| Popis: |
Paper is still regarded as the most common carrier of information. Encouraged by environmental policies, the papermaking technology recently changed, resulting in an increased production of recycled paper. Two types of contemporary paper, non-recycled and recycled, were thus investigated to evaluate possible differences in their rate of degradation. The analyses were carried out using unaged paper to evaluate acidity, dry matter and ash content, lignin presence, and fibre furnish. Accelerated ageing experiments were performed at different temperatures (from 50 to 80 °C) and water vapour pressures (from 90.5 to 227.5 torr). Viscometric measurements were carried out to evaluate the extent of paper degradation as a function of time, upon various accelerated ageing conditions. The results indicate that the rates of degradation follow second-order kinetics with respect to the degree of polymerization, as displayed in Figure 1. Although the kinetic constants for recycled and non-recycled paper are comparable within experimental limits, the degradation rates of recycled paper are systematically found to be slightly higher than those of non-recycled paper. As shown in Figure 2, the kinetic constants were not found to increase monotonically with increasing water vapour pressure. The Arrhenius dependence of the kinetic constants on temperature for both kinds of paper supplied the activation energies, which fall in the typical range (100-140 kJ mol-1) expected for paper degradation. Finally, the measured kinetic constants fit fairly well the recently modelled dose-response function for historic paper. Colour changes were found to be visible to the human eye for samples aged for more than 40 days at 60, 70 and 80 °C, the recycled paper showing smaller colour variations than the non-recycled paper. |
