Poly(lactic acid)/modified chitosan-based microcellular foams: Thermal and crystallization behavior with wettability and porosimetric investigations

This article addresses a less expensive and elegant method for the fabrication of hydrophobic poly(lactic acid) (PLA)/modified chitosan (MC)-based bionanocomposite foams with high porosity (>~80%) and open cellular interconnected morphology. An increment of ~2.3-fold of cell density and reduction of ~1.3-fold of cell size are observed at highest loading of MC (i.e. 3 wt %). The MC also influences the hydrophobicity (up to ~10 increment in contact angle) of the foams. Structure–property relationship of the fabricated foams has been investigated along with wettability behavior. Thermal degradation kinetics and degradation mechanism of the fabricated foams have been investigated by using different approaches like modified Coats Redfern (modified CR), Flynn-Wall-Ozawa (FWO), Kissinger, and Criado. Crystallization behavior of the fabricated foams are also investigated. Increase in surface area with MC-loading and nucleating behavior of MC in the PLA matrix is confirmed by the porosimetric investigation of the fabricated foams. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47236.     

Biodegradable packaging foams of starch acetate blended with corn stalk fibers

Starch acetate–corn fiber foams were prepared by extrusion. Corn starch was acetylated (DS 2) to introduce thermoplastic properties. Corn stalks were treated with sodium hydroxide to remove the lignin and to obtain purified cellulose fibers. Starch acetate was blended with treated fiber at concentrations of 0, 2, 6, 10, and 14% (w/w) and extruded in a corotating twin‐screw extruder with 12 to 18% w/w ethanol content and 5% talc as a nucleating agent. The samples were extruded at 150°C and selected physical and mechanical properties were evaluated. Micrographic properties were analyzed using scanning electron microscopy to observe the interaction of fiber and starch. Fiber incorporation at the lower concentrations enhanced the physical properties of the foams. Fiber contents greater than 10% decreased expansion and increased density and shear strength. Good compatibility between starch and corn fiber was observed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2627–2633, 2004     

Physicomechanical and hydrophobic properties of starch foams extruded with different biodegradable polymers

Blends of hydroxypropylated high amylose starch and various functional aids listed below were extruded into foams using a twin‐screw extruder ZSK ‐ 30. In this study, the hydrophobic character and mechanical properties of starch foams were improved by using other biodegradable polymers, such as poly‐caprolactone (PCL), poly (butylene adipate‐co‐terephthalate) (PBAT), cellulose acetate (CA), methylated pectin (MP), and polyvinyl alcohol (PVA), and crosslinkers like glyoxal. The hydrophobic character was improved in terms of a reduction in steady state weight gain, and an increase in dimensional stability (reduction in loss of radial and longitudinal dimensions) on moisture sorption. At the same time, efforts were made to maximize the expansion ratios by reduction of unit densities. Formulations of these foams (in terms of additive content and other processing parameters) were optimized. Particular formulations with PVA, polyesters like PCL and PBAT, and glyoxal with PVA gave foams with unit densities lower than 25 kg/m³. The dimensional stability increased with an increase in the polyester content, but the density increased beyond an optimum polyester content, too. The loss in radial and longitudinal dimensions under steady state conditions was 12–20% with polyesters as compared to about 50–55% for control starch. Addition of these processing aids did decrease the water sensitivity of the starch foams. Foams with CA and methylated pectin, in the presence/absence of glyoxal, had marginally lower unit densities and slightly higher expansion ratios, as compared to those of control starch. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 58–68, 2006     

Development of active cassava starch films reinforced with waste from industrial wine production and enriched with pink pepper extract

This study investigated the influence of grape stalk (GS) from the Bordo grape variety (Vittis labrusca L.) as a reinforcing agent, and pink pepper (Schinus terebinthifolius Raddi) extract (PPE) as an antioxidant, in cassava starch (CS)-glycerol (GLY) films. The developed biodegradable films were characterized according to structural, barrier, mechanical, antioxidant and optical properties, as well as biodegradability and compared to both the control and blank films. Films containing a high GS content exhibited a significant increase in tensile strength (TS) values by 73%, whereas the films containing a high PPE content exhibited an important increase elongation (ELO) values by 20%, comparing to the control film (CO). The films containing 5.52% v/v of PPE presented an improving on antioxidant activity and barrier properties, leading DPPH and ABTS percentual radical scavenging activity by 51.79% and 58.18%, and decreasing water vapor permeability and solubility by expressive values of 34.11% and 79.43%, respectively. According to the results obtained in this study, the films using GS and PPE exhibited valuable characteristics and are an alternative for applications as a promising biodegradable packaging material.     

