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

Poly?lactic acid??PLA?is the starch in natural plants,which is fermented and polymerized by modern biotechnology.After the use of PLA products can be degraded to H₂O and CO₂,it has no harm to the environment and overcomes the disadvantages of traditional plastic degradation.However,there is obvious deficiency in the performance of oxygen resistance of PLA film.In this paper,hydroxypropyl methyl cellulose?HPMC?,polyvinyl alcohol?PVA?and tannic acid?TA?were used to construct a coating to solve the problem of oxygen resistance of PLA.All the materials are green and environmental protection.First of all,HPMC and TA were used as materials,through layer by layer self-assembly?LBL?construct HPMC/TA coating.The PVA/TA coating was constructed by LBL method with PVA and TA.At last,PVA and TA were used to structure PVA/TA composite coating by co precipitation method.By characterization of surface chemical structure and morphology,the coating on the surface of PLA growth was investigated.Study the influence rules and mechanism of three different coatings on the oxygen resistance,light transmittance and mechanical properties of PLA.The main results were as follows:With the increase of the number of HPMC/TA layers,the thickness of the coating on the surface of the PLA film increases exponentially.When the HPMC/TA coating reaches 20 double layers,the average thickness of the coating is about 1.95±0.11?m,and the oxygen transmission rate is 551.24 cc/m²·day,which is about 38.13%lower than that of the pure film,which effectively improves the PLA film's oxygen resistance.At the same time,the coating also endowed the PLA film with a good UV absorption capacity.At 281 nm,the UV transmittance of the 20 layer coating was only 6.04%.The other properties of the film,such as light transmittance and tensile strength decreased slightly,but the strain at break was improved.The variation of the thickness of PVA/TA coating on the surface of PLA film increases exponentially with the raise of the number of layers.When the PVA/TA coating reaches 20double layers,the average thickness of the coating is about 8.91±0.57?m,and the oxygen transmission rate is 1.43 cc/m²·day,which is reduced by 99.84%compared with the pure film,which significantly improves the oxygen resistance.As with the HPMC/TA coating,the PVA/TA coating also endowed the PLA film with a good UV absorption capacity.At 281 nm,the UV transmittance of the 20 layer coating was 0.8%.The transmittance and mechanical property of the film decreased slightly.Change of the mixture ratio of PVA and TA,the thickness and morphology of the coating on the surface of the PLA film changes.When PVA:TA is 1:0.05,the film has the best oxygen barrier performance,the coating thickness is 0.68?m,and the oxygen transmission rate is 2.43cc/m²·day,which is 99.73%lower than that of the original film,which significantly improves the oxygen resistance.Compared with HPMC/TA coating and PVA/TA coating,the UV absorbability of the coating is low.At 281 nm,the UV transmittance of the coating with 1:0.05 of PVA:TA is 66.80%.The transmittance and mechanical property of the film gradually decrease.Compared with the LBL method,the oxygen resistance of the coating is higher than that of the HPMC/TA coating,which is slightly lower than that of the PVA/TA coating.However,the preparation process takes less time and simple operation.