Degumming,Modification And Characterization Of Banana Pseudo-stem Fiber

As a natural cellulosic fiber,banana pesudo-stem fiber has the advantage of bast-fiber and can be used as a raw material for textile and chemical industry.However,a thousand million tons of banana pesudo-stems was treated as a waste in China,which results in a huge land pollution of banana plantation and microbe or insect outbreaks.The problem is that the traditional degumming methods for bast-fiber is not suitable to banana pesudo-stem fiber.Therefore,it is very important to develop a pollution-free degumming technology and value-added modification for the pesudo-stem fiber from the main banana variety（Musa AAA Cavendish cv’Baxijiao）cultivated in China.Therefore,this study was to develop different degumming technologies including chemical degumming,bio-degumming and steam explosion degumming.The chemical compositions,structures and properties of the fiber during the degumming processes were investigated.Furthermore,the bio-sorbent and cellulose-based film were made from the degummed fiber after dissolution and modification treatment.The absorption mechanism and reaction characteristic of bio-sorbent on heavy metal and oil were revealed.The biodegradability and preservation function for tropical fruits of the films were also evaluated.Our findings of this study were listed below:The degumming capability of alkali soaking pretreatment was better than the pretreatment by acid,water,or urea and oxygen.The amount of residual gum and lignin were mainly affected by the first boiling including the boiling time,Na₂SO₃,Na₅P₃O₁₀andNaOH concentrations.The optimal degumming condition for the first boiling was determined to be the following:14 g/L of NaOH,boiling time of 150 min,3%of Na₂SO₃ and 2.75%of Na₅P₃O₁₀.The optimal condition of the second was boiling time of 120 min,14 g/L of NaOH,and 8%of H₂O₂.Under these treatment conditions,the amount of residual gum and lignin were 8.85%and 4.68%,respectively.After the chemical degumming process,the cellulose content,thermal stability,crystallinity and finesse of the degummed fiber increased,while its contents of hemicellulose and lignin,and breaking strength decreased.The results indicated that the amorphous area of the fiber was broken down after the chemical degumming.The capability of Streptomyces lydicus in hydrolyzing pectin and hemicelluloses was observed though the clear colonies on the pectin-agar and hemicelluloses-agar plates inoculated by Streptomyces lydicus strain.In this study,the fermentation conditions（temperature,pH,nitrogen source,carbon source and inoculums size）of Streptomyces lydicus for degumming the banana fiber were evaluated based on the content of residual gum and activity of pectinase.The results indicated that the optimal degumming medium for the strain was at pH 5.0,4g/L of NH₄NO₃,10 g of wheat bran and inoculums volume of 9 mL.After 72 h of the fermentation,the activity of pectinase was 75μg/（m L·min）,while the residual gum of banana fiber was 4.86%,and the yield of retted banana fiber was 59.48%（dry weight）.The structure and surface analysis of the degummed banana fiber showed a reduction in diameter and changes in surface morphology from that of the original fibers.The average diameter of the fibers was approximately 5-10μm,which was lower than that of the fiber bundles before the fermentation treatment.The size reduction was due to the dissolution of hemicelluloses and lignin which was confirmed by the chemical and fourier transform infrared spectroscopy analysis.The treated fiber had a higher percentage of cellulose and a lower percentage of hemicelluloses,lignin,pectin and wax compared with the untreated fibers.The physical property of the treated fibers showed an increase in fineness,and a decrease in breaking strength for the retted fibers,while the thermal stability of the treated fibers was improved.The X-ray diffraction pattern of retted fiber exhibited an increase of crystallinity.The results indicated that Streptomyces lydicus stain had a great potential in degumming of the banana fiber.A steam explosion degumming method was developed by combination of alkaline soaking pretreatment,steam explosion and bleaching process with a 16（4⁴）orthogonal array design.The optimal treatment conditions were 10%of banana fiber moisture,1.2%of NaOH,steam pressure of1.75 MPa,and residence time of 90 s.Under the optimized