(1) Book papers, when exposed to sunlight, are suffered from a loss in tensile strength, elongation and folding endurance, but minor loss in bursting strength.
(2) Retention of tensile strength and folding endurance in machine direction are less than that in acrose machine direction, but retention of elongation in machine direction is greater than that in across machine direction.
(3) When book papers are exposed to sunlight, the sizing quality is seriously injured and the luminocity decreases. Alpha-cellulose content, copper number and acidity reflect chemical changes that are to be expected.
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