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    Decay resistance and dimensional stability of Araucaria angustifolia using siloxanes synthesized by solegel process
    (Elsevier, 2013-05-16) Giúdice, Carlos Alberto; Alfieri, Paula; Canosa, Guadalupe
    Solid wood specimens of Araucaria angustifolia were impregnated with alkoxysilanes hydrolyzed and condensed “in situ” by the solegel process. Alkoxysilanes selected were aminopropyl methyldiethoxysilane and aminopropyl triethoxysilane; it was also used the aminopropyl methyldiethoxysilane/aminopropyl triethoxysilane mixture in 50/50 ratio w/w. The pH was adjusted to alkaline value for controlling kinetic of hydrolysis and condensation reactions. Impregnation process was carried out under controlled operating conditions to achieve different weight gains of the chemical modifier. Unmodified and modified wood specimens were exposed to brown rot (Polyporus meliae) and white rot (Coriolus versicolor) under laboratory conditions. The results indicate that the improved resistance to fungal exposure would be based on the wood chemical modification (the protection of cellulose caused by steric hindrance of hSieOeCellulose preventing the formation of enzymeesubstrate complex). Moreover, the results also would be based on the enhanced dimensional stability of the treated wood; the quoted high dimensional stability, which limits the growth of the spores, is supported in the hydrophobicity generated by both the decreasing of the amount of polar hydroxyl groups and the partial occupation of pores with polysiloxanes.
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    Dimensional stability, fire performance and decay resistance in wood impregnated with alkylalkoxysilanes
    (2013-11-20) Canosa, Guadalupe; Alfieri, Paula; Giúdice, Carlos Alberto
    The wood, very heterogeneous and complex material, changes its volume by water absorption or desorption causing swelling or shrinkage and also it can be degraded both by action of microorganisms and fire; the above-mentioned is a great inconvenient for most commercial uses. In this research, wood specimens of Pinus radiata were previously pretreated in a Soxhlet extractor for 2 hours with a solution of sodium hydroxide (activation of the cellulose) and then impregnated with alkylalkoxysilanes hydrolyzed and condensed "in situ" by the sol-gel process. Silanes selected were triethoxysilane, methyltriethoxysilane, n-propyltriethoxysilane, n-buthyltriethoxysilane and n-octhyltriethoxysilane. Impregnation process was carried out under controlled operating conditions to achieve similar weight gains of the chemical modifier. The pH was adjusted to alkaline value for controlling kinetic of hydrolysis and condensation reactions. Results indicated that dimensional stability increased with the increase of the length of the hydrocarbon chain of the alkoxydes, which would be based essentially on their enhanced hydrophobicity but without discarding the partial occupation of the pores by polymerized siloxanes and the interaction of alkoxides with cell wall components. In addition, wood specimens impregnated with mentioned alkylalkoxysilanes also showed an excellent fire performance and decay resistance.
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    High solids, one coat paints based on aliphatic epoxi resin siloxanes for steel protection
    (Elsevier, 2014-05-01) Canosa, Guadalupe; Alfieri, Paula; Giúdice, Carlos Alberto
    This research involved the design of high-solids, one-coat paints for the protection of metal structures with low maintenance requirements. The main paint components were: (i) an aliphatic epoxy resin cured with an aminosilane and chemically modified with alkoxysilanes as film-forming material, and (ii) rutile titanium dioxide as opaque pigment, a polysilicate strontium and zinc as corrosion inhibitor and, a synthetic calcium silicate and barites as extenders. Some paints displayed excellent performance in salt spray apparatus (degree of rusting) and in 100% relative humidity cabinet(degree of blistering). Results indicate that as the aliphatic epoxy resin/alkoxide ratio increased, the degree of rusting improved while the degree of blistering worsened, in total agreement with film permeability. In addition, binders based on dimethyldiethoxysilane, methyltriethoxysilane and tetraethoxysilane, in that order, displayed an improved corrosion performance and a decreased blistering resistance. The reactivity of alkoxides and the chemical interaction with the metal substrate supports the obtained results. Initial gloss and gloss and color retention improved as the alkoxide level increased; no significative differences were registered when the alkoxide type variable was considered. In summary, the use of alkoxides as modifiers of an aliphatic epoxy resin allowed the formulation of hybrid paints with high anticorrosive and weathering resistance performance. The more suitable hybrid organic–inoganic paint must be selected according to the requirements of each structure in service
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    Hybrid finishing coatings applied on laminar zinc primers
    (American Chemical Society, 2013-05-29) Giúdice, Carlos Alberto; Canosa, Guadalupe; Alfieri, Paula
    Hybrid finishing coatings were formulated with several film-forming materials and reinforcement fibers. In all cases, the same tri-pigmented epoxy-polyamide coating based on laminar zinc was used as primer. The results indicated that wellwetted fibers improved mechanical properties of finishing coating films, such as tensile strength, modulus of elasticity, hardness, adhesion, and impact resistance; on the other hand, elongation decreased according with type and level of reinforcement fibers selected. In addition, finishing coatings with semiconductive fibers displayed in salt spray (fog) apparatus, a high dissolution of metallic zinc of primer since these fibers would act as cathode in galvanic cells. According to IR spectrum analysis, chemical degradation was observed only in coatings with the binder susceptible to basic hydrolysis due to the action of hydroxyl ions formed on semiconductive fibers. Furthermore, nonconductive fibers included in finishing coatings displayed no changes in any film-forming material (even when alkyd resin was used) nor promoted excessive zinc dissolution of primer.
