Recycled Pulp Research Articles

Properties of Cementitious Composite Reinforced with Recycled Pulp from Beverage Cartons

This study presents a comprehensive evaluation of the effects of the refining level of recycled pulp from beverage cartons (RPBC) on the properties of its cementitious composite. The RPBC with various freeness levels, ranging from 400 to 650 mL of the Canadian Standard Freeness test method (CSF), was prepared using a high-speed fruit blender. The specimens were formed by the slurry de-watering method with 8wt% fiber content and mortar matrix with a sand-to-cement ratio of 1:1. The key findings reveal that the cementitious composites reinforced with the RPBC exhibited a maximum value of flexural strength of 11.17 MPa and the freeness of 550 mL CSF. The fracture toughness values of the RPBC composites were significantly improved compared to that of the control specimen. However, the values decreased by about 14% to 20 % as the freeness reduced from 650 to 400 mL CSF. The bulk density and porosity of the RPBCC were not significantly affected by the freeness of RPBC.

Valorizing recycled paper through chitosan and glyoxal-chitosan treatments: Synergistic effects on mechanical and physical properties

The present study investigates the efficacy of chitosan and glyoxal-crosslinked chitosan (Chi-Gly) as reinforcing agents for enhancing the mechanical, physical, and functional properties of recycled paper. The research aims to evaluate the comparative performance of these two forms of chitosan in imparting strength characteristics and improved functionality to recycled paper substrates. Chitosan and Chi-Gly solutions prepared via glyoxal crosslinking were incorporated into recycled pulp suspensions at varying dosages. Laboratory handsheets were fabricated, and their properties were systematically evaluated through mechanical testing, morphological analysis, wettability measurements, and antibacterial assays. The results demonstrated significant improvements in the tensile index, burst index, and bending resistance for the chitosan and Chi-Gly treated papers, with the Chi-Gly exhibiting superior reinforcement. Notably, the Chi-Gly treated paper exhibited a higher wet tensile index and lower water absorption capacity than the control. SEM analysis revealed a denser, more cohesive fiber network facilitated by chitosan and Chi-Gly, aiding the reinforcement. The treated papers exhibited reduced hydrophobicity and pronounced antibacterial activity against E. coli (a gram-negative bacterium) and S. aureus (a gram-positive bacterium), with the Chi-Gly treatment outperforming chitosan. Notably, the treatments improved the functional properties without negatively impacting optical brightness. The findings highlight the synergistic effects of glyoxal crosslinking on chitosan’s reinforcing ability and the potential of these biopolymers as sustainable and multifunctional additives for the recycled paper industry.

Evolution law of conductivity value in wet-end system of recycled pulp and its regulation strategy

The closed cycle of white water in the paper-making process is an important way to reduce material loss, water consumption, and wastewater discharge. However, how to improve the quality of white water and increase the efficiency of white water recycling is still a challenge. Faced with the increasing conductivity value of white water in the process of white water circulation, in this study, the factors affecting the conductivity value of white water for recycled pulp and the strategies for regulating the conductivity value were investigated by simulating the white water circulation during the paper-making process. The experimental results indicate the accumulation of inorganic salts is one of the reasons for the increasing conductivity value of white water. When inorganic salts accumulate to dynamic equilibrium, the increase amplitude of conductivity caused by inorganic salts does not exceed 5 % of the initial conductivity. Under the white water circulation, the polyelectrolytes formed by degradated starch are the main factor for the continuous increasing conductivity value of white water. The retention of starch, during the paper-making process, can be improved by adding in-situ generated aluminum hydroxide colloids and the polyelectrolytes from starch degradation in white water can also be adsorbed by aluminum hydroxide precipitates. The effects of soluble organic matter and dissolved inorganic matter on white water conductivity were revealed, and the formation pattern of conductivity value in the wet-end system of recycled pulp was derived. At the same time, methods for removing organic matter and polyelectrolytes were proposed. Both are helpful to improve the quality of white water for paper-making industry and reduce the pollution of the wastewater.

