The Multiple-Phase Pressure (MPP) Process achieves treatment and fixation as combined process using hot CCA, within a 2-3 hour time-frame. Timber is treated to saturation with hot CCA using an empty cell process. During the pneumatic pressure phase, hot solution is held in the wood in an otherwise liquid-free treatment vessel until fixation is >95% complete. This report details a factorial design series of treatments undertaken to determine the effect of key process variables, particularly CCA solution temperature and time held at pneumatic pressure, on the degree of fixation achieved during treatment and the resultant Cu, Cr, As and Total Carbon concentration in kickback solutions. Increasing the CCA solution temperature resulted in greater fixation. At a solution temperature of 75°C, extending the time at pneumatic pressure beyond 60 minutes did not result in any significant increase in preservative fixation.

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