A recent development in mechanical pulping in which wood chips are sandwiched between the two revolving disks of a disk refiner in the presence of water and at atmospheric pressure. Heat due to friction softens the lignin and allows greater separation of the cellulose fibers, while contributing less fiber damage. Refiner mechanical pulp has greater strength than traditional groundwood, which reduces the need to supplement it with chemical pulps. RMP also is able to utilize more tree species, as well as various types of scrapwood and waste chips. Most RMP pulpmills, however, have been supplanted by even newer pulping techniques.
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