Efeito do teor de dieno na cura da borracha etileno-propileno-dieno (EPDM): ênfase na fabricação de gaxetas para trocadores de calor
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Data
2020-12-15
Autores
Sartori, Cibele de Moraes Lima [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A borracha Etileno-Propileno-Dieno (EPDM) é uma borracha sintética composta por um terceiro monômero, sendo o mais utilizado o etilideno-norboneno (ENB). A presença desse ENB influencia diretamente nas propriedades mecânicas e térmicas do material. A vulcanização por peróxidos é frequentemente usada na cura da borracha EPDM e, embora aumente a vida útil, oferece propriedades mecânicas, e tempo de pré-vulcanização mais baixo do que os sistemas utilizando enxofre. A utilização dos peróxidos é primordial na fabricação de gaxetas para trocadores de calor a placas, devido a esse tipo de material trabalhar em temperaturas elevadas, porém para fabricar esse tipo de artefato é necessário um tempo alto de pré-vulcanização para garantir a qualidade do processo produtivo e minimizar as falhas. O objetivo principal deste trabalho foi desenvolver um sistema de cura com um tempo de prévulcanização adequado para a fabricação das gaxetas, atendendo os requisitos para um bom desempenho operacional. Os requisitos estabelecidos foram de tensão de ruptura maior de 12 MPa, alongamento menor que 300%, resistência ao rasgo maior de 45 N/mm e tempo de prévulcanização maior que 50 segundos. Neste trabalho, foram executadas duas etapas, na primeira etapa foi utilizado três tipos de peróxidos, sendo o Di(terc-butilperoxiisopropil)benzeno, Dicumila e 2,5-Dimetil-2,5-di(terc-butilperoxi)hexano, conhecidos comercialmente como Perkadox 1440, Perkadox BCFF e Trigonox 101 e na segunda etapa foi utilizado o doador de enxofre Dipentametileno thiuram tetrasulfeto (DPTT) e dois coagentes, o N,N’-m-Fenileno Dimaleimida (HVA-2) e Trimetilolpropano Trimetacrilato (TMPTMA) em conjunto com o peróxido de Dicumila. Em todas as etapas as amostras continham diferentes teores de ENB. Para realizar as etapas propostas, um reômetro foi usado para determinar os parâmetros de vulcanização (ts1, t90 e delta torque), as técnicas de Flory-Rehner e Mooney-Rivlin foram utilizadas para determinação da densidade de ligação-cruzada, e para quantificar as propriedades mecânicas, foram realizadas os ensaios de tensão de ruptura, alongamento, dureza e resistência ao rasgo, Com os resultados encontrados foi observado que o tipo de peróxido tem um efeito significativo nos tempos ts1 e t90, enquanto o teor de ENB agiu de forma significativa nos valores do delta torque. Essa diferença encontrada no delta torque com o aumento do teor de ENB foi confirmada pelos resultados de densidade de ligação-cruzada e refletidos nas propriedades mecânicas. Quando adicionado o DPTT, os resultados mostraram que houve um aumento no ts1 e t90, e uma diminuição no delta torque. O coagente do tipo HVA-2, apresentou uma maior densidade de reticulação, mantendo o ts1, diminuindo o t90 e aumentando o delta torque, porém apresentando propriedades mecânicas inferiores. Enquanto os resultados obtidos pelo TMPTMA, em relação as propriedades mecânicas, foram inferiores aos das amostras com DPTT, mais com um aumento no ts1. Portando, a adição do DPTT foi essencial para garantir a segurança de processo necessária, otimizando as propriedades fornecidas pelos peróxidos, assim como o uso do coagente TMPTMA foi de suma importância para adequar as propriedades requeridas para a fabricação de gaxetas para trocadores de calor.
