•A gradual deconstruction process for the determination of the chemical composition of the banana stem is described.•A method for the production of long fibres at approx. 60% yield is shown.•The ...mechanical behaviour of the long fibres is assessed.•Mechanical properties of long fibres compare favorably to those of similar fibres reported in the literature.
Banana Pseudo–stem (BPS) is an annual renewable agricultural by–product with a potential for valorization in the production of paper, textile fibre or new bio–based materials. A gradual deconstruction process was implemented to determine BPS chemical composition and isolate sub–components that may be valorized in the formulation of bio–based polymer composites. At each step, the residues were analyzed by FTIR, X–ray diffraction and TGA–DTG. The chemical composition of the starting material (% of dry weight) was evaluated as: 13.4% total extractives, 6% pectins, 14.7% lignins, 28% hemicelluloses and 38% cellulose. The deconstruction process for BPS was efficient but led to mercerized cellulose (cellulose II) as a final residue, as assessed by the intense X–ray scattering peaks centered at 20.5° and 21.5°. Cellulose II formation was induced by the high concentration of the alkaline KOH solution used to dissolve hemicelluloses in holocellulose. The step–wise removal of non–cellulosic sub–components led to a more thermally stable residue. Long fibres were also obtained from BPS at a yield of 60%. These fibres display cellulose I structure and a thermal stability similar to the extracted cellulose. SEM analyses of long fibres showed transversal and lateral defects, the presence of surface hairiness and an almost cylindrical morphology. Uniaxial tensile tests were carried out at room temperature on 150 specimens randomly chosen among the less hairy fibres, with diameters ranging from 40 to 140 μm. Mechanical investigations (Young modulus: 6.3–26 GPa; nominal stress at break: 140–768 MPa; nominal strain at break: ∼3%) reveal a significant disparity strongly influenced by fibre diameter, except for the nominal strain at break which remains fairly constant around 3%. These results are comparable to the upper range of the values reported for fibres extracted from BPS through alternative chemical routes or for fibres obtained from other annual plants such as jute and hemp.
The purpose of this study was to comparatively investigate the behavior of silicate and sol-silicate coatings non-modified or modified with an organosilane on wood and on wood pre-coated with ...silica-mineralized primers. Adhesion strength, morphology, and water permeability and related damages were studied to evaluate the possibility of utilizing such inorganic-based coating systems for durable protection of wood without or with relatively cheap and water-borne primers. Potassium silicate and potassium methylsiliconate aqueous solutions and a colloidal silica were used for the preparation of the coatings. The white coating paints were brushed on beech wood substrates at a rate of 220 g·m
. The coatings exhibited good coverage ability. The pull-off adhesion strength values appeared to be related to pH following a polynomial law. The adhesion strength for the silicate coatings were adequate (above 3 MPa and up to 5 MPa) for wood, whereas the values for the sol-silicates were too low for practical applications. The adhesion values were in general higher for the samples cured in a climate room (23 ± 3 °C and 75 ± 2% relative humidity) than the samples cured in the ambient atmosphere of the laboratory (23 ± 3 °C and 25 ± 5% relative humidity). The presence of microdefects (cracks, holes) was revealed in the coating layers by optical and scanning electron microscopy. The surface roughness parameters assessed by confocal scanning laser microscopy were dependent on the magnification applied for their measurement. The arithmetic average roughness
was between 5 µm and 10 µm at magnification 5× and between 2.5 μm and 10 µm at magnification 20×. The maximum peak-to-valley height
confirmed the presence of open pores emerging through the coatings. The open pores constitute free pathways for water ingress through the coatings, and could explain the high water absorption of the coatings including the methysiliconate-containing silicate coating and despite the relatively high water contact angle and low wettability exhibited by this sample. The post-application of a hydrophobizing solution containing hexadecyltrimethoxysilane and dimethyloctadecyl3-(trimethoxysilyl)propylammonium chloride considerably reduced the water permeability, while application of nanosilica-containing organic primers increased the adhesion for the coatings. Silicate coatings with adhesion great enough and resistance against water damages can be generated on wood even without a primer using low silica-to-alkali ratio binders and an organosilane additive. The sol-silicate coatings appear to be applicable only with a primer. The improvement of the paint formulations to control the formation of microcracks and open pores could be useful to reduce the liquid water permeability and increase durability. Otherwise, the application of a hydrophobizing treatment can be used for this purpose.
