drying experiments were carried out under constant process conditions such as inlet and outlet temperatures, gas and liquid flow rates and concentrations of CNCs. We focus on the effects of 10-mole ethoxylated octylphenol surfactant (OPE-100) and methyl cellulose polymer (MC) as additives and foaming of CNCs suspension on the morphology of dried CNC aggregates and their dispersion in water. Our work also describes the molecular interaction mechanisms of CNCs with methyl cellulose and OPE-100 by means of isothermal titration calorimetry and surface charge of the coated CNCs. The addition of nonionic surfactant OPE-100 along with methyl cellulose polymer resulted in spray drying of CNC aggregates with the best water dispersion characteristics. While methyl cellulose generated foams, OPE-100 lowered the inverse thermal gelling of methyl cellulose in spray drying.

Cellulose nanocrystals (CNCs) reinforced chitosan based antifungal films were prepared by encapsulating essential oils (EOs) nanoemulsion. Vapor phase assays of the chitosan-based nanocomposite films loaded with thyme-oregano, thyme-tea tree and thyme-peppermint EO mixtures showed significant antifungal activity against Aspergillus niger, Aspergillus flavus, Aspergillus parasiticus, and Penicillium chrysogenum, reducing their growth by 51-77%. Combining the bioactive chitosan films loaded with thyme and oregano EOs produced ~2 log reduction in fungal growth in inoculated rice during 8 weeks of storage at 28 °C. The bioactive films showed a slow release (26%) of volatile components over 12 weeks of storage. Sensorial evaluation of rice samples packed with the bioactive films showed no significant change in odor, taste, color and general appreciation compared with untreated rice. Incorporation of cellulose nanocrystals (CNCs) with the chitosan matrix played an important role in stabilizing the physicochemical and release properties of the nanocomposite films. In addition, combining the bioactive chitosan films with a dose of 750 Gy of ionizing radiation showed significantly higher antifungal and mechanical properties than treatment with the bioactive film or irradiation alone.

The edible coating has been used for covering fruits and vegetables, bringing surface protection, and extending product shelf-life. Due to the outstanding properties, nanomaterials have become a part of the packaging/coating new generation, demonstrating improvements in the barrier capacity of materials starting from construction products to the food industry. In the food industry, on the other hand, Agaricus bisporus mushrooms have a limited shelf-life from 1 to 3 days because of their high respiration rate and enzymatic browning. With the aim to reduce these two parameters and prevent rapid senescence, the objective of this study was to incorporate a natural source of nanomaterials (cellulose nanocrystals (CNCs) into a gellan gum-based coating and sprayed the surface of the mushrooms with the coating material. To evaluate the effect of CNCs, oxygen consumption, carbon dioxide production rate, and color change were recorded during the mushroom storage at 4 ± 1 °C. Results showed that all coatings were able to decrease total color change (ΔE) of mushrooms from 12 to 8 at day 10 when the coating was applied in all samples compared to control. In addition, significant differences were observed in the respiration rate when CNCs were added to the mushrooms. Oxygen consumption results exhibited a 44 mL O2 /kg · day production at day 5 with 20% CNCs compared to 269 mL O2 /kg · day observed in noncoated samples. This trend was similarly observed in the carbon dioxide production rate. PRACTICAL APPLICATION: With this research, it was remarkable to see the presence of CNCs in the coating solution reduced the respiration rate and increased the shelf-life of mushrooms. Similar applications can be industrially scaled-up to protect fruits and vegetables by CNCs-based coating or packaging materials. A variety of sustainable materials are available nowadays that serve as packaging matrix, and scientists are working on expanding the compatibility of these nanomaterials. In addition, it has been studied that CNCs enhance the degradation of polymers, an effort that many companies are making to reduce the environmental impact in their products.

