Paper sheet treatment with polyvinyl alcohol

Wood pulp paper sheets were dipped in polyvinyl alcohol (PVA) of different grades [i.e., degree of hydrolysis and molecular weight; e.g., Vinarol(R) (DV) and Mowiol(R) (4-80, 40-88)] and different chain lengths, as well as at different concentrations (1-5%) for different time intervals (10-60 sec). The retained polymer (grams per square meter of paper sheet) on the paper sheets was highly affected by the chain length, degree of hydrolysis, polymer concentration, and dipping time. The effect of Schoper regular (degrees SR) of the dipped paper sheets on the retained polymer was studied. Mechanical properties of treated sheets were increased by increasing polymer concentration and dipping time. The effect of thermal treatment of treated sheets at different temperatures (100-120 degrees C) for half an hour was studied. Also, the effect of thermal treatment at 100 degrees C for different time intervals (0.5-2 h) was clarified. Generally, the mechanical properties of treated paper sheets were highly affected by thermal treatment. It was seen that the mechanical properties were increased by increasing temperature up to 100 degrees C, and then decreased with increasing temperature. Also, the mechanical properties of thermally treated sheets at 100 degrees C increased with increasing heating time to half an hour, and then decreased with increasing time. On the other hand, the percent of improvement of dipped paper sheets of low degrees SR in polymer solution was higher than of high degrees SR dipped paper sheets.