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.

Mechanical and thermal properties of biocomposites from poly(lactic acid) and DDGS

“…. 30 After thermal compounding of PLA and DDGS with MDI, the peak of AN¼ ¼C¼ ¼O in the composites totally disappeared, indicating that all free isocyanate groups from MDI were consumed during thermal compounding. Moreover, the strong absorption peak of AOH and ANH observed in DDGS became very weak, indicating that most AOH and ANH groups were reacted with MDI in forming urethane and urea linkages.…”

Strengthening and toughening of poly(L-lactide) composites by surface modified MgO whiskers

“…The results may be explained that the grafted PLLA chains on the surfaces of g-MgO whiskers, as inter-tying molecules, played an important role in forming the molecule chains entanglement and improving the interfacial adhesion between the g-MgO whiskers and PLLA matrix. And it also can be contributed to the Hbonding between the free PLLA in the matrix and the -OH groups on the surface of the MgO whiskers [14]. The strong interfacial adhesion can result in efficient stress transfers from PLLA matrix to the g-MgO whiskers, which can increase the ability of the material to absorb energy and improve the mechanical properties of composite.…”

“…Moreover, aliphatic polyesters are lack of osteoconductivity and osteoinductivity so that it is hard for the new bone tissue bond on the materials surface tightly [8]. To overcome these limitations, many kinds of inorganic particles such as hydroxyapatite (HAP), -tricalcium phosphate, clay, magnesia (MgO) and titanium dioxide, etc., have been introduced into the aliphatic polyester matrix [9][10][11][12][13][14][15]. However, the mechanical strength and elastic modulus of polymer matrix may be improved by introduction of a certain amount of inorganic particles, but the particles also may cause stress concentration which results in the decrease of the toughness for particle-filled polymer.…”

The study of poly(L-lactide) grafted silica nanoparticles on the film blowing of poly(L-lactide)

“…To improve the distribution of nanoparticles and control the interaction force between the nanoparticles and matrix 7 , one more effective method is surface pretreatment for nanoparticles. For the covalent functionalization of nanoparticles, two strategies have been well established, "grafting from (grafting side chains from the backbone)" and "grafting to (attachment of side chains to the backbone)" approaches [8][9][10] . Using "Grafting to" method, side grafted chains with high molecular weight can be obtained, although the reaction condition for this polymerization method is much harsher.…”