A MICROWAVE-INDUCED ACOUSTIC TECHNIQUE FOR THE MONITORING OF RELATIVEPAPER ACIDITY - THE PROTECTIVE EFFECT OF LIGNIN

A microwave-induced acoustic (MIA) technique is described, which can b e used to follow changes in the relative acidity of papers during the aging processes. Rapid aging is simulated by exposure of paper samples to atmospheres containing gaseous NOx and HCI. The MIA results correl ate well with tensile strength measurements and are consistent with in creasing acidity causing decreased fibre strength due to acid hydrolys is. The presence of some lignin content in papers appears to slow at l east the initial detrimental effects caused by NOx exposure. The MIA t echnique is non-destructive and can be adapted to on-line measurements .