Foaming of polymers with supercritical fluids and perspectives on the current knowledge gaps and challenges

Maio, Ernesto Di; Kiran, Erdoǧan

doi:10.1016/j.supflu.2017.11.013

Cited by 186 publications

(145 citation statements)

References 90 publications

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“…In addition, among all foaming conditions applied, the foaming temperature (T f ) and foaming pressure (P f ) have the most significant influence. On one hand, when P f increases, the dissolved CO 2 content also increases accordingly, and the dissolved CO 2 has a plasticization effect that reduces the viscosity of the PLA/CO 2 mixtures, [35,36] leading to a lower T g and melting temperature (T m ). On the other hand, the presence of high-pressure CO 2 can also contribute to the cold crystallization of PLA, which will increase the crystallinity of the PLA matrix when the temperature is between T g and T m of the PLA, [37,38] and the extra crystals in the PLA will make the matrix stiffer and help preserve the structural integrity.…”

Section: Effects Of Foaming Conditions On Structural Integritymentioning

confidence: 99%

“…Tissue engineering scaffolds are a type of biomaterial‐based media that can help the regeneration of tissues after damage caused by a resection or trauma. [ 1 ] There are several valuable features of a tissue engineering scaffold, namely, a high porosity with open pores for cell ingrowth; [ 2 ] a dual network of interconnected pores providing separate pathways for the growth of cells and the delivery of nutrients and waste extraction; [ 3 ] and biodegradability, allowing the scaffold to be absorbed by growing tissue to avoid a surgical removal. [ 4 ]…”

Section: Introductionmentioning

confidence: 99%

“…Tissue engineering scaffolds are a type of biomaterial-based media that can help the regeneration of tissues after damage caused by a resection or trauma. [1] There are several valuable features of a tissue engineering scaffold, namely, a high porosity with open pores for cell ingrowth; [2] a dual network of interconnected pores providing separate pathways for the growth of cells and the delivery of nutrients and waste extraction; [3] and biodegradability, allowing the scaffold to be absorbed by growing tissue to avoid a surgical removal. [4] Microcapillary films (MCFs) are films with embedded multiple hollow capillaries that can be considered as having a pulsed ultrasound to rupture the cell wall after foaming, [18] applying a pressure-induced flow method to the samples before foaming to enhance the crystallization and heterogenous nucleation of the PLA in scCO 2 foaming, [19] and the blending of two semicrystalline polymers with different crystallization temperatures (T c ) to achieve a structural inhomogeneity in a polymer matrix consisting of hard and soft regions.…”

Section: Introductionmentioning

confidence: 99%

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Solvent‐Free Generation of Foamed Microcapillary Films with a Dual Network of Interconnected Pores and Internal Channels

Zhao

Zheng

et al. 2020

Macro Materials & Eng

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A dual‐pore network is favored in applications such as tissue engineering scaffolds. In this paper, foamed microcapillary films (FMCFs) are prepared based on a poly(lactic acid)/poly(butylene succinate) blend using melt extrusion and batch foaming with supercritical carbon dioxide. Such films are characterized by multiple hollow microcapillaries (diameter of 100–360 µm) connected with cells (size of 3–194 µm, open‐cell content of over 80%) within the scaffold. By plugging the ends of the MCF before foaming, the formation of a solid skin layer is successfully avoided. Furthermore, the diameter of the microcapillaries of an FMCF can be adjusted using the designed foaming strategy. The effects of the foaming condition on the FMCF foaming behavior are also investigated. When other conditions are fixed, the foaming behavior changes dramatically when the foaming temperature changes within the range of 120–123 °C.

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Section: Effects Of Foaming Conditions On Structural Integritymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Solvent‐Free Generation of Foamed Microcapillary Films with a Dual Network of Interconnected Pores and Internal Channels

Zhao

Zheng

et al. 2020

Macro Materials & Eng

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“…Though efforts have been made to increase nucleation, improve mechanical properties, remove skin layer, and improve foam expansion of TPU foams, study on reducing foam shrinkage has not been reported. TPU elastomer foams could undergo substantial foam shrinkage, like other elastomer and rubber foams . Typically, elastomers have T g that is well below T r , which can prevent T g from acting as the anchor point to fix the foamed structure.…”

Section: Introductionmentioning

confidence: 99%

TPU/PLA blend foams: Enhanced foamability, structural stability, and implications for shape memory foams

