Structure-Property Relationships in Isotactic Poly(propylene)/Ethylene Propylene Rubber/Montmorillonite Nanocomposites

Abstract

Nanocomposites based on isotactic polypropylene/ethylene propylene rubber (iPP/EPR) were prepared adding different amounts of montmorillonite and maleated polypropylene. The structure and morphology of the samples were characterized by small angle X-ray scattering, wide angle X-ray diffraction, electronic and optical microscopy and differential scanning calorimetry, iPP showed a polymorphic behavior. Clay disrupted the ordered crystallization of iPP and had a key role in shaping the distribution of iPP and EPR phases: larger filler contents brought about smaller, less coalesced and more homogeneous rubber domains. Clay distributed itself only in the continuous phase and not in the rubber domains. Tactoids persisted on the surface of the sample, while delamination proceeded to a greater degree in the bulk of the materials. Melt flow rate, impact strength, flexural and tensile properties, were also measured and a structure-property correlation was sought. Clay produced its most significant effect on physical-mechanical properties by controlling the size of rubber domains in the heterophasic matrix. This allowed to obtain nanocomposites with increased stiffness and impact strength, a remarkable achievement for polymer layered-silica nanocomposites that usually suffer the drawback of being stiffer than the unfilled matrix, but at the same time with a lower resistance to impact. A beneficial effect of clay on thermal stability was also observed.

Quantification of organoclay dispersion and lamellar morphology in poly(propylene)–clay nanocomposites with small angle X-ray scattering

“…HPP 68 87 --HPP-NC 57 75 --RCP 58 71 10 6 RCP-NC 62 68 53 69 ICP 54 70 --ICP-NC1 52 74 13 7 ICP-NC2 52 74 12 8 thicknesses in the nanocomposites are related to multiple parameters such as initial crystal structure of PP matrix, nucleators and dispersed phases, processing conditions, etc., hence further investigations would be required to comprehensively explain the changes seen in lamellar thickness of nanocomposites. Changes in a lamellar thicknesses reported on a PP-EPR composition [54] were found to lie in the range of 15.8-17.4 nm for the nanocomposites as compared to 16.7 nm for neat PP-EPR. Local crystallinity F was also estimated as a weighted average of H/L for the g fraction and a fraction and is given in Table 2.…”

“…Increased g-fraction in PP has also been reported in the presence of organoclay [54,65,66], pointing to the role of organoclay in promoting g-fraction of PP. This effect has been ascribed to decreased chain mobility induced by clay particles, leading to the formation of smaller, less ordered crystallites [65].…”

“…In RCP and RCP-NC, SAXS response was seen to consist of two prominent peaks, and is attributed to the presence of a and g lamellae. Lamellar thickness for g crystals is usually lower, so the peak at higher q is assigned to g lamellae in both the samples [54]. SAXS peaks corresponding to both a and g lamellae in RCP showed a significant shift to lower angles in RCP-NC.…”

“…This approach was demonstrated by Causin et al for the quantification of organoclay dispersion in polypropylene and poly(butene) [49][50][51]53,54]. Influence of additives and processing conditions on extent of nanoclay dispersion was explained with quantitative data such as the number of clay layers, interlayer spacing and its distributions.…”

“…Estimation of level of exfoliation has also been demonstrated using an integrated correlation functions' approach, with a new parameter introduced as exfoliation factor as a measure of extent of exfoliation, and will be communicated in a future correspondence [59]. It may be noted that addition of nanoclay leads to breakup and better dispersion of discrete EPR particles, and hence the impact performance for such a three-phase system is an interplay between EPR morphology and nanoclay dispersion [54,60]. Since ICP is a three component system with dispersed organoclay and EPR phases in PP matrix, possible changes in EPR morphology were explored to understand further factors leading to improved impact performance of ICP-NC1, in addition to high level of organoclay exfoliation, as explained earlier.…”