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Hybrid Composition (hybrid + composition)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Property enhancement of epoxy resins by using a combination of polyamide and montmorillonite

ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2007
M. Bakar
Abstract A bisphenol-A epoxy resin cured with triethylenetetramine was modified with the addition of a polyamide oligomer and a small amount of montmorillonite. Compositions with different amounts of modifiers were obtained and tested for their impact strength, flexural strength, and resistance to crack propagation. The latter was assessed by measuring the critical stress intensity factor in a three-point bending mode. Scanning electron microscopy was used to examine the sample fracture surfaces. It was found that the addition of 2% montmorillonite or 5% polyamide resulted in the best improvement of the impact strength and the critical stress intensity factor relative to the unmodified epoxy resin. However, the flexural strength and toughness measured under three-point bending mode was found to increase to a lesser extent. Hybrid compositions containing specific combinations of both modifier and nanofiller not only exhibited a higher impact strength and resistance to crack propagation but also displayed a synergistic effect in relation to the fracture energy. The results indicate that the improvement in mechanical properties of the epoxy resin was due to the formation of a heterogeneous morphology resulting from phase separation of the polymeric modifier. From the scanning electron microscopy and thermal analysis, it appears that the toughening may arise from chemical reactions that have taken place between the epoxy resin and the polymeric modifier, which was partially solubilized in the resin matrix. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:223,231, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20103 [source]

Preparation and Characterization of Hybrid Nanocomposites Coated on LDPE

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 22 2006
Laura Mazzocchetti
Abstract Summary: Hybrid organic-inorganic nanocomposites containing hyperbranched structures were prepared through a dual-curing process, which involves photopolymerization and condensation alkoxysilane groups. In particular, an oligomer containing PEO units and ,,, -methacrylate groups was used together with a HBP bearing acrylic groups as the organic phase precursors. MEMO, as the organic-inorganic linker, and TEOS, as inorganic phase precursor, were also employed. The kinetics of both photopolymerization and condensation reactions were investigated by double bond conversion analysis (via FT-IR) and weight loss determination, respectively. The mobility of the organic phase was studied by means of DSC and DMTA and correlated with hybrid composition. TEM analyses performed on microtomed film slices indicated the formation of nanoscale silica domains. Hybrids were coated onto an LDPE film previously subjected to a plasma treatment, and substrate-coating interfacial adhesion was investigated through stress-strain and DMTA experiments. Reaction scheme showing the insertion of furanic units in copolyester chains by ester interchange reaction. [source]

Preparation and characterization of PBT nanocomposites compounded with different montmorillonites

POLYMER ENGINEERING & SCIENCE, Issue 6 2004
Domenico Acierno
Because of their superior mechanical and thermal properties, light weight, and favorable cost/performance ratio, nanocomposite materials appear to be suitable replacements for metals and alloys in many industrial applications in fields such as automotive, structural plastics, electronics, packaging, and so on (1). The technological relevance of this large-scale market for polymers is evidenced by the numerous patents issued over the last few years, even though only few applications have entered the market. Polymer-clay nanocomposite systems were successfully prepared by melt compounding using several thermoplastic matrices (polyamides, polyolefins, etc.), but few data are reported in the scientific literature on polyester-based nanocomposites (2). Because of the high commercial relevance of polyesters, we have investigated the effect of organoclay inclusion on the structure and properties of these hybrid systems. In particular, we have studied the relationships between processing conditions, hybrid composition (organoclay type and content), nanoscale morphology and properties of poly(butylene terephthalate) (PBT) nanocomposites based upon several commercial organo-modified montmorillonites at different weight percentages. The melt compounding was performed using a twin-screw extruder, at extrusion rates of 90 or 150 rpm. Polym. Eng. Sci. 44:1012,1018, 2004. © 2004 Society of Plastics Engineers. [source]

Lunar regolith breccia Dhofar 287B: A record of lunar volcanism

METEORITICS & PLANETARY SCIENCE, Issue 4 2003
S. I. Demidova
The present study is directed mainly at the breccia portion of this meteorite. This breccia consists of a variety of lithic clasts and mineral fragments set in a fine-grained matrix and minor impact melt. The majority of clasts and minerals appear to have been mainly derived from the low-Ti basalt suite, similar to that of Dho 287A. Very low-Ti (VLT) basalts are a minor lithology of the breccia. These are significantly lower in Mg# and slightly higher in Ti compared to Luna 24 and Apollo 17 VLT basalts. Picritic glasses constitute another minor component of the breccia and are compositionally similar to Apollo 15 green glasses. Dho 287B also contains abundant fragments of Mg-rich pyroxene and anorthite-rich plagioclase grains that are absent in the lithic clasts. Such fragments appear to have been derived from a coarse-grained, Mg#-rich, Na-poor lithology. A KREEP component is apparent in chemistry, but no highlands lithologies were identified. The Dho 287 basaltic lithologies cannot be explained by near-surface fractionation of a single parental magma. Instead, magma compositions are represented by a picritic glass; a low-Ti, Na-poor glass; and a low-Ti, Na-enriched source (similar to the Dho 287A parental melt). Compositional differences among parent melts could reflect inhomogeneity of the lunar mantle. Alternatively, the low-Ti, Na-poor, and Dho 287A parent melts could be of hybrid compositions, resulting from assimilation of KREEP by picritic magma. Thus, the Dho 287B breccia contains lithologies from multiple magmatic eruptions, which differed in composition, formational conditions, and cooling histories. Based on this study, the Dho 287 is inferred to have been ejected from a region located distal to highlands terrains, possibly from the western limb of the lunar nearside, dominated by mare basalts and KREEP-rich lithologies. [source]