Reinforcement Fiber Production from Wheat Straw for Wastepaper-Based Packaging Using Steam Refining with Sodium Carbonate

Locally sourced agricultural residues are a promising feedstock for the production of reinforcement fibers for wastepaper-based packaging papers. An eco-friendly high yield process to generate fibers from wheat straw using high pressure steam and sodium carbonate is presented. The wheat straw was impregnated with up to 16% of sodium carbonate and steam treated for 10 min at temperatures from 148 °C to 203 °C. The pulps were characterized concerning their chemical composition and test sheets with 100% straw fibers and with 15% and 30% straw fibers blended with recycled pulp were prepared. Fiber yields ranged from 70% to 45%, wherein more severe treatment conditions contributed to increased paper strength but lower yields. At comparable fiber yields, treatments featuring a higher chemical input, coupled with lower treatment temperatures, resulted in improved paper strength. By blending recycled pulp with up to 30% of straw fibers with a beating degree of roughly 45 °SR, the burst, compression and tensile strength was enhanced by up to 66%, 74% and 59%, respectively. As the enhancement effect decreases with a high steam treatment intensity and a high proportion of wheat straw, a moderate treatment and limited use of wheat straw may be the best choice.

Improved drainage of LNFC-reinforced recycled pulp and mechanical properties of end papers by the zeolite-chitosan microparticle drainage aid system

Good drainage of the pulp suspension is vitally important for stable papermaking. Although the addition of lignocellulosic nanofibers (LNFC) in pulp could highly reinforce the end paper sheets, the application of LNFC could diminished the pulp drainage. To solve this problem, the impact of the zeolite-chitosan and bentonite-chitosan microparticle drainage aid systems on the LNFC-reinforced recycled pulp was systematically investigated. Results indicated that the mentioned microparticle systems improved the drainage and retention especially in applying 1% chitosan with 0.3% zeolite. In mechanical properties, applying the microparticle systems, not only did not deteriorate these properties, but also improved most of them, especially in treatment containing zeolite-chitosan. It seems that the improved pulp drainage and the mechanical properties of the end papers was due to successful mission of microparticle system and synergistic interactions of pulp fibres, LNFC, chitosan, and zeolite, which could also lead to denser and more uniform structure of handsheets.

Detection of trace chlorine pollutants in recycled pulp using gas chromatography-tandem mass spectrometry with response surface-optimized carbon structure online catalysis.

Detection of trace chlorine pollutants in recycled pulp using gas chromatography-tandem mass spectrometry with response surface-optimized carbon structure online catalysis.

Advancing sustainability in China's pulp and paper industry requires coordinated raw material supply and waste paper management

As the largest global producer and consumer of pulp and paper, China faces significant sustainability challenges in fiber supply and waste paper management. A comprehensive material flow analysis of China's pulp and paper industry (CPPI) is needed to understand the interaction between raw material supply and waste paper management. Here, we construct a closed-loop material flow analysis model for CPPI, examine the evolution patterns of material metabolism from 1990 to 2019, and explore the demand for paper production, waste paper recycling, and virgin fiber supply in 2030 and 2050 under multiple scenarios considering critical factors. Results show that the industry has undergone rapid expansion, increased material use efficiency, and a shift towards recycled pulp from 1990 to 2019. China's paper demand will grow to 186 Mt in the next 30 years, resulting in a significant increase in both demand for fibers (173 Mt) and the generation of waste paper (138 Mt). To ensure a sustainable fiber supply for CPPI, domestic waste paper recycling needs to be prioritized. However, attention should also be paid to the availability of virgin pulp supply and proper disposal of organic solid waste. Proper management of these factors is crucial for achieving a circular economy in the industry and reducing its environmental impact. The findings highlight the importance of addressing both raw material supply and waste paper management for CPPI's sustainable development.

