1) This test is based on Tappi Method T-233.
2) Fiber fractionation can be measured by the Bauer McNett (see figure 28). For TMPs, 14, 28, 48, 100 and 200 mesh screens will be used. It needs 10 g of OD weight pulp agitated with a 10 liter per minute flow for twenty minutes in one test. The sample is around 3333 ml of pulp suspension of 0.3% consistency, or a 1000 ml of suspension of 1% consistency.
Figure 28: Bauer McNett Fiber Fractionator.
3) Before using the Bauer McNett, check the cleanliness of all components including constant level tank, agitation vessels, screen plates and sample cups. Use brush and water jet to clean them if dirty, check all surfaces, vessels and screens for dried fibres.
4) Install the screens to the slots and hold them in position with the PE tubes. The screen side faces the agitator and the slotted plate side faces the overflow outlet (see figure 29). Plug drain holes and install sample cups with cloth secured by rubber O-rings.
Figure 29: The screen plate is installed by facing the screen towards agitator.
5) After all the screen plates are installed, turn on the compressed air to secure them. Fill up the vessels with 10 liters per minute flow rate. The flow rate is verified by using a graduated bucket and timer (see figure 30). Place the hose and lid back on the Constant Level Tank and increase the flow rate gradually until a slight overflow from its side.
Figure 30: One the left, valves for compressed air and water; on the right, verifying the flow rate with a graduated bucket.
6) When the last vessel (200 mesh) starts overflowing, turn on the power and check again to make sure the screen plates are firmly held and there is no leaking. Pour in pulp suspension carefully to the center of first vessel (14 mesh) and start a timer. Shut the water and power off exactly at twenty minutes. Unplug the holes when the overflowing stops and shower the vessels and screens thoroughly to wash out all of the fibers (see figure 31).
Figure 31: Collection of fibers. One the left, shower the screen to wash fibers off; in the middle, shower the vessel to wash out all of the fibers to sample cups; on the right, collecting fibers into sample cups.
7) When there is no more dripping, unscrew the sample cups, and carefully transport them to the sink in a bucket. Transfer the fibers using a beaker, or directly on to labeled and tared filter papers in Buchner funnel. Remove water using vacuum flask. Dry them in the speed dryer. This procedure is similar to the consistency determination (see figure 32). Note: If the 100 and 200 mesh sample cups drain too slowly at the very end, you can unscrew them carefully and use a vacuum flask to accelerate the water removal.
Figure 32: Procedure for fiber collection and drying. On the left, water removal is accelerated by using vacuum flask; in the middle, wash fibers to tared filter paper in funnel; on the right, dry the pulp pads in speed dryer.
8) Check the dried pads until constant weight is reached, the result is expressed by percentage. For example, the total dry weight of 14 mesh is 2.223 g and the filter paper is 1.245 g, the fiber fraction of 14 mesh is (2.223 g – 1.245g)/10 g*100%= 9.78%.
9) Place all of the screens and sample cups in and under the vessels and fill them up with water. Shut off compressed air and unplug the power. Scrape spilled water off of floor and place the yellow wet floor safety sign by the Bauer McNett to warn other lab users about the wet floor.
