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The influence of nanofibrillated cellulose (NFC) was investigated as a reinforcing agent to improve strength properties of papersheets fabricated from recycled pulp fibers of mixtures of old newspapers, old magazines, and old corrugated cardboards. To determine the effects of the NFC on the mechanical and physical properties of the recycled pulp papers, cellulose nanofibrils (NFC) were isolated from wheat straw, pretreated chemically and enzymatically (NFC-OX), and then added to the bulk suspensions of papermaking pulp slurries at various percentages. The electrokinetic and drainage properties of the pulps and the mechanical and physical properties of the papersheets were analyzed and compared. As expected, the addition of NFC/NFC-OX significantly increased the strength properties of papers. Papers containing 4% of NFC-OX (periodate pretreated) presented higher increases in tensile index (43%) and burst index (59.3%) than other papers. However, a high addition of NFC/NFC-OX increased the water retention, which is undesirable for papermaking. Hence, with optimum selection of NFC/NFC-OX and process conditions, higher mechanical properties could be acquired without increasing drainage rate. Compared to the other pretreated NFC/NFC-OX types, sodium-periodate-oxidized NFC-OX samples significantly increased the mechanical properties of the papers fabricated from the recycled pulps. TUBITAK-TEYDEBTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [1505, 5180044] The authors would like to thank to KMK Paper Co. for their kind support and provision of recycled pulps. This work was supported by TUBITAK-TEYDEB 1505 (The Scientific and Technological Research Council of Turkey, Technology and Innovation Funding Programs Directorate 1505), Project No. 5180044. WOS:000616046900065

Research has been undertaken to investigate how the tensile strength efficiency and Z-strength efficiency in twin-wire roll forming is affected when changing formation through the softwood kraft content in a mixture with recycled pulp. The effect of a change in formation through the softwood kraft content and the effect of a change in formation through headbox consistency were also compared. Five kraft contents (0, 25, 50, 75 and 100%) were investigated at volumetric headbox flow rates of 111 and 1,77l/sm. Three additional flow rates were used at a kraft content of 50%. Impaired formation through the softwood kraft content reduced tensile strength efficiency and Z-strength efficiency. Both these properties were similarly affected whether the formation was changed by the softwood kraft content or the headbox consistency. The relative impact of formation was larger for Z-strength efficiency compared with tensile strength efficiency. The reduction in tensile strength efficiency was replicated in a smaller relative increase in tensile strength for machine-made paper than for handsheets made of the furnish. Considering the effect on strength efficiency when evaluating furnishes has been demonstrated as an important concern.

In this work, we studied the infl uence on the mechanical and physical properties of paper made of pulp from recycled cardboard and paper (printing/writing and newsprint) by adding different percentages of nanofi brillated cellulose. For each type of recycled pulp, we formed paper with incorporation of 0, 5 and 10 wt% nanofi brillated cellulose. The results showed that addition of nanofi brillated cellulose reduced the paper thickness and increased the density values. Papers with nanofi brillated cellulose presented resistance properties with values statistically superior to the treatments without addition. Addition of 10 % provided the best results, with improvement of tensile, burst and tear resistance of 97, 133 and 104 %, respectively, in comparison to normal papers. The paper produced with the recycled newspaper pulp had lower increase in mechanical properties from the nanofi brillated cellulose in relation to the papers with recycled pulp from cardboard and printing and writing paper. The considerable improvement in the mechanical properties is related to the increase of hydrogen bonds between the fi bers and nanofi bers, forming a dense network, resulting in greater surface area of nanofi brillated cellulose.

White ledger is white-grade recycled pulp that replaces the bleached kraft pulp (BKP) that typically forms the top ply of duplex boards. However, sheets made from white ledger are inferior in strength compared with those made from virgin pulp. Therefore, it is necessary to select a proper additive in order to overcome the disadvantages of using white ledger. In this study, the physical properties of white ledger used at a mill that produced duplex boards were analyzed. The effect of cationic polyacrylamides (C-PAMs) with different charge densities and molecular weights on first-pass retention and paper strengths was simultaneously measured. White ledger contains fiber fines and filler fines, which reduced the strength of paper made from white ledger compared with paper made with BKP. This indicates that the improvement of first-pass retention and paper strength is important when the amount of white ledger increases in the top ply of a duplex board. The charge density of C-PAM, which acts as a retention aid, is more important than its molecular weight in terms of improving the first-pass retention and paper strength of white ledger. The charge density of C-PAM must be high enough to catch anionic fine particles.

