Rubber-Thermoplastic Compositions. Part I. EPDM-Polypropylene Thermoplastic Vulcanizates

Abstract

Thermoplastic elastomers are rubbery materials which can be fabricated by techniques usually associated with thermoplastic resins. Classical elastomers rely upon the crosslinked network, developed during vulcanization, to provide the retractive forces of rubber type elasticity. Thermoplastic elastomers contain rubber domains and resinous thermoplastic domains. The thermoplasticity results from the melting characteristics of the hard thermoplastic phase, while the rubber properties arise from the rubbery domains. Thermoplastic elastomers are, therefore, almost by definition, heterogeneous in their phase morphology. Such materials can be blends or block polymers. In the case of block polymers, the rubbery phase is not crosslinked chemically. However, hard or resinous phase domains occur as the hard segments of the block polymer which separate from the composition by agglomeration during cooling from the molten state. These domains act both as well-bonded reinforcing filler particles and as crosslinks. This is, of course, because the hard blocks are connected to the soft or rubbery segments by primary chemical bonds. In the case of the blend compositions, the hard and soft domains are separate polymeric species. However, there must be some form of interaction between the domains if useful properties are to be realized. Recently, uncured or partially cured EPDM rubber has been blended with polyolefin resin to make thermoplastic elastomer-like compositions. However, these compositions suffer deficiencies in performance as well as in certain aspects of fabricability. Only poor to fair performance at temperatures above 70°C in air or in oil has been achieved with the uncured to partially cured compositions. More recently, it has been found in our laboratories that fully cured EPDM compositions which are fabricable as thermoplastics can be prepared. Such compositions, referred to here as thermoplastic vulcanizates, have superior strength, high-temperature mechanical properties, hot oil and solvent resistance, better compression set, etc. This report outlines critical parameters associated with these unique materials.

Studies on the influence of structurally different peroxides in polypropylene/ethylene alpha olefin thermoplastic vulcanizates (TPVs)

“…Gessler was the first to claim dynamically vulcanized blends in 1962 [3]. Significant improvement in the field of TPVs was achieved by Coran and Patel [4] by fully vulcanizing the rubbery phase without affecting the thermoplasticity of the blends. Further development in this field was advanced by Abdou-Sabet and Fath [5] by using phenolic resin as curative in polypropylene/ ethylene propylene diene rubber (PP/EPDM) which not only crosslink rubbery phase but also involve in compatibilizing the two phases by forming graft-links between the blend components.…”

Electron-induced reactive processing of thermoplastic vulcanizate based on polypropylene and ethylene propylene diene terpolymer rubber

“…The dynamic vulcanization process was first reported by Gessler 9 in 1962, and then further developed by Fisher 10 as well as Coran and Patel. 11,12 Most commercial TPVs are based on blends of EPDM rubber as the dispersed cross-linked rubber and PP as the thermoplastic matrix. PP is one of the most widely used polymers; it has excellent stiffness and tensile properties, but owing to its high glass-transition temperature, it exhibits poor impact strength at low temperatures, which limits its applications.…”

Thermal and rheological behavior of reactive blends from metallocene olefin elastomers and polypropylene

“…The TPV morphology is attained even if the thermoplastic polymer is present as the minority component [3] , and the material shows elastic properties at room temperature approaching those of thermoset elastomers, and even can be melt reprocessed. These materials were first described by Gessler [2] , and commercially introduced in the 70's by Fisher [4] , and studied by several authors having a wide variety of elastomer-plastic systems afterwards [5][6][7][8][9][10][11] . In particular, the most significant work in TPV technology was developed by Coran yielding "fully" crosslinked compounds [6] .…”

“…In recent work, Arroyo [8] summarizes the long time regarded knowledge that optimum dispersion of rubber particles guide to superior physical properties and are practicable by matching viscosities of the polymer pair. Also, some reports indicated that due to the small interfacial tension and the limited degree of compatibility, the methylol-phenolic crosslinked ethylene-propylene-diene terpolymer/polypropylene (EPDM/PP) pair had presented the best balance of physical properties and achieved the biggest commercial significance [9][10] , calling attention of many industrial players and a large number of academic researchers [11][12][13][14][15][16][17][18][19][20][21][22][23] . The advent of Metallocene Single-site Constrained geometry catalysts allowed the production of tailor made polymers with narrow molecular weight distribution and consistent co-monomer incorporation in levels not achievable by using conventional Ziegler-Natta type of catalysts [18,19] .…”