Photodegradation of sugar cane bagasse acidolysis lignins

Acidolysis lignins of unbleached (SCB) and peroxide bleached (PB-SCB) sugar cane bagasse fibers were submitted to UV irradiation to approach photodegradation of materials made from these fibers. Similar degradation was observed by UV-vis absorption on dilute solution (0.04 g mL−1) of lignins after irradiation at 254 nm (low pressure mercury lamp) or at wavelengths higher than 300 nm (medium pressure mercury lamp filtered by Pyrex glassware). Irradiation of PB-SCB and SCB lignins reveals that the bleaching process increases the sensibility of lignin to light, as revealed by fluorescence emission and UV-vis absorption. In other hand, efficient fragmentation of these two lignins was observed by size exclusion chromatography. 1H and 31P RMN spectroscopic analyses before and after irradiation were performed to observe the behavior of phenolic units in the lignin samples. They show an important decrease of the syringyl, guaiacyl and biphenyl phenolic elements, whereas p-hydroxyphenyl ones are less degraded. This point appears very important to promote the use of sugar cane bagasse fiber base materials when they have to be exposed to daylight.