Cellulose (2018) 25:3595–3607
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Structural and mechanical properties testing
Post-treatment
Paper samples were conditioned according to ISO 187:1990 standard. All properties were determined in accordance with adequate ISO standards: • Thickness and apparent density (ISO 534:2005) • Tensile index and elongation (ISO 1924-2:2008) • Elmendorf tear resistance (ISO 1974:1990) • Bendtsen surface roughness (ISO 8791-2:1990) • Bendtsen air permeance (ISO 5636-3:1992) • Folding endurance (Schopper device—ISO 5626:1993) • Bursting strength (ISO 2758:2001) PG-X Goniometer of Testing Machines Inc. was used for contact angle measurements. The tests were carried out according to TAPPI T 458 standard method.
Two post-treatment methods were employed. In the first one, marked as NH (No Heating), the solvent was washed out immediately after the coating application. In the second method, marked as HA (Heating Applied), before the washing out operation, coated papers were subjected to heating at a temperature of 80 ± 2 C for a time period of 5, 10, 20, 40 or 60 min. The applied procedures are shown in Fig. 1. Heating stages were added in order to keep the cellulose solution in a liquid state to observe possible effects related to the further interactions between paper and NMMO. In particular, it was expected that cellulose from the solution would migrate in the presence of NMMO, and that the solvent itself could also interact with cellulosic fibers. The samples of coated paper were exposed to heat treatment in a KBC-32 drier of WAMED, Poland. NMMO removal from the cellulose coating was carried out by means of immersing a sample of coated paper in a water bath at a temperature of 37 C ± 2 C for 120 s. The duration and temperature of the washing bath was selected based on the conducted experiments. According to the study, under the chosen conditions, it was possible to remove all NMMO in a relatively short time and to obtain reproducible sample properties.
SEM analysis
The observation of the paper surface was performed with the use of Scanning Electron Microscope (SEM) VEGA3-SBU. The samples for SEM examination were gold- and palladium-coated using ‘Mini’ Sputter Coater/Glow Discharge System SC7620.
Results and discussion
The influence of cellulosic coating on the properties of paper products was studied. Additionally, the effect of the coating post-treatment (heating), carried out before the solvent washing-out operation, was investigated.
Fig. 1 Diagram of the research
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