Acid methanolysis: An analytical tool for estimating the proportions of different pulp types in deinked pulp or recovered paper

A method was developed to estimate the composition of deinked pulp or recovered paper in terms of hardwood kraft pulp, softwood kraft pulp, and mechanical pulp through analysis of the sugar units in hemicelluloses and pectins.Different pulps (i.e., bleached chemical pulp from hardwoods and softwoods and mechanical pulp) were obtained from different mills. The pulps were mixed in different proportions and dried. The content of arabinose, xylose, mannose, galactose, rhamnose, galacturonic acid, and 4-O-methyl-glucuronic acid, sugar units in hemicelluloses and pectins in the different pulps and in the mixtures were determined by acid methanolysis and gas chromatography. The contents of the sugar units were significantly different in the three pulp types but quite similar in the same pulp type, irrespectively of bleaching sequence.The modeling was performed using standard partial least squares regression (PLSR) and cross-validation using venetian blinds subsets. The data were autoscaled before regressions. The best model had two latent variables. The cumulative variation of X captured by the model was 0.988 (R2X), the cumulative variation of Y captured by the model was also 0.988 (R²Y), and the cumulative cross-validated variation of Y captured by the model was 0.974 (Q²). Accordingly, the PLS model is more than capable of predicting the validation set.It was concluded that the proportion of chemical pulp from hardwoods, chemical pulp from softwoods, and mechanical pulp can be estimated in recovered paper or deinked pulp using a mathematical model based on the content of selected sugar units in hemicelluloses and pectins.