Effect of matrix−nanoparticle supramolecular interactions on the morphology and mechanical properties of polymer foams

Abstract

In this study, we report the fabrication of supramolecular polymer nanocomposite foams with a uniform cell structure, high cell density and high expansion ratio using a soft matrix of poly(methyl acrylate-co-2-hydroxyethyl methacrylate) and silica nanoparticle fillers, both functionalized with ureido-pyrimidinone (UPy) supramolecular groups. Microcellular structures were formed using a batch foaming process at 90 ∘ C under a 9 MPa nitrogen atmosphere. Nanocomposites were characterized and compared before and after the foaming process to investigate the effect of supramolecular interactions on the thermomechanical properties and morphology of the foams. TEM images revealed that while strong inter-filler supramolecular interactions do not have a positive effect on their dispersion state, matrix−filler interactions derived from hydrogen bonding UPy motifs result in a rather uniform distribution of nanoparticles. Competing filler−filler and matrix−filler supramolecular interactions can be balanced and optimized by adjusting UPy populations along the chains and on the surface of nanoparticles. At a given chain functionality, increasing the nanoparticle loading up to an optimum concentration improves the mechanical properties and formability of the system. Above such concentration strong interactions between fillers, which are not compensated by the matrix, result in large aggregates and consequently undermine the material performance. Supramolecular polymer foams illustrate a similar thermal and viscoelastic behavior to that of neat samples but after foaming, due to the formation of a cellular structure and rearrangement or dissociation of UPy dimers under the foaming conditions, the elastic modulus is reduced.

Dynamics of supramolecular associative polymer networks at the interplay of chain entanglement, transient chain association, and chain‐sticker clustering

“…Supramolecular associative polymer networks consist of (macro)molecular building blocks associated by physical transient bonds such as ionic interactions, hydrogen bonds, metal–ligand complexes, and host–guest interactions . These physical bonds are in a tunable and dynamic equilibrium between associated and dissociated states, and can therefore be utilized to provide stimuli‐responsive and self‐healing materials .…”

Vegetable Tannin as a Sustainable UV Stabilizer for Polyurethane Foams

“…The water contained in the tannin powder is not readily available and this reduces the reaction kinetics, thus promoting the development of the blowing agent when the viscosity of the polymer is higher and reducing the gas escape towards the outside. Furthermore, CT particles act as cell nucleation sites and enhance the formation of supramolecular structures contributing to the increase of the expansion ratio and cell density [7]. These effects are not significant at low CT content, and pristine PU, TaPU-10, and TaPU-20 foams have similar density.…”

“…It determines color loss, macroscopic fragmentation, and progressive reduction of molecular weight; hence, bettering understanding of the involved mechanisms and developing new methods to slow down this type of degradation are extremely active fields [4,5,6]. Modern additives for polymers are capable of absorbing the UV radiation or blocking the free radicals and peroxides produced during the degradation process [7,8]. These substances are generally produced from non-renewable sources, and bio-based materials should not rely on them to improve their performances [9,10,11].…”