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Analysis of the production conditions of geopolymer matrices from natural pozzolana and fired clay brick wastes
The improvement of the mechanical properties of geopolymer matrices relies on the characteristics of the source materials as well as in proper optimization of the alkaline activating solution and curing...
Año de publicación: 2019
Laccase mediated grafting of polyphenols onto cationized cotton fibers to impart UV protection and antioxidant activities

Laccase from ascomycete Myceliophthora thermophila was used for enzymatic functionalization of bleached white woven 100% cotton fabrics. The molecules grafted to the cotton fabrics were morin and caffeic acid, both flavonoids. Fabrics grafted with flavonoids have applications in biological, medical and pharmaceutical areas due to the antioxidant, antiapoptotic, and anti-inflammatory capacities. The activity of laccase was determined spectrophotometrically by measuring the enzymatic oxidation of ABTS. The modified cotton fibers were characterized by spectrometrical detection of polyphenols on fibers by measurements of color strength, by SEM analysis, differential scanning calorimetry. The tests realized were color durability test, ultraviolet protection and resistance test, and water absortion test. Antioxidant activity were also measured following the ABTS radical cation decolorization assay.

Palabras clave: Antioxidant activity; Controlled release; Laccase; o-quinones; Enzymatic grafting
Año de publicación: 2018
Eco-friendly improvement of water erosion resistance of unstable soils with biodegradable polymers

Two biodegradable polymers, chitosan and carragenan, were studied as non-invasive modifyers of sand's mechanical and chemical properties. The properties evaluated were surface wettability and resistance to erosion, from both, water flow and drop impact. Surface wettability was measured through contact angle of a sessile water drop deposited on a sand surface. Erosion by water flow was evaluated through Run-off water test, in which a container full with sand was tilted 27° from horizontal position and water with a 234 mL/min flow rate flowed downhill. Erosion by water drop impact before and after polymer application was evaluated by a drip test. In this test, water from a container placed 1 m above the sand sample fell at 50 mL/min. Damaged from the impact was measured after one minute. The polymer studied were applied in their aquous solution form, at different concentrations. For the case in which both polymer where applied over the same sample, order of application was considered as an important factor.

Palabras clave: Chitosan; Carragenan; soil erosion; water resistance
Año de publicación: 2018
A comparative study of linen (flax) fibers as reinforcement of fly ash and clay brick powder based geopolymers

Geopolymers have great potential for the development of sustainable building materials due the utilization of industrial by-products and waste materials for their production. The introduction of natural fibers to geopolymer matrices has shown interesting results for producing alternative building materials with improved mechanical properties.

Palabras clave: Geopolymers; Fly-ash; Linen fibers; Flax fibers
Año de publicación: 2018
Eco-friendly modification of earthen construction with carrageenan: Water durability and mechanical assessment

Carrageenan, a biodegradable natural polymer, was evaluated as a bioadditive to improve the physical and mechanical properties of adobe constructions. The results show that its incorporation in the mixture during blocks fabrication, or as a coating in existent earth constructions, positively modify their behavior providing water impermeability and resistance to erosion by water drops. Results of mechanical tests also show a considerable enhancement in compressive and tensile strength when the bioadditive is incorporated during the blocks fabrication process. The obtained results show the feasibility of using natural and eco-friendly compounds to modify the behavior of traditional construction materials.

Palabras clave: Bioadditive; Carrageenan; Earthen construction; Water erosion; Water impermeability; Mechanical resistance
Año de publicación: 2017
Modulating antioxidant activity and the controlled release capability of laccase mediated catechin grafting of chitosan

Laccase from ascomycete Myceliophthora thermophila was used for the oxidation and grafting of catechin (CA) and chitosan (CS). The enzymatic grafting of CA into CS resulted in the improvement of natural properties of chitosan films. The successful grafting of CA to CS was supported by UV–vis and Fourier transform infrared (FTIR) spectroscopies. The differences in the molecular weight and the degree of deacetylation of the CS affected on the enzymatic grafting rate and thus on the film properties like swelling behaviour, erosion rate, thermal property, tensile strength and breaking strain. The CS films prepared by enzymatic grafting presented high antioxidant activity compared to native CS films. The controlled release profiles of methylene blue and coomassie brilliant blue dye, having different acidity/basicity properties, loaded films were also studied with different release medium. The types of molecule loaded into films, the preparation manner of films and the release medium were decisive parameters affecting the release rate.

Palabras clave: Antioxidant activity; Controlled release; Laccase; o-quinones; Enzymatic grafting
Año de publicación: 2017
The potential use of chitosan as a biopolymer additive for enhanced mechanical properties and water resistance of earthen construction

The study investigates the feasibility of using chitosan biopolymer as an admixture, or as an external coating, for earthen constructions to improve their resistance in two components: water induced degradation and key mechanical properties. The resistance to water induced degradation was evaluated in terms of contact angle and drip erosion tests, while the influence on mechanical properties was measured through compressive, tensile and three-point bending tests. The results indicate that the use of low concentrations of chitosan can improve significantly the performance in the two components and therefore was found to be a promising treatment for new or existing construction.

Palabras clave: Earthen construction
Año de publicación: 2016
Formation, antimicrobial activity, and controlled release from cotton fibers with deposited functional polymers

Chitosan and alginate are biopolymers with interesting bioactivity that can be transferred to cotton fibers for medical and health care applications. These polymers in solution can be attached onto cotton fibers by a layer-by-layer technique. Confirmation of polymer deposition onto fibers was verified by morphology analysis, coomassie blue dye coloration, and contact angle of water on fibers. Also, weight gain and level of whiteness after each layer deposition were determined. Antimicrobial activity on treated cotton samples against E. coli and S. aureus was evaluated after each layer deposition and high inhibition rate of bacteria growth was observed in samples with chitosan outer layer (∼ 100%). Polyelectrolyte layers on cotton fibers not only provide interesting bioactivity by themselves, but can also serve as a matrix for small bioactive molecules. In this regard, a model molecule was added during sample preparation to study its release behaviors in a buffer solution by monitoring with UV–vis spectroscopy.

Palabras clave: Biocompatibility; Biodegradable; Biomaterials; Biomedical applications; Fibers
Año de publicación: 2016
SEM-EDS Study of Ionically Crosslinked Alginate and Alginic Acid Bead Formation

Alginate is a natural polysaccharide that is widely employed in industrial applications. Here, beads of alginic acid, calcium and copper alginate were prepared by addition of soluble sodium alginate into a solution of hydrochloric acid or the corresponding cation. The progress of gelation inside the beads was followed by the degree of opacity at different times, which corresponded well to an apparent morphology change observed in freeze-dried bead cross sections analyzed by scanning electron microscopy. Furthermore, diffusion of Cu2+ ions across the beads was followed by energy dispersive X-ray spectroscopy, which revealed colocalization of the crosslinking cation and the morphologically distinct bead regions.

Palabras clave: Sodium alginate; Alginic acid; Ionotropic gelation; Structure; Morphology; SEM-EDS
Año de publicación: 2016