Construction And Performance Of Oxygen Barrier Coatings On The Surface Of Alkalized Polylactic Acid Film

Polylactic acid(PLA)is a kind of biodegradable polymer material,which is polymerized with lactic acid as the main raw material.The film made of PLA has good mechanical properties,transparency and biocompatibility.However,compared with the traditional packaging film,PLA film has poor oxygen barrier performance.The construction of oxygen barrier coating is one of the effective methods to solve this problem,but the adhesion of the surface of the PLA film is weak,which affects the deposition of hydrophilic polymer materials on its surface.Although the plasma surface modification method can effectively improve the affinity of the PLA film to the coating materials,it requires professional equipment and has problems such as timeliness.In this work,sodium hydroxide and anhydrous ethanol were used to alkalize the PLA film,and the deposition behaviors of PLA film with different hydrophilic polymer materials were compared and analyzed before and after alkalization.Then,the layer by layer(LBL)assembly method was used to construct the coating on the surface of alkalized PLA film,the oxygen barrier property of the film was optimized by adjusting the composition of the coating.The main research contents and results are as follows:Firstly,the PLA film was alkalized by the mixed solution of sodium hydroxide and anhydrous ethanol,and then chitosan(CS),polyvinyl alcohol(PVA)and sodium alginate(SA)coatings were constructed on the surface of PLA film before and after alkalization.The chemical structure,surface morphology and hydrophilic properties of the coating were analyzed by FT-IR,SEM and WCA.The oxygen barrier and optical properties were tested by oxygen permeameter and UV-Vis spectrophotometer,respectively.The results showed that alkalization treatment can promote the adsorption of CS,PVA and S A on the surface of PLA film,and the coating formed after deposition can effectively improve the oxygen barrier performance.After deposition of CS,PVA,and SA,the oxygen transmission rate of the PLA film before alkalization was 72.00,7.09 and 787.71 cc/m2·day,respectively.And after deposition of CS,PVA,and SA,the oxygen transmission rate of the PLA film after alkalization decreased to 10.60,2.48 and 4.40 cc/m2·day,respectively.Secondly,KGM/PA multilayer coating was constructed on the surface of alkalized PLA film by LBL assembly.The chemical structure and surface morphology were analyzed by FT-IR and SEM.the oxygen barrier performance was tested by oxygen permeameter and the antioxidant and optical properties were analyzed by UV-Vis spectrophotometer.The results showed that the thickness of the coating increases linearly with the increase of the number of assembly layers.When the assembly reached three bilayers,the oxygen transmission rate of PLA film decreased from 676.68 cc/m2·day to 5.21 cc/m2·day,the free radical scavenging rate reached 12.5%and maintained high transparency.Finally,KGM/TA multilayer coating was constructed on the surface of alkalized PLA film by LBL assembly.The chemical structure and surface morphology were analyzed by FT-IR and SEM,the oxygen barrier performance was tested by oxygen permeameter and the antioxidant and optical properties were analyzed by UV-Vis spectrophotometer.The results showed that the thickness of the coating increases linearly with the increase of the number of assembly layers.When the assembly reached three bilayers,the oxygen transmission rate of PLA film decreased from 676.68 cc/m2·day to 2.37 cc/m2 day,the free radical scavenging rate reached 66.7%and maintained high transparency.In addition,KGM/TA multilayer coatings endowed PLA films almost 100%UV absorption performance in the range of 250～340 nm.In summary,a new method for the surface treatment of PLA films was studied in this work.The treated PLA film effectively promoted the deposition of hydrophilic polymer materials on its surface.The coating formed after deposition endowed PLA films high oxygen barrier properties and oxidation resistance,which provides theoretical and experimental basis for the research and development of high barrier PLA film.