Fluorescent Whitening Agents Research Articles

Optical properties of dissolved organic matter in Japanese rivers and contributions to photoformation of reactive oxygen species

The optical properties of dissolved organic matter (DOM) from five rivers (Kokubu, Kurose, Ohta, Yamato, and Yodo) in Japan were investigated and contributions of DOM to photoformation of three reactive oxygen species (ROS) (hydroxyl radicals (OH), nitric oxide radicals (NO), and singlet oxygen (1O2)) were assessed. The lowest and highest mean dissolved organic carbon concentrations were for the Ohta River (0.95 (mg C) L−1) and Yamato River (2.85 (mg C) L−1), respectively, and the concentrations correlated with some optical parameters. Absorption ratios (e.g., the E2:E3 and A280/A350 ratios) and the spectral slope S275–295 indicated that DOM from the Yodo and Kokubu rivers had the lowest and highest molecular weights, respectively. PARAFAC models and DOM excitation–emission matrices were used to assess the sources and fates of DOM in the rivers. The PARAFAC model indicated that the main types of fluorescent DOM in the rivers were terrestrial humic-like (TH-L) and tryptophan-like (TP-L) substances. The Kokubu River contained other compounds such as fluorescent whitening agents, autochthonous humic-like substances, and extracellular polymeric substances. Statistically significant relationships between the dissolved organic carbon and TH-L, TP-L, and extracellular polymeric substance concentrations suggested that TH-L, TP-L, and extracellular polymeric substances are important contributors to total DOM in the rivers. TH-L and TP-L substances strongly contribute to ROS photoformation, but TH-L substances play roles in both ROS generation and scavenging. Comprehensive models for estimating the photoformation rates of different ROS (in M s−1) were established by integrating the contributions of the relevant major and minor sources. Examples are ROH (10−12) = 21.0 [NO2−]_μM + 0.460 [TH-L]_QSU + 10.9, RNO (10−12) = 67.9 [NO2−]_μM + 35.2 [a300]_m−1 − 2.51 [TH-L]_QSU − 0.765 [TP-L]_QSU − 8.14, and R1O2 (10−9) = 3.81 [a300]_m−1 − 0.101 [TP-L]_QSU + 11.1.

The light aging behavior of daylight fluorescent paints: a colorimetric, photographic, Raman spectroscopic and fluorescence spectroscopic study

Daylight fluorescent pigments with their intense color effects have attracted great interest among artists since their market launch in the mid-twentieth century. Since then they have been widely used in the visual arts. The pigments are mainly compositions of organic fluorescent dyes and optical brighteners diluted in an insoluble resin. Due to the susceptibility of the dyes to visible and UV radiation, their lightfastness is comparatively low. This paper presents a comprehensive study of the color and fluorescence changes of daylight fluorescent paints upon exposure in visible light and ultraviolet radiation conducted on mock-ups of commercial daylight fluorescent pigments. The different aging characteristics of the pigments depend on the color tone. They were recorded by means of photographic and colorimetric documentation. In addition, Raman spectroscopy was used to identify the main dyes of the various pigments, even in the complex system of paints, consisting of primer, binder, resin and dyes, and to determine their degradation during aging. Fluorescence spectroscopy revealed that the change in fluorescent color may not only be due to the decrease in dye concentration, but also to the transformation of the original dyes into other fluorescent compounds during light aging. Finally, this paper provides recommendations for the presentation of artworks containing daylight fluorescent pigments.

Benzodifuran-based fluorescent brighteners: A novel platform for plant cell wall imaging

Herein we designed three novel fluorescent brightening agents based on a benzodifuran skeleton. The compounds are colorless fluorophores emitting in the blue region with an improved water solubility and ability to interact with living cells. A complete understanding of the emission mechanisms was achieved by Density Functional Theory study based on X-ray crystallographic analysis. The fluorescence quantum yields were measured in different solvents and at different pH values. The ability of the different fluorophores to stain cell compartments of plant root samples was tested in water- and glycerol-based solutions. Through fluorescence microscopy technique two probes with a different functionalized branching chain proved to be efficient stains for plant root cell wall. The cationic probe has no harmful effect on plant tissues and is suitable for in vivo fluorescent visualization of plant root cell boundaries. This study sheds light on the potential use of brighteners containing a central benzodifuran core as tools for imaging of fixed and alive plant tissues.

