Microwave-vacuum drying of flax fiber for biocomposite production

Flax fiber is one of the important bast fiber available in North America which has low density and good mechanical properties for reinforcing various polymers to develop industrial biocomposite. But the hydrophilic nature of the fiber leads to poor adhesion between the fiber and the polymer matrices which, in turn, leads to poor dimensional stability. To enhance the adhesion between polymer matrix and fiber, chemical treatments of the fiber are necessary. After these treatments, the fiber needs to be uniformly dried to minimum moisture content for better compounding of flax in polymer matrices. Drying by conventional dryers at higher temperature usually results in overall quality loss due to surface drying, and it is also time consuming and energy intensive. In recent years, the microwave has been effectively used for enhancing bulk drying of biomaterials especially when coupled with vacuum. Such a volumetric heat transfer mechanism coupled with drying in vacuum provides an ideal low-temperature drying technique resulting in better organoleptic quality. In this study, the drying characteristics of flax fiber were studied under microwave-vacuum condition. The drying experiments were conducted in Enwave Microwave-vacuum dryer using three different process variables viz., microwave power (750 W and 375 W), vacuum level (25, 10, and 0 in Hg) and time of drying (0 to 14 mins). In order to select the appropriate drying curve equation, the drying data was fitted in three different models viz., Page model, single exponential model and approximation of diffusion model.