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Biodegradable Polyesters (biodegradable + polyester)
Selected AbstractsBiodegradable polyester layered silicate nanocomposites based on poly(,-caprolactone)POLYMER ENGINEERING & SCIENCE, Issue 9 2002Nadège Pantoustier Nanocomposites based on biodegradable poly(,-caprolactone) (PCL) and layered silicates (montmorillonite, MMT) were prepared either by melt interaction with PCL or by in situ ring-opening polymerization of ,-caprolactone as promoted by the so-called coordination-insertion mechanism. Both non-modified clays (Na+ -MMT) and silicates modified by various alkylammonium cations were studied. Mechanical and thermal properties were examined by tensile testing and thermogravimetric analysis. Even at a filler content as low as 3 wt% of inorganic layered silicate, the PCL-layered silicate nanocomposites exhibited improved mechanical properties (higher Young's modulus) and increased thermal stability as well as enhanced flame retardant characteristics as a result of a charring effect. It was shown that the formation of PCL-based nanocomposites depended not only on the nature of the ammonium cation and related functionality but also on the selected synthetic route, melt intercalation vs. in situ intercalative polymerization. Interestingly enough, when the intercalative polymerization of ,-caprolactone was carried out in the presence of MMT organo-modified with ammonium cations bearing hydroxyl functions, nanocomposites with much improved mechanical properties were recovered. Those hybrid polyester layered silicate nanocomposites were characterized by a covalent bonding between the polyester chains and the clay organo-surface as a result of the polymerization mechanism, which was actually initiated from the surface hydroxyl functions adequately activated by selected tin (II) or tin (IV) catalysts. [source] Synthesis and characterization of multiblock copolymers based on L -lactic acid, citric acid, and poly(ethylene glycol)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2003Fanglian Yao Abstract Because poly(L -lactic acid) (PLLA) is a biodegradable polyester with low immunogenicity and good biocompatibility, it is used as a biomaterial. However, hydrophobic PLLA does not have any reactive groups. Thus, its application is limited. To increase the hydrophilicity of PLLA and accelerate its degradation rate, functionalized pendant groups and blocks were introduced through copolymerization with citric acid and poly(ethylene glycol) (PEG), respectively. This article describes the synthesis and characterization of poly(L -lactic- co -citric acid) (PLCA)-PLLA and PLCA-PEG multiblock copolymers. The results indicated that the hydrolysis rate was enhanced, and the hydrophilicity was improved because of the incorporation of carboxyl groups in PLCA-PLLA. The joining of the PEG block led to improved hydrophilicity of PLCA, and the degradation rate of PLCA-PEG accelerated as compared with that of PLCA-PLLA. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2073,2081, 2003 [source] Micromechanical behavior related to the nanostructure of biodegradable polyestersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010M. E. Cagiao Abstract The microhardness of a series of biodegradable polyesters was determined. The nanostructural features of these materials were studied by wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and differential scanning calorimetry. Analysis of the SAXS and WAXS patterns allowed direct derivation of the degree of crystallinity and crystal thickness values, and correlations of the micromechanical properties are presented. The differences in the thermal and mechanical properties exhibited by the studied systems and the ones found in other aromatic polyesters are explained as due to the different chemical natures of the monomeric units. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] The effect of hyperbranched polymers on processing and thermal stability of biodegradable polyestersPOLYMER ENGINEERING & SCIENCE, Issue 3 2009Yanir Shaked Nanomodification of poly-hydroxy-butyrate (PHB), with hyperbranched polymers (HBP), was studied. Solid-hyperbranched polyesters of different generations were incorporated into a biobased and biodegradable, thermoplastic, polyester. Thermal, rheological, and molecular weight measurements had indicated that due to the interactions between the hydroxyl groups and the polar esters in PHB, the rate of recrystallization was significantly increased. Furthermore, the degree of crystallinity and nonisothermal crystallization temperature were also increased. Molecular weight measurements did not indicate a reduction or retention when HBPs were incorporated. These results are of great significance for the processing of biodegradable polymers and specifically for PHB, where improved processability and enhanced crystallization are of importance. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Biosynthesis of biodegradable polyesters from renewable carbon sources by recombinant bacteria ,POLYMER INTERNATIONAL, Issue 10 2002Seiichi Taguchi Abstract Based on the metabolic pathways for polyhydroxyalkanoate (PHA) biosynthesis, we succeeded in establishing the recombinant Pseudomonas sp 61-3 strains that synthesize random copolyesters consisting of (R)-3-hydroxybutyrate (3HB) and (R)-medium-chain-length 3-hydroxyalkanoate (mcl-3HA) units, P(3HB- co -3HA), with very high 3HB compositions (up to 94 mol%) from glucose. The mechanical properties of P(94% 3HB- co -3HA) copolyester were very similar to those of low-density polyethylene. We carried out the molecular cloning and characterization of a PhaGPs encoding (R)-3-hydroxyacyl-acyl carrier protein coenzyme A transferase of Pseudomonas sp 61-3. It was concluded that the PhaGPs gene product is involved in providing mcl-3HA-CoA from glucose in the original strain. Heterologous expression of the PhaGPs gene with the PhaC1Ps gene encoding PHA synthase from Pseudomonas sp 61-3 was performed in the PhbCRe negative mutant (PHB,4) of Ralstonia eutropha. The recombinant PHB,4 strain successfully produced PHA copolyesters consisting of 3HB and mcl-3HA units of 6,12 carbon atoms from sugars. The 3HB fraction in copolyesters was very high (95,97 mol%). The PHA content in the recombinant strain could further be increased by the additional introduction of the PhbABRe genes from R eutropha encoding ,-ketothiolase and NADPH-dependent acetoacetyl-coenzyme A reductase. Moreover, we have established an in vivo assay system to analyze mutational effects of R eutropha synthase (PhbCRe) on the level of PHB accumulation in recombinant strains of Escherichia coli. The activity of the PhbCRe could be efficiently estimated using the in vivo system constructed here, and would be useful for in vitro evolution of PhbCRe. © 2002 Society of Chemical Industry [source] | ||||||||||