Supramolecular bionanocomposites, part 2: Effects of carbon nanoparticle surface functionality on polylactide crystallization

Abstract

Two types of supramolecular carbon nanostructures, carbon nanospheres (CNS) and multiwalled carbon nanotubes, (MWCNTs) are investigated for their potential as nanofillers in the bioplastic polylactide (PLA). Modification of the surfaces of both carbon nanostructures by covalent attachment of dodecylamine is accomplished and the effects of this compatibilizing functionality are explored. Crystallization kinetics, thermal properties, and mechanical properties are investigated. Addition of a small amount of carbon to the PLA increases the thermal stability by as much as 20-30 C. Incorporation of the MWCNT and CNS increases the heat distortion temperature by up to 10 C. Speed up in crystallization rate is observed for small to intermediate loading levels; however, at higher nanofiller loading, the rate decreases. Functionalized nanostructures are more effective at increasing crystallization rates than unfunctionalized nanostructures. It is concluded that the dodecylamine (DDA) grafted to the carbon surfaces aids in dispersing the materials and preventing aggregation, thereby providing higher surface area for heterogeneous nucleation of the biopolymer. The resulting materials are composed of the supramolecular carbon nanostructure embedded in a semicrystalline biopolymer matrix.

Miscible blends of biobased poly(lactide) with poly(methyl methacrylate): Effects of chopped glass fiber incorporation

“…Poly(lactide) (PLA) is the most widely used bio‐based synthetic thermoplastic polymer and is suitable for diverse engineering applications . Increasingly, there exists great interest in development of engineering materials derived from renewable resources including recyclable, PLA‐based composites . When PLA is used as the matrix in conjunction with natural fibers such as cellulose, the resulting composite is completely bio‐based and biodegradable .…”

Supramolecular bionanocomposites 3: Effects of surface functionality on electrical and mechanical percolation

“…Other factors such as interactions of the polymer chains with the surface of the MWCNT can contribute, and it may be that the DDA chains on the surface of the tubes act as a surfactant, keeping viscosity, and modulus values lower even though dispersion is improved. Previous work32 shows that T g is unchanged in these composites, as measured by both differential scanning calorimetry and mechanical spectroscopy, likely due to competing effects of plasticization and chain confinement on the nanosurface.…”

“…The lowest A for MWCNT‐DDA indicates a higher effective aspect ratio in these composites. Evidence of enhanced dispersion based on crystallization kinetics was found for DDA‐functionalized carbon in earlier work 32. It is unclear how the surface functionality affects specific interactions between the polymer chains and the nanotube surface; however, because the effects of dispersion and surface interaction cannot be easily decoupled.…”

“…The CNT have an entangled network structure, and the inset shows the graphitic structure of the tube walls. The thermal stability of the materials and the amount of functionalization achieved is detailed in Ref 32…”

“…PLA is a renewable, biodegradable polymer commercially produced by catalytic polymerization of lactide monomers derived from renewable resources 28. Researchers have incorporated many types of fillers into PLA in the recent years in attempts to improve the heat distortion temperature, gas barrier, crystallization kinetics, and mechanical properties 29–32. Percolation properties of PLA composites have been investigated for layered silicate fillers33 as well as CNTs 34, 35.…”