conditions,the yields of residual gum（5.47±0.22%）and lignin（3.78±0.12%）were close to their predicted yields.The treated fibers increased in cellulose content,thermal stability and crystallinity and decreased in lignin and hemicellulose contents.The results were further confirmed by the X-ray diffraction pattern and fourier transform infrared spectroscopy analysis.The treated fibers showed a change in their surface morphology compared with that of the original fibers.The steam explosion degumming enhanced thermal stability of the treated fibers.It indicated that the steam explosion could be a pollution-free degumming method compared with the chemical degumming and bio-degumming processes for the banana pesudo-stem fiber.The banana pseudo-stem fiber treated by the steam explosion（SEBF）and cellulose xanthogenate（SEBF-CX）methods enhanceed the capacity of absorbing heavy metal ions Pb²⁺and Cd²⁺.The results showed that the optimal adsorption condition of heavy metal was at 30℃,pH 6,equilibrium adsorption time of 60 min,and Pb²⁺and Cd²⁺concentration of 100 mg/L.Under these conditions,the absorbed amounts of Pb²⁺and Cd²⁺were 98.87 mg/g and 66.21 mg/g,respectively.Desorption of Pb²⁺and Cd²⁺by the SEBF-CX treatment with 20 m L 1 mol/L HCl（three times）resulted in 92.21%and 91.31%of recoveries,respectively.However,the SEBF-CX treatment exhibited higher absorption capacity at high concentration of Pb²⁺,while the treatment had higher adsorption capacity of removing Cd²⁺as well.The mechanism of adsorption Pb²⁺and Cd²⁺by the fiber treated with SEBF-CX was found to be complex and dominated by physical adsorption,accompanied with a minor ion exchange,chelation and intra-particle diffusion process.The adsorption kinetic was fit to the pseudo second-order.The increases of intensities of–C=S and-O-CS-S-groups were observed after the SEBF-CX treatment,while the cellulose crystallinity and thermal stability were increased based on the results of X-ray diffraction and thermal analysis.The surface morphologies of the SEBF and SEBF-CX treated fibers were in loose form and had more surface area.The SEBF treated fiber had higher adsorption capacity at Pb²⁺concentration below100 mg/L.In general,the SEBF-CX treated fiber could be used as an economical and efficient absorbent for removing heavy metal ion pollutes in water.Banana celluloses were acylated by a succinic anhydride in 1-allyl-3-methylimidazolium chloride ionic liquid and alkaline water system in order to produce oil sorbent with a high oil absorption capacity.The optimal reaction condition was the ratio of succinic anhydride and anhydroglucose at 6:1（M:M）and the reaction time and temperature 60 min and 90℃,respectively.The maximum degree of the acylation reaction reached to 0.37.The optimal reaction conditions for the alkaline water system（7%NaOH,7.5%thiourea,and 9%urea）were the ratio of succinic anhydride and anhydroglucose was at 8:1（M:M）and the reaction time 60 min and temperature90℃.The modified banana cellulose had larger surface area,lamellar holes and lower thermal stability than those of untreated banana cellulose.The crystal of the modified cellulose was decreased after the dissolution and regeneration.The results showed that the modified banana cellulose was efficient bio-sorbent for oil adsorption.The sorption of oil on IL-cellulose and AL-cellulose could be described as chemisorptions,because the sorption process followed the pseudo-second-order mechanism.It suggested that adsorption had different rates,which may involve intra particle diffusion and non-intra particle diffusion models.Therefore,both of IL-cellulose and AL-cellulose exhibited good oil sorption properties and re-usability.The water vapor transmission（1969.1±88.5 g/（m²·24h））and gas transmission（4280.7±608.3s/（in²·100cc·1.22KPa））of the banana-based film were higher than those of polythene film.The tensile strength and elongation of the banana-based film were 32.8±7.2 MPa and 4.0±0.5%,respectively.The film had smooth surface,low thermal stability and crystallinity than those of the untreated banana cellulose.The disease and yellow indices of the banana and mango coated by the cellulose-based film declined,while the fruit commodity rates of these fruits increased.The remain of the cellulose-based film was only 7.0%of the original weight after a 4-week of soil burial test.Therefore,the cellulose-based film displayed good bio-degradability.