Highly anisotropic crosslinked HDPE foams with a controlled anisotropy ratio: Production and characterization of the cellular structure and mechanical properties
Producción CientíficaIn this paper a two-step foaming process was used to produce highly anisotropic foams with controlled anisotropy
ratio. Anisotropic cellularmaterials are of great interest due to the enhanced mechanical properties that they show
in the anisotropy direction. Therefore, the production of foams with high and controlled anisotropy ratios is an essential
topic when it comes to designmaterialswith goodmechanical performance. In thiswork, high density polyethylene
(HDPE) foams with anisotropy ratios larger than 3 have been produced. A foaming process consisting of
two consecutive heating steps: pre-foaming and foaming, has been employed. Foaming kinetics at four different
pre-foaming temperatures (145 °C, 155 °C, 170 °C and 180 °C) and at a constant foaming temperature (180 °C)
have been performed. Results showed that the pre-foaming temperature is the key parameter that allows controlling
the anisotropy ratio of the final foam. A relationship between the pre-foaming temperature, the number of cells
and the anisotropy ratio has been established. Low pre-foaming temperatures lead to low numbers of cells, which
eventually results in high anisotropy ratios. Mechanical properties in compression were measured and compared
with the anisotropy of the cellular structure, being that the elastic modulus increases with the anisotropy ratio.Financial support from FPU grant FPU14/02050 (V. Bernardo) from the Spanish Ministry of Education and from PIRTU contract (E. Laguna-Gutierrez) by Junta of Castile and Leon (EDU/289/2011) and cofinanced by the European Social Fund are gratefully acknowledged. Financial assistance from MINECO and FEDER program (MAT 2012 – 34901)MINECO, FEDER, UE (MAT2015-69234-R) and the Junta de Castile and Leon (VA035U13) are gratefully acknowledged
