Research On The Design And Functionalization Of Polylactic Acid Multi-layer Structur

Poly（lactic acid）（PLA）is a renewable and biodegradable thermoplastic polyester with a wide range of application prospects in many fields such as oil-water separation,adsorption,electromagnetic shielding,biological scaffolding,and phase change energy storage because of its light weight,good biocompatibility,excellent permeability,high specific surface area and good processability.However,the disadvantages of PLA functional materials,such as complex preparation process and harsh conditions,seriously limit the application of PLA in hydrophobic and electromagnetic shielding fields.Therefore,this thesis develops PLA materials with hydrophobicity,folding resistance,and electromagnetic shielding properties by structural design of PLA based on a non-solvent induced phase separation method.The main work of this thesis consists of the following three parts:（1）Poly（L-lactic acid）acid（PLLA）film with porous structure was successfully designed by a non-solvent induced phase separation method,which has excellent hydrophobic properties and bending resistance.The surface roughness and internal pore structure of PLLA films were controlled by adding different contents of ethanol.When ethanol was added at 3 m L,a porous structure appeared inside the PLLA film;when ethanol was added at 7 m L,the bending resistance could reach 659 times;when ethanol was added at 13 m L,a large number of continuous protruding structures appeared on the surface of the porous PLLA film with excellent hydrophobic effect,and the apparent contact angle could reach 150°.This method provides new ideas for the functionalization of PLA materials by making special porous structures and rough surface structures in one step.（2）Environmentally friendly EMI shielding silver nanowires（Ag NWs）/poly（L-lactic acid）/poly（D-lactic acid）（SC-PLA）/ferroferric oxide（Fe₃O₄）composites with step-wise asymmetric structures were prepared by a facile one-step non-solvent-induced phase separation method.The conductive Ag NWs network is constructed at a low mass fraction of 5 wt%on the surface of SC-PLA film（1.08×10⁴ S/m）.Moreover,magnetic Fe₃O₄ is mainly distributed in the skeleton of porous SC-PLA film.Due to the synergistic effect of Ag NWs and Fe₃O₄,the EMI SE of SC-PLA films reaches up to50.3 d B in X-band.Interestingly,SC-PLA film modified with triethoxy-1H,1H,2H,2H-tridecafluoro-n-octylsilane（TTO）demonstrates an outstanding water contact angle of about 150.2°compared to the pure PLLA film（134.7°）,stemming from the synergistic effect of denser SC-PLA nano-protrusions and low-surface-energy TTO.Thus,we successfully fabricate the high EMI shielding SC-PLA film with wonderful superhydrophobicity,which extends the application performance and service life of portable electronics in moist environments.（3）Conductive layers of silver nanoparticles（Ag NPs）were pre-layered by reduction method,and then multilayer poly（lactic acid）riser composite films（Ag NPs/SC-PLA/Ag NWs@Fe₃O₄）with asymmetric structures were successfully designed based on phase separation method.The introduction of Ag NPs conductive layer and Ag NWs@Fe₃O₄ hybrid material synthesized by chemical precipitation method resulted in 5-Ag NPs/SC-PLA/Ag NWs@Fe₃O₄ with excellent conductivity（1.78×10³ S/m）.The EMI SE can reach 52.9 d B in X-band with the synergistic effect of Ag NPs and Ag NWs@Fe₃O₄ hybrid materials.meanwhile,the addition of Ag NWs@Fe₃O₄ hybrid materials helps to construct the protruding structure,and the hydrophobic angle of the multilayer SC-PLA composite film can reach 152.5°with the synergistic effect of triethoxy-1H,2H,2H,2H-trifluoro-n-octylsilane（TTO）.In addition,the results show that the multilayer SC-PLA composite membrane can maintain good hydrophobicity for strong acid and alkali aqueous solutions,and has good self-cleaning ability in practical applications,which prolongs the service life of the multilayer SC-PLA composite film.