Relative modulus–relative density relationships in low density polymer–clay nanocomposite foams

Abstract

Polymer-clay nanocomposite (PCN) foams represent an important class of new materials in structural engineering, biomedical fields and packaging. This paper reports the relative modulus-relative density relationship, a crucial correlation in cellular solids, for low-density PCN foams. Polyurethane (PU)-natural clay nanocomposite foams with a porosity of 97% were used for studies of such relationship. The foam structures were characterised by Scanning Electron Microscopy and X-ray Micro-Computed Tomography and the modulus was obtained from compressive testing. It was found the relative modulus-relative density relationship of low-density PCN foams with porosities higher than 95% closely followed the normalised Gibson-Ashby models for open cells and closed cells, and in the case of PU-clay nanocomposite foams the geometric constant of foam C 1 was determined to be approximately 0.45-0.88 in the well-established model for conventional open-cell foams, namely E f /E s ¼ C 1 (r f /r s ) 2 where E and r refer to modulus and density and subscripts f and s stand for foam and solid. The effects of clay, clay content and mixing sequence on the cell structure, physical and mechanical properties of the polymer foam were also discussed.

Evaluation of the anisotropic mechanical properties of reinforced polyurethane foams

“…Numerous studies have reported improvements in the mechanical properties of polymer foams 79 reinforced with short fibers [9,10,11,12,13], particles [14,15,16,17,18], and nano-particles 80 [19,20,21,22], but relatively few have made use of cellular models to interpret the results of 81 mechanical tests and to develop predictive tools. Barma et al [15] related the foam stiffness (E f ) 82 to the solid stiffness (E s ) and cell size in particle-reinforced foams at the same density.…”

“…Zhang et al [20] used a Mori-85 Tanaka model to account for carbon nanotube reinforcement and cellular voids [23]. Goods et al 86 [14] used a cellular model in the form of Equation (1) to describe the foam modulus (E f ) of PU 87 foams reinforced with metal particles, along with the Kerner equation to account for changes in 88 the solid modulus (E s ); others have taken a similar approach with various composite models to 89 estimate E s for different materials [13,17,21,22]. The effect of additives on mechanical 90 anisotropy has been reported in several studies on chopped aramid and glass fibers [10,11,12], 91 but was only qualitatively attributed to a combination of cell shape (R) and preferential fiber-92 alignment.…”

“…where P is the mechanical property of interest, ρ is density, the parameters C and n depend on 38 the property of interest and the particulars of the foam (including the foam microstructure and 39 deformation mode) [2,3,4], and the subscripts s and f indicate the properties of the fully dense 40 solid and of the foam, respectively. 41…”

“…In foams with a low relative density (ρ f /ρ s <0. 4), 34 many of the mechanical properties can be related to the relative density according to a power law 35 of the form [1]: 36…”

Estudio de Nanocompuestos de Espumas de Poliuretano Reforzadas con Nanocargas en Base Carbono

“…Meanwhile, the nucleation effect depends on the degree of dispersion of nanofillers on the polymer matrix. [281] The final structure of the RPU nanocomposite foams is observed by scanning electron microscopy (SEM). Figure 5.5 shows the closed-cell structure of these nanocomposite foams and the average cell size is summarised in Table 5.4.…”