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991.
Summary Copolymeric poly(acrylic acid-co-methyl methacrylate) hydrogels for three different compositions: (90/10), (80/20) and (60/40),
have been studied. Drug release has been examined as a function of the hydrogel composition by HPLC (High Pressure Liquid
Cromatography). The release experiments were carried out at 37 °C. The fraction of available drug release was linear in t1/2. The values of the diffusional coefficient (0.50<n<1.0) indicate that the nafcillin release mechanism from the hydrogels
in study is non-Fickian. The diffusion coefficients for this drug release have been calculated. The molecular diffusion of
nafcillin through hydrogels is controlled by the swelling. 相似文献
992.
993.
994.
Bituminous coal samples from 84 distinct sources were analysed by conventional British Standards (BS) methods for phosphorus, sulphur, chlorine, ash and the ash-forming elements (calcium, silicon, aluminium, iron, sodium, magnesium, potassium, titanium and manganese). In most cases four determinations were made per element per source. Samples were crushed to ?212 μm (72 BS mesh) and pressed into aluminium cups at 20 t in?2 (309 MPa) without binder or backing. Two pellets from each sample were analysed by wave-length dispersive X-ray fluorescence techniques, using a spectrometer equipped with a rhodium rube; the X-ray count took 60 s. The X-ray results were calibrated against the conventional results using multiple regression. The accuracy obtained was comparable with routine ‘wet chemical’ techniques. The X-ray technique is suitable for the routine determination of large numbers of samples. 相似文献
995.
996.
High resolution XPS analysis of chemical functionalised multi-wall carbon nanotubes (MWCNTs) and single wall carbon nanotubes (SWCNT) was done with ESCA300 (overall instrument resolution of 0.35 eV). Information to the degree of functionalisation was ascertained by argon ion bombardment of the samples followed by XPS analysis to detect the functional groups, the percentage atomic concentration of various elements present and whether or not the detected functional groups imposed a chemical shift on the CNT atoms. The results show that true chemical functionalisation was achieved and by argon ion bombardment these functional groups can be altered relative to the C 1s carbon atoms of the CNT. The choice of chemicals used for functionalisation, the techniques employed and the types of nanotubes treated are important factors in chemical characterisation. The carbon atom on the nanotube ring to which the functional group (atom) is bonded, the chirality of the CNT, the electronegativity of the functional group, the bond type and whether the CNT is single-wall or multi-wall, or cut (short) could play a role in determining the chemical shift on the CNTs atoms. These investigations are relevant to chemical functionalisation of carbon nanotubes for various applications for example DNA sensors and other biomedical sensors. 相似文献
997.
Polylactide (PLA) has been melt spun to produce multifilament continuous yarns. The thermal characteristics of PLA filaments have been investigated using modulated differential scanning calorimetry (MDSC). With MDSC, it is possible to separate the different thermal events and to analyze them more precisely. The influence of hot drawing on thermal properties of PLA filaments has been studied. Hot drawing promotes an increase of glass transition temperature (Tg) and a decrease of heat capacity. The cold crystallization spreads on a larger range of temperature and the peak occurs at a lower temperature. The initial degrees of cristallinity of PLA filaments have been calculated thanks to the reversing and non reversing curves of MDSC. Tensile properties of PLA filaments are also investigated. 相似文献
998.
X‐ray diffraction methods, DSC thermal analysis, and polarized light microscopy (PLM) were used to investigate the structural changes of nylon 66/clay nanocomposites. PA 66/clay nanocomposites were prepared by the method of melt intercalation. The results indicate that the addition of the intercalated organo‐montmorillonite (OMMT) can induce generation of the β‐form crystal of PA 66 and substantially affect the arrangement of molecules in the α‐form crystal, although the crystallinity scarcely changes. Also, the DSC results indicate that the addition of OMMT in the PA 66 matrix leads to increases of crystallization temperatures and the full width at half maximum (FWHM) of the exothermic peaks. Moreover, the viscosity factor is the main influence on FWHM of the exothermic peaks of PA 66/clay nanocomposites. The results of nonisothermal crystallization kinetics show that OMMT has the effect of heterogeneous nucleation and leads to the decrease of the size of the spherocrystal. The heterogeneous nucleation effects of OMMTs influence the mechanism of crystallization and the growth mode of PA 66 crystals. PLM photographs verify that the size of spherocrystal is decreased and visually confirm the theory of crystallization kinetics. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 756–763, 2005 相似文献
999.
The structural changes and mechanical performance of virgin poly(vinyl chloride) (PVC) bottle (VB) compounds blended with postconsumer PVC bottles collected from a specified factory (RB‐F) and houses (RB‐H), were examined before and after UV irradiation at 313‐nm UV wavelength for different periods of time up to 28 days. The results indicated that, when exposed to UV light, the RB‐F/VB blends containing greater conjugated double bonds with higher yellowness index appeared to exhibit better mechanical performance than that of the RB‐H/VB blends. It was found that the amount of conjugated double bonds was not a linear function of the discoloration level of PVC compounds. Tensile strength of the VB compounds was not affected when incorporated with RB‐F recyclate, but progressively decreased with increasing RB‐H recyclate. An optimum concentration for RB recyclates to be added into the virgin compound was recommended for obtaining a maximum impact strength. Both tensile and impact strengths decreased with increasing UV exposure time, a severe degradation being obvious after a UV exposure time of 21 days. Hardness was not affected significantly by the addition of PVC recyclate, but increased with increasing UV exposure time. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 84–94, 2004 相似文献
1000.
Ningping Chen 《Polymer》2004,45(7):2403-2411
Hydrophilic polymer segments, consisting of styrene sulfonic acid (SSA) units, were uniformly embedded into hydrophobic poly(vinylidene fluoride) (PVDF) matrix through the mediation of poly(methyl methacrylate) (PMMA) segments, with which SSA segments form a copolymer. Discrete domains (∼100 nm) assembled by the SSA segments have been identified throughout the matrix of the membrane, which was prepared through blending of the copolymer P(MMA-SSA) and the PVDF. The thermal stability of the SSA was largely boosted in such hydrophobic environment. This unique matrix structure offers proton conductivity of as high as 10−3 S/cm at a low SSA equivalent (0.6 mmol -SO3H/g of membrane), which is accompanied with a low level of water uptake (26%) at ambient temperature. Using this type of polymer membrane as electrolyte, the electrochemical cell possesses obvious capacitive resistance when the membrane is in the anhydride form according to the impedance analysis. However, the capacitive character vanishes when the membrane is hydrated; this response is attributed to the existence of highly dispersed SSA domains in the membrane. This work also analyzes the impedance spectra of the membranes at different hydrated states or with different SSA contents by using an equivalent electrical circuit. 相似文献