| Cellulolytic enzyme lignin(CEL)is main ingredient of bio-ethanol production residue,which is generated during the production of bio-ethanol via fermentation process of corn stalks.Compared with the Kraft lignin and alkali lignin,it was obtained without high temperature and high pressure conditions,so it excellently reserves chemical structures and reactivity of phenolic hydroxyl and alocholic hydroxtyl group.Lignin has been shown to have great potentials for a wide range of applications,such as phenol-formaldehyde resin(PF),epoxy resin,polyurethane and so on.To some extent,the effective utilization of CEL can reduce the cost of bioethanol industry,also make great contributions to environmental protection.Currently,due to the bigger molecular weight and the lower reactivity,CEL did not widely apply to industrialization.The purpose of the research is to improve reaction activity of CEL,better and more fully utilize it.In this study,we have explored effect of various ultrasound treatment conditions on CEL structure and reactivity.The key structural modifications were characterized by using a combination of analytical methods,including Fourier Transform-Infrared spectroscopy(FTIR),Proton Nuclear Magnetic Resonance(~1H NMR),Gel permeation chromatography(GPC),X-ray photoelectron spectroscopy(XPS),and Folin-Ciocalteu(F-C)method.Chemical reactivity of the modified CEL samples was determined by both DPPH free radical scavenging activity and their reactivity towards formaldehyde.It was observed that the modified CEL had a higher phenolic hydroxyl group content,a lower molecular weight,a higher reactivity towards formaldehyde,and a greater antioxidant property.The higher reactivity demonstrated by the samples after treatment suggesting that ultrasound is a promising method for modifying enzymatic hydrolysis lignin for value-added applications.To promote the reactivity of the lignin isolated by the CEL,water-alcohol(1:1,v/v)was also introduced as co-solvent in the process of the hydrothermal treatment.The degradation conditions including reaction temperature and time,solid-to-liquid ratio,and catalysts(NaOH and NaOAlO2)has been investigated in terms of the specific lignin properties,such as the phenolic hydroxyl content(OHphen),DPPH free radical scavenging activity,and reactivity towards formaldehyde.The CELs were also characterized by GPC,FT-IR and ~1H NMR spectroscopy,and pyrolysis-gas chromatography-mass spectrometry(Py-GC/MS).The key data are under optimal lignin degradation conditions(solid-to-liquid ratio of 1:10(w/v)and a temperature of 250°C for 60 min)are:OHphen content:2.5 mmol/g;IC50 towards DPPH free radicals:0.09 mg/mL;reactivity towards formaldehyde:0.45 g/g.Both base catalysts decrease the residue rate,but phenol reactivities of the products were also detracted.Py-GC/MS analysis revealed that degraded lignin shows a higher phenolic composition than the CEL,especially the degraded lignin without catalyst(DL)represented 74.51%phenolic content.The 50%lignin-phenol-formaldehyde resin(50%L-PF)was synthesized with 50%phenol substituted with degraded lignin via ultrasonic or hydrothermal treatment method.Properties of50%L-PF resins,including solid content,viscosity,free phenol content,brominable substance content and bonding strength,all meet the standard requirements(GB/T14732-2006).FT-IR analysis shows that the chemical structure of 50%L-PF is similar to that of PF,so the introduced lignin didn't change the basic structure of PF resin.TG analysis suggests that the thermal stability of PF is apparently influenced duo to addition of lignin.The DSC curves imply that suitable lignin could accelerate curing process of PF resin. |
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