International audience; Microfluidization was used to develop methyl cellulose (MC)/cellulose nanocrystal CNC based nanocomposite films containing a plant essential oil (EO) blend (oregano: thyme) emulsion. A three factorial experimental design was used to systematically optimize the microfluidization pressure based on size and antifungal activity of the prepared emulsion. Results showed that microfluidization of the film forming dispersions provide a novel approach for the development of high strength bionanocomposite films. Incorporation of 7.5% CNC into MC containing 0.50–0.75% EO and application of a pressure of 15 k psi (103 MPa) created a nanoemulsion with particle size ≤ 100 nm which exhibited significant antifungal activity in vitro against Aspergillus niger, A. flavus, A. parasiticus and P. chrysogenum. In situ tests with MC/CNC based bioactive films containing EO emulsion produced a 2 log reduction in fungal growth in infected rice during 8 weeks of storage at 28 °C. Methyl cellulose nanocomposite films containing EOs nanoemulsion showed a slow release (35%) of volatile component over 12 weeks of storage period. The addition of CNC as reinforcing filler improved the tensile strength of the MC based films by 30% and decreased water barrier and release properties by 9 and 25% respectively. In addition, combined treatment of bioactive films with an irradiation treatment at 750 Gy showed more pronounced antifungal and mechanical properties than treatment with the bioactive film or irradiation alone. These results show the potential for EO-loaded methyl cellulose-based films to prolong shelf life of food products.

Surface-initiated atom transfer radical polymerization was used to graft hydrophobic poly(butyl acrylate) from cellulose nanocrystals (CNCs) resulting in compatibilized CNCs that were successfully incorporated inside the core of polymer latex particles. CNCs are anisotropic nanoparticles derived from renewable resources and have potential as reinforcing agents in nanocomposites. However, challenges due to the incompatibility between cellulose and hydrophobic polymers and processing difficulties, such as aggregation, have limited the performance of CNC nanocomposites produced to date. Here, CNCs were incorporated into the miniemulsion polymerization of methyl methacrylate by adding polymer-grafted CNCs to the monomer phase. A poly(methyl methacrylate)-CNC nanocomposite latex was subsequently produced in situ, whereby polymer-grafted CNCs (with optimized graft length) were located inside the latex particles, as shown by transmission electron microscopy. This work provides a method for controlling the location of CNCs in latex-based nanocomposites and may extend the use of CNCs in commercial adhesives and coatings.

Cellulose nanocrystals were successfully oxidized with sodium hypochlorite using catalytic amounts of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical at pH 10 in water. Carboxylate groups were selectively introduced at the surface of the crystals up to a total acid content of 1200 mmol kg−1 without damaging the integrity of the crystals. The final acid content can easily be tuned by varying the amount of oxidant introduced. The effect of temperature, the quantity of oxidant and co-catalyst on the reaction kinetics were studied. Several methods were used for the characterization of the oxidized material like field emission scanning electron microscopy, diffuse reflectance infrared spectroscopy and thermogravimetric analysis.

International audience; Thyme essential oil (EO) loaded alginate beads (1–3%) containing cellulose nanocrystals (CNCs) (0–40% polymer dry basis) were prepared in order to study EO release profile in simulating solvent and the antimicrobial effect against Listeria innocua via in vitro and in situ tests. Introduction of CNCs from 0 to 30% in alginate beads exhibited an increase of EO loading capacity from 0.12 to 0.17% and a kinetic release constant (k) decrease from 9.85 to 6.77 when beads were prepared with 3% thyme EO, respectively. These optimal concentrations were selected in order to assess the antimicrobial efficiency to eliminate L. innocua and to reduce the mesophilic total flora (MTF) on ground meat during storage. Results showed that ground meat containing active alginate beads showed a 2 log reduction of L. innocua during more than 10 days as compared to the control. The influence of gamma-irradiation treatment was studied on MTF of ground meat, allowing a 4 log reduction during 14 days when alginate beads containing 3% thyme EO were added. A synergy between thyme EO and irradiation was observed in terms of L. innocua elimination and shelf-life extension.

