Caracterização tecnológica da madeira de schizolobium parahyba (Vell.) blake modificada termicamente
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Data
2017-11-13
Autores
Calonego, Fred Willians [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
No Brasil, a espécie pioneira Schizolobium parahyba (Vell.) Blake, conhecida como Guapuruvu, tem potencial para os projetos de restauração ecológica da Floresta Atlântica, e quando atingem cerca de 15 anos podem ser retiradas mediante plano de manejo. Entretanto, uma característica indesejável da sua madeira é a presença acentuada de lenho juvenil e uma das suas limitações é a baixa durabilidade natural. Uma forma de minimizar este problema é a modificação térmica logo após a sua secagem. Porém, esses tratamentos provocam mudanças na cor da madeira. Assim, o objetivo desse estudo foi avaliar o efeito do tratamento de modificação térmica nas propriedades físicas, químicas e colorimétricas e na resistência dos lenhos juvenil e adulto de S. parahyba aos organismos xilófagos e ao intemperismo. Para tanto, foram usadas tábuas provenientes de toras de Guapuruvu, com cerca de 15 anos de idade, retiradas de uma área de recuperação florestal da Faculdade de Ciências Agronômicas, da UNESP, de Botucatu-SP. Cada tábua foi seccionada de modo a fornecer peças controle e outras destinadas para os tratamentos de modificação térmica, com temperaturas finais de 180ºC, 200ºC e 220ºC. Corpos de prova foram retirados para a caracterização tecnológica dos lenhos juvenil e adulto através dos ensaios de propriedades físicas, químicas, de caracterização colorimétrica da madeira e de resistências aos fungos de podridão parda Gloeophyllum trabeum e de podridão branca Pycnoporus sanguineus, ao cupim de madeira seca Cryptotermes brevis e ao intemperismo. Os resultados mostraram que: (1) o aumento da temperatura de modificação térmica promove decréscimos significativos de até 9,1% na massa específica aparente a 21ºC e 65% de umidade relativa da madeira de S. parahyba, e reduz em até 51,1% e 54,1% os seus respectivos teores de umidade de equilíbrio e inchamento volumétrico; (2) a massa específica básica e os coeficientes de retratibilidades não variam com os tratamentos térmicos e não são indicados para avaliar a qualidade da madeira modificada termicamente; (3) a modificação térmica provoca reduções significativas de até 25,0% nos teores de holocelulose e um aumento proporcional de até 41,7% e 286,5% nos respectivos teores de lignina e de extrativos totais da madeira; (4) a cor da madeira sem tratamento é classificada como branco amarelada, pois apresenta alta claridade (L* de 80,41 a 80,85) e presença marcante do pigmento amarelo (b* de 19,06 a 20,07), e o tratamento térmico provoca o seu escurecimento e avermelhamento; (5) a madeira sem tratamento é classificada como não resistente ao cupim de madeira seca e ao fungo de podridão parda, e, de resistência moderada ao fungo de podridão branca, sendo que os tratamentos térmicos provocam reduções significativas de até 90,6% nas perdas de massa provocadas pelos fungos apodrecedores e não mudam a classe de resistência da madeira aos cupins; e (6) a madeira sem tratamento ficou mais escurecida, avermelhada e amarelada após o intemperismo, e o tratamento térmico aumenta a sua resistência aos agentes abióticos. Pode-se concluir que a modificação térmica possui um grande potencial para melhorar a estabilidade dimensional e a resistência natural da madeira de S. parahyba aos fungos apodrecedores e ao intemperismo, embora, modifique a sua cor e não altera a sua classe de resistência aos cupins.
