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

http://dx.doi.org/10.1590/S0104-14282012005000030 Nei S. Domingues Junior Kraton Polymers do Brasil, São Paulo Departamento de Engenharia de Materiais, UFRGS Maria M. de C. Forte Departamento de Engenharia de Materiais, UFRGS Izabel C. Riegel Instituto de Ciências Exatas e Tecnológicas, Feevale Introduction 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[11-23]. 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]. New polymer families of ethylene α-olefin copolymers with elastomeric behavior are now commercially available, reported as impact modifiers for polypropylene rich blends[20], and recently it had been considered for use as modifiers in soft olefin based blends[21], and TPVs[22,23]. In addition to this scenario, Waymouth and co-workers[24] reported a new way to synthesize a thermoplastic elastomeric PP based on an unbridged metallocene using oscillating stereo control. The isotacticity of the polymer, described by the isotactic pentad content, namely measured by the [mmmm] content, suggests a block structure PP with different stress-strain profile and unusual elastomeric properties. Whereby they are claimed elastomeric in its nature, and also could potentially play a role in dynamic vulcanizated blends both as a plastic matrix or even as a dispersed elastomeric phase provided using a suitable curing agent[25]. The emergent new classes of polyolefin elastomers (POEs) coupled with dramatically improved means of controlled synthesis through metallocene-catalyzed polymerization and with new alternatives for curing polyolefins[26] have opened up a wider range of potential commercial applications than ever thought possible in TPE/TPV arena. Autor para correspondência: Nei S. Domingues Junior, Kraton Polymers do Brasil, R&D Group, Av. Roberto Simonsen, 1500, CEP 13140-000, Paulínia, SP, Brasil, e-mail: Polímeros, vol. 22, n. 3, p. 213-219, 2012 213 CIENTÍFICO Thermoplastic elastomers (TPEs) based on rubber and plastic blends are materials that combine properties of thermoplastic and elastomeric materials, not achievable by other means. Thermoplastic Vulcanizates (TPVs) – a sub-class of TPEs[1], are engineering materials obtained by blending elastomeric and plastic polymers through a process called dynamic vulcanization[2]. Dynamic vulcanization is a process in which the elastomeric component is vulcanized in situ under continuous flow and shear to avoid coalescence and expedite dispersion. This process produces a characteristic and stable morphology where the crosslinked elastomer can became the dispersed phase with dimensions on the order of 1 µm, immersed in the thermoplastic matrix. 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[5-11]. In particular, the most significant work in TPV technology was developed by Coran yielding “fully” crosslinked compounds[6]. Rubber elasticity of TPV is usually attributed to a result of combined factors as morphology, plastic matrix, processing conditions, dispersed rubber microstructure and its particle size domains[7]. 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 TÉCNICO Abstract: Reactive blends of metallocene polyolefin elastomers (POE)/polypropylene (PP) with 60/40 composition were prepared with an organic peroxide, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, and a bis-azide derivative, diphenyloxid-4,4’-bis(sulfonylazide) (BSA). Ethylene-1-butene (EB) and ethylene-1-octene (EO) copolymers and elastomeric polypropylene (ePP) were used as the elastomeric phase. The effect of elastomeric phase on the thermal, rheological, morphological and mechanical properties of the thermoplastic vulcanizates (TPVs) or dynamic vulcanizates were studied. All TPVs depicted pseudoplastic behavior and blends cured with azide curative showed higher viscosities. The TPVs showed both dispersed and continuous phase morphology that depends on the elastomeric phase type revealing a limited degree of compatibility between PP and the elastomers EO or EB. On the other hand, the TPV PP/ePP showed a uniform morphology suggesting an improved compatibility. Substantial changes observed in physical properties were explained on the basis of blends’ morphology and dynamic vulcanization. The results confirm that the mechanical properties are more influenced by the elastomeric phase than by the curative agent. This study revealed a broad new range of opportunities for POE-based TPVs. Keywords: Reactive blend, thermoplastic vulcanizates, metallocene polyolefin elastomers, rheology. ARTIGO Thermal and Rheological Behavior of Reactive Blends from Metallocene Olefin Elastomers and Polypropylene Domingues Junior, N. S. et. al. - Thermal and rheological behavior of reactive blends from metallocene olefin elastomers and polypropylene The present study focuses on the properties of blends using random polypropylene copolymer (PP) as the hard component and polyolefin elastomers (POE) as the soft ingredient. The POEs consists of two (ethylene-α-olefin) copolymers, and one elastomeric polypropylene are metallocenic polymers. The blends compositions contain higher concentration of the elastomeric component and were evaluated before and after the dynamic vulcanization. The material characterization is mainly concerned with the polymer crystallization, melt rheology, viscoelastic behavior, physical properties, and morphology of such blends. Experimental Typical properties of the PP and the POEs employed in this work are listed in Table 1. Both (ethylene-α-olefin) copolymers, poly(ethylene-1-butene) (EB) and poly(ethylene-1-octene) (EO), and the elastomeric polypropylene (ePP) were produced with commercial metallocene catalysts, and were used as elastomeric phase in the blends with a commercial Ziegler-Natta polypropylene as described in a previous paper[27]. The blends and TPVs formulations (in phr) are described in detail in (...truncated)