Preparation And Properties Of Nano-microcrystalline Cellulose/Aqueous Polyurethane Composites Based On Electrospinning Technology

Cellulose nanocrystals(CNC)is not only light-weighed,degradable and environmental-friendly,but also has some nano-characteristics,such as high strength,large specific surface area,small size effect.Therefore,it is often used as enhancer in various polymers.Although the dispersing medium of waterborne polyurethane(WPU)is water,which highlights the environmental advantages of the material,the mechanical properties of the material are sacrificed.After the CNC was modified by silane coupling agent,it can react with the waterborne polyurethane,so as to effectively solve the problem of poor compatibility of CNC,achieving the aim of improving the performance of waterborne polyurethane composite.CNC was prepared by the sulfuric acid hydrolysis method.Through the single factor experiment of sulfuric acid concentration,acid hydrolysis time and acid hydrolysis temperature,the yield of CNC was used as the evaluation index to optimize and analyze the acid hydrolysis process,so as to obtain the best conditions of acid hydrolysis.After grafting modification of the prepared CNC with silane coupling agent(called KH550),KH550-CNC was prepared and then analyzed by Fourier transform infrared(FTIR)spectra,X-ray diffraction(XRD)and thermogravimetric analysis(TGA)to obtain the optimal conditions.Waterborne polyurethane(WPU)was synthesized using isophorone diisocyanate(IPDI),polypropylene glycol(PPG)and 2,2-hydroxymethylpropionic acid as raw materials.Two kinds of KH550-CNC/WPU composite films were prepared by mechanical blending and in-situ polymerization.Various factors affecting properties of composites were discussed by means of characterization tests.Comparing with pure WPU films,KH550-CNC/WPU composite films which were made by two methods gained the enhancement in comprehensive properties.Meanwhile,the advantages of in-situ polymerization have been demonstrated in many performance tests.The section morphology of the composite film was observed by scanning electron microscopy.The results showed that KH550-CNC and WPU had better compatibility in the film prepared by in-situ polymerization than those prepared by mechanical blending.The analysis of mechanical properties revealed that the tensile strength and elongation at break of the composite film,which was prepared by in-situ polymerization,showed a significant rise with the increase of the content of KH550-CNC.When the addition amount of KH550-CNC was 5%,the tensile strength reached 15.645 MPa,the elongation at break was 418.15%,and the water resistance was greatly enhanced.Taking KH550-CNC/WPU/PVAL composite spinning solution as raw material,the KH550-CNC/WPU/PVAL composite nanofibers were prepared by electrospinning,and the optimal preparation scheme of the composite fibers was explored by orthogonal experiment.The morphology,chemical structure and thermal stability of the composite fiber membrane were characterized by SEM,FTIR and TG,and the porosity of the nanofiber film was tested by image algorithm.The results of orthogonal experiments indicated that the spinning effect was best when the spinning voltage was 19 kV,the curing distance was 15 cm and the pushing speed was 0.0003 mm/s.The addition of KH550-CNC had a positive effect on the thermal stability and porosity of the composite fiber.When the amount of kh550-cnc was 1%,the thermal stability and porosity of the composite fiber membrane obtained the optimal effect.Therefore,the composite material will have a potential value as a filter material in the future.