Spectroscopic Stability Studies of Pressure Sensitive Labels Facestock Made from Recycled Post-Consumer Waste and Agro-Industrial By-Products

To support circular economy and sustainability, the use of synthetic polymers should be minimized due to their excessive accumulation in the environment and low biodegradation rate which leads to a global waste problem. Thus, the quota of natural resources should be increased, as well as the use of agriculture and industrial waste or by-products as raw materials in industrial processes. Agro-industrial wastes were found to have high cellulose fiber potential which makes them an excellent resource for paper production. This study investigates the influence of artificial aging test on the stability of commercially available fiber based self-adhesive pressure sensitive labels (PSL), in which the facestock is made of 15% agro-industrial byproducts, 40% post-consumer recycled paper and 45% virgin wood pulp and compared to ones made of biobased polyethylene. The results showed that optical brighteners are present in the composition of fiber based PSL. Moreover, the fluorescence and UV-Visible spectroscopy results indicated that by the action of UV irradiation and temperature. The oxidation of cellulose was not found by FTIR spectroscopy, indicating its high stability.

Producing Direct Food Packaging Using Deinked Office Paper Grades—Deinkability and Food Contact Suitability Evaluation

Paper recycling is the most eco-efficient waste management option, since the use of recycled fibers reduces the need for virgin wood fiber and lowers energy consumption, and hence has a positive effect on the environment. The use of recycled paper is by far the highest in the packaging industry. In food packaging production, recycled paper is often favored over paper and board made from virgin fibers. However, due to the possible hazardous chemicals that can be found in recycled paper, there is a dilemma of how to overcome food safety issues while making food packaging more circular. The objective of the study was to determine if deinked office paper grades could be used as an alternative fiber source in the production of food packaging white top linerboards. For that purpose, three different types of digitally printed papers were submitted to a chemical deinking flotation in laboratory conditions, and the handsheets formed after each recycling trial were tested on the suitability for direct food contact. Evaluation of deinkability for each group of recycled prints was performed, as well. Deinkability was evaluated by calculating the flotation yield, pulp’s brightness and whiteness increase, ink elimination factor, determination of residual ink area, as well as ash content elimination. Food safety evaluation was performed by determining the content of heavy metals (Cd, Pb, Hg, and Cr VI), primary aromatic amines, diisopropylnaphthalenes (DIPN), phthalates, and polychlorinated biphenyls (PCB) from aqueous or organic solvent extracts of recycled paper pulp. The fastness of the fluorescent whitening agents was determined, as well. Of all evaluated deinking flotation efficiency parameters, only flotation yield and ash reduction by flotation were positively assessed. High content of residual ink particles detected after the flotation stage indicates that the flotation was not a successful method for the elimination of disintegrated ink particles, which was also confirmed by deficient results of ink elimination measurements and whiteness increase. Flotation proved to be the least efficient in the recycling of inkjet prints, where the lowest ink elimination, whiteness, and brightness values were achieved. As far as food safety assessment of deinked pulp is concerned, all tested deinked handsheets were found suitable to be used in direct contact with foods.

Novel amino acid‐stilbene quaternary ammonium salt fluorescent whitening agents: synthesis, optical properties, acid resistance and anti‐bacterial activity

AbstractWith 4,4'‐diaminostilbene‐2,2'‐disulfphonic acid, 2,4,6‐trichloro‐1,3,5‐triazine and N,N‐dimethyldodecylamine as main raw materials, a stilbene quaternary ammonium salt intermediate was synthesised by condensation and quaternisation reaction under the catalysis of sodium hydroxide, and then reacted with two different amino acids to prepare novel amino acid‐stilbene quaternary ammonium salt fluorescent whitening agents. The structures of target compounds were characterized by Fourier Transform–infrared and proton nuclear magnetic resonance spectroscopy. Their photophysical properties, whitening performance and firmness in aqueous solution were assessed by means of ultraviolet absorption spectra, fluorescence emission spectra and a cotton fibre application test. The results showed that the two amino acid‐stilbene quaternary ammonium salt fluorescent whitening agents had a good whitening effect on cotton fibres and displayed strong acid resistance. Compared with the traditional fluorescent whitening agent C186, their firmness was greatly improved. The anti‐bacterial activities against three strains were evaluated in vitro. The results showed that they exhibited significant anti‐bacterial activity against the selected strains, and the respective minimum inhibitory concentration values against Candida albicans and Escherichia coli were 16.8 and 8.16 μg/ml.

