Recycling disposable diaper waste pulp after dehydrating the superabsorbent polymer through oxidation using ozone

Ichiura, Hideaki; Nakaoka, Hiroko; Konishi, Takayoshi

Recycling disposable diaper waste pulp after dehydrating the superabsorbent polymer through oxidation using ozone

2020

Ichiura, Hideaki | Nakaoka, Hiroko | Konishi, Takayoshi

A method for recycling diaper waste pulp was developed. Super-absorbent polymer (SAP) in diapers was dehydrated by oxidizing it using ozone, then the pulp in the diaper waste was recycled. The diaper waste was washed and centrifugally separated, then the SAP and pulp mixture was oxidized using ozone to separate the SAP and pulp to allow the pulp to be recycled. A sample of SAP that had absorbed either 400 mL of distilled water or 80 mL of a 0.9% NaCl solution was placed in 2000 mL of a 45 g/m³ ozone solution produced by passing ozone through the solution at a flow rate of 1.0 mL/min. The SAP concentration decreased as the reaction time increased. Oxidation by ozone destroyed the cross-linked SAP structure and therefore eliminated the ability of the SAP to retain water. Ozone treatment also broke the ether bonds of the cross-linking agent in the SAP. This caused the water-insoluble SAP to be converted into a water-soluble sodium acrylate polymer. The molecular weight and degree of dispersion of the SAP also decreased as the reaction time increased. The water-absorptivity of the recovered pulp was almost the same as the water-absorptivity of virgin pulp and was higher than the standard value of 10 g/g. The water-absorptivity of the recovered pulp was not affected by the ozone treatment. We concluded that the method can be used to recycle disposable diaper pulp.

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