Molecular absorption spectroscopy d

Molecular absorption spectroscopy data in the ultraviolet (UV) and visible (VIS) range of wavelengths are presented in Figure 4 for spruce nanopaper prepared from PAA and enzymatic CNF nanopaper. The optical transparency of PAA CNF nanopaper is significantly improved compared with enzymatic CNF nanopaper over the entire range of wavelengths. For both materials, the optical transparency was gradually increased with longer wavelength. In the case of spruce PAA CNF nanopaper, the transmittance at 800 nm reached 80%, approaching to the reported value for TEMPO-oxidized cellulose nanopaper at about 90%.43 One should also note that the present films have substantially larger thickness, so the results may be very similar to TEMPO CNF nanopaper. The demonstration photograph in Figure 4 illustrates the substantialdifference in apparent optical transparency between the two materials. The enzymatic CNF colloid, and corresponding nanopaper, certainly contain a fraction of CNF agglomerates as indicated by a peak in the dynamic light scattering data at 400 nm.15 PAA holocellulose CNF show uniform and small diameter of the CNFs, as demonstrated in the AFM height profile data.The high content of hemicelluloses on not only has positive influence on nanofibrillation behavior,but may also stabilize the PAA holocellulose CNF in colloidal suspension. The effect may be partly sterical, but the PAA CNF also has a charge of 207 µ eg/g, see Table 2. This adds electrostatic repulsion as a contributing mechanism. CNF agglomeration becomes limited in the colloid and in the solid film, resulting in high optical transparency.