Progress in the development of bead foams – A review

Kuhnigk, Justus; Standau, Tobias; Dörr, Dominik; Brütting, Christian; Altstädt, Volker; Ruckdäschel, Holger

doi:10.1177/0021955x221087603

Cited by 47 publications

(47 citation statements)

References 83 publications

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“…The two-step manufacturing process consists of (i) foaming and (ii) fusing micro cellular single beads into molded parts. [1][2][3][4][5] In the history of bead foams the first 50 years only focussed on the commodity plastics polystyrene (as expandable polystyrene (EPS) [6,7] ), polyethylene (as expanded polyethylene (EPE) [8,9] ), and polypropylene (as expanded polypropylene (EPP) [10][11][12] ). These materials are cost-efficient applications that require good insulating properties and high energy absorption.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the Fusion Quality of Bead Foams Made from Polybutylene Terephthalate (E‐PBT) Depending on the Processing Temperature

Kuhnigk

Krebs

Standau

et al. 2022

Macro Materials & Eng

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Increasing requirements are leading to new developments in bead foam materials. Engineering thermoplastics such as polybutylene terephthalate (PBT) outperform standard bead foams in thermal stability. In order to obtain molded parts, beads are fused together using steam chest molding. Classical theories for the fusion mechanism, explaining the molding of amorphous EPS (expandable polystyrene) or semi‐crystalline EPP (expanded polypropylene), cannot be applied to E‐PBT (expanded polybutylene terephthalate). In previous studies, sufficient time for polymer interdiffusion during molding is identified as crucial and requires adjusted crystallization kinetics. This study consequently examines to which extent the crystalline properties and the bead fusion behavior of E‐PBT can be influenced by the bead foaming process. By varying the underwater granulation (UWG) water temperature, different cooling rates of the expanding melt are generated. The foamed beads show different cell morphologies, thermal and dynamic mechanical properties depending on the UWG water temperature. Those beads that show a pronounced shrinkage behavior in the thermomechanical analysis, caused by an increased open cell content and a pronounced cold‐crystallization, exhibit a reduced bead fusion quality. The bead fusion quality is examined by the fracture surface. The shrinkage phenomenon causes a reduced bead to bead contact and partially separation between the beads.

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Section: Introductionmentioning

confidence: 99%

Evaluation of the Fusion Quality of Bead Foams Made from Polybutylene Terephthalate (E‐PBT) Depending on the Processing Temperature

Kuhnigk

Krebs

Standau

et al. 2022

Macro Materials & Eng

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“…10 So the objective of this work is to present a novel method combining mechanical compression and vapor treatment to transform the structure of polymer foams (EPE waste) into an improved cellular morphology leading to auxetic materials. 1,2 Based on different treatment conditions, samples with positive, negative, and zero PR are produced and compared in terms of their mechanical response. As a starting point, PE foams with three different densities were studied in this work and the samples were characterized under uniaxial tension to get their stress-strain behavior, Poisson's ratio and energy dissipation under cyclic loading.…”

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confidence: 99%

Conversion of low density polyethylene foams into auxetic metamaterials

Chen

Hamdi

Rodrigue

2022

Polymers for Advanced Techs

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Cellular polymers, such as polyethylene foams, are commonly used in the packaging industry. These materials have short service life and generate a high volume of waste after use. In order to valorize this waste and produce added‐value applications, it is proposed to convert these materials into highly efficient energy absorption structures. This was done by modifying the original cellular morphology of the foams (spheroidal or polygonal) into a re‐entrant structure to produce auxetic materials. This work presents an optimized process combining mechanical compression and solvent vapor evaporation‐condensation leading to low density foams (77–200 kg/m3) having negative Poisson's ratios (NPR). Three series of recycled low density polyethylene (LDPE) foams with an initial density of 16, 21, and 36 kg/m3 were used to optimize the processing conditions in terms of treatment temperature, time, and pressure. From all the samples prepared, a minimum Poisson's ratio of −3.5 was obtained. To further characterize the samples, the final foam structure was analyzed to relate with mechanical properties and compare with conventional foams having positive Poisson's ratios. The results are discussed using tensile properties and energy dissipation which were shown to be highly improved for auxetic foams. Overall, the resulting foams can be used in several applications such as sport and military protection equipment.

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“…Here, the major advantage of bead foaming is that low densities and complex geometries can be combined. Therefore, solely foamed beads, produced in a separate first step (either in continuous or discontinuous processes), are fused in a second step into a molded part (usually with superheated steam). − Nowadays, mainly commodity polymers that is, expandable polystyrene (EPS), , expanded polyethylene (EPE), , and expanded polypropylene (EPP) since the late 1970sare established in the industry. − The production routes for the foamed beads vary, as do their properties and applications. EPS and EPP are commonly used for packaging (e.g., transport boxes), thermal insulation (e.g., food trays, building insulation), and shock absorption (e.g., bicycle helmets, bumper cores) .…”

Section: Introductionmentioning

confidence: 99%

Influence of Molecular Weight on the Bead Foaming and Bead Fusion Behavior of Poly(butylene terephthalate) (PBT)

Kuhnigk

Krebs

Mielke

et al. 2022

Ind. Eng. Chem. Res.

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A current trend in the progress of bead foams is the use of engineering polymers (i.e., poly(butylene terephthalate) (PBT)), which are more temperature resistant than commodity polymers and thus offer new areas of application. Currently, foaming and molding of PBT bead foams seem to be possible only with an epoxy-based chain extender. This modification leads not only to an increase in molecular weight but also to a changed PBT chain architecture (i.e., branching or even cross-linking). Thereby, the crystallization behavior is considerably slowed down so that the time for chain interdiffusion across neighboring bead surfaces is prolonged. This study investigates the molecular weight influence separately. The crystallization behavior is controlled by varying the length of linear PBTs in such a way that different bead fusion phenomena result. With increasing molecular weight, a lower open cell content (OCC), and therefore a higher expansion behavior during thermomechanical analysis, was observed, which increases the contact area between the beads in the cavity during the steam chest molding process. Adding to the literature shown so far, this study shows that linear chemically unmodified PBT can also be processed into bead foam components using PBTs having a higher molecular weight.

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Progress in the development of bead foams – A review

Cited by 47 publications

References 83 publications

Evaluation of the Fusion Quality of Bead Foams Made from Polybutylene Terephthalate (E‐PBT) Depending on the Processing Temperature

Evaluation of the Fusion Quality of Bead Foams Made from Polybutylene Terephthalate (E‐PBT) Depending on the Processing Temperature

Conversion of low density polyethylene foams into auxetic metamaterials

Influence of Molecular Weight on the Bead Foaming and Bead Fusion Behavior of Poly(butylene terephthalate) (PBT)

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