Polystyrene foams: II. Structure-impact properties relationships

In the first part of this series of articles, the relations between the foaming conditions and the microstructure of expanded polystyrene (EPS) were explored. In this part, the effects of the foaming conditions and the microstructure of EPS in impact properties are discussed. Regression analysis was conducted on the data and expressions were developed to quantify these relationships. Moreover, the importance of the individual structural parameters was determined. Statistical analysis of the data showed that foaming time was the most important factor determining the impact strength, while foaming temperature was the most important factor controlling the specific impact strength. The deformation of cells at the crack tip, as a result of bending and/or buckling of cell walls, can increase the failure strain, which leads to an increase in failure energy. In expanded polymers, the majority of the absorbed energy during impact loading is dissipated as plastic work. The transition of plane stress conditions to plane strain conditions, due to expansion, can be considered as another source of toughening in EPS.