Improving the Processability and Performance of Micronized Fiber-Reinforced Green Composites through the Use of Biobased Additives.

Green composites made of bioplastics reinforced with natural fibers have gained considerable attention over recent years. However, the use of natural fibers in composites usually compromise some key properties, such as the impact strength and the processability of the final materials. In the present study, two distinct additives, namely an epoxidized linseed oil (ELO) and a sugar-based surfactant, viz. GlucoPure® Sense (GPS), were tested in composite formulations of poly(lactic acid) (PLA) or poly(hydroxybutyrate) (PHB) reinforced with micronized pulp fibers. Both additives showed a plasticizing effect, which led to a decrease in the Young's and flexural moduli and strengths. At the same time, the elongation and flexural strain at break were considerably improved on some formulations. The melt flow rate was also remarkably improved with the incorporation of the additives. In the PHB-based composites, an increment of 230% was observed upon incorporation of 7.5 wt.% ELO and, in composites based on PLA, an increase of around 155% was achieved with the introduction of 2.5 wt.% GPS. ELO also increased the impact strength to a maximum of 29 kJ m-2, in formulations with PLA. For most composites, a faster degradation rate was observed on the formulations with the additives, reaching, in the case of PHB composites with GPS, a noteworthy weight loss over 75% under burial testing in compost medium at room temperature.

Effect of the Micronization of Pulp Fibers on the Properties of Green Composites.

Green composites, composed of bio-based matrices and natural fibers, are a sustainable alternative for composites based on conventional thermoplastics and glass fibers. In this work, micronized bleached Eucalyptus kraft pulp (BEKP) fibers were used as reinforcement in biopolymeric matrices, namely poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB). The influence of the load and aspect ratio of the mechanically treated microfibers on the morphology, water uptake, melt flowability, and mechanical and thermal properties of the green composites were investigated. Increasing fiber loads raised the tensile and flexural moduli as well as the tensile strength of the composites, while decreasing their elongation at the break and melt flow rate. The reduced aspect ratio of the micronized fibers (in the range from 11.0 to 28.9) improved their embedment in the matrices, particularly for PHB, leading to superior mechanical performance and lower water uptake when compared with the composites with non-micronized pulp fibers. The overall results show that micronization is a simple and sustainable alternative for conventional chemical treatments in the manufacturing of entirely bio-based composites.

Unravelling the distinct crystallinity and thermal properties of suberin compounds from Quercus suber and Betula pendula outer barks.

The main purpose of this study was to investigate the potential of suberin (a naturally occurring aromatic-aliphatic polyester ubiquitous to the vegetable realm) as a renewable source of chemicals and, in particular, to assess their physical properties. A comparison between cork and birch suberin fragments obtained by conventional depolymerisation processes (hydrolysis or methanolysis) is provided, focusing essentially on their thermal and crystallinity properties. It was found that suberin fragments obtained by the hydrolysis depolymerisation of birch had a high degree of crystallinity, as indicated by their thermal analysis and corroborated by the corresponding XRD diffractions, as opposed to hydrolysis-depolymerised cork suberin counterparts, which were essentially amorphous.

Nanostructured bacterial cellulose-poly(4-styrene sulfonic acid) composite membranes with high storage modulus and protonic conductivity.

The present study reports the development of a new generation of bio-based nanocomposite proton exchange membranes based on bacterial cellulose (BC) and poly(4-styrene sulfonic acid) (PSSA), produced by in situ free radical polymerization of sodium 4-styrenesulfonate using poly(ethylene glycol) diacrylate (PEGDA) as cross-linker, followed by conversion of the ensuing polymer into the acidic form. The BC nanofibrilar network endows the composite membranes with excellent mechanical properties at least up to 140 °C, a temperature where either pure PSSA or Nafion are soft, as shown by dynamic mechanical analysis. The large concentration of sulfonic acid groups in PSSA is responsible for the high ionic exchange capacity of the composite membranes, reaching 2.25 mmol g(-1) for a composite with 83 wt % PSSA/PEGDA. The through-plane protonic conductivity of the best membrane is in excess of 0.1 S cm(-1) at 94 °C and 98% relative humidity (RH), decreasing to 0.042 S cm(-1) at 60% RH. These values are comparable or even higher than those of ionomers such as Nafion or polyelectrolytes such as PSSA. This combination of electric and viscoelastic properties with low cost underlines the potential of these nanocomposites as a bio-based alternative to other polymer membranes for application in fuel cells, redox flow batteries, or other devices requiring functional proton conducting elements, such as sensors and actuators.

Bacterial cellulose membranes as transdermal delivery systems for diclofenac: in vitro dissolution and permeation studies.

