Phosphomolybdic acid-catalyzed oxidation of waste starch: a new strategy for handling the OCC pulping wastewater

When old corrugated cardboard (OCC) is returned to the paper mill for repulping and reuse, the starch, which is added to the paper surface as a reinforcement agent, is dissolved into the pulping wastewater. Most of the OCC pulping wastewater is recycled to save precious water resources; however, during the water recycling process, the accumulation of dissolved starch stimulates microbial reproduction, which causes poor water quality and putrid odor. This problem seriously affects the stability of the papermaking process and product quality. In this study, phosphomolybdic acid (H₃PMo₁₂O₄₀, abbreviated as PMo₁₂) was utilized to catalyze the waste starch present in papermaking wastewater to monosaccharides, realizing the resource utilization of waste starch. The results showed that the optimized yield of total reducing sugar (78.68 wt%) and glycolic acid (12.83 wt%) was achieved at 145 °C with 30 wt% PMo₁₂ at pH 2, which is equivalent to 91.51 wt% starch recovered from wastewater for resource utilization. In addition, the regeneration of the reduced PMo₁₂ was realized by applying a potential of 1 V for 2 h. Overall, this study has theoretical significance and potential application value for resource utilization of waste starch in OCC pulping process and cleaner management of OCC waste paper.

Resource utilization and ionization modification of waste starch from the recycling process of old corrugated cardboard paper

Generally, the mechanical strength and stiffness of old corrugated cardboard (OCC) waste paper are decreased after multiple recycling procedures. Surface sizing starch, which is extensively used in the surface sizing of paper making, accumulates after dissolving from the fibers and is transformed into pollutant during the OCC re-pulping process. To overcome the pollution and reutilization problem of the waste starch during the recycling process of OCC paper, waste starch was ionized using hydrogen peroxide (H₂O₂) to improve the mechanical properties of OCC paper during the reutilization. The results showed that the carboxyl group of waste starch increased with an increasing degree of ionization, resulting in enhanced copper ion adsorption capacity. Furthermore, the retention rate of the modified starch in the wet-end increased from 18.0% to 48.2%. The OCC paper presented the highest burst index and tensile strength of 8.94 kPa m²/g and 112.5 N m/g, respectively, when MS-2 was added. This work has great significance for implementation of the cleaning production of OCC waste papers and the reutilization of the waste starch.