Rafael A. Ozzetti  Antonio Pedro De Oliveira Filho  Ulf Schuchardt  Dalmo Mandelli 《应用聚合物科学杂志》2002,85(4):734-745

A method for determination of tacticity in polypropylene (PP) using FTIR associated with multivariate analysis is presented. Blends of PP with known tacticity were prepared with isotactic, syndiotactic, and atactic polymer and analyzed by ¹³C‐NMR. The FTIR spectra were recorded and processed through principal components regression (PCR) and partial least‐squares regression (PLS), using information from several different portions of the spectra. The method was compared with the classical methods of tacticity determination by FTIR based on the intensities of the bands at 998 cm^?1 (isotactic), 868 cm^?1 (syndiotactic), and 975 cm^?1 (internal standard), which are known to be dependent on the crystallinity of the polymer and, thus, affected by temperature and sample preparation. The models obtained with multivariate calibration, both with PCR and PLS, gave prediction errors up to fivefold smaller than that of the classical methods, and were also shown not to be heavily dependent on the bands that are affected by the crystallinity of the polymer, but rather on the methyl and methylene bendings at 1375 and 1462 cm^?1. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 734–745, 2002  相似文献   

    

Marlene Lopes  Carla Araújo  Mário Aguedo  Nelma Gomes  Cristiana Gonçalves  José António Teixeira  Isabel Belo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2009,84(4):533-537

BACKGROUND: The aim of this work was to study the ability of two different wild type strains of the yeast Yarrowia lipolytica to grow on olive mill wastewater (OMW) and their potential to produce high‐value products such as lipases. Factors that affect cellular growth and OMW degradation were studied, such as nitrogen supplementation, cells concentration and surfactant addition. RESULTS: Both strains, W29 and IMUFRJ 50682, were able to grow in OMW with 19 g L^?1 of COD and approximately 800 mg L^?1 of total phenols concentration. The strain W29 presented the highest potential for extracellular lipase production in OMW medium. Lipase productivity was improved by the medium supplementation with ammonium sulphate up to 6 g L^?1, leading to 80% of COD degradation and 70% of total phenols reduction. The surfactant Tween 80 enhanced cell growth and COD degradation, but had a negative effect on lipase activity. CONCLUSIONS Y. lipolytica has a great potential for OMW valorisation by its use as culture medium for biomass and enzymes production. The operating conditions that favoured lipase production differ from the conditions that improve COD reduction. Copyright © 2008 Society of Chemical Industry  相似文献   

    

Siriyupa Netramai  Maria Rubino  Rafael Auras  Bassam A. Annous 《应用聚合物科学杂志》2009,114(5):2929-2936

The mass transfer profile (permeability, diffusion, and solubility coefficients) of chlorine dioxide (ClO₂), a strong oxidizing agent that is used in food and pharmaceutical packaging, was determined through various common polymeric packaging materials. A continuous system for measuring permeation of ClO₂, using an electrochemical detector, was developed. It was observed that biaxially‐oriented poly(propylene), poly(ethylene terephthalate), poly(lactic acid), nylon, and a multilayer structure of ethylene vinyl acetate and ethylene vinyl alcohol were better barriers for gaseous ClO₂, as compared to polyethylene, poly(vinyl chloride), and polystyrene. The activation energies of permeation for ClO₂ through poly(ethylene terephthalate) and poly(lactic acid) were determined to be 51.05 ± 4.35 and 129.03 ± 2.82 kJ/mol, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, , 2009  相似文献   

    

Rafael L. Quirino  Richard C. Larock 《应用聚合物科学杂志》2009,112(4):2033-2043

The tensile and flexural properties of new thermosetting composites made by the free radical polymerization of a conjugated soybean oil (CSO)‐based resin reinforced with soy hulls have been determined for various resin compositions. The effects of reinforcement particle size and filler/resin ratio have been assessed. The thermal stability of the new materials has been determined by thermogravimetric analysis and the wt % of oil incorporation has been calculated after Soxhlet extraction (the extracts have been identified by ¹H‐NMR spectroscopy). The resin consists initially of 50 wt % CSO and varying amounts of divinylbenzene (DVB; 5–15 wt %), dicyclopentadiene (DCPD; 0–10 wt %), and n‐butyl methacrylate (BMA; 25–35 wt %). Two soy hull particle sizes have been tested (<177 and <425 μm) and two different filler/resin ratios have been compared (50 : 50 and 60 : 40). An appropriate cure sequence has been established by differential scanning calorimetry (DSC) analysis. The results show a decrease in the properties whenever DVB or BMA is substituted by DCPD. Also, larger particle sizes and higher filler/resin ratios are found to have a negative effect on the tensile properties of the new materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

    

S. V. Jaecques  J. A. Helsen  J. Teixeira 《应用聚合物科学杂志》1996,61(5):819-826

Two thermoplastic polyolefin elastomers, Santoprene™ 281–82 and Sarlink™ 3280, were studied by small-angle neutron scattering (SANS) and swelling. Sorption was performed in 3% (volume/volume) aqueous acetic acid (HAc) solutions at 65°C. Increase in mass and volume were followed separately. For SANS studies, swelling was also performed in D₂O solutions of HAc. Samples were subjected to mechanical fatigue, causing mainly shear stresses. A Sarlink variety with partly deuterated mineral oil was prepared to study by SANS the influence of fatigue on distribution of the oil. Absorption of the HAc solution follows Type I Fickian diffusion. Diffusion coefficients D, calculated in three ways, revealed a discrepancy between values obtained from measurements of mass or volume increase. D values were of a 10⁻¹³m²/s order of magnitude. Influence of fatigue on D was not significant, although saturation liquid uptake differed markedly between fatigued and control samples. Also, remarkable differences between control Sarlink and Santoprene in saturation uptake were observed. From SANS experiments, no influence of fatigue on void size or distribution, or on distribution of mineral oil, could be observed. However, marked differences between control Sarlink and Santoprene was observed when data were interpreted in terms of fractal dimensions of phase boundaries. © 1996 John Wiley & Sons, Inc.  相似文献   