Properties of rigid polyurethane foams prepared from recycled aircraft deicing agent with hexamethylene diisocyanate

Polyurethane (PUR) rigid foams were prepared from recycled aircraft deicing agent (aircraft deicing fluid) with reaction of hexamethylene diisocyanate at temperature of 55°C. The effect of [NCO]/[OH] ratio on properties of microscopic structure, cell size distribution, compressive strength, apparent density, as well as thermal conductivity (k) was studied. Higher [NCO]/[OH] ratio helped achieve better micromorphology, higher apparent density, and compressive strength of the PUR foams. With the [NCO]/[OH] ratio of 0.75 and 0.8, some shrinking happened during foam rising, causing a decrease in total volume of the PUR foam, and leading to higher apparent density as well as sharply increased compressive strength. All PUR foams displayed good thermal insulation properties in this study. With [NCO]/[OH] ratio increased from 0.7 to 0.8, the k value increased significantly from 34.3 to 42.2 mW m^?1 K^?1. The k value here was chiefly governed by the apparent density of the foams, which was in turn a function of the ratio of [NCO]/[OH]. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci., 2013     

Open-celled silicon carbide foams with high porosity from boron-modified polycarbosilanes

Open-Celled silicon carbide (SiC) foams were prepared from a mixture of a boron-modified polycarbosilane as a preceramic polymer and poly(methymetacrylate) (PMMA) microbeads as sacrificial agents. The process consists in the cross-linking of the liquid allylhydridopolycarbosilane (AHPCS, SiC precursor) with borane dimethylsulfide (BDMS, boron source) to form a solid boron-modified polycarbosilane with an adjusted cross-linking degree. The latter is mixed with PMMA microbeads (25 μm) in a 20:80 ratio and the mixture is warm-pressed at 120 °C forming consolidated green bodies to be pyrolyzed at 1000 °C under argon and to deliver open-celled SiC foams with an interconnected porosity of 73.4 _vol%. These foams combine a low density with a compressive strength of 3.49 ± 0.56 MPa and a thermal and mechanical stability under argon up to 1300 °C. Ageing and microfiltration tests in the conditions of a primary loop of coolant in a Pressurized Water Reactor (PWR) showed that foams display a relatively high stability while retaining particles of 5 μm in diameter making these materials as appropriate candidates to work in separation techniques under harsh environments.     

Highly porous and hierarchical MgAl2O4 ceramics with improved pore connectivity prepared from gelled particle-stabilized foams

Ultralight ceramics with striking mechanical properties and improved pore connectivity could have wide applications in areas ranging from catalyst support to hot gas filtration. However, creating such materials has proven to be a challenging target. This work demonstrated a novel methodology to prepare porous MgAl₂O₄ ceramics by calcining gelled MgO–Al₂O₃–SiO₂ particle-stabilized foams. The striking green strength of dried foams can be achieved as a consequence of MgO hydration and subsequent formation of gelled Mg(OH)₂ and MgO–SiO₂–H₂O skeleton. The decomposition of colloidal substance at elevated temperature resulted in the formation of small pores on the cell wall, thus forming the hierarchical porous architecture and improving the pore connectivity. The highly porous MgAl₂O₄ ceramics fired at 1600°C possessed the integrated properties of ultrahigh porosity (87.0%), improved pore connectivity and satisfactory compressive strength (7.93 MPa), showing great potential to be used in multiple industrial fields.     

Mechanically robust ZrO2 foams with 3D reticular architecture prepared from chemical-modified ZrO2 powder

Engineering mechanically robust ZrO₂ foams with three-dimensional (3D) reticular architecture and high porosity is extremely challenging. In current work, we presented an approach for constructing such cellular ceramics via a combined polyurethane foaming and chemical grafting method. Ester functional groups were chemically grafted on the ZrO₂ powder surface to enhance its dispersibility. This approach caused the micron-sized windows to assemble onto the cell wall of porous framework, contributing to 3D interconnected reticular architecture. The resulting products with such cellular architecture possessed a high porosity level of 89.2% and maintained an ultrahigh compressive strength of 8.5 MPa. Our results open up new opportunities for fabricating high-performance ZrO₂ foams toward practical applications.     

Properties of extruded starch–poly(methyl acrylate) graft copolymers prepared from spherulites formed from amylose–oleic acid inclusion complexes

Mixtures of high‐amylose corn starch and oleic acid were processed by steam jet cooking, and the dispersions were rapidly cooled to yield amylose–oleic acid inclusion complexes as micron‐ and submicron‐sized spherulites and spherulite aggregates. Dispersions of these spherulite particles were then graft polymerized with methyl acrylate, both before and after removal of uncomplexed amylopectin by water washing. For comparison, granular, uncooked high‐amylose corn starch was also graft polymerized in a similar manner. Graft copolymers with similar percentages of grafted and ungrafted poly(methyl acrylate) (PMA) were obtained from these polymerizations. The graft copolymers were then processed by extrusion through a ribbon die, and the tensile properties of the extruded ribbons were determined. Although extruded ribbons with similar tensile strengths were obtained from the three starch–PMA graft copolymers, much higher values for % elongation were obtained from the spherulite‐containing systems. Also, the tensile properties were not significantly affected by removal of soluble, uncomplexed amylopectin by water washing before graft polymerization. These results are consistent with the observation that these PMA‐grafted starch particles did not melt during extrusion, and that continuous plastic ribbons were formed by fusing these particles together in the presence of small amounts of thermoplastic PMA matrix. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40381.     