The impact of the Helmholtz-Kohlrausch effect on the appearance of near-white paper colours

This paper investigates the impact of the Helmholtz-Kohlrausch effect on near-white substrate colours. As the luminance of the test colour (or its simulated reflectance in a softproof setup) approaches that of the adapting white point the viewing mode changes from 'surface mode' to 'aperture mode', and the appearance of the test colour becomes self-luminous. However, some substrates with optical brighteners fall close to this threshold between viewing modes, since the OBAs not only increase the perceived reflectance but also increase the H-K effect, where it is very prominent in bluish colours. For graphic arts content shown on a display system, this essentially breaks the soft-proofing paradigm. The practical application of this work relates to cross-media colour reproduction, where the lightness appearance of some substrates is not adequately described by their colorimetric values, and this may impact on choice of proofing strategies.

Shedding Light on Daylight Fluorescent Artists’ Pigments, Part 1: Composition

ABSTRACT The vivid colors and luminosity of daylight fluorescent pigments have secured them a spot on the artists’ palette since their inception in the 1930s. However, these colorants pose unique challenges to conservators due to their complex formulations consisting of a mixture of dyes and optical brighteners impregnated in a formaldehyde-rich polymer resin. Furthermore, these pigments are often intended for display under blacklights, which accelerate fading and polymer degradation reactions and pose demanding inpainting requirements of conservators. This research provides a comprehensive report on the dye composition of pigments made by the major European and American manufacturers, as well as those sold as artists’ dry pigments. Differences in the dyes and additives were identified for the first time using liquid chromatography with mass spectrometry, while subtle variations in the resin matrix were revealed using infrared spectroscopy. Specific identification of the dye and matrix components can differentiate the pigment sources and be taken advantage of in conservation treatments. This is demonstrated in the analysis of Stefano Castronovo’s fluorescent Mona Lisa painting on a Stephen Sprouse designed silver leather motorcycle jacket. Analysis of a mid-twentieth century designer’s manual produced by the Day-Glo Corporation revealed how the pigments’ dye components have shifted over time.

Low Concentrations of Chlorhexidine Inhibit the Formation and Structural Integrity of Enzyme-Treated Multispecies Oral Biofilms

The self-produced matrix of biofilms, consisting of extracellular polymeric substances, plays an important role in biofilm adhesion to surfaces and the structural integrity of biofilms. In dentistry, biofilms cause multiple diseases such as caries, periodontitis, and pulpitis. Disruption of these biofilms adhering to dental hard tissues may pose a major challenge since biofilms show higher tolerance to antimicrobials and antibiotics than planktonic cells. In this study, the effect of low concentrations of chlorhexidine (CHX) on enzyme-treated multispecies oral biofilm was investigated in an in vitro model. Six-species biofilms were enzymatically treated by anaerobic growth in a medium containing DNase I and proteinase K. Biofilms were exposed to a low concentration of CHX at defined time points. After 64h, biofilms were either harvested and quantified by cultural analyses or stained for confocal laser scanning microscopy (CLSM) analyses using either Live/Dead kit or different fluorescent dyes. A mixture of YoPro1 and SYTOX™ Green, Fluorescent Brightener 28 (Calcofluor), and SYPRO™ Ruby Protein Gel Stain was used to stain total DNA, exopolysaccharides, and extracellular proteins, respectively. Extracellular DNA (eDNA) was visualized via an indirect immunofluorescence assay (Mouse anti-DNA IgG, Goat anti-Mouse IgG, Streptavidin-Cy3). Overall, the total colony-forming units significantly decreased after combined treatment with a low concentration of CHX and enzymes compared to the group treated with CHX alone (p<0.001). These findings also apply to five species individually (Streptococcus mutans, Streptococcus oralis, Actinomyces oris, Veillonella dispar, and Candida albicans) occurring in the biofilms, with Fusobacterium nucleatum being the only exception. Furthermore, CLSM images showed less dense biofilms and a reduction in cell numbers after combined treatment compared to the group without enzymes. The combination of enzymes capable of disturbing the matrix integrity with antimicrobial agents thus appears to be a promising approach for biofilm disruption and killing.

Fluorescent whitening agents in Baiyangdian Lake in North China: Analysis, occurrence, distribution and ecological risk assessment

Fluorescent whitening agents (FWAs) are very important chemical additives that are widely applied in the industrial production field. The history of global FWA production and use spans more than 60 years, but the environmental fate of FWAs has been less reported in the public literature and most studies predate 2000; in addition, the studied FWAs were still limited to FWA71 and FWA351. In this study, the occurrence and distribution of 9 commonly used FWAs in a lake in North China were reported for the first time. We found that 6 target FWAs were prevalent in the lake, and the concentration levels were usually at the ng L−1 level. Decreasing FWA levels with increasing distance from the estuary area were observed in summer. FWA135, FWA185, and FWA367, the most detected 3 FWAs, with the ecological risk at high levels, and ΣRQ >10 were obtained from all the investigated samples, suggesting that all the sampling sites could be considered with certain ecological risk for aquatic life. As a category of heavily and widely used dyes, FWAs in environmental media have been ignored for a long time. Substantial additional research needs to be conducted to determine the environmental behavior and ecological toxicology of FWAs.

