EFFECT OF CHITOSAN ADDITION DURING PAPER-MAKING ON AGEING STABILITY OF DOCUMENT PAPER

The aim of the present work has been to study the influence of chitosan addition into the composition of paper intended for documents on its ageing stability, with a view of enhancing the resistance of paper strength and optical properties over time. The chitosan solution was added during the formation of the paper sheets in various amounts: 0.2%, 1% and 2% o.d.f. Paper samples of different fibrous compositions were prepared from bleached sulphate softwood pulp (BSWP) and bleached sulphate hardwood pulp (BHWP) in the following ratios: 50% BSWP:50% BHWP, 80% BSWP:20% BHWP, 100% BSWP and 100% BHWP. Then, paper samples were subjected to accelerated thermal ageing for 24 hours at 105 °C. It was found that the use of chitosan as additive in the composition of bleached cellulose paper samples led to improved strength and hygroscopic properties. The study showed that chitosan could be used in the production of kraft document papers comprising aluminium sulphate, as the presence of aluminium sulphate had no negative effect on the action of the biopolymer. Regarding the complex evaluation of the properties of the obtained papers, it could be summarized that, for the studied fibrous compositions, the optimum amount of the additive was 1% chitosan for a fibrous composition of 50% bleached softwood pulp and 50% bleached hardwood cellulose. Therefore, preparing document paper with the addition of chitosan is a convenient procedure to enhance a number of paper properties, even after the ageing process.

Application of DSA to improve strength of thermomechanical pulp blended paper

A more efficient application of a dry strength agent (DSA) was investigated to improve the strength of thermomechanical pulp (TMP) blended paper. Strength improvement by DSA application was more effective for hardwood bleached kraft pulp (Hw-BKP) than TMP. The degree of strength improvement of DSA further increased with the increasing degree of refining of Hw-BKP. The strength of the paper was decreased by the fines fractionation of TMP, but the strength improvement efficiency of DSA for the fines fractionated TMP increased. In order to increase the strength of TMP mixed paper using DSA, it is expected that DSA should be adsorbed only to Hw-BKP with high strength improvement efficiency, not TMP fines. When the DSA was mixed with Hw-BKP before contact with other stocks, it was confirmed that the effect of improving the strength by the DSA is the best. The strength improving effect increased as TMP fines were removed. Therefore, to improve the strength of the paper containing TMP in Hw-BKP by adding a DSA, it is preferable to selective apply the DSA to Hw-BKP while blending only the fibers of TMP by fractionation.

Locust bean gum adsorption onto softwood kraft pulp fibres: isotherms, kinetics and paper strength

The adsorption of locust bean gum (LBG) onto Northern Bleached Softwood Kraft (NBSK) pulp improved paper tensile and burst strength and lowered refining energy by strengthening inter-fibre bonding. Adsorption kinetics and isotherms were investigated to develop a fundamental understanding of the adsorption mechanism. The adsorption rate followed pseudo-second-order kinetics and the activation energy was 99.34 kJ·mol−1, suggesting chemisorption. The adsorption rate constant increased rapidly with temperature from 25 to 45 °C (k = 1.93 to 24.03 g·mg−1·min−1), but the amount adsorbed at equilibrium decreased (qe = 1.91 to 0.48 mg·g−1 o.d. fibre). LBG adsorption to NBSK at 25 °C was consistent with the Langmuir adsorption model for LBG < 2.1 wt% of o.d. fibre, suggesting reversible, homogenous adsorption to a finite number of sites on the fibre surface. Refining to 3000 rev increased the heterogeneity of the NBSK pulp surface leading to multi-layer Freundlich adsorption with adsorption constant n = 5.00, and the equilibrium constant Kf = 2.57 mg·g−1·(mg·L−1)−1/n at 25 °C. Favorable adsorption conditions for negatively charged LBG were identified: 25 °C for 10 min, low dosage level (< 2 wt%), lightly refined (< 3000 rev) NBSK pulp at low fibre consistency (< 0.5 wt%), high agitation rate (> 150 r.p.m.), acidic or neutral conditions (pH 2–7) without salt addition. Graphic abstract

Effect of uniaxial stress on bursting energy absorption of paper

The overall usefulness of the bursting energy absorption (BEA) was studied for a better analysis of paper strength properties. Additionally, the changes of the BEA during more complex deformations of paper products, e.g., preliminary or simultaneous tensile and burst, were determined. For the purpose of the research, an experimental setup was designed. The results showed that the correlation between BEA and bursting strength was linear, but the proportionality strongly depended on paper grade. Thus, a more accurate method to characterize the bursting resistance (BR) of paper was proposed. The BR parameter is described by the three following parameters: average bursting strength, average bursting energy absorption, and the slope of the fitted linear regression curve (relationship between the bursting energy absorption and the bursting strength). This method revealed new mechanical behaviors of papers related to their preloading.

