| Cotton stalk is a common agricultural waste.At present,China produces about 10million tons of cotton stalks per year.Considering the traditional way of cotton stalks processing,it can not adapt to social development.Therefore,it is of great significance to study the high value application of cotton stalk resources.In this paper,preparation of microcrystalline cellulose,its pharmaceutical tablet compressing and PCL material strengthening performance were discussed.It would provide a theoretical basis for the application of cotton stalk-based microcrystalline cellulose.In order to further deepen the understanding of cotton stalk cellulose,cotton stalk-based nanocellulose was prepared,which provided a theoretical basis for the deep utilization of cotton stalk-based nanocellulose.?1?In order to investigate whether cotton stalk can be used as a raw material to prepare microcrystalline cellulose,the structure and main components of cotton stalks were analyzed.The content of?-cellulose,acid insoluble lignin,ash content and hemicellulose were 50.0%,22.2%,5.7%,and 20.2%,respectively.The crystallinity of the cotton stalk raw material powder was 35%.The cotton stalk had a high cellulose content and could be used as a raw material for preparing microcrystalline cellulose.The calcium content accounted for 25.3%of the ash,which required pretreatment to remove most of the ash.Cotton stalk has a high cellulose content and can be used as a raw material for preparing microcrystalline cellulose.However,cotton stalk has a high ash content,in which the calcium content accounts for25.3%of the ash content,and most of the ash content needs to be pretreated.Combined with the cotton stalk's structure and chemical composition,a pretreatment method based on acetic acid-ethanol method was established in this paper.Combined with pulping,bleaching and acid hydrolysis,cotton stalk-based microcrystalline cellulose was prepared.The optimal reaction conditions for acetic acid-ethanol pretreatment were:temperature 100?,cotton stalk:acetic acid:ethanol?w:v:v?was 1:1:1,and the solid-liquid ratio was 1:10.The yield of the obtained cotton stalk was 87.0%,the ash content was reduced to 1.10%,and the removal rate reached 80.7%.?2?The optimum reaction conditions for the preparation of pharmaceutical grade microcrystalline cellulose from cotton stalks?1.5mol/L HCl,90°C,60min,solid-liquid ratio1:10?were discussed.It was found that with the increase of hydrolysis degree,the particle size D90 of microcrystalline cellulose decreased as well as the yield,and the parameter D90indicated the degree of hydrolysis of cellulose well,which was more convenient to characterize the hydrolysis process in reaction time.The cotton stalk-based microcrystalline cellulose crystal form belongs to the typical natural cellulose type I,and the crystallinity is80.3%.The drying temperature has an important influence on the morphology of microcrystalline cellulose.The appropriate drying temperature?105-120??should be controlled to prevent the microcrystalline cellulose from being damaged by excessive temperature.Moreover,the microcrystalline cellulose prepared by cotton stalk has good thermal stability and can be applied to medicines,foods and other biocomposites.?3?Cotton stalk nanocellulose was prepared by acid hydrolysis,and the physicochemical properties of cotton stalk nanocellulose were studied.During the hydrolysis reaction,the acid ions cut off the cellulose chain in the amorphous region,especially in 002 crystal plane.As the degree of acid hydrolysis deepened,the main chain of the cotton stalk-based nanocellulose would be destroyed.Acid hydrolysis mainly acted on intramolecular hydrogen bonds of cellulose macromolecules,especially on O?3?H...O?5?bonds.The crystal model was analyzed and obtained by XRD.The research on nanocellulose crystal model could provide theoretical basis for the structure performance relationship of nanocellulose materials and the future modification of nanocellulose.?4?In this paper,the differences of basic physicochemical properties of microcrystalline cellulose caused by different cellulose sources on the micro-scale and the differences of mechanical properties of tablets caused by different cellulose sources were discussed.Aspirin tablets were prepared by direct compression of microcrystalline cellulose.The mechanical properties of the tablets were tested by tensile compression material tester.With the increase of microcrystalline cellulose particle size?D50=30-100?m?,the hardness of tablets compressed by softwood,hardwood and cotton stalks showed a downward trend,and the hardness of bamboo and hemp tablets remained basically unchanged.The results indicated that the mechanical properties of the hardness and tensile strength of the microcrystalline cellulose sample tablet strongly depended on the difficulty of hydrolysis?t value?.According to the SPSS analysis,the t value of the hydrolysis of the raw material was positively correlated with the hardness and degree of polymerization of the microcrystalline cellulose tablet.The mechanical properties of microcrystalline cellulose sample tablets hardness and tensile strength were strongly dependent on the cellulose source.The mechanical properties of cotton stalk microcrystalline cellulose were better than that of bamboo and hemp microcrystalline cellulose.The order of mechanical properties was similar to the t-value.The order was:softwood>hardwood>cotton stalk>bamboo>hemp.When selecting microcrystalline cellulose,the source of cellulose should be fully considered.The results of this study could provide a reference for the selection of microcrystalline cellulose.?5?Microcrystalline cellulose could be used as an additive.When cotton stalk-based microcrystalline cellulose was added as an additive to PCL.A strong interface was formed between them.This interface was derived from the formation of hydrogen bonds and enhanced the mechanical properties of the PCL matrix.At the same time,the particle size of the cotton stalk-based microcrystalline cellulose also affected the mechanical properties of the PCL.Microcrystalline cellulose had a heterogeneous nucleation effect on PCL,and the addition of microcrystalline cellulose did not change the melt thermodynamic properties of PCL,but could increase the melting temperature of PCL.?6?Although cotton stalk-based microcrystalline cellulose could enhance the mechanical properties of PCL,the interfacial compatibility was poor.The compatibility of PCL with microcrystalline cellulose was improved by MA modified PCL.When the m?MA?/m?PCL?was40%,m?benzoyl peroxide:BPO?/m?PCL?was 7%,reacting duration was 3h,the contact angle was the highest up to 87.5°,which improved the hydrophobicity.And the roughness decreased by66.7%.The increase of tensile stress was 77.8%.The interaction of PCL-MA and microcrystalline cellulose through hydrogen bonding could form a relatively strong network.In addition,the polymer of PCL and MA underwent heterogeneous nucleation,and the addition of microcrystalline cellulose solid particles exacerbated heterogeneous nucleation.Due to the effect of double heterogeneous nucleation,the mechanical properties of PCL-MA blended microcrystalline cellulose film were improved. |
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