The mechanism of bonding

Three factors are involved in cellulose bonding-available area, contact, and hydrogen bonding. Since the use of the electron microscope and the synthesis of cellulose, it has become clear that the primary form of cellulose is elementary fibrils with about 100 molecules cross-section and about 400 sq. m. area per g. Because of internal bonding only a small part of this area is available. Con- sideration of various possibilities indicates that exterior surface of fibers, which varies from 1.0 to 2.3 sq. m. per g. depending on the degree of beating, is the main source of usable area. Wet pressing, which is much more intense than average pressure applied, is first factor in securing contact and is much assisted by softening due to internal fibrillation by beating. More intimate contact is brought about by liquid internal tension on drying. Final bydro- gen bonding differs from crystallizing force in that there is no need for parallel orientation in the fibers to be bonded but does require close contact. Tension during drying will diminish the bonding between surfaces at right angles to the tension.