| Due to its excellent biodegradability,biocompatibility and mechanical properties,polylactic acid(PLA)materials are widely used in the fields of tissue engineering,oil-water separation,drug sustained release and commercial plastics,which could potentially improve the environmental hazards caused by petroleum-based plastics.However,PLA is a semi-crystalline polymer,and its crystalline morphology is difficult to control,leading to challenges in achieving multi-scale micro/nano structures.The multi-scale micro/nano structures can provide PLA materials with broader application prospects and usage range.Therefore,this study focuses on the regulation of multi-scale micro/nano structures in PLA,the preparation of micro/nano structures on the surface of PLA,and the internal porous hierarchical structure,as well as their functional research.The specific research content and results are as follows:(1)In this study,corn straw was utilized as a source material for the synthesis of biomass carbon quantum dots(CQDs)through a microwave-assisted hydrothermal technique.The prepared CQDs were employed to assist the formation of a honeycomb-like porous surface on the CQDs/poly(L-lactic acid)(PLLA)composite film using a static breath-figure(BF)pattern combined with Picking emulsion mechanism.The pore size of the resulting CQDs/PLLA composite film was modulated by tuning the CQDs content or PLLA solution concentration,leading to an increase in pore size from 1.85 μm to 30.59 μm and a decrease from 5.78 μm to 2.36μm,respectively.A proposed mechanism elucidates the impact of the crystallization capacity of the adsorption layer,which forms at the interface between a polymer solution and water droplets,on the resulting pore size.Additionally,the mechanism underlying the assisting effect of CQDs was investigated,and a novel one-step template formation method with dynamic control was developed.Notably,this work overcomes the limitations of traditional breath-figure methods,including high humidity,flowing gas,and amphiphilic surface activators.It is expected that this approach could be utilized as a substrate material for cell culture research.(2)An in-situ polymerization reaction was used to graft poly(D-lactic acid)(PDLA)chains onto CQDs.Then,a new method of CQDs-induced phase separation by nucleation at the interface was used to investigate the preparation of multi-level adjustable nanostructures(layered structure,microspheres,petal-like structure,and micro/nano-sphere structure)by controlling different CQDs-g-PDLA concentrations.The mechanism of the formation of multi-level structures in PLA materials by the stereoisomeric composite crystals formed by PLLA and PDLA in the presence of CQDs as heterogeneous nucleating agents was also explored.The water contact angle of the 30wt% CQDs-g-PDLA/PLLA film was as high as 168°,and the maximum oil absorption capacity was up to 9.7 g/g demonstrating excellent performance in terms of self-cleaning and oil-water separation on the surface.This strategy for achieving superhydrophobicity by constructing controllable hierarchical structures diverges from conventional methods that rely on the introduction of nanoparticles or hydrophobic agents,and provides a new approach for designing superhydrophobic materials.(3)Cellulose nanocrystals(CNC)were grafted with PDLA via grafting reaction to improve the compatibility between CNC and hydrophobic polyester matrix,as well as to enhance the mechanical and crystallization properties of the nanocomposites.A low-temperature induced phase separation method was used to prepare porous CNC-g-PDLA/PLLA films for oil-water separation.The tensile strength of CNC-g-PDLA/PLLA films increased from 36.1 MPa to 49.5 MPa,the elastic modulus increased from 877.1 MPa to 1188 MPa,and the elongation at break increased from18.4% to 31.9%.The surface contact angle of the 5wt% CNC-g-PDLA/PLLA porous film reached 146°,and the oil absorption capacity was 8.4 g/g,showing great potential for application in the field of oil-water separation. |
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