Ligninas acetosolv e formacell de eucalipto e de bagaço de cana : isolamento, fracionamento, caracterização e uso como componente de resinas fenolicas do tipo resol

AUTOR(ES)
DATA DE PUBLICAÇÃO

1996

RESUMO

Lignins are naturally-occuring polyphenols with a crosslinked structure. The general properties and the nature of the functional groups in lignins depend both on their source and on the extraction process. Lignins from eucalyptus wood and sugar-cane bagasse were isolated by the Acetolsov (EAc and BAc) and the Formacell (EFo and BFo) pulping processes. A greater number of acetyl groups are found in EAc and BAc, while EAc and EFo have more methoxy groups. Pyrolysis coupled with GC shows that EAc and EFo have more S units (4-hydroxy-3,5-dimethoxyphenylpropane), while a larger number of H units (4-hydroxyphenylpropane) are found in BAc and BFo. Fractionation with organic solvents shows lower polarity for EAc and EFo and a higher condensation degree in EAc and BAc. Three EFo and BFo fractions showing low polydispersity and an increasing Mw were isolated. Elemental and functional group analysis for each fraction indicate a similar C9 unit. The kinetics of the hydroxymethylation reaction of EAc and BAc was monitored using IR spectroscopy. Univariate and principal component analysis of the normalized absorption bands show that equilibrium is reached after ca. 2 h for EAc and 4 h for BAc. TG analysis for hydroxymethylated EAc, EFo, BAc, and BFo show higher thermal stability than the untreated lignins. DH, Ea and reaction order data for the exothermic hydroxymethylation and crosslinking processes were obtained by DSC analysis. DH (-6 to -16 kJ.mol) is comparable to phenol and lignins, but lower DH was determined for the lignins. The Ea for phenol, the lignins and their fractions are comparable (60 kJ.mol). On the other hand, Ea for the lignins is greater. The synthesis of resols with lignins was carried out following multivaried factonal design experiments. All variables analyzed show a significant effect on viscosity (h) and synthesis time. Resins with h ranging between 100 and 400 mPas.s, gelification time (ca. 90 min at 90°C) and cure temperature (ca. 150°C) similar to those of lignin-free resols were obtained. The partiaI substitution of phenol by lignins is desirable because the standard resin properties are maintained.

ASSUNTO(S)

lignina resinas fenolicas

ACESSO AO ARTIGO

Documentos Relacionados