Preparation And Properties Of Porous Lignin Based Polyacrylic Acid Composite

This research is part of the Chinese"Twelfth Five Year"National Science and Technology Plan Project in Rural Areas?2012BAD24B0403?,the State Forestry Bureau of Forestry Public Welfare Industry of Science and Technology Projects?201304614?and the Youth Science Foundation of Heilongjiang Province of China?QC2014C011?.Several lignin-g-polyacrylic acid hydrogels?ab.lignin-g-PAA?were prepared by changing lignin origin of alkali lignin,lignin from furfural residue,acid hydrolyzed alkali lignin,or altering the crosslinking degree of polyacrylic acid network.Lignin-g-polyacrylic acid hydrogels included that alkali lignin-g-polyacrylic acid hydrogel?AL-g-PAA?,lignin from furfural residue-g-polyacrylic acid hydrogel?FRL-g-PAA?and acid hydrolyzed alkali lignin-g-polyacrylic acid hydrogel?AHL-g-PAA?.Water absorbency,release behavior of pesticide?beta-cyfluthrin,paraquat and cyhalofop-butyl?and adsorption behavior of heavy metal ions(Pb²⁺,Cu²⁺and Cd²⁺)were researched for making their application and prospects clear.The main results are summarized as follows:?1?Grafting reaction of the phenolic hydroxyl of lignin and polyacrylic acid prepolymer was initiated by composite initiator of FeSO₄/H₂O₂,and formed porous lignin-g-PAA by principle of phase separation.The results showed that the rate of water absorption and water release on lignin-g-PAA hydrogels were significantly higher than PAA,Maximum water absorbency of AL-g-PAA,FRL-g-PAA and AHL-g-PAA were 465.741 g/g,411.257 g/g and392.814 g/g,respectively.After naturally dried 80 hours,water release rates of AL-g-PAA,FRL-g-PAA and AHL-g-PAA are more than 92%,those had a distinct difference on pH value,temperature sensitivity and salt tolerance.?2?To extend application of lignin in agriculture,the above lignin-g-PAA hydrogels contained many hydrophilic groups to help expansion performance.The cumulative release rate of pesticides about beta-cyfluthrin,paraquat and cyhalofop-butyl were research to clarify pesticide release behavior of lignin-g-PAA hydrogels.The results showed that the release time of lignin-g-PAA hydrogels for pesticides are all arrived at 90 h;the release kinetic curves of 3pesticides were all followed Ritger-Peppas model that of release mechanism is synergistic effect on matrix corrosion and Fick diffusion.?3?In order to increasing the added application value of lignin,the above lignin-g-PAA hydrogels had many functional groups of hydroxyl and carboxyl groups to removing heavy metal ions.The results showed that the optimum pH value of lignin-g-PAA hydrogels for adsorption heavy metal ions are 5.It is benefit for rapid and efficient adsorption of Pb²⁺,Cu²⁺,Cd²⁺by lignin-g-PAA hydrogels that decreasing temperature.Those kinetic adsorption data were obeyed the pseudo-second order model.The adsorption isotherms of lignin-g-PAA hydrogels for removing heavy metal ions were followed the Freundlich model,which adsorption mechanisms for Pb²⁺,Cu²⁺and Cd²⁺are a spontaneous exothermic reaction with synergistic effect of the characteristics of physical adsorption and chemical adsorption.Those XPS spectra show that there is chemical complexation between ions and the hydroxyl and carboxyl groups of lignin-g-PAA hydrogels in the proceed of Pb²⁺,Cu²⁺and Cd²⁺adsorption.The adsorption capacity order of lignin-g-PAA hydrogels was Q_FRL-g-PAA>Q_AL-g-PAA>Q_AHL-g-PAA>Q_PAA.AL-g-PAA hydrogel has the best performance of water absorption,pesticide slow-release and heavy metal ion adsorption among the above lignin-g-PAA hydrogels.?4?Highly crosslinked alkaline lignin-g-polyacrylic acid was prepared by adding the amount of crosslinker and reducing polymerization time of polyacrylic acid prepolymer.The performance of water absorption,adsorption Pb²⁺ion and releasing of cyhalofop-butyl were carried out to explore the relationship of polyacrylic acid prepolymer structure with that properties of highly crosslinked AL-g-PAA.The results showed that the water absorption capacity of highly crosslinked AL-g-PAA has excellently rapid swelling absorption ability,which water absorption capacity was 175.421 g/g that was lower than AL-g-PAA?465.741 g/g?,but its swelling degree was 98%at 1h.In agreement with lignin-g-PAA hydrogels,the release kinetic curves of highly crosslinked AL-g-PAA was all followed Ritger-Peppas model that of release mechanism is synergistic effect on matrix corrosion and Fick diffusion.The adsorption isotherms of highly crosslinked AL-g-PAA hydrogels for removing Pb²⁺ion were followed the Freundlich model,the kinetic adsorption data were obeyed the pseudo-second order model,which adsorption mechanisms for Pb²⁺ion is a spontaneous exothermic reaction with synergistic effect of the characteristics of physical adsorption and chemical adsorption.Those XPS spectra of highly crosslinked AL-g-PAA showed that there is chemical complexation between ions and the hydroxyl and carboxyl groups of lignin-g-PAA hydrogels in the proceed of Pb²⁺ion adsorption.