Super High‐Expansion Poly(Lactic Acid) Foams with Excellent Oil‐Adsorption and Thermal‐Insulation Properties Fabricated by Supercritical CO₂ Foaming

Abstract

current materials are mostly traditional petroleum-based polymers. [5,6] This will consume petrochemical resources and produce massive hardly degradable waste. [7] Second, toxic organic solvents or flammable foaming agents are widely used in the current preparation processes. [2,3] In addition, the relationship between the foam structure and the oil-adsorption and thermal-insulation performance is still unclear, thus limiting the development of high-performance foams.Poly(lactic acid) (PLA) is one of the biobased and biodegradable polymers with the most potential to replace traditional petroleum-based polymers. [8] Microcellular foaming is a green and safe technology in which supercritical CO 2 or N 2 is used as the physical foaming agent. [9] Therefore, it is an eco-friendly solution to use the microcellular foaming technology to prepare PLA foams for oil-adsorption and thermal-insulation application. Highperformance oil-adsorption materials should have high expansion ratio and open-cell structure, [10] and thermal-insulation materials generally require high expansion ratio and closed-cell structure. [11] However, the preparation of PLA foam with high expansion ratio is still very challenging. [12] The factors affecting the expansion ratio are very complex and can be divided into material structure and process parameters. The material structure mainly includes chain structure, crystalline structure, blend phase structure, etc. [12,13] And the process parameters mainly contain temperature, gas pressure, depressurization rate, etc. [12,14] These factors will affect the gas concentration, polymer viscoelasticity, heterogeneous nucleation, etc.; and then act on the cell nucleation, cell growth and cell stabilization; and finally influence the expansion ratio. [9,12,14] Specially, the PLA is a semi-crystalline polymer with low melt strength and complicated relationship between crystallization and foaming. First, CO 2 can reduce the crystallization and melting temperature of PLA, [9] and change its crystal morphology. [15,16] Meanwhile, crystals in turn can hinder the dissolution of CO 2 in the PLA. [17,18] Second, excessive crystallization will severely limit the cell growth, and ultimately lead to low expansion ratio and non-uniform cell morphology. [17][18][19] Third, the linear PLA generally possesses poor melt strength, which easily leads to cell collapse and gas loss, thereby restricting continuous foam expansion. [12] Fourth, the requirements of high expansion and Bio-based and biodegradable poly(lactic acid) (PLA) foams with a high expansion ratio show great application potential in oil-adsorption and thermal-insulation, which are crucial for oil-spill cleanup and energy saving. However, it is difficult to prepare high-expansion PLA foam due to the poor melt strength and complex crystallization behavior of PLA. Herein, super high-expansion PLA foams with excellent oil-adsorption and thermal-insulation properties are successfully prepared using a modified supercritical CO 2 foaming technology without introducin...

Three-Dimensional Polymer Nanofiber Structures for Liquid Contamination Adsorption

“…The preparation methods of the referred oil adsorption materials, the corresponding adsorption capacity, and the density of used organic solvents are summarized in Table S1. Compared with base materials such as PS, , PU, − PP, ,, PVA, PLA, graphene, and silicone foams, the EVOH foam prepared in this work exhibits better adsorption capacity. This indicates that the EVOH foam exhibits strong adsorption properties.…”

“…In these preparation processes, toxic organic solvents or chemical reagents are frequently used, which cause secondary environmental pollution and endanger Figure 7b shows the kinetic constant of EVOH/10 wt % MDI-g-EOPO foam prepared in this paper compared with oil adsorption materials for organic solvents reported in the literature. 30,32,[39][40][41]59 It is noted that the kinetic constant of EVOH/MDI-g-EOPO foam is larger than that of the adsorbent in the literature when adsorbing the same solvent. This is because EVOH/MDI-g-EOPO foam has a large specific surface area from 3D nanofibers and a large interconnected 3D storage space.…”

“…Finally, a 3D polymer nanofiber structure with high porosity and a large interface was obtained in the modified EVOH system. After testing, the adsorption material has high adsorption performance for liquid contamination, for instance, with a fast adsorption rate, that is, a kinetic constant as high as 1.14 g/g·s –1 , for carbon tetrachloride (CCl 4 ), much faster than polylactic acid (PLA) foam, PP/POE blend foam, polystyrene (PS)/polyacrylonitrile fiber, and so on. The mechanism for obtaining this superior 3D polymer nanofiber structure was then clarified to guide the fabrication of the high-performance amphiphilic adsorber.…”

Supercritical CO2 foaming of open‐cell polypropylene/ethylene propylene diene monomer composite foams with oriented cellular structures for water treatment

“…Nowadays, porous hydrophobic/oleophilic materials (PHOMs) 5 have been shown to be one of the most promising candidates for filtering wastewater. For example, PHOMs, like functional polymer membranes 6 and carbon aerogels, 7 are attractive alternative for water treatment due to their highly open‐cell structures and surface chemistries 8,9 . Nowadays, the main production methods of PHOMs are phase separation, 10 electrostatic spinning, 11 freeze‐drying, 12 and surface modification, 13 but there are some disadvantages with them, like solvent abuse, time‐consuming, and high precise.…”

“…For example, PHOMs, like functional polymer membranes 6 and carbon aerogels, 7 are attractive alternative for water treatment due to their highly open-cell structures and surface chemistries. 8,9 Nowadays, the main production methods of PHOMs are phase separation, 10 electrostatic spinning, 11 freeze-drying, 12 and surface modification, 13 but there are some disadvantages with them, like solvent abuse, time-consuming, and high precise. Therefore, it is great significance to develop environmentally friendly PHOMs, which have the characteristics of easy promotion, high throughout and high efficiency.…”