Correlation Of Structure And Properties Of Natural Rubber Vulcanizates

Author : Tian Liang
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (134 download)

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Download or read book Structure and Properties of Rubbers and Their Blends Affected by Ultrasonically Assisted Extrusion written by Tian Liang and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The extrusion of star SBR, BR, NR, SBR/BR and NR/BR blends was carried out without and with ultrasonic treatment at amplitudes of 3.5, 5.0, 7.5 and 10 [micron]m and frequency of 20 kHz. The ultrasonic power consumption and die pressure during extrusion were measured. The power consumption increased and the die pressure generally decreased with the increase of ultrasonic amplitude. The gel fraction of untreated and treated rubber gums and rubber blends have been measured. Gel formation in star SBR and BR was found to start to occur at ultrasonic amplitudes of 5 [micron]m and 7.5 [micron]m, respectively, while no gel formation occurred in NR at any amplitude. Gel formation in treated SBR/BR blend occurred at amplitudes of 7.5 [micron]m and 10 [micron]m. No gel formation was observed in NR/BR blend treated up to an amplitude of 7.5 [micron]m. Generally, the gel content increased with the increase of ultrasonic amplitude in rubbers that are prone to gel formation. Molecular weight of the soluble part of gel was measured. The measurements indicated that ultrasonic treatment of star SBR, BR and SBR/BR blend at small amplitudes created molecules with a higher molecular weight, while at high amplitudes, chain scission took place. At the same time, ultrasonic treatment of NR only resulted in chain scission. Dynamic properties of the untreated and ultrasonically treated rubber gums and blends as a function of frequency at a small strain amplitude indicated the strong correlation with gel fraction and molecular weight. Specifically, gel formation resulted in a higher storage modulus, loss modulus and complex viscosity and a lower loss tangent in the low frequency region. Chain scission caused a lower storage modulus, loss modulus, complex viscosity and a higher loss tangent in the high frequency region. Compounds of untreated and treated star SBR, BR, SBR/BR blends with CB, silica and silica/silane were prepared. Also, compounds of untreated and treated NR and NR/BR blends with silica and silica/silane were prepared. The high molecular weight fraction created during ultrasonic treatment was found to increase the bound rubber content and rubber-filler interaction in the silica filled compounds. The higher bound rubber content was found to increase the thickness of bound rubber layer and reduce the flocculation of silica and filler-filler interaction. However, in the CB-filled and silica/silane-filled compounds did not show changes in bound rubber content and flocculation behavior. Higher level of flocculation was generally observed in filled compounds made from rubber gums and blends containing gel. This was due to the fact that filler was not dispersed in the gel part, such that the dispersion becomes inhomogeneous with the filler becoming more susceptible to flocculation. The stress-strain behaviors of vulcanizates were measured. The tensile strength of vulcanizates prepared from star SBR/silica compound ultrasonically treated at an amplitude of 3.5 [micron]m and not containing gel was increased in comparison with that of untreated rubber. Generally, the gel formation resulted in a lower tensile strength and elongation at break, as a result of the inhomogeneous dispersion of filler. The rolling resistance predicted based DMA measurements showed a reduction for vulcanizates prepared from SBR/BR/Silica and BR/Silica compounds ultrasonically treated at an amplitude of 5 [micron]m. For treated rubber gums and blends containing gel, DMA measurements of filled vulcanizates predicted a lower snow and wet traction, and a high rolling resistance. This is due to the stronger filler-filler interaction as a result of poor dispersion of filler.