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Cracks and ring bands of poly(3-hydroxybutyrate) on precrystallized poly(l-lactic acid) template / Siti Nurkhamidah in Industrial & engineering chemistry research, Vol. 50 N° 8 (Avril 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 8 (Avril 2011) . - pp. 4494–4503 Titre : Cracks and ring bands of poly(3-hydroxybutyrate) on precrystallized poly(l-lactic acid) template Type de document : texte imprimé Auteurs : Siti Nurkhamidah, Auteur ; E. M. Woo, Auteur Année de publication : 2011 Article en page(s) : pp. 4494–4503 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Cracks  Ring  banded  Precrystallized  Poly Résumé : The lamellar morphology, cracks, and ring-banded spherulites were analyzed by allowing crystallization of poly(3-hydroxybutyrate) (PHB) on previously crystallized lamellar templates of poly(l-lactic acid) (PLLA) in mixtures of two semicrystalline polymers, PHB/PLLA (50/50) blend. PHB/PLLA blends were two-step crystallized first at crystallization temperature (Tc = 115−120 °C) and then cooled to ambient temperature. At Tc, only PLLA crystallized while PHB was an amorphous liquid; then at ambient temperature PHB crystallized and followed the preformed PLLA lamellar crystals. In addition, the amorphous PHB in PHB/PLLA blends induces the formation of ring-banded spherulites of PLLA at lower Tc. The radial short-segmental cracks aggregated on the circumferential bright bands occur in crystallized PHB/PLLA blends, which cannot be adequately interpreted by the temperature-induced coefficient of thermal expansion (CTE) upon cooling, but more likely they are related to interlamellar structuring of PLLA crystals at primary stage that are to be superimposed by the PHB crystals at later stage. The solvent etching of blends not only creates a valley−ridge depth profile in outer lamellar plates, but also exposes the internal branched crystals underneath the bright band (ridge after etching), which are housed underneath the concave portion of lamellae with lenticular-shaped radial cracks. PHB and PLLA in crystallized blends are intermixed in the dark bands, and these two lamellae also are interwound as radial bundles in the bright bands. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1024547 [article] Cracks and ring bands of poly(3-hydroxybutyrate) on precrystallized poly(l-lactic acid) template [texte imprimé] / Siti Nurkhamidah, Auteur ; E. M. Woo, Auteur . - 2011 . - pp. 4494–4503. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 8 (Avril 2011) . - pp. 4494–4503 Mots-clés : Cracks  Ring  banded  Precrystallized  Poly Résumé : The lamellar morphology, cracks, and ring-banded spherulites were analyzed by allowing crystallization of poly(3-hydroxybutyrate) (PHB) on previously crystallized lamellar templates of poly(l-lactic acid) (PLLA) in mixtures of two semicrystalline polymers, PHB/PLLA (50/50) blend. PHB/PLLA blends were two-step crystallized first at crystallization temperature (Tc = 115−120 °C) and then cooled to ambient temperature. At Tc, only PLLA crystallized while PHB was an amorphous liquid; then at ambient temperature PHB crystallized and followed the preformed PLLA lamellar crystals. In addition, the amorphous PHB in PHB/PLLA blends induces the formation of ring-banded spherulites of PLLA at lower Tc. The radial short-segmental cracks aggregated on the circumferential bright bands occur in crystallized PHB/PLLA blends, which cannot be adequately interpreted by the temperature-induced coefficient of thermal expansion (CTE) upon cooling, but more likely they are related to interlamellar structuring of PLLA crystals at primary stage that are to be superimposed by the PHB crystals at later stage. The solvent etching of blends not only creates a valley−ridge depth profile in outer lamellar plates, but also exposes the internal branched crystals underneath the bright band (ridge after etching), which are housed underneath the concave portion of lamellae with lenticular-shaped radial cracks. PHB and PLLA in crystallized blends are intermixed in the dark bands, and these two lamellae also are interwound as radial bundles in the bright bands. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1024547

