Thermal expansion coefficient and bulk modulus of polyethylene closed‐cell foams

Almanza, Ovidio; Masso-Moreu, Y.; Mills, N. J.; Rodríguez‐Pérez, Miguel Ángel

doi:10.1002/polb.20230

Cited by 23 publications

(15 citation statements)

References 21 publications

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“…The subsequent contraction of the edges probably caused the faces to wrinkle. These issues were partly addressed by Almanza et al (2004) who attempted to predict the thermal expansion coefficient of PE foams of different densities. The predicted effect of initially-bowed faces in a LDPE foam model compressed in the [1 1 1] direction, was to reduce the compressive yield stress by 11%, which is not large given the uncertainties in the polymer properties.…”

Section: Discussionmentioning

confidence: 99%

Finite element micromechanics model of impact compression of closed-cell polymer foams

Mills

Stämpfli

Marone

et al. 2009

International Journal of Solids and Structures

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a b s t r a c tFinite element analysis, of regular Kelvin foam models with all the material in uniformthickness faces, was used to predict the compressive impact response of low-density closed-cell polyethylene and polystyrene foams. Cell air compression was analysed, treating cells as surface-based fluid cavities. For a typical 1 mm cell size and 50 s À1 impact strain rate, the elastic buckling of cell faces, and pop-in shape inversion of some buckled square faces, caused a non-linear stress strain response before yield. Pairs of plastic hinges formed across hexagonal faces, then yield occurred when trios of faces concertinaed. The predicted compressive yield stresses were close to experimental data, for a range of foam densities. Air compression was the hardening mechanism for engineering strains <0.6, with face-toface contact also contributing for strains >0.7. Predictions of lateral expansion and residual strains after impact were reasonable. There were no significant changes in the predicted behavior at a compressive strain rate of 500 s À1 .

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Section: Discussionmentioning

confidence: 99%

Finite element micromechanics model of impact compression of closed-cell polymer foams

Mills

Stämpfli

Marone

et al. 2009

International Journal of Solids and Structures

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“…This ratio is expressed as a percentage. On the other hand, there is no exact reference method for comparison although the values are in congruence with the literature for these materials (Almanza et al, 2004;Rodíguez-Pérez et al, 2008). This result is a consequence of the thicker cell walls of Foam-1 in comparison to Foam-2, Foam-3, and Foam-4 (see Fig.…”

Section: Svfmentioning

confidence: 60%

“…This type of corrugation is typically found in closed-cell flexible foams and has important effects on their final properties (Almanza et al, 2004). It can also be observed that materials are organized according to their apparent crumpled grade (i.e., from left to right the single cells show increasing presence of corrugations in the cell walls), parameter that will depend on the processing technique used.…”

Section: Methodsmentioning

confidence: 93%

μCT-Based Analysis of the Solid Phase in Foams: Cell Wall Corrugation and other Microscopic Features

et al. 2015

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This work presents a series of three-dimensional computational methods with the objective of analyzing and quantifying some important structural characteristics in a collection of low-density polyolefin-based foams. First, the solid phase tortuosity, local thickness, and surface curvature, have been determined over the solid phase of the foam. These parameters were used to quantify the presence of wrinkles located at the cell walls of the foams under study. In addition, a novel segmentation technique has been applied to the continuous solid phase. This novel method allows performing a separate analysis of the constituting elements of this phase, that is, cell struts and cell walls. The methodology is based on a solid classification algorithm and evaluates the local topological dissimilarities existing between these elements. Thanks to this method it was possible to perform a separate analysis of curvature, local thickness, and corrugation ratio in the solid constituents that reveals additional differences that were not detected in the first analysis of the continuous structure. The methods developed in this work are applicable to other types of porous materials in fields such as geoscience or biomedicine.

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“…In the temperature range between − 40 °C and room temperature, the main factor that governs the thermal expansion of the materials is the expansion of the polymer matrix. It is possible to use the model of Almanza et al 35 to analyse in more detail this concept. In this model the volumetric thermal expansion is given by where β, β P and β A are the coefficients of volumetric expansion of the foam, solid polymer and air, respectively, K A is the bulk modulus of air and K is the bulk modulus of the foam.…”

Section: Discussionmentioning

confidence: 99%

“…When the temperature increases, the cell walls become progressively softer and the thermal expansion starts to depend on the cellular structure 35. This is because when the temperature increases, the thermal expansion is related mainly to two driving forces.…”

Section: Discussionmentioning

confidence: 99%

Modifying the structure and properties of polyethylene foams using thermal treatments

Rodríguez‐Pérez

González-Peña

Saja

2009

Polymer International

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BACKGROUND: The physical properties of polymer foams depend on many factors: density, cellular structure, matrix polymer morphology, etc. Therefore, these properties can be adapted by appropriate control of the structure. However, this simple and attractive concept has some limitations because the cellular structure of foams cannot be fully controlled during manufacturing. Therefore, in order to make possible the control of properties, it is highly desirable to develop simple procedures, such as thermal treatments, to modify the cellular structure. In the work reported, low-density polyethylene foams were thermally treated at temperatures below the melting temperature of the base polymer. The cellular structure, polymer base morphology and several thermal and mechanical properties were studied before and after the thermal treatments. RESULTS: It is shown that the anisotropy of the cellular structure is reduced by using adequate treatments. This modification of the structure influences physical properties that are sensitive to the cell shape, such as thermal expansion, elastic modulus and collapse stress.CONCLUSION: A simple procedure to allow further control of the structure and properties of polyethylene-based foams has been presented. The use of adequate thermal treatments is able to modify the cellular structure and hence the physical properties of these materials.

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Thermal expansion coefficient and bulk modulus of polyethylene closed‐cell foams

Cited by 23 publications

References 21 publications

Finite element micromechanics model of impact compression of closed-cell polymer foams

Finite element micromechanics model of impact compression of closed-cell polymer foams

μCT-Based Analysis of the Solid Phase in Foams: Cell Wall Corrugation and other Microscopic Features

Modifying the structure and properties of polyethylene foams using thermal treatments

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