2.11. Soil Burial Biodegradability Test

The soil biodegradation study was performed in laboratory scale following a method described by [30] with some modifications. The paper samples were cut in specimens with the size of 2.5 cm × 2.5 cm and dried in a hot air oven at 50 °C until a constant weight. Three replicates for each sample were buried into a commercial soil at 4–6 cm depth in a plastic box and left at 58 °C for 56 days. The distilled water was added at a certain level into the soil every 2–3 days to ensure the sufficient moisture during the test. The samples were removed from the soil for every 7 days, brushed softly, washed several times with distilled water and then dried at 50 °C until a constant weight. The degree of degradation of paper samples were calculated by normalizing the paper sample weight at different days of incubation respect to the initial value by using following Equation (6):

where m_i = the initial weight of the dry sample; m_r = the weight of the dry sample after the test.