To prevent the photodegradation process, a wide range of coatings have been developed. This study evaluated wood color change (DE*) and the surface quality index (SQI) generated by ASTM D-660 standards in wood protected with polyurethane and varnish finishes of three tropical species (Acacia mangium, Cedrela odorata and Tectona grandis) in two weathering conditions (natural and accelerated condition). In addition, a model was developed to predict DE* and SQI in natural weathering based on DE* and SQI from accelerated weathering. The results showed that the application of these finishes generated variations in the color parameters of wood before being exposed to the elements. Additionally, it was found that finishes generated increases in DE*, especially the varnish type finish, and decreasing of SQI. Finally, models were found to predict color changes or surface quality in natural weathering based on color changes or surface quality in accelerated weathering. The model algorithm was expressed by DE* or SQI measured (X) and time exposure (t) in accelerated weathering by equationWith these models, it is possible to predict the equivalence of exposure times in natural weathering in tropical conditions for different kinds of finishes in three tropical species.

No abstract

No abstract

RESUMENCedrela odorata y Carapa guianensis son maderas utilizadas para la elaboración de muebles, puertas e inmobiliario de casas en Costa Rica. Así mismo, dos tipos de acabados (tipo nitrocelulosa y de poliuretano) son muy utilizados en estas maderas. No obstante, los cambios en los parámetros del color (CIE L*a*b*) por el intemperismo es poco conocido para estas especies y estos acabados. Al evaluar estos acabados ante el intemperismo se encontró que el acabado con poliuretano y nitrocelulasa producen cambios en la coloración de la madera apreciables en los primeros 40-60 días de exposición a la interperie y este cambio del color fue diferente en cada acabado. Ademas, los resultados mostraron que en C. guianensis los cambios medido por ∆E* de color fueron inferiores a los obtenidos en la C. odorata en los dos acabados con el tiempo y que estos a su vez son inferiores si no se aplica ningún tipo de acabado. Finalmente fue encontrado que las relaciones de los parámetros de color (L*, a*, c*) y la relación entre los mismo parámetros (L*-a*, L*-b* y a*-b*) son alterados ante la intemperie por la aplicación de los acabados.Palabras claves: CIE Lab, fotodegradación, UV, cambio de color, madera tropical ABSTRACT Carapa guianensis and Cedrela odorata wood are used for furniture and doors manufacturing in Costa Rica. Similarly, two kind wood coatings (nitrocellulose and polyurethane) are widely used in these manufactures. However, the effects of degradation in the components of color (CIE L* a* b*) of these coatings by the weathering is little known for these wood species and these coatings. It was evaluated these coatings under weathering and it was found that surface painted with polyurethane and nitrocellulose produced significant change in wood color during the first 40-60 days of weathering and the intensity of color change was different in two coatings. The results showed that color changes in Carapa guianensis wood were lower measured by ∆E* than Cedrela odorata wood in two coating of surface treatments. Finally, it was found that there are relationships among wood color parameters (L*, a*, c*) with weathering time and the relationship between color parameters (L*-a*, L*-b* and a*-b*) are altered by the coatings.Key words: CIE Lab, photodegradation, UV, color change, tropical wood INTRODUCCIÓN La madera ha sido usada por su durabilidad natural, por ser un material sumamente versátil y con excelentes características de trabajabilidad (Peña y Rojas 2005). Sin embargo, una de las principales debilidades de este material es la susceptibilidad a la degradación del color natural por el intemperismo. La degradación del color de la madera ocurre rápidamente, en especial cuando es expuesta al intemperismo sin ningún tipo de protección o aislante (Peña y Rojas 2005). Factores ambientales como la radiación solar, la temperatura, el viento y la lluvia inciden sobre el cambio del color y se da en superficie debido a la penetración de luz ultravioleta y luz visible en la madera (George et al. 2005). La incidencia de estos tip...

Evaluación de la composición química, secado al aire, preservación y trabajabilidad de ocho especies de rápido crecimiento en plantación de Costa Rica AbstrAct Costa Rica has successfully planted various forestry species for wood production. However, the use of their wood is limited, due to poor knowledge about their chemical properties, air-dry, preserved and workability performance. The present study details information of these properties for the species: Alnus acuminata (Aa), Acacia mangium (Am), Bombacopsis quinata (Bq), Cupressus lusitanica (Cl), Swietenia macrophylla (Sm), Terminalia amazonia (Ta), Terminalia oblonga (To) and Vochysia guatemalensis (Vg). Among the results obtained, it was found that the wood of these species is in general slightly acidic, except Bq, which presented tendency to be basic. Different species show considerable variability in the content of holocellulose, lignin and extractable micronutrients. Regarding micronutrients, and in relation to other species it was found a high percentage in Vg. The use of boron as a preservative, may be applied in the 8 plantation species. The presence of heartwood in some species made it not possible to be preserved by the vacuum-pressure method, but the sapwood was possible to preserve in all species. The drying rate increased with increasing board thickness and drying time was different among species. The fastest drying rate was found in Ta and Am, followed by Sm, To, Aa and Cl with intermediate values and Vg with the slowest air-drying rate. Am, Bq, Cl, Sm and To present from excellent to good planing, sanding , drilling and molding, but Ta, Bq, Aa and Vg, especially Aa and Vg, in the workability operations were catalogued as poor or very poor quality.