This paper presents the effects of the composition of different media (i.e., Tryptic soy broth (TSB), Brain heart infusion (BHI), Listeria enrichment broth (LEB), Fraser broth (FB) and University of Vermont medium (UVM)) on the detection of a short peptide fragment PepD specific to the p60 protein (p60) of L. monocytogenes by a monoclonal antibody (anti-PepD mAb). Expression of the p60 obtained was demonstrated to be proportional to the cellular growth of Listeria monocytogenes regardless of the tested growth medium. However, the early growth of L monocytogenes and the expression of the p60 were negatively affected by the presence of selective agents present in LEB, FB and UVM. Among those three selective enrichment media commonly used for L. monocytogenes, LEB allowed a better expression of L. monocytogenes p60 after an incubation period of 18 h. Optimization of the LEB revealed that the dextrose concentration was the critical factor for improving the expression of p60 and promotes the early expression of p60. Moreover, an optimal dextrose concentration of 0.5% (w/v) in LEB, coupled with anti-PepD mAb immobilized to solid support, reduced the detection of p60 from 18 h to 9 h for an initial concentration of L. monocytogenes of 10(8) CFU/ml. (C) 2019 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.

This paper presents the development of a support membrane based on chitosan, cellulose nanocrystals and glycerol (m-CCG) for the antibody immobilization by a covalent crosslinking using glutaraldehyde. The chemical characterization of the support by FTIR showed that m-CCG formation process was stabilized by the formation of hydrogen bonding between each component of m-CCG and the reactive amine groups allowing the antibody immobilization on m-CCG via glutaraldehyde. Moreover, this immobilization on m-CCG was optimized by mathematics modeling approaches, and it exhibited robustness and predictable detection in presence of 0.6% of cellulose nanocrystals (CNCs), 0.5 g of CCG solution per well, after 2 h of antibody immobilization. Results also showed that CNCs (0.6% w/v) was the most important factor of the optimization. At this concentration, CNCs improve the resistance of m-CCG during the crosslinking treatment by a modification of the surface topography and the reinforcement of the tensile strength of m-CCG at >30%.

Recent findings indicate there is only a small window of sulfuric acid concentration (60–65 %) and temperature (45–65 °C) which allows efficient extraction of cellulose nanocrystals in significant quantities from bleached chemical pulp. In the present report, we develop a systematic explanation for how hydrolysis temperature, at a specific acid concentration, governs CNC surface properties. We demonstrate that CNCs with different suspension viscosity, stability in electrolyte-containing solutions, and optical properties can be produced, based on the presence or not of a precipitated oligosaccharide layer (OSL) on the surface of the nanocrystals. At hydrolysis temperatures below 65 °C, the degree of polymerization (DP) distribution of cellulose chains in CNC samples exhibits a bimodal distribution, indicating an accumulation of oligosaccharides on the CNC surface which increases as the hydrolysis temperature is decreased. At low hydrolysis temperature (45 °C), the oligosaccharides dissolved in the strong acid phase have a DP between 7 and 20 and precipitate onto CNCs when the reaction is quenched by diluting with water. As the temperature of hydrolysis is increased (50–60 °C), the dissolved oligosaccharides are hydrolyzed faster and their DP decreases such that they remain soluble after quenching. At 65 °C, no precipitated oligosaccharides can be detected on the CNC surface. Based on these results, we propose possible explanations to account for the effects of the OSL on the CNC suspension viscosity and stability and on optical properties of CNC films.

Cellulose nanocrystals (CNCs) have evolved from a laboratory curiosity to an industrial material manufactured at a scale of up to 1 ton/day. In order to maximize their use in various applications such as composites, it is critical to evaluate the influence of the surface chemistry on their thermal stability. The effect of temperature on native CNCs is heavily damaging to the material integrity, but the early stage temperature-catalyzed degradation process can be prevented by neutralization of the surface sulfate half-ester groups, either by organic or inorganic counterions. In addition, we studied the influence of the hydrolysis conditions on the CNCs’ resistance to elevated temperatures. The observations were carried out by thermogravimetric analysis (TGA). Finally, complementary work regarding color formation when CNCs are exposed to heat is presented.

