Sentence:  Polyphosphates gave renewed <WSD>life</WSD> to soap products at a time when surfactants were a threat though expensive , and these same polyphosphates spelled the decline of soap usage when the synergism between polyphosphates and synthetic detergent actives was recognized and exploited . 
Meaning of the word marked with <WSD> tags:  the period during which something is functional (as between birth and death)