Effect of a miscible polymeric diluent on complex formation between isotactic and syndiotactic poly(methyl methacrylate) / L. Chang in Industrial & engineering chemistry research, Vol. 48 N° 7 (Avril 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 7 (Avril 2009) . - pp. 3432–3440 Titre : Effect of a miscible polymeric diluent on complex formation between isotactic and syndiotactic poly(methyl methacrylate) Type de document : texte imprimé Auteurs : L. Chang, Auteur ; E. M. Woo, Auteur Année de publication : 2009 Article en page(s) : pp. 3432–3440 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Syndiotactic  poly(methyl  methacrylate)Thermal  treatment  Isotactic  Miscible  polymeric Résumé : Formation of a stereocomplex structure in a blend of isotactic and syndiotactic poly(methyl methacrylate)s (iPMMA/sPMMA) was found to be significantly enhanced by introducing a mutual miscible diluent of poly(ethylene oxide) (PEO) in the blend, even when prepared using a kinetically hindered noncomplexing CHCl3 solvent. Mechanisms and influencing factors, such as thermal treatment, annealing temperature, annealing time, or PEO content in blends, on structures of stereocomplexes in the ternary iPMMA/sPMMA/PEO blends are discussed. WAXD result showed that addition of PEO in the iPMMA/sPMMA blend did not alter the crystal cells in the complexes. Melting peaks associated with the complexes were analyzed for discerning possible structural mechanisms. When annealed at specific temperatures, multiple endothermic peaks of the complexes increased in intensity as PEO contents increased in the ternary blends. Analysis shows that the lower melting peak (P1) represents shorter stereocomplex sequences or stereocomplex detached from PEO or connected with partial PEO, but the higher melting peak (P3) is related to the stereocomplex physically interconnected in the presence of PEO. The PEO molecules are thought to more easily interact with the stereocomplexes in blends by acting as a plasticizer, which decreases Tg of the more rigid PMMA chain segments. Physical interaction or miscibility-enhanced chain entanglement probably exists between PEO and the stereocomplex of tactic PMMAs, leading to stereocomplex formation in the iPMMA/sPMMA/PEO ternary blend. FT-IR characterization provided evidence of weak interactions between PEO and the stereocomplex of PMMA. IR peaks sensitive to complex structures with respect to temperature were analyzed for discerning effects by adding PEO. The stereocomplex formation of ternary blends with PEO is due to the weak interaction of ester groups and methoxy groups between PMMA and PEO. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801488u [article] Effect of a miscible polymeric diluent on complex formation between isotactic and syndiotactic poly(methyl methacrylate) [texte imprimé] / L. Chang, Auteur ; E. M. Woo, Auteur . - 2009 . - pp. 3432–3440. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 7 (Avril 2009) . - pp. 3432–3440 Mots-clés : Syndiotactic  poly(methyl  methacrylate)Thermal  treatment  Isotactic  Miscible  polymeric Résumé : Formation of a stereocomplex structure in a blend of isotactic and syndiotactic poly(methyl methacrylate)s (iPMMA/sPMMA) was found to be significantly enhanced by introducing a mutual miscible diluent of poly(ethylene oxide) (PEO) in the blend, even when prepared using a kinetically hindered noncomplexing CHCl3 solvent. Mechanisms and influencing factors, such as thermal treatment, annealing temperature, annealing time, or PEO content in blends, on structures of stereocomplexes in the ternary iPMMA/sPMMA/PEO blends are discussed. WAXD result showed that addition of PEO in the iPMMA/sPMMA blend did not alter the crystal cells in the complexes. Melting peaks associated with the complexes were analyzed for discerning possible structural mechanisms. When annealed at specific temperatures, multiple endothermic peaks of the complexes increased in intensity as PEO contents increased in the ternary blends. Analysis shows that the lower melting peak (P1) represents shorter stereocomplex sequences or stereocomplex detached from PEO or connected with partial PEO, but the higher melting peak (P3) is related to the stereocomplex physically interconnected in the presence of PEO. The PEO molecules are thought to more easily interact with the stereocomplexes in blends by acting as a plasticizer, which decreases Tg of the more rigid PMMA chain segments. Physical interaction or miscibility-enhanced chain entanglement probably exists between PEO and the stereocomplex of tactic PMMAs, leading to stereocomplex formation in the iPMMA/sPMMA/PEO ternary blend. FT-IR characterization provided evidence of weak interactions between PEO and the stereocomplex of PMMA. IR peaks sensitive to complex structures with respect to temperature were analyzed for discerning effects by adding PEO. The stereocomplex formation of ternary blends with PEO is due to the weak interaction of ester groups and methoxy groups between PMMA and PEO. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801488u