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21.
Poly(lactic acid) (PLA) stereocomplexes have high potential as renewable materials for advanced polymer applications, mainly due to their high melting temperature (Tm, typically 230–240°C). The properties of PLA stereocomplexes consisting of linear high molar mass homopolymers have been studied extensively in the past, but the available information about the possibilities to affect the thermal properties of the stereocomplex by varying the structure of the blend components has not been sufficient. Novel stereocomplexes containing linear or star‐shaped D ‐lactic acid (D ‐LA) oligomers and high molar mass poly(L ‐lactide) (L‐ PLA) were thus prepared. The Tm and melting enthalpy (ΔHm) of the racemic crystallites were found to depend strongly on both the blending ratio and the arm‐length of the D ‐lactic acid oligomer. The preparation method of the oligomers, i.e. step‐growth polymerization or ring‐opening polymerization (ROP), did not affect the Tm or ΔHm of the blends significantly. Slightly higher ΔHm values were, however, obtained, when linear oligomers were used. The results thus indicated that the Tm and ΔHm of PLA stereocomplexes could be optimized, simply by selecting a D ‐LA oligomer having a suitable arm‐length and structure as the other blend component. The possibility to adjust the melting behavior of the stereocomplex blend is a significant advantage and could make PLA suitable for a wider range of products used at elevated temperatures. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
22.
Saara Mikkonen Johan Jacksén Åsa Emmer 《Analytical and bioanalytical chemistry》2014,406(14):3521-3524
A new instrumental concept for extraction of nanovolumes from open microchannels (dimensions 150 μm?×?50 μm, length 10 mm) manufactured on silicon microchips has been used in combination with a previously developed method for preconcentrating proteins and peptides in the open channels through electromigration. The extracted nanovolumes were further analyzed using nanoelectrospray ionization (nESI) or matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) directly or with subsequent enzymatic protein digestion in a nanodroplet prior to the MS analysis. Preconcentration of the samples resulted in a 15-fold sensitivity increase in nESI for a neurotensin solution, and using MALDI-MS, amyloid beta (Aβ) peptides could be detected in concentrations down to 1 nM. The method was also successfully applied for detection of cell culture Aβ. 相似文献
23.
Jun Liu Risto Korpinen Kirsi S. Mikkonen Stefan Willför Chunlin Xu 《Cellulose (London, England)》2014,21(4):2587-2598
The residual cellulose of wood processing waste, sawdust, which was leftover after sequential hot-water extraction processes to isolate hemicelluloses and lignin in a novel forest biorefinery concept, was explored as the starting material for preparation of a highly value-added polymeric material, nanofibrillated cellulose (NFC) also widely termed as cellulose nanofiber, which has provided an alternative efficient way to upgrade sawdust waste. The residual cellulose in sawdust was converted to a transparent NFC suspension in water through the 2,2,6,6-tetramethylpiperidine-1-oxyl radical/NaClO/NaBr oxidization approach. The resultant NFC with a dimension of ca. 5 nm in width and hundreds of nanometers in length were further processed into NFC films. The morphological features of the NFC suspension and its films were assessed by transmission electron microscopy and scanning electron microscopy. Highly even dispersion of NFC fibrils in the films originated from sawdust feasibly contributes to the outstanding mechanical performance of the films. NFC suspension with higher carboxylate content and its resultant NFC films were found to show higher transmission of light. 相似文献
24.
Chiral ITP of the weak base methadone using inverse cationic configurations with H+ as leading component and multiple isomer sulfated β‐CD (S‐β‐CD) as leading electrolyte (LE) additive, has been studied utilizing dynamic computer simulation, a calculation model based on steady‐state values of the ITP zones, and capillary ITP. By varying the amount of acidic S‐β‐CD in the LE composed of 3‐morpholino‐2‐hydroxypropanesulfonic acid and the chiral selector, and employing glycylglycine as terminating electrolyte (TE), inverse cationic ITP provides systems in which either both enantiomers, only the enantiomer with weaker complexation, or none of the two enantiomers form cationic ITP zones. For the configuration studied, the data reveal that only S‐methadone migrates isotachophoretically when the S‐β‐CD concentration in the LE is between about 0.484 and 1.113 mM. Under these conditions, R‐methadone migrates zone electrophoretically in the TE. An S‐β‐CD concentration between about 0.070 and 0.484 mM results in both S‐ and R‐methadone forming ITP zones. With >1.113 mM and < about 0.050 mM of S‐β‐CD in the LE both enantiomers are migrating within the TE and LE, respectively. Chiral inverse cationic ITP with acidic S‐β‐CD in the LE is demonstrated to permit selective ITP trapping and concentration of the less interacting enantiomer of a weak base. 相似文献
25.
Juha K. Vilhunen Alex von Bohlen Martina Schmeling Leena Rantanen Seppo Mikkonen Reinhold Klockenkämper Dieter Klockow 《Mikrochimica acta》1999,131(3-4):219-223
Particulate matter of Diesel emissions collected from diluted exhaust during standard test runs with two Diesel fuels of
different sulfur content was analysed by total-reflection X-ray fluorescence (TXRF). The trace elements determined were S,
Ca, Cr, Mn, Fe, Ni, Cu, Zn and Pb. Additionally, some filter materials were tested with respect to their applicability for
sample collection. Quartz fibre filters were found to be most suitable, both from a technical and a chemical point of view.
A clear reduction of total particulate emissions during the whole test was observed when the fuel with very low sulfur content
was used. In addition, it was found that the wear metal content of particulate matter emitted by a cold engine was higher
than that observed during normal engine working temperature.
Received September 10, 1998. Revision March 2, 1999 相似文献