Loading...
9 results
Search Results
Now showing 1 - 9 of 9
- Surface properties of suberinPublication . Cordeiro, Nereida; Aurenty, Patrice; Belgacem, Mohamed Naceur; Gandini, Alessandro; Neto, Carlos PascoalThe surface energy of suberin was determined by four different methods, namely, (i) contact angle measurements, (ii) Wilhelmy plate measurements, (iii) maximum bubble pressure, and (iv) inverse gas chromatography (IGC). The first three methods gave a gammasub value in the range 40-50 mN m-1 at room temperature. The major component of this value reflects the dispersive contribution. The IGC measurements showed a higher dispersive term, which is common with this method of characterization. The surface acid (A)/base (B) properties were also evaluated, and the results indicated that suberin has an acidic character.
- Conductive bacterial cellulose-polyaniline blends: Influence of the matrix and synthesis conditionsPublication . Alonso, Emanuel; Faria, Marisa; Mohammadkazemi, Faranak; Resnik, Matic; Ferreira, Artur; Cordeiro, NereidaBacterial cellulose/polyaniline (BC/PANi) blends present a great potential for several applications. The current study evaluates the impact of using different BC matrixes (drained, freeze-dried and regenerated) and different synthesis conditions (in situ and ex situ) to improve the inherent properties of BC, which were monitored through FTIR-ATR, EDX, XRD, SEM, AFM, swelling, contact angle measurement and IGC. The employment of in situ polymerization onto drained BC presented the most conductive membrane (1.4 × 10-1 S/cm). The crystallinity, swelling capacity, surface energy and acid/base behavior of the BC membranes is substantially modified upon PANi incorporation, being dependent on the BC matrix used, being the freeze-dried BC blends the ones with highest crystallinity (up to 54%), swelling capacity (up to 414%) and surface energy (up to 75.0 mJ/m2). Hence, this work evidenced that the final properties of the BC/PANi blends are greatly influenced by both the BC matrixes and synthesis methods employed.
- Influence of mild alkaline treatment on the cellulosic surfaces active sitesPublication . Ashori, Alireza; Ornelas, Mariana; Sheshmani, Shabnam; Cordeiro, NereidaAgro-residues fibers are inexpensive environmentally friendly alternatives to synthetic fibers in fiber reinforced polymer composites. The natural fiber properties and bondability with adhesive can be modified by subjecting the fibers to a pre-treatment procedure. The knowledge ofthe modified fibers sur face properties is essential to explain and predict their applications. The present study is focused on the effect of alkaline treatment on the surface characteristics of stalk fibers from rapeseed, tobacco, cotton, lemon balm and kiwi. The chemical composition of fibers and Fourier transform infrared spectroscopy show components extraction and the X-ray diffraction show improvement in the crystallinity index of the treated fibers. But only the IGC analysis allows us to know in detail the alterations on the fiber surface and the effect on the adhesion of the fibers. IGC shows that alkaline treatment produces changes in the nature and number of the active sites, responsible for the physico-chemical activity of the surface of the fibers. The fiber hydrophobicity was improved by the increase of more energetic and active sites in the surface. Also,the creation of new basic active sites and removal of acidic active sites from the fiber surface due to alkaline treatment has been clearly shown.
- Influence of the matrix and polymerization methods on the synthesis of BC/PANi nanocomposites: an IGC studyPublication . Alonso, Emanuel; Faria, Marisa; Ferreira, Artur; Cordeiro, NereidaInverse gas chromatography (IGC) is a technique for evaluating surface properties. The current work emphasizes the use of IGC to evaluate the surface physicochemical changes during different bacterial cellulose (BC) processing methods as well as upon polyaniline (PANi) incorporation. The processing methods (oven-drying, freeze-drying, and regeneration) caused changes in the BC surface group distribution, where upon freeze-drying and regeneration, a more acidic behavior is obtained, compared to oven-drying (Kb/Ka decreased up to 24%). Through freeze-drying, the structural pore preservation increases (54%) the BC porosity, whereas through regeneration, the porosity decreases (23%), compared to BC oven-drying. Regarding the nanocomposites, with PANi incorporation, the overall properties evaluated by IGC were significantly changed. The γtotals increases up to 150%, indicating a more reactive surface in the nanocomposites. Also, is observed a sevenfold increase in the Kb/Ka and a less porous surface (up to 85%). Hence, the current work highlights the use of IGC as a viable technique to evaluate the physicochemical changes upon different BC modifications.