International audience; Antiradical properties were introduced on cellulose nanocrystals (CNCs) by redox pair (RP) initiator and γ-radiation treatments. Different procedures were tested on CNC, first a 2 h reaction of hydrogen peroxide (H2O2)/ascorbic acid (AA) was performed on CNC solution. γ-Radiation treatment at 20 kGy dose was then applied and immediately after GA was reacted during 24 h with the pretreated CNCs, giving CNC-H2O2-AA-γ-GA. The formation of new carboxylic acids and carbonyl groups were characterized by FT-IR at 1650 and 1730 cm−1 respectively. Carboxylic acid functionalities were also analyzed by conductometric titration where an increase from 49 to 134 mmol COOH kg−1 was found from native to irradiated CNCs. A similar increase in the carboxylic acid content (132 mmol kg−1) was observed for CNC-H2O2-AA-γ-GA, showing the highest radical scavenging properties (8 mM Trolox eq/mg CNC). Thermogravimetric analysis confirmed the structural changes onto CNC. Film packaging containing 20% of CNC-H2O2-AA-γ-GA was then added to a gellan-based film packaging. A significant improvement (p

UV barrier properties and the oxygen permeability (OP) of alginate based films loaded from 0 to 30% CNCs (w/w polymer, dry basis) were evaluated at 0, 50, and 70% RH. The best performing film was used to coat chicken breasts and lipid oxidation was assessed during storage through lipid peroxide value (PV), thiobarbituric acid reagent substances (TBARS) quantification and color variability measurements. Results showed promising UV barrier effects and 25% decrease of OP at 70% RH when 30% CNCs were loaded in alginate films. Edible coating on chicken breasts also demonstrated a decrease of PV and TBARS at day 1 and 3 when 30% CNCs were used and no oxidative changes were indicated by chicken color.

This work describes the development of membrane based on chitosan (CHI), cellulose nanocrystals (CNCs), and glycerol (GLY), and optimization of the formulation for immobilization of monoclonal anti-Shiga toxin 2B antibody (mAnti-stx2B-Ab) for E. coli O157:H7 detection. The effect of CHI deacetylation degree & viscosity, CNCs and GLY concentrations on Anti-stx2B-Ab immobilization efficiency was evaluated. Fractional factorial and Box-Behnken designs were applied to screen the effects of compounds interactions and optimize their concentrations for detection of Anti-stx2B-Ab. The results demonstrated that the use of 0.6 % (w/v) CNCs improved significantly the Anti-stx2B-Ab immobilization and the level of signal detection. The detection limit of Escherichia coli O157:H7 by developed optimized membrane is 1 log CFU/mL. The time needed for detection of E. coli O157:H7 was only 4 h of enrichment compared to 24 h with conventional methods. The developed immobilization support has potential for future pathogen detection in food and biomedical samples.

The research described herein shows the treatment of cellulose nanocrystals (CNCs) led to antioxidant properties after 2 h of interaction with a redox pair—hydrogen peroxide (H2O2) and ascorbic acid (AA)—and 20 kGy irradiation. This procedure enhanced the surface of CNCs to react for 24 h with the antioxidant gallic acid (GA) at different mass ratios of CNC/GA (R=0.66 and 8). Each step of the modification was evaluated, but optimal results were found on CNC-H2O2-AA-γ-GA. Different analysis such as Fourier transform infrared spectroscopy exposed the apparition of a new band at 1730 cm−1, which can be explained by the formation of carbonyl groups on CNC. By studying the ultraviolet spectra of the different solutions, it was noticed that at wavelengths ∼290-nm intensity increases, showing a possible formation of aldehyde and carboxylic acids groups. This latter group was evaluated via conductometric titration, observing that CNC-H2O2-AA-γ-GA possesses 132 mmol COOH/kg and 8 mM Trolox eq/mL solution....

International audience; Probiotic (Lactobacillus rhamnosus ATCC 9595) was encapsulated in alginate-CNC-lecithin microbeads to produce nutraceutical microcapsules. Addition of CNC and lecithin in alginate microbeads (ACL-1) improved the viability of L. rhamnosus during gastric passage and storage. The compression strength of the freeze-dried ACL-1 microbeads improved 40% compared to alginate microbeads alone. Swelling studies revealed that addition of CNC and lecithin in alginate microbeads decreased (around 47%) the gastric fluid absorption but increased the dissolution time by 20min compared to alginate microbeads (A-0). During transition through the gastric passage, the viability of L. rhamnosus in dried ACL-1 microbeads was increased 37% as compared to A-0 based beads. At 25 and 4°C storage conditions, the viability of L. rhamnosus encapsulated in ACL-1 microbeads decreased by 1.23 and 1.08 log respectively, whereas the encapsulation with A-0 microbeads exhibited a 3.17 and 1.93 log reduction respectively.

