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Schematic representation of the recycling process for paper network structures, including the fiber dispersion, paper-sheet formation by filtration, drying by Rapid Kö then, soaking in water, disintegration, and return to the fiber dispersion form.
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Cellulosic paper products based on sustainable resources are of interest as replacement for petroleum-based plastics, e.g. in packaging applications. Improvements are desired for mechanical performance, recyclability and possibilities to shape fiber networks into complex geometries. Commercial bleached wood fibers from the Kraft process have insuff...
Contexts in source publication
Context 1
... and Recycling. Figure 2 shows the overall paper recycling process in the present study. Starting from a wood fiber dispersion (kraft or Holo), fairly dense paper structures were prepared by vacuum filtration followed by Rapid Kö then drying. ...
Context 2
... weighted-average length decreases from 3.17 to 2.98 mm for the Holo fibers and from 2.90 to 2.70 mm for the kraft fibers. The main reason for this decrease in length is that short fiber fragments are generated in the disintegration step of recycling (highlighted in orange box in Figure 2B). Regarding fiber diameter (measured in the wet state), no changes were observed for the Holo fibers (∼34.5 μm), while a significant decrease was observed for the kraft fibers (from 30.0 to 25.7 mm). ...
Citations
... Despite the abundance of plant resources, there is still a gap in the availability of raw materials for papermaking (Abd El-Sayed et al. 2020). As a result, waste paper recycling has become a crucial means of addressing the shortage of papermaking materials Yang and Berglund 2019). However, recycling paper can lead to a degradation in paper performance, reducing the overall utility of recycled Abstract Holocellulose fibers exhibit excellent recycling performance and are increasingly gaining attention for addressing the hornification effect that occurs during the recycling of waste paper products. ...
... Remarkably, fibers with a high hemicellulose content exhibit superior recycling performance, as seen in the case of high-yield pulp (Andreasson et al. 2003;Wan et al. 2010). Holocellulose fiber, derived from plants through mild delignification, retains a substantial amount of hemicellulose and offers unique advantages in the recycling process for papermaking (Yang and Berglund 2019). In our previous work (Qin et al. 2022), we demonstrated that holocellulose fiber outperforms cellulose fiber, particularly in the case of sisal-based materials, when it comes to recycling properties. ...
... After undergoing five rounds of recycling, the primary recycling stress of holocellulose paper decreased from 81 to 56 MPa (Fig. 4a), marking only a 31% decrease. The result was comparable with value of 26% reported by other authors (Yang and Berglund 2019). However, the stress for alkalitreated paper (1-AT, and 2-AT paper) decreased significantly, going from 48 to 17 MPa (Fig. 4b) and from 44 to 6 MPa (Fig. 4c) after 5 cycles of recycling, respectively. ...
Holocellulose fibers exhibit excellent recycling performance and are increasingly gaining attention for addressing the hornification effect that occurs during the recycling of waste paper products. However, the mechanism by which hemicellulose components in holocellulose fibers impact fiber reuse remains unknown. In this study, birch holocellulose was prepared through peracetic acid delignification. The hemicellulose content was adjusted using alkali treatment and xylanase treatment, both based on holocellulose. The removal of hemicellulose resulted in an increase in hornification and porosity growth rate during the recycling process due to these pretreatments. Consequently, fibers subjected to alkali treatment and xylanase treatment exhibited diminished mechanical performance with each recycling cycle. In particular, after five recycling runs, alkali treatment paper experienced a significant reduction in ultimate strength, dropping from 48 to 11 MPa, representing a 77% decrease. In contrast, hemicellulose-rich holocellulose paper retained an ultimate strength as high as 56 MPa (reduced from 81 MPa), marking a 33% decrease. The high hemicellulose content in holocellulose fibers proved advantageous for preserving the network structure of fibers and impeding the co-crystallization and aggregation of fibers during the recycling process, ultimately ensuring the maintenance of mechanical performance, including tensile, tearing, and bursting strength.
... From a recycling perspective, the fibers separate more easily when wet. This phenomenon is considered a disadvantage when the sheet is being used by the consumer (lower strength when wet) but as an advantage or success when the sheet is being recycled or repulped in the mill [35][36][37][38][39][40]. ...
Additives are ingredients used in papermaking to enhance fiber properties, introduce special properties to the paper and improve the efficiency of the paper making process. Wet strength agents, sizing agents, dry strength agents, fillers, retention aids, defoamers, dyes and pigments are common additives used in paper mills. Poor retention of wet strength additive such as PAAE (polyamide epichlorohydrin) and hydrophobicity loss due to ASA (alkenyl succinic anhydride) and AKD (alkyl ketene dimer) size reversion not only increase cost and reduce product quality in the mill but also increase customer complaints and rejections.
