Recursos de colección

Estudo Geral - Universidade de Coimbra (19.630 recursos)

ESTUDO GERAL é a designação do repositório digital da produção científica da Universidade de Coimbra, com o objectivo de divulgar conteúdos digitais de natureza científica de autores ligados à Universidade de Coimbra. A sua criação insere-se no movimento de Acesso Livre à Literatura científica (Open Access), ao qual o Conselho de Reitores das Universidades Portuguesas aderiu em 2006 e que a Universidade de Coimbra subscreveu. À semelhança de outras grandes universidades nacionais e internacionais, a UC tem o maior interesse em aumentar a sua presença na rede informática mundial, sendo cada vez mais - e também por essa via - um emissor de conhecimento e cultura.

FCTUC Eng.Química - Artigos em Revistas Internacionais

Mostrando recursos 1 - 20 de 220

  1. An experimental design methodology to evaluate the importance of different parameters on flocculation by polyelectrolytes

    Pinheiro, I.; Ferreira, P.J.; Garcia, F.A.; Reis, M.S.; Pereira, A.C.; Wandrey, C.; Ahmadloo, H.; Amaral, J.L.; Hunkeler, D.; Rasteiro, M.G.
    Aggregation of particles is fundamental for improving the performance of many solid/liquid processes. Aggregation can be induced by different means, and one of the most common is based on the addition of polymeric additives, namely polyelectrolytes. In this work we have studied the flocculation of precipitated calcium carbonate (PCC), which is used as a filler in papermaking, and is induced by a range of cationic polyacrylamides with different structures, varying in molar mass and degree of branching. The flocculation process was monitored continuously using the LDS technique (laser diffraction scattering), which provides information about the size distribution and structure (fractal...

  2. Evaluation of silica-coated PCC as new modified filler for papermaking

    Lourenço, Ana F.; Gamelas, José A. F.; Zscherneck, Christin; Ferreira, Paulo J.
    Silica-coated precipitated calcium carbonate (PCC) prepared by a sol-gel method in a previous study, was used, for the first time, as filler for papermaking. Three samples of modified PCC, containing 11 wt%, 21 wt% and 29 wt% of silica, were prepared. The handsheets produced with an eucalyptus kraft pulp furnish containing the new PCC-based materials showed better paper strength properties than those with the unmodified PCC, whereas the structural properties and brightness were not affected (for similar filler retention values (ca. 80%)). The results suggest that a thin film of silica coating the calcium carbonate crystals has a positive impact...

  3. Industrial Crops and Products

    Ferreira, Paulo J. T.; Gamelas, José A. F.; Carvalho, Maria G. V. S.; Duarte, Gustavo V.; Canhoto, Jorge M. P. L.; Passas, Raphael
    In this work, Ailanthus altissima (tree-of-heaven) wood was analyzed for its chemical, morphological and papermaking properties. The A. altissima wood was cooked under kraft conditions using different active alkali charges and then handsheets were produced with the pulps having a kappa number of 16. Based on structural, strength and optical data it was found that the kraft pulp of A. altissima is not suitable to be used alone for the production of printing and writing papers. Notwithstanding, the handsheets exhibit a favorable value of brightness in comparison to those produced from Eucalyptus globulus pulp (with similar kappa number). Therefore, the...

  4. Inverse gas chromatography and XPS of extracted kraft pulps

    Gamelas, José A.F.; Duarte, Gustavo V.; Ferreira, Paulo J.
    Kraft pulps at the kappa number level of 15 obtained from Acer saccharum (sugar maple) and Eucalyptus globulus prepared with and without hot water pre-extraction (HWE) were analysed by inverse gas chromatography (IGC) and X-ray photoelectron spectroscopy (XPS). In the case of A. saccharum pulps, the dispersive component of the surface energy (γsd) at 40ºC determined by IGC was 39.8 mJ m-2 (control pulp without HWE) and 36.7 mJ m-2 (HWE pulp). E. globulus pulps resulted in γsd values of 30.8 mJ m-2 (control) and 34.9 mJ m-2 (HWE). The higher values of γsd for sugar maple pulps were interpreted...

  5. Supercritical solvent impregnation of poly(ɛ-caprolactone)/poly(oxyethylene-b-oxypropylene-b-oxyethylene) and poly(ɛ-caprolactone)/poly(ethylene-vinyl acetate) blends for controlled release applications

    Natu, Mădălina V.; Gil, M. H.; Sousa, Hermínio C. de
    Poly(ɛ-caprolactone) blends were successfully impregnated with timolol maleate, an anti-glaucoma drug, using a supercritical solvent impregnation (SSI) technique. Supercritical fluid impregnation efficiency results suggested that the best impregnating conditions were obtained when a cosolvent was used and when specific drug–polymer interactions occurred as a consequence of different chemical structures due to polymer blending. Pressure can be either a favourable factor, when there is enough drug affinity for the polymers, or an unfavourable factor when weaker bonding is involved. In order to determine the relative hydrophilicity/hydrophobicity of the blends, contact angle analysis was performed, while crystallinity determination was also useful to...

