1 January 2016
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In the last decade, a new fiber pretreatment has been proposed to make easy cellulose fibrillation into microfibrils. In this context, different surface cationized MFC was prepared by optimizing the experimental parameters for cellulose fibers pretreatment before fibrillation. All MFCs were characterized by conductometric titration to establish degree of substitution, field emission gun scanning electron microscopy (FEG-SEM), atomic force microscopy (AFM) and optical microscopy assessed the effect of pretreatment on the morphology of the ensuing MFCs. Antibacterial activities of neat and cationized MFC samples were investigated against Gram positive bacteria (Bacillus subtilis, Staphylococcus aureus) and Gram negative bacteria (Escherichia coli). The CATMFC sample at DS greater than 0.18 displayed promising results with antibacterial properties without any leaching of quaternary ammonium into the environment. This work proved the potential of cationic MFCs with specific DS for contact active antimicrobial surface applications in active food packaging, medical packaging or in health and cosmetic field.
Since the mid of 80s, the emergence of resistant bacteria is considered as a major issue and an important threat to the public health as a result of the evolution of new infectious diseases (Feighner and Dashkevicz, 1987, Gilbert and Moore, 2005). The progressive reduction of the effectiveness of antimicrobial toward these resistant bacteria underlines the necessity (i) to evaluate the efficiency of available antimicrobial, (ii) the need to develop novel classes of antimicrobials, (iii) to limit their release in the environment which leads to the emergence of resistant bacteria (Magiorakos et al., 2012, Poverenov et al., 2013). Since 2000s, cationic compounds have emerged as promising candidates for further improvement as antimicrobial agents decreasing evolution of resistant strain. Among these cationic compounds, quaternary ammonium moieties-bearing molecules are widely used, since decades, as antiseptic and disinfectant (Grare et al., 2009), however, their release still limits their applications.
Meanwhile, new contact active antimicrobial surfaces have been developed to restrict the release of active molecule and subsequently the evolution of new resistant bacteria. When biobased and renewable materials are concerned, some successful studies can be quoted with chitosan based materials (Antunes et al., 2015, Zarei et al., 2014), active protein release (Cozzolino et al., 2013, Lavoine et al., 2014, Li et al., 2014) and grafted fibers (Illergard et al., 2012, Österberg et al., 2013). Recently, high specific area microfibrils of cellulose (MFC) have been grafted with active molecules (Fernandes et al., 2013, Missoum et al., 2014, Saini et al., 2015). MFC are produced from cellulose fibers as a result of high shear mechanical fibrillation process. After its discovery in 80s by Turbak, Snyder, and Sandberg (1983), an exponential increase of research and application was recorded with the development of fiber pretreatments. With regard to the commercial production of MFC, the most common fiber pretreatments are enzymatic or oxidation, aiming at reducing the energy consumption during fibrillation (Isogai et al., 2011, Lavoine et al., 2012, Siro and Plackett, 2010). Recently, a new cationization pretreatment has been developed, which, not only reduces the energy consumption for the production of MFC, but also adds new functionalization to the fibrils.
Various cationization agents, such as chlorocholine chloride (ClChCl) (Ho, Zimmermann, Hauert, & Caseri, 2011), Girard's reagent T ((2-hydrazinyl-2-oxoethyl) trimethyl azanium chloride) (Liimatainen, Suopajärvi, Sirviö, Hormi, & Niinimäki, 2014), and 2,3-epoxypropyl trimethylammonium chloride (EPTMAC) (Olszewska et al., 2011, Pei et al., 2013) are mentioned in the literature. However, very few investigations dealing with the experimental optimization of such systems have been performed due to the novelty of these cationized MFCs. Cationic MFC demonstrates the potential to improve compatibility and homogeneous dispersion within polymer matrix (Kalia, Boufi, Celli, & Kango, 2014) and decreases energy consumption at the last step of mechanical disintegration process (Habibi, 2014). As a result of cationization, fibrils with highly swollen outer layer facilitate effective fibrillation in aqueous media (Olszewska et al., 2011).
