2) R.J. Statz and M.C. Dorris, “Proceedings of the Symposi-um on Degradable Plastics, ”the Society of Plastics In-dustries, Inc. Washington D.C., June 10 (1987) , p.15.
3) J.E. Guillet, “Proceedings of the Synposium on Degradable Plastics”, the Society of Plasticts Industyies, Inc., Washing-ton D.C., Iune 10 (1987). p.33.