  6. In vitro and in vivo evaluation of an intraocular implant for glaucoma treatment

    Natu, Mădălina V.; Gaspar, Manuel N.; Ribeiro, Carlos A. Fontes; Cabrita, António M.; Sousa, Hermínio C. de; Gil, M. H.
    Implantable disks for glaucoma treatment were prepared by blending poly(ɛ-caprolactone), PCL, poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) and dorzolamide. Their in vivo performance was assessed by their capacity to decrease intraocular pressure (IOP) in normotensive and hypertensive eyes. Drug mapping showed that release was complete from blend disks and the low molecular weight (MW) PCL after 1 month in vivo. The high MW PCL showed non-cumulative release rates above the therapeutic level during 3 months in vitro. In vivo, the fibrous capsule formation around the implant controls the drug release, working as a barrier membrane. Histologic analysis showed normal foreign body reaction...

  7. Effects of drug solubility, state and loading on controlled release in bicomponent electrospun fibers

    Natu, Mădălina V.; Sousa, Hermínio C. de; Gil, M. H.
    Bicomponent fibers of two semi-crystalline (co)polymers, poly(ɛ-caprolactone), and poly(oxyethylene-b-oxypropylene-b-oxyethylene), were obtained by electrospinning. Acetazolamide and timolol maleate were loaded in the fibers in different concentrations (below and above the drug solubility limit in polymer) in order to determine the effect of drug solubility in polymer, drug state, drug loading and fiber composition on fiber morphology, drug distribution and release kinetics. The high loadings fibers (with drug in crystalline form) showed higher burst and faster release than low drug content fibers, indicating the release was more sustained when the drug was encapsulated inside the fibers, in amorphous form. Moreover, timolol maleate...

  8. Controlled release gelatin hydrogels and lyophilisates with potential application as ocular inserts

    Natu, Mădălina V.; Sardinha, José P.; Correia, Ilídio J.; Gil, M. H.
    Hydrogels and lyophilisates were obtained by chemical crosslinking of gelatin using N-hydroxysuccinimide and N, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride. The systems were characterized with respect to the degree of crosslinking, morphology, water uptake, in vitro drug release and biocompatibility studies. Pilocarpine hydrochloride, a drug for the treatment of glaucoma, was loaded by soaking in an aqueous solution containing the drug. In vitro, the released drug percentage varied between 29.2% and 99.2% in 8 h of study. The release data were fitted to the Korsmeyer–Peppas equation to calculate the release exponent, which indicated anomalous transport for the release of pilocarpine. The corneal endothelial cell...

  9. A poly(ε-caprolactone) device for sustained release of an anti-glaucoma drug

    Natu, Mădălina V.; Gaspar, Manuel N.; Ribeiro, Carlos A. Fontes; Correia, Ilídio J.; Silva, Daniela; Sousa, Hermínio C. de; Gil, M. H.
    Implantable dorzolamide-loaded discs were prepared by blending poly(ε-caprolactone), PCL, with poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), Lu. By blending, crystallinity, water uptake and mass loss were modified relative to the pure polymers. Burst was diminished by coating the discs with a PCL shell. All samples presented burst release except PCL-coated samples that showed controlled release during 18 days. For PCL-coated samples, barrier control of diffusion coupled with partition control from the core slowed down the release, while for 50/50 Lu/PCL-coated samples, the enhancement in the porosity of the core diminished partition control of drug release. Nonlinear regression analysis suggested that a degradation...

  10. Influence of polymer processing technique on long term degradation of poly(ε-caprolactone) constructs

    Natu, Mădălina V.; Sousa, Hermínio C. de; Gil, M. H.
    Films, fibers, sponges and disks, based on poly(ε-caprolactone), PCL were prepared using solvent-casting, electrospinning, supercritical fluid processing and melt-compression, respectively. The extent of degradation was determined by measuring the change in morphology, crystallinity and molecular weight (MW). The influence of processing method, MW and drug presence on degradation rate was also evaluated. The different processing techniques produced samples of various morphology and crystallinity. Nevertheless, the differences in degradation rate were not so significant during the advanced stage (18–36 months), while some differences existed during the initial stage (up to 18 months). MW had an important effect on degradation rate, while...

