155
edits
Difference between revisions of "Pulping and fractionation"
Jump to navigation
Jump to search
m
→Groundwood
(combined groundwood versions) |
m (→Groundwood) |
||
| Line 28: | Line 28: | ||
===Mechanical pulping=== | ===Mechanical pulping=== | ||
Mechanical pulping is inexpensive and results in the highest yields. However, mechanical pulp also results in paper with a large number of imperfections. Technological advances are improving the quality of mechanical pulps, while maintaining the low cost and high yields.<ref name=":0" /> | Mechanical pulping is inexpensive and results in the highest yields. However, mechanical pulp also results in paper with a large number of imperfections. Technological advances are improving the quality of mechanical pulps, while maintaining the low cost and high yields.<ref name=":0" /> | ||
====Groundwood==== | |||
Stone groundwood pulping is the oldest mechanical pulping method, where the biomass is pressed against a rotating grindstone. The grindstone breaks apart the biomass into thin fibres and fragments, which are washed away with a water stream. The friction results in an increased temperature, which helps the process. The product stream is scanned to remove the larger particles, then the water is removed to thicken the pulp. The process has high yields (about 95%), because most lignin remains in the product. Next to stone groundwood, there are also '''pressure groundwood''', where additional pressure is applied and '''thermal groundwood''', which sues elevated temperatures.<ref name=":1" /> | |||
====Refiner==== | ====Refiner==== | ||
=====Refiner mechanical pulping (RMP)===== | =====Refiner mechanical pulping (RMP)===== | ||
| Line 33: | Line 35: | ||
=====Thermomechanical pulping (TMP)===== | =====Thermomechanical pulping (TMP)===== | ||
In this refiner process the biomass is preheated by impregnation of steam under pressure. The high temperature (115-155 °C) softens the lignin and helps in fibre separation. The refining takes place in two steps, the first at elevated pressure and temperature, around the glass transition temperature of lignin (140 °C), the second at atmospheric pressure and temperature. The resulting yields are high (>93%) and the pulp is characterised by its high strength.<ref name=":1" /> | In this refiner process the biomass is preheated by impregnation of steam under pressure. The high temperature (115-155 °C) softens the lignin and helps in fibre separation. The refining takes place in two steps, the first at elevated pressure and temperature, around the glass transition temperature of lignin (140 °C), the second at atmospheric pressure and temperature. The resulting yields are high (>93%) and the pulp is characterised by its high strength.<ref name=":1" /> | ||
===Biological pulping=== | ===Biological pulping=== | ||
Biological pulping takes advantage of natural methods to break down fibrous materials. For example, white-rot fungi can be used to soften and remove lignin.<ref name=":1" /> | Biological pulping takes advantage of natural methods to break down fibrous materials. For example, white-rot fungi can be used to soften and remove lignin.<ref name=":1" /> | ||