Papers by Keyword: Biodegradable Polyester

Abstract: Bacterial cellulose (BC) is the cellulose which is produced by specific bacteria such as Acetobacter xylinum, Agrobacterium, Gluconacetobacter, Rhizobium, Achromobacter, Alcaligenes, Aerobacter, Azotobacter, Salmonella, Esherichia, and Sarcina. Surface modification of bacterial cellulose (BC) by coating with synthetic biodegradable polyester on it was reported. BC films were coated with the polymer at different concentrations in order to improve the surface structure of BC. Tear and burst indices of the BC film were increased with such modification.

Abstract: Nowadays, polymers are finding increasing use in a bewildering array of specialist applications. A good example of this is in the biomedical field. In this paper, some of the research work which is being carried out in Chiang Mai will be described. In its wider context, this paper also aims to show how the development of new polymers for such specialist applications depends on being able to control the polymers microstructure at each stage of its synthesis and processing.

Abstract: Four metal tert-butoxides, namely: aluminum (III) tert-butoxide, Al (Ot-C₄H₉)₃, tin (II) tert-butoxide, Sn (Ot-C₄H₉)₂, titanium (IV) tert-butoxide, Ti (Ot-C₄H₉)₄, and lithium tert-butoxide, Li (Ot-C₄H₉), were used as initiators in the bulk ring-opening polymerization (ROP) of ε-caprolactone (CL). The polymerizations were carried out at 120 °C for 72 hrs. It was found that the Al (Ot-C₄H₉)₃ only partially dissolved in the CL monomer and gave a low % conversion. The Li (Ot-C₄H₉) initiator did not dissolve and gave no polymerization. In contrast, the Sn (Ot-C₄H₉)₂ initiator dissolved completely, albeit very slowly, and gave a high % conversion. The Ti (Ot-C₄H₉)₄ initiator was by far the easiest and quickest to dissolve and also gave a high % conversion. Consequently, Ti (Ot-C₄H₉)₄-initiated polymerization was studied further by dilatometry at 120°C. From the kinetic results, a first-order rate constant, k_p, of 0.120 l mol^-1 min^-1 was obtained.

Abstract: This paper describes the molecular design of a speciality polyester for use as a fast-absorbable monofilament surgical suture. In the surgical context, fast-absorbable means tensile strength loss within a period of 10-14 days, the minimum period required for secure wound approximation, after which the suture gradually loses its mass integrity leading to complete mass loss within 2-3 months. In order to be fast-absorbable, it is necessary that the main monomer used in synthesizing the polymer is glycolide since the polymer repeating unit, -OCH₂CO-, is the chemical structure which hydrolyses the most rapidly in the human body. However, glycolide alone would give a monofilament suture fibre which would be too stiff and unwieldy for practical purposes and so it needs to be copolymerised with other cyclic ester monomers such as L-lactide and caprolactone to modify its mechanical properties. In this way, a monofilament fibre can be obtained which has an appropriate balance of hydrolysability and flexibility. Thus, this work enters the realm of molecular engineering insofar that it involves the strict control of both the chemical and physical microstructure of the polymer during the synthesis and processing steps respectively. This paper will describe how this controlled molecular architecture can be achieved and some preliminary results will be presented.

Abstract: The biodegradation and biodegradable mechanism of the polyesters ,such as poly (lactic acid) (PLA), poly (butylene succinate) (PBS) and poly (caprolactone) (PCL) have been investigated; the soil of Shanxi local land and activated sludge from Ningde waste water plant played the biodegradable medium in this study. The results shown the remarkable eroded trace of the surface of the films could be found after degradation by the results of Polarized Light Microscope (PLM) and scanning electron microscope (SEM); the biodegradation of PCL is best, the PLA′s is better than that of PBS. The structures of the films determined with Fourier-Transformation Infrared Spectrum (FT-IR) after degradation.

Abstract: Biodegradable polyesters with free hydroxyl groups were synthesis by the lipase-catalyzed polycondensation of L-malic acid with different diacids (succinic acid, adipic acid and sebacic acid) and diols (ethandiol, 1,4-butanediol, 1,6-hexanediol and 1,8-octanediol). The molecular weight (Mw) of the copolymers was affected by the alkylene chain lengths of diacids and diols. It was found that diacids and diols with longer alkylene chain lengths have a higher reactivity than that of shorter chain-length diacids and diols. The crytallizability of the copolymers were affected by the alkylene chains length of diacids and diols. The crytallizability decreased with the decreasing of the alkylene chains length of diacids and diols.

Abstract: Two novel tin(II) alkoxides, namely: tin(II) hexoxide, Sn(OC6H13)2, and tin(II) octoxide, Sn(OC8H17)2, have been synthesized for use as coordination-insertion initiators in the bulk ring-opening polymerization of ε-caprolactone. The kinetics of the polymerization reactions were studied at 140 °C by dilatometry. It was found that both alkoxides were slow to dissolve in the ε-caprolactone monomer due to their molecular aggregation in the solid state. As a result, the slow solubilization of the initiators gave rise to deviations from the expected first-order kinetics. Instead, the kinetic results adhered more closely to zero-order kinetics with apparent zero-order rate constants k0 of 6.58 x 10-2 and 4.63 x 10-2 mol l-1 min-1 for the hexoxide and octoxide respectively

Abstract: A significant number of poly a-ester homologues of poly(L-lactide) (PLLA) have been synthesized and used in miscibility studies together with conventional isomeric diacid-diol polyester variants, poly β-esters (based on β-hydroxybutyrate (HB) and β-hydroxyvalerate (HV)), poly e-caprolactone (PCL), poly e-caprolactone copolymers (e.g. poly(L-lactide-co-caprolactone), and a series of cellulose-based polymers (e.g. cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP)). A combinatorial approach to rapid miscibility screening using 96-well plates and a uv-visible multi-wavelength plate reader has been developed enabling the clarity of PLLA-based multi-component blend films to be observed. Using these techniques and materials, the ternary phase compatibility diagrams of a range of three-component blend films was prepared, illustrating ranges of behavior varying from miscible blends giving rise to clear films to immiscible blends which are opaque. In this way, novel three-component blends of PLLA/CAB/PCL were developed which are miscible when the CAB content is more than 30%, PLLA less than 80% and PCL less than 60%.

Abstract: The bulk ring-opening copolymerisation of L-lactide (LL) and ε-caprolactone (CL) with an initial comonomer feed ratio of LL:CL = 75:25 mol % was carried out using stannous acetate as the initiator at 120 oC for 48 hrs. The copolymer was characterised by GPC, DSC and TGA. Due to its ability to biodegrade in the human body, this type of copolymer has potential for use as an absorbable surgical suture. The copolymer obtained was melt spun at 153 oC using a small-scale melt-spinning apparatus and extruded into ice-cooled water to produce an as-spun monofilament fibre which was largely if not completely amorphous. Alternate off-line hot-drawing and annealing (3 cycles) was carried out in order to develop the fibre’s oriented semi-crystalline morphology. To complete the processing operation, thermal treatment was necessary to stabilize the fibre morphology. It was found that fixed annealing at 60 oC followed by free annealing at 60 oC stabilized the fibre morphology as a result of molecular relaxation. In vitro hydrolytic degradation studied in a phosphate buffer saline (PBS) solution of pH 7.4 at 37.0 ± 0.1 oC indicated that, after 6 weeks immersion in the buffer, the fibre’s tensile strength decreased by approximately 50% whereas a commercial ‘PDS’ suture of similar size lost its strength completely after only 4 weeks.