International audience; Gamma irradiation is a common process mostly used for sterilization against bacteria growth. However, when the process is applied to a material, physical and chemical changes may alter its integrity and behaviour. The aim of this study was to observe the effect of γ-irradiation on the surface chemistry of CNCs. The carbonyl content (both carboxylic acid and aldehyde functionalities) was followed to investigate the influence of the irradiation dose. Thermal stability, wettability and antioxidant properties were also measured. Conductometric titration showed that the carboxylic acid groups content (COOH) was increased from 43 mmol COOH kg⁻¹ CNCs for native CNCs to 631 mmol COOH kg⁻¹ CNCs when a dose of 80 kGy was applied. These changes were confirmed by FTIR and fluorescence spectroscopy. At high irradiation doses, a significant decrease of approximately 30% was observed in the cellulose degree of polymerization while the aldehyde groups content was increased to 379 mmol CHO kg⁻¹ CNCs due to the cleavage of glycosidic linkages. These physicochemical changes led to enhanced antioxidant properties of CNCs.

This paper presents the application of a new support based on chitosan and reinforced with cellulose nanocrystals (m-CCG) for the detection of Listeria monocytogenes p60 protein in sandwich ELISA. This support consists of biopolymer membrane optimized for the covalent immobilization of the specific monoclonal antibodies against the unique short peptide of eleven amino acids (PepD, QQQTAPKAPTE) of L. monocytogenes p60 protein (anti-PepD mAb). Using the optimized immobilization method of anti-PepD mAb on m-CCG (m-CCG + anti-PepD mAb), the detection of L. monocytogenes culture was improved by 17% in Tryptic soy broth and by 24% in Listeria enrichment broth containing 0.5% of dextrose (modified LEB) on m-CCG compared to standard ELISA support. Moreover, the evaluation of the selectivity of detection of L. monocytogenes by anti-PepD mAb immobilized on m-CCG allowed the absence of any cross-reaction between the support and the nine other bacteria commonly found in food environment.

The isothermal crystallization from the melt of a poly(1,3-dioxolan) having a number-average molecular weight of 5100 was investigated by optical microscopy, differential scanning calorimetric and X-ray diffraction. A single spherulitic morphology (Phase I) of negative sign is observed at crystallization temperatures below 19 °C while multiple morphologies are observed at crystallization temperatures above 19 °C (Phases IIa, IIb and III). Phase IIa crystallizes first and is characterized by a low birefringence until its sporadic transformation into Phase IIb, characterized by a sudden increase in birefringence. Phase IIb acts as a nucleating agent for Phase III (cross-nucleation process). Phases I and III exhibit distinct growth rates that are two orders of magnitude lower than the transformation rate of Phase IIa into Phase IIb. Relationships between the crystalline structures of the different morphologies and their melting temperatures are also discussed. The transformation IIa/IIb is easily detected optically by a huge increase in birefringence but there is a more subtle Ia/Ib transformation which is hardly seen optically, although it gives rise to a large increase in melting temperature of that phase.

Polycaprolactone (PCL)/cellulose nanocomposites were prepared by mixing PCL with surface modified sisal nanowhiskers (CNW) and microfibrillated cellulose (MFC) extracted from sisal fibers. The influence of cellulosic nanoparticles on the crystallization behavior of PCL was investigated by differential scanning calorimetry. Isothermal crystallization data were modeled with Avrami’s kinetics, Lauritzen–Hoffman secondary nucleation theory and equilibrium melting points were determined with the Hoffman–Weeks method. The cellulose nanoparticles, acting as nucleating agents, drastically accelerate the crystallization of PCL while depressing its equilibrium melting by 9–10 °C. The crystallization of MFC-nanocomposites is slightly faster than that of CNW-nanocomposites, in agreement with the slightly lower bulk activation energy for crystallization and nucleation parameter in the former. The results are discussed based on the differences of specific surface area and surface chemistry of nanoparticles, as well as the confinement phenomenon.

