Study On Ultraviolet Blocking Performance And Mechanism Of Windmill Palm Fiber

People pay closer attention to utizliation of natural resources due to the lack of resources,while palm fiber(palm leaf sheath fiber),as a kind of natural fibers,and renewable resources,has been applied to elastic materials,composite materials and other fields owing to its huge production,excellent anti-corrosion and elasticity.Comprehensive research of properties is very important to make the most use of palm fiber and enhance its values.Palm fiber maintains well properties although exposed to sun and rain for a long time,and this may be related to its excellent anti-corrosion and better resistance to ultraviolet radiation.Besides,palm fiber is dark brown and has rough surfaces,lumen in the cross section and high lignin content.Thus,it is practicable to study the ultraviolet blocking performance of palm fiber.This work was carried out to explore the ultraviolet blocking performance based on palm fiber,and the relationship between the extracts and ultraviolet absorption performances through extracting melanin and lignin.The research aims at broadening application fields of this natural fiber,providing valuable references for ultilizing as anti-oxidant additives and ultraviolet absorbers,which is of great practical significance.In this study,artificial ultraviolet was used to irradiate palm fiber for different time lengths.After irradiation,SEM,FTIR,XRD and TG were used to explore the influence of ultraviolet on the fibers' macro-and micro-properties;And the mechanical properties were also studied to characterize the ultraviolet blocking performance of palm fiber;Based on this,the ultraviolet absorption properties were evaluated comparing that of bamboo fiber and ramie fibers;Lignin was also extracted from palm fibers and bamboo fibers,and their structures were characterized and compared to study the ultraviolet absorption mechanism,and reveal its contribution to ultraviolet blocking performances;Based on the pretty good ultraviolet absorption properties of melanin and lignin,the antioxidant activity of palm fiber extracts were investigated,and the contributions of ultraviolet blocking properties were also analized.The results show that:(1)After being irradiated by artificial ultraviolet,the morphology structures,aggregation structures,thermal stability and mechanical properties of palm fiber have little change.The FTIR results showed that the content of methylene group of palm fiber increased after irradiation,which illustrates the internal bonds,like the triple bonds were broken;The appearance of carbonyl characteristic peaks demonstrated that oxidation of palm fiber took place after irradiation.After being irradiated for 20 days,the crystallinity index of palm fiber increased slightly from 44.28% to 46.20%,which indicated the ultraviolet undermine the amorphous region.While the mechanical properties of palm fiber deduced to some extent with the increasing of irradiation time.After being irradiated for 60 days,its breaking strength,breaking elongation and Young's modulus lowered by 16.78%,19.15% and 15.25%,at the same time,the surface became rougher and the crystallinity index of palm fiber also reduced to 40.32%,which suggested the ultraviolet damaged the crystalline region to a certain extent.Based on comprehensive study,palm fiber exhibites excellent ultraviolet blocking performance and it is related to the rough surfaces and silica.(2)Palm fiber exhibits excellent ultraviolet blocking performance,which is related to its high content of lignin.Polar solvent(ethanol),non-polar solvents(hexane and acetone)and a dioxane solution(dioxane/water,9?1(v/v)),were able to extact the chemical components responsible for the ultraviolet absorption property,besides,the dioxane solution could extract lignin from palm fiber effectively.Compared with bamboo and ramie fibers,palm fiber displayed the greatest ultraviolet absorption property.The maximum absorption peaks of lignin are 288 nm(extracted from oalm fiber),288 nm(extracted from bamboo fiber)and 295 nm(extracted from ramie fiber).Likewise,among the lignin extracts of the three fibers,the palm fiber's lignin extracts still exhibit the strongest ultraviolet absorption property.The results showed that the higher the lignin content in the fiber is,the more excellent the fiber's ultraviolet absorption properties and ultraviolet blocking performances are.(3)The excellent ultraviolet blocking performance of palm fiber is largely attributed to the unique structure of its lignin.The alkali lignin of palm fiber exhibited superior ultraviolet absorption performance compared with bamboo fiber.And the excellent UV-blocking performance of palm fiber is mainly due to the existence of functional groups,including the phenolic OH,aliphatic OH,and the aromatic rings,especially the unique triple structure,and the results of 1H NMR.Compared with bamboo lignin extracts,the lignin extacted form palm fiber exhibithed higher N element content and the residual carbon reached 59% even at 810?.The higher protein percentage and the highly condensed aromatic structures also contribute to the superior UV-blocking performance of palm fiber.(4)The strong radical-scavenging activities of melanin and lignin extracted from palm fiber contribute to the ultraviolet blocking performance of palm fiber,thus it can defer and block the oxidation resulted from ultraviolet irradiation.The melanin of palm fiber also exhibited superior ultraviolet absorption performance because of the existence of aromatic and phenolic substances in melanin.The results also showed that the melanin exhibited strong radical-scavenging activity,and it increased as the concentration of melanin increase.The ·OH scavenging activity is especially higher(the IC50 is 224.444 ug/mL),followed by ·O2-and ·DPPH scavenging activity.Similarly,palm fiber lignin also displays strong radical-scavenging activity,and its ·DPPH and ·OH scavenging activity are higher than bamboo fiber lignins'.This research may provide the foundation for exploring the high-end utilization of palm fiber.