1. Struik, L.C.E. (1978) Physical Aging in Amorphous Polymers and Other Materials, Elsevier, Amsterdam.
2. Greco, R. and Ragosta, G. (1988) Isotactic polypropylenes of different molecular characteristics: Influence of crystallization conditions and annealing on the fracture behaviour, J. Mat. Sci., 23, 4171–4180.
3. Agarwal, M.K. and Schultz, J.M. (1981) The physical aging of isotactic polypropylene, Polymer Engng. Sci., 21, 776–781.
4. Tomlins, P.E. and Read, B.E. (1996) Creep and Physical Ageing of Polypropylene: A Comparison of Models, NPL-report CMMT(A)23, National Physics Laboratory, Teddington, Middlesex TW11 OLW, UK.
5. ISO 899-1 (1993) Plastics — Determination of Creep Behaviour, Part 1: Tensile Creep, Part 2: Flexural Creep by Three-point-bending.