In this study, a method was developed to quantify and study the parameters that govern PAAE retention in paperboard. PAAE applications, performance, and recyclability were also investigated. In addition, ASA bonding mechanism to the fiber was investigated, and experiments were performed under different environmental conditions to determine the environmental parameters that initiate or catalyze ASA and AKD size reversion.
The results of these studies indicated that PAAE can be quantified after hydrolysis and derivatization to diethyl adipate. PAAE retention increases as the pulp freeness decreases. Instead of freeness, fiber surface charge can be used to predict PAAE retention. The results also indicated that high presence of lignin in the sheet provides wet strength and low PAAE retention due to low availability of carboxylic groups on the fiber. On the contrary, when the lignin is removed, the retained amount of cationic PAAE increases due to the availability of anionic carboxylic groups on the fiber resulting in high wet strength; lignin is potential biomaterial based wet strength.
Investigations revealed that ester bond formation between ASA and cellulose is insignificant and is not a prerequisite for sizing effectiveness. Although, hydrolyzed ASA contributes to the sizing performance, direct application of hydrolyzed ASA to the pulp leads to flocculation and does not achieve sizing. The results revealed that ASA and AKD size reversions are significantly light and oxygen dependent. The oxidative photodegradation mechanisms of the sizing agents are explored and possible mechanisms are proposed.
... Besides, since the existence of core-shell distributed hemicellulose hinders the co-crystallization and aggregation of cellulose fibril, the hornification effect of paper is weakened. Holocellulose papers prepared from spruce and sisal display a good recycling performance Yang and Berglund 2019). However, the properties of paper are easily affected by the fibers based on different preparation methods (kraft process, peracetic acid method, etc.) and conditions (temperature, time, etc.), except for the non-uniform raw materials. ...
Holocellulose fibers provide great potential to make paper with high performance. However, inappropriate reaction conditions may limit its improvement in paper performance due to the lack of sufficient research data. In this work, paper is prepared from the birch holocellulose fibers based on peracetic acid treatment and the papermaking process. The features of resulting holocellulose fibers are evaluated for different peracetic acid treatment conditions such as temperature and time. It reveals that high temperature and long treatment time lead to the degradation of hemicellulose/cellulose and the destruction of fibers, which further results in the poor mechanical performance of paper. By optimization for the treatment condition of holocellulose fibers, the corresponding paper exhibits the highest tensile strength (93 MPa), good bursting strength (601 kPa), and tearing strength (647 mN). The determination of optimum conditions will provide guidelines for the industrial production of holocellulose fibers and paper.
... Paper from bleached pulp is more easily repulpable than paper from unbleached pulp (Blechschmidt et al. 2021). A high lignin concentration is in general known to increase the resistance to disintegration for various types of fiber products (Blechschmidt et al. 2021;Harter et al. 2022a,b;Yang and Berglund 2020). Additionally, due to higher fiber length, softwood fibers are less repulpable than hardwood fibers (Blechschmidt et al. 2021;Tervahartiala et al. 2018). ...
... The chemical additives in papermaking, such as sizing agents, wet-and dry strength agents, and coatings, are also modifying the repulping process (Blechschmidt et al. 2021). The mechanical properties can be increased by a higher hemicellulose content, which might be helpful for disintegration since hemicelluloses are water soluble (Duan et al. 2019;Yang and Berglund 2020). Repulpability is directly correlated to the wet strength (Su et al. 2012), addition of wet strength agents is hindering it (Yang et al. 2019). ...
Water-dispersible paper is useful for packaging applications as it disintegrates into its fibers after usage, and also is a fully biodegradable material. Here, we first introduce a laboratory testing method for the disintegration performance of different paper grades under low agitation in water. Then a quantitative analysis on the technological and physical mechanisms responsible for dispersibility of paper is performed. We identify lignin content, degree of refining and addition of starch as relevant factors reducing paper dispersibility. Addition of a debonding agent, a non-ionic surfactant, was not found to be effective here. We found a strong correlation of both, wet- and dry tensile strength to dispersibility. From all water absorption related paper properties only ultrasonic liquid penetration measurements were correlated to paper dispersibility. Principal component analysis revealed that paper strength and water penetration speed are not governed by different latent variables but instead are all strongly associated with the first principal component. This suggests that the same mechanisms are responsible for reduction of water penetration speed and wet/dry strength. Hence we suggest to decouple network strength and water penetration, e.g. by identifying suitable additives imparting bonding strength without reducing the access of water which is required to break the fiber–fiber bonds.
... [11][12][13][14] Furthermore, compression analysis of large MPPs using isotropic material method for MPM was performed, 15 along with measurements of the strength and porosity of paper. 16,17 Other studies measured the uniaxial tensile properties and elastic modulus of molded pulp made from three kinds of non-wood pulp and their mixed pulp. 18,19 All these researchers worked on sheet-scale samples 20 and did not consider the fiber network scale. ...