Структурно-морфологические свойства вторичного волокна из влагопрочного сырья при мягком размоле. Часть 2. Характеристика волокнистой мелочи

The process of recycled pulp refining is usually associated with a significant change in the morphological characteristics of the secondary fiber and the formation of additional amounts of fines. It is well known that fines have a great impact on the pulp properties, the papermaking process and the quality of the resulting paper. At the same time, the effect of fines both on the paper properties and on the papermaking process depends on the morphological characteristics of the fines. The aim of the study was to evaluate the changes in the morphological characteristics of the fines during gentle low-consistency refining of the recycled pulp. The recycled pulp was obtained from commercial wet-strength tissue paper, consisting of 100 % bleached softwood kraft pulp (BSKP) made from pine (Pinus sylvestris L.). The repulping of wet-strength paper was performed at 60 °C in three ways, namely, repulping with sodium hydroxide (indicated as RP (NaOH)), repulping with sodium hydroxide and sodium persulfate (RP (NaOH + Na2S2O8)), and finally repulping with sodium hydroxide and potassium monopersulfate (RP (NaOH + KHSO5)). Using an optical fiber analyzer, L&W Fiber Tester, it was found that accelerated persulfate and monopersulfate repulping of the wet-strength paper led to an increase in fines content after pulp refining by 0.20…0.28 % on length and by 0.9…1.5 % on number of particles. In addition, some fines were not detected due to the limited resolution of the measuring device. The morphological characteristics of the recycled pulps showed that the studied fines were relatively straight particles (Sl = 93.5...94.0 %) with low length polydispersity ((Ll/Ln) = 1.08...1.09). Fines had a mean slenderness ratio (L/W)l and (L/W)w of about 7, which in some length classes reached 8...9. Taking into account the experimental data on fines length (Ll = 132…134 µm) and fiber width (Wl = 29.7…30.0 µm), as well as SEM images of recycled paper, we can conclude that these particles can form fines-assisted bridges between several close deposited fibers in the fiber network, thus strengthening the paper web. For citation: Penkin A.A., Kazakov Y.V. Changes in the Morphological Characteristics of Secondary Fiber Obtained from Wet-Strength Paper During Gentle Refining of the Recycled Pulp. Part 2. Fines Characteristics. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 4, pp. 169–179. (In Russ.). https://doi.org/10.37482/0536-1036-2023-4-169-179

Detection of trace chlorine pollutants in recycled pulp using gas chromatography-tandem mass spectrometry with response surface-optimized carbon structure online catalysis.

Chlorinated aromatics and alkanes are widely used for their flame retardancy, but they need to be monitored when used in recycled pulp. This paper reports the use of palladium acetate/activated carbon (Pa/Ac) activated by nitric acid as an online catalyst to determine chlorinated aromatics and chlorinated alkanes in recycled paper products using gas chromatography-tandem mass spectrometry (GC-MS/MS), which significantly improves the sensitivity of the method and remarkably lowers the detection limits. The Pa/Ac catalyst was prepared using a self-made catalytic device and used as key to the online catalytic conversion of target chlorinated aromatic hydrocarbons and chlorinated alkanes for GC-MS/MS analysis. The response surface model was used to optimize catalytic conditions. Then GC-MS/MS in the multireaction monitoring mode with online catalysis was applied for the analysis of polychlorinated biphenyls, polychlorinated terphenyls, polychlorinated naphthalene, and chlorinated paraffins (CP) in recycled paper products. Compared with traditional methods, the Pa/Ac catalyst can transform chlorinated aromatic hydrocarbons into aromatic hydrocarbons through dechlorination hydrogenation, thus lowering the detection limit of the GC-MS/MS method significantly. It can transform paraffin chloride into the corresponding alkane to better distinguish short-chain, medium-chain, or long-chain CPs. Online catalytic conversion significantly improved the sensitivity and reproducibility (88.7%-113.1%) of the method. Tissue samples with various concentration levels of chlorinated aromatics and chlorinated alkanes were tested. The linearity range of the reduced target compounds in the reduction product solution was 0.02-1.00 μg/ml (R2 >0.995). The quantitative detection limit was 0.03-0.05 μg/kg, and relative standard deviation was less than 6.9%. This study was the first to introduce the Pa/Ac catalytic device as an online catalytic unit in the determination of chlorinated aromatics and chlorinated alkanes using the GC-MS/MS method. The target compounds were converted into alkanes and aromatic hydrocarbons with unchanged carbon structures, and the method could achieve a low detection limit with no need for high-end methods such as GC-chemical ionization ion source (CI)-MS or high-resolution mass spectrometry. These methods are suitable for the determination of chlorine pollutants in recycled paper and its raw materials.

