Abstract
In this study, nanocomposites based on polycaprolactone (PCL) and two types of mesoporous silicas, MCM-41 and SBA-15, were attained by melt extrusion. The effect of the silica incorporated within the PCL matrix was observed, firstly, in the morphological characteristics and degradation behavior of the resultant composites. DSC experiments provided information on the existence of confinement in the PCL–SBA-15 materials through the appearance of an additional small endotherm, located at about 25–50 °C, and attributed to the melting of constrained crystallites. Displacement to a slightly lower temperature of this endothermic event was observed in the first heating run of PCL–MCM-41 composites, attributed to the inferior pore size in the MCM-41 particles. Thus, this indicates variations in the inclusion of PCL chains within these two mesostructures with different pore sizes. Real-time variable-temperature small-angle X-ray scattering (SAXS) experiments with synchrotron radiation were crucial to confirm the presence of PCL within MCM-41 and SBA-15 pores. Accurate information was also deduced from these measurements regarding the influence of these two mesoporous MCM-41 and SBA-15 silicas on PCL long spacing. The differences found in these morphological and structural features were responsible for the ultimate mechanical response exhibited by the two sets of PCL nanocomposites, with a considerably higher increase of mechanical parameters in the SBA-15 family.
Highlights
Details of the mesoporous MCM-41 and SBA-15 particles were obtained by highresolution field-emission scanning electron microscopy (FESEM), as well as the dispersion of those silica particles within the PCL matrix
The results showed that the channels of the PCL–MCM-41 composites led to an inferior, and less satisfactory, reinforcewell-defined hexagonal arrangement exhibited by both of the pristine silicas was mainment when comparedparticles with thatembedded exhibited within by the PCL–SBA-15 materials
Composites based on PCL and different amounts of mesoporous MCM-41 or SBA-15 particles were achieved by melt extrusion
Summary
The study of the crystalline characteristics of organic solids formed in small spaces of controlled pore glasses has been relevant for a long time [1]. A melting point depression was found by differential scanning calorimetry (DSC), and the influence of pore diameter on the magnitude of the reduction in melting temperature (Tm ) and in the apparent melting enthalpy ∆Hm has been reported [2]. The formation of small crystals was described theoretically in a classical discussion by Gibbs [3] and results from the effect of surface curvature on the equilibrium state of a pure substance [4]. A related theory was derived by Thomson [5] for the effect of curvature on the vapor pressure of liquid droplets
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