Preparation And Properties Of Plant Residue Based Modified Functional Materials

Polyhydroxyalkanoate(PHA)have great potential for applications in food packaging,textile and apparel,automotive manufacturing and other fields due to their good biocompatibility and completely biodegradable properties.Coffee grounds(CG),as a byproduct of coffee production,have a wide range of sources and is completely biodegradable.Adding coffee grounds to PHA to prepare fully biodegradable composites can reduce the cost of using,which is very promising.However,the poor interfacial compatibility between hydrophilic coffee grounds and hydrophobic PHAs affects the overall application performance of the composites.At the same time,the coffee grounds themselves contain a large amount of sugars and polyphenols,which provide favorable conditions for the growth and reproduction of bacteria and greatly reduce the service life of the composites.In this thesis,PHA/CG composites were prepared by melt blending with coffee grounds and PHA as raw materials.Firstly,the effects of particle size and content of coffee grounds on the properties of PHA/CG composites were investigated.Secondly,the effects of different chemical modification methods on the interface of PHA/CG composites were studied,and the mechanism of improving the compatibility of PHA/CG interface was explored.Then,the effects of chemical modification concentration on the properties of PHA/CG composites was explored.Finally,the antibacterial effect of PHA/CG composites modified by silver nitrate was investigated.The following study conclusions were obtained.(1)The effects of coffee grounds particle size(50 mesh,80 mesh,100 mesh,120 mesh,150 mesh)and coffee grounds content(10wt%,20wt%,30wt%)on the properties of the composites were investigated.The results showed that: the addition of coffee grounds had little effect on the processing rheological properties of the composites,and the appropriate particle size of coffee grounds(120 mesh)can enhance the mechanical properties,surface hydrophobicity and water resistance of the composites,and can play a role in heterogeneous nucleation and promote the crystallization of PHA matrix.With the increase of coffee grounds content,the interfacial compatibility between coffee grounds and PHA matrix became worse,and the mechanical properties,surface hydrophobicity and water resistance of the composites showed a decreasing trend.(2)The effects of different chemical modification methods(alkali treatment,silane treatment,alkali/silane treatment)on coffee grounds and the interface of composite materials were investigated.The results showed that: the alkali treatment removed the noncellulose part of coffee grounds,which made the shape of coffee grounds irregular and cavity structure,increased the specific surface area,changed the crystalline structure of cellulose,and increased the crystalline index;the silane treatment resulted in a rough surface with pits,decreased the crystalline index,increased the reactivity,generated chemical bonds,and improved the polarity of coffee grounds;the alkali/silane treated coffee grounds combine the advantages of both,with higher physical entanglement and better chemical bonding,resulting in further reduced polarity of coffee grounds.The cross section of the modified composite was smooth,the structure became compact,and the interfacial compatibility became better.(3)The effects of chemical modification concentrations(alkali concentration 3wt%,6wt%,9wt%,12wt%,15wt%,silane concentration 2wt%,4wt%,6wt%,8wt%,10wt%)on the properties of the composites were investigated.The results showed that: the greatest improvement in mechanical properties was achieved at a concentration of 12 wt% for alkali treatment alone,but the surface hydrophobicity decreased,water absorption increased,and water resistance decreased.The maximum improvement of mechanical properties,the increase of surface hydrophobicity,the decrease of water absorption rate and the increase of water resistance were observed at the concentration of 2-6wt% of silane treatment alone.The above properties were further enhanced by the synergistic treatment of alkali/silane.Rheological and DSC tests showed that moderate alkali treatment concentration(9-12wt%)or moderate silane treatment concentration(2-6wt%)could improve the interfacial compatibility of CG and PHA,enhance the interfacial bond strength and improve the mechanical properties.(4)The effects of different silver nitrate concentrations(0.02 mol/L,0.04 mol/L,0.06mol/L,0.08 mol/L,0.1 mol/L)on the properties of the composites were investigated.The results showed that with the increase of the concentration of silver nitrate,the reductionfixed Ag NPs increased,and the antibacterial effect of the composite became better and better.When the concentration of silver nitrate was 0.06 mol/L,the better antibacterial effect was achieved.In summary,this thesis improved the interfacial compatibility of CG and PHA,and improved the performance of PHA/CG composites.And the good antimicrobial properties obtained by modifying it with antimicrobial functionalization widened its application scope.