title: Crystalline structure of poly(hexamethylene adipate). Study on the morphology and the enzymatic degradation of single crystals.
abstract: The crystalline structure of polyester 6 6 was studied by means of X-ray and electron diffraction and real-space electron microscopy. An orthorhombic unit cell containing eight chain segments with a quasi planar zigzag conformation was derived. The chain axis projection could be defined by a small rectangular cell containing only two molecular segments. Simulation of electron diffraction patterns indicates that molecular segments were arranged with azimuthal angles close to +/-46 degrees . X-ray diffraction patterns suggested that the large dimensions of the unit cell were a consequence of a slight shift between neighboring chains that improved the electrostatic interactions. Chain-folded lamellar crystals were obtained by isothermal crystallization of dilute n-hexanol or n-octanol solutions. The crystalline habit was studied, and the influence of temperature was evaluated. A regular folding surface was observed by using polyethylene decoration techniques. Lamellar crystals were easily degraded with different lipases. A preferential enzymatic attack was, in some cases, observed to occur in the crystal edges, giving rise to highly irregular borders with a fringed texture.
authors.affiliation: Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Avenida Diagonal 647, E-08028, Barcelona, Spain.
authors.forename: Sebastià
authors.initials: S
authors.lastname: Gestí
authors.forename: Ahmed
authors.initials: A
authors.lastname: Almontassir
authors.forename: María Teresa
authors.initials: MT
authors.lastname: Casas
authors.forename: Jordi
authors.initials: J
authors.lastname: Puiggalí
mesh_terms: D000272:Adipates / Q000737:chemistry*; D002151:Calorimetry; D003460:Crystallization; D004583:Electrons; D004798:Enzymes / Q000737:chemistry*; D000441:Hexanols / Q000737:chemistry; D018625:Microscopy, Atomic Force; D008854:Microscopy, Electron; D008968:Molecular Conformation; D000442:Octanols / Q000737:chemistry; D011091:Polyesters / Q000737:chemistry*; D020959:Polyethylene / Q000737:chemistry; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D000272:Adipates; D004798:Enzymes; D000441:Hexanols; D000442:Octanols; D011091:Polyesters; C511860:poly(hexamethylene adipate); C029900:adipic acid; D020959:Polyethylene