Nanocellulose addition to recycled pulps in two scenarios emulating industrial processes for the production of paperboard

Nanocellulose addition to recycled pulps in two scenarios emulating industrial processes for the production of paperboard

Assessing life-cycle GHG emissions of recycled paper products under imported solid waste ban in China: A case study

Changes of raw materials in China's recycled paper industry after the imported solid waste ban affect products' life-cycle greenhouse gas (GHG) emissions as well. This paper presented a case study of newsprint production with prior- and post-ban scenarios with life cycle assessment, including using imported waste paper (P0) and its three substitutions, i.e., virgin pulp (P1), domestic waste paper (P2), and imported recycled pulp (P3). The function unit is 1 ton of newsprint produced in China, and the study is conducted from cradle to grave which consists pulping and papermaking process, from raw material acquisition to manufacturing, with associated energy production and wastewater treatment, transport, and chemicals production. Our results showed that P1 holds the highest life-cycle GHG emission of 2724.91, followed by 2400.88 from P3. P2 has the lowest emission of 1619.27, only slightly lower than 1742.39 before the ban using route P0 (unit: kgCO2e/ton paper). Scenario analysis showed that current average life-cycle GHG emission for one ton of newsprint is 2049.33 kgCO2e, increased by 17.62 % due to the ban, while this number could be reduced to 12.22 % or even −0.79 % if switching from P1 to P3 and P2. Our study highlighted the importance of domestic waste paper as a promising way to reduce GHG emissions, which still has great potential to increase if with an enhanced waste paper recycling system in China.

Morphological Differences between Virgin and Secondary Fibers

The properties of the fibers determine the quality of the pulp and, thus, the quality of the paper made from it. Recognition of properties, which fiber and paper pulp should be characterized by, in order to achieve required paper properties, is, therefore, a subject of research and interest of many papermaking research experts and scientists. Fibers are subject to deformation and possible weakening under the influence of chemical and mechanical factors, and therefore the quality of the fibers decreases each time they are used in production when it comes to recycled pulps. Then again, the key factor determining the quality of the primary fiber is the degree of pulp delignification. In the article, an attempt was made to define the impact of delignification of virgin pulp on morphological properties of fibers, and compare them with the properties of recycled paper pulp, in order to find correlations. The current economic and raw material situations in the wood market force one to seek new solutions to limit the use of virgin fibers, which is extremely important for the economy of the paper mill, environmental protection and raw material management.

Nanocellulose and polysiloxane coatings for strength enhancement and oil-proof and hydrophobicity improvement of recycled pulp sheets

Recycled fibers are essential raw materials used by the paper industry. However, the strength of the formed paper may fall off excessively after several cycles of reuse of the fibers. Herein, the authors measured the changes in physical properties and fiber size after multiple recycling of fibers and prepared a handsheet from fiber recycled different times. Then the handsheets made with fibers that had been recycled 5 times were double-coated with nanocellulose derivatives to obtain oleophobic and hydrophobic paper. The first layer applied to the paper was cellulose nanofibril (CNF), and the second coating contained polydimethylsiloxane (PDMS) and CNF (CNFmp). The physical properties and barrier performance of coated paper were greatly improved compared to recycling paper. The water contact angle of the coated paper was as high as 139.8° and the Cobb60 value was 35.18±2.15 g/m2. The oil contact angle was 97.1°, and the oil kit number was 12/12.

Which Wastepaper Should Not Be Processed?

In the 21st century, numerous economic and environmental initiatives have significantly increased paper recycling, which continues to expand due to environmental awareness. With increasing recycling rate, low-quality paper fractions may be included in the process, leading to the overproduction of very low-value papers that cannot be reprocessed. Moreover, the production of paper from poor-quality wastepaper can result in the introduction of chemicals from the recycled paper into the recycling loop and unintended spread of chemical substances. Therefore, reliable and conscious selection of recycled pulp is imperative. To this end, the present study verified the properties of recycled pulp critical for the assessment of its papermaking ability for the production of high-quality sanitary paper. Following an examination of samples, it was found that the key parameters that influence the papermaking ability of wastepaper include presence of impurities, content of extractive substances, freeness, and length of fiber. On this basis, types of wastepaper that, at the very beginning, did not portend well for obtaining paper products with high potential for utility were eliminated.

