1. W. J.Roff and J. R.Scott, Fibres, Films, Plastics and Rubbers, Butterworths 1971, Section 11.
2. Techniques and Methods of Polymer Evaluation, edited by P. E.Slade and L. T.Jenkins. Volume 1, page 78. Edward Arnold (Publishers) Ltd. 1966.
3. United States patent No. 3607798.