  11. Preparation and evaluation of biocide-loaded particles to control the biofouling zebra mussel, Dreissena polymorpha

    Costa, R.; Aldridge, D. C.; Moggridge, G. D.
    The freshwater zebra mussel Dreissena polymorpha is a powerful biofouling bivalve, which has tremendous impact on industrial facilities whose operation depends on the intensive use of freshwater, such as waterworks and power stations. The control of the pest in industrial environments remains a major challenge due to low selectivity over non-target organisms and the expense of the large quantities of biocides required. A novel delivery technique involving the encapsulation of a toxin within hundred micron-sized particles, edible for the bivalves, has been recently proposed. This strategy exploits the mussels’ filtration activity and minimises their avoidance responses to certain chemicals, resulting...

  12. Numerical assessment of diffusion-convection-reaction model for the catalytic abatement of phenolic wastewaters in packed-bed reactors under trickling flow conditions

    Rodrigo, J. G. Lopes; Quinta-Ferreira, Rosa M.
    Computational Fluid Dynamics (CFD) modeling of trickle-bed reactors with detailed interstitial flow solvers has remained elusive mostly due to the extreme CPU and memory intensive constraints. Here, we developed a comprehensible and scalable CFD model based on the conservative unstructured finite volume methodology to bring new insights from the perspective of catalytic reactor engineering to gas-liquid-solid catalytic wet oxidation. First, the heterogeneous flow constitutive equations of the trickle bed system have been derived by means of diffusion-convection-reaction model coupled within a Volume-of-Fluid framework. The multiphase model was investigated to gain further evidence on how the effect of process variables such as liquid velocity, surface tension and wetting phenomena...

  13. Properties of extracted Eucalyptus globulus kraft pulps

    Duarte, G. V.; Gamelas, J. A. F.; Ramarao, B. F.; Amidon, T. E.; Ferreira, P. J.
    This work was a comprehensive study of the properties of extracted Eucalyptus globulus kraft pulps. Five levels of hot water extraction were performed, each followed by kraft cooking to three different kappa numbers. As extraction took place, the hemicelluloses content of the kraft pulps was reduced from 21%-22% to 3%-4% and, conversely, the cellulose fraction increased from 73%-75% to 85%-90%. Fiber length decreased for all pulps and kink index increased greatly with extraction. The dispersive components of the surface energy for the control (unextracted) and extracted (120 min) kappa no. 15 kraft pulps, as determined by inverse gas chromatography, were...

  14. Effect of Hot Water Extraction on Hardwood Kraft Pulp fibers (Acer saccharum, Sugar Maple)

    Duarte, Gustavo V.; Ramarao, Bandaru V.; Amidon, Thomas E.; Ferreira, Paulo T.
    This study focuses on the properties of fibers obtained from the kraft pulping of pre-extracted sugar maple wood chips. Hot-water pre-extraction was carried out for different times characterized by P-factors in the range of 12 and 600 h. It was found that pre-extraction of the chips significantly accelerates delignification during Kraft pulping such that the H-factors necessary to obtain equivalent delignification (i.e., the same k numbers) were substantially smaller than control cooks (i.e., with unextracted chips). Unbleached pulps of k numbers of 35, 25, and 15 were prepared, and their papermaking properties were tested. The hemicellulose content of the pulps decreased...

  15. Hygroexpansivity profiles on a commercial paper machine

    Mendes, Afonso H. T.; Park, Song W.; Ferreira, Paulo J. T.; Almeida, Fábio S.

  16. Paper surface chemistry as a tool to improve inkjet printing quality

    Moutinho, Isabel M. T.; Ferreira, Paulo J. T.; Figueiredo, Margarida L. F.

  17. A influência das formulações de revestimento na qualidade de impressão de papéis para jato de tinta

    Ferreira, Paulo; Santos, Natércia; Oliveira, Pedro; Velho, José

  18. Efeito da secagem no potencial papeleiro de pastas Kraft de eucalipto : uma experiência industrial

    Carvalho, M. Graça; Fernandes, João R.; Ferreira, Luís A.; Van Zeller, Carlos A.; Ferreira, João Pinho; Ferreira, Paulo J.T.

  19. Aplicação da microscopia confocal ao estudo de fibras de E. globulus : medição das dimensões transversais

    Ferreira, P.J.; Sousa, M.N.; Vaz, M.H.; Figueiredo, M.M.

  20. Effect of extended cooking and oxigen prebleaching on the surface energy of Eucalyptus globulus Kraft pulp

    Carvalho, M.G.; Ferreira, P.J.; Santos, J.M.R.C.A.; Amaral, J.L.; Figueiredo, M.M.

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