The Effect of Fines on the Change of the Friction Coefficient of Recycled Linerboard during Calendering Treatment

When linerboard is manufactured by blending recycled OCC pulp with recycled pulp from aseptic carton, the results reported that factors other than surface roughness are related to the coefficient of friction. Calendering exacerbated the problem of a sharp decrease in coefficient of friction according to the mixing of aseptic carton pulp. Therefore, we tried to understand the aforementioned changes in the coefficient of friction by evaluating the effect of the surface residue of fines derived from aseptic carton on the sliding angle and surface roughness of aseptic carton-based recycled paper. Handsheets were made from recycled pulp extracted from aseptic cartons and then coated with fines slurries at 3% and 5% concentrations. It was confirmed that the higher the proportion of recycled pulp fines used in handsheet coating, the lower is the coefficient of friction of the handsheets. Coating the handsheets with a large amount of recycled pulp fines reduced friction after calendering. This study suggested that influence factors such as changes in actual contact area are essential to be investigated in controlling the friction coefficient of recycled paper.

Структурно-морфологические свойства вторичного волокна из влагопрочного сырья при мягком размоле. Часть 1. Характеристика волокон

The efficient use of papermaking potential of secondary fiber by gentle refining of recycled pulp is one of the basic principles for the recovered paper stock preparation. The use of mild refining modes for recycled fiber is more important in the case of wetstrength paper than for conventional waste paper. This is due to the fact that recycled fiber is weakened by hard conditions of wet-strength paper repulping, in particular, long repulping time, elevated temperature, the use of alkali and oxidizers. The study aims at evaluating the changes in the morphological characteristics of secondary fiber during gentle low-consistency refining of recycled pulp. The analysis of the secondary fiber morphological characteristics was carried out in two complementary directions, i.e. the analysis of the fibers (part 1) and the analysis of the fines (part 2). Recycled pulp (RP) was obtained from commercial wetstrength tissue paper consisting of 100 % bleached softwood kraft pulp (BSKP) made of pine (Pίnus sylvéstris L.). The wet-strength paper repulping was performed at 60 °C in three ways, namely, repulping with sodium hydroxide (indicated as RP(NaOH)), repulping with sodium hydroxide and sodium persulfate (RP(NaOH + Na2S2O8)), and finally repulping with sodium hydroxide and potassium monopersulfate (RP(NaOH + KHSO5)). Secondary fibers as well as primary fibers of BSKP had similar length distribution before and after gentle refining. Mean fiber length after first recycle reduced by 5–6 %. The calculated values of the fibershortening index showed that fiber cutting practically does not occur during gentle refiningof the recycled pulps. The increase in the refining degree of the pulps is mainly explained by the fibrillation of secondary fibers, rather than the formation of a large amount of fines. Secondary fibers obtained from the wet-strength paper have a high slenderness ratio ((L/W)l from 66.3 to 66.5 and (L/W)w from 83.6 to 84.3; where L – length, W – width) corresponding to pulp with good papermaking potential. The results showed that low-consistency gentle refining of the recycled pulp obtained by accelerated persulfate and monopersulfate repulping of the wet-strength paper leads to fiber straightening. The overall increase in the shape factor of secondary fibers was achieved due to a combination of accelerated repulping of the wetstrength waste paper (by ~ 60 %) and gentle refining of the pulp (by ~ 40 %).

Techno-economic and environmental evaluation of a market pulp reinforced with micro-/nanofibers as a strengthening agent in packaging paper

Partly inspired by the concept of masterbatch in plastics manufacturing, we developed a strategy to improve the technical viability, the economic feasibility, and the environmental performance of lignocellulosic micro-/nanofibers. Instead of investing strenuous efforts in dewatering and/or drying nanocellulose suspensions to maximize their consistency without significantly hampering redispersion, which still stands as an unresolved challenge, we used them in high proportions (up to 50 wt%) to reinforce a high-yield pulp. The suspension can be dewatered-pressed (0.70–1.75 MPa) to obtain wet laps of never-dried reinforced pulps, or dried to consistencies over 90% to produce dry boards, but at the cost of lower strengthening capability. In any case, both wet and dry reinforced boards succeeded in enhancing the breaking length of a recycled pulp by up to 62% and 56%, respectively. In light of these results, we proposed a tentative upscaling and subsequent assessment of the process, evaluating different scenarios. From the technical point of view, reinforced pulp boards are much easier to handle and to deliver than dilute aqueous suspensions. In economic terms, savings in transportation costs are worth remarking. Last but not least, this strategy fulfills at least three goals associated with the concept of cleaner production: water recovery (internal recycling), lower CO2 emissions (especially if transportation takes place by road), and avoiding hazardous chemicals such as hypochlorite.

