A unified view on the effect of fibers and loading on sfrc creep through linear projection to latent structures

Creep of Steel Fiber Reinforced Concrete (SFRC) under flexural loads in the cracked state and to what extent different factors determine creep behaviour are quite understudied topics within the general field of SFRC mechanical properties. A series of prismatic specimens have been produced and subjected to sustained flexural loads. The effect of a number of variables (fiber length and slenderness, fiber content, and concrete compressive strength) has been studied in a comprehensive fashion. Twelve response variables (creep parameters measured at different times) have been retained as descriptive of flexural creep behaviour. Multivariate techniques have been used: the experimental results have been projected to their latent structure by means of Principal Components Analysis (PCA), so that all the information has been reduced to a set of three latent variables. They have been related to the variables considered and statistical significance of their effects on creep behaviour has been assessed. The result is a unified view on the effects of the different variables considered upon creep behaviour: fiber content and fiber slenderness have been detected to clearly modify the effect that load ratio has on flexural creep behaviour.

HYPOXIC ADAPTATIONS AND CAROTENOIDS OF TWO INTERTIDAL MOLLUSCS

The present investigation is to find the hypoxic adaptations and role of carotenoids in the anaerobic catabolism of two intertidal bivalves-Sunetta scripta and Perna viridis. Physiological and cytological responses during hypoxic stress have been studied and compared to that of sublethal heavy metal (copper) exposure using two indices : total carotenoid concentration and accumulation of lipofuscin granules. A close similarity has been observed between hypoxic exposed and copper (sublethal) exposed animals regarding the total carotenoid concentration and lipofuscin accumulation. In the case of S.scripta, the total caroteniod increase at 48h of both hypoxic and heavy metal exposure was found to be nearly 40% greater than that of the control (0h). Whereas in P.viridis, the increment in the total carotenoid concentration at 48h of hypoxic exposure and 48h of heavy metal exposure were found to be nearly 87% and 95% higher than that of the control (0h) respectively.Regarding the lipofuscin accumulation, in both S.scripta and P.viridis , the characteristic features of the granule at 48h of hypoxia is very much similar to that observed at 48h of heavy metal exposure. Thus, the present study suggests that the increase in carotenoid concentration and lipofuscin accumulation expressed by bivalves under heavy metal stress can be due to the indirect effect of hypoxia.

Sisal chemically modified with lignins: Correlation between fibers and phenolic composites properties

Sisal fibers have been chemically modified by reaction with lignins, extracted from sugarcane bagasse and Pinus-type wood and then hydroxymethylated, to increase adhesion in resol-type phenolic thermoset matrices. Inverse gas chromatography (IGC) results showed that acidic sites predominate for unmodified/modified sisal fibers and for phenolic thermoset, indicating that the phenolic matrix has properties that favor the interaction with sisal fibers. The IGC results also showed that the phenolic thermoset has a dispersive component closer to those of the modified fibers suggesting that thermoset interactions with the less polar modified fibers are favored. Surface SEM images of the modified fibers showed that the fiber bundle deaggregation increased after the treatment, making the interfibrillar structure less dense in comparison with that of unmodified fibers, which increased the contact area and encouraged microbial biodegradation in simulated soil. Water diffusion was observed to be faster for composites reinforced with modified fibers, since the phenolic resin penetrated better into modified fibers, thereby blocking water passage through their channels. Overall, composites` properties showed that modified fibers promote a significant reduction in the hydrophilic character, and consequently of the reinforced composite without a major effect on impact strength and with increased storage modulus. (c) 2008 Elsevier Ltd. All rights reserved.

An investigation into transition metal ion binding properties of silk fibers and particles using radioisotopes

Silk is a structural protein fiber that is stable over a wide pH range making it attractive for use in medical and environmental applications. Variation in amino acid composition has the potential for selective binding for ions under varying conditions. Here we report on the metal ion separation potential of Mulberry and Eri silk fibers and powders over a range of pH. Highly sensitive radiotracer probes, ⁶⁴Cu²⁺, ¹⁰⁹Cd²⁺, and ⁵⁷Co²⁺ were used to study the absorption of their respective stable metal ions Cu²⁺, Cd²⁺, and Co²⁺ into and from the silk sorbents. The total amount of each metal ion absorbed and time taken to reach equilibrium occurred in the following order: Cu²⁺ > Cd²⁺ > Co ²⁺. In all cases the silk powders absorbed metal ions faster than their respective silk fibers. Intensive degumming of the fibers and powders significantly reduced the time to absorb respective metal ions and the time to reach equilibrium was reduced from hours to 5-15 min at pH 8. Once bound, 45-100% of the metal ions were released from the sorbents after exposure to pH 3 buffer for 30 min. The transition metal ion loading capacity for the silk sorbents was considerably higher than that found for commercial ion exchange resins (AG MP-50 and AG 50W-X2) under similar conditions. Interestingly, total Cu²⁺ bound was found to be higher than theoretically predicted values based on known specific Cu²⁺ binding sites (AHGGYSGY), suggesting that additional (new) sites for transition metal ion binding sites are present in silk fibers.