In another study, the ability of cationic MFC to be used as dye removal from aqueous waste streams due to their high anionic dye adsorption capability was also examined. In addition, cellulose nanopapers prepared with that cationized MFCs displayed high tensile strength (ca. 200MPa) and Young's modulus (ca. 10GPa) despite high porosity (37–48%) as well as ultrahigh water absorbency (750g/g) (Pei et al., 2013). Moreover, high flocculation capacity of cationized cellulose and MFC was confirmed over a wide range of pH for wastewater treatment (Liimatainen et al., 2014, Song et al., 2010, Yan et al., 2009). However, so far no study dealt with the utilization of cationic pretreatment for antimicrobial activity estimation.
Nevertheless, quaternization is also employed as a post treatment of nanofibrils for antimicrobial properties against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa (Andresen et al., 2007). Recently, Hua et al. investigated the cytocompatibility of trimethylammonium-modified MFC and proposed the potentiality of cationized MFC films in tissue engineering applications (Hua et al., 2014). However, post treatment imposes extra cost and also restricts its large scale application.
Therefore, this work first optimizes experimental conditions for fiber pretreatment considering the production of cationized microfibrillated cellulose to attain high degree of substitution (Fig. 1). The second part deals with the detailed investigation of antimicrobial release and quantification of the microbial growth inhibition by cationic MFC with promising results.
Materials and chemical
Cellulose pulp JELUCEL® from oat is obtained from Jelu-Werk, Germany and used as supplied. Chemicals have been purchased from different suppliers (detailed in brackets): cationising agent 2,3-epoxypropyl trimethylammonium chloride (Sigma–Aldrich), sodium hydroxide (Roth, France), sodium thiosulphate anhydrate (Roth, France), sodium chloride (Roth, France), acetic acid (Chimie Plus, France), FiberCare® R cellulase (Novozyme, Sweden), nutrient agar (Roth, France) and nutrient Broth (Roth,
Efficiency of pretreatment
During the cationization reaction, the trimethylammonium chloride groups were chemically grafted onto cellulose through nucleophilic addition of the alkali-activated hydroxyl groups of cellulose to the epoxy moiety of EPTMAC (Hasani et al., 2008, Pei et al., 2013). Therefore, in order to have an efficient reaction with high DS, the following four parameters should be taken into consideration: (i) the amount of NaOH must be high enough to sufficiently activate the surface hydroxyl groups of
This work focuses on optimization of experimental parameters for cationization pre-treatment in order to obtain economically viable contact active antimicrobial microfibrillated cellulose for large scale applications. Cationic MFCs at different DS were obtained by changing the cationization reaction conditions. Results obtained evidently showed the energy consumption reduction of fivefold at fibrillation stage.
Moreover, for the first time, this work demonstrated that such cationic MFC can be
This research was supported by new generation packaging (NEWGENPAK) project of the seven framework program of European research under grant agreement n°290098. LGP2 is part of the LabEx Tec 21 (Investissements d’Avenir – grant agreement n°ANR-11-LABX-0030) and of the Énergies du Futur and PolyNat Carnot Institutes (Investissements d’Avenir – grant agreements n°ANR-11-CARN-007-01 and ANR-11-CARN-030-01). This research made possible thanks to the facilities of the TekLiCell platform funded by the
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Efficient biocoagulants/bioflocculants are desired for removal of Microcystis aeruginosa, the dominant harmful bloom-forming cyanobacterium. Herein, we reported cationic hydroxyethyl cellulose (CHEC) inactivated M. aeruginosa cells after forming coagulates and floating-flocculated them with aid of Agrobacterium mucopolysaccharides (AMP) and surfactant. CHEC exhibited cyanocidal activity at 20mg/L, coagulating 85% of M. aeruginosa biomass within 9h and decreasing 41% of chlorophyll a after 72h. AMP acted as an adhesive flocculation aid that accelerated and strengthened the formation of flocs, approaching a maximum in 10min. Flocs of M. aeruginosa were floated after foaming with cocoamidopropyl betaine (CAB), which facilitated the subsequent filter harvest. 82% of M. aeruginosa biomass was suspended on water surface after treated with the coagulation/flocculation-flotation (CFF) agents containing CHEC (25mg/L), AMP (177mg/L) and CAB (0.1mg/L). All components in CFF agents at the applied concentrations did not inhibit acetylcholinesterase or Vibrio fischeri. Our findings provide new insights in developing bio-based materials for sustainable control of cyanobacterial blooms.
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