Evaluation of acid methanolysis for analysis of wood hemicelluloses and pectins

The efficiency of acid methanolysis toward cleavage of glucuronosyl linkages in hemicelluloses and pectins was studied. Two aldo-uronic acids (a dimer and a tetramer) were submitted to methanolysis with different acidic strength and methanolysis time. The aldo-uronic acid tetramer was only affected by the acidity of the medium, whereas the dimer was sensitive towards both reaction time and acidity. It was concluded that methanolysis of 0.5–1 mg of model compounds with 2 ml of 2 M HCl/MeOH at 100°C for 3–5 h was the best compromise between good cleavage of the glucuronosyl bonds (≈70%, mol/mol) and little degradation of the uronic acid released (below 20%, mol/mol). The acid methanolysis of reference oligo- and polysaccharides verified the good accuracy of the method. The application of acid methanolysis on mechanical pulp fibres was tested on a thermomechanical pulp.