The Morphological Regulation Of Cellulose Nanofibers From Sunflower Pith And Their Liquid-crystal Self-assembly

The biomass form agriculture and forestry is known as economical,abundant and renewable bioresources.A numerous of researches were developed to efficiently use these biomasses.Herein,we employed the core pith of sunflowers as a starting material to isolate nanocellulose.In particular,the cellulose content in sunflower pith was up to 48 wt%.Thus,the utilization of these materials is promising for sustainable and environmental applications.In this study,sunflower pith was pretreated by thermochemical method and then purified into cellulose raw materials.The chemical components of the sunflower pith before and after pretreatment were established.Thereafter,cellulose nanofibers were isolated from the sunflower pith via acid hydrolysis and oxidation strategies.The as-resulted nanocellulose fibers with various diameters were then casting into films for further characterization.For example,the diameters and zeta-potentials of the obtained nanofibers were characterized by dynamic light scattering（DLS）,the morphologies of resultant cellulose fibers and thin films were investigated by scanning electron microscopy（SEM）and atomic force microscopy（AFM）.The chemical and crystalline structural of sunflower pith cellulose were investigated by Fourier transform infrared spectroscopy（FTIR）and X-ray diffraction（XRD）.Overall,the major results of this study were summarized as follows:1.In this article,sunflower pith cellulose was directly extracted by sodium hydroxide-sodium chlorite bleaching method（Na OH-Na Cl O₂）.The extraction conditions were presented as follows:solid-liquid ratio 1:25,benzenol:alcohol（2:1）,Treatment,7%sodium hydroxide alkali treatment（water bath temperature 90℃）,1.5%（w/v）sodium chlorite solution（p H=3～4）bleaching treatment（water bath temperature 80℃）,reaction time of 120 min.After the pretreatment,FTIR spectra indicated that the peaks of lignin and hemicellulose were significantly decreased,compared to that of the peaks in initial microcrystalline cellulose.The XRD patterns showed that the crystallinity of cellulose was increased after pretreatment,while the crystal sizes before and after pretreatment were in consistent.In addition,the SEM images showed a smoothly surface of cellulose with the lignin and hemicellulose were significantly removed.The TG curves indicated that the decomposition temperature of cellulose in sunflower pith was up to 350°C.2.The sunflower pith nanofibers were prepared by sulfuric acid hydrolysis and TEMPO oxidation.The resultant cellulose nanofibers presented differences in their morphologies and diameters.According to the AFM diagrams,the nanofibers obtained by sulfuric acid hydrolysis（NC-SPS/NC-PSPS）presented short rod-like shapes with a diameter of 2～8 nm.In comparison,the cellulose nanofibers obtained by TEMPO oxidation（NC-SPT/NC-PSPT）that presented linear shapes with a diameter of 1～9 nm.In additional,the Zeta potential of NC-SPS was-27.4 m V,which was higher than that of-23.9 m V in NC-PSPS.The results suggested that the NC-PSPT were more stable that NC-SPT in aqueous conditions.the Zeta potential of NC-PSPT was-18.2 m V,which was higher than that of-12.8 m V in NC-SPT.The results suggested that the NC-PSPT were more stable that NC-SPT in aqueous conditions.3.The hydrolysis conditions of sunflower pith via sulfuric acid were optimized in this section.The following method was applied in this section:the sunflower pith was hydrolysis by 64 wt%sulfuric acid for 40 min at 50°C.The solid-liquid ratio of this reaction was 1:40.A multi-layered structure was indicated by SEM obversion in the as-casted cellulose nanofiber membranes.Meanwhile,these nanofiber membranes showed a humidity-sensitivity to environmental waters that they could reversal to 180°within 1.2 S.4.The nanofibers were prepared by sulfuric acid hydrolysis combined with physical sonication approaches.The morphology and size distribution of the resultant nanofibers were regulated by sonication times.Meanwhile,the self-assembly of CNCs suspension and the structural color of as-casted cellulose films were investigated by a polarized microscopy.