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USE OF KAPOK PULP TO IMPROVE PROPERTIES OF RECYCLED PAPER 242 The Journal of the Royal Institute of Thailand Vol. 37 No. 1 Jan.-Mar. 2012 As shown in Figure 1, the handsheets made from 100% recycled paper were the brightest and their brightness values were very close to those made from 100% softwood pulp (84.31% brightness) while those made from 100% kapok pulp had the lowest brightness (19.15% brightness). Also, the effect of recycling on brightness was so small as compared to the effects of pulp types. Clearly, the effect of kapok pulp on brightness is more pronounced than softwood pulp. Brightness was decreased more by adding kapok pulp as compared to those of the softwood pulp at the same ratio. This might be because kapok fibers are so yellowish. So, adding a higher amount of kapok can lead to lower brightness eventually. Whiteness Opacity Opacity of handsheets made from 100% recycled pulp was highest and it was higher than those made from kapok and softwood pulps which were 69.19% and 82.05%, respectively (Figure 3). The effect of numbers of recycling on opacity was small as compared to the effects of pulp type and percentage. Unlikely, increasing amount of kapok pulp in the pulp mixture provided the Figure 2 The Effects of Recycling Cycles, Kapok Pulp and Softwood (SW) Pulp on Whiteness (Note: Kapok and SW pulps have whiteness values of 72.62% and 83.44%, respectively) Figure 2 illustrates the effects of recycling, kapok pulp and softwood pulp on whiteness. It was apparent that the results obtained from whiteness followed the same trend as in the case of brightness with the same explanation.