Effect of extrudate swell on extrusion foam of polyethylene terephthalate

Tammaro, Daniele; Walker, Claudio; Lombardi, Lorenzo; Trommsdorff, Ulla

doi:10.1177/0021955x20973599

Cited by 20 publications

(9 citation statements)

References 34 publications

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“…The bubble density of the foamed strands at

increases exponentially as a function of the CO 2 concentration within the investigated concentration range, as reported in Figure 1 c. This result is in good agreement with the prediction of the Classical Nucleation Theory, which assumes that no bubble coalescence or collapse occurs during the foaming process [ 20 , 21 , 22 ]. The bubble density in the microfoamed strands with CO 2 was higher than that obtained by Tammaro et al [ 2 ] by using acetone.…”

Section: Resultssupporting

confidence: 87%

Microfoamed Strands by 3D Foam Printing

2022

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We report the design, production, and characterization of microfoamed strands by means of a green and sustainable technology that makes use of CO2 to create ad-hoc innovative bubble morphologies. 3D foam-printing technology has been recently developed; thus, the foaming mechanism in the printer nozzle is not yet fully understood and controlled. We study the effects of the operating parameters of the 3D foam-printing process to control and optimize CO2 utilization through a maximization of the foaming efficiency. The strands’ mechanical properties were measured as a function of the foam density and explained by means of an innovative model that takes into consideration the polymer’s crystallinity content. The innovative microfoamed morphologies were produced using a bio-based and compostable polymer as well as polylactic acid and were then blown with CO2. The results of the extensive experimental campaigns show insightful maps of the bubble size, density, and crystallinity as a function of the process parameters, i.e., the CO2 concentration and temperature. A CO2 content of 15 wt% enables the acquirement of an incredibly low foam density of 40 kg/m3 and porosities from the macro-scale (100–900 μm) to the micro-scale (1–10 μm), depending on the temperature. The foam crystallinity content varied from 5% (using a low concentration of CO2) to 45% (using a high concentration of CO2). Indeed, we determined that the crystallinity content changes linearly with the CO2 concentration. In turn, the foamed strand’s elastic modulus is strongly affected by the crystallinity content. Hence, a corrected Egli’s equation was proposed to fit the strand mechanical properties as a function of foam density.

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“…The bubble density of the foamed strands at

Section: Resultssupporting

confidence: 87%

Microfoamed Strands by 3D Foam Printing

2022

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“…A bell‐shaped curve typically describes the effect of T foam on the foam density, with a maximum of the expansion ratio at an optimal temperature,

T_{foam}^{optimal}

. [ 31 ] Below

T_{foam}^{optimal}

, the viscosity of the polymer increases and crystallization or vitrification may occur. Above

T_{foam}^{optimal}

, the reduction of the polymer viscosity induces bubble coalescence and the increased diffusivity of the blowing agent is responsible for its loss through the external surface of the strand, followed by a corresponding reduction of foaming efficiency.…”

Section: Resultsmentioning

confidence: 99%

Continuous 3D Printing of Hierarchically Structured Microfoamed Objects

et al. 2021

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We report the design and results of a novel process combining 3D printing and foaming to produce microfoamed polymeric structures, from simple strands to more complex architectures, using physical blowing agents. Foaming processes are extensively operated in polymeric cellular materials industry to produce pores, yet without spatial control of their positioning. This intrinsic stochasticity may introduce imperfections, which reduce the mechanical properties of the material, thus regular (e.g., periodic) porous structures would be more desirable. 3D printing allows to fabricate polymeric cellular materials with empty spaces in a well‐defined periodic structure. To this end, very expensive 3D printers are required to achieve micron‐resolution pores. Correspondingly, the production time is dramatically large and becomes a bottleneck to the industrial scale‐up. Herein, an innovative technique combining the simplicity of polymer foaming with the precision of 3D printing is presented. The resulting materials have the advantages of both the techniques: they have a micron‐controlled cell structure and can be printed at reasonable costs and time. The proposed approach is validated using a bio‐based and compostable polymer, namely, polylactic acid (PLA). The resulting foamed strands and hierarchical structures are novel in terms of morphology and show a controlled local porosity and superior mechanical properties.

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“…The test sweeps the angular frequency from ω = 0.1 to 50 rad s −1 , with a fixed strain rate of 1%. The non-linear rheological response of the HMS PP, at high shear rates and deformation, was measured by means of a stress-controlled microcapillary rheometer [ 21 ]. The microcapillary has a diameter of D = 70 μm and a land length of L = 1500 μm.…”

Section: Methodsmentioning

confidence: 99%

Expanded Beads of High Melt Strength Polypropylene Moldable at Low Steam Pressure by Foam Extrusion

et al. 2022

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We explore the foam extrusion of expanded polypropylene with a long chain branched random co-polypropylene to make its production process simpler and cheaper. The results show that the presence of long chain branches infer high melt strength and, hence, a wide foamability window. We explored the entire window of foaming conditions (namely, temperature and pressure) by means of an ad-hoc extrusion pilot line design. It is shown that the density of the beads can be varied from 20 to 100 kg/m3 using CO2 and isobutane as a blowing agent. The foamed beads were molded by steam-chest molding using moderate steam pressures of 0.3 to 0.35 MPa independently of the closed cell content. A characterization of the mechanical properties was performed on the molded parts. The steam molding pressure for sintering expanded polypropylene beads with a long chain branched random co-polypropylene is lower than the one usually needed for standard polypropylene beads by extrusion. The energy saving for the sintering makes the entire manufacturing processes cost efficient and can trigger new applications.

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Effect of extrudate swell on extrusion foam of polyethylene terephthalate

Cited by 20 publications

References 34 publications

Microfoamed Strands by 3D Foam Printing

Microfoamed Strands by 3D Foam Printing

Continuous 3D Printing of Hierarchically Structured Microfoamed Objects

Expanded Beads of High Melt Strength Polypropylene Moldable at Low Steam Pressure by Foam Extrusion

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