Mimicking the Anisotropic Behavior of Natural Porous Structures by
Controlling the Reinforcing Particles Distribution in Polymeric Foams
Luigi Sorrentino
1,a,
*, Marco Aurilia
1,b
, Marco D'Auria
2,c
, Daniele Davino
3, d
,
Pasquale Mei
3,e
, Ciro Visone
3,f
, Salvatore Iannace
1,g
1
CNR – Institute for Composite and Biomedical Materials, P.le V. Tecchio 80, 80125 Napoli Italy
2
Department of Materials and Production Engineering, University of Naples “Federico II”,
P.le Tecchio 80, 80125 Napoli - Italy
3
Dipartimento di Ingegneria, Università degli Studi del Sannio, I-82100 Benevento, Italy
a
[email protected] (corresponding author),
b
[email protected],
c
[email protected],
d
[email protected],
e
[email protected],
f
[email protected],
g
[email protected]
Keywords: Polymeric Foams, Mechanical Anisotropy, Reinforcing Particles, Magneto-Elastic
Behavior.
Abstract. Natural porous materials, like wood or bone, are multiscale cellular composite structures
which exhibit mechanical (such as elasticity and strength) and functional (such as the thermal or
acoustic insulating properties) behaviors dependent on the measuring direction. They show the best
performance/weight ratio among all materials because their response is optimized in the needed
direction by removing matter where not strictly functional, giving as a result a strong structural as
well as morphological anisotropy.
A new approach has been developed to mimic this behavior in polymeric foams, in which the
mechanical and/or functional response of the cellular structure is tailored in a specific direction
through the control of the spatial distribution and configuration of reinforcing particles. In order to
demonstrate the concept, polymeric foams were produced with micro- or nano-sized reinforcement
distributed along specific directions by means of the magnetic field. The effects of particles content,
production parameters, and magnetic field strength were investigated and related to the mechanical
(both elastic and magneto-elastic) performances.
Introduction
Composites are based on the concept of reinforcing along a main selected direction or plane. By
means of this approach it is possible to enhance the structural behavior by combining different
materials in specific directions (for weight reduction) and provide functional anisotropic (often
orthotropic) mechanical properties. Considerable efforts were spent to realize low density structures
with fine morphology, but few results were obtained to produce lightweight composites.
This goal is usually obtained by incorporating in the structure polymeric foams, which are gas/solid
biphasic materials where gas bubbles are dispersed in a polymeric matrix. These heterogeneous
materials own peculiar properties that make them suitable for many potential uses, in several non-
structural (such as packaging, cushioning, thermal and acoustic insulation [1, 2]) and structural
applications (such as shock absorbing, or sandwiches, where lightweight and high stiffness to
weight ratio are required [3]). Among polymeric foams, polyurethane foams are obtained from the
reaction of two or more components to form the foam and consolidating this structure with
reticulation. During this stage the gas responsible for the bubble formation is produced, and the
system expands reducing its apparent density. Elastic modulus, yield point [3] and length of stress
plateau [4, 5] are the main parameters which must be considered in foam design for specific
applications. Furthermore, mechanical properties of foams are strongly related to the expansion
ratio (defined as the ratio between foam density and bulk polymer density) and to the cell
morphology [6-8]. The regularity of cell shape is mostly influenced by the foaming process. In
particular foams expanded in a mould present elongated cells due to the geometrical constraints
during cell growth. Advances in Science and Technology Vol. 84 (2013) pp 1-6
© (2013) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AST.84.1