Impact of bleaching pine fibre on the fibre/cement interface

The goal of this article was to evaluate the surface characteristics of the pine fibres and its impact on the performance of fibre–cement composites. Lower polar contribution of the surface energy indicates that unbleached fibres have less hydrophilic nature than the bleached fibres. Bleaching the pulp makes the fibres less stronger, more fibrillated and permeable to liquids due to removal the amorphous lignin and its extraction from the fibre surface. Atomic force microscopy reveals these changes occurring on the fibre surface and contributes to understanding the mechanism of adhesion of the resulting fibre to cement interface. Scanning electron microscopy shows that pulp bleaching increased fibre/cement interfacial bonding, whilst unbleached fibres were less susceptible to cement precipitation into the fibre cavities (lumens) in the prepared composites. Consequently, bleached fibre-reinforced composites had lower ductility due to the high interfacial adhesion between the fibre and the cement and elevated rates of fibre mineralization.     

Effect of fibre curl on the properties of wood pulp fibre-cement and silica sheets

Curl has been induced in unbleached softwood kraft pulp fibres by treatment in the laboratory at 20% consistency in a planetary mixer. Steam treatment of the fibres to set the curl more strongly was found to be detrimental to fibre properties as deduced from handsheet properties. A means of producing two-ply specimens in the laboratory was devised and a tensile test for interlaminar bond strength was developed. The use of curly fibres in reinforced cement and silica sheets gave sheets with improved wet interlaminar bond strengths, relative to sheets prepared from conventionally treated fibres but had little effect on the values of modulus of rupture and fracture toughness.     

Autoclaved beaten wood fibre-reinforced cement composites

The need to beat (or refine) wood pulp fibres before using as a reinforcement in cement composites has been re-examined. In the case of Pinus radiata unbleached kraft pulp, it has been confirmed that beating the fibres does contribute to attaining optimum mechanical properties for composites fabricated from such modified fibres.     

Toxicity of Silver Nanoparticles in Macrophages

Silver nanoparticles (nanosilver) are broadly used today in textiles, food packaging, household devices and bioapplications, prompting a better understanding of their toxicity and biological interactions. In particular, the cytotoxicity of nanosilver with respect to mammalian cells remains unclear, because such investigations can be biased by the nanosilver coatings and the lack of particle size control. Here, nanosilver of well‐defined size (5.7 to 20.4 nm) supported on inert nanostructured silica is produced using flame aerosol technology. The cytotoxicity of the prepared nanosilver with respect to murine macrophages is assessed in vitro because these cells are among the first to confront nanosilver upon its intake by mammals. The silica support facilitates the dispersion and stabilization of the prepared nanosilver in biological suspensions, and no other coating or functionalization is applied that could interfere with the biointeractions of nanosilver. Detailed characterization of the particles by X‐ray diffraction and electron microscopy reveals that the size of the nanosilver is well controlled. Smaller nanosilver particles release or leach larger fractions of their mass as Ag⁺ ions upon dispersion in water. This strongly influences the cytotoxicity of the nanosilver when incubated with murine macrophages. The size of the nanosilver dictates its mode of cytotoxicity (Ag⁺ ion‐specific and/or particle‐specific). The toxicity of small nanosilver (<10 nm) is mostly mediated by the released Ag⁺ ions. The influence of such ions on the toxicity of nanosilver decreases with increasing nanosilver size (>10 nm). Direct silver nanoparticle–macrophage interactions dominate the nanosilver toxicity at sizes larger than 10 nm.     

Transverse dimensions of wood pulp fibres by confocal laser scanning microscopy and image analysis

Cross-sectional images of wood-pulp fibres were generated using optical sectioning by a confocal laser scanning microscope. The technique has a distinct advantage over mechanical sectioning with a microtome, as it simplifies specimen preparation. Cross-sectional images were obtained for unbleached softwood kraft pulp fibres using epifluorescence mode. The accuracy of cross-sectional images was verified by imaging fluorescent microspheres. An image analysis procedure, in which the boundaries of fibre cross-sections were defined with a maximum-gradient edge-finding technique, was developed for measuring fibre cross-sectional area and wall thickness rapidly and accurately. The measurements were insensitive to the confocal microscope's asymmetric resolution, signal deterioration through the specimen thickness, overall image quality and operator bias.     

Air-cured woodpulp,fibre/cement mortars

The mechanical properties of cement mortars reinforced with kraft wood-pulp fibres have been studied. The composites were air-cured for up to 450 days. Although the fibre mortars have lower flexural strength values than either autoclaved fibre mortars or air-cured fibre cements, they do have improved values of fracture toughness of approximately 3kJ m⁻² at fibre loadings of 8% fibre by mass. This would suggest there may be a use for such products in areas where the materials are subjected to impact, eg, renders on walls or products which are handled frequently such as outdoor gardenware.     

