Poly(η-caprolactone) layered silicate nanocomposites: effect of clay surface modifiers on the melt intercalation process

Abstract

Nanocomposites based on biodegradable poly(ε-caprolactone) (PCL) and layered silicates (montmorillonite) modified by various alkylammonium cations were prepared by melt intercalation. Depending on whether the ammonium cations contain non-functional alkyl chains or chains terminated by carboxylic acid or hydroxyl functions, microcomposites or nanocomposites were recovered as shown by X-ray diffraction and transmission electron microscopy. Mechanical and thermal properties were examined by tensile testing and thermogravimetric analysis. The layered silicate PCL nanocomposites exhibited some improvement of the mechanical properties (higher Young's modulus) and increased thermal stability as well as enhanced flame retardant characteristics as result of a charring effect. This communication aims at reporting that the formation of PCL-based nanocomposites strictly depends on the nature of the ammonium cation and its functionality, but also on the selected synthetic route, i.e. melt intercalation vs. in situ intercalative polymerization. Typically, protonated ω-aminododecanoic acid exchanged montmorillonite allowed to intercalate ε−caprolactone monomer and yielded nanocomposites upon in situ polymerization, whereas they exclusively formed microcomposites when blended with preformed PCL chains. In other words, it is shown that the formation of polymer layered silicate nanocomposites is not straightforward and cannot be predicted since it strongly depends on parameters such as ammonium cation type and functionality together with the production procedure, i.e., melt intercalation, solvent evaporation or in situ polymerization.

Polymer/layered silicate nanocomposites by combined intercalative polymerization and melt intercalation: a masterbatch process

“…However, this beneficial effect is decreased when the clay content is increased (Fig. 4), as recently observed for PCL-based nanocomposites prepared by direct melt intercalation within (MMT-OH) 2 [18][19]. Such a continuous decrease of the improved thermal stability at higher clay content has been explained by a lower extent of clay delamination as a result of reduced free room within the thermoplastic matrix (as attested by XRD).…”

“…1). This situation is a remarkable progress compared to the microcomposite structure which is formed when PCL is directly melt blended with the native sodium montmorillonite (MMT-Na) [18]. It thus appears that the intercalated structure found in the PCL/MMT-Na masterbatch is preserved upon melt blending with high molar mass PCL chains.…”

“…Indeed, the organo-clay was first melt blended with preformed PCL, and then compounded with SAN, which is known to be miscible with PCL. In addition to the in situ -CL polymerization [13][14], some of us prepared PCL layered silicate nanocomposites by melt intercalation [18][19]. The key role of both the structure of the alkyl ammonium modifier and the dispersion technique, i.e.…”

Biodegradation and Applications of Nanobiocomposites

“…PCL/nanobiocomposites provide significant overall improvements in the processability, thermal, mechanical moisture barrier and gas permeability properties, in comparison to neat polycaprolactone (PCL) [14][15][16][17][18][19].…”

Fire Properties of Polymer Nanocomposites

“…Poly( -caprolactone)/clay nanocomposites were prepared by melt intercalation of the polymer with sodium montmorillonite and organically-modified montmorillonite [101,102]. Microcomposites or nanocomposites were prepared depending on the clay; the thermal stability improved with the filler loading up to 5 wt %.…”