Mechanical properties of a catalyst- and surfactant-free rigid castor-oil polyurethane foam

Abstract

Foams are essential materials in engineering designs across the building and transport sectors, as they provide a unique combination of light weight, structural support, thermal and acoustic properties, and energy absorption. This study focuses on a rigid biofoam made from castor-oil polyurethane (PU) and examines its mechanical properties under compressive and three-point bending loads. No chemical additives are used except a castor-oil polyol, diisocyanate, and water. The elastic compressive modulus is evaluated for loads applied both parallel and perpendicular to the foam expansion direction, and results demonstrate that the foam is mildly anisotropic with an anisotropy shape index close to 1. A microtomographic scan analysis is conducted to investigate the internal structure of the foam. The elastic flexural modulus obtained is 9.2 ± 1.5 MPa. The compressive modulus (9.08 ± 0.71 MPa) and the elastic collapse stress (405 ± 29 kPa) are comparable to or higher than those reported for other rigid PU foams within the same density range in the literature. This finding indicates that a rigid biofoam can be successfully produced without the use of additives, such as catalysts and surfactants, while still exhibiting mechanical performance comparable to other rigid PU foams.