Application of lignin as natural adhesion promoter in cotton fibre-reinforced poly(lactic acid) (PLA) composites

This study investigated how lignin—used as a natural adhesion promoter in biodegradable, thermoplastic cotton fibre-reinforced composites—influences the composites’ mechanical properties. Composites with fibre mass proportions of 40% were produced by compression moulding. Poly(lactic acid) (PLA), a biopolymer, served as matrix. Cotton/PLA composites with and without lignin content were manufactured. As reference samples of bast fibre-reinforced composites, kenaf/PLA composites were produced under the same conditions. The composites were tested for stiffness, tensile strength, elongation at break and impact strength. Fractured surfaces were analysed using scanning electron microscopy (SEM). The results of the composite investigations showed that the addition of lignin has an influence on the cotton/PLA composite characteristics. SEM investigations showed that the adhesion between fibre and matrix could be improved by the addition of lignin. Tensile characteristics like tensile strength and Young’s modulus could be improved clearly, while the impact properties were decreased.     

Brazilian waste fibres as reinforcement for cement-based composites

Fibre reinforced cement-based composites were prepared using kraft pulps from sisal and banana waste and from Eucalyptus grandis pulp mill residues. The study adapted conventional chemical pulping conditions for the non-wood strands and a slurry vacuum de-watering method for composite preparation followed by air-curing. Plain cement paste and Pinus radiata kraft reinforced cement composites were used as reference materials. Mechanical testing showed that optimum performance of the various waste fibre reinforced composites was obtained at a fibre content of around 12% by mass, with flexural strength values of about 20 MPa and fracture toughness values in the range of 1.0–1.5 kJ m⁻². Experimental results showed that, of the waste fibres studied, E. grandis is the preferred reinforcement for low-cost fibre-cement.     

Preparation of lumen-loaded kenaf pulp with magnetite (Fe3O4)

Magnetic pulps were prepared from unbleached kenaf (hibiscus cannabinus L.) kraft pulps. Fe₃O₄ or magnetite powder was used to load into the pulp’s lumen and pit. Aluminum sulphate [Al₂(SO₄)₃] (alum) and polyethylenimine (PEI), both mainly function as retention aid were used throughout the experiment and found to be beneficial in the preparation of this magnetic pulps. The ash content method was used to determine the amount of magnetite retained in the lumen and pit. The utilization of PEI up to 2% per pulp fibres was found to be the best result on lumen loading. The deposition of magnetite powder in lumen and pit is found decrease as the addition of PEI used is more than 2% per pulp fibres. Scanning electron microscope (SEM) clearly shows the distribution of magnetite deposited in the lumen. Tensile index and folding endurance of the loaded fibre decreased slightly as the percentage of loading pigment increased.     

Effect of calcium rich and alkaline solutions on the chemical behaviour of hemp fibres

Chemical reactivity of hemp fibres placed into a cimentitous matrix was studied by using a lime solution as a simplified cement solution. The hemp fibres contain 56.1 wt.% of cellulose, 20.1 wt.% of pectin, 10.9 wt.% of hemicellulose and 6 wt.% of lignin. These compounds are not solubilised in a basic medium rich in calcium but a part located at the fibre surface should be degraded. This treatment leads also to the decrease of the cristallinity index of the cellulose. Calcium ions adsorb in a large quantity onto the fibre surface due to the high concentration of pectin. The structure of the homogalacturonic part of pectin forms with Ca²⁺ a stable chelate called “egg-box”, supporting cation adsorption. The fibres are then covered by Ca(OH)₂ nodules after immersion in a lime solution.     

Extrusion and mechanical properties of highly filled cellulose fibre–polypropylene composites

This study focused on manufacturing of highly filled cellulose fibre–polypropylene composites and evaluation of the mechanical properties of the composites. Cellulose fibre reinforced polypropylene composites with up to 60 wt% of fibres with and without coupling agent were manufactured by extrusion. In order to achieve consistent feeding of the fibres into the extruder a pelletization technique was used where the fibres were pressed into pellets. Two commercial grades of cellulose fibres were used in the study, bleached sulfite and bleached kraft fibres. Fibre dimension measurements showed that the pelletization process and extrusion at high fibre loading caused the most severe fibre breakage. Flexural testing showed that increased fibre loading made the composites stiffer but reduced the toughness. Addition of maleic anhydride grafted coupling agent (MAPP) increased the stiffness and strength of the composites significantly. In general, there was no significant difference in the mechanical properties between the composites with kraft and sulfite fibres. An interesting finding was that the flexural modulus and strength of the MAPP modified cellulose fibre–polypropylene composites were not higher than what has previously been reported for wood flour–polyolefin composites. Scanning electron microscopy showed that addition of coupling agent improved the interfacial adhesion between the fibres and polypropylene matrix.     