A Kinetic and Thermodynamic Study of CI fluorescent brightener 113 on cotton

Fluorescent brightening agents are dyestuffs in which adsorption is the primary mechanism involved in the dyeing process. They are commonly used to improve the brightness in various industrial products, especially textiles. FBA 113 is widely used in the dyeing process for cotton. This study aims to evaluate the optimum dyeing process of FBA 113 on cotton to assess the dyeing behavior, the adsorption isotherm model, and thermodynamic parameters. The study examined various parameters, including dyeing times, dyeing temperature, the amount of dye, and auxiliary. Variations in conditions were observed to define the dyeing equilibrium time, the Langmuir and Freundlich adsorption isotherm, the pseudo-first-order, pseudo-second-order dyeing kinetic model, and the thermodynamic parameters, such as enthalpy (H0), entropy (S0), and Gibb's energy (G0). The results show that the appropriate dyeing was FBA 113 0.25% owf with 20 g/l KCl as an auxiliary, the best dyeing temperature was 323 K, and the equilibrium time was 120 min. This dyeing reflected an adsorption behavior that displayed multilayer adsorption that corresponded to the Freundlich isotherm. Also, the adsorption model had a pseudo-second-order of 0.9874 using linear regression. The dyeing reaction was exothermic, with H0 -26.58 kJ/mol, S0 34.19 J/mol, and the spontaneous process had a negative G0 value. The fiber and dye interacted physically. The study can enhance our understanding of FBA 113 dyeing behavior and identify situations in which it can be used in other dyeing process models, which will help optimize further dyeing studies.

Mechanochemical Preparation and Self-Assembly of Protein:Dye Hybrids for White Luminescence.

Protein nanofibrils (PNFs) functionalized with multiple dyes are prepared by a combination of mechanochemistry and liquid-phase self-assembly. The three employed dyes are Fluorescent Brightener 378 (F378), 2-butyl-6-(butylamino)-1H-benzo[de]isoquinoline-1,3(2H)-dione (Fluorol 555), and Nile red (NR). F378 acts as the donor with Fluorol 555 as the acceptor. F555 in turn acts as the donor and NR as the acceptor. This enables a FRET cascade that enables conversion of UV light to white light. The efficiency of FRET can be influenced by the details of the self-assembly process. If proteins milled with different dyes are mixed prior to self-assembly, nanofibrils are formed containing all three dyes, thus favoring FRET processes. By tuning the ratio of the three luminescent dyes, PNF dispersions are obtained that display bright white light emission. Moreover, the PNF dispersions can be converted into white luminescent films and gels where the PNFs may help to organize dye molecules. Additionally, the PNF materials can be employed as coatings on commercial LEDs, enabling emission of white light.

The Influence of Iron Ions on Optical Brighteners and Their Application to Cotton Fabrics.

The influence of iron ions at concentrations of 0.2, 0.5, and 1.0 g/L on optical brighteners of the groups stilbene and biphenyl in solution and on cotton fabric was investigated. Both groups of optical brighteners are intended for detergent formulations. The influence of iron ions was studied by absorption and fluorescence spectra in solution and by whiteness degree, identifying color differences using CIEL*a*b* coordinates and Ultraviolet Protection Factor (UPF) of cotton fabrics. The obtained results in solutions and cotton fabrics showed different behavior of optical brighteners stilbene and biphenyl in the presence of iron. Stilbene compounds with metal ions produced new species capable of absorbing in the UV-B region of the spectrum. A biphenyl compound in combination with iron had no effect on the absorption properties. Both optical brighteners were influenced by iron ions in the sense of fluorescence quenching. The influence of iron ions in single- and two-bath treatments of cotton fabrics after one cycle on whiteness degree and UPF was negligible.

Evaluating the accuracy and diagnostic value of CFW and a new fluorescent reagents, fluorescent brightener 85, for the diagnosis of vulvovaginal candidiasis.

