For pretreatment experiments, the heating controller was set on maximum output and reaction material was stirred at 60 rpm. Water was pushed through the cooling coil using the maximum water valve opening to rapidly cool the system (about 15 min).
When reaction material reached 90 C the slurries were immediately decanted and the insoluble fractions (solids) were recovered by vacuum filtration using a Büchner funnel and Whatman glass microfiber GF/A filters. Solids were water washed until a neutral pH was achieved. Recovered solids were sampled and dried at 50 C and stored at room temperature until further compositional analysis.
Recovered soluble fractions were sampled, filtered (0.45 lm Minisart syringe filter, Sartorius) and stored at 20 C until further compositional analysis.
In the case where solids were not separated post-pretreatment, the whole slurries were pH adjusted to 5.0 with NaOH.
For pretreatment reaction conditions a central composite design (CCD) incorporating variables of temperature, time and acid concentration was employed to define the optimum pretreatment process. Each independent variable was assessed at five coded levels (2, 1, 0, 1, 2) (Table 1).