The Effect of the Knife Tacking Type on the Process of Producing Microcrystalline Cellulose

The article shows the possibility of intensifying the process of producing microcrystalline cellulose via pregrinding of fibrous semi-finished products before hydrolysis. The technological factors determining the grinding of fibrous materials have been considered. The efficiency of the microcrystalline cellulose production process is influenced by the choice of its production technology. For grinding, a semi-industrial disc mill with a tacking with rectilinear and curvilinear knives has been used. Multiphysics models of the flow of fibrous mass in the grinding zone of a disc mill with different knife tacking patterns have been constructed. The morphological properties of the fiber have been measured on the Morfi Neo automatic fiber analyzer after grinding to 65 °SR. The nature of the change in the properties of bleached sulfate hardwood and softwood cellulose has been analyzed. It has been found that it is identical for all degrees of grinding, but the quantitative characteristics change to the greatest extent when grinding softwood cellulose using a tacking with rectilinear knives: the weighted average length of fibers decreases by 17 %, the width – by 14 %; the content of broken fibers increases by 22 %, the content of fines along the length – by 67 % and the fibrillation index – by 1.9 times. A comparative analysis of the values of the degree of polymerization depending on the knife tacking pattern has been carried out. The conditions for producing microcrystalline cellulose after grinding the fibrous mass in a semi-industrial disc mill, depending on the degree of grinding, have been determined. It has been shown that with an increase in the degree of grinding of the fibrous mass from 15 to 65 °SR, the degree of polymerization of microcrystalline cellulose decreases from 272 to 120, the concentration of hydrochloric acid – from 2.5 to 1.5 N and the duration of hydrolysis – from 120 to 90 min. The developed method for producing microcrystalline cellulose makes it possible to reduce the cost of chemical treatment of the fibrous mass (acid concentration, treatment duration and hydrolysis temperature) by 1.5 times.