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Fabrication of lightweight microcellular polyimide foams with three-dimensional shape by CO2 foaming and compression molding / Wentao Zhai in Industrial & engineering chemistry research, Vol. 51 N° 39 (Octobre 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 39 (Octobre 2012) . - pp. 12827-12834 Titre : Fabrication of lightweight microcellular polyimide foams with three-dimensional shape by CO2 foaming and compression molding Type de document : texte imprimé Auteurs : Wentao Zhai, Auteur ; Weiwei Feng, Auteur ; Jianqiang Ling, Auteur Année de publication : 2012 Article en page(s) : pp. 12827-12834 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Molding  Compression  Foaming  Carbon  dioxide  Morphology  Foam Résumé : Microcellular structure endows polymeric foams with the improved mechanical properties, but the preparation of lightweight microcellular polyimide (PI) foams with a large size is challenging and inefficient, because of low gas solubility, high stiffness, and an extremely long saturation time. In this study, PI foam was prepared by solid-state microcellular foaming technology with the compressed CO2 as a physical blowing agent and tetrahydrofuran as coblowing agent The presence of coblowing agent was verified to increase the gas sorption of PI, causing a dramatic increase in the expansion ratio of miaocellular PI beads from 2.9 to 15.7. Using a novel compression molding process, the prepared PI foams were molded into the 3-D shaped products. Before the molding, the foamed PI beads were coated by poly(ether imide) (PEI)/chloroform solution. The contact angle tests indicated that PEI/chloroform could infiltrate well PI foams' surface, which facilitated the formation of strong interbead bonding between bead foams. The thickness of the coated PEI layer and the interbead bonding regions were the important parameters to adjust the bending and compression properties of the molded PI foam (MPI) product. The experimental results indicated that the bending strength and compression strength (at 10% strain) of MPI sample with density of 137.7 kg/m3 were 1.27 and 1.59 MPa, respectively. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=26419239 [article] Fabrication of lightweight microcellular polyimide foams with three-dimensional shape by CO2 foaming and compression molding [texte imprimé] / Wentao Zhai, Auteur ; Weiwei Feng, Auteur ; Jianqiang Ling, Auteur . - 2012 . - pp. 12827-12834. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 39 (Octobre 2012) . - pp. 12827-12834 Mots-clés : Molding  Compression  Foaming  Carbon  dioxide  Morphology  Foam Résumé : Microcellular structure endows polymeric foams with the improved mechanical properties, but the preparation of lightweight microcellular polyimide (PI) foams with a large size is challenging and inefficient, because of low gas solubility, high stiffness, and an extremely long saturation time. In this study, PI foam was prepared by solid-state microcellular foaming technology with the compressed CO2 as a physical blowing agent and tetrahydrofuran as coblowing agent The presence of coblowing agent was verified to increase the gas sorption of PI, causing a dramatic increase in the expansion ratio of miaocellular PI beads from 2.9 to 15.7. Using a novel compression molding process, the prepared PI foams were molded into the 3-D shaped products. Before the molding, the foamed PI beads were coated by poly(ether imide) (PEI)/chloroform solution. The contact angle tests indicated that PEI/chloroform could infiltrate well PI foams' surface, which facilitated the formation of strong interbead bonding between bead foams. The thickness of the coated PEI layer and the interbead bonding regions were the important parameters to adjust the bending and compression properties of the molded PI foam (MPI) product. The experimental results indicated that the bending strength and compression strength (at 10% strain) of MPI sample with density of 137.7 kg/m3 were 1.27 and 1.59 MPa, respectively. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=26419239

Ultrasonic irradiation enhanced cell nucleation in microcellular poly (lactic Acid) / Jing Wang in Industrial & engineering chemistry research, Vol. 50 N° 24 (Décembre 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 24 (Décembre 2011) . - pp. 13840-13847 Titre : Ultrasonic irradiation enhanced cell nucleation in microcellular poly (lactic Acid) : a novel approach to reduce cell size distribution and increase foam expansion Type de document : texte imprimé Auteurs : Jing Wang, Auteur ; Wentao Zhai, Auteur ; Jianqiang Ling, Auteur Année de publication : 2012 Article en page(s) : pp. 13840-13847 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Expansion  Foam  Particle  size  distribution Résumé : The preparation of poly(lactic acid) (PLA) foam with a well-defined cell structure, high crystallinity, a high expansion ratio, and good mechanical properties is critical to its broader applications. However, achieving these properties in PLA foam simultaneously is challenging, because high crystallinity generally results in nonuniform cell nucleation and suppresses cell growth in the case of solid-state foaming. This study presents a novel approach using ultrasonic irradiation (UI) to achieve the desired properties in PLA simultaneously. As expected, CO2-saturated PLA samples at 5 MPa have a high crystallinity (23.4%), and foamed PLA samples at various foaming temperatures exhibit low foam expansion and nonuniform cell structure. By introducing UI at the very start of the foaming, however, the resultant PLA foams presented a significant and concurrent increase in cell structure uniformity and cell density: cell density increased about 2 orders of magnitude, the expansion ratio increased 1–2 times, the elongation at break increased 2 times, and the specific tensile strength increased 1.1 times, compared to samples without UI. Further investigation indicated that the enhanced cell nucleation induced by UI was the main reason for this unique phenomenon. Our study provides a simple but efficient and cost-effective method to fabricate PLA foams that possess excellent mechanical properties. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=25299849 [article] Ultrasonic irradiation enhanced cell nucleation in microcellular poly (lactic Acid) : a novel approach to reduce cell size distribution and increase foam expansion [texte imprimé] / Jing Wang, Auteur ; Wentao Zhai, Auteur ; Jianqiang Ling, Auteur . - 2012 . - pp. 13840-13847. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 24 (Décembre 2011) . - pp. 13840-13847 Mots-clés : Expansion  Foam  Particle  size  distribution Résumé : The preparation of poly(lactic acid) (PLA) foam with a well-defined cell structure, high crystallinity, a high expansion ratio, and good mechanical properties is critical to its broader applications. However, achieving these properties in PLA foam simultaneously is challenging, because high crystallinity generally results in nonuniform cell nucleation and suppresses cell growth in the case of solid-state foaming. This study presents a novel approach using ultrasonic irradiation (UI) to achieve the desired properties in PLA simultaneously. As expected, CO2-saturated PLA samples at 5 MPa have a high crystallinity (23.4%), and foamed PLA samples at various foaming temperatures exhibit low foam expansion and nonuniform cell structure. By introducing UI at the very start of the foaming, however, the resultant PLA foams presented a significant and concurrent increase in cell structure uniformity and cell density: cell density increased about 2 orders of magnitude, the expansion ratio increased 1–2 times, the elongation at break increased 2 times, and the specific tensile strength increased 1.1 times, compared to samples without UI. Further investigation indicated that the enhanced cell nucleation induced by UI was the main reason for this unique phenomenon. Our study provides a simple but efficient and cost-effective method to fabricate PLA foams that possess excellent mechanical properties. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=25299849