Utilization of tire rubber and recycled polyolefins into thermoplastic elastomers
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phase inside the plastic matrix. So, the bitumen can act as an additional curing agent. This is the reason why the term dynamic vulcanization can be used although bitumen is not at all a traditional curative for rubbers. The HDPE-pc/EPDM/(GTR/bitumen) blend (sample B11) produced by the method “C” is characterized by significant reduction of E" and tan δ values (cf. Figures 18 and 20) as well as a further uptrend of the E'=f(T) curve (cf. Figure 19) compared to sample B9. Undoubtedly, such changes evidence a further growth in the crosslink degree of the dispersed EPDM/GTR rubber phase in sample B11 compared to B9. However, based on the increasing ultimate elongation value of sample B11 (cf. Table 11) an improved interfacial adhesion between the components can be unequivocally quoted. We consider that this is due to the higher degree of bitumen induced devulcanization of GTR at preheating of GTR/bitumen blend before mastication additionally reflected by the significant decrease of Tg1 onset of rubber phase (cf. Figure 18) from –65 oC (for the sample B9) to –75 oC (for the sample B11). This result agrees well with the conclusions made on the base of sol-gel analysis (cf. section “Tensile Properties”). As it was noted above the (re)covulcanization of partly devulcanized GTR with EPDM and bitumen is occurred during mastication of composition in Brabender plasticorder and finally, sample B11 exhibits high values of tensile strength and ultimate elongation (cf. Table 11). Certainly, this is a result of the improved compatibility of the blend components. Based on analysis of the DMTA data it can be concluded that at producing GTR/bitumen-containing TPE by method “C” the bitumen first acts as devulcanizing agent for GTR and then simultaneously as an effective Table 13. DMTA data for individual components and blends produced. Blend code
Tg, oC / E"a), MPa for phases rich in:
Composition
Tg1 / E"
EPDM amorphous Tg2 / E"
HDPE-pc amorphous Tg3 / E"
HDPE-pc crystalline Tg4 / E"
-15 / 65 −b) −b) −b)
60 / 100 68 / 30 54 / 21
GTR
B7 B8
HDPE-pc EPDM HDPE-pc/EPDM HDPE-pc/EPDM/ GTR
-50 / 160
-36 / 102 -31 / 134 -42 / 150
B9 B11
HDPE-pc/EPDM/ GTR/ bitumen HDPE-pc/EPDM/ GTR/ bitumen
-49 / 121 -48 / 63
-35 / 158 -33 / 110
a) b)
E" value taken at Tgi Tg3 is overlapped with Tg2.
−b) −b)
42 / 35 53 / 41