... According to equation (17), it can be inferred that E zz can be determined by E xx , V p , and k. By comparing the calculated value of E zz with the experimental result, it can be observed that the accuracy of the calculated value is heavily influenced by the error range of E xx , whereas the error range of V p has a minor effect. ...
Molded pulp products can improve the utilization of recycled paper by achieving close to zero waste emission and a 100% recycling rate, while satisfying the national goals for recycled packaging materials of various countries. Molded pulp products are often designed using finite-element simulations to optimize their performance, which requires the input of accurate material properties. However, studies on the constitutive model, an essential factor related to material properties, are still rare. This study investigated the mechanical behavior of the molded pulp material to simplify the parameters and improve the accuracy of the constitutive model. The fiber distribution and connection within the molded pulp material were investigated; treating the pores of the molded pulp as a virtual material enhances the meso-mechanical model and gives a transversely isotropic constitutive model. The elastic modulus in the thickness direction was calculated as 1.5997 MPa, and the experimentally measured value is 1.5368 MPa. The error of proposed model is 4.1%, but significantly smaller than treating molded pulp as an isotropic material, the error of which is ~80 times larger of experimental result.
... As a first criterion, the repulpability of coated paper feedstock is assessed through evaluation of fiber yield and morphology after the repulping process [183]. The recyclability of paper fibers is further evaluated after introduction of a recovered fiber fraction in combination with virgin pulp into new paper materials [184]. Although the field relies on long tradition of experimental research and test methods to simulate standard stock preparation, advances have long been hampered through the lack of unified standards for evaluation. ...
Packaging for liquid products is mainly made from petroleum-based polymers, either rigid or flexible. The multilayer packaging provides small and handy packs available for the common masses. However, an alternative bio-sourced material for liquid products is urgently needed due to the limitation of fossil fuel, restrictions from environmental regulations, and its non-biodegradable nature. Paper is used as a packaging material that mainly provides structural strength to the package with some barrier properties if required after suitable surface treatment. Here we review the use of lignocellulosic pulp to produce paper-based sachets and paper bottles for liquid product packaging, emphasizing the detailed manufacturing process. The barrier properties of various conventional polymers and barriers required by a specific liquid product package are also discussed and detailed, as a barrier is required to increase further or maintain the product’s shelf-life. Current research and new product development at an industrial scale and their materials are critically discussed. Suitable coating materials on paper sheets and paper bottles are detailed, as paper alone cannot be used for liquid products due to wettability in the hydrophilic region and poor barrier properties. The potential of biopolymers like polylactic acid, polyhydroxyalkanoates, and their nanocomposites are further explored to ensure the package’s sustainability compared to conventional polymers. Moreover, the emerging biomaterial such as cellulose fatty ester, cellulose nanopaper, waterborne acrylic emulsion, and natural wax-based dispersion for coating on paper packaging is detailed. Furthermore, the barrier, mechanical properties, and finally, recyclability are a concept taken into account from the design phase onwards.
Graphical Abstract
... All this is the cause of the low strength of individual secondary fibers. As noted by the authors of work [3], secondary fibers are characterized by low ability to swelling, fibrillation, a propensity to shorten, and the loss of ability to form hydrogen bonds. ...
The possibility to dispose of paper mill sludge as part of a composition of container cardboard from secondary raw materials has been investigated. The fractional composition of the sludge was studied and it was shown that the main part of the fibers is represented by small particles with a size of up to 1.2 mm. Studying the processes of formation of container cardboard when using paper mill sludge showed that an increase in the consumption of fibrous-inorganic waste leads to a deterioration in the physical and mechanical properties of cardboard. However, the increase in sludge consumption does not affect the surface absorption of water during one-sided wetting. The value of these indicators is within the normal range and is 25 and 70 g/m2, respectively. In addition, an increase in sludge consumption from 10 to 50 % in the manufacture of cardboard leads to a decrease in the degree of fiber retention on the grid from 86.3 to 82.1 %. Regularities of using strengthening additives, namely industrial cationic and anionic flocculants, as well as native corn and modified starches for the strength of cardboard and the quality of sub-grid waters, have been established. Research results show that the effect of flocculants is quite ambiguous. On the one hand, there is a clearly observed positive impact on the quality of the sub-grid waters. This is due to the reduction of their turbidity due to smaller fiber washes. Nevertheless, the positive effect on physical and mechanical parameters is minimal, and in some cases, there is a decrease in strength indicators. The greater the efficiency of keeping fine fiber on the grid when using flocculants, the lower the values of physical and mechanical indicators. In general, when using sludge in the composition of cardboard in combination with flocculants and starch, the indicators were achieved that are considered standard for waste paper container cardboard of grade KT-1 according to TU U 17.1-41085075-002:2017
... Возврат и многократное использование в бумагоделательном цикле растительных волокон также является важным фактором, приводящим к существенному, но мало управляемому изменению их структурных и размерных характеристик: уменьшению средней длины волокон, увеличению доли мелочи и полидисперсности волокон, появлению локальных деформаций волокон [15,20,33]. Степень влияния рециклинга на структурно-морфологические свойства получаемого вторичного волокна во многом зависит от особенностей реализации стадий роспуска макулатуры и размола волокнистой массы. ...
