Role of the aggregation behavior of hydrophobic particles in paper surface hydrophobation

Three types of hydrophobic particles with different charge, i.e. cationic (SP+), anionic (SP-) and amphoteric (SPA) have been synthesized by emulsion polymerizations and evaluated in paper surface hydrophobation performance (frequently referred to as surface sizing). The surface sizing evaluation was done according to a well-established process, i.e. mixing of the particles with negatively charged starch followed by application in a conventional puddle size press using a fine paper grade containing calcium carbonate filler as model system. Prior to the application, the particles were characterized by light scattering and the surface charge was determined by particle charge density titrations and ζ-potential measurements. The SP+ particles were determined to be 30. nm in diameter while SP- and SPA particles were around 65. nm. Their colloidal behavior in the presence of anionic starch differed. The SP+ particles formed aggregates via bridging flocculation up to a charge ratio of 1:1 of starch:particles. At higher starch content the aggregates were partly redispersed. The SP- and SPA particles showed no sign of aggregation in the presence of anionic starch. In addition, the sizing performance of the different particles was evaluated by assessing the decrease of water uptake in a surface treated paper as well as water contact angle measurements on the paper surface. All three types of particles decreased the water penetration. However, the SP+/starch mixtures showed superior performance, which was attributed to a stronger sensitivity to the high electrolyte concentration usually found in the vicinity of the paper surface when the semi-soluble minerals composing the filler are exposed to water

Using Hansen solubility parameters to predict the dispersion of nano-particles in polymeric films

We suggest a rough and straightforward method to predict the dispersibility of modified cellulose nanocrystals (CNC) in nanocomposites using Hansen solubility parameters (HSP). The surface of CNC was modified using a novel approach where Y-shaped substituents with two different carbon chain lengths were attached to the surface. Approximate HSP values were calculated for the modified CNC, and dispersions of unmodified and modified CNC in solvents with varying HSPs were studied. The best dispersibility was observed in dichloromethane, when the CNC surface was modified with longer carbon chains. Dichloromethane has HSP similar to low-density polyethylene (LDPE). Nanocomposites with both unmodified and modified CNC were produced. The materials with modified CNC showed increased adhesion between the filler and the matrix, followed by a decreased water permeability compared to unmodified CNC, suggesting a better dispersibility of modified CNC in LDPE and confirming the usefulness of this approach

A family of double-bowl <i>pseudo</i> metallocalix[6]arene discs

We report the synthesis and magnetic characterisation of a series of planar [M7] (M = NiII, ZnII) disc complexes [Ni7(OH)6(L1)6](NO3)2 (1), [Ni7(OH)6(L1)6](NO3)2·2MeOH (2), [Ni7(OH)6(L1)6](NO3)2·3MeNO2 (3), [Ni7(OH)6(L2)6](NO3)2·2MeCN (4), [Zn7(OH)6(L1)6](NO3)2·2MeOH·H2O (5) and [Zn7(OH)6(L1)6](NO3)2·3MeNO2 (6) (where HL1 = 2-iminomethyl-6-methoxy-phenol, HL2 = 2-iminomethyl-4-bromo-6-methoxy-phenol). Each member exhibits a double-bowl pseudo metallocalix[6]arene topology whereby the individual [M7] units form molecular host cavities which are able to accommodate various guest molecules (MeCN, MeNO2 and MeOH). Magnetic susceptibility measurements carried out on complexes 1 and 4 indicate weak exchange between the NiII centres