Preparation and Application of Polyurethane Coating Material Based on Epoxycyclohexane-Epoxychloropropane Protective for Paper

Paper historic relics are of great value to research and preserve. However, with the change of environment, paper cultural relics are constantly aging and damaged. Therefore, the reinforcement and conservation of the paper is an important topic in the field of cultural relics protection; thus, it is a crucial and arduous task to discover high-performance protective materials. The coating reinforcement method is a kind of commonsense method to strengthen the paper. Additionally, it is key to select appropriate reinforcing resins. Polyurethane has influence on the improvement of paper strength, stability, and appearance. The epoxycyclohexane-epoxychloropropane polyether polyol was prepared with epoxycyclohexane and epoxychloropropane as materials, glycerol as the initiator, boron trifluoride diethyl etherate as the catalyst, and dichloromethane as the solvent. Infrared (IR) spectroscopy as well as proton nuclear magnetic resonance (1HNMR) spectroscopy were adopted to characterize the structure of the synthetic copolyether. Then, polyurethane based on epoxycyclohexane-epoxychloropropane was prepared by the synthetic copolyether reacting with hexamethylene diisocyanate (HDI) trimer. The effect of the mass concentration of polyurethane on the tensile strength, elongation, folding endurance, and the tearing strength of paper samples were tested. When 10% polyurethane solution was applied to paper, not only were the mechanical properties greatly improved, but the gloss and brightness also changed slightly, which conformed to the principle of “repair as old”. The above results indicate that the synthetic polyurethane combines the advantages of epoxycyclohexane-poxychloropropane polyether polyol along with polyurethane, presenting excellent properties in paper reinforcement or conservation.

Effect of Nanocellulose on the Properties of Cottonseed Protein Isolate as a Paper Strength Agent

Currently, there is an increasing interest in the use of biopolymers in industrial applications to replace petroleum-based additives, since they are abundantly available, renewable and sustainable. Cottonseed protein is a biopolymer that, when used as a modifier, has shown improved performance for wood adhesives and paper products. Thus, it would be useful to explore the feasibility of using cellulose nanomaterials to further improve the performance of cottonseed protein as a paper strength agent. This research characterized the performance of cottonseed protein isolate with/without cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs) to increase the dry strength of filter paper. An application of 10% protein solution with CNCs (10:1) or CNFs (50:1) improved the elongation at break, tensile strength and modulus of treated paper products compared to the improved performance of cottonseed protein alone. Further analysis using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) indicated that the cottonseed protein/nanocellulose composites interacted with the filter paper fibers, imparting an increased dry strength.

Cellulose nanofibrils manufactured by various methods with application as paper strength additives

Recycled paper and some hardwood paper often display poorer mechanical properties, which hinder its practical applications and need to be addressed. In this work, cellulose nanofibrils (CNFs) obtained by a combined process of enzymatic hydrolysis and grinding (EG-CNFs), grinding and microfluidization (GH-CNFs) or TEMPO-mediated oxidation and grinding (TE-CNFs) were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, CNFs were made into films on which some characterizations including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV–Vis transmittance spectroscopy were implemented. Results showed that CNF fibrillation was promoted as times of passes increased in microfluidization, and CNFs pretreated by enzyme possessed shorter length. Crystallinity of CNFs was related to CNF manufacturing methods, while CNF films’ transparency was correlated to CNF diameter distributions. Moreover, CNFs were applied with different dosages on recycled and hardwood paper. Lengths of CNFs, strength of CNF network, and pulp properties were critical factors affecting the mechanical strength of CNFs-enhanced paper. GH-CNFs showed better strengthened effect on tensile strength of paper than TE-CNFs and EG-CNFs. The best overall improvement was achieved at GH-CNF10 dosage of 5.0 wt% on hardwood paper. The increment of tensile index, burst index, and folding endurance were 108.32%, 104.65%, and 600%, respectively. This work aims to find out the relationship between production methods and morphologies of CNFs and how the morphological characteristics of CNFs affecting the mechanical performance of paper when they are added as strength additives.

Preparation and Application of Polyurethane Coating Material Based on Epoxy Cyclohexane Protective for Paper

Paper is important to most historical and cultural relics, however, these paper heritages are facing a crisis of disappearance, damage and aging. For increasing the paper strength, delaying the paper aging, and improving the weak stability and permeability of former resins used for paper, another material is necessary to be produced on preservation and protection of the paper items. The synthesis of epoxy cyclohexane polyetherpolyol was as follows: Epoxy cyclohexane was as the starting material, ethylene glycol was as the initiator, boron trifluoride ether was as catalyst, and dichloromethane was as the solvent. The synthesized homopolyether was characterized by infrared (IR) spectroscopy and proton nuclear magnetic resonance (1HNMR) spectroscopy to determine the structure. Then the epoxy cyclohexane homopolyether reacted with the hexamethylene diisocyanate (HDI) trimer, and the polyurethane was obtained. With the tests of the physical and chemical properties of paper samples, it showed that the paper processed with 10% polyurethane liquid had excellent performance, the increase in the tensile strength was from 1105 to 2317 N/m, and the increase in the folding endurance was from 20 to 504 times. What’s more, the paper processed with 10% polyurethane liquid had good brightness and gloss. The results of the paper samples for the test have shown that the synthesized material simultaneously has the advantages of epoxy cyclohexane homopolyether and polyurethane, possessing excellent performance in paper reinforcement. Thus, the synthesized polyurethane material has broad application prospect in paper protection field.

Incorporation of post-consumer pizza boxes in the recovered fiber stream: Impacts of grease on finished product quality

Grease and cheese contamination of used pizza boxes has led to misunderstanding and controversy about the recyclability of pizza boxes. Some collection facilities accept pizza boxes while others do not. The purpose of this study is to determine whether typical grease or cheese contamination levels associated with pizza boxes impact finished product quality. Grease (from vegetable oil) and cheese are essentially hydrophobic and in sufficiently high concentration could interfere with interfiber bonding, resulting in paper strength loss. Findings from this study will be used to determine the viability of recycling pizza boxes at current and future concentrations in old corrugated containers (OCC) recovered fiber streams. These findings will also be used to inform the acceptability of pizza boxes in the recycle stream and educate consumers about acceptable levels of grease or cheese residue found on these recycled boxes.