Scalable One-Step Wet-Spinning of Graphene Fibers and Yarns from Liquid Crystalline Dispersions of Graphene Oxide: Towards Multifunctional Textiles

Key points in the formation of liquid crystalline (LC) dispersions of graphene oxide (GO) and their processability via wet-spinning to produce long lengths of micrometer-dimensional fibers and yarns are addressed. Based on rheological and polarized optical microscopy investigations, a rational relation between GO sheet size and polydispersity, concentration, liquid crystallinity, and spinnability is proposed, leading to an understanding of lyotropic LC behavior and fiber spinnability. The knowledge gained from the straightforward formulation of LC GO “inks” in a range of processable concentrations enables the spinning of continuous conducting, strong, and robust fibers at concentrations as low as 0.075 wt%, eliminating the need for relatively concentrated spinning dope dispersions. The dilute LC GO dispersion is proven to be suitable for fiber spinning using a number of coagulation strategies, including non-solvent precipitation, dispersion destabilization, ionic cross-linking, and polyelectrolyte complexation. One-step continuous spinning of graphene fibers and yarns is introduced for the first time by in situ spinning of LC GO in basic coagulation baths (i.e., NaOH or KOH), eliminating the need for post-treatment processes. The thermal conductivity of these graphene fibers is found to be much higher than polycrystalline graphite and other types of 3D carbon based materials.

One-Step Wet-Spinning Process of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) Fibers and the Origin of Higher Electrical Conductivity

A simplified wet-spinning process for the production of continuous poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) fibers is reported. Conductivity enhancement of PEDOT:PSS fibers up to 223 S cm−1 has been demonstrated when these fibers are exposed to ethylene glycol as a post-synthesis processing step. In a new spinning approach it is shown that by employing a spinning formulation consisting of an aqueous blend of PEDOT:PSS and poly(ethlylene glycol), the need for post-spinning treatment with ethylene glycol is eliminated. With this approach, 30-fold conductivity enhancements from 9 to 264 S cm−1 are achieved with respect to an untreated fiber. This one-step approach also demonstrates a significant enhancement in the redox properties of the fibers. These improvements are attributed to an improved molecular ordering of the PEDOT chains in the direction of the fiber axis and the consequential enrichment of linear (or expanded-coil like) conformation to preference bipolaronic electronic structures as evidenced by Raman spectroscopy, solid-state electron spin resonance (ESR) and in situ electrochemical ESR studies.

Propyl gallate and butylated hydroxytoluene influence the accumulation of saturated fatty acids, omega-3 fatty acid and carotenoids in thraustochytrids

Schizochytrium sp. S31 was shown to have potential for production of the functional food ingredients docosahexaenoic acid (DHA) and astaxanthin, with coproduction of biodiesel. Biomass and lipid levels were greater with glycerol than with glucose as carbon source. Addition of propyl gallate or butylated hydroxytoluene to the media resulted in increased biomass and lipid levels, with propyl gallate being the more effective of the two antioxidants. Medium supplementation with propyl gallate at 0.03% and glycerol as the carbon source resulted in enhanced biomass productivity (28.50 g L^-1), lipid accumulation (24.87 g L^-1) and astaxanthin levels (452.26 μg L^-1).

THE EFFECT of E-GLASS FIBERS and ACRYLIC RESIN THICKNESS on FRACTURE LOAD IN A SIMULATED IMPLANT-SUPPORTED OVERDENTURE PROSTHESIS

Statement of problem. Implant overdenture prostheses are prone to acrylic resin fracture because of space limitations around the implant overdenture components.Purpose. The purpose of this study was to evaluate the influence of E-glass fibers and acrylic resin thickness in resisting acrylic resin fracture around a simulated overdenture abutment.Material and methods. A model was developed to simulate the clinical situation of an implant overdenture abutment with varying acrylic resin thickness (1.5 or 3.0 mm) with or without E-glass fiber reinforcement. Forty-eight specimens with an underlying simulated abutment were divided into 4 groups (n=12): 1.5 mm acrylic resin without E-glass fibers identified as thin with no E-glass fiber mesh (TN-N); 1.5 mm acrylic resin with E-glass fibers identified as thin with E-glass fiber mesh (TN-F); 3.0 mm acrylic resin without E-glass fibers identified as thick without E-glass fiber mesh (TK-N); and 3.0 mm acrylic resin with E-glass fibers identified as thick with E-glass fiber mesh (TK-F). All specimens were submitted to a 3-point bending test and fracture loads (N) were analyzed with a 2-way ANOVA and Tukey's post hoc test (alpha=.05).Results. The results revealed significant differences in fracture load among the 4 groups, with significant effects from both thickness (P<.001) and inclusion of the mesh (P<.001). Results demonstrated no interaction between mesh and thickness (P=.690). The TN-N: 39 +/- 5 N; TN-F: 50 +/- 6.9 N; TK-N: 162 +/- 13 N; and TK-F: 193 +/- 21 N groups were all statistically different (P<.001).Conclusions. The fracture load of a processed, acrylic resin implant-supported overdenture can be significantly increased by the addition of E-glass fibers even when using thin acrylic resin sections. on a relative basis, the increase in fracture load was similar when adding E-glass fibers or increasing acrylic resin thickness. (J Prosthet Dent 2011;106:373-377)