| Windmill palm tree is an ancient species which has been widely planted in Yunnan and Guizhou province in China,due to their resistance to salt,alkali,sand,easy to plant and the ability to absorb a variety of harmful gases.As a result,a large number of biomass fiber resources have been produced.However,because of the lack of research on the structure and properties of windmill palm fiber,the material can only be processed into low value-added products such as ropes,brushes,mats and so on.Most of these bio-resources even been discarded as garbage,in turn bring environmental pollution and waste.The preparation,structure and property research on the multiscale fiber can increase the value of windmill palm fiber product.It has important significance for the rational use of resources.This paper was focued on the study of windmill palm fiber.On the macro scale,the windmill palm fiber with different chemical composition and process fiber modified by the chemical combined enzyme treatment had been prepared.The windmill palm fiber/cotton yarn had been prepared by the process fiber.The application of windmill palm materials in textile field had been made.On the macroscopic scale,the single fiber extracted by the alkaline oxygen method,and hydrophobic fiber velvet extracted by acetylation modification had been prepare.Windmill palm fiber velvet/polyvinyl alcohol(PVA)nonwoven functional material with sound absorption properties had been made.On the micro scale acid or alkali hydrolsis methods had been used to study the fibril structure.Multiscale structural nano cellulose fiber had been prepared.All these provided new ideas for comprehensive development and utilization of windmill palm resource,as well as new resource for the textile engeneering.The main research methods and conclusions were as follows:(1)The windmill palm fiber directly extracted from the palm sheet was mainly composed of lignin,hemicellulose and cellulose.Windmill palm fiber had a cylindrical shape,and the longitudinal surface covered with scaly parenchyma cells.A large number of polygonal horns were linearly arrayed on the surface of the fiber.And the cross section was honeycomb with the hollowness about 47±10%.Sodium chlorite was used to multiple bleaching the windmill palm fiber to remove the lignin directly.And different concentrations of sodium hydroxide solution for stepwise extraction were used to directionally remove hemicellulose,in order to study of the effects of different chemical composition on fiber structure and mechanical properties.The results showed that the untreated windmill palm fiber had the highest elongation at break of 35.78±4.39%.After removing the hemicellulose,the cell wall of the fiber swelled,the lumen became smaller,and the fiber diameter decreased.The mechanical properties were significantly increased,and the breaking strength and Young’s modulus were 392.13±101.36 MPa and 7799.70 MPa,respectively.After alkali treatment,the lumen was reduced and the cell wall was thickened,which reduced the stress concentration on the cross section and promoted the improvement of mechanical properties.However,the mechanical properties of fiber after 30 days of soil burial were extremely poor,and the tensile strength droped to 50%.After removing lignin,the fiber cavity was obvious,the hollowness was increased to 50±9%,the storage modulus was the lowest of 4700 MPa,became the softest one.(2)The process fiber with a linear density of 4.52±0.82 tex and an initial modulus of 21.73±1.98 cN/dtex were prepared on a macro scale by chemical combined biological enzyme treatment.When the content of the palm process fiber and cotton was 30:70,24 metric yarns with fine quality had been prepareed and used for weaving.The response surface method was used to optimize the process conditions of the preparation of windmill palm single fiber by alkali-oxygen treatment.The correlation between the predicted value and the actual value was as high as 92.3%.Tensile mechanical properties of windmill palm single fibers less than 1 mm in length were achieved by adding resin microspheres at both ends of the palm monofilament.The tensile strength at break,Young’s modulus and elongation at break were 263±127 MPa,0.62±0.40 GPa and 25±10%,respectively.(3)The acetylation of windmill palm single fibers was modified with acetyl chloride and acetic anhydride,respectively.The hydrophilic hydroxyl groups on the cellulose surface were replaced with aqueous acetyl groups to improve the agglomeration of fibers.Hydrophobic fiber velvet with the static contact angle more than 150° and low moisture absorption were prepared.The destruction of the hydrogen bond of the cellulose macromolecular chain leaded to a large number of mesopores on the fiber surface.The meso-cavity of the mesoscale can retain a large amount of still air,so that the material had good thermal insulation properties.The nano-scale mesoporous network optimized the pore structure of the material,increased the path length of the sound wave,and improved the sound performance.The surface density on the acoustic property of hydrophobic acetylated fiber velvet/polyvinyl alcohol(PVA)nonwoven material was studied.When the concentration of PVA was 0.5%and the surface density was 0.140 g/cm2,the sound absorption coefficients for acetic anhydride modified fiber were 0.66.The error between Miki numerical models predict and test result when above 1000 Hz was less than 8%.Miki model can be used to simulate the sound absorption properties of palm materials and guided product development(4)Sulfuric acid and alkali hydrolysis combined with ultrasonic treatment were used to study the mutiscle fibril structure.By controlling the acid hydrolysis process conditions,the cell wall was longitudinally paralyzed to obtain giant fibrils(3.32±1.35μm),macrofibrils(622±165 nm),microfibrils(36±13 nm)and elementary fibrils(9±1nm).Alkali hydrolysis caused the spiral cleavage of windmill palm cell wall.The final products were elementary fibrils(7±1 nm)and microfibrils(33±19 nm).Microfibrils had the highest adhesion and were easy to self assemble into films.(5)Based on the microscopic morphology and morphological parameters of the windmill palm fibers at all levels,the microcrystalline structure model and hierarchical microstructure model of the fiber were established.The windmill palm nanocellulose prepared by acid and alkali hydrolysis consisted of 45 and 40 cellulose molecular chains respectively,and had a rectangular cross section of 7.51×3.95 nm and 8.25x4.05 nm.The elementary fibrils were closely packed into microfibrils with a circular cross section about 46 The plurality of microfibrils was composed of hemicellulose to form a spindle macrofibril.The plurality of macrofibril aggregated to make a giant fibril.And 7 giant fibrils were connected by lignin to form a complete fiber cell wall.Acid hydrolysis mainly removed lignin and longitudinally cleaved the cell wall.Alkali hydrolysis mainly removed hemicellulose that causing spiral hydrolysis of the cell wall. |