Relationship between wettability of pulp fibers and tensile strength of paper during recycling

The wettability of the paper surface is greatly affected by the wettability of the pulp fibers. We conducted this study in order to understand the relationship between the wettability of a single fiber of recycled pulp and the strength of recycled paper, as well as the inter-fiber bonding strength. The contact angle was determined from a series of photographs of the pulp fiber and the water silhouettes at the point of contact. The contact line and profile history were continuously photographed in every 1 s after the initial contact. The recycled softwood kraft pulp fibers were clearly much less hydrophilic than the original fibers, regardless of whether the fibers had been bleached or not. The contact angle of the original chemi-thermomechanical pulp fiber was much higher than that of the original softwood bleached kraft pulp fiber. Furthermore, increased number of recycling decreased the contact angle of the chemi-thermomechanical pulp fiber. The Page equation was used to evaluate the strength contributions of single fiber and fiber–fiber bonding to tensile strength of paper. As a result, an increase in weakness factor of fiber–fiber bonding strength was obtained for the recycled softwood kraft pulp handsheet. On the other hand, the weakness factor of the original chemi-thermomechanical pulp handsheet decreased with recycling. In addition, the weakness factor of fiber–fiber bonding strength and the contact angles of the provided softwood bleached kraft pulp fibers bore a proportional relationship to each other.

Interaction of the electrical conductivity of recycled pulp colloidal suspension with chitosan and bentonite as a papermaking additive system

The performance of chitosan biopolymer-bentonite microparticle system in recycled pulp colloidal suspension of old corrugated containers with different electrical conductivities was considered. Various instrumental analyses (atomic force microscopy, field emission scanning electron microscopy, dynamic light scattering, and Fourier-transform infrared spectroscopy) were applied to characterize the applied chemicals. The results indicated that the mentioned system could increase the process and mechanical properties in comparison to the control sample. Although increasing the electrical conductivity of the recycled pulp decreased the performance of chitosan-bentonite system to some extent, the system was successful in its mission even at the highest electrical conductivity, i.e., increasing the retention, drainage, tensile index, tear index, bending strength and internal bonding strength, with improvement of approximately 41%, 32%, 8%, 16%, 26%, and 57% in comparison with the control samples, respectively. Therefore, this method can be a fascinating approach to the papermaking process. Moreover, the probable reasons of the mentioned achievements were considered and discussed.

Grafting nanocellulose with diethylenetriaminepentaacetic acid and chitosan as additive for enhancing recycled OCC pulp fibres

This paper develops a novel paper additive for effectively recycling old corrugated container (OCC) by functionalizing nanocellulose (NC) with diethylenetriaminepentaacetic acid (DTPA) and chitosan (CS), and investigate the reinforcing mechanisms and effect of the developed additive on the physical properties of recycled OCC pulp handsheets. The tensile, tear and burst index, air permeability, tensile energy absorption (TEA), and drainage performance of the recycled OCC handsheets are examined. Fourier transform infrared FTIR) spectroscopy, thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM) are used for the chemical and microstructure characterization of both NC based additives and paper from recycled OCC pulp. The results show that functional groups on the NC based additive, such as carboxyl, amino and hydroxyl groups, can bond with the hydroxyl groups on the recycled OCC fibres to generate a chemical bond. This leads to an increase in the crosslinks and bonding area between the fibres, which increases their tensile strength and improves their recycling rate. SEM shows that the paper with NC based additives had tighter inter-fibre bonds and smaller paper pore structure. Addition of 0.3% NC-DTPA-CS additive results in optimal properties of the recycled OCC paper with an increase by 31.64%, 22.28% and 36.6% of tensile index, tear index, burst index respectively, and the air permeability decreases by 36.92%.Graphical