- Surface modification of banana fibers using organosilanes: an IGC insightPublication . Alonso, Emanuel; Pothan, Laly A.; Ferreira, Artur; Cordeiro, NereidaBanana fibers are an agricultural waste material with a great exploitation potential due to their cellulose-rich content. Raw banana fibers (RBF) were treated with 3-aminopropyltriethoxy silane and glycidoxypropyltrimethoxy silane to improve the inherent limitations of banana fibers, namely its poor cell adhesion. The fibers’ modification was evaluated by inverse gas chromatography (IGC). Similar cs d values were observed between the RBF and silane-treated fibers (39–41 mJ/m2 ), which indicates similar reactivity towards apolar probes. However, the decrease in the entropic parameter indicates the silane covalent bonding with the cellulose chains making a stiffer structure. Organosilane grafting was confirmed by an increased basic character in the silane-treated fibers (Kb/Ka from 1.03 to 2.81). The surface morphology also changed towards higher contact area (SBET increases 6.7 times) and porosity (Dp increases up to 67%). Both morphological and functional group reactivity changes suggest that the organosilane treatment offers new opportunities for these fibers to be used as adsorbents for proteins as well as to cell adhesion. Therefore, IGC proved a simple and viable technique in the characterization of silane-treated fibers.
- Effect of chitosan and cationic starch on the surface chemistry properties of bagasse paperPublication . Ashori, Alireza; Cordeiro, Nereida; Faria, Marisa; Hamzeh, YahyaThe use of non-wood fibers in the paper industry has been an economical and environmental necessity. The application of dry-strength agents has been a successful method to enhance the strength properties of paper. The experimental results evidencing the potential of chitosan and cationic starch utilization in bagasse paper subjected to hot water pre-extraction has been presented in this paper. The research analyzes the surface properties alterations due to these dry-strength agents. Inverse gas chromatography was used to evaluate the properties of surface chemistry of the papers namely the surface energy, active sites, surface area as well as the acidic/basic character. The results of the study revealed that the handsheets process causes surface arrangement and orientation of chemical groups, which induce a more hydrophobic and basic surface. The acid-base surface characteristics after the addition of dry-strength agents were the same as the bagasse handsheets with and without hot water pre-extraction. The results showed that the dry-strength agent acts as a protecting film or glaze on the surfaces of bagasse paper handsheets.
- Characterization of the cork surface by inverse gas chromatographyPublication . Cordeiro, Nereida; Neto, Carlos Pascoal; Gandini, Alessandro; Belgacem, Mohamed NaceurInverse gas chromatography (IGC) at infinite dilution has been used to study the surface properties of cork from Quercus suber. The dispersive component of its surface energy was determined at different temperatures using n -alkanes as probes, and a γDS value of 38 ± 1 mJ · m-2 at 40°C was obtained. The surface acid (A)/base (B) properties were also evaluated by using polar probes and the results indicate that cork has an amphoteric character, with a KA /KB = 1.1. The advantages of IGC, compared with the technique of contact angle measurements in the characterization of the cork surface, are discussed.
- Investigation on the surface properties of chemically modified natural fibers using inverse gas chromatographyPublication . Cordeiro, Nereida; Ornelas, Mariana; Ashori, Alireza; Sheshmani, Shabnam; Norouzi, HorThis paper presents the application of inverse gas chromatography (IGC) technique for characterization and comparison of the surface properties of the natural fibers as reinforcement fillers in wood plas tic composites. The effects of chemical modification using 1% NaOH were also studied. The fibers used for this work were Iranian cultivated eucalyptus, spruce, bagasse, and wheat straw. Chemical composi tion of fibers was found to be modified after treatment as characterized by Fourier transform infrared spectroscopy (FTIR). The crystallinity of fibers and the specific interaction was improved by the alkaline treatment, with more relevance to the agro-fibers. The IGC shows also a general increase in the wettability of the modified fiber when compared with the raw (unmodified) samples. Alkaline treatment achieves the best overall improvement in the properties evaluated of the agro-fibers when compared to the wood fibers.
- Physicochemical surface properties of bacterial cellulose/polymethacrylate nanocomposites: an approach by inverse gas chromatographyPublication . Faria, Marisa; Vilela, Carla; Silvestre, Armando J.D.; Deepa, Bhanumathyamma; Resnik, Matic; Freire, Carmen S. R.; Cordeiro, NereidaNanocomposites of poly(glycidyl methacrylate) and bacterial cellulose (BC), or poly(poly(ethylene glycol) methacrylate) and BC were produced via the in-situ polymerization of methacrylic monomers, inside the BC 3D network. The nanocomposites surface properties were evaluated by inverse gas chromatography (IGC). The dispersive component of surface energy (γsd) varied between 35.64 - 83.05 mJ m-2 at 25 °C. The surface of the different nanocomposites has a predominant basic character (Kb/Ka = 4.20-4.31). Higher specific interactions with polar probes were found for the nanocomposite bearing pendant epoxide groups, that apart from the low surface area (SBET = 0.83 m2 g-1) and monolayer capacity (nm = 2.18 μmol g-1), exhibits a high value of γsd (88.19 mJ m-2 at 20 °C). These results confirm the potential of IGC to differentiate between nanocomposites with different surface functional groups and to predict their potential interactions with living tissues, body fluids and other materials.