Preparation, Structure And Properties Of HDPE/EPDM And POE/EPDM Based Thermoplastic Vulcanizates

Thermoplastic vulcanizates (TPVs) based on high density polyethylene (HDPE)/ ethylene-propylene-diene monomer (EPDM) blends and polyolefin elastomer (POE)/ ethylene-propylene-diene monomer (EPDM) blends were prepared by dynamic vulcanization, the influence of composition, preparing technique on the morphology and mechanical properties of the TPVs were researched, the dynamic viscoelastic behavior, stress relaxation, the influence of reprocessing and UV aging on mechanical properties of the prepared TPVs were also investigated systematically, the multi-yielding behavior and the morphology of the spherical crystals of nylon-6 were researched. The results were as follows:(1) A series of TPVs were prepared by changing the composition and species of raw materials, and processing techniques, the mechanical properties and microstructure were studied. Considering the proper elasticity, strength and low hardness, the optimal weight ratio of HDPE/EPDM blend should be 40/60.(2) The influence of POE and paraffin oil on the toughening effect of the resin phase, the elasticity, tension set at break, hardness and mechanical properties of the HDPE/EPDM TPVs were researched. The results showed that the hardness and tensile set at break of the prepared TPV were decreased obviously with the addition of POE in the matrix. For the HDPE/POE/EPDM TPVs with the paraffin oil filled in the matrix the operability of dynamic vulcanization process could be improved obviously, the hardness were decreased significantly. The mechanical properties of HDPE/POE/EPDM TPVs were markedly enhanced with the increase of carbon black (CB) content in EPDM phase, however, the mechanical properties of the TPVs will be decreased when the CB content exceeds a certain value.(3) The dynamic viscoelastic behavior of HDPE/POE/EPDM TPVs showed that with the increase of scanning frequency, it was hard for the mobility of chain segments to keep up with the increasing frequency, the storage modulus showed a linear increase, the peak of loss modulus occurred, and the loss factor tended to decrease. Increasing the content of POE in the TPVs, the mobility of chain segments was increased, leading to the obviously decreased friction among macromolecule chains, the storage modulus, the loss modulus was decreased obviously, however, the loss factor had almost no change.(4) The fracture surface morphology of the HDPE/EPDM TPVs was observed. The cluster-like nanofibres could be found on the fracture surface of the TPV, which were formed from the plastic deformation of spherical crystals of HDPE during the tensile test.The morphology of the microstruture of the etched TPVs was observed. The results showed that, the resin phase of the TPVs crystallized and presented cascaded and staggered sheet structure, while the rubber phase was distributed in the gaps among the lamellar sheets of HDPE. Strong interfacial interaction could be formed between the resin phase and the rubber phase of the TPVs due to the large interfacial area, leading to high mechanical properties of TPVs.(5) The influence of reprocessing times and UV accelerated aging time on the mechanical properties of the HDPE/POE/EPDM TPVs were studied. The results showed that reprocessing times and UV accelerated aging time had less influences on TPV's properties, indicating the excellent reprocessing properties and aging resistance of the TPVs.(6) The POE/EPDM TPVs were prepared by dynamic vulcanization. The hardness and tensile set of the POE/EPDM TPVs reached a lower level than pure POE. Compared with that of POE/EPDM TPVs prepared with phenolic resin vulcanization system, the POE/EPDM TPVs prepared with sulfur vulcanization system showed more excellent mechanical properties due to the smaller size and better dispersion of the EPDM dispersed phase. The stress relaxation rate of the prepared TPVs decreased with the increase of the EPDM content. RPA results show that the storage modulus of POE/EPDM TPVs was higher than that of pure POE, however, the storage modulus decreased with increasing EPDM content, in addition, with the increase of scanning frequency, the storage modulus showed a linear increase, the loss modulus increased slightly, the loss factor had almost no change.(7) The multi-yielding behavior and the morphology of the spherical crystals of nylon-6 were researched. The results showed that the multi-yielding phenomenon could be observed obviously when the tensile rate was 50 mm/min below, which could be caused by the weakness in micro-fibers structure of nylon-6 specimens. The radicalized micro-fibers, the morphology of the spherical crystals and the crystals boundary could be observed remarkably by the optical microscope.