Electret materials

Disclosed are electret materials with outstanding thermal and charge stability. The electret materials comprise a melt blend of a thermoplastic polymer and one or more hindered hydroxylamine ester compounds that comprise at least one moiety of the formula I where Ra′ is a monoacyl or diacyl radical; R1-R4 are each C1-C6alkyl; and R5 and R6 are each, independently of one another, hydrogen, C1-C6alkyl or C6-C10aryl; or R5 and R6 are together oxygen. The melt blends are subjected to an electet treatment, for example a corona treatment. The electret materials are for example nonwoven polyolefin webs and are employed as filter materials, wipes, absorbent materials, filter masks, acoustic materials, printing substrates, measuring devices or contactless switches. The present electret materials may also comprise a further additive selected from the group consisting of the hindered amine light stabilizers, the hydroxyphenylalkylphosphonic esters or monoesters and the aromatic trisamide nucleating agents.