Radiation-induced modification of polyamide 6
Polimery 1999, No 1, 38
The PP/PA 6 system was studied in a chemical modification involving reactive co-extrusion with a new 2-oxazoline derivative (ricinyl-2-oxazoline maleate) to produce less hygroscopic PA 6 with the mechanical properties of the unmodified polymer maintained unaffected. At stageI, PP and the maleate were melted in a twin-screw extruder and the modified PP was irradiated with a fast-electron beam (20 kGy); at stage II, the reactive PP was extruded together with PA 6 at 235—245°C for 5 min to yield a (25:75 bywt.) PP/PA 6 system. Neither DSC (Table 1, Fig. 1) nor DMTA (Table 1, Figs. 2, 3) thermograms allowed to follow structural changes occurring at phase boundaries or caused by sporadic branching of polymer chains. SEM measurements (Figs. 4, 5) showed themodified PA 6 to be heterogeneous; at 25%, PP formed spherical domains in PA 6.The size of the dispersed-phase domains varied with the modification conditionsapplied. In the physical blends, domains were 10 pm in size, oblong, and pulledout of the matrix (Fig. 4). The chemical compositions had smaller domains (Fig.5), were morphologically more stable, and their phases adhered to each other soas to form interpenetrating phases of PP and PA 6. In contrast to physical modification involving simple mixing of molten components, the present method affordsa compatible (though heterogeneous) system with the (heterophase) structure stabilized at the microphase level and with advantageous macroscopic properties, viz., hygroscopicity reduced by 35%, enhanced dimensional stability, and high strain crack resistance (Table 3).