Study On The Structure And Performance Characterization Of Modified Eggshell Powder/PBAT Based Composites

At present,the environmental protection situation is becoming more and more serious,the problem of"white pollution"caused by petroleum based plastics has been paid more and more attention,and the development of high-quality biodegradable plastics has gradually become a new trend of the development of plastic industry.Polyadipic acid/butylene terephthalate（PBAT）is a biodegradable plastic with great potential for development.Due to its good ductility and heat resistance,PBAT has become one of the most widely used biodegradable materials in the research and market of biodegradable plastics.However,the large-scale industrial production of PBAT based materials is limited by high cost,high crystallisation,and poor mechanical properties such as rigidity and tensile strength.Therefore,adding inorganic fillers is an effective method to improve the performance of PBAT based composites and solve the high production cost of biodegradable plastics.Eggshell is a renewable resource with low price,excellent mechanical properties and abundant raw materials.It is an idea to make effective use of waste by-products and reduce industrial costs by grinding the waste eggshell into powder as filler and blending it with polymer to prepare composite materials.The main component of eggshell is Ca CO₃ and the content is as high as 93%,which leads to strong overall hydrophilicity of eggshell powder and poor compatibility when directly blended with polymer,thus affecting product quality.The material prepared by using aluminate coupling agent to surface modify eggshell powder and then blend with PBAT has better system stability and dispersion.In this study,eggshell powder was used as the basic raw material to optimize the preparation process of aluminate modified eggshell powder,and the changes of the structure and properties of the modified eggshell powder were studied.The hot pressing process of eggshell powder/PBAT composite was optimized based on response surface optimization method,and the effect of the addition of modified eggshell powder on the improvement of material properties and structure was studied under the optimal process conditions.The effects of nano-TiO₂ on mechanical properties and structure of eggshell powder/PBAT composites were investigated,and the antibacterial properties of nano-composites were characterized by antibacterial zone experiments.To explore the influence of nano-TiO₂ on the weatherability of eggshell powder/PBAT composite,and lay a theoretical foundation for the industrial development and application of new biodegradable materials.The main research contents and results of this paper are as follows:1.The preparation process of the modified eggshell powder modified by aluminate was optimized,and the structure and properties of the modified eggshell powder were investigated.The experimental results show that the modification effect is the best when the modification conditions are set as the modification time of 40 min,the addition amount of aluminate of2.75%,and the modification temperature of 90℃.Under the above optimal modification conditions,the polarity value of eggshell powder decreased by 91.90%,the surface tension decreased by 50.04 m J/m^-1 compared with the unmodified eggshell powder,and the eggshell pink after hydrophobic modification The hydroxyl absorption peak intensity of the external spectrum was significantly reduced,both of which indicated that the hydrophobicity of eggshell powder was enhanced after aluminate treatment.XRD showed that the aluminate coupling agent did not change the internal crystal form of the eggshell powder,that was,hydrophobic modification of the eggshell powder would not affect the crystalline properties of the particles.2.The optimal preparation process of eggshell powder/PBAT composite was explored based on response surface optimization method,and the influence of modified eggshell powder on material properties was studied.The experimental results showed that the conditions of eggshell powder/PBAT hot pressing process are set as hot pressing time 3.5min,hot pressing temperature 160℃,hot pressing pressure 20MPa,its performance was the best.In the performance test,it was confirmed that the addition of eggshell powder improved the tensile properties of the material.When the amount of eggshell powder was 15%-25%,the tensile strength and elongation at break were higher.The water absorption rate and water dissolution rate of the composite material increased first and then decreased with the increase of eggshell powder addition.The light transmittance of the composite material continued to decrease with the increase of eggshell powder content.The electron microscope photos of the material show that the internal structure of the system was the most compact and the surface was smoother when the eggshell powder content is 15-20%.Considering the influence of the above properties comprehensively,it was considered that the performance of the prepared composite packaging material was optimal when the addition amount of eggshell powder was 15%.3.The influence of nano-TiO₂ on the properties and structure of eggshell powder/PBAT composites was studied and analyzed by a variety of characterization methods.The results showed that the free-OH and unsaturated dangling bonds on the nano-TiO₂ surface could form hydrogen bonds and covalent bonds with PBAT,thereby improving the interfacial compatibility and structural stability inside the composite.In addition,the internal crystal structure of nano-TiO₂ significantly improved the crystalline properties of the polymer system.In terms of performance,this structural change resulted in composites with stronger tensile strength,lower water absorption,and higher thermal stability.With the increase of the amount of nano-TiO₂,the shading properties and surface hydrophobicity of the nanocomposites were also improved to some extent.The antibacterial test results showed that the nano-TiO₂ in the composite exhibited certain antibacterial activity against two bacteria（Escherichia coli and Staphylococcus aureus）.4.The change trend and mechanism of nano-TiO₂ in the aging process of composite materials were studied.The research showed that the initial tensile strength of the nano-TiO₂material is increased by 8.689MPa,and the change of the tensile strength retention rate of the material during the aging process was smaller.As the aging progresses,the transmittance of the composites increased continuously,and the contact angles of both types of samples decreased.The results of FITR showed that the intensity of the absorption peak at 1470 cm^-1 of the composite material increased continuously with the prolonging of aging time,which was manifested as the increase of crystallinity.The change in chromaticity during aging reflected the changes of various color groups in the material under photothermal conditions.Electron micrographs of different stages of aging under xenon lamp irradiation showed that a large number of voids and layered cracks appeared on the surface of the composite without nano-TiO₂ addition.Compared with the control group,the nanocomposite was added.There were very few spalling and cracking and hole gathering areas,and the surface of the material still showed a relatively flat structure.This study provides a new idea for the selection of inorganic fillers for PBAT matrix composites,and provides some references for the development of biodegradable plastics with various functions.