Bacterial cellulose (BC) membranes were explored as novel nanostructured transdermal delivery systems for diclofenac sodium salt (a typical non-steroidal anti-inflammatory drug). Diclofenac sodium salt loaded BC membranes were prepared through a simple methodology, using glycerol as plasticizer, and characterized in terms of structure, morphology and swelling behavior. The membranes were very homogeneous, quite flexible and presented a considerably higher swelling behavior when compared with pure BC. In vitro diffusion studies with Franz cells, were conducted using human epidermal membranes, and showed that the incorporation of diclofenac in BC membranes provided similar permeation rates to those obtained with commercial patches and substantially lower than those observed with a commercial gel. This release profile together with the ease of application and the simple preparation and assembly of the drug-loaded membranes clearly indicates the enormous potentialities of using BC membranes for transdermal administration of diclofenac.

Ultra-high performance liquid chromatography coupled to mass spectrometry applied to the identification of valuable phenolic compounds from Eucalyptus wood.

Ultra-high performance liquid chromatography (UHPLC) was applied for the first time in the analysis of wood extracts. The potential of this technique coupled to ion trap mass spectrometry in the rapid and effective detection and identification of bioactive components in complex vegetal samples was demonstrated. Several dozens of compounds were detected in less than 30min of analysis time, corresponding to more than 3-fold reduction in time, when compared to conventional HPLC analysis of similar extracts. The phenolic chemical composition of Eucalyptus grandis, Eucalyptus urograndis (E. grandis×E. urophylla) and Eucalyptus maidenii wood extracts was assessed for the first time, with the identification of 51 phenolic compounds in the three wood extracts. Twenty of these compounds are reported for the first time as Eucalyptus genus components. Ellagic acid and ellagic acid-pentoside are the major components in all extracts, followed by gallic and quinic acids in E. grandis and E. urograndis and ellagic acid-pentoside isomer, isorhamnetin-hexoside and gallic acid in E. maidenii. The antioxidant scavenging activity of the extracts was evaluated, with E. grandis wood extract showing the lowest IC50 value. Moreover, the antioxidant activity of these extracts was higher than that of the commercial antioxidant BHT and of those of the corresponding bark extracts. These results, together with the phenolic content values, open good perspectives for the exploitation of these renewable resources as a source of valuable phenolic compounds.

Antifungal activity of transparent nanocomposite thin films of pullulan and silver against Aspergillus niger.

Silver has been mainly investigated as an antibacterial agent and less as a fungicide in which concerns antimicrobial properties. In this research, the antifungal activity of composite films of pullulan and Ag nanoparticles (NP) against Aspergillus niger was evaluated using standard protocols. These new materials were prepared as transparent cast films (66-74 µm thickness) from Ag hydrosols containing the polysaccharide. Fungal growth inhibition was observed in the presence of such silver nanocomposite films. Moreover, disruption of the spores cells of A. niger was probed for the first time by means of scanning electron microscopy (SEM). This effect occurred in the presence of the nanocomposites due to Ag NP dispersed as fillers in pullulan. This polysaccharide was used here as a biocompatible matrix, hence making these nanocomposites beneficial for the development of antifungal packaging materials.

Bacterial cellulose membranes applied in topical and transdermal delivery of lidocaine hydrochloride and ibuprofen: in vitro diffusion studies.

Bacterial cellulose (BC) is a biomaterial with unique physical and mechanical properties that triggered considerable interest, but there are few studies addressing the use of such membranes for drug loading and controlled release. This study aimed to investigate the applicability of BC membranes in topical or transdermal drug delivery systems. To assess its therapeutic feasibility, the permeation through human epidermis of two model drugs (lidocaine hydrochloride and ibuprofen) in BC and other formulation systems was compared in vitro. A uniform distribution of both drugs in the BC membranes was achieved. Diffusion studies with Franz cells showed that the incorporation of lidocaine hydrochloride in BC membranes provided lower permeation rates than those obtained with the conventional formulations. However, the results obtained with the lipophilic drug were quite different, since permeation of ibuprofen in BC was almost three times higher than that of the drug in the gel or in a PEG400 solution. These results indicate that this technology can be successfully applied to modulate the bioavailability of drugs for percutaneous administration, which could be particularly advantageous in the design of delivery systems that have, simultaneously, the ability to absorb exudates and to adhere to irregular skin surfaces.

Antibacterial activity of optically transparent nanocomposite films based on chitosan or its derivatives and silver nanoparticles.

