مجله تحقیقات علوم چوب و کاغذ ایران
سال سی و هشتم شماره 4 (پیاپی 85، زمستان 1402)

In addition to reducing the consumption of various resources such as water, energy, and wood, paper recycling is constantly increasing in different countries due to less pollution. One of the major defects of the old corrugated container (OCC) is its relatively weak strength, which has limited its use in various sections of the packaging industry. In this study, the effect of using some additives was studied to improve the strengths of OCC to make the top liner of cartons in both wet and dry conditions. OCC was prepared from domestically produced cartons. To determine the performance and optimal amount of additives, corn cationic starch (at 1, 1.4 and, 2%), wet strength resin (at 1, 2 and, 3%), AKD (at 1, 2 and, 3%), and imported tea envelope recycled long fiber paper (at 10, 15 and, 20%) were separately used as additives based on the dry weight of OCC pulp. The handsheets made by laboratory sheet former with a basis weight of 120 g/m2 and then tensile, burst, and tear indices were measured at wet and dry conditions to compare the effect of additives. Also, water absorption was measured by the Cobb test on the test samples. The optimal level of each additive was determined based on the results, then handsheets made from optimal combination treatment including appropriate levels of all additives, and different properties of handsheets were statistically compared. The water absorption of handsheet was decreased by 90% compared to the control by adding AKD. This additive was able to decline the water absorption of handsheet made from OCC to about 20 g/m2 as the suitable range. The greatest increase of wet tensile strength of the handsheet was achieved using 3% wet strength resin compared to the control. The resin maintained the wet tensile, burst, and tear indices of the residual strength of handsheet by 25, 46, and 58%, respectively, compared to dry strengths so it has good performance. The results showed that by adding cationic corn starch and recycled long fiber paper, all the dry strengths of handsheet independently increased compared to the control. The optimal combination treatment was determined according to the independent use of additives in OCC pulp, including 1% cationic starch, 1% AKD, and 3% wet strength resin based on technical-economic considerations. There is no significant difference between dry tensile and burst strength of handsheet using this treatment and 20% recycled long fiber paper, which both means ranked statistically in the same group.  The use of 20% recycled long fiber paper of tea wrapper has significantly improved the dry strength of OCC pulp, but adding 1% cationic corn starch to OCC pulp caused a few increases of dry strength. The wet strength of handsheet was significantly improved by adding 3% wet strength resin whereas 1% AKD significantly decreased the water absorption of the OCC pulp to 14 g/m2. The optimal combination treatment of chemical additives including 1% cationic corn starch, 1% AKD, and 3% wet strength resin improved the wet and dry strength of handsheet made from OCC pulp that could be used for packaging products that should be kept in refrigerator and freezer.

Waste paper recycling has grown as an industry in Iran and the world and offers many benefits to the environment and humans. Municipal waste is also reused after recycling processes. Cardboard recycling industry has great environmental and economic importance and with the lack of wood resources and high demand for paper products, it plays an important role in the development of paper-related industries. However, recycling can be associated with a reduction in the optical properties of the paper. The use of nanoparticles in the paper industry is also expanding day by day. Nanosilica is one of the most important nanoparticles used as a retention aid in the paper industry. In order to reduce the consumption of long fibers and obtain the desired optical properties, the use of nanosilica alone or in combination with other materials such as cationic starch and cationic polyacrylamide is investigated. The purpose of this research is to compare the effect of separate and combined use of nanosilica additives, cationic polyacrylamide, cationic starch and long fibers on the optical properties of white liner paper pulp. In this study, white paper pulp with a brightness of at least 78% and a gloss of at least 45% was used to prepare handmade papers. Long fiber chemical paper pulp from coniferous kraft imported from Russia with a brightness of 89% was used in the laboratory. Nanosilica powder (NanoSiO2) produced by Degussa, Germany, cationic polyacrylamide with Farinret K325 brand, produced by Degussa, Germany, and cationic starch from LyckebyAmylex, Slovakia, were used. Independent treatments include the addition of 10% refined long fibers paper pulp, 6% nanosilica, 1.5% cationic starch and 0.15% cationicpolyacrylamide and combined treatments include 6% nanosilica and 1.5% cationic starch and 6% nanosilica and 0.15% cationic polyacrylamide. Then 127 g.m-2 handmade papers were prepared and their optical and microscopic properties were evaluated. The results showed that by adding 10% of long fibers, the brightness decreased and by using 6% of nanosilica, the maximum brightness was obtained. Meanwhile, the whiteness of papers with 6% nanosilica was minimum and maximum with 0.15% cationic polyacrylamide. Opacity showed its highest value with the combination of 6% nanosilica and 0.15% cationic polyacrylamide. Also, by increasing the amount of polyacrylamide and cationic starch, individually or in combination with nanosilica, the opacity increased. The light absorption coefficient was the lowest in papers with 6% nanosilica and the light scattering coefficient was the highest in papers containing 6% nanosilica and 0.15% cationic polyacrylamide. A colorimeter was used to measure the color components and the results showed that the additives had an effect on the brightness and whiteness of the papers. Also, changes in the color spectrum and the amount of color change were also observed. Additives increased the darkness and changes in different colors. The use of nanosilica separately and in combination with starch and cationic polyacrylamide increases the brightness of papers. Also, the use of cationic polyacrylamide separately and in combination with nanosilica leads to an increase in the whiteness and opacity of papers. The brightness factor of the papers, which is representative of the L* component, decreased with the exception of the addition of 10% long fibers and 6% nanosilica. The amount of overall color change with ∆E* was the lowest in samples containing 1.5% cationic starch and the highest in samples containing 0.15% cationic polyacrylamide. The use of some treatments can lead to a decrease in the optical properties and a decrease in the printability quality of the white liner. To solve this problem, mechanical paper pulp that has been decolorized or coated on the surface of the paper can be used. The presence of nano-silica particles in the structure of the paper improves the bond surface and reduces the prosity, which results in the reduction of surface roughness and less light refraction, and increases the light reflection and brightness of the paper.