High molecular weight poly(L-lactide)s (PLLAs) and poly(D-lactide)s (PDLAs) were synthesized in toluene at 70 °C by ring-opening polymerization of optically pure L-lactide and D-lactide, using tin(II) 2-ethylhexanoate (SnOct2) and 2-(2-methoxyethoxy)ethanol as initiator and coinitiator, respectively. Under these conditions, polarimetry as well as 13C NMR spectroscopy indicated that the synthesized poly(lactide)s (PLAs) are more than 99% isotactic. The molecular weight was successfully controlled by adjusting the monomer-to-initiator molar ratio. Gel permeation chromatography and MALDI-TOF mass spectrometry analyses showed that the polydispersity index of the PLAs is below 1.1. Moreover, MALDI-TOF spectra showed two different chain distributions, one characterized by an even number of lactic acid repeat units and the other by an odd number of lactic acid repeat units. The second distribution, indicative of the presence of intermolecular transesterification reactions, appears at the very beginning of the polymerization and its intensity increases with the polymerization time. Finally, a reversible reaction kinetic model was used to determine the monomer equilibrium concentration ([M]eq = 1.4 ± 0.5%) and the propagation rate constant (kp = 14.4 ± 0.5 L mol−1 h−1) of the polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1944–1955, 2007

Optically pure S(−) and R(+)-poly(α-methyl-α-ethyl-β-propiolactones) (PMEPLs) of controlled low molecular weights were synthesized by anionic polymerization of the corresponding optically active monomers, and characterized using gel permeation chromatography, Maldi-TOF mass spectrometry, and NMR spectroscopy. Blends of PMEPLs of opposite configurations and different molecular weights were investigated. All blends lead to the formation of a stereocomplex and its crystallization prevails over a wide range of mixing ratios. The stereocomplex melts 30–40 °C above that of the corresponding pure polymers, depending on the molecular weight; pairs of polymers having similar molecular weights exhibit the highest melting temperatures and enthalpies of fusion. Finally, when the stereocomplex is dispersed in a PMEPL matrix, it acts as a very effective nucleation agent for the crystallization of the polymer in excess. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2380–2389, 2007

International audience

Regioselectively substituted maltooligosaccharides were prepared by enzymatic transformation of modified cyclodextrins by using simultaneously two different enzymes: cyclodextrin glucanotransferase (CGTase) and amyloglucosidase. Oligosaccharides were obtained in very good yields and their structures were identified by 1D and 2D NMR spectroscopy. These results provided new information about the specificity of the catalytic sites of CGTase and amyloglucosidase. They also offered new ways for the synthesis of regioselectively modified maltooligosaccharides.

International audience; Cellulose nanocrystal (CNC) reinforced chitosan based antimicrobial films were prepared by immobilizing nisin on the surface of the films. Nanocomposite films containing 18.65 μg/cm(2) of nisin reduced the count of L. monocytogenes by 6.73 log CFU/g, compared to the control meat samples (8.54 log CFU/g) during storage at 4 °C in a Ready-To-Eat (RTE) meat system. Film formulations containing 9.33 μg/cm(2) of nisin increased the lag phase of L. monocytogenes on meat by more than 21 days, whereas formulations with 18.65 μg/cm(2) completely inhibited the growth of L. monocytogenes during storage. Genipin was used to cross-link and protect the activity of nisin during storage. Nanocomposite films cross-linked with 0.05% w/v genipin exhibited the highest bioactivity (10.89 μg/cm(2)) during the storage experiment, as compared to that of the un-cross-linked films (7.23 μg/cm(2)). Genipin cross-linked films were able to reduce the growth rate of L. monocytogenes on ham samples by 21% as compared to the un-cross-linked films. Spectroscopic analysis confirmed the formation of genipin-nisin-chitosan heterocyclic cross-linked network. Genipin cross-linked films also improved the swelling, water solubility, and mechanical properties of the nanocomposite films.