The deformation and fracture behaviour of glass-filled ABS

The tensile and fracture characteristics of pigmented ABS containing 30 wt % rubber reinforced with 30 wt % glass fibre have been examined over a range of strain-rates extending from approximately 10⁻⁴ to 10⁻¹ sec⁻¹ within the temperature range 293 to 353 K. The glass fibre-reinforced composite had significantly increased fracture strength compared with the base polymer but possessed decreased ductility. The marked yield point which is characteristic of the ABS base polymer was absent from the reinforced material. Two different regions were found to exist on the fracture surfaces of composite specimens. One region possessed the characteristics of a weak interfacial bond while the other showed evidence of strong, interfacial bonding. In both regions extensive fibre pull-out was observed. The variation in fracture strength and morphology with strain-rate and temperature of testing is explained in terms of the properties of an interfacial region adjacent to the fibres which possesses viscoelastic properties different from those of the bulk polymer. The effect of adiabatic heating at the crack tip is also taken into account in the high temperature—high strain rate regime.     

Laccase and alkali treatments of cellulose fibre: Surface lignin and its influences on fibre surface properties and interfacial behaviour of sisal fibre/phenolic resin composites

This paper is an attempt to investigate the influences of enzyme (laccase) and alkali treatments on the surface lignin of single cellulose fibre. The fibre surface characteristics and the interfacial behaviour of the sisal fibre/phenolic resin composites were also studied by SEM, AFM, XPS. The surface lignin greatly affected the surface physical and chemical properties of single cellulose fibres. The surface lignin concentration was up to 35% for the raw fibre without any treatment, and then it decreased to 24%, 20% and 18% for the fibres with laccase treatment, alkali treatment and laccase/alkali treatment, respectively. The removal of lignin from fibre surface could enhance the interfacial strength of composites, and thus increase the tensile strength and internal bonding strength by 43% and 51%, respectively, for the composites obtained from laccase/alkali treated fibres.     

Synthesis,characterization and antibacterial activity studies of poly-{styrene-acrylic acid} with silver nanoparticles

This work reports the preparation and characterization of copolymer poly-{styrene-acrylic acid} with monomeric ratio of styrene/acrylic acid of 9:1 using benzoyl peroxide as initiator and furthermore filled with nanosilver (25 ppm and 50 ppm) in water/acetone (1:40 v/v). The nanosilver emulsion was obtained from chemical reduction using NaBH₄ as reducing agent and sodium citrate as the stabilizer. The preparation of nanosilver emulsion was monitored by the appearance of a Plasmon Resonant Absorption band in a UV–visible spectrophotometer and the particles sizes were observed through TEM. Microbiological studies were performed to investigate the antimicrobial activity of this new material against the microorganisms Escherichia coli (ATCC-25922) and Staphylococcus aureus (ATCC-6538), used as reference strains. The antimicrobial activity of the poly-{styrene-acrylic acid} filled with nanosilver was confirmed by the presence of an inhibition halo of the bacterial growth in seeded culture media, but was not found with the poly(styrene-acrylic acid) alone. The present work suggests that silver ions are released from the polymeric matrix to the culture media and have the ability to tune the Ag⁺ ions released by controlling the amount of Ag nanoparticles embedded in the composite.     

Preparation of novel fibre–silica–Ag composites: the influence of fibre structure on sorption capacity and antimicrobial activity

Novel fibre–silica–Ag composites with biocidal activity were successfully produced by chemical modifying cotton (CO), wool (WO), silk (SE), polyamide (PA) and polyester (PES) fabrics and CO/PES and WO/PES fabric blends. A silica–Ag coating was prepared using a two-step procedure that included the creation of a silica matrix on the fibre surface via the application of an inorganic–organic hybrid sol–gel precursor [reactive binder (RB)] using a pad-dry-cure method, followed by the in situ synthesis of AgCl particles within the RB-treated fibres from solutions of 0.10 mM and 0.50 mM AgNO₃ and NaCl. The presence of the coating on the fibres was verified by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The bulk concentration of Ag in the coated fibres was determined using inductively coupled plasma mass spectroscopy. The antimicrobial activity was determined for the bacteria Escherichia coli and Staphylococcus aureus and the fungus Aspergillus niger. The results show that the chemical and morphological structures of the fibres directly influenced their absorptivity and affinity for the Ag compound particles. As the amorphous molecular structure of the fibres and the amount of functional groups available as binding sites for Ag⁺ were increased, both the silver solution uptake and the concentration of the absorbed Ag compound particles increased. The chemical binding of Ag to the fibres significantly reduced the effectiveness of the antimicrobial activity of the Ag compound particles. Accordingly, an increase in the concentration of absorbed Ag was required to achieve a biocidal effect.     