 Surface modification and coating is one of the effective methods to increase the performance and service life of wooden structures. All kinds of super-hydrophobic techniques with a contact angle above 150 degrees and a sliding angle less than 10 degrees, in addition to creating high hydrophobicity, also improve the antimicrobial and other surface properties of the substrate. Nevertheless, resistance to mechanical and moisture damage are very important in connection with super-hydrophobic surfaces. Natural waxes are one of the efficient and healthy materials for creating a durable super-hydrophobic coating with high biocompatibility. In this research, nano-silica modified with non-fluorine alkyl materials in the presence of epoxy resin has been used to create superhydrophobic surfaces of birch wood (Betula pendula). Also, carnauba wax has been used to improve water repellency, self-cleaning property and durability in conditions of mechanical damage, humidity and harsh environments, comparatively.

Dodecyltrichlorosilane was used in the presence of toluene solvent for functionalizing and hydrophobicizing silica nanoparticles. A formulation containing 2% of modified nano silica and some epoxy resin was used by spray method to fabricate super-hydrophobic coating on birch wood. Also, the optimal amount of vegetable carnauba wax (Brazilian palm) was used as a reinforcing agent to make the nanohybrid formulation. Durability and stability to mechanical damage (sandpaper abrasion, water impact) and harsh environments (acidic, alkaline, ultraviolet rays and solvents) were investigated. Finally, the self-cleaning potential of the processed wooden surfaces was evaluated by qualitative (inclined surface) and quantitative (dropping) methods using edible liquids.

Both types of nanocomposite (without wax) and nanohybrid (containing wax) coatings caused the super-hydrophobicity on birch wood. The adding the optimal amount of carnauba wax to the epoxy-based nanocoating structure leads to a contact angle of 170 degrees and a sliding angle of less than 3 degrees by water drops. In addition, carnauba wax caused the stability and strength of superhydrophobic surfaces in aging and mechanical conditions. The highest level of stability in harsh environments was related to the hybrid nanocoating. The highest contact angle was observed for pomegranate juice and the lowest for milk. Also, the self-cleaning potential with various types of Fanta and Coca-Cola drinks on the superhydrophobic surface was successful.

