The influence of the newly developed binary accelerator 1-phenyl-2,4-dithiobiuret (DTB) in combination with sulphenamides like DCBS, MBS, TBBS on the cure characteristics, mechanical properties, viscoelastic behaviour and network characteristics of styrene butadiene rubber (SBR) is studied. Kinetics of vulcanisation is followed at three different temperatures. Mechanical properties are found to be improved upon DTB addition. Attempts have been made to correlate the observed properties with extent of crosslinking of DTB. Effect of aging on tensile properties of the vulcanisates was also done. The extent of crosslinking was also improved with DTB cured vulcanisates. Dynamic mechanical analysis has been done and the influence of the new accelerator systems on the modulus, glass transition and entanglement densities of the vulcanisates was investigated. The effect of fillers like carbon black and silica on DTB on technological properties of SBR vulcanisates and the extent of reinforcement caused by the fillers were also studied.
The fracture mechanical response of a glass fiber (GF) mat-reinforced polypropylene (GMT-PP) was studied by instrumented Charpy impact testing. The GMT- PP was produced by hot pressing a needle-punched composite textile preform consisting of non-woven PP and continuous GF swirl mat layers. It was established that fracture mechanical values strongly depend on the width of the specimens. The free ligament width of the Charpy specimens (W-a, where W is the specimen width and a is the notch length) should exceed ca. 15 mm due to the inherent material flaw and the large damage zone de veloped. For the size of the inherent flaw, caused by the local arrangement of the GF-mat and its dislodgement due to machining, ca. 2 mm was deduced. This inherent flaw size should be considered when dynamic fracture toughness ( Kd) and initiation fracture energy (Gd,1) values are calculated. It was shown that Kd was unaffected, whereas Gd,1 decreased with increasing fiber fraction (Vf) in the range of Vf ~ 0.2 to 0.3. Contrary, the ductility index (DI), indicating the energy absorption ratio in the crack propagation stage, and the overall impact resistance increased with V f. The pressing conditions (temperature in the range of 190 to 200°C and pressure from 4 to 6 MPa) of the textile preform did not affect the fracture mechanical data which showed always a big scatter.
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