Ethylene-Propylene-Diene rubber (EPDM) is a synthetic rubber composed of a third monomer, the most used being ethylidene-norbonene (ENB). The presence of this ENB directly influences the mechanical and thermal properties of the material. Peroxide vulcanization is often used to cure EPDM rubber and, although it extends its useful life, it offers mechanical properties and a lower scorch time than systems using sulfur. The use of peroxides is essential in the manufacture of gaskets for plate heat exchangers, due to this type of material working at high temperatures, however, to manufacture this type of artifact, a high scorch time is necessary to guarantee the quality of the process productive and minimize failures. The main objective of this work was to develop a curing system with an adequate scorch time for the manufacture of gaskets, meeting the requirements for good operational performance. The established requirements were a tensile strength greater than 12 MPa, elongation less than 300 %, tear strength greater than 45 N/mm and scorch time greater than 50 seconds. In this work, two stages were performed, in the first stage three types of peroxides were used, being Di(tertbutylperoxyisopropyl)benzene, Dicumila and 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane, known commercially such as Perkadox 1440, Perkadox BCFF and Trigonox 101 and in the second stage the sulfur donor Dipentamethylene thiuram tetrasulfide (DPTT) and two coagents, N, N'-m-Phenylene Dimaleimide (HVA-2) and Trimethylolpropane Trimethacrylate (TMPTMA) were used together with Dicumila peroxide. In all stages, the samples contained different levels of ENB. To perform the proposed steps, a rheometer was used to determine the vulcanization parameters (ts1, t90 and delta torque), the Flory-Rehner and Mooney-Rivlin techniques were used to determine the cross-link density, and to quantify the mechanical properties, tensile strength, elongation, hardness and tear resistance tests were performed. With the results found it was observed that the type of peroxide has a significant effect on times ts1 and t90, while the ENB content acted significantly delta torque values. This difference found in the delta torque with the increase in the ENB content was confirmed by the results of cross-link density and reflected in the mechanical properties. When DPTT was added, the results showed that there was an increase in ts1 and t90, and a decrease in delta torque. The HVA-2 type coagent showed a higher crosslink density, maintaining ts1, decreasing t90 and increasing the delta torque, but presenting lower mechanical properties. While the results obtained by TMPTMA, in relation to mechanical properties, were lower than those of samples with DPTT, more with an increase in ts1. Therefore, the addition of DPTT was essential to guarantee the necessary process safety, optimizing the properties provided by the peroxides, as well as the use of the TMPTMA coagent was extremely important to adapt the properties required for the manufacture of gaskets for heat exchangers.
Ethylene-Propylene-Diene rubber (EPDM) is a synthetic rubber composed of a third monomer, the most used being ethylidene-norbonene (ENB). The presence of this ENB directly influences the mechanical and thermal properties of the material. Peroxide vulcanization is often used to cure EPDM rubber and, although it extends its useful life, it offers mechanical properties and a lower scorch time than systems using sulfur. The use of peroxides is essential in the manufacture of gaskets for plate heat exchangers, due to this type of material working at high temperatures, however, to manufacture this type of artifact, a high scorch time is necessary to guarantee the quality of the process productive and minimize failures. The main objective of this work was to develop a curing system with an adequate scorch time for the manufacture of gaskets, meeting the requirements for good operational performance. The established requirements were a tensile strength greater than 12 MPa, elongation less than 300 %, tear strength greater than 45 N/mm and scorch time greater than 50 seconds. In this work, two stages were performed, in the first stage three types of peroxides were used, being Di(tertbutylperoxyisopropyl)benzene, Dicumila and 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane, known commercially such as Perkadox 1440, Perkadox BCFF and Trigonox 101 and in the second stage the sulfur donor Dipentamethylene thiuram tetrasulfide (DPTT) and two coagents, N, N'-m-Phenylene Dimaleimide (HVA-2) and Trimethylolpropane Trimethacrylate (TMPTMA) were used together with Dicumila peroxide. In all stages, the samples contained different levels of ENB. To perform the proposed steps, a rheometer was used to determine the vulcanization parameters (ts1, t90 and delta torque), the Flory-Rehner and Mooney-Rivlin techniques were used to determine the cross-link density, and to quantify the mechanical properties, tensile strength, elongation, hardness and tear resistance tests were performed. With the results found it was observed that the type of peroxide has a significant effect on times ts1 and t90, while the ENB content acted significantly delta torque values. This difference found in the delta torque with the increase in the ENB content was confirmed by the results of cross-link density and reflected in the mechanical properties. When DPTT was added, the results showed that there was an increase in ts1 and t90, and a decrease in delta torque. The HVA-2 type coagent showed a higher crosslink density, maintaining ts1, decreasing t90 and increasing the delta torque, but presenting lower mechanical properties. While the results obtained by TMPTMA, in relation to mechanical properties, were lower than those of samples with DPTT, more with an increase in ts1. Therefore, the addition of DPTT was essential to guarantee the necessary process safety, optimizing the properties provided by the peroxides, as well as the use of the TMPTMA coagent was extremely important to adapt the properties required for the manufacture of gaskets for heat exchangers.
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Palavras-chave
EPDM, ENB, Peróxido orgânico, Gaxetas, Hydrogen peroxide, Gaskets