    

Galia Salzman  Rafael Tadmor  Serge Guzy  Samuel Sideman  Noah Lotan 《Chemical Engineering and Processing: Process Intensification》1999,38(4-6):289-299

The use of immobilized enzyme reactors in biotechnology and biomedicine is rapidly expanding. This study concentrates on hollow-fiber (HF) enzymic reactors for continuous, single-pass operation. The enzyme, in a soluble form, is physically confined within the shell section of the reactor and the substrate solution flows through the lumen section of it. We consider here a two-substrate reaction proceeding via the Ping-Pong mechanism, with substrates and reaction products diffusing through the fiber wall. The developed analytical model enables to calculate the expected conversion as a function of the volumetric flow rate, kinetic constants, diffusion coefficients, geometric dimensions of the reactor, the flow regimen in the apparatus and substrates concentrations. The model equations are solved by a numerical procedure and the system performance is simulated. Depending on the operation conditions employed, the reactor is controlled by kinetic processes, diffusion processes, or both.  相似文献   

    

Renn Arriagada  Rafael García 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1999,74(9):870-876

The rate and equilibrium retention of pentachlorophenol, in an aqueous medium, by activated carbons obtained from peach stones and Eucalyptus globulus chips are studied and related to the chemical and textural properties of the adsorbents. E globulus‐activated carbons exhibited a higher pentachlorophenol initial retention rate, due to the higher contribution of the macropores to the porosity of these materials. However, the pentachlorophenol retention rate in activated carbons from peach stones increases to a greater extent than in E globulus with the burn‐off growth, due to the greater development of mesopores in the former. Under the experimental conditions used, the initial retention rate of pentachlorophenol in both adsorbents showed a mixed chemical and diffusional dependence, and the most important variables are the particle size of the adsorbents and the temperature of the medium. Pentachlorophenol equilibrium retention capacity depends on the apparent specific surface area, the presence of carbonylic‐like surface functional groups and the accessibility of the adsorbate to the adsorption sites. The dependence of pentachlorophenol retention capacity with the surface concentration of carbonylic functional groups suggests some chemical interactions between the aromatic pentachlorophenol ring and the carbonylic‐like surface functional groups present in the activated carbons. © 1999 Society of Chemical Industry  相似文献   

    

Antnio A. Vicente  Marin Dluhý  Jos A. Teixeira 《加拿大化工杂志》1999,77(3):497-502

Static mixers were introduced in the draught tube of a three-phase, concentric tube type airlift bioreactor, resulting in a 30% increase in ethanol productivity during glucose fermentation with a highly flocculent strain of Saccharomyces cerevisiae. Increased productivity was obtained as a consequence of the floe size reduction provoked by the new design of the draught tube and of the smaller applied aeration rates, allowing a higher dilution rate to be used. Steady state data at different dilution rates were measured for both systems and the results were compared in terms of specific consumption / production rates and ethanol productivity. An approach based on heterogeneous catalysis principles was used in order to consider the presence of porous yeast flocs. Total glucose conversion was achieved at a dilution rate of 0.34 h^?1. The smaller floe size contributed to the higher observed reaction rates by reducing diffusional limitations inside the flocs. The respiratory quotient had a constant value (around 23) at all dilution rates, meaning that the metabolic state of the cells in the flocs remained constant, having a strong fermentative metabolism.  相似文献   

    

Alberto García-Villoria  Rafael Pastor 《国际生产研究杂志》2013,51(16):4911-4920

The response time variability problem (RTVP) is a scheduling problem that has a wide range of real-world applications in mixed-model assembly lines, multi-threaded computer systems, machine maintenance, waste collection and others. The RTVP arises whenever products, clients or jobs need to be sequenced in such a way that the variability in the time between the points at which they receive the necessary resources is minimised. The RTVP has been demonstrated to be NP-hard and heuristic and metaheuristic techniques are needed to solve large, real-life instances. The best results, on average, in the literature for the RTVP were obtained with variable neighbourhood search hybidised with multi-start. Several algorithms based on simulated annealing are proposed to solve the RTVP. An extensive computational experiment is carried out and it is shown that the solution of the RTVP is clearly improved.  相似文献   

    

Amaia Lusa  Albert Corominas  Rafael Pastor 《国际生产研究杂志》2013,51(8):2123-2142

Annualizing working hours (AH) is a means of achieving flexibility in the use of human resources to cope with the seasonal nature of demand. Some existing planning procedures are able to minimize costs through the use of overtime and temporary workers. However, due to the great difficulty in solving the problem, it is normally assumed both that holiday weeks are fixed beforehand and that workers from different categories who are able to perform a specific type of task have the same efficiency. Often the reality is different, and thus there is a gap between academic and real problems. In the present paper, those constraints are relaxed and a much more general and true-to-life problem is solved in an exact and very efficient way.  相似文献