Controlling fiber strength loss is crucial for improving the quality of recycled paper during the recycling and reuse of corrugated box. Fiber strength decline primarily stems from factors such as fiber keratinization, loss of fine fibers, and impurity contamination during recycling. These factors collectively weaken the bonding force between fibers and degrade the physical properties of the paper. Optimizing pulping processes, strengthening fiber modification, improving impurity removal techniques, and enhancing surface treatment can effectively slow down fiber strength decline and enhance the practical value of recycled corrugated box.
Optimizing the pulping process is the first step in controlling fiber damage. Traditional pulping methods, due to excessive time or high temperature, easily lead to excessive fiber cutting and keratinization, weakening its flexibility and bonding ability. Using gentle pulping techniques, by shortening pulping time, lowering temperature, and combining low-concentration, high-speed thermal dispersion treatment, can reduce fiber breakage while removing adhesives. For example, adding an appropriate amount of dispersant during the pulping stage can promote the separation of impurities from fibers, preventing fiber damage due to mechanical friction and thus preserving more intact fiber structure.
Fiber modification technology is a key means of improving the strength of recycled fibers. Recycled fibers are prone to surface passivation due to repeated processing, leading to a decrease in hydrogen bonding ability. Chemical modification (such as graft copolymerization) or bio-enzymatic treatment can introduce active groups onto the fiber surface, enhancing its interaction with adjacent fibers. For example, polyacrylate polymers, as paper reinforcing agents, can fill fiber gaps through bridging, significantly improving the ring crush strength and bursting strength of paper. Furthermore, interlayer self-assembly technology, through polyelectrolyte adsorption, can form multilayer structures on the fiber surface, further enhancing the bonding force between fibers.
The thoroughness of impurity removal directly affects the fiber strength recovery effect. Impurities such as adhesive residue, hot melt adhesive, and ink particles mixed in during corrugated box recycling can clog the pores between fibers, hindering hydrogen bond formation. A multi-stage screening and thermal dispersion combined process can efficiently separate impurities of different particle sizes: first, large adhesive particles are removed by screening; then, small impurities are dispersed into the pulp using thermal dispersion equipment; finally, they are thoroughly removed by flotation or washing processes. For example, thermal dispersion treatment can refine hot melt adhesive particles to a level that does not affect fiber bonding, thereby reducing paper breakage. Surface sizing technology is a supplementary means to compensate for insufficient fiber strength. Recycled fibers, due to increased surface roughness and enhanced water absorption, easily lead to a decrease in paper wet strength. Surface sizing with starch-based or synthetic polymers can form a continuous film on the fiber surface, sealing pores and reducing water penetration. For example, a modified starch and polyvinyl alcohol composite sizing agent can improve both paper dry strength and water resistance, making it particularly suitable for corrugated box applications in humid environments.
The retention of fine fiber components has a dual impact on paper strength. While fine fibers can fill fiber gaps and promote interlacing, excessive loss weakens the internal bonding of the paper. A balance must be struck between the removal and retention of fine fibers during recycling: optimizing the pulping process (e.g., controlling the degree of freeing) allows for appropriate fibrillation of fine fibers, enhancing their intercalation with longer fibers while avoiding strength reduction due to excessive cutting. Furthermore, adding functional fillers (such as nanocellulose) can partially replace the role of fine fibers, further improving paper density.
The graded utilization of recycled fibers is an important strategy for improving resource efficiency. Fibers are graded based on quality (such as length and degree of keratinization), with high-quality fibers used to produce high-strength corrugated base paper, while inferior fibers are used to manufacture low-strength products such as paper tubes and pallets. This differentiated utilization avoids the overall performance degradation caused by fiber mixing and extends the fiber recycling cycle. For example, after appropriate modification, the ring crush strength of primary recycled fibers can approach that of virgin fibers, meeting the demands of high-end packaging.
Fiber strength control in the recycling and reuse of corrugated boxes needs to be integrated throughout the entire process chain. From pulping and impurity removal to modification and sizing, each step requires a targeted solution designed to address the fiber damage mechanism. Through technological integration and innovation, efficient recovery of the strength of recycled fibers can be achieved, driving the corrugated box circular economy towards high-quality development. In the future, with the maturation of new technologies such as bio-enzyme modification and nano-reinforcement, the problem of strength loss in recycled fibers will be more thoroughly solved, providing solid support for the sustainable development of the packaging industry.
