IntroductionDiapers are consumer products designed to absorb excretory fluid from the human body, such as urine and feces. In this research, five major types of adult diapers (tape, pull-on, flat, pad, and light incontinence pad) and two major types of baby diapers (tape and pull-on) were studied. The aim of the research was to analyze representative and reproducible compositions, to estimate fossil carbon fractions, and to quantify fossil CO
2 emissions for different types of diapers in Japan. The composition of a diaper depends on the manufacturing region, manufacturing year, and type of diaper, and affects the fossil carbon fractions and related emissions from diapers. Therefore, it is necessary to analyze the actual compositions of different diapers.
MethodologyThe criteria for selecting samples were: brands with major market share, percentage of production weight and numbers, coverage of different functions, capacities, and gender. A total of 70 samples of 7 different types of diapers were analyzed in this study. Each sample was manually dismantled and weighed to determine the weight and percentage of its constituents. There are five different layers/materials in a diaper: surface layer, absorbing layer, leakage prevention layer, binder/tape material, and elastic/stretch material. From the information on the diaper labels and through Fourier-transform infrared spectroscopy, the following were identified as the constituents: polyolefin non-woven fabric (polypropylene) for the surface layer, cellulose pulp and superabsorbent polymers (SAP) for the absorbing layer, polyolefin (polyethylene) for the leakage prevention layer, polystyrene (PS) for the binder/tape material, and polyurethane for the elastic/stretch material. The carbon fraction (CF) of each diaper was calculated by multiplying the percentage of each constituent in the diaper with the carbon percentage of that constituent according to its molecular formula. The fossil carbon fraction (FCF) was calculated as the ratio of CF excluding biomass carbon from cellulose pulp to the total CF. The fossil carbon emission factor of diaper incineration (dry basis) was obtained by multiplying CF, FCF, oxidation factor, and 44/12 (total atomic weight of CO
2 divided by atomic number of a carbon atom). The fossil carbon emissions from different diapers were then calculated by multiplying the fossil carbon emission factor with the annual weight of incinerated diaper (ton), which in turn was based on annual production weight data for various diapers, obtained from the Ministry of Economy, Trade and Industry (METI, 2017).
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