| Polylactic acid(PLA),as a fully biodegradable polyester derived from renewable resources,is considered to be the most promising material on the market due to its good biocompatibility,biodegradability,mechanical properties and transparency.It is widely used in food packaging and health care industries.In this paper,three kinds of PLA-based composite films with different functions were designed and developed by solvent blending technology.Their mechanical properties and food packaging applications were studied respectively.The applications of composite films in the fields of detectability,antibacterial properties and gas barrier properties were discussed,and the performance defects of PLA films in specific packaging applications were overcome.As follows:1.Using PLA,chitosan(CS),alizarin(AL)and environmentally friendly plasticizer tributyl citrate as raw materials,a PLA-based functional partition(bacteriostatic zone in the edge part and p H response detection zone in the center part)composite film was designed by solution casting method,and its application in intelligent food packaging was tested.The results showed that the elongation at break of the composite film was 340% higher than that of pure PLA.At the same time,CS and AL were uniformly dispersed in the PLA matrix,and the oxidation resistance and water contact angle of the composite film were improved to varying degrees without changing the thermal stability of the film.At the same time,because AL contains three benzene rings,the molecular structure can change with the change of p H value,and the hydroxyl group is also connected with carbonyl oxygen,which can be transmitted by protons under intramolecular hydrogen bonding.Therefore,when the environmental p H(ammonia and acetic acid vapor)changes repeatedly,the p H response detection area of the central part can show a reversible color change of yellow under acidic conditions and purple under alkaline conditions.During the storage of packaged chicken breast,the freshness of chicken breast can be detected by the color change of PLA composite film.2.Dimethylaminoethyl methacrylate and isobornyl methacrylate were used as monomers,and 1,3-propanesultone was introduced for zwitterionization after copolymerization to prepare bio-based antibacterial agent PDI.Then,a series of PLA/oVL/PDI composite membranes were prepared by solution casting method by mixing the bio-based antibacterial agent PDI,the antioxidant lead vanillin and the plasticizer glycerol with PLA at the same time.The successful synthesis of bio-based antibacterial agent PDI was verified by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.The results of field emission scanning electron microscopy,Fourier transform infrared spectroscopy and differential scanning calorimeter showed that the PLA/oVL/PDI series composite membranes had mechanical properties that met the conditions of use,antiultraviolet and anti-oxidation properties,and the antibacterial rate and Staphylococcus aureus could reach more than 95%.Packaging experiments showed that the PLA/oVL/PDI series composite films could effectively extend the shelf life of fresh bananas and apples by 5 days,which had great application prospects in anti-corrosion food packaging.3.A bio-based polymer PU-PLLA with PLLA block was successfully prepared by using hydroxyl-terminated polylactic acid(PLLA)and polypropylene glycol as raw materials,reacting with isophorone diisocyanate to prepare prepolymer,and then introducing chain extender 4,4’-diaminodiphenylmethane and 2,2’-bis(hydroxymethyl)propionic acid.The results show that the bio-based polymer material has good mechanical properties,excellent room temperature self-healing properties and good recyclability.At the same time,in view of the pearl layer inspired structural design,the barrier properties of PU-PLLA were improved by adding different contents of BN.The results of water vapor permeability test showed that 5 wt% BN could reduce the permeability of PU-PLLA materials by more than 50%,and the improvement of barrier ability was further confirmed in the packaging test of ibuprofen tablets.This film opens up a new way for the practical application of PLLA in flexible laminated moisture-proof packaging. |
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