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    Impregnación de maderas de baja densidad con hidrofugantes organosilícicos
    (2017) Alfieri, Paula; Traversa, Luis; Canosa, Guadalupe; Giúdice, Carlos Alberto
    En este trabajo se estudiaron las propiedades de madera de Araucaria angustifolia modificada químicamente por impregnación con alquilalcoxisilanos con diferente longitud de cadena hidrocarbonada, hidrolizados y condensados “in situ” por el proceso sol-gel, con el fin de lograr fundamentalmente alta estabilidad dimensional, baja absorción de agua, como así también satisfactoria permeabilidad al vapor de agua. Los impregnantes organosilícicos seleccionados mejoraron la estabilidad dimensional, disminuyeron la absorción capilar de agua y mantuvieron la permeabilidad al vapor de agua con respecto a las muestras no tratadas, debido a la formación del recubrimiento en las paredes celulares de la madera. Este recubrimiento se produce en algunas áreas que rodearían áreas no tratadas lo cual fundamentaría que es posible alcanzar la protección de toda la madera con el bajo nivel de impregnante empleado. Por último, se observó que la naturaleza química del impregnante define la hidrofobicidad del recubrimiento formado sobre la pared celular e incide sobre la cinética de la absorción capilar; por su parte, la estructura del impregnante influye sobre la continuidad y forma del citado recubrimiento e incide en el grado de estabilidad dimensional.
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    Pinturas híbridas de terminación sobre fondos anticorrosivos de zinc modificados
    (Atipat, 2013-10-01) Giúdice, Carlos Alberto; Alfieri, Paula; Canosa, Guadalupe
    Las pinturas basadas en zinc metálico presentan una mayor eficiencia contra la corrosión en relación con otros recubrimientos. Sin embargo, éstas necesitan generalmente una pintura de terminación ya sea para conferirle al sistema un mejor acabado o bien para otorgarle una protección adecuada contra la acción del medio; en otros casos, la pintura de terminación también se aplica para conferirle dureza superficial (puentes de acero, estructuras metálicas portantes, etc.). En este trabajo se seleccionaron tres sistemas en lo referente al ligante; en todos los casos se empleó el mismo “primer” epoxi-poliamídico basado en zinc laminar mientras que para la capa de terminación se seleccionaron como ligantes una resina acrílica pura, una vinílica y una alquídica. En la formulación de estas pinturas, se emplearon fibras para conferirle elevada resistencia a la rotura y alto módulo de elasticidad a la película (grafito, nitruro de silicio, vidrio o cuarzo). Los resultados indican que en las estructuras híbridas con fibras semiconductoras se observó una elevada disolución del zinc ya que las citadas fibras actuarían como cátodos de la celda galvánica; también se constató que en el caso del ligante susceptible a la hidrólisis básica se produjo su degradación y la pérdida de propiedades de la película
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    Siloxanes synthesized in situ by solgel process for fire control in wood of Araucaria angustifolia
    (Elsevier, 2013-10-10) Giúdice, Carlos Alberto; Alfieri, Paula; Canosa, Guadalupe
    Panels of Araucaria angustifolia were chemically modified with alkoxysilanes, hydrolyzed and condensed “in situ” by the sol–gel process. Alkoxysilanes selected were aminopropyl methyldiethoxysilane (A), aminopropyl triethoxysilane (B) and a mixture of both (C). Ethanol was used as solvent in 4/1 ethanol/ alkoxide molar ratio. The pH was adjusted to alkaline value for controlling the kinetic of hydrolysis– condensation reactions. Impregnation process was carried out at 45–50 1C in an autoclave, controlling the operating conditions for achieving different weight gains. Laboratory tests were carried out in Two-Foot Tunnel (flame spread index, panel consumption and smoke density) and in TGA detector (mass loss). The performance in laboratory tests can be explicated according the reactivity of the alkoxides. The results support the conclusion that the best fireproof efficiency was observed in woods treated with the alkoxide B, followed by those modified with the mixture C and the alkoxide A, in this order; the results also indicates that as weight gain increased the performance of impregnants against fire