Silica or silica-precursor systems are attractive for the protection of wood against biotic and abiotic damages and for improvement of the fire resistance. Alkali metal silicate solutions, also known ...as water glasses, colloidal silica (nanosilica dispersions) and other inorganic–organic hybrids resulting from the sol-gel chemistry of alkoxysilane compounds, are products available for this purpose. These chemicals are increasingly considered to formulate wood modification products or to develop surface coatings. This review article is focused on in-depth treatments of wood through dipping, soaking or vacuum-pressure impregnation methods. The techniques used to convert monomers and low molecular weight silicate species in water glasses into less soluble and leaching-resistant silica particles, such as heat treatment, acid treatment and reactions with multivalent metal cation salts, are discussed. The similarities and differences between the various raw-impregnation materials and the properties of the final products are highlighted. Water glasses after appropriate curing, colloidal silica and tetraalkoxysilane-based formulations all lead to deposition of silica particles (SiO
2
) at the surface of the cell walls, in lumens and pores. Low molecular weight organosilanes and other organo-modified formulations that are able to penetrate the wood cell walls and react with wood components are good dimensional stabilizers. The treated wood exhibits, in general, increased mechanical properties (strength, hardness) and improved resistance to biodegradation and fire retardancy. The efficiency of the treatments can significantly be enhanced to a level fulfilling the requirements for industrial applications by the addition of biocides, ultraviolet absorbers or antioxidants, fireproofing compounds (boron or phosphorus-based compounds, multivalent metal salts) and hydrophobic alkylalkoxysilanes. Silica acts as a barrier/support to many of these additives preventing them from leaching.
The present study focuses on the synthesis of phosphorus-containing epoxy resins and their use as reactive flame retardants. Phosphorus-functionalized epoxy resins were synthesized using different ...aliphatic diols. First, phosphorus was grafted by reacting phosphoryl chloride with three different aliphatic diols: 1,5-pentanediol, 1,4-butanediol, or 1,3-propanediol. The ensuing phosphorus-triol compounds were epoxidized with epichlorohydrin in an alkaline medium. Fourier transform infrared and nuclear magnetic resonance spectroscopy confirmed the presence of the epoxy-end group in the structure of synthesized epoxy resins. The phosphorus-containing epoxy resins were mixed with diglycidyl ether of bisphenol A at a fixed mass ratio of 9:1, and the hybrid formulations were cured with triethylene tetramine as a hardener. Their thermal behaviour was assessed by differential scanning calorimetry and thermogravimetric analysis. Furthermore, the hybrid epoxy resins were blended with nanoclay and applied as a finishing on the grain surface of the leather. Thermal analyses of the coated leather showed an enhancement of thermal performance with an increase of statistical heat resistant index temperature from 100 to 121 °C. The flame retardation properties were also assessed and it was found that after coating leather with epoxy nanocomposites, the limiting oxygen index of leather increased from 26.7 ± 0.5 to 28.6 ± 0.7%, while the ignition time of 6.0 s developed to 8.1 s. Consequently, all the leather samples coated with phosphorus-based epoxy nanocomposites exhibited a self-extinguishing behaviour due to the synergistic effect of phosphorus atoms and clay nanoparticles.
