I found this text about the fiber:
Acrylic was introduced to the carpet industry in 1957 as a synthetic imitation to wool. Acrylic carpet has the appearance of wool with a far lower price tag. Because of several performance problems acrylic disappeared from the carpet market in 1988. In 1990 it was re-introduced in Berber styles for it’s wool like appearance and it being used as a blend with nylon. Acrylics advantages are that it is resistant to water based stains and has low absorbency. Disadvantages are that traffic areas maintain a dirty appearance after thorough cleaning. Poor resilience means that crush marks from heavy furniture may be permanent. Acrylic area rugs may be susceptible to color bleeding.
But since our cleaning and chemistry has improved, maybe the mills should reinvestigate this fiber as a possibility.?.