Tapio Saarinen

Flocculated flow of microfibrillated cellulose water suspensions: an imaging approach for characterisation of rheological behaviour

Our aim was to characterise the suspension rheology of microfibrillated cellulose (MFC) in relation to flocculation of the cellulose fibrils. Measurements were carried out using a rotational rheometer and a transparent cylindrical measuring system that allows combining visual information to rheological parameters. The photographs were analyzed for their floc size distribution. Conclusions were drawn by comparing the photographs and data obtained from measurements. Variables selected for examination of MFC suspensions were degree of disintegration of fibres into microfibrils, the gap between the cylinders, sodium chloride concentration, and the effects of changing shear rate during the measurement. We studied changes in floc size under different conditions and during network structure decomposition. At rest, the suspension consisted of flocs sintered together into a network. With shearing, the network separated first into chain-like floc formations and, upon further shear rate increase, into individual spherical flocs. The size of these spherical flocs was inversely proportional to the shear rate. Investigations also confirmed that floc size depends on the geometry gap, and it affects the measured shear stress. Furthermore, suspension photographs revealed an increasing tendency to aggregation and wall depletion with sodium chloride concentration of 10−3 M and higher.

Network formation of nanofibrillated cellulose in solution blended poly(methyl methacrylate) composites

Composites of poly(methyl methacrylate) (PMMA) and nanofibrillated cellulose (NFC) were prepared by solution blending and further processed by injection and compression molding. To improve adhesion at the PMMA/NFC interface, the nanofibrils were covalently grafted with PMMA. Formation of a percolating nanofibril network was observed between 1 and 5 wt.% of NFC by dynamic rotational rheometry in molten state. This observation was further supported by the behavior of glass transition temperature which decreased at low NFC concentrations but recovered above the percolation threshold, indicating a decreased mobility of the matrix polymer. This effect was more pronounced with ungrafted NFC, possibly due to a stronger network. The unmodified NFC induced a minor degradation of the molar mass of PMMA. As thin plates, the composites were transparent at low NFC concentrations but became partially aggregated at the highest NFC concentrations. Despite the continuous NFC network, tensile testing showed no improvement of the mechanical properties.

Modifying the flocculation of microfibrillated cellulose suspensions by soluble polysaccharides under conditions unfavorable to adsorption

Carboxymethylcellulose (CMC) and xanthan gum were studied as dispersants for microfibrillated cellulose (MFC) suspension using a rotational rheometer and imaging methods. The imaging was a combination of photography and optical coherence tomography (OCT). Both polymers dispersed MFC fibers, although CMC was more effective than xanthan gum. The negatively charged polymer chains increased the viscosity of the suspending medium and acted as buffers in between the negatively charged fibers. This behavior decreased the number and strength of contacts between the fibers and subsequently dispersed the flocs. The stronger separation of the fibers was reflected in the frequency sweep where the MFC/polymer suspensions had lower gel strength than pure MFC suspension. Dispersing effect was also observed in the flow measurements, where the floc size was more uniform with polymers in the decelerating flow and after long, slow constant shear, which normally induces a heterogeneous structure with large flocs into the MFC suspension.

Erratum to: Surface functionalization of nanofibrillated cellulose using click-chemistry approach in aqueous media (Cellulose, (2011), 18, 5, (1201), 10.1007/s10570-011-9573-4)

The article “Surface functionalization of nanofibrillated cellulose using click-chemistry approach in aqueous media”, written by Nikolaos Pahimanolis, Ulla Hippi, Leena-Sisko Johansson, Tapio Saarinen, Nikolay Houbenov, Janne Ruokolainen and Jukka Seppälä, was originally published Online First without open access.

Erratum to: Flocculated flow of microfibrillated cellulose water suspensions: an imaging approach for characterisation of rheological behaviour (Cellulose, (2012), 19, 3, (647-659), 10.1007/s10570-012-9661-0)

The article “Flocculated flow of microfibrillated cellulose water suspensions: an imaging approach for characterisation of rheological behaviour,” written by Eve Saarikoski, Tapio Saarinen, Juha Salmela and Jukka Seppälä, was originally published Online First without open access.

Erratum to: Effect of cationic polymethacrylates on the rheology and flocculation of microfibrillated cellulose (Cellulose, (2011), 18, 6, (1381-1390), 10.1007/s10570-011-9597-9)

The article “Effect of cationic polymethacrylates on the rheology and flocculation of microfibrillated cellulose”, written by Anni Karppinen, Arja-Helena Vesterinen, Tapio Saarinen, Pirjo Pietikäinen and Jukka Seppälä, was originally published Online First without open access. After publication in volume 18, issue 6, pages 1381–1390, the author decided to opt for Open Choice and to make the article an open-access publication. Therefore, the copyright of the article has been changed to

Erratum to: Flocculation of microfibrillated cellulose in shear flow

The article “Flocculation of microfibrillated cellulose in shear flow”, written by Anni Karppinen, Tapio Saarinen, Juha Salmela, Antti Laukkanen, Markus Nuopponen and Jukka Seppälä, was originally published Online First without open access.