BackgroundVulvovaginal candidiasis (VVC) is a common vaginitis in females. The commonly used diagnostic method, 10% potassium hydroxide (KOH) smear microscopy, makes it not very easy to recognize fungi.MethodsVaginal secretions were collected from clinically suspected VVC patients and divided into four groups and examined using KOH, CFW (Calcofluor White), FB 85(fluorescent brightener 85), and culture. The data were statistically analyzed.ResultsIn total, 110 patients with suspected VVC were recruited. The positive rates of KOH, CFW, FB 85, and the culture method were 68.2%, 64.5%, 61.8%, and 77%, respectively. According to the McNemar test, there was no statistically significant difference between the KOH, CFW, and the FB 85 methods (p > 0.05). However, CFW had a shorter diagnosis time than the KOH method and had a statistically significant difference (p < 0.001). Moreover, CFW has the highest sensitivity, specificity, and accuracy. In morphological recognition, it was easier to recognize fungal structures with CFW and FB 85 than with the KOH.ConclusionsThe fluorescent method is a good method for the diagnosis of VVC. And the fungi can be found more quickly. Similar to CFW, FB 85 is also a potential good fluorescent reagent for the diagnosis of VVC and has potential value for application in clinical fungal infection diseases.

Removal of COD, aromaticity and color of a pretreated chemical producing industrial wastewater: a comparison between adsorption, ozonation, and advanced oxidation processes.

A wide range of products are produced in the chemical producing industry such as textile dyes, chemicals, printing dyes and chemicals, paper chemicals, electrostatic powder dyes, and optical brighteners. The aim of this study is to investigate the treatability of chemical oxygen demand (COD), aromaticity, and color in the wastewater of this sector, where highly complex chemicals are used. Most of the studies in the literature are related to the treatment of synthetically prepared dyed wastewater. This study is important as it is carried out with real wastewater and gives results of many treatment methods. In the study, COD, UV-vis absorbance, and color values were attempted to be removed from the wastewater of a chemical producing industry that was pretreated by coagulation-flocculation. The COD value of the pretreated wastewater discharged to the central treatment system was restricted as 1000 mg/L. Pretreated wastewater characterization is as follows: COD: 2117 mg/L, UV-vis absorbance values at; 254 nm: 9.91, 280 nm: 8.65, 341 nm: 12.77, 436 nm: 5.01, 525 nm: 2.24, and 620 nm: 1.59. In the study, adsorption, ozonation, and advanced oxidation processes (Fenton and persulfate oxidation) were used to remove COD and UV-vis absorbance values (aromaticity, organics, and color). The method by which the best removal efficiency was obtained for all parameters was the adsorption process using powdered activated carbon (PAC). The equilibrium PAC dose was found as 6 g/L. At this adsorbent dose, the removal efficiencies of UV-vis absorbance values were all around 99% and the efficiency of COD removal was 77%. The Langmuir isotherm constants were found to be qmax= 30.4 mg/g and KL = 487.9 (L/mg). The COD concentration at this adsorbent dose was 486 mg/L and wastewater was suitable for discharge to the central wastewater treatment plant in that region.

Metal‐Free Oxidative Condensation of Catechols, Aldehydes and NH4OAc towards Benzoxazoles

AbstractBenzoxazoles extensively exist in biologically active compounds, natural products, pharmaceuticals and functional materials. Thus, facile and green synthesis of such valuable compounds from easily available substrates will make a contribution to drug, material, and fine chemistry. A method for the synthesis of benzoxazoles from catechols, aldehydes and ammonium acetate is developed using NaIO4 as oxidant under metal‐ and additive‐free conditions. A broad range of benzoxazoles including some fluorescent whitening agents, JTP‐426467 and tafamidis analogues are synthesized in 56–95% yields with outstanding functional group tolerance. Mechanistic investigations suggest that an interesting o‐iminocyclohexa‐diene alcohol intermediate is involved in the reaction. These salient features of the protocol make it an alternative for the synthesis of benzoxazoles.magnified image

Study on the Removal of Fluorescent Whitening Agent from Paper-Mill Wastewater Using the Submerged Membrane Bioreactor (SMBR) with Ozone Oxidation Process

In this study, paper-mill wastewater was treated using the Submerged Membrane Bioreactor (SMBR) process. In particular, the ozone oxidation treatment process is applied after SMBR to remove the fluorescent whitening agent, which is a trace pollutant and non-biodegradable. Fluorescent whitening agent concentration was indirectly measured by UV scanning and COD concentration. The concentration of COD before SMBR and ozone oxidation was 449.3 mg/L, and the concentration of treated water was 100.3 mg/ℓ. The COD removal efficiency of paper-mill wastewater through SMBR and the ozone oxidation process was about 77.68%. The optimized amount of ozone was required for the removal of the fluorescent whitening agent after SMBR was 95 mg·O3/ℓ calculated by UV scan results. Additionally, the optimized amount of required ozone to remove COD was calculated to 0.126 mg·COD/mg·O3.