Permissible crack widths in steel fibre reinforced marine concrete

The paper presents some results from a continuing study of the marine durability of steel fibre reinforced concrete. The overall aim of the investigation is to develop the material for marine applications. The results reported here pertain to pre-cracked specimens of steel fibre reinforced concrete which were exposed to wet-dry cycles of marine spray in the laboratory simulating tidal zone conditions of exposure. Two types of concrete mixes were used in the investigation—one with standard concrete constituents and OPC and the second replacing about 26% of cement with pfa. The cement content of the mixes was 590 and 435 kg m⁻³, respectively. Fibre reinforcement was provided by means of low carbon steel fibres and melt extract steel fibres at a v _f ℓ/d ratio of 100 and 147. Prism specimens were manufactured and these were precracked to induce cracks of width ranging between 0.03 and 1.73 mm. After cracking, both sealed and unsealed specimens were exposed to laboratory marine spray cycles using sea water. Some control specimens were cured in the laboratory air throughout. Tests were carried out after 650 marine cycles (450 days) and 1450 marine cycles (900 days). Based on data on flexural strength, energy absorption capacity, stiffness and state of corrosion of the fibres, recommendations are made regarding suitable permissible crack widths for the design of steel fibre reinforced concrete for marine applications. The results indicate that a permissible crack width of 0.2 mm is satisfactory for concrete reinforced with melt extract fibres. A smaller value is recommended for concrete reinforced with low carbon steel fibres. Complete healing of open cracks of small widths is observed under exposure to marine cycles.     

Structure and properties of fibres from sea-grass (<Emphasis Type="Italic">Zostera marina</Emphasis>)

This paper presents results from a study of fibres extracted from Zostera marina eel-grass collected from the Baltic coast. This species of sea-grass is shown to contain small diameter (around 5 μm) fibres composed of ∼57% cellulose, ∼38% of non-cellulosic polysaccharides (mainly xylan) and ∼5% of residual matter so-called Klason lignin. This composition is quite different to that of commonly used terrestrial fibres. Single fibre stiffness values up to 28 GPa were measured. This stiffness combined with a low density could provide an attractive reinforcement for composite materials, and may be particularly suitable for use in bio-degradable structures.     

Magnetic nanoparticles/graphitic carbon nanostructures composites: Excellent magnetic separable adsorbents for precious metals from aqueous solutions

A facile, low-cost and high-yield route was used for synthesis of magnetic nanoparticles/graphitic carbon nanostructures (MNPs/GCNs) adsorbents with adjustable GCNs structues, in which the cheap ion-exchanged resins and iron salts were adopted as the precursors. The synthesized MNPs/GCNs composites could be used as effective mobile adsorbents for removal of precious metal ions (Ag⁺ and Au³⁺). The adsorption quantity of the adsorbents for Ag⁺ and Au³⁺ ions is up to 7.88 mg/g and 7.92 mg/g, respectively, which is much higher than that of activated carbon. Notably, the adsorbents could be easily separated from solution with a commercial magnet due to the magnetic property, which is very beneficial to their practical application. The kinetics for Ag⁺ and Au³⁺ ions adsorption on MNPs/GCNs composites followed the pseudo-second-order kinetics. The XPS analyses demonstrated that the adsorbed Ag⁺ and Au³⁺ ions exsited in the form of the zero valence state silver and gold, respectively.     

Photographic Properties of the Gelatin Macromolecule

A survey of the literature concerning the photographic properties of the gelatin macromolecule is given. The following subjects are treated:—(l) Binding of Ag⁺ , Au⁺ and other metal ions; (2) Adsorption of AgX and Ag; (3) Protective colloid power; (4) Bromine acceptance; (5) Photographic consequences:- grain-growth-chemical ripening-exposition-development; (6) Basic gelatin.     

Long-term antimicrobial polyamide 6/silver-nanocomposites

Elemental silver nanoparticles were generated in polyamide 6 (PA6) by the thermal reduction of silver ions during the melt processing of a PA6/silver acetate mixture. The silver ion release from PA6 filled with 2 wt% nanosilver obeys a zero-order rate law for at least 100 days. During this time about 17 μg silver per day, per litre immersion liquid and per cm² sample surface are released. The PA6/Ag-nanocomposite was shown to be active against Escherichia coli whereas the pure PA6 did not show any antimicrobial efficacy. Immersion of a nanocomposite containing 2 wt% silver in water for 100 days does not reduce its antimicrobial efficacy against Escherichia coli. Thus PA6 filled with 2 wt% nanosilver is an effective antimicrobial material for long-term applications.