Brightness is defined as the reflectance of a thick stack of paper
by a visible light having a mean wavelength of around 457 nm and
band widthof about 40 nm(blue light). TAPPI brightness also known
as directional brightness is measured by illuminating the product
with a fixed angle of 45◦ relative to the angle of observation
[5]. Measurements were performed following TAPPI std 452 om-
08 and shown in Fig. 7. The data show the average brightness of
each coating for different coating weights. The reflectance of blue
light by the PVA coated samples is the greatest resulting in higher
brightness values than base paper. DG gum and modified DG gum
samples exhibited brightness values similar to base paper, however
with higher coating weights a reduction in brightness values were
observed. This reduction can be attributed to the brown color of DG
gum due to the presence of residual lignin (