The use of waste fibers for the reinforcement of brittle matrices is considered opportune for the sustainable management of urban solid residues. This paper examines the microstructure and mechanical properties of a composite material made of gypsum reinforced with cellulose fibers from discarded Kraft cement bag. Two different kinds of gypsum were used, natural gypsum (NG) and recycled gypsum (RG), both with an addition of 10% by mass of limestone. For the production of samples, slurry vacuum de-watering technique followed by pressing was evaluated revealing to be an efficient and innovative solution for the composites under evaluation. The composite was analyzed based on flexural strength tests, scanning electron microscopy (SEM) imaging, secondary electron (SE) detection, and pseudo-adiabatic calorimetry. The morphology of the fractured surfaces of flexural test samples revealed large gypsum crystals double the original size surrounding the fibers, but with the same overall aspect ratio. Natural fibers absorb large amounts of water, causing the water/gypsum ratio of the paste to increase. The predominance of fiber pullout, damaged or removed secondary layers and incrusted crystals are indicative of the good bonding of the fiber to the gypsum matrix and of the high mechanical resistance of composites. This material is a technically better substitute for the brittle gypsum board, and it stands out particularly for its characteristics of high impact strength and high modulus of rupture.

The aim of this work is to study the reinforcement capacity of pulps obtained from Hesperaloe funifera using a simple and low energy consumption process (chemi refiner mechanical pulping) once they are added in different percentages to recycled pulps from newspaper and from old corrugated containers (OCC). Pinus radiata kraft pulp was used as a referent reinforcement material. H. funifera acted as a reinforcement material in newspaper and OCC recycled pulps, improving their optical and mechanical properties. While a 25% of H. funifera was the optimal amount added to reinforce the OCC pulp, only a 10% was needed for newspaper pulp. However, the OCC optimal mixture was better reinforced as it showed higher increase in all properties than the optimal newspaper mixture, apart from tensile index. Finally, all mixtures with P. radiata kraft pulp produce handsheet with lower properties, apart from tear index, suggesting than H. funifera is a better reinforcement material. El objetivo de este trabajo es estudiar la capacidad de refuerzo de pastas de Hesperaloe funifera obtenidas mediante un proceso simple de bajo consumo energético (pasteado químico-mecánico de refino) una vez añadidas en diferentes porcentajes a pastas recicladas de periódicos y de cartón ondulado (OCC). Se utilizó como material de refuerzo de referencia pasta kraft de Pinus radiata. H. funifera mejoró las propiedades ópticas y mecánicas de todas las pastas recicladas estudiadas, demostrando su capacidad de refuerzo. Mientras que un 25% de H. funifera fue la cantidad óptima para reforzar la pasta de OCC, sólo un 10% fue necesario para la pasta de periódicos. Sin embargo, la mezcla óptima de OCC mostró un mayor incremento en todas las propiedades que la mezcla óptima de periódicos, a excepción del índice de tracción. Por último, todas las mezclas de pasta kraft de P. radiata proporcionaron hojas con menores propiedades mecánicas, a excepción del índice de desgarro, lo que sugiere que H. funifera es un material de refuerzo más eficaz.

Twelve samples of collected waste papers used for paper manufacturing were analysed. The PCDD/F values ranged from 2.96 to 9.97 ng I-TE/kg dry matter. All samples showed a different pattern of PCDD/Fs compared to those of chlorine bleached pulps, therefore it is obvious that the measured PCDD/F levels could be caused by different contamination sources during former processing and use. The investigation of two carbon-less copy papers showed only low amounts of PCDD/F, 0.88 and 7.27 ng I-TE/kg, respectively. The PCDD/F values of four printing ink samples ranged between 17.5 to 90.1 ng I-TE/kg application mixture, whereby all samples showed the same PCDD fingerprints as found in the waste paper samples. In a sample of sodium pentachlorophenate (PCP-Na) very high amouts (3 374 μg I-TE/kg) were measured. It could be clearly shown that the use of pentachlorophenol (and its sodium salt) and printing inks cause an additonal PCDD/F input into the waste paper and therefore in recycled pulp products, too.