Ahmed

Yao

et al. 2018

J of Applied Polymer Sci

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A series of thermoplastic polyurethane (TPU)/poly(lactic acid) (PLA) blends are studied in terms of morphological, thermal, and rheological properties by scanning electron microscopy, differential scanning calorimetry, and rheometry. Using supercritical CO 2 batch foaming, the foamability of the blends is systematically investigated. It is found that the 80/20 (wt %/wt %) TPU/PLA blend (TPU80%) shows vastly enhanced foamability over a wide range of foaming conditions to produce foams with a myriad of cellular morphology. The foamability enhancement results from the improved cell nucleation and growth, and the changes in the polymer microstructure. Compared to elastic TPU foams, the TPU80% retain their shapes 3.4 times better. Mechanism for the enhanced stability is proposed and verified using Kohlrausch-Williams-Watts model. The materials developed in the study and the mechanistic understanding of the shape fixation process may facilitate the advancement of elastomeric foams in conventional use as well as in novel shape memory applications.

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“…Consequently, the rheological properties (i.e. viscosity and modulus) play a vital role to finalize the size and morphology of the cells [16][17][18]. Regardless the changes of the processing conditions (i.e.…”

mentioning

confidence: 99%

A developed, eco-friendly, and flexible thermoplastic elastomeric foam from SEBS for footwear application

Zhang¹,

Dai²,

Zou³

et al. 2019

Express Polym. Lett.

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In search of new materials to develop comfortable shoe sole, nowadays the researchers have resorted to the thermoplastic elastomers (TPEs) usually used as cushioning materials for its easy processability and adorable physical properties that can meet both the comfort as well as other functional requirements (i.e. fashion, ultralight, aging, etc.). TPEs are a class of copolymers or physical mixes of polymers and have the morphology of non-miscible blends of elastomer and thermoplastic matrix simultaneously. Low or room temperature elastomeric behavior and high temperature processablitiy makes TPE as a suitable material for developing lightweight and recyclable microcellular foams [1]. Most of the commercial TPE foams for footwear application are developed either from thermoplastic polyurethane (TPU) or ethylenevinyl acetate (EVA) copolymer in which the soft matrix provides sufficient free space for gas absorption whereas the rigid matrix prevents the gas diffusion during foaming process [2][3][4][5][6]. Styrene-(ethylene-cobutylene)-styrene polymers (SEBS) derived from the hydrogenation of styrene-butadiene-styrene (SES) polymers is a typical TPE which shows a better weather resistance, lower compression set, lower density, etc., can be a potential alternative of TPU or EVA [7,8]. SEBS consists of a soft midblock of ethylene-butylene (E-co-B) and hard end-blocks of 948 Abstract. Developing eco-friendly, flexible thermoplastic elastomeric foams based on poly(styrene-(ethylene-co-butylene)styrene) (SEBS) is a challenging task because of its poor melt strength. A promising approach to overcome this challenge is the use of synergistic technologies, such as combination of irradiation, supercritical fluid foaming, and steam-chest molding technologies. Herein, foamed beads were produced from pre-crosslinked SEBS beads using supercritical nitrogen as blowing agent, followed by subsequently efficient steam-chest molding to obtain midsole part. The crosslinking was accomplished under the assistance of electron beam. The rheology properties and foaming behavior reveals that the viscosity and modulus of the matrix increase with the increase of crosslinking resulting from increasing the irradiation dose (ID). With increasing the ID, successful foaming with larger expansion and improved cell morphology was achieved. SEBS bead foams were successfully obtained from 65 kGy-derived pre-crosslinked beads through steam-chest molding which showed a specific gravity of 0.252 g·cm -3 and comparable/superior mechanical properties to/than that of commercial thermoplastic polyurethane (TPU) or ethylene-vinyl acetate copolymer (EVA) foams. Especially, the higher elasticity and resilience of SEBS foams meet well the desirable properties for footwear application which supports SEBS to be an alternative for TPU or EVA.

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Foaming of polymers with supercritical fluids and perspectives on the current knowledge gaps and challenges

Cited by 186 publications

References 90 publications

Solvent‐Free Generation of Foamed Microcapillary Films with a Dual Network of Interconnected Pores and Internal Channels

Solvent‐Free Generation of Foamed Microcapillary Films with a Dual Network of Interconnected Pores and Internal Channels

TPU/PLA blend foams: Enhanced foamability, structural stability, and implications for shape memory foams

A developed, eco-friendly, and flexible thermoplastic elastomeric foam from SEBS for footwear application

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