title: Preparation and characterization of polymer-inorganic nanocomposites by in situ melt polycondensation of L-lactic acid and surface-hydroxylated MgO.
abstract: Compared with pristine polymers, bionanocomposites derived from biopolymers and inorganic nanoparticles have significantly improved electrical/magnetic properties, mechanical properties, thermal stability, gas barrier properties, and fire retardance. In this study, poly(lactic acid) (PLA) nanocomposites were prepared by in situ melt polycondensation of L-lactic acid with different loading ratios of surface-hydroxylated magnesium oxide (MgO) nanocrystals. Molecular weight, structure, morphology, and thermal properties of the nanocomposites were characterized. PLA-grafted MgO (PLA-g-MgO) was isolated from free PLA for the nanocomposite with 3% MgO via repeated dispersion/centrifugation processes and characterized. The weight-average molecular weight of the PLA-0.01%MgO nanocomposite was 55500, which was 30% higher than that of pure PLA. Discoloration of PLA was obviously depressed in the presence of MgO nanocrystals. Formation of hydrogen bonding between PLA chains and surface -OH groups from MgO was detected by Fourier transform infrared spectroscopy. Morphological images showed uniform dispersion of MgO nanocrystals in the PLA matrix and demonstrated a strong interfacial interaction between the PLA matrix and MgO nanocrystals. PLA-MgO nanocomposites exhibited improved thermal stability compared with pure PLA. Calculations based on thermogravimetric analysis revealed that more than 42.5% PLA was successfully grafted into PLA-g-MgO.
authors.affiliation: Bio-Materials and Technology Lab, Department of Grain Science and Industry, Kansas State University, Manhattan, Kansas 66506, USA.
authors.forename: Yonghui
authors.initials: Y
authors.lastname: Li
authors.forename: Xiuzhi Susan
authors.initials: XS
authors.lastname: Sun
mesh_terms: D006860:Hydrogen Bonding; D006900:Hydroxylation; D019344:Lactic Acid / Q000138:chemical synthesis* / Q000737:chemistry; D008277:Magnesium Oxide / Q000737:chemistry; D008970:Molecular Weight; D053761:Nanocomposites / Q000737:chemistry*; D053758:Nanoparticles; D011091:Polyesters; D011108:Polymers / Q000138:chemical synthesis*; D013818:Thermogravimetry
chemical_list: D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; D008277:Magnesium Oxide; C033616:poly(lactide)