• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1
  • Tagged with
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Propriedades tecnol?gicas e qualidade de ades?o de madeiras de Corymbia citriodora e Eucalyptus pellita termorretificadas / Technological properties and adhesion quality of the heat-treated Corymbia citriodora and Eucalyptus pellita woods

Nunes, Cintia Silva 29 June 2012 (has links)
Submitted by Sandra Pereira (srpereira@ufrrj.br) on 2017-04-27T11:59:34Z No. of bitstreams: 1 2012 - Cintia Silva Nunes.pdf: 1126230 bytes, checksum: 45346dd33d53277fd3bc88d1d3d22157 (MD5) / Made available in DSpace on 2017-04-27T11:59:34Z (GMT). No. of bitstreams: 1 2012 - Cintia Silva Nunes.pdf: 1126230 bytes, checksum: 45346dd33d53277fd3bc88d1d3d22157 (MD5) Previous issue date: 2012-06-29 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Heat treatment provides desirable characteristics to the wood such as higher dimensional stability, higher natural durability and, in some cases, changes on original color. However, the treatment can also drastically alter the physical and chemical characteristics of wood surfaces, which affect the adhesion quality and coating application. In this context, the objectives of this study were: (1) to evaluate the effect of heat treatmens on physical properties (density, equilibrium moisture content and mass loss) of Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson and Eucalyptus pellita F. Muell. woods; (2) to determine the effect of heat treatment on color change of both woods; (3) to evaluate the effect of heat treatments on adhesion quality of glued joints by shear strength testing; and (4) to evaluate the effect of physical and chemical modifications following heat treatment on adhesion characteristics. Heat treatments were performed in a laboratorial electric oven at 180 and 200?C. Color measurements were carried out on the CIE-L*a*b* space by using the CM-2600d portable spectrophotometer. Shear strength tests of the glued joints and solid woods were performed according to ASTM D 905 and ASTM D 143 standards, respectively. Three adhesive types were used: resorcinol, resorcinol-tannin 80:20 and resorcinol-tannin 60:40. Density and equilibrium moisture content of both wood species were reduzed by heat treatment. Both woods had mass loss, which increased with the increase of temperature and was more pronounced for Eucalyptus pellita. The original color of the woods changed following heat treatment, mainly to Eucalyptus pellita. The shear strength of solid wood and glued joints of both species was severely affected by heat treatments. The resorcinol-tannin 80:20 adhesive showed the best performance for untreated woods, however, after heat treatment, the adhesive type did not affect the shear strength. Glued joints of heat-treated woods had high percentage of wood failure due to higher porosity and adhesive penetration. The acidity of heat-treated woods affected the shear strength and presented a strong correlation with equilibrium moisture content due to degradation of hemicelluloses. Heat treatments at 180 and 200oC are extremely severe to Corymbia citriodora and Eucalyptus pellita woods / O tratamento de termorretifica??o proporciona ? madeira caracter?sticas desej?veis tais como maior estabilidade dimensional, maior durabilidade natural e, em alguns casos, altera??o da cor original. Entretanto, o tratamento tamb?m pode alterar drasticamente as caracter?sticas f?sicas e qu?micas das superf?cies da madeira, as quais afetam a qualidade de ades?o e a aplica??o de revestimentos. Neste contexto, os objetivos deste estudo foram: (1) avaliar o efeito dos tratamentos nas propriedades f?sicas (densidade, teor de umidade de equil?brio e perda de massa) da madeira de Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson e Eucalyptus pellita F. Muell.; (2) determinar o efeito dos tratamentos termorretificadores na altera??o da cor da madeira de ambas as esp?cies; (3) avaliar o efeito dos tratamentos na qualidade de ades?o de juntas coladas atrav?s de testes de resist?ncia ao cisalhamento; e (4) avaliar o efeito das altera??es f?sicas e qu?micas causadas pela termorretifica??o nas caracter?sticas de ades?o. A termorretifica??o foi realizada em um forno mufla el?trico laboratorial a 180 e 200?C. As medi??es de cor foram realizadas no espa?o CIE-L*a*b* com o aux?lio do espectrofot?metro port?til CM-2600d. Os ensaios de cisalhamento das juntas de madeira colada e das madeiras s?lidas foram realizados segundo as normas ASTM D 905 e ASTM D 143, respectivamente. Foram utilizados tr?s tipos de adesivos: resorcinol, resorcinol-tanino 80:20 e resorcinol-tanino 60:40. A densidade aparente e o teor de umidade de equil?brio das madeiras de ambas as esp?cies foram reduzidos pela termorretifica??o. Ambas as madeiras apresentaram perda de massa, sendo esta crescente com o aumento da temperatura e mais acentuada para a madeira de Eucalyptus pellita. A cor original das madeiras foi alterada pelo tratamento, principalmente para o Eucalyptus pellita. A resist?ncia ao cisalhamento da madeira s?lida e das juntas coladas de ambas as esp?cies foi severamente afetada pelos tratamentos termorretificadores. O adesivo resorcinol-tanino 80:20 apresentou o melhor desempenho para as madeiras n?o termorretificadas de ambas as esp?cies; entretanto, ap?s a termorretifica??o, o tipo de adesivo n?o afetou a resist?ncia ao cisalhamento. As juntas coladas das amostras de madeiras termorretificadas apresentaram uma alta porcentagem de falhas na madeira devido ? maior porosidade e maior penetra??o do adesivo. A acidez das amostras da madeira termorretificada afetou a resist?ncia ao cisalhamento e apresentou uma forte correla??o com o teor de umidade de equil?brio devido ? degrada??o das hemiceluloses. Os tratamentos termorretificadores a 180 e 200?C s?o extremamente severos para as madeiras de Corymbia citriodora e Eucalyptus pellita

Page generated in 0.0772 seconds