Polybutadiene irradiated with electrons

Ivchenko et al. [1981] investigated the possibility of producing elastic films and coatings for synthetic leathers by introducing elastomers into PE (Table 11.9), followed by irradiation to increase their strength and heat resistance, and prevent ply separation (delamination). Six different elastomers (butyl rubber, HR, chlorinated-PE, CPE, chlorsulphonated-PE, CSR, polyisobutylene, PIB, and two polybutadiene rubbers, BR, were added to PE. Films were made on a roll mill at 105°C, and were then pressed at 130°C. The samples were irradiated at 20°C with electrons (dose rate = 0.4 kGy/s). 

Elastomers such as cis-l,4-polyisoprene (natural rubber), polybutadiene, polybutadiene-styrene (SBR), and poly-chloroprene have large amounts of unsaturatiOTi in the polymer backbone and aU undergo crosslinking upon irradiation with either electron beam or 7-irradiation. Table 52.3 gives some values for G(X) and the ratio of scission to crossUnk-ing G(S)/G(X) for several elastomers. The protective effect of the aromatic ring is shown by the decrease in yield as the percentage of styrene is increased for the SBR series. 

PS blends with EPDM were compatibilized by addition of either SB (polystyrene/polybutadiene di-block copolymer) or SEP (polystyrene/ethylene propylene di-block copolymer) and were blended in a corotating twin-screw extruder T = 200°C (Table 11.9). The strands were quenched and pelletized. Some of the pellets were injection-molded (200°C) into 4 mm-thick specimens and irradiated to 50 kGy (3-MeV electron accelerator). Another part of the pellets was similarly irradiated and then injection-molded. The samples for notched Izod impact testing (ASTM D256) were annealed for 24 h at 80°C, or were left at RT for 3 weeks, before testing [van Gisbergen et al., 1990,1991b]. 

Reasonably early however in the development of telechelic polybutadiene/acrylonitrile, Brenner and Drake (22) showed that mercaptan- and carboxyl-terminated liquid polybutadiene/acrylonitrile did respond to electron-beam (1-5 megarads) and cure (2-3 seconds/pass) from the liquid to the solid state. The mercaptan polymer (3.1% RSH, 23% bound acrylonitrile, Mn 1700) cured more readily. CTBN as expected required 50-100% higher irradiation dosage levels. With both MTBN and CTBN-type products of higher acid content (6% vs 3%), gum rubber properties of 13.8-34.5 mPa were obtained with 60-100% elongation. The E-beam cures were carried out in air at ambient temperature. Thus, unformulated telechelic polybutadienes were shown to be substantive to cure in the presence of ionizing radiation. 

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