High strength papers impregnated with urea/melamine formaldehyde resin/nanosilica nanocomposite coatings: the effects of paper type, blend ratio and nano-content

The aim of this work was to study mechanical properties of two types of papers impregnated with melamine formaldehyde(MF)/urea formaldehyde(UF)/nanosilica nanocomposite coatings. A full factorial experimental design was used to study the effects of the type of paper (mechanical or Kraft), nanosilica content (0,2,4%) and UF:MF weight ratio (60:40, 75:25 and 90:10) on the mechanical properties of the coated papers. The tensile index (TI), breaking length (BL) and tear index (Tin) of the mechanical papers were not affected significantly by addition of nanosilica to the resin while the Kraft paper was more responsive to nanosilica and showed higher mechanical properties. Kraft paper coated with UF:MF 60:40 resin containing 4% nanosilica showed the highest TI, BL and Tin in machine direction among the samples. The microstructure of the mechanical and Kraft papers impregnated with this nanocomposite coating was further characterized by FTIR, XRD, SEM/EDX and AFM. FTIR spectra proved the formation of chemical bonds between the resin and nanosilica in Kraft paper. SEM/EDX and XRD patterns revealed that nanosilica was well dispersed in the nanocomposite coating without any aggregation. The findings of this study suggest that naonsilica can be used as a promising additive for improving the properties of Kraft papers.