Colloidal silver nanoparticles (NPs) were prepared using the citrate and borohydride reduction methods and were then investigated as fillers in three matrices: unmodified chitosan, water-soluble chitosan and a N-alkyl chitosan derivative. The nanocomposites were used to prepare cast thin films (9-19 µm thickness) and characterized for their optical and antimicrobial properties. The optical properties of the materials were adjusted either by varying the Ag NPs content in the films (0.5-3.9% w/w) or by using samples of Ag NPs with distinct particle size distributions. The antibacterial activity towards both Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Klebsiella pneumoniae and Escherichia coli) was investigated for the various composites. For the unmodified chitosan nanocomposites, the bactericidal effect depended on their Ag content while such an effect was always observed for water-soluble chitosan and N-alkyl chitosan based materials. This research provides a basis for the evaluation of chitosan/silver composites in applications requiring flexible films with tuned optical properties and antimicrobial activity.

Biocellulose membranes as supports for dermal release of lidocaine.

Biocellulose (BC) is a highly pure form of cellulose, produced in the form of a swollen membrane, with several applications in the biomedical area. In this study, the behavior of BC membranes as systems for topical delivery of lidocaine was evaluated. The BC-lidocaine membranes were prepared and characterized in terms of structural and morphological properties. A uniform distribution of the drug inside the BC membranes was observed. In vitro diffusion studies with Franz cells were conducted using human epidermal membranes and showed that the permeation rate of the drug in BC membranes was slightly slower than that obtained with the conventional systems, which was attributed to the establishment of interactions between the lidocaine molecules and the BC membrane, as evidenced by FTIR and NMR analysis. These results indicate that this methodology can be successfully applied for the dermal administration of lidocaine regarding the release profile and ease of application.

Utilization of residues from agro-forest industries in the production of high value bacterial cellulose.

Bacterial cellulose (BC), a very peculiar form of cellulose, is gaining considerable importance due to its unique properties. In this study, several residues, from agro-forestry industries, namely grape skins aqueous extract, cheese whey, crude glycerol and sulfite pulping liquor were evaluated as economic carbon and nutrient sources for the production of BC. The most relevant BC amounts attained with the residues from the wine and pulp industries were 0.6 and 0.3 g/L, respectively, followed by biodiesel crude residue and cheese whey with productions of about, 0.1 g/L after 96 h of incubation. Preliminary results on the addition of other nutrient sources (yeast extract, nitrogen and phosphate) to the residues-based culture media indicated that, in general, these BC productions could be increased by ~200% and ~100% for the crude glycerol and grape skins, respectively, after the addition organic or inorganic nitrogen.

Miscanthus x giganteus bark organosolv fractionation: fate of lipophilic components and formation of valuable phenolic byproducts.

The behavior of Miscanthus x giganteus bark lipophilic extractives during three acid organosolv pulping processes (Acetosolv, formic acid fractionation, and Milox) was investigated. It was demonstrated that nearly 90% of the lipophilic extractives were removed from pulps by either dissolution in the organosolv liquors (fatty acids and alcohols) or extensive degradation (sterols). The organosolv liquors were found to be rich in vanillin, syringaldehyde, and ferulic, vanillic, and p-coumaric acids. The Acetosolv fractionation process was found to be the most efficient in the removal of lipophilic components from pulps, and it was also the process that generated higher amounts of valuable monomeric phenolic compounds that could be exploited within the biorefinery context.

Antibacterial activity of nanocomposites of silver and bacterial or vegetable cellulosic fibers.

Cellulose/Ag nanocomposites were prepared using two distinct methodologies and two cellulose substrates: vegetable and bacterial cellulose. These nanocomposites were characterized in terms of their morphology and chemical composition. Detailed studies on the antibacterial activity of these materials were carried out for Bacillus subtilis, Staphylococcus aureus and Klebsiella pneumoniae. Silver nanoparticles present in the cellulosic fibers in concentrations as low as 5.0x10(-4)wt.% make these nanocomposites effective antibacterial materials. We anticipate that the versatile use of these cellulose-based nanocomposites can bring a promising strategy to produce a wide range of interesting materials where antibacterial properties are crucial.

Superhydrophobic cellulose nanocomposites.

Superhydrophobic cellulose nanocomposites were prepared using a multi-step nanoengineering process. The combination of different techniques made it possible to construct novel features at the ensuing surface, characterized by both an increase in its roughness induced by amorphous silica particles and a reduction in its energy insured by perfluoro moieties, giving rise to water contact angles approaching 150 degrees . The modification calls upon an aqueous LbL system followed by siloxane hydrolysis, both conducted at room temperature in air. Each modification was followed by scanning electron microscopy (SEM) and atomic force microscope (AFM). These original cellulose-silica-silane composite materials open the way to further valorisations of a ubiquitous renewable resource in applications such as water repellence and self-cleaning.

Bi-phobic cellulose fibers derivatives via surface trifluoropropanoylation.

