Tom Blackwood Forum Moderator 18 Posts
Re: Will thermal dispersion units separate the 'stickies'?5 January 2010 at 1:29pm
This is a rather difficult problem that has been made worse by the use of recycled fiber stock. The "stickies" are usually resins or other organic materials that agglomerate to form small holes in the final product or coat the equipment, resulting in excessive downtime or poor product quality.
The thermal dispersion units attempt to limit the problem by keeping these organics from agglomerating. Normally, a surfactant is used to prevent the agglomeration, but this may alter the product properties. I'm only familiar with one type of thermal dispersion unit and it uses an electrically heated wire that is placed just after the sheet forming device. The floating pulp is consolidated by a series of wires and the extra heat prevents the organics from coming out of solution as the sheet dries. This only works for small amounts of organics. It is better to remove these stickies in the front end of the process, such as de-inking of the recycled materials. This can be done by steam injection and/or heating of the recycled material followed by floatation of the pulp using screens. However, bleaching chemicals are usually still required to destroy the stickies. Inks, which are often fine carbon particles, are more difficult to separate by thermal means because of their poor solubility.