Effect of Methacrylate Co-Agents on Peroxide Cured PP/EPDM Thermoplastic Vulcanizates

Abstract

Thermoplastic vulcanizates (TPVs) have gained large technical and economic importance. TPVs are characterized by a chemically crosslinked rubber phase, embedded in a thermoplastic matrix, produced by dynamic vulcanization during mixing with the thermoplastic in its molten state. Methacrylate species are investigated as co-agents for peroxide vulcanization of polypropylene/ethylene-propylene-diene-rubber (PP/EPDM) TPVs, whereby the weight fraction of the EPDM is varied from 30, 50 to 70%. Ethylene glycol dimethacrylate (EDMA), trimethylol propane trimethacrylate (TMPTMA, often referred to as TRIM) and zinc dimethacrylate (ZDMA) are tested. A fixed amount of dicumyl peroxide as crosslinker and varying contents of co-agents are employed, the latter to boost EPDM-crosslinking and prevent degradation of the PP by β-scission. Differences observed in mechanical properties point to diverse structures of the crosslink networks of the TPVs. Of the three co-agents, TMPTMA gives the best overall balance of properties by EPDM crosslinking and preventing PP-degradation. This is explained by the positioning of the solubility parameter of this co-agent between those of EPDM and PP, whilst EDMA presents a value far away from either one. ZDMA, although giving very good room temperature properties like tensile strength, shows signs of thermo-reversion of the crosslinks in the compression set measured at 70 °C.

TPVs PA/NBR: sistema de reticulação e propriedades

“…O processamento do TPV foi realizado em câmara de mistura HAAKE RHEOCORD munido de rotores tipo "roller" em específicas [1,8,15] . Da diversidade de sistemas investigados apenas alguns se tornaram comercializáveis, destacando-se os TPVs a base de borrachas de EPM ou EPDM e o termoplástico PP.…”

“…Valores de tensão e alongamento da ordem de 20 MPa e 500%, respectivamente, podem ser alcançados com domínios elastoméricos em torno de 5 µm. A morfologia é definida durante a vulcanização dinâmica e depende, entre outros fatores, do sistema de cura que, além do agente principal, pode envolver coagentes [1,23,24] . Grimma et al [25] ao reticular borracha EPDM da forma convencional, com peróxido de dicumila (DCP) combinado com enxofre ou agentes doadores de enxofre, como o 2-mercapto benzotiazol (MBT), obtiveram uma borracha termofixa com alto módulo e alta resistência à ruptura.…”

“…Elastômeros termoplásticos (TPEs) reúnem as propriedades elásticas das borrachas em temperaturas usuais de aplicação com a facilidade de processamento dos polímeros termoplásticos em temperaturas elevadas [1][2][3][4] . Estas características são consequência da morfologia bifásica decorrente da natureza química diferenciada dos constituintes e do seu processo de obtenção.…”

Hydrotalcite/unsaturated Carboxylic Acid Systems as Coagents in Ethylene-Propylene Copolymer Vulcanization

“…It was concluded that coagent bonds were formed as additional crosslinks because of graft polymerization of the allyl moieties of the coagent and covulcanization of coagent domains with the elastomer matrix. De Risi and Noordermeer applied methacrylate coagents to the peroxide curing of ethylene-propylene-diene elastomer and polypropylene blends [3]. The highest crosslinking activity occurred with trimethylol propane trimethacrylate, which also prevented the degradation of polypropylene through chain scission.…”

“…Peroxide vulcanization of polymers is a widely discussed process [1][2][3][4][5]. This process is usually used when good aging resistance, high processing temperature or good compression set at elevated temperature of rubber products is required [6].…”