title: Ageing of radiation-sterilized polypropylene: changes in semicrystallinity.
abstract: Studies on radiation sterilization of isotactic polypropylene intended for biomedical applications were carried out for uncovered and covered samples. The effect of ageing on these samples was studied by determining the changes in relative crystallinity. The semicrystalline nature of the polymer is responsible for the changes in crystallinity. The transitions between short- and long-range order and short- and long-duration stiffness in both covered and uncovered samples, reflected in changes in relative crystallinity, were highly affected by the formation of branches in the backbone of the polymer. The high degree of branching in covered samples resulted in greater long-duration stiffness in the transition between short- and long-duration stiffness. The high degree of branching in covered samples was attributed to the high diffusion of energized oxygen into the polymer matrix compared with uncovered samples. The changes in relative crystallinity were rapid in uncovered samples (70% max; 34% min) but rather slow in covered samples (87% max; 43% min).
authors.affiliation: Division for Technical Evaluation of Biomaterials, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, India.
authors.forename: M
authors.initials: M
authors.lastname: Jayabalan
authors.forename: P D
authors.initials: PD
authors.lastname: Nair
authors.forename: K
authors.initials: K
authors.lastname: Sreenivasan
mesh_terms: D001672:Biocompatible Materials; D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D008422:Materials Testing; D010084:Oxidation-Reduction; D010969:Plastics / Q000528:radiation effects*; D011126:Polypropylenes / Q000528:radiation effects*; D013055:Spectrophotometry, Infrared; D013242:Sterilization / Q000379:methods*; D013997:Time Factors
chemical_list: D001672:Biocompatible Materials; D010969:Plastics; D011126:Polypropylenes