IPP/EPR blends

Grein C, Beguelin P, Plummer CJG, Kausch H-H, T6z6 L, Germain Y (2000) Influence of the morphology on the impact fracture behaviour of iPP/EPR blends. In Williams JG, Pavan A (eds) Fracture of polymers, composites and adhesives, ESIS Publication 27. Elsevier, Oxford... 

KEYWORDS iPP/EPR blends, ductile-brittle transition, toughness evaluation, LEFM, plastic zone correction, intrinsic parameters... 

Two important types of elastomeric polyolefin blends are reactor-made iPP/ EPR blends and postreactor blend iPP/EPDM. The latter is called thermoplastic vulcanizates (TPVs), produced by dynamic vulcanization of blends containing a thermoplastic and an elastomer. To make iPP/EPDM TPV, the two polymers PP and EPDM are mixed with curatives, such as peroxides, phenolic resins, or sulfur with accelerators, and dynamically cured in an extmder resulting in a blend consisting of micrometer-sized elastomer particles dispersed in the PP matrix (20-24). Paraffinic oils are added in the melt mixing process for viscosity control and cost. In iPP/ EPDM TPV, the crystalline iPP resin is normally the minor phase. Recently, polyolefin plastomers have been added to the class of elastomeric polyolefin blends. Polyolefin plastomers are ultralow molecular weight linear low density polyethylenes (ULMW-LLDPE). Nonelastomeric polyolefin blends are blends of polyolefins with mostly nonpolyolefin (other thermoplastic) matrices as mentioned earlier. 

Binary blends of iPP and EPR copolymers have been extensively investigated from the commercial point of view. Although the control of compatibility plays an important role in the improvement of mechanical properties in the iPP/EPR blend systems, the strong incompatibility in iPP and EPR blends limits the modifications of morphology and mechanical properties (9). 

Figure 11.5 Strain rate dependence of yield stress for (a) a-PP and (J-PP homopolymers, and (b) 15% toughened iPP/EPR and (J-nucleated iPP/EPR blends at room temperature. (From Reference 31 with permission from Elsevier.)...

For the (3-nucleated iPP/EPR blend containing 15% impact modifier, Grein and coworkers determined the radius of plastic zone at 30, 5, 23, and 60°C under... 

Grein C and Gahleitner M (2008) On the influence of nucleation on the toughness of iPP/EPR blends with different rubber molecular architectures, eXPRESS Polym Lett 2 392-397. 

IPP/EPR blends have been the subject of coimtless papers and phase separation in the melt with as low as 8% ethylene observed [350], based on SANS results. Seki et al. [351] noted that earlier studies were based on Ziegler-Natta catalyst prepared EPR and metallocene catalyst yield more random structures. Their results on iPP blends with metallocene prepared EPRs with perdeuterated ethylene contents of 19 and 47 mol% showed single phase behavior, as determined by SANS. 

In the case of iPP/EPR and (3-PP/EPR blends containing 15 vol% impact modifier, Grein et al. indicated that the (3-nucleation had little effect on the brittle-ductile transition at —30, —5, 25, and 60°C on the basis of the results of Kiq versus dKIdt plots. Thus, elastomer particles play a major role during deformation of... 

Table 5.9 Fracture mechanical values of ternary iPP/EPR/PE blends determined at the instru-mented ...

Scho SchoBig, M. Struktur und Eigenschaftscharakterisierung von temaren iPP/EPR/PE-Blends. Martin-Luther-Universitat Halle-Wittenberg, Masterthesis, 2003. 

In other systems, such as in iPP/EPR, PE/iPP, and iPP/polyamide (PA) blends, a deviation from the additivity law given by equation (5) is detected (19,28,29). Figure 6 illustrates, as an example, the obtained deviation oiH from the additivity law (dashed line) for PE/iPP blends, 4> being in this case the weight fraction of polypropylene. If one takes into accoimt the measured crystallinity values for the Hi and H2 components within the blends, and the He values of the homopolymers, then equation (5) leads to the dotted line in Figure 6. Still, the experimental data are clearly deviated from the predictions of equation (5). The low experimental H values found for the PE/iPP blends are due to a depression in the H and values as a consequence of an increase in the surface free energy of the crystals (see eq. (3)) (28). 

In the PS/EPR blends, Radonjic and co-workers (179) found the S-B-S triblock copolymer with Mn of the PS blocks of 7,000, to be localized at the PS/EPR interface. The compatibilization efficiency of this block copolymer was further confirmed by finer dispersion in the resulting PS/EPR/S-B-S blends, as well as by improved PS/EPR adhesion. This short triblock copolymer appears to be a good compatibilizer also in iPP/aPS blends. According to mit and Radonjic (180), S-B-S forms an interfacial layer between dispersed honeycomb-like PS/S-B-S particles and PP matrix and influences also crystallization in iPP. 

Extremely soft and fluid blends of E-plastomers with iPP have been made by incorporating a large amount of a low-density E-plastomer with added process oil for fluidity and softness with a minor amount of iPP [10]. In a representative formulation, 56 parts of an impact copolymer (ICP) which had 62 wt% of iPP and the balance an EPR, 22 parts of an E-plastomer (hexene comonomer), 11 parts of an E-plastomer (octene comonomer), and 5 parts of talc showed a Rockwell R hardness 77,... 

In rubber-plastic blends, clay reportedly disrupted the ordered crystallization of isotactic polypropylene (iPP) and had a key role in shaping the distribution of iPP and ethylene propylene rubber (EPR) phases larger filler contents brought about smaller, less coalesced and more homogeneous rubber domains [22]. Clays, by virtue of their selective residence in the continuous phase and not in the rubber domains, exhibited a significant effect on mechanical properties by controlling the size of rubber domains in the heterophasic matrix. This resulted in nanocomposites with increased stiffness, impact strength, and thermal stability. 

Harnischfeger et al. [1990] also investigated the effect of electron irradiation on the mechanical properties of blends of iPP and PP-PE, with EPDM (Table 11.9). Immiscible blends of PP and EPR exhibit high impact strength because of... 

The morphological feature is in accordance with that of binary blends of iPP and true diblock iPP-b-EPR copolymers (63). For the immiscible blends showing phase separation, the EP domains have no ability to affect the lamellar or crystalline morphology of iPP. It follows that the strength of iPP lamellae is essentially independent of the addition of EP copolymers although the magnitude of bulk stress is reduced by the addition of EP copolymers with a lower modulus. 

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