Size-selective absorption into pigmented coating structures: suspension starch polymer vs. nanofibrillar cellulose, 2012 Advanced Coating Fundamentals Symposium

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The use of nano- or microfibrillar cellulose (NFC or MFC) in papermaking is generally hampered by high cost and potentially wasteful use in typical wet end applications. The solubility and fines nature of the material makes it inefficient to retain, and when retained it is generally inefficiently applied within the spatial distribution of the paper fibre matrix. The benefits of capturing the important NFC in a layer structure to enhance surface and stiffness properties of paper and board whereby NFC is entrapped at the surface of a fibrous web by forming an in-situ composite, was previously shown, consisting in the exemplified case of modified calcium carbonate (MCC), [1]. The NFC can integrate itself within the porous structure providing excellent holdout and thin layer continuity, essential in developing an efficient concentration of the NFC at the surface of the substrate. The effect is likened to the well-known I-beam construction.

The absorptive layer in the previous work [1] was comprised of an inkjet MCC pigment. This need not be the case, as any pigment coating structure that absorbs and holds the NFC creating an in-situ composite could be used. The aim of this study is to look at a range of different pigments and investigate how these could be used as coating structures by measuring the effect on the pore structure before and after absorbing NFC or starch into porous tablet blocks made from the respective coating formulations. The effect of water alone on the coating structure has also been measured as a comparison. The results illustrate the size-exclusion properties of the pore structure in relation to the material being absorbed, and describe the distribution of the absorbate throughout the pore network, which is deemed critical in respect to controlling the end performance properties, be they, for example, barrier applications or strength applications, or both.