Preparation Of PLLA/Hollow Mesoporous Silica Microsphere Composite Film And Its Effect On Fresh-keeping Of Strawberry

To extend the shelf life of strawberries and improve the performance of poly（lactic acid）（PLLA）films for fruit and vegetable air conditioning packaging.In this thesis,poly-butylene glycol butyrate（PBI）was first introduced into PLLA as a flexible chain segment to improve its flexibility.Hollow mesoporous silica microspheres（HMSM）with special spatial structure were further introduced as gas permeation"channels"to fill the polymer material to improve its gas permeability.The effects of soft segment embedding,nano-microsphere addition ratio and microsphere size on the mechanical,thermal and gas per-meability of the composite film were investigated,and the effect of different gas permea-bility on strawberry gas preservation was studied.1.PBI was introduced into PLLA by melt polycondensation of itaconic acid（IA）and1,4-butanediol（BDO）to synthesize poly（butylene glycol）copolymer of itaconic acid（PLBI）.Then HMSM with different particle size distribution was prepared by soap-free emulsion polymerization method,and finally PLBI-HMSM film was prepared by solution casting method.The results showed that the elongation at break of PLBI films reached156.4%after the introduction of PBI,which was about 14.3 times that of PLLA,and the flexibility of the films was improved;the Tg of PLBI films was 55.1℃,which was 5.4℃ lower compared to PLLA,indicating that the chain segment motility of PLLA was im-proved.The CO₂ and O₂ permeability of the films were substantially improved by the fill-ing of HMSM compared with PLLA.The CDTR and OTR of PLBI/0.9-700 composite films increased to 5115 and 1034 cm³/m²·d at 0.9%of microsphere addition,and the OTR was about 2.2 times that of pure PLLA,while the CDTR increased to 3.3 times that of PLLA,but the water vapor barrier of both modified composite films decreased.2.PLBI/0.9%-HMSM with different particle sizes was applied to strawberries for aer-ation storage and preservation to evaluate its preservation effect.The results showed that PLBI/0.9-700 maintained a better atmosphere composition,sensory quality and color dif-ference.PLBI/0.9-700 was further applied to strawberries of different weights for storage and preservation.The results showed that on the 25th day of storage,the sensory score of strawberries in the 40PLBI/0.9-700 package remained above 6,and the gas concentration in the bags was in the ideal atmosphere:7.9%CO₂ and 2.9%O₂;the soluble solids of strawberries was 6.5%,which was only 3.25%lower than on day 0;the hardness was on-ly 3.4 kg/cm³ lower,and the vitamin C content was 24.32 mg/100 g.The malondialdehyde content was also significantly lower than in the other groups.The content of malondialde-hyde was also significantly lower than the other groups,at 2.13 nmol/g,and the titratable acid content decreased by only 0.3%.60PLBI/0.9-700 package maintained the storage quality of strawberries well and significantly extended the shelf life.