A series of aliphatic homopolyesters and copolyesters was prepared from 1,4 butanediol and dimethylesters of succinic and adipic acids through a two-step process of transesterification and polycondensation. The synthesized polyesters were characterized by means of nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), viscosity measurements, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and mechanical property measurements. The homopolymer poly(butylene succinate) exhibited the highest tensile strength, which decreased with increasing adipate unit content, passed through a minimum at copolyester composition close to equimolarity and then increased towards the value of poly(butylene adipate). It is interesting to note that in contrast to tensile strength, the elongation at break increased for adipate unit content of 20-40 mol%. The biodegradation of the polymers was investigated by soil burial and enzymatic hydrolysis using three enzymes, Candida cylindracea lipase, Rhizopus delemar lipase, and Pseudomonas fluorescens cholesterol esterase. It appears that the key factor affecting material degradation was its crystallinity. 相似文献
Three high molecular weight aliphatic polyesters derived from adipic acid and the appropriate diol - poly(ethylene adipate) (PEAd), poly(propylene adipate) (PPAd) and poly(butylene adipate) (PBAd) - were prepared by two-stage melt polycondensation method (esterification and polycondensation) in a glass batch reactor. Intrinsic viscosities, GPC, DSC, NMR and carboxylic end-group measurements were used for their characterization. Mechanical properties of the prepared polyesters showed that PPAd has similar tensile strength to low-density polyethylene while PEAd and PBAd are much higher. From TGA analysis it was found that PEAd and PPAd have lower thermal stability than poly(butylene adipate) (PBAd). The decomposition kinetic parameters of all polyesters were calculated while the activation energies were estimated using the Ozawa, Flynn and Wall (OFW) and Friedman methods. Thermal degradation of PEAd was found to be satisfactorily described by one mechanism, with activation energy 153 kJ/mol, while that of PPAd and PBAd by two mechanisms having different activation energies: the first corresponding to a small mass loss with activation energies 121 and 185 kJ/mol for PPAd and PBAd, respectively, while the second is attributed to the main decomposition mechanism, where substantial mass loss takes place, with activation energies 157 and 217 kJ/mol, respectively. 相似文献
Poly(hydroxyalkanoate)s (PHAs) are a class of microbially synthesized polyesters that combine biological properties, such as biocompatibility and biodegradability, and non-bioproperties such as thermoprocessability, piezoelectricity, and nonlinear optical activity. PHA monomer structures and their contents strongly affect the PHA properties. Using metabolic engineering approaches, PHA structures and contents can be manipulated to achieve controllable monomer and PHA cellular contents. This paper focuses on metabolic engineering methods to produce PHA consisting of 3-hydroxybutyrate (3HB) and medium-chain-length 3-hydroxyalkanoates (3HA) in recombinant microbial systems. This type of copolyester has mechanical and thermal properties similar to conventional plastics such as poly(propylene) and poly(ethylene terephthalate) (PET). In addition, pathways containing engineered PHA synthases have proven to be useful for enhanced PHA production with adjustable PHA monomers and contents. The applications of PHA as implant biomaterials are briefly discussed here. In the very near term, metabolic engineering will help solve many problems in promoting PHA as a new type of plastic material for many applications. 相似文献
Four saturated polyesters poly(hexamethylene adipate), poly(ethylene adipate), poly(hexamethylene terephthalate) and poly(ethylene terephthalate) were prepared. The resulting materials were characterized by IR and 1H NMR, end group analysis and gel permeation chromatography. The effect of blending these polyesters (5 and 10%) with poly(vinyl chloride) (PVC) in the melt was investigated in terms of changes in the thermal behaviour of PVC by studying the weight loss after 50 min at 180 °C, colour changes of the blend before and after aging for one week at 90 °C, the variation in glass transition temperature and the initial decomposition temperature. The results gave proof for the stabilizing role played by the investigated polyesters against the thermal degradation of PVC. The best results are obtained when PVC is mixed with 5% aliphatic polyesters rather than with aromatic ones. This is well illustrated not only from the increase in the initial decomposition temperature (IDT), but also from the decrease of % weight loss and from the lower extent of discolouration of PVC, which is a demand for the application of the polymer. It was also found that blending PVC with 5% of the four investigated polyesters before and after aging for one week at 90 °C gave better mechanical properties even than that of the unaged PVC blank. 相似文献
The biodegradability, morphology, and mechanical properties of composite materials consisting of acrylic acid-grafted poly(butylene succinate adipate) (PBSA-g-AA) and agricultural residues (rice husk, RH) were evaluated. Composites containing acrylic acid-grafted PBSA (PBSA-g-AA/RH) exhibited noticeably superior mechanical properties compared with those of PBSA/RH due to greater compatibility with RH. The dispersion of RH in the PBSA-g-AA matrix was highly homogeneous as a result of ester formation, and the consequent creation of branched and cross-linked macromolecules, between the carboxyl groups of PBSA-g-AA and hydroxyl groups in RH. Each composite was subject to biodegradation tests in an Azospirillum brasilense BCRC 12270 liquid culture medium. The bacterium completely degraded both the PBSA and the PBSA-g-AA/RH composite films. Morphological observations indicated severe disruption of the film structure after 20-40 days of incubation. The PBSA-g-AA/RH (20 wt%) films were not only more biodegradable than those made of PBSA but also exhibited lower molecular weight and intrinsic viscosity, implying a strong connection between these characteristics and biodegradability. 相似文献
Aliphatic polyesters have attracted industrial attention as environmentally degradable thermoplastics to be used for a wide range of applications. Besides intensive studies on the biodegradability of aliphatic polyesters, understanding of the thermal stability has importance for processing, application, and recycling. The details of thermal degradation processes of five types of aliphatic polyesters; namely, poly(L-lactide), poly(3-hydroxybutyric acid), poly(4-hydroxybutyric acid), poly(delta-valerolactone), and poly(epsilon-caprolactone), were investigated by means of several thermoanalytical techniques under both isothermal and non-isothermal conditions. In this feature article, the thermal degradation behaviors of aliphatic polyesters with different numbers of carbon atoms in the main chain of the monomeric unit are reviewed. In addition, the effects of chain-end structure and residual metal compounds on the thermal degradation processes of aliphatic polyesters consisting of hydroxyalkanoic acid monomeric units are presented. Schemes of thermal degradation reaction of poly(hydroxyalkanoic acid)s. 相似文献
A series of biodegradable polyesters were synthesized from dicarboxylic acids and 1,3-propanediol catalyzed by transestrification polycondensation reaction in the bulk. The structure, average molecular weights and physical properties of the resulting aliphatic polyesters were characterized by 1H NMR, FT-IR, solution viscosity, GPC, DSC and TGA. Homopolyesters show higher degree of crystallinity, melting and thermal stability in comparison to copolyesters. The biodegradability of the polyesters was determined by monitoring the normalized weight