Graphical abstract
Cellulose is a natural polymer obtained from plants with applications in various industrial sectors such as pulp and paper, textiles, coatings, fibre composites, and nanomaterials. This work studied ...the extraction of cellulose from a tropical agricultural plant residue
Ceiba pentandra
(
C. pentandra
) using the organosolv method formic acid (FA)-acetic acid (AA)-water (Wa) mixtures as a function of temperature, time, and composition the cooking solvent mixture. Three different volume ratios FA:AA:Wa of 50:30:20, 40:40:20 and 20:30:50 were investigated. Reaction temperature was varied between 80 and 107 °C and the duration between 40 and 200 min. The efficacy of the cooking reaction was determined by the fibre percent yield and Kappa number of the cooking residue. Cooking residues with relatively higher yields (50–70%) were compared with the conventional Kraft method. The residues with yields between 50 and 60% were bleachable as revealed by their Kappa numbers of around 10–12. Some residues were bleached and the products were characterised by Fourier Transform Infrared (FTIR) spectroscopy, thermogravimetric analyses (TG-DTG) and x-ray diffraction (XRD). The results showed that the bleached products had properties close to those of commercial cellulose exhibiting almost similar FTIR spectra and TG-DTG curves. The optimum formic acid-acetic acid-water mixture 50:30:20 at a mild temperature of 107 °C for 3 h, exhibited an activation energy E
a
= 141.12 kJ mol
-1
K
-1
and a high crystallinity rate of 72.95% compared to Kraft and Alcell celluloses. This method can be used as a relatively soft route (at mild temperatures, atmospheric pressure) to produce cellulose from the lignocellulosic residues of tropical eteng,
C. pentandra
.
The present work focuses on the preparation of epoxy acrylate/titania materials using lithography-based additive manufacturing. A series of polymeric nanocomposite resin blends is formulated and ...cured with digital light processing (DLP) through three-dimensional printing studies. Epoxy acrylate oligomers are synthesized by reacting glycidyl methacrylate with acrylic acid, poly(ethylene glycol) dimethacrylate and poly(ethylene glycol) methyl ether methacrylate in the presence of triphenylphosphine as the catalyst and benzoin as the photoinitiator. The impact of TiO
2
nanoparticles in various formulations is investigated, and 3D designed specimens are successfully printed with a Creality LDR002-DLP machine. The resulting materials are characterized using Fourier Transform infrared spectroscopy, mechanical and thermal analyses, allowing for the determination of their chemical and physical properties. Although all the resin formulations investigated in this study are compatible with DLP-3D printing technology, the nanoparticle-incorporated formulations required less time to UV-cure compared to the other formulations. Notably, the printed specimens containing the TiO
2
nanoparticles exhibit better thermal stability and gel content. The highly crosslinked structure formation of these systems provides good dimensional stability, which is crucial for 3D printing.
Cellulosic fibers were extracted from the pseudo-stem of Musa sapientum cultivated in two different sites in Cameroon. The FBY (Yaounde Banana Fibers) and FBP (Penja Banana Fibers) studied in this ...work were obtained by a bio-extraction method and characterized. The apparent densities of FBP and FBY were 0.90 ± 0.02 g/cm
3
and 1.03 ± 0.04 g/cm
3
, while the moisture contents were 10.6 ± 0.2% and 12.4 ± 0.3%, respectively. Their chemical compositions were as follows: extracts 15.32% and 17.79%; pectin 5.7% and 14.77%; lignin 10.1% and 9.8%; and cellulose 47.1% and 58.3%, respectively. The water absorption rate at saturation was 140% and 170% by mass and was reached rapidly in the first 30 min of immersion. The tensile strengths of fibers were 743.9 MPa and 730.6 MPa, the elastic moduli were 260 MPa and 242 MPa, and the elongations at break were 2.8% and 2.2%, respectively. From the thermal analysis, the fibers' stability temperatures were in the neighborhood of 250°C. Only slight differences were noticed in the properties of both fibers. Long outdoor conservation of the banana pseudo-stems before processing provided fibers with properties comparable to the properties of natural fibers reported in the literature. Independently of the harvesting locations, both fibers can be envisaged as cost-cutting fillers in the plastic industry.
Silicate coatings are environmentally friendly inorganic-based products that have long been used for mineral substrates and protection of steel against corrosion. The development and acceptance of ...these coatings in the wood sector require some adjustments in formulations or special preparation of the surface to be coated to obtain durable finishes. In this work, the adhesion of various silicate-based formulations to a beech wood substrate (Fagus sylvatica L.), was assessed with the main objective to study relevant parameters and potential improvements. Adhesion strength was determined by pull-off and cross-cut tests. Other coating properties such as scratch, impact, and water resistance were also determined. Surface roughness and interface were analyzed using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM), and coating curing was studied by attenuated total reflection-infrared spectroscopy (ATR FTIR). The results showed that adhesion was highly dependent on formulation, penetration of the coatings into wood, and mechanical anchoring. Increasing the content of solid particles in the coating formulations or adding a polyol (glycerol, xylose), which probably acted as a coalescent, considerably decreased the adhesion strength, probably by blocking penetration into the wood by forming aggregates. Adhesion was improved by pre-mineralization of the surface, and substitution of a part of the potassium silicate binder with potassium methyl siliconate reduced the formation of cracks caused by dimensional instability of the wood.
