Morphology Characterization of PP/Clay Nanocomposites Across the Length Scales of the Structural Architecture

Abstract

Summary: The structure and rheological properties of a large number of layered silicate poly(propylene) nanocomposites were studied with widely varying compositions. Morphology characterization at different length scales was achieved by SEM, TEM, and XRD. Rheological measurements supplied additional information about structure. The results showed that these materials possess a very complex structural architecture. The introduction of functionalized polymer decreased the size of the original clay particles and improved their interaction with the polymer matrix. However, relatively large silicate particles were found also in composite samples yielding XRD traces without silicate reflection. XRD supplies information of limited value if the amount of silicate is low, the gallery distance of the stacks is large or their regularity is limited. On the other hand, XRD indicates intercalation well. Although exfoliated individual layers can be detected by TEM, the method cannot be used to draw general conclusions about the structure of layered silicate nanocomposites because of statistical sampling and bias. A large number of individual layers, i.e. large extent of exfoliation, led to the formation of a silicate network structure, which can be detected very sensitively by Cole‐Cole plots of dynamic viscosity. We found that all four morphological entities (particles, intercalated stacks, individual layers, network) may be present simultaneously in the composites. The presence and relative amount must definitely influence composite properties. However, currently used experimental protocols do not supply sufficient information even to estimate the relative influence as well as interplay among different structural features quantitatively. We may conclude, however, that XRD and TEM alone are not sufficient for the characterization of nanocomposites with a complex structure.

Effect of organic peroxides on the morphological, thermal and tensile properties of EVA-organoclay nanocomposites

“…This was expected as a result of the known weak interaction between organoclay and EVA with low VA content. It is, however, possible that minimal intercalation also occurred in the case of the 1% clay containing sample, because it has been shown that XRD is not a very reliable technique for establishing clay intercalation/exfoliation at low clay contents [13]. This observation is supported by the TEM image in Figure 2 that show the clay particles with little evidence of intercalation and no exfoliation.…”

Competitive interactions, structure and properties in polymer/layered silicate nanocomposites

“…Although the appearance of the silicate reflection in the XRD patterns proves the presence of tactoids and particles, it does not tell anything about their amount. In order to obtain a more quantitative estimate, the silicate peaks were integrated [24]. Integration was done in the Origin 8.5 software.…”

“…XRD is used to supply information on intercalation or exfoliation and the disappearance of the silicate reflection from the XRD pattern is falsely interpreted as a sign of complete exfoliation [19][20][21][22][23]. Usually subtle changes in gallery structure are not analyzed sufficiently thoroughly and reflection intensity indicating the amount of non-exfoliated silicates is not evaluated quantitatively practically at all [24]. Several studies clearly proved that the structure of layered silicate composites is complex [24][25][26][27].…”

“…Usually subtle changes in gallery structure are not analyzed sufficiently thoroughly and reflection intensity indicating the amount of non-exfoliated silicates is not evaluated quantitatively practically at all [24]. Several studies clearly proved that the structure of layered silicate composites is complex [24][25][26][27]. Usually it contains individual layers and tactoids, but a silicate network may also form at larger extent of exfoliation and large non-exfoliated particles are also present in the composite practically always [24].…”

“…Several studies clearly proved that the structure of layered silicate composites is complex [24][25][26][27]. Usually it contains individual layers and tactoids, but a silicate network may also form at larger extent of exfoliation and large non-exfoliated particles are also present in the composite practically always [24]. These latter usually are not detected, because they are not looked for; their presence must be checked by scanning electron microscopy (SEM).…”