Strength versus toughness of emulsion templated Poly(Dicyclopentadiene) foams

Abstract

In this work the mechanical properties of high internal phase emulsion templated Ring-opening Metathesis Polymerization cured poly(dicyclopentadiene) (pDCPD) foams of 90% porosity prepared with varying surfactant amounts are studied. Using tensile-testing instead of conventionally compression testing of foam samples reveals a distinct influence of the surfactant loading on the mechanical properties. Although void sizes (and similarly window sizes) linearly decrease with increasing surfactant amounts, the strength and toughness do not. The strength of the foams is greatly unaffected by variations of the surfactant amount in the regime of 1–5 vol%. Above these levels the strength decreases with increasing surfactant loading. The modulus of toughness increases with increasing surfactant amount until a maximum is reached at around 2–4 vol% of surfactant. More surfactant causes a decrease in toughness. Accordingly, in terms of mechanical properties an optimal surfactant amount of 3 vol% in respect to DCPD is found. Applying this formulation to the preparation of foams with 80, 70, 60, and 50% nominal porosity gives materials with high strength (Young's moduli in between 116 and 416 MPa) and toughness (moduli of toughness between 600 kJ/m3 to 2 MJ/m3).