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 wet-strength 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 wet-strength 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 fiber shortening index showed that fiber cutting practically does not occur during gentle refining of 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 wet-strength waste paper (by ~ 60 %) and gentle refining of the pulp (by ~ 40 %).
... Because these variables reduce fiber swellability and length, and therefore fiber-tofiber bonding, the paper produced from recycled fibers is often weaker. 13,28 Chemical treatment of pulp is a method of increasing and restoring its bonding potential. Recognizing the basic changes and bonding ability of recycled cellulose fibers may open the way for enhanced waste paper recycling. ...
This study aimed to determine the effects of butylamine treatment on cellulose fibers during the recycling processes. Three recycling stages have been carried out and two different butylamine (Ba) treatments (5.0% and 7.5%) were applied to old corrugated containers (OCC) papers during recycling. After each recycling process, papers were produced and the mechanical and optical properties of these papers were measured. SEM images and FTIR spectra were taken and the crystallinity index of the cellulose fiber was calculated by the XRD peak height method. Some improvement (11.0-15.2%) in paper brightness with the Ba treatment was realized in the third recycling stage, while yellowness values typically decreased by 1-2 points. Chemical treatments resulted in definite differences in water absorptiveness (Cobb value) for papers. The highest water absorptiveness of 160.0 g/m 2 was observed with a 7.5% Ba treatment in the second recycling stage (75Ba2), indicating a value about 15.6% higher than that of the control. The highest tensile and burst indices were observed with 7.5% Ba treatment in the third recycling stage, indicating approx. 28.7% higher tensile and 34.5% burst indices, compared to the control at similar recycling stages. In contrast, the highest tear strengths of 4.54 Nm 2 /g, followed by 3.86 Nm 2 /g, were observed for untreated samples in the second and first recycling stage, respectively. The butylamine treatment in the recycling processes increased the cellulose crystallinity more (1.3%), compared to the control. It seems that the strength properties of recycled paper, such as tensile and burst, are closely related to the individual fiber strength and fiber bonding potential, which are typically reduced in recycling, but could be improved by Ba treatment..
... This is probably the reason for the excellent strength and toughness of the unfibrillated pseudo-CNF paper. On the other hand, although the nanofibrils in a single pseudo-CNF layer have highly oriented structures, the layers are randomly arranged ( Figure S4), indicating the lesser effect of orientation on the mechanical 30,31 (2) a microfiber/nanofiber hybrid, 29 (3) cationic CNFs, 19,32,33 and (4) lignin containing cationic CNFs. 34 The ellipsoids with black borders represent the data of the samples from this work, including HP, NBKP, HP-NF, and pseudo-CNF. ...
... We propose that, if the microfibers undergo further delamination during recycling (i.e., a redispersion and material formation process), the weakening of their mechanical properties during recycling may be overcome. 30 Remarkably, the HP-2h sample was highly strengthened and toughened as the number of recycling runs increased (Figure 2b). The SEM images and dispersion state of HP-2h revealed that the microfibers gradually disappeared ( Figures S11 and S12), while the fraction of delaminated thin layers increased, as the number of recycling runs increased. ...
... 36 For cellulose-microfiber-based paper, the fiber length shortens during recycling, resulting in decreased strength. 30 In a CNF-based nanopaper, hornification hinders the redispersibility of dried nanofibers, reducing the recycling performance. 37 Using the current pseudo-CNFs would be a facile strategy for obtaining strengthened and toughened paper after recycling. ...
Energy consumption and post-treatment of chemical reagent residues are important issues that hinder the sustainable production of the natural building blocks of cellulose nanofibrils (CNFs). In this study, we realize a low-energy, zero-waste process for CNF production by designing a novel reactive deep eutectic solvent (DES), the residue of which can be directly used as a plant growth regulator. After pretreatment with the DES, cellulose fibers self-delaminate into thin layers referred to as pseudo-CNFs, as their strength, toughness and transmittance are comparable to those of CNFs. Pseudo-CNFs break into smaller particles during recycling and thus display unique mechanical upcycling. After facile fibrillation, the obtained CNFs can independently form freestanding sub-micrometer films that show a strong, full coloration, which is demonstrated for the first time. Our concept can enable a green process, and the developed cellulosic materials may find various applications as structural materials and optical coatings.