Dispersed cellulose ribbons from bacterial cellulose were subjected to digestion with cloned Cel7A (cellobiohydrolase [CBH] I) and Cel6A (CBH II) from Humicola insolens either alone or in a mixture and in the presence of an excess of β-glucosidase. Both Cel7A and Cel6A were effective in partially converting the ribbons into soluble sugars, Cel7A being more active than Cel6A. In combination, these enzymes showed substantial synergy culminating with a molar ratio of approximately two-thirds Cel6A and one-third Cel7A. Ultrastructural transmission electron microscopy (TEM) observations indicated that Cel7A induced a thinning of the cellulose ribbons, whereas Cel6A cut the ribbons into shorter elements, indicating an endo type of action. These observations, together with the examination of the digestion kinetics, indicate that Cel6A can be classified as an endo-processive enzyme, whereas Cel7A is essentially a processive enzyme. Thus, the synergy resulting from the mixing of Cel6A and Cel7A can be explained by the partial endo character of Cel6A. A preparation of bacterial cellulose ribbons appears to be an appropriate substrate, superior to Valonia or bacterial cellulose microcrystals, to visualize directly by TEM the endo-processivity of an enzyme such as Cel6A.

This note is a response to Zhang et al. [Zhang J, Beshra A, Domb AJ, Ozaki Y. d -Poly(lactide) and LHRH decapeptide stereointeractions investigated by vibrational spectroscopy. Eur Polym J 2007;43:3016–27] who reported spectroscopic data for blends of poly- d -lactide and LHRH (a leuprolide decapeptide analog). These authors concluded to the presence of a stereocomplex between those two species but it is shown, in this note, that the results obtained as well as literature results do not support this conclusion.

National audience; Nanocrystalline cellulose (NCC) reinforced alginate-based nanocomposite film was prepared by solution casting. The NCC content in the matrix was varied from 1 to 8% ((w/w) % dry matrix). It was found that the nanocomposite reinforced with 5 wt% NCC content exhibits the highest tensile strength which was increased by 37% compared to the control. Incorporation of NCC also significantly improved water vapor permeability (WVP) of the nanocomposite showing a 31% decrease due to 5 wt% NCC loading. Molecular interactions between alginate and NCC were supported by Fourier Transform Infrared Spectroscopy. The X-ray diffraction studies also confirmed the appearance of crystalline peaks due to the presence of NCC inside the films. Thermal stability of alginate-based nanocomposite films was improved after incorporation of NCC.

Stereocomplexes between poly(D-lactide) (PDLA) and poly(L-lactide) (PLLA) have been extensively studied, including, in recent years, several reports on the stereocomplexation of PDLA with small molecules such as peptides. Here, the possible complexation between PDLA and luteinizing hormone releasing hormone (LHRH), a l-configured decapeptide, is considered for which several observations were made: (1) in calorimetry an additional endothermic peak appears at a lower temperature than the melting temperature of pure PDLA; (2) in Raman analyses a band splitting of the C=O stretching mode (not present in pure PDLA) shows up; (3) in X-ray diffraction, however, no change is observed after mixing the two species, indicating no crystal structure modification (and the absence of any stereocomplex crystal structure). The calorimetric double melting peak is merely explained by the presence of two distinct morphological forms of PDLA, whereas the spectroscopic band splitting can be due to simple differences of crystallinity. From these observations it is concluded that the LHRH modifies the crystallization of PDLA without, however, the formation of a stereocomplex.

Beta-cyclodextrin (beta-CD) was reacted with catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO), sodium hypochlorite and sodium bromide at 2 degrees C and a pH value of 10 in water. The primary alcohol groups were selectively oxidized into carboxylate groups within a few minutes, and mono- and dicarboxy-beta-cyclodextrin sodium salts were isolated and characterized by 1H, 13C NMR and mass spectroscopy. With this reaction system, the degradation of the cyclodextrin was limited, provided the oxidation was performed at 2 degrees C, at constant pH value of 10, with catalytic amounts of TEMPO and controlled quantities of sodium hypochlorite and sodium bromide for the continuous regeneration of the oxoammonium salt.