Investigation of structural, mechanical and biodegradation of controlled composting media by preparation of cross-linked starch and bilayer polylactic acid (PLA) biofilms

In this study, the preparation of crosslinked and bilayer starch polylactic acid biofilms as packaging material was carried out by casting method. Firstly, the industrial waste potato starch separated from the stripping, washing and slicing water was treated with certain proportions of NaOH and HCl as H2O2 a bleach and purification was achieved by pure potato starch (SPN). SPN-MA and SPN-3-APTMS powder samples were synthesized using malonic acid and 3- (aminopropyl) trimethoxy silane as crosslinkers. The synthesized compounds were characterized by FTIR, TGA / DTA, XRD, 13C and 1H NMR. Bilayers of SPN-PLA, SPN-MA-PLA and SPN-3-APTMS-PLA films were prepared with crosslinked starch films and crosslinked films using glycerol as plasticizer. The films were characterized by FTIR, TGA and XRD methods. The prepared films were subjected to mechanical testing, solubility, water vapor permeability, optical, biodegradation, water intake and moisture content tests. Solubility, water uptake and moisture content of films in crosslinked and bilayer films decreased. Mechanical test was found to be between 1.298 and 1.437 MPa in crosslinked films, while it was between 9.414 and 10.918 MPa in bilayer films. While elongation at break was not observed in cross-linked films, bilayer films show an elongation between 9.34 and 21.94%. Compared to unmodified starch, crosslinked and bilayer films was reduced water vapor permeability. When the water vapor permeability of the films was examined, it was found that in the crosslinked films 28.96 x10-7 g s-1 m-1 Pa-1 and 27.08 x10-7 g s-1 m-1 Pa-1, whereas in the bilayer films this value was ranged from 10.66 to 15.1 x10- 7 g s-1 m-1 Pa-1. Modified starch films were found to be more opaque. According to the ISO-14855 standard, the SPN film was degraded by 9.30% after 46 days of biodegradation, whereas in SPN-MA and SPN-3APTMS films it was 3.71% and 5.46%, respectively. The bilayer SPN-PLA was 6.91%, 3.48% and 5.08% in SPN-MA-PLA and SPN-3-APTMS-PLA films, respectively. The results obtained in this study show that the cross-linking of starch and bilayer PLA biofilms can improve mechanical, physical properties and can be used as an alternative to renewable food packaging material.