The effect of processing variables on the soda pulping of olive tree wood

A central composite design was developed to study the effect of processing variables (temperature, pulping time and soda concentration) on the properties of pulp (holocellulose, α-cellulose and lignin contents, yield and brightness) and the paper sheets obtained (breaking length, burst index and tear index). The proposed equations fit the experimental results for the dependent variables with errors less than 10% (15% for the breaking length). Obtaining pulp with acceptably high yield, holocellulose and α-cellulose contents, a high brightness and low lignin contents, requires cooking at a low pulping temperature (155–160°C), using a high soda concentration (10%) for a short pulping time (15 min). On the other hand, obtaining paper sheets with acceptable strength properties requires rather different conditions. Consequently, it is preferable to use the pulping conditions that result in the best pulp properties and to improve the characteristics of the paper sheets by refining.