The surface modification of cellulose fibers with 3,3,3-trifluoropropanoyl chloride (TFP) was studied in a toluene suspension. The characterization of the modified fibers was performed by elemental analysis, Fourier transform infrared (FTIR), 13C-solid-state NMR, X-ray diffraction, thermogravimetry, and surface analysis (XPS, ToF-SIMS, and contact angles measurements). The degree of substitution (DS) of the ensuing trifluoropropanoylated fibers ranged from less than 0.006 to 0.30, and in all instances the fibers' surface acquired a high hydrophobicity and lipophobicity resulting from a drastic reduction in its energy. The hydrolytic stability of these cellulose derivatives was also evaluated and shown to be permanent in time in the presence of neutral water, still appreciable in basic aqueous solution at pH 9, but, as expected quite poor at pH 12.

Characterization and evaluation of the hydrolytic stability of trifluoroacetylated cellulose fibers.

The controlled heterogeneous modification of cellulose fibers with trifluoroacetic anhydride was investigated. The characterization of the ensuing materials was performed by elemental analysis, FTIR spectroscopy, X-ray diffraction (XRD), thermogravimetry, and surface analysis (XPS, ToF-SIMS, and contact angles measurements). The trifluoroacetylation enhanced significantly the hydrophobic and lipophobic character of the fibers, whereas their thermal stability and cristallinity were only modestly affected by this treatment, except under the most severe conditions for the latter. Their hydrolytic stability to water vapour was also assessed as a function of the air humidity and shown to be lower than that of still liquid water in the case of a saturated atmosphere.

Electrostatic assembly and growth of gold nanoparticles in cellulosic fibres.

Synthetic studies of nanocomposites containing gold nanoparticles attached onto wood or bacterial cellulosic fibres have been performed in situ in the presence of the fibres or by polyelectrolyte-assisted deposition. The optical properties of the final nanocomposites could be tailored not only by the starting Au nanoparticles characteristics but also by the preparative method associated to the type of cellulosic fibres used as the substrate. Thus, gold nanoparticles assembled or generated in situ within cellulosic fibres, are excellent components for long term optical and chemically stable nanocomposites, which appear particularly interesting for security paper applications.

Demonstration of long-chain n-alkyl caffeates and delta7-steryl glucosides in the bark of Acacia species by gas chromatography-mass spectrometry.

The GC-MS identification of several abundant long-chain aliphatic n-alkyl caffeates, together with other phydroxycinnamic acid esters, in the dichloromethane extracts of the bark of Acacia dealbata and A. melanoxylon, is reported. In addition, the unambiguous differentiation between two delta7-steryl glucosides (namely, spinasteryl glucoside and dihydrospinasteryl glucosides) and the homologous delta5-steryl glucosides was achieved based on the EI-MS fragmentation features of their trimethylsilyl derivatives.

Reversible hydrophobization and lipophobization of cellulose fibers via trifluoroacetylation.

The surface modification of cellulose fibers with trifluoroacetic anhydride (TFAA) was studied using the heterogeneous cellulose/TFAA/pyridine/toluene system. The degree of substitution (DS) of the ensuing trifluoroacetylated fibers ranged from 0.04 to 0.30. This treatment conferred a high degree of both hydrophobicity and lipophobicity on the fibers' surface, even at low DS values. Both the dispersive and the polar contributions to the surface energy were drastically reduced. However, the original cellulose hydrophilicity could be readily restored through hydrolysis, by treating the modified fibers with neutral water.

Characterization of an acetylated heteroxylan from Eucalyptus globulus Labill.

A heteroxylan was isolated from Eucalyptus globulus wood by extraction of peracetic acid delignified holocellulose with dimethyl sulfoxide. Besides (1-->4)-linked beta-D-xylopyranosyl units of the backbone and short side chains of terminal (1-->2)-linked 4-O-methyl-alpha-D-glucuronosyl residues (MeGlcA) in a 1:10 molar ratio, this hemicellulose contained galactosyl and glucosyl units attached at O-2 of MeGlcA originating from rhamnoarabinogalactan and glucan backbones, respectively. About 30% of MeGlcA units were branched at O-2. The O-acetyl-(4-O-methylglucurono)xylan showed an acetylation degree of 0.61, as determined by 1H NMR spectroscopy, and a weight-average molecular weight (M(w)) of about 36 kDa (P=1.05) as revealed from size-exclusion chromatography (SEC) analysis. About half of the beta-D-xylopyranosyl units of the backbone were found as acetylated moieties at O-3 (34 mol%), O-2 (15 mol%) or O-2,3 (6 mol%). Practically, all beta-D-xylopyranosyl units linked at O-2 with MeGlcA residues were 3-O-acetylated (10 mol%).