Micro-nano Decolorized Spent Coffee Grounds/Polylactic Acid Composites And It's Application In 3D Printing

With the awareness of environmental protection and the concept of sustainable development in the hearts of the people,biomass resources have received great attention due to their reproducible and easily degradable characteristics.However,the biomass in many industrial productions was regarded as waste because it is not properly used,which caused a great burden for economic development and environmental protection.It is worth noting that as a product of the food industry,millions of tons spent coffee grounds were produced every year.However,spent coffee grounds were usually landfilled or burned on-site.The treatment causes a great waste of resources and serious environmental pollution problems.According to the report,spent coffee grounds contain a lot of substances beneficial to humans,such as cellulose,hemicellulose and caffeine,etc.The classification and utilization of these substances can not only reduce the impact on the environment,but also make spent coffee grounds as industrial raw materials to enhance it' s economic value.At present,many studies have focused on increasing valorization of spent coffee grounds and improving the utilization of spent coffee grounds,but it is still a challenge to use spent coffee grounds as a functional filler to enhance the performance of degradable polymers and application in 3D printing.Based on the highvalue utilization of spent coffee grounds,this thesis prepares 3D printed micro-nano decolorized spent coffee grounds/polylactic acid biomass composites with excellent color reduction and good processing performance through chemical-mechanical methods.And based on biomass composites,the interface compatibility between micro-nano decolorized spent coffee grounds and polylactic acid was studied,and the micro-nano decolorized spent coffee grounds/polylactic acid biomass composites with high filler addition and good mechanical properties was prepared.Firstly,in this thesis,alkali treatment and sodium chlorite bleaching were used to prepare decolorized spent coffee grounds,and then prepare decolorized spent coffee grounds with a micro-nano structure through mechanical processing.The whiteness index of the spent coffee grounds is 78.15 after being characterized by a whiteness analyzer.After bleaching,the whiteness index of spent coffee grounds was increased to 16.53,and the whiteness index was increased by 78.8%.The micro-nano processing is beneficial to further enhance the whiteness of decolorized spent coffee grounds and increase the whiteness index to 3.30.In addition,SEM analysis shows that the particle size of the original spent coffee grounds and decolorized spent coffee grounds is not much different and the size is ?700 ?m.However,compared with the original spent coffee grounds,the decolorized spent coffee grounds exposes a large number of pores after the non-cellulose components were removed.After mechanical treatment,the particle size of decolorized spent coffee grounds was reduced to about 2 ?m and is rich in micronano structures.Infrared analysis shows that after chemical treatment,non-fiber components in decolorized spent coffee grounds and micro-nano decolorized spent coffee grounds were effectively removed.In addition,thermogravimetric analysis shows that the micro-nano decolorized spent coffee grounds have better thermal stability than the original spent coffee grounds.In this thesis,micro-nano decolorized spent coffee grounds were used as functional fillers and polylactic acid were compounded to prepare 3D printing materials.With the addition of micro-nano decolorized spent coffee grounds,the polylactic acid matrix changes from transparent to slightly yellow.According to SEM analysis,the micro-nano decolorized spent coffee grounds can be uniformly dispersed in the polylactic acid matrix without agglomeration.Then through the mechanical performance characterization,with the addition of micro-nano decolorized spent coffee grounds,the tensile strength and bending strength of the composites decreased.However,the flexural modulus of the composite material has gradually increased.When 20 w/w% micro-nano decolorized spent coffee grounds were added,the flexural modulus of the composites has increased by 42%.According to thermogravimetric analysis,the initial degradation temperature of the composites gradually decreases as the content of micro-nano decolorized spent coffee grounds increases.Even with the addition of 20 w/w% micro-nano decolorized spent coffee grounds,the initial degradation temperature of the composites(255 °C)is still much higher than the 3D printing temperature(?200 °C).According to DSC analysis,the micro-nano decolorized spent coffee grounds have little effect on the glass transition temperature and melting temperature of the composites,but it reduces the cold crystallization temperature of the composites and increases it's crystallinity.This is because it acts as a nucleating agent in the composite material.Then,rheological analysis shows that the micronano decolorized spent coffee grounds reduces the viscosity of the composites and improves the fluidity of the composites.In addition,the CIELab analysis shows that compared with the original spent coffee grounds/PLA composites,the color difference of the micro-nano decolorized spent coffee grounds/PLA composites in red,yellow and blue is reduced by 69.26%,84.79% and 69.65%,respectively.The micro-nano decolorized spent coffee grounds/polylactic acid composites has excellent color reduction ability.In this thesis,3-aminopropyltriethoxysilane was used to modify the micro-nano decolorized spent coffee grounds.The surface contact angle analysis showed that the surface contact angle of the silane-modified micro-nano decolorized spent coffee grounds increased significantly,showing a more hydrophobic characteristic.In the 5 w/w% silane coupling agent modified micro-nano decolorized spent coffee grounds,when the addition amount of silanized micro-nano decolorized spent coffee grounds is 10 w/w%,compared with that of pure polylactic acid,the tensile strength and tensile modulus of the composites were increased by 18.26% and12.48% respectively.The surface silanized micro-nano decolorized spent coffee grounds can well enhance the interface effect of the composites.