In Brazil, the pioneer plant species Schizolobium parahyba (Vell.) Blake, known as Guapuruvu, has potential for ecological restoration projects in the Atlantic Forest, and when they reach about 15 years can be taken by the management plan. However, an undesirable feature of this wood is the pronunced presence of juvenile wood and a limitation is low biological resistance. An attractive way to mitigate this problem is this thermal modification process after its drying. However, these thermal treatments cause changes in color of wood. The aim of this study was to evaluate the effect of thermal modification on physicochemical and colorimetric properties and biological resistance of juvenile and mature woods from S. parahyba to xylophagous organisms and weathering. Boards were taken from a 15-year-old S. parahyba forest recovery area of Agronomy Sciences College from UNESP, located in Botucatu, SP, Brazil. Each board was sawed into smaller pieces measuring 0.60 m in length. One small piece was kept in its original condition (untreated wood), whereas the other pieces were reserved for the thermal treatments at final temperature of 180ºC, 200ºC, and 220ºC. Subsequently, samples were cut from all the boards (untreated and thermally modified woods) to technological characterization for both juvenile and mature wood across to tests of physical and chemical properties, colorimetric characterization of wood, decay resistance at brown-rot fungus Gloeophyllum trabeum and white-rot fungus Pycnoporus sanguineus, biological resistance to térmite dry wood Cryptotermes brevis, and weathering resistance. The results showed that: (1) the increase in the thermal modification temperature causes significant decreases of up to 9,1% in the density at 21ºC and 65% relative humidity of the S. parahyba wood and reduces the equilibrium moisture content and volumetric swellings in up to 51.1% and 54.1%, respectively; (2) the density basic and dimensional change coefficient of wood were not the most suitable for evaluating the quality of thermally modified wood; (3) the thermal modification causes significant decreases of up to 25.0% in the holocelulloses contents, an proportional increase of up to 41.7% e 286.5% in the lignin and extractives contents, respectively; (4) the color of untreated wood can be classified by yellowish white, because presents high brightness (L* of 80.41 to 80.85) and strong presence of yellow pigment (b* of 19.06 to 20.07), and the thermal treatment causes the darkening and reddening of timber; (5) the untreated wood was classified as non-durable to the dry wood termites and brown-rot fungus, and also was classified as moderate resistance to the white-rot fungus, whereas the thermal modification promotes significant reductions of up to 90.6% in the weight losses caused by rot fungi and do not change the damage caused by termites in wood; and (6) the untreated wood showed darkening, a reddish behavior and a yellowish behavior after weathering tests, and the thermal modification causes significant decreases in the weathering of wood. We concluded that the thermal modification has a great potential to improve the dimensional stability and the natural resistance of S. parahyba wood to decay fungi and weathering, although it modifies the color of wood and does not change its resistance class to the termite.
In Brazil, the pioneer plant species Schizolobium parahyba (Vell.) Blake, known as Guapuruvu, has potential for ecological restoration projects in the Atlantic Forest, and when they reach about 15 years can be taken by the management plan. However, an undesirable feature of this wood is the pronunced presence of juvenile wood and a limitation is low biological resistance. An attractive way to mitigate this problem is this thermal modification process after its drying. However, these thermal treatments cause changes in color of wood. The aim of this study was to evaluate the effect of thermal modification on physicochemical and colorimetric properties and biological resistance of juvenile and mature woods from S. parahyba to xylophagous organisms and weathering. Boards were taken from a 15-year-old S. parahyba forest recovery area of Agronomy Sciences College from UNESP, located in Botucatu, SP, Brazil. Each board was sawed into smaller pieces measuring 0.60 m in length. One small piece was kept in its original condition (untreated wood), whereas the other pieces were reserved for the thermal treatments at final temperature of 180ºC, 200ºC, and 220ºC. Subsequently, samples were cut from all the boards (untreated and thermally modified woods) to technological characterization for both juvenile and mature wood across to tests of physical and chemical properties, colorimetric characterization of wood, decay resistance at brown-rot fungus Gloeophyllum trabeum and white-rot fungus Pycnoporus sanguineus, biological resistance to térmite dry wood Cryptotermes brevis, and weathering resistance. The results showed that: (1) the increase in the thermal modification temperature causes significant decreases of up to 9,1% in the density at 21ºC and 65% relative humidity of the S. parahyba wood and reduces the equilibrium moisture content and volumetric swellings in up to 51.1% and 54.1%, respectively; (2) the density basic and dimensional change coefficient of wood were not the most suitable for evaluating the quality of thermally modified wood; (3) the thermal modification causes significant decreases of up to 25.0% in the holocelulloses contents, an proportional increase of up to 41.7% e 286.5% in the lignin and extractives contents, respectively; (4) the color of untreated wood can be classified by yellowish white, because presents high brightness (L* of 80.41 to 80.85) and strong presence of yellow pigment (b* of 19.06 to 20.07), and the thermal treatment causes the darkening and reddening of timber; (5) the untreated wood was classified as non-durable to the dry wood termites and brown-rot fungus, and also was classified as moderate resistance to the white-rot fungus, whereas the thermal modification promotes significant reductions of up to 90.6% in the weight losses caused by rot fungi and do not change the damage caused by termites in wood; and (6) the untreated wood showed darkening, a reddish behavior and a yellowish behavior after weathering tests, and the thermal modification causes significant decreases in the weathering of wood. We concluded that the thermal modification has a great potential to improve the dimensional stability and the natural resistance of S. parahyba wood to decay fungi and weathering, although it modifies the color of wood and does not change its resistance class to the termite.
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Palavras-chave
Modificação térmica da madeira, Propriedades físicas, Resistência a fungos e cupins, Caracterização colorimétrica, Lenhos juvenil e adulto, Guapuruvu, Thermal modification of wood, Physical properties, Fungi and termite’s durability, Colorimetric characterization, Juvenile and mature wood