After 1st step of wetting and drying, except sample B, other samples treated with single solvent (A, C, D) show intense light blue-orange color. Moreover, paper samples treated with proportional mixtures of EtOH, MeOH and NaOH (EJ) have various levels of intermediate orange to dark orange color. This is clear evidence that addition of alkali to acidic condition affects the increase of pore size of fibers. Because Direct Blue I has smaller molecular size (ca. 1 nm) and weaker affinity for cellulose compared to Direct Orange 15 which has larger molecular size (5-36 nm) and stronger affinity. But after 5th step of wetting and drying, most of the samples were dyed dark blue to light blue-orange, with the exception of sample F (EtOH-NaOH, 1:3 by vol), which dyes fibers intermediate orange and slightly dark orange. This is clear evidence that increasing alkali concentration in acidic solvents can have fiber pore size restoring effects and less damaging effects with continued drying and wetting. It has taiwan email list already been indicated above that, Direct Orange 15 molecules can be preferentially adsorbed on the fiber surface where the pore size is appropriate (e.g. >5 nm) to access the Direct Orange 15 molecules. For small capillary pores (e.g. <5 nm), where Direct Orange 15 molecules are not accessible, Direct Blue I molecules can be adsorbed. Therefore, the ratio of adsorbed Direct Orange 15 to adsorbed Direct Blue I is anticipated to serve as an indicator of the pore structure, specifically, the pore size population distribution of the paper. The results of Simons stains generally correlate with the strength and sorption properties of papers (Figures 1-5).
The FTIR spectra of solvent-treated paper samples of various levels were obtained in the range of 400–4000 cm−1. However, the characteristic spectrum of the concentrated cellulose structure in the range of 800–2000 cm−1 and the main peaks in this range had been identified. Comparative FTIR spectra of various solvent-treated papers after the 5th repeated drying–wetting step are shown in Figure 7(ag).
Comparative FTIR spectrum of papers treated with solvent mixture systems.
All spectra exhibit multimodal absorption in the 600–1000 cm−1 region due to OH groups in cellulose. The out-of-plane CH vibration was assigned at 750 cm−1. The band at 900–1150 cm−1 is attributed to out-of-plane CC stretching, CCO stretching at 1060 cm−1; symmetric COC stretching at 1150 cm−1 (Figure 7a). However, the spectra of solvent-treated samples (