Step 4. Comparison of Phosphonates with Biodegradable Chelants

Step 4. Comparison of Phosphonates with Biodegradable Chelants 

An initial screening test was developed to measure the peracid release of a fully formulated chelant-free detergent powder to which equimolar amounts of chelants were added. Peracid release was measured at 40 °C over 30 min in a synthetic hard water with transition metal ions added at ppm levels representative of those found in wash liquors of a typical washing machine with added soil [36] Ca 76, Mg 15, Fe 

The residual peracetic acid after 30 min [37] is shown in Table 10.6. EDDS gave the most stable peracid release, followed by DTPMP and EDTMP. HEDP and other biodegradable chelants did not prevent peracid decomposition and there was no peracid remaining after 10 min under these conditions. 

EDDS and the three phosphonates were also compared for stain removal and dye damage in a full wash test in a washing machine using the same synthetic hard water. The results are summarized in Table 10.6 and showed that EDDS and DTPMP were comparable on stain removal followed by EDTMP, whereas HEDP gave very poor stain removal. On dye protection, EDDS clearly protected dyes better than DTPMP and EDTMP, whereas HEDP use resulted in significant amounts of dye damage. 

Chelant 30 min peracid release (%) Stain removal Dye protection Amount required for 60% after IS min (wt%) 

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