Avaliação da densidade de ligações cruzadas da borracha natural reticulada em diferentes sistemas de vulcanização por meio de ensaios mecânicos
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Data
2020-01-31
Autores
Hiranobe, Carlos Toshiyuki
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Universidade Estadual Paulista (Unesp)
Resumo
Propriedades mecânicas e térmicas da borracha natural (BN) podem ser modificadas no processo de vulcanização, variando-se as quantidades de enxofre e acelerador para atender as especificações desejadas. A influência da taxa acelerador/enxofre foi analisada e suas propriedades mecânicas foram comparadas de acordo com o desempenho de cada uma nos respectivos sistemas de reticulação. Preparou-se compostos de BN reticulados com enxofre por três sistemas de vulcanização: convencional (CV), semieficiente (SEV) e eficiente (EV). Os sistemas foram processados utilizando MBTS (dissulfeto de dibenzotiazol), TMTD (dissulfeto de tetrametiltiuram) e CBS (n-ciclohexil 2-benzotiazol sulfenamida). As misturas foram preparadas em misturador aberto de rolos, de acordo com a norma ASTM D3182. A caracterização foi realizada por meio da reometria (ASTM D2084), ensaios mecânicos e térmicos, envelhecimento acelerado e determinação das densidades de ligações cruzadas por inchamento, análise dinâmico mecânica, ensaio de tração e por ressonância magnética nuclear utilizando hidrogênio em baixo campo magnético (RMN1H). O sistema SEV, utilizando TMTD e CBS, foi o que apresentou resultados superiores nos tempos de cura e nas propriedades mecânicas como a rigidez, dureza, abrasão e resistência à tração. Quando utilizado o MBTS, obteve-se vulcanizados com grande resistência quanto à deformação, além de apresentar pós-cura no processo de envelhecimento acelerado. O sistema de cura não alterou a estrutura físico-química dos vulcanizados. Observou-se, ainda, por meio dos ensaios de DMA que o aumento da densidade de reticulação aumenta a temperatura de transição vítrea do composto vulcanizado.
The vulcanization process can modify mechanical and thermal properties of natural rubber (NR) by varying the amount of sulfur and accelerator to meet the preferred specifications. The influence of the accelerator/sulfur rate was analyzed and its mechanical properties were compared according to the performance of each one on the respective crosslinking systems. NR composites crosslinked with sulfur were prepared by three systems: conventional (CV), semi-efficient (SEV) and efficient (EV). The systems were processed using MBTS (dibenzothiazole disulfide), TMTD (tetramethyltiuram disulfide) and CBS (n-cyclohexyl 2-benzothiazole sulfenamide). The mixtures were prepared in an open rolled mixer, following the ASTM D3182 standard. The characterization was carried out by rheometry (ASTM D2084), mechanical and thermal tests, accelerated aging and crosslinking density determination by swelling, dynamic mechanical analysis, tensile tests and nuclear magnetic resonance tests using hydrogen in low magnetic field (NMR1H). The SEV system, using TMTD and CBS, was the one that has presented superior results in curing times and mechanical properties, such as rigidity, hardness, abrasion and tensile strength. Vulcanized composites with great resistance to deformation and presenting post-cure in the accelerated aging process were obtained using MBTS. The curing system did not alter their physical-chemical structure. It was also observed, through DMA tests, that the increasing in the crosslinking density increases the glass transition temperature of the vulcanized composites.
The vulcanization process can modify mechanical and thermal properties of natural rubber (NR) by varying the amount of sulfur and accelerator to meet the preferred specifications. The influence of the accelerator/sulfur rate was analyzed and its mechanical properties were compared according to the performance of each one on the respective crosslinking systems. NR composites crosslinked with sulfur were prepared by three systems: conventional (CV), semi-efficient (SEV) and efficient (EV). The systems were processed using MBTS (dibenzothiazole disulfide), TMTD (tetramethyltiuram disulfide) and CBS (n-cyclohexyl 2-benzothiazole sulfenamide). The mixtures were prepared in an open rolled mixer, following the ASTM D3182 standard. The characterization was carried out by rheometry (ASTM D2084), mechanical and thermal tests, accelerated aging and crosslinking density determination by swelling, dynamic mechanical analysis, tensile tests and nuclear magnetic resonance tests using hydrogen in low magnetic field (NMR1H). The SEV system, using TMTD and CBS, was the one that has presented superior results in curing times and mechanical properties, such as rigidity, hardness, abrasion and tensile strength. Vulcanized composites with great resistance to deformation and presenting post-cure in the accelerated aging process were obtained using MBTS. The curing system did not alter their physical-chemical structure. It was also observed, through DMA tests, that the increasing in the crosslinking density increases the glass transition temperature of the vulcanized composites.
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Palavras-chave
Borracha natural, Inchamento, Propriedades mecânicas, Ressonância magnética nuclear, Reticulação, Natural rubber, Swelling, Mechanical properties, Nuclear magnetic resonance, Crosslinking