EVOH/clay nanocomposites produced by melt processing

Abstract

Ethylene‐vinyl alcohol copolymer(EVOH)/clay nanocomposites were prepared via a dynamic melt‐intercalation process. The phase morphology and the crystallization behavior of the nanocomposites were investigated, using DSC, DMTA, XRD and SEM. It was found that the treated clay content and dynamic processing time affect the viscosity of the EVOH/clay mixtures: higher clay contents and longer mixing times result in higher torque/viscosity levels. This is due to the increased interaction of the molten polar matrix (EVOH) with the treated organosilicate surface. Under the dynamic high shearing forces, the polymer penetrates the clay agglomerates/aggregates, intercalates within the organoclay galleries, and finally causes delaniination. Thermal analysis of the EVOH/clay nanocomposites showed that the melting temperature, crystallization temperature and heat of fusion of the EVOH matrix, sharply decrease with increasing both, the clay content and processing time. The intercalation level was characterized by X‐ray diffraction (XRD), which verified an increased gallery height. The DMTA spectra showed that longer processing times resulted in higher damping (E″ intensity) levels of the EVOH/clay composites, indicating higher fractions of the EVOH amorphous phase. However, no Tg changes were seen in spite of the high polymer/treated clay interaction levels, which may be attributed to a plasticizing effect of the low molecular weight organic cations.

Development of EVOH-kaolinite nanocomposites

“…An increase in melting temperature and melting enthalpy (the melting enthalpy has been normalized for the amount of polymer in the nanocomposites) are also observed in the nanocomposites. This observation is surprising, since some authors have reported crystallinity decreases in EVOH nanocomposites with montmorillonite [6,23,24]. This increase in melting enthalpy is likely to be caused by clay nanoplatelets having a nucleating role on cooling from the melt [25].…”

Experimental and computational investigation of EVOH/clay nanocomposites

“…11 In a recent study, it was shown that during melt mixing the processing torque (viscosity) of the EVOH composite with untreated clay (85/15 EVOH/untreated clay) was practically constant, implying that the clay particles remain intact, behaving essentially as regular filler particles. However, the viscosity of the composite with treated clay (85/15 EVOH/treated clay) was rising due to clay fracturing processes, formation of new surfaces, and additional interaction with the EVOH matrix (Fig.…”

Effect of Type of Surfactants and Organoclay Loading on the Mechanical Properties of EVOH/Clay Nanocomposite Blown Films

“…By mixing the organoclay of interest with EVOH, the obtained nanocomposites were shown to provide better mechanical properties than pure EVOH [21][22][23][24][25] . In reality the surfactant is expected to affect the degree of clay dispersion in the polymer matrix, thereby reflecting on the mechanical properties of the nanocomposites.…”

“…In the melt-mixing preparation, the organoclay is melt-mixed with the host polymer in an extruder. In fact, the structure and properties of bulk samples of EVOH=clay nanocomposites prepared by the solution precipitation method [25] and melt-mixing method [21][22][23][24] have been investigated. In contrast, this study is focused on the solid-state properties of EVOH=clay nanocomposite films intended for packaging applications.…”