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991.
Sirirung Wongsakul Poonsuk Prasertsan Uwe T. Bornscheuer Aran H‐Kittikun 《European Journal of Lipid Science and Technology》2003,105(2):68-73
Commercial immobilized lipases were used for the synthesis of 2‐monoglycerides (2‐MG) by alcoholysis of palm and tuna oils with ethanol in organic solvents. Several parameters were studied, i.e., the type of immobilized lipases, water activity, type of solvents and temperatures. The optimum conditions for alcoholysis of tuna oil were at a water activity of 0.43 and a temperature of 60 °C in methyl‐tert‐butyl ether for ~12 h. Although immobilized lipase preparations from Pseudomonas sp. and Candida antarctica fraction B are not 1, 3‐regiospecific enzymes, they were considered to be more suitable for the production of 2‐MG by the alcoholysis of tuna oil than the 1, 3‐regiospecific lipases (Lipozyme RM IM from Rhizomucor miehei and lipase D from Rhizopus delemar). With Pseudomonas sp. lipase a yield of up to 81% 2‐MG containing 80% PUFA (poly‐unsaturated fatty acids) from tuna oil was achieved. The optimum conditions for alcoholysis of palm oil were similar as these of tuna oil alcoholysis. However, lipase D immobilized on Accurel EP100 was used as catalyst at 40 °C with shorter reaction times (<12 h). This lead to a yield of ~60% 2‐MG containing 55.0‐55.7% oleic acid and 18.7‐21.0% linoleic acid. 相似文献
992.
S.‐P. Rwei A.‐Y. Liu G.‐S. Liou K.‐C. Cheng W. Guo 《Polymer Engineering and Science》2004,44(2):376-387
This study investigates the curing kinetics, thermal properties and decomposition kinetics of cresol novolac epoxy (CNE) with two curing agents, 2‐(6‐oxido‐6H dibenz(c,e)(1,2) oxaphosphorin‐6‐yl)‐1,4‐benzenediol (ODOPN), and phenol novolac (PN). In comparison with the conventional PN system, introducing ODOPN, a phosphorus‐containing bulky pendant group, into CNE increases Tg by 33°C, char yield from 30% to 38%, and LOI from 22 to 31. The DSC curing study reveals that the Ea of the CNE/ODOPN epoxy can be obtained by Kissinger's method. The resulting Ea values indicate that the catalytic effect of EMI is insignificant on CNE/ODOPN but is marked on CNE/PN, whose Ea was reduced from 131.5 to 75.6 KJ/mole. This result may be caused by the fact that the symmetric diol attached to the 1 and 4 positions of the naphthalene ring in ODOPN sets up a steadily resonating structure and inhibits the catalytic action. Further investigating the conversion ratio with curing temperature yielded experimental data that agreed closely with Kaiser's model. The orders of the autocatalyzed reaction, m, and the crosslinking reaction, n, are close to 0.5 and 1.0, respectively, independently of the scan rate. Finally, the TGA decomposition study by Ozawa's method demonstrates that the mean Ea declines with the phosphorus content, because the easy decomposition of the phosphorus compound in the initiation stage facilitates the formation of an insulating layer. However, results in this study further reveal an increasing tendency for Ea with decomposition conversion for an ODOPN/PN mixture with the ODOPN content of over 50%, probably because of the retardation of gas diffusion by the insulating layer of phosphorus compound. 相似文献
993.
Lignin‐based wood adhesives are obtained that satisfy the requirements of relevant international standards for the manufacture of exterior‐grade wood particleboard. Formulations based on low molecular mass lignin and presenting an increase in the relative proportion of reactive points yield better results than the higher molecular mass lignin used in the past. These lignins allow a higher proportion of hydroxymethylation during preparation of methylolated lignins. These lignin‐based adhesives also yield acceptable results at particleboard pressing times that are sufficiently low to be of industrial significance. Lignin‐based wood adhesives, in which a nonvolatile nontoxic aldehyde (glyoxal) is substituted for formaldehyde in their preparation, are prepared and tested for application to wood panels such as particleboard. The adhesives yield good internal bond strength results for the panels, which are good enough to comfortably pass relevant international standard specifications for exterior‐grade panels. The adhesives also show sufficient reactivity to yield panels in press times comparable to that of formaldehyde‐based commercial adhesives. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1690–1699, 2007 相似文献
994.
The solubility of propane in sulpholane has been determined at temperatures in the range 298‐403 K at pressures up to 17.6 MPa. The experimental results were correlated by the Peng‐Robinson equation of state, and binary interaction parameters have been obtained for this system. The parameters in the Krichevsky‐Ilinskaya equation were calculated from these interaction parameters. 相似文献
995.