A dye combination for the staining of pollen coat and pollen wall.

The pollen coat, which forms on the pollen surface, consists of a lipid-protein matrix. It protects pollen from desiccation and is involved in adhesion, pollen-stigma recognition, and pollen hydration during interactions with the stigma. The classical methods used for pollen coat observation are scanning and transmission electron microscopy. In this work, we screened a collection of fluorescence dyes and identified two fluorescent brighteners FB-52 and FB-184. When they were used together with the exine-specific dye, Basic fuchsin, the pollen coat and the exine structures could be clearly visualized in the pollen of Brassica napus. This co-staining method was applied successfully in staining pollen from Fraxinus chinensis, Calystegia hederacea, and Petunia hybrida. Using this method, small pollen coat-containing cavities were detected in the outer pollen wall layer of Oryza sativa and Zea mays. We further showed these dyes are compatible with fluorescent protein markers. In the Arabidopsis thaliana transgenic line of GFP-tagged pollen coat protein GRP19, GRP19-GFP was observed to form particles at the periphery of pollen coat. This simple staining method is expected to be widely used for the studies of the palynology as well as the pollen-stigma interaction.

Fine structure of Drosophila larval salivary gland ducts as revealed by laser confocal microscopy and SEM

The functions of the larval salivary glands (SGs) of Drosophila are traditionally associated with the production of a massive secretion during puparium formation; it is exocytosed into a centrally located lumen and subsequently expectorated via ducts, the pharynx and mouth. This so-called proteinaceous glue serves as an adhesive to attach the puparial case to a solid substrate. Great attention has been paid to the secretory cells of SGs, which are famous for their giant polytene chromosomes. However, substantially less attention has been devoted to individual or common ducts that form the most proximal portion of the SG organ via which the glue is released into the pharynx. In the present paper, we describe the organization and fine structure of the taenidia, highly specialized circumferential ring-like extracellular (cuticular) components on the internal side of these tubes. Two chitin-specific probes that have previously been used to recognize taenidia in Drosophila tracheae, Calcofluor White M2R (also known as Fluorescent Brightener 28) and the novel vital fluorescent dye SiR-COOH, show positively stained ductal taenidia in late larval SGs. As seen using scanning electron microscopy (SEM), the interior of the ductal tube contains regular and densely-arranged ridge-like circumferential rings which represent local thickenings of the cuticle in various geometries. The microtubular arrays that optically colocalize with taenidia in both the trachea and SG ducts are specifically and strongly recognized by fluorescently-conjugated colchicine as well as anti-tubulin antibody. In contrast to taenidia in the tracheae, the analogous structures in SG ducts cannot be detected by fluorescently-labeled phalloidin or even actin-GFP fusion protein, suggesting that the ducts lack a cortical network made of filamentous actin. We speculate that these taenidia may serve to reinforce the duct during the secretory processes that SGs undergo during late larval and late prepupal stages.

Influence of sisal fibers on the mechanical performance of ultra-high performance concretes

This paper investigated the utilization of natural sisal fibers in ultra-high performance concrete (UHPC). UHPC mixtures containing sisal fibers with different lengths (6, 12, and 18 mm) and volume contents (1.0%, 2.0%, and 3.0%) were prepared. Flowability, mechanical strength, and interfacial bond behavior between fiber and matrix were tested for every mixture. The distribution of sisal fibers in the UHPC matrix was evaluated using the ultraviolet (UV) light and fluorescent whitening agent (FWA). Finally, the microstructures of typical samples were observed by a scanning electron microscope (SEM). Experimental results indicated that the flowability of the fresh UHPC mixture decreased with the increase of length and volume fraction of sisal fibers. The content of 2.0% sisal fibers with a length of 18 mm increased flexural strength and toughness of UHPC by 16.7% and 540.0%, respectively, compared with plain UHPC specimens. The pull-out load and pull-out energy increased with the length of sisal fibers. Moreover, the sisal fibers can be uniformly distributed in the UHPC matrix. Therefore, the utilization of sisal fibers to manufacture a low-cost and low energy-consumption UHPC has great potential.