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Pinheiro I.,University of Coimbra | Ferreira P.J.,University of Coimbra | Garcia F.A.,University of Coimbra | Reis M.S.,University of Coimbra | And 4 more authors.
Powder Technology | Year: 2013

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 dimension) of the aggregates, for each sampling instant and, thus, about the kinetic curve for the flocculation process. This information has then been used to produce a model, based on an experimental design strategy, which allows us to relate flocculation efficiency with the PEL characteristics and concentration. The Partial Least Squares (PLS) regression method was selected to perform the regression, given the significant co linearity among the input variables. The results obtained lead us to conclude that the polymer intrinsic viscosity (related with the PEL molar mass and charge density, and supplying information about the volume of the polymer molecule in the solution) and the degree of branching are the parameters with a stronger influence on flocculation efficiency. The PLS models developed were also successfully validated using an independent data set, which provides confidence on their consistency and prediction accuracy. © 2012 Elsevier B.V. Source


Sousa S.,University of Beira Interior | de Sousa A.M.,RAIZ Institute of Forest and Paper Research | Reis B.,RAIZ Institute of Forest and Paper Research | Ramos A.,University of Beira Interior
Medziagotyra | Year: 2014

With surface sizing process, the paper surface can be tailored in order to achieve excellent print quality. Present study reports paper surface modifications carried out by surface sizing treatment with formulations composed by different polymer binders systems and subsequent evaluation of inkjet print quality of the produced papers. Binders as cationic starch (used on surface sizing in paper mill) and polyvinyl alcohol (used as binder in coating process) had been used in order to improve the inkjet print quality. These binders systems provide papers with different structure and physical-chemical properties and as consequence differentiated print quality. Parameters, such as, line width, blur, raggedness, inter-color bleed, circularity and dot gain, gamut area and optical printing densities were measured and correlated with the structural and physical-chemistry features of the paper samples. The results revealed higher performance of the paper surface sized with only polyvinyl alcohol. Multivariate analysis demonstrates that hydrophilicity and roughness are properties particularly detrimental for gamut area. Source


Sousa S.,RAIZ Institute of Forest and Paper Research | De Sousa A.P.M.,RAIZ Institute of Forest and Paper Research | Koskela J.P.,University of Oulu | Vaz A.,University of Beira Interior | Ramos A.,University of Beira Interior
Appita Journal | Year: 2010

The present study reports the performance of a new surface sizing agent, quaternary ditallow methyl epoxypropyl ammonium halogens (EPK2), in relation to styrene acrylate latex (S/A), used as reference. Surface sizing was carried out in a lab size press and the treated papers were characterised by surface energy, ink affinity and print quality. Different paper surface acid-base characters have been found for EPK2 and S/A surface treated papers. In printing tests, EPK2 presents better line performance and dot quality, lower ink spreading compared with S/A latex, but lighter intensity in colour reproduction. Source

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