Adsorption and flocculation behavior of two series of synthetic polycations was investigated in dispersions of silica and polystyrene latices with various particle size and surface charge densities. Polycations of the first series (polydiallyldimethyl ammonium chloride‐PDADMAC) varied in molecular weight only, while polycations of the second series (derivatives of polymethacrylic acid) varied in both molecular weight and hydrophobicity. We have found that maximum adsorbed amount of high molecular weight PDADMAC on latex particles was nearly independent of the surface charge density when the particle size was comparable to the polymer coil dimensions in solution. Both low and high molecular weight PDADMACs were efficient flocculants, although significantly lower amounts of high molecular weight polyelectrolyte were required for the phase separation in the dispersions due to particles aggregation through “charge patch” mechanism. The increase of polymer hydrophobicity leads to higher adsorbed amounts and broadening of flocculation window by polycations of the second series on both substrates. However, no strong enhancement of segment–surface interactions on hydrophobic substrates was observed. Since formation of multilayers upon adsorption was also excluded, the difference in adsorption and flocculation behavior was related to the more compact conformation of hydrophobically associating derivatives in solution and at the interface. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3422–3429, 2006 相似文献
996.
Dietary stearic acid and risk of cardiovascular disease: Intake,sources, digestion,and absorption 总被引:1,自引:2,他引:1
Individual FA have diverse biological effects, some of which affect the risk of cardiovascular disease (CVD). In the context
of food-based dietary guidance designed to reduce CVD risk, fat and FA recommendations focus on reducing saturated FA (SFA)
and trans FA (TFA), and ensuring an adequate intake of unsaturated FA. Because stearic acid shares many physical properties with the
other long-chain SFA but has different physiological effects, it is being evaluated as a substitute for TFA in food manufacturing.
For stearic acid to become the primary replacement for TFA, it is essential that its physical properties and biological effects
be well understood. 相似文献
997.
Gina‐Gabriela Bumbu Cornelia Vasile Maria Cristina Popescu Hristea Darie Gabrielle Charlotte Chianu Gheorghe Singurel Adrian Carpov 《应用聚合物科学杂志》2003,88(11):2585-2597
The compatibility of the hydroxypropyl cellulose (HPC) with maleic acid–vinyl acetate copolymer in the solid state was studied by thermogravimetry, thermo‐optical analysis, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and optical microscopy. It was established that physical interactions are prevalent in blends with a high content of HPC, whereas chemical interactions predominate in blends with a medium and low content of HPC. By increasing the temperature, the thermochemical reactions are favored. Thermal properties are dependent on the mixing ratio of the components. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2585–2597, 2003 相似文献
998.
Z. A. Mohd Ishak P. Y. Wan P. L. Wong Z. Ahmad U. S. Ishiaku J. Karger‐Kocsis 《应用聚合物科学杂志》2002,84(12):2265-2276
Hygrothermally decomposed polyurethane (HD‐PUR) was mixed up to 20 phr in epoxidized natural rubber (with 50 mol % epoxidation; ENR50) recipes, and the curing and mechanical behaviors were studied. Mechanical testing of the ENR50/HD‐PUR vulcanizates determined the tensile, tear, compression‐set, hardness, abrasion, hysteresis, and resilience properties. No significant changes were observed in the tensile properties with the incorporation of HD‐PUR. The ENR50 compounds showed an increase in compression set with increasing HD‐PUR content. Rubbers cured by a semi‐efficient vulcanization system gave the best overall performance. A further improvement in curing and mechanical properties was achieved by the carbon black grade N330 being replaced with a more active grade (N375). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2265–2276, 2002 相似文献
999.
During the preparation of alumina as a catalyst support from aluminium nitrates by precipitation with a NH4OH base, NO
2
⋅
radicals have been formed in the catalyst after calcination under air in the solid at different temperatures. These radicals
remained stable until a calcination temperature of 800°C. When the calcined catalyst was degassed under vacuum above 300 °C,
the NO
2
⋅
was reduced to give NO⋅ and O- species which were both tightly trapped in the solid. These latter species remained stable until vacuum treatment at 800
°C.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
1000.
Caroline Fauquant Valrie Briard Nadine Leconte Marie‐Caroline Michalski 《European Journal of Lipid Science and Technology》2005,107(2):80-86
The aim of this study was to characterize the fatty acid composition of the core and membrane of differently sized milk fat globules separated by microfiltration, which can now be used to manufacture dairy products. Native milk fat globules of various mean diameters, ranging from d43 = 2.3 µm to 8.0 µm, were obtained using microfiltration of raw whole milk. After milk fat globule washing, the milk fat globule membrane (MFGM) and the triglyceride core (TC) were separated by manual churning. After total lipid extraction from each fraction, their fatty acid composition was characterized using methyl ester analysis by gas chromatography. Regardless of season, no significant differences were observed in the fatty acid composition of the MFGM phospholipids. Conversely, significant differences were found in the fatty acid composition of TC; particularly, small fat globule TC contained more medium‐chain fatty acids and less stearic acid than large fat globule TC. These results show that the previously observed differences in total fatty acid composition among differently sized milk fat globules are due to their triglyceride composition and MFGM amount rather than to the composition of the MFGM. 相似文献