The Influence of Graft Length and Density on Dispersion, Crystallisation and Rheology of Poly(ε-caprolactone)/Silica Nanocomposites.

Maria Eriksson,Joris Hamers,Han Goossens,Ton Peijs

doi:10.3390/molecules24112106

Abstract

Different techniques of grafting polymer chains to filler surfaces are often employed to compatibilise filler and polymer matrices. In this paper the influence of graft length and graft density on the state of dispersion, crystallisation and rheological properties of poly(ε-caprolactone) (PCL)/silica (SiO2) nanocomposites are reported. Grafted silica nanoparticles were prepared through polymerisation of PCL from the nanoparticle surface. Graft length was controlled by the reaction time, while the grafting density was controlled by the monomer-to-initiator ratio. Grafted nanoparticles were mixed with PCL of different molecular weights and the state of dispersion was assessed. Different matrix-to-graft molecular weight ratios resulted in different states of dispersion. Composites based on the higher molecular weight matrix exhibited small spherical agglomerates while the lower molecular weight matrix revealed more sheet-like microstructures. The state of dispersion was found to be relatively independent of graft length and density. Under quiescent conditions the grafts showed increased nucleation ability in the higher molecular weight PCL, while in the lower molecular weight matrix the effect was less pronounced. Rheological experiments showed an increase in viscosity with increased filler content, which was beneficial for the formation of oriented structures in shear-induced crystallisation.

Highlights

Due to their large surface-to-volume ratio and poor compatibility with most polymers, inorganic nanofillers are rather difficult to disperse in many polymer matrices
It has been shown that the toughness of polyamide 6 (PA6)/silica nanocomposites depends on the ligament thickness between nanoparticles and that above a critical ligament thickness no toughening effect was observed [4]
The length of the grafts could not be determined in a quantitative way, but the thermogravimetric analysis (TGA) experiments showed that an increased reaction time lead to increased weight of grafted material for a constant number of initiating sites, an indirect proof that graft length was increased

Summary

Introduction

Due to their large surface-to-volume ratio and poor compatibility with most polymers, inorganic nanofillers are rather difficult to disperse in many polymer matrices. In these matrices, filler-filler interactions are favoured over polymer-filler interactions and filler agglomerates are readily formed. It has been shown that the toughness of polyamide 6 (PA6)/silica nanocomposites depends on the ligament thickness between nanoparticles and that above a critical ligament thickness no toughening effect was observed [4] This is only true for well-dispersed nanofillers which are smaller than the critical crack size of the polymer matrix.

Methods

Results

Conclusion