Performance of three types of laundry detergents in soft and hard water

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Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University

This study was designed to evaluate the performance of current formulations of three types of laundry detergents in soft (60 ppm) and hard (172 ppm) water using home laundry equipment. Standard loads were washed with two brands from each of three types of detergents (phosphate-built and carbonate-built granular, and unbuilt liquid) to measure soil removal, soil deposition, and carbonate deposition. For the 5 replications of the soil removal test, swatches of soiled test cloth in 100% cotton, 50% cotton/50% polyester with no finish, and 50% cotton/50% polyester with permanent press finish were used. Untreated swatches of the same fabrics were used for the 10 replications of the soil deposition test and soil was introduced via a solution of Bandy black research clay and hot water. Swatches of the test cloth were attached to items in the test load. Carbonate deposition was observed after 5, 10, and 15 washings of a load composed of nine dark blue items (three 100% cotton terry washcloths, three men's 100% cotton T-shirts, and three boy's 50% cotton/50% polyester sport shirts) plus sufficient filler cloths of unbleached muslin to complete the load.

Numerous significant interactions indicate that the results are not clear cut. However, the following conclusions were reached. The unbuilt liquid detergent was most effective in soil removal, especially in hard water, and the carbonate-built granular product was least effective. The phosphate detergent was the best of the three types in holding soil in suspension. Soil deposition increased with the number of washings and the increase was greater in hard water than in soft water. The appearance of "tattletale gray", which results as suspended soil is deposited on fabrics, was most noticeable for fabrics of untreated 100% cotton.

Carbonate deposition was more apparent in hard water than in soft, but the buildup of the white precipitate occurred in both soft and hard water. Deposition of the carbonate precipitate was progressive and occurred at a faster rate in hard water than in soft. Items washed in hard water felt harsher than those washed in soft water, and the presence of the precipitate was more noticeable in areas with irregular surface texture or thickness.

Detergent formulations change frequently and the differences in detergent types are becoming increasingly blurred. Therefore, when purchasing and using laundry detergents, consumers need to be aware of the properties of their water supply, laundry detergent, and washing machine, plus the articles to be washed, including types of soil. Laundering clothes is a complex process; satisfactory results depend on appropriate combinations of variables in the laundry system. At present, unbuilt liquid products are a practical and effective alternative to phosphate-built laundry detergents.