The purpose of the present study was to evaluate the composition of fatty acids, antioxidant, and phenolic compounds in Acacia polyacantha and Azadirachta indica seed extracts for their potential ...uses in nutrition. Extractions of oil using several techniques (Soxhlet, ultrasound, and microwave) in several solvents were carried out and the oils were characterized. Total phenolic content ranged between 4.22 and 31.48 mg GAE/g. Antioxidant activity (CE50) ranged between 1.95 and 22.91 mg/ml. Oleic and linoleic acids were the major unsaturated fatty acids while palmitic and stearic acids were the major saturated fatty acids in both oils. 3‐hydroxybenzoic acid, resveratrol rutin, and flavan were identified by HPLC‐DAD at high contents while chlorogenic acid, vanillic acid, syringic acid, epicatechin, p‐coumaric acid, transferulic acid, ellagic acid, rutin, cinnamic acid, chlorogenic acid, and caffeic acid were lower in Neem oil. In case of A. polyacantha oil, the percentages of ellagic acid and rutin were high.
Practical applications
This study investigated the best method which gives a high oil extraction yield from among Soxhlet, ultrasound, and microwave using green solvents. Results revealed that acetone and isopropanol can be used for oil extraction from seeds using microwave or ultrasound with shorter extraction times (30 min with ultrasound and 15 min for microwave). These solvents provided oils with high phenolic content and good antioxidant properties. The main fatty acids identified were oleic, linoleic, palmitic, and stearic acids. These oils thus have a high potential for pharmaceutical, food, and cosmetic industrial uses.
The use of wood-based materials in building and construction is constantly increasing as environmental aspects and sustainability gain importance. For structural applications, however, there are many ...examples where hybrid material systems are needed to fulfil the specific mechanical requirements of the individual application. In particular, metal reinforcements are a common solution to enhance the mechanical properties of a wooden structural element. Metal-reinforced wood components further help to reduce cross-sectional sizes of load-bearing structures, improve the attachment of masonry or other materials, enhance the seismic safety and tremor dissipation capacity, as well as the durability of the structural elements in highly humid environments and under high permanent mechanical load. A critical factor to achieve these benefits, however, is the mechanical joint between the different material classes, namely the wood and metal parts. Currently, this joint is formed using epoxy or polyurethane (PU) adhesives, the former yielding highest mechanical strengths, whereas the latter presents a compromise between mechanical and economical constraints. Regarding sustainability and economic viability, the utilization of different adhesive systems would be preferable, whereas mechanical stabilities yielded for metal-wood joints do not permit for the use of other common adhesive systems in such structural applications. This study extends previous research on the use of non-thermal air plasma pretreatments for the formation of wood-metal joints. The plasma treatments of Norway spruce
Picea abies
(L.) Karst. wood and anodized (E6/EV1) aluminum AlMgSi0.5 (6060) F22 were optimized, using water contact angle measurements to determine the effect and homogeneity of plasma treatments. The adhesive bond strengths of plasma-pretreated and untreated specimens were tested with commercial 2-component epoxy, PU, melamine-urea formaldehyde (MUF), polyvinyl acetate (PVAc), and construction adhesive glue systems. The influence of plasma treatments on the mechanical performance of the compounds was evaluated for one selected glue system
via
bending strength tests. The impact of the hybrid interface between metal and wood was isolated for the tests by using five-layer laminates from three wood lamellae enclosing two aluminum plates, thereby excluding the influence of congeneric wood-wood bonds. The effect of the plasma treatments is discussed based on the chemical and physical modifications of the substrates and the respective interaction mechanisms with the glue systems.
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