Efeito da hidrólise ácida e sulfitação de taninos de Eucalyptus grandis W. Hill ex Maiden e Anadenanthera peregrina Speg., nas propriedades dos adesivos

• Autor(a) principal: Carneiro, Angélica de Cássia Oliveira
• Data de Publicação: 2006
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/549
• topic: Taninos; Adesivos; Chapas de madeira; Propriedades físicas; Propriedades mecânicas; Tannins; Adhesives; Particleboard; Physical properties; Mechanical properties; CNPQ::CIENCIAS AGRARIAS::RECURSOS FLORESTAIS E ENGENHARIA FLORESTAL::TECNOLOGIA E UTILIZACAO DE PRODUTOS FLORESTAIS

The main objective of this study was to evaluate the effect of acid hydrolysis and of sulphitation on the properties and strength of joints made with adhesives from tannins extracted from barks of Eucalyptus grandis and Anadenanthera peregrina. The tannins were hydrolysed and sulphited using four pH values, two types of acid and three reaction times in the presence or absence of sodium sulphite. After the production of the adhesives, the adhesive properties of each treatment were evaluated. A total of 384 joints composed by two veneers of Eucalyptus grandis glued with tannic adhesives were produce to evaluated the glued line strength. An amount of 250 g/m2 of adhesive in double face was applied. To produce the tannic adhesives, 10% of formaldehyde was added to the dry solid mass of the tannins. Shearing strength of the joints of the wood was determined according to the ASTM 2339-93 standard. The tannins molecular weights were determined using the chromatographic techniques of gel permeability. The kinetic parameters were obtained using exploratory differential calorimetry. In adition, 15 particleboards made from particles of Pinus elliottii were produced with sizes about 40 x 40 x 1 cm, with an average density of 0,70 g/cm3 constituting a total of five treatments with three repetitions. An amount of 8% of adhesive formulations was used, containing hydrolysed tannins of Anadenanthera peregrina and of urea-formaldehyde, based on the dry mass of the particles. The physical and mechanical properties of the boards were determined according to the ASTM D-1037-93 standard. The results of the mechanical tests were compared to the minimum values established by the ANSI/A 208.1-1993 standard (Wood Particleboard), and the results of the water absorption and swelling in thickness tests were compared to the maximum values established by the DIN 68m761 (1)-1961 standard. Adhesive properties were changed by hydrolysis and sulphitation of the tannins. The reaction time did not significantly influence their properties. Reduction of pH during tannins hydrolysis reduced the viscosity and increased the gel processing time and the adhesives working time. The tannins molecular weight was reduced with their hydrolysis and sulphitation, due to breakage of interflavonoid links. In relation to the kinetic parameters, the results show that activation energy, enthalpy and curing temperature of the adhesives were reduced by the hydrolysis and the sulphitation of the tannins; nevertheless, they showed a large band of polymerization. The shearing strength of the tannic adhesives was increased by the hydrolysis and sulphitation of the tannins; this was mainly due to rupture of interflavonoid links that consequently reduced adhesives viscosity. The mean values observed for shearing strength were close to those observed with the commercial adhesive made from urea-formaldehyde. It was observed that the mechanical properties of the particleboards produced with the adhesive based on the tannins of Anadenanthera peregrina, with the exception of the module of elasticity, surpassed the minimum values established by the ANSI/A1-280/93 standard. The water absorption and swelling in thickness, after 2 and 24 hours of immersion of all the boards, exceeded the established maximum value.