A Polycaprolactone-Based Compatibilization Treatment to Improve Dispersion and Interphase Structure of Silica Polyurethane Composites

Abstract

Silica nanoparticles (SNs) were grafted with ecaprolactone using an environmentally friendly approach. By using tartaric acid as a catalyst and the silanol groups as initiators, grafted nanoparticles (GNs) with organic weight fractions (wof) within the range 0–46 wt% were synthesized. Thermogravimetric (TGA) and infrared analysis were used to measure the wof and to corroborate the covalent bond between the SN and the caprolactone monomer. Transmission electron micrographs of the polyurethane (PU) nanocomposites based on the SN and the GN revealed that the interfacial area of the GNbased PU increased by the reduction of agglomerate dimensions from 10 mm to around 0.1 mm. Dynamic mechanical analysis showed that the GN nanocomposites improved the storage shear modulus from 616611 to 84968 MPa for a GN with wof5 16.7% and 3 wt% filler concentration. In addition, the GN particles prevented a relevant decrease of the transition temperature (Tg). Differential scanning calorimetry corroborated that GN increased the enthalpic energy associated to the physical crosslinking of the hard segments (HS). Wide-angle X-ray diffraction proved that the GN formed a HS structure with improved crystallinity. The thermal stability of the GN-based PU a nanocomposite was improved by an increase of the thermal stability of the castor oil soft segments.