The use of carnauba wax increased the contact angle and decreased the sliding angle. The use of carnauba wax significantly improved the mechanical properties and water-repellency of the super-hydrophobic coating. The chemical nature and morphological structure of wax in the coating is the reason for this superiority. The super-hydrophobic surface made with nanohybrid coating in the presence of carnauba wax has the potential of self-cleaning, biocompatibility and stability in service conditions and can be used to protect all types of general surfaces in the field of food, especially lignocellulosic substrates such as wood and paper.
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Paper bleaching is a concern of many conservationists. Research has been conducted with the aim of evaluating some traditional bleaching materials used in the preservation of documents and books, such as hydrogen peroxide and sodium borohydride, which shows that these materials do not significantly improve the mechanical properties of historical papers. Also, investigating the effect of reducing agents on oxidized papers has shown the effectiveness of tert-butylamine borane complex. In another study, five dyeing processes with oxidizers (calcium hypochlorite, hydrogen peroxide in two concentrations, light bleaching and potassium permanganate) and two dyeing processes with reducing agents (sodium borohydride and tert-butylamine borane) were compared. And their effect on pure cellulose (Whatman filter paper) and two different historical papers have been investigated. The results indicate that all the tested dye removal methods have led to a clear increase. Due to the differences of opinion, in this research, the effectiveness of two reducing agents sodium borohydride and sodium dithionite on the appearance and structural characteristics of paper is investigated. In this research, Whatman Filter Paper No. 1 (Whatman Filter Paper No. 1) made in England with a thickness of 180 microns, a diameter of 11 cm, a base weight of 87 grams per square meter and an ash percentage of 0.06% was used. Chemical reagents including potassium persulfate, sodium borohydride and sodium dithionite in the highest purity were prepared in a laboratory from Merck, Germany.Three solutions including potassium persulfate (2% by weight/volume), sodium borohydride (1% by weight/volume), sodium dithionite (1% by weight/volume) in distilled water (distilled water, pH; 7), to perform tests on zinc. Paper samples have been used by immersion.Whatman filter paper samples were subjected to oxidation in 2% peta persulfate in distilled water for 2 days (48 hours) and then the samples were immersed. Next, the identified samples were modified by two solutions of sodium borohydride and sodium dithionite 1% in distilled water for 1 to 5 hours and then purified in holy water. Also, the samples were subjected to accelerated aging according to ASTM standard number D4714-96 at a temperature of 90±2 centigrade and a relative humidity of 50±2% for 384 hours. Test methods include potentiostat, colorimetry, tensile strength, pH measurement, scanning electron microscope and infrared examination. The results show that potassium persulfate is the most neutralizing solution among the three solutions used on the first day, and it also indicates the reducing power of two solutions of sodium dithionite and sodium borohydride, which according to the test results, sodium borohydride is the reducing power. Compared to sodium dithionite. The sample prepared with pH 92.3, after accelerated aging, was accompanied by an increase of several units of pH after modification with two reducing substances. Examining the data obtained from the tensile strength test shows that in comparison with the tested samples with a tensile index of 1.06, the samples modified with sodium borohydride and sodium dithionite increased the index in all five modified periods. Tensile of paper samples. The infrared spectrometry investigation of the samples modified with sodium borohydride and sodium dithione shows that this old material improves the structure of cellulose after aging by reviving the C=O bonds to C-O and reducing the area of 1640 cm-1. Accelerated. The reduction of the absorption band in the region of 1640 cm-1 has been opened in almost all time cases with this material compared to the modified sample. Based on the data, samples modified with sodium borohydride and sodium dithionite had a significant increase (approximately 25 units) in the L-factor (light-darkness) after aging, indicating that two substances have increased the brightness of the sample by reviving the color compounds. In the microscopic examination of the surface of the fibers, in the samples identified with potassium persulfate, local separation of the fibers is observed. In the samples modified with sodium borohydride and sodium dithionite, fibers with higher consistency and entanglement are observed. Double bonds and carbon groups in paper samples formed with potassium persulfate have been the main responsible for the yellowness and darkness of the paper, the reducing agents sodium borohydride and sodium dithionite reduce this aldehyde and ketone to hydrocarbon and as a result. With the loss of multiple conjugates, the light absorption of the paper is reduced and this causes the paper to lighten. The double bonds and their regeneration also cause rearrangement of the chain cells, which has resulted in increasing the mechanical resistance and strength of the paper samples.

In the production of pulp, materials such as sodium hypochlorite, chlorine dioxide, ozone, hydrogen peroxide, etc. are used in the bleaching process.  In addition, the above-mentioned materials can be used as oxidizing materials to increase the surface charge of fibers, can help the paper to be more resistant. Therefore, this research was conducted to investigate the effect of fiber oxidation with hydrogen peroxide and sodium hypochlorite on the characteristics of NSSC and OCC pulps as fresh and recycled pulps, respectively.

The pulps required for this research, unbleached NSSC pulp and OCC pulp were obtained from Mazandaran wood and paper factory, and first, the percentage of consistency, initial freeness and brightness of the pulp were measured. Also, the required chemicals were all of industrial grade, hydrogen peroxide (in liquid form 52%) from Chlor Pars Tabriz Company and sodium hypochlorite (in liquid form 16.4%) from Kleran Semnan Company and sodium silicate from Bawand Shimi Qazvin Company, caustic (Liquid soda) with a purity of 47% for bleaching with peroxide was obtained from Arvand Abadan Petrochemical, and soda ash (solid soda) with a purity of 90% for bleaching with hypochlorite was obtained from Chloran Pars, Semnan. In order to control the destructive effects of transition metals, all pulps were treated with 0.2% DTPA, in 2% dryness conditions, time 30 minutes, temperature 90 degrees Celsius and pH=5.5-5, before bleaching. At the end of this step, the pulp is thoroughly washed with distilled water and used for the next steps. For the oxidation of both types of pulp, 3, 4, 5% hydrogen peroxide and sodium hypochlorite were used for oxidation of NSSC pulp using the above ratios (similar to peroxide) and for OCC pulp, 0.5, 1 and 1.5% hypochlorite ratios were used. Then the structural characteristics of the fibers such as pulp freeness, kappa number, WRV, viscosity, carboxyl groups were investigated and finally, the pulps were evaluated by FT-IR spectroscopy.

The results showed that with the increase in the consumption of hypochlorite, freeness increased in the oxidized NSSC pulps, but the trend of freeness decreased in the oxidized OCC pulp. This issue shows the situation regarding the use of peroxide. Also, the oxidation of pulp by sodium hypochlorite compared to peroxide has resulted in the release of more lignin, and in this sense, the effectiveness of OCC pulp (with 1.5% hypochlorite, equivalent to 56.68% Kappa loss) has been higher compared to NSSC pulp (with 5% hypochlorite, equivalent to 83.27% Kappa loss).The amount of water retention value in the pulp fibers in the NSSC pulp treatments has increased compared to the control pulp, and in the case of the OCC treatments, it has not changed significantly compared to the control treatment, and only in one case (OC-Na1) has a significant decrease. With the increase of peroxide consumption in the oxidation process of both types of NSSC and OCC pulp, despite the increase in viscosity, there is no significant difference between different consumption levels. In addition, with the increase in the level of hypochlorite consumption, a significant increase in the viscosity of the aforementioned pulps is observed So that the highest increase related to the sample using 5% hypochlorite for NSSC pulps was equal to 731.87 ml/g. The amount of carboxyl groups of pulps treated with peroxide increased in both types of NSSC and OCC pulps compared to the control sample so that the highest amount of carboxyl groups related to 5% treatment was equal to 0.0468 mmol/g for NSSC samples. The evaluation of FT-IR spectroscopy also shows that the oxidation treatment with peroxide and hypochlorite has increased the carboxyl groups on both types of pulp compared to the control samples.

The effectiveness of hypochlorite compared to peroxide in the creation of carboxyl groups in both types of pulp was more, which seems that the increase of carboxyl groups on the cellulose chain occurred more on C6 by peroxide and more on C2 and C3 by hypochlorite. The oxidation process increases the viscosity of paper pulp by increasing the carboxyl groups and due to the creation of a higher molecular weight. In addition, the increase of carboxyl groups due to higher chemical activity has made them able to absorb higher water and thus higher WRV.

The destructive effects of heat increasing in cellulose substrates, which are the basic materials for the packaging industries, high-quality hygiene packaging, and ammunition packaging, are obvious and inevitable. Therefore, it is essential to modify the structure of these bio-based products with green and environmentally friendly materials, to increase their durability against heat.

In the current study, TEMPO-oxidized CNFs and CNCs, were initially and separately retarded using flame retardant mixtures, including dual “ammonium monophosphate+albumin”, “silica+methyltri-methoxysilane”, and quadruple “ammonium monophosphate+albumin+silica+methyltri-methoxysilane”. Using a rod coater, each combination was then coated individually on the produced cellulosic paperboards. Flame retardancy properties were evaluated by three thermal experiments, including a Mini Fire Tube, Limited Oxygen Index, and Mass Loss Calorimeter.

Based on the observed results, the role of mono-ammonium phosphate, due to the presence of phosphorus-containing groups as the driving force of the charring during combustion, was more prominent and significant in the dual coating mixture than the quadruple coating mixture, containing silica and phosphorus, both in the paperboards coated based on CNFs and paperboards coated based on CNCs. Comparison of the CNFs and CNCs based-flame retardant, as the main basis of the coating formulation, showed that paperboards coated with CNFs based-flame retardant, due to having amorphous and crystalline regions, had much lower amount of mass loss in the Mini Fire Tube test, almost similar Limited Oxygen Index, and Peak Heat Release Rate (PHRR) and Heat Release Rate (HRR) in the Mass Loss Calorimeter test, compared to those of the paperboard coated with CNCs based-flame retardant.

In general, CNFs and CNCs based-flame retardants with mono-ammonium phosphate and albumin, even in low concentrations, can be used as effective retardants and replacements for conventional flame retardants, in high-quality cellulose-based packaging production.