The effect of preheating and refining conditions on radiata pine MDF fibre quality.

The production of quality MDF fibre is dependant on a careful balance between preheating and refining conditions. This paper describes the impact of preheater residence time, preheater temperature and refiner energy input on MDF fibre quality. Increasing the preheating temperature from 129 to 174 degrees C caused a reduction in Pulmac shive content, Bauer McNett +14 fraction, average fibre length, width index and brightness for a given preheating residence time. Increasing the preheating residence time caused the Pulmac shive content, Bauer McNett +14 fraction and the brightness to all reduce when compared at a given preheating temperature. The preheating severity index is an excellent predictor of Pulmac shive content and brightness. Increasing the preheating severity caused the Pulmac shive content, brightness and the percent insoluble fibre to all decrease. As the refiner energy input was increased, the fibre length, Pulmac shive content and Bauer McNett +14 fraction were all reduced. The MDF fibre quality can be modified substantially by altering the preheating and refining conditions. Ultimately the process conditions will need to be adjusted to ensure that the fibre quality is able to meet the needs of the end product. These results show that the MDF process is flexible and thus it is possible to produce fibres for a wide variety of products.