ABSTRACT:The carbon nanotubes (CNTs) contents, ultrahigh-molecular-weight polyethylene (UHMWPE) concentrations and temperatures of UHMWPE, and CNTs added gel solutions exhibited significant influence on their rheological and spinning properties and the drawability of the corresponding UHMWPE/CNTs as-prepared fibers. Tremendously high shear viscosities (gs) of UHMWPE gel solutions were found as the temperatures reached 1408C, at which their gs values approached the maximum. After adding CNTs, the gs values of UHMWPE/CNTs gel solutions increase significantly and reach a maximum value as the CNTs contents increase up to a specific value. At each spinning temperature, the achievable draw ratios obtained for UHMWPE as-prepared fibers prepared near the optimum concentration are significantly higher than those of UHMWPE as-prepared fibers prepared at other concentrations. After addition of CNTs, the achievable draw ratios of UHMWPE/CNTs as-prepared fibers prepared near the optimum concentration improve consistently and reach a maximum value as their CNTs contents increase up to an optimum value. To understand these interesting drawing properties of the UHMWPE and UHMWPE/CNTs as-prepared fibers, the birefringence, thermal, morphological, and tensile properties of the as-prepared and drawn fibers were investigated. Possible mechanisms accounting for these interesting properties are proposed.
ABSTRACT:We have investigated the mechanical and morphological properties of un-vulcanized and dynamically vulcanized ethylene propylene diene terpolymer/ polypropylene (EPDM/PP) thermoplastic elastomers prepared under various processing conditions and possessing various compositions. After melt-blending EPDM and PP resins twice in a twin-screw extruder, the values of tensile strength (r f ) of the un-vulcanized EPDM/PP samples were at most equal to that of the pure EPDM specimen, but were much lower than those of the pure PP specimens. The elongations at break (e f ) of the un-vulcanized EPDM/PP samples were, however, dramatically higher than those of their respective virgin PP resins, and they improved significantly upon increasing the shear viscosity (g s ) of the PP resins. The tensile properties of the dynamically vulcanized EPDM/PP samples were significantly better than those of the corresponding un-vulcanized EPDM/ PP specimens. Similar to the behavior of the un-vulcanized EPDM/PP specimens, the tensile properties of the dynamically vulcanized EPDM/PP specimens were optimized when prepared at a screw rate of 115 rpm. Morphological analysis revealed that the un-vulcanized and dynamically vulcanized EPDM/PP specimens both featured many EPDM domains finely dispersed in continuous PP matrices. Such domains were present on the surfaces of the dynamically vulcanized EPDM/PP specimens; the relative sizes of the vulcanized EPDM domains were minimized when the vulcanized EPDM/PP specimens were prepared at the optimal screw rate (115 rpm). In fact, under these conditions, the average sizes of the vulcanized EPDM domains decreased upon increasing the values of g s of the PP resins used to prepare the vulcanized EPDM/PP specimens. To understand these interesting tensile and morphological properties of the un-vulcanized and dynamically vulcanized EPDM/PP specimens, we measured the rheological properties of the base polymers and performed energy-dispersive x-ray (EDX) analyzes of the compositions of the un-vulcanized and dynamically vulcanized EPDM/PP specimens.
In the title coordination polymer, [CdBr2(C12H12N2O2)]n, the CdII ion, situated on an inversion centre, is coordinated by four bridging Br atoms and two N atoms from two 1,4-bis(4,5-dihydro-1,3-oxazol-2-yl)benzene (L) ligands in a distorted octahedral geometry. The L ligand, which also lies across an inversion centre, bridges two CdII ions, forming layers parallel to (010).
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