Kazue Ueda

New polylactide-layered silicate nanocomposites. 2. Concurrent improvements of material properties, biodegradability and melt rheology

Abstract Our continuing research on the preparation, characterization, materials properties, and biodegradability of polylactide (PLA)-layered silicate nanocomposites has yielded results for PLA–montmorillonite nanocomposites. Montmorillonite modified with trimethyl octadecylammonium cation was used as an organically modified layered silicate for the nanocomposites preparation. The internal structure of the nanocomposites in the nanometer range has been established by using wide-angle X-ray diffraction and transmission electron microscope analyses. All the nanocomposites exhibited superior improvement of practical materials properties such as storage modulus, flexural modulus, flexural strength, heat distortion temperature, and gas barrier property as compared to that of neat PLA. The biodegradability of neat PLA and a representative nanocomposite was also studied under compost, and the rate of biodegradation of neat PLA significantly increased after nanocomposites preparation. The melt rheology of neat PLA and various PLACNs was also studied.

Polyamides from lactams by centrifugal molding via anionic ring-opening polymerization

Abstract This paper deals with a study of some properties of the polymers obtained by centrifugal molding via activated anionic ring-opening polymerization of ϵ-caprolactam and copolymerization of ϵ-caprolactam with laurolactam. Ethyl magnesium bromide, as initiator and N -benzoyl ϵ-caprolactam and N , N ′-isophthaloyl-bis-ϵ-caprolactam, as activators were used. The initial mold temperature (initial polymerization temperature) was kept constant at 160°C. Our experimental data demonstrated that the degree of crystallinity depends on the activator type and concentration. The incorporation of laurolactam into nylon 6 chain depresses both in the degree of crystallinity and the melting temperature of nylon 6/12 copolymers. The notched Izod impact strength of the copolymers increased as the laurolactam content was increased, while the flexural modulus and the water absorption decreased.

New polylactide/layered silicate nanocomposites, 4. Structure, properties and biodegradability

Our exhaustive research on the preparation, characterization, materials properties and biodegradability of polylactide (PLA)/organically modified layered silicate (OMLS) nanocomposites has yielded results for PLA/montmorillonite (MMT) nanocomposites. Natural Na+-MMT modified with octadecylammonium cation, is used as an OMLS for nanocomposites preparation. The internal structure of the nanocomposites at the nanometer scale is established using wide-angle X-ray diffraction (WAXD) patterns and transmission electron micrographic (TEM) observations. All nanocomposites show improved material properties and crystallization behavior with a simultaneous improvement in biodegradability than that of neat PLA.

Electronic structure of SrNb8O14 and Mg3Nb6O11 studied by spectroscopic methods

Although there are many studies about oxides containing Nb 6 O 12 cluster, the electronic structure has not been elucidated experimentally. Therefore, those around the Fermi level (E F ) for SrNb 8 O 14 and Mg 3 Nb 6 O 11 , which contain 14 valence electrons per cluster, were evaluated using electronic spectroscopies. Photoemission spectra showed that the occupied states were roughly split into two bands, and the shallower band was primarily composed of Nb 4d orbital. On the other hand, the bottom of the unoccupied state was attributed to 4d orbitals of Nb 6 cluster mainly on the basis of information obtained by inverse photoemission and Nb L 3 -edge X-ray absorption near-edge structure spectra, showing that the electronic structure around E F of these oxides were dominated by the nature of Nb 6 cluster. The optical transition in the region 0.1-4 eV was interpreted as Nb4d-4d intratomic electronic transitions, compared with those of niobium oxides. This indicates that these materials were semimetals or semiconductors with a considerable narrow band gap.