A vegetable tannin, a flavonoid-type natural polyphenolic compound, was used to promote the stabilization of polyurethane foams against UV radiation. Several polyurethane foams were synthesized by using an isocyanate, and a mixture of ethoxylated cocoalkyl amine and vegetable tannin. The content of vegetable tannin was varied from 0 to 40 wt %. The effects of tannin and water (used as a blowing agent) on the foaming kinetics and cellular morphology of foams were investigated. Samples were subjected to accelerated weathering under UV radiation for 3 to 24 h, and FTIR and DMA analyses were conducted to assess the performance change. The former analysis revealed a strong inhibiting effect of tannin on urethane linkage degradation during the UV treatment. The mechanical properties were significantly affected by the addition of tannin. The capability of the foams to withstand UV radiation was dependent on the amount of tannin. At tannin contents higher than 20%, the decrease in mechanical properties under UV irradiation was almost avoided.

A new class of lightweight smart materials based on a polymeric matrix with embedded magnetic micro-particles was developed. The application of a magnetic field (MF) during the foaming of samples induced, along the MF lines, the alignment of magnetic particles dispersed in the polymer thus forming chain-like reinforcing structures. The aligned micro-particles induced an anisotropic mechanical behaviour, strongly improving the mechanical stiffness and strength along the MF direction compared to unfilled systems. Most notably, the chain-like structures imparted a magneto-sensitive behaviour to the lightweight materials. In fact, foams showed a direct relationship between the foams elastic response and the intensity as well as the shape of the time dependent MF applied during their magneto-elastic characterisation. This magneto-elastic behaviour has been obtained at low MF strength (below 200 kA m ⁻¹ ).

Poly(ethylene 2,6-naphthalate)- PEN is a thermoplastic polyester characterized by a high glass transition temperature (125°C), comparable to that of polyetheretherketone (143°C), but with a significantly lower melting temperature (265°C). Its physical and chemical properties are very promising for applications in transport industry and aeronautics. Nanocomposite matrices based on PEN and expanded graphite were developed to be used as matrix for foams. Expanded graphite was melt blended with the polymer by means of extrusion process and its effects on the foaming properties were investigated through solid state foaming process. Graphite nanoparticles increased the crystallization kinetics of the polymer, inducing the formation of small crystals but lowering the total amount of crystalline phase. Transmission electron microscopy analysis showed a good dispersion of the nanofiller but some aggregates were still present, as also confirmed by graphite peak in the X-ray diffraction patterns of all nanocomposites. The elastic modulus of nanocomposites with amorphous matrix increased with respect to the neat amorphous PEN, while the modulus of crystallized nanocomposites decreased. Nanocomposite foams were successfully prepared, and an higher cell density was obtained when compared to the neat PEN. In the latter case, a strong increase in both yield and strain at break was measured. Furthermore, the elastic modulus and compressive yield stress of foamed PEN nanocomposites increased with the expanded graphite.