AbstractIn this study, CaCO3 nanoparticle/pulp fiber composites were prepared by formation of ultrafine bubbles of CO2 gas in aqueous Ca(OH)2 solution containing beaten or unbeaten pulp fibers. Scanning electron microscopy images of the fiber/CaCO3 composites showed that primary CaCO3 nanoparticles with average diameters of 50–80 nm densely formed on the pulp fiber surfaces. The average sizes and morphologies of the precipitated CaCO3 nanoparticles can be controlled by controlling the CO2 flow rate into the pulp slurry. From dynamic drainage analysis of the CaCO3/pulp slurries with high shear force, retention of the CaCO3 nanoparticles on the pulp fiber mats was ∼10 % higher for the slurry formed by the ultrafine bubble method than for that formed by mixing precipitated CaCO3 and pulp fiber. Therefore, precipitated CaCO3 nanoparticles stably formed on the pulp fiber surfaces in the slurry by the ultrafine bubble method. Compared with reference handsheets, handsheets prepared with the CaCO3 nanoparticle/pulp fiber composites had higher CaCO3 contents and had consequently higher specific surface areas and surface smoothness values. In contrast, the tensile strength and elongation at break decreased because the sheet density decreased with increasing CaCO3 content in the handsheets.
In recent years, ultraviolet (UV)-curable ink has been developed and widely used in various printing applications. However, using UV-printed products (UV prints) in recovered paper recycling causes end-product dirt specks and quality issues.
A new method was developed that can distinguish UV prints from other prints by means of attenuated total reflectance infrared (ATR-IR) spectroscopy. Application of this method could allow more efficient use of UV prints as raw materials for paper recycling.
First, a mill trial was performed using UV prints alone as raw materials in a deinked pulp (DIP) process. Second, test prints were made with four types of UV inks: a conventional UV ink and three different highly-sensitive UV inks. Each print sample had four levels of four-color ink coverage patterns (100%, 75%, 50%, and 25%). Next, drinkability of all prints was evaluated by laboratory experiments. Finally, each print was measured using the ATR-IR method,
and the relationship between the IR spectra and deinkability was investigated.
Mill trial results showed that UV prints caused more than 20 times as many dirt specks as those printed with conventional oil-based ink. There were variations in recycling performance among UV prints taken from bales used for the mill trial. Lab tests clearly revealed that not all UV-printed products lead to dirt specks.
In order to clarify the factors that affected deinkability of UV prints, the print samples were investigated by lab
experiments. Key findings from lab experiments include:
• The number of dirt specks larger than 250 μm in diameter increased as the ink coverage increased.
• Higher ink coverage area showed stronger intensity of ATR-IR spectral bands associated with inks. These results
indicate that deinkability of UV prints could be predicted by analysis of ATR-IR spectra.
• Finally, the method was applied for assessment of recovered paper from commercial printing presses. It was confirmed that this method made it possible to distinguish easily deinkable UV prints from other UV prints.
Based on these findings, we concluded that the ATR-IR method is applicable for inspection of incoming recovered
paper.
Studies on the synthesis and characterization of a hybrid fi ber (HF) consisting of precipitated calcium carbonate (PCC) and cellulose fi ber were conducted. The PCC-HF has been prepared by modifying the carbon dioxide (CO 2) method for PCC synthesis under high-pressure fl uid-jet cavitation in hardwood bleached kraft pulp (HBKP) slurry. Scanning electron microscopy (SEM) observations of the HF showed that almost all fi ber surfaces were covered with nano-size PCC particles. By using this PCC-HF as raw materials, the handsheet containing more than 50% PCC by weight with a high first-pass ash retention (greater than 80%). Unlike ordinary paper such as printing paper, the sheet showed remarkable physical properties, such as high fl exibility without crumbling despite extreme high ash content. The SEM images from a cross section of the sheet containing 74% PCC revealed that a very little number of fi bers embedded in PCC layer. This implied that the bonding mechanism of HF sheet was diff erent from ordinary paper. In order to clarify the mechanism, the slurry of PCC-HF for handsheet making was separated into two fractions, long fi bers and fi nes, by using the Dynamic Drainage Analyzer (DDA). It was found that the nano-size PCC was attached onto not only the surfaces of the long fi bers but also those of fi ber fi nes. Thus, the PCC-hybrid fi ber fi nes contributed sheet properties and high ash retention.
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