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Analysis of the possibilities of increasing resistance to plastic deformation of new biopolymers by means of modification through radiation

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Operational durability of the polymer-metal kinematic systems used in technology and endoprosthesoplasty depends to a considerable degree on the resistance of polyethylene to plastic deformation and wear [1÷6]. In about 90% of applications, conventional and the cheapest polymer-metal couples are still used in alloplastic procedures. In one of such cases, a ca. fivefold reduction of susceptibility to permanent deformation and tribological wear was obtained for the polyethylene Chirulen 1120. The effect was a result of a combined application of small plastic deformation (ef. ≈ 0.2, initiating the transitions) and electron beam irradiation [7÷9]. Those factors modified the morphology of the polymer. As a result, in operational conditions, the thickness of the deformed upper layer of polyethylene reduced, its degree of crystallinity and reorientation of the lamellar phase were modified, the degree of structure order increased, and in consequence, the operational durability improved. The reference literature of the last decade shows, however, that in order to increase resistance to wear and ageing, what should be aimed at is to ensure a very high molecular weight and an appropriate proportion of crystalline and amorphous phases [10÷13]. In the shaping of the properties, a more and more significant role of irradiation with an electron beam is being recognized. Doses higher than 25 kGy are conducive to decomposition of long macrochains, spatial arrangement of the structure and UHMWPE crosslinking. A growing dose, to as much as 150 kGy, causes a very significant increase of resistance to wear [14, 15]. According to the presented information from the reference literature, two grades of polyethylene have been recently introduced to production. Polymers GUR 1020 and GUR 1050 have replaced Chirulen 1120 of a molecular weight of ca. 106 g/mole. New materials weigh many times more: 5·106 and 9.2·106 g/mole, and are intended e[...]

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