Poly(vinyl alcohol) composite films with high percent elongation prepared from amylose‐fatty ammonium salt inclusion complexes

Amylose inclusion complexes prepared from cationic fatty ammonium salts and jet‐cooked high amylose starch were combined with poly(vinyl alcohol) (PVOH) to form glycerol‐plasticized films. For the octadecylammonium salt complexes, elongation was significantly higher than the PVOH control when the amount of complex incorporated was from 20% to 70%. For the dodecyl‐ and hexadecylammonium salt complexes, elongation was significantly higher than PVOH films for 20% to 40% incorporation of cationic complex. Tensile strength declined with increasing levels of amylose‐ammonium salt complex, and surface hydrophobicity (contact angle) was significantly higher than PVOH films. Microscopy showed no phase separation or phase inversion, suggesting intimate mixing due to ionic interactions between cationic ammonium salt complexes and the hydroxyl groups of PVOH. The high elongations of these films and increased water contact angles are marketable advantages, along with the lower cost and increased biodegradability of the starch‐based component. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44110.     

Thermosets resins prepared from soybean oil and lignin derivatives with high biocontent,superior thermal properties,and biodegradability

A bio-based monomer, methacrylated vanillyl alcohol (MVA), had been synthesized from vanillyl alcohol with methacrylate anhydride (MAA) via a solvent-free, efficient method. The synthesis of MVA was confirmed by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR). It was used to copolymerize with acrylated epoxidized soybean oil (AESO) to prepare a bio-based resin (MVA–AESO). Excess MAA of MVA synthesis was further used to modify AESO with hydroxyl groups, generating (MVA–MAESO) with higher unsaturation degree. Their chemical structure and modification were characterized using ¹³C NMR and Fourier transform infrared analyses. Pure AESO and MVA resins were used to compare with MVA–AESO and MVA–MAESO in terms of their viscosity, curing performance, mechanical, and thermal properties. The synthesized MVA–AESO and MVA–MAESO resins showed much lower viscosities than pure AESO due to the dilution of MVA. In addition, the incorporation of MVA reduced curing temperatures, activation energies which caused MVA–AESO and MVA–MAESO had higher curing degree than pure AESO. With the combination of MVA and modification of MAA, flexible AESO networks exhibited superior flexural properties, storage modulus, glass-transition temperature, and thermal stability. Furthermore, the biodegradation of the formulated bio-based resins were also investigated. Results showed that the addition of monomer and the increase in the content of CC bonds did not significantly affect the biodegradability of AESO, which may be due to the fact that the degradable groups of AESO were not affected. This environmentally friendly, low (volatile organic) resin, prepared by a high efficiency and environmental protection synthetic route, can potentially replace typical petroleum-based thermosets for the production environmentally friendly thermosetting resins. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48827.     

Optimized pore structure and high permeability of metakaolin/fly-ash-based geopolymer foams from Al– and H2O2–sodium oleate foaming systems

Geopolymer foams have been widely studied as adsorbents owing to their high specific surface areas, high heavy metal immobilization efficiencies, low cost, environmental friendliness, and resource-recycling benefits. In this study, geopolymer foams with different pore structures were prepared from Al– and H₂O₂–sodium oleate foaming systems, and their chemical properties, pore structures, and permeabilities were characterized. The effects of the foaming agent type and surfactant content on the crystal structure and chemical bonding of the materials were analyzed by X-ray diffraction analysis and Fourier-transform infrared spectroscopy, and the pore morphology and structural characteristics were characterized by morphological observations, three-dimensional (3D) reconstruction, and compression tests. Numerical simulations were also carried out to study the structural characteristics of the 3D-reconstructed pores. Furthermore, variations in the permeability coefficient and flow characteristics were tested and analyzed by experiments and simulations. The pores in the geopolymer from the H₂O₂–sodium oleate foaming system tended to be more connected, whereas those in the Al–sodium oleate geopolymers were more complete and closed. The highly connected pore structure facilitates the even diffusion of the solution and effectively increases the amount of adsorption sites. These properties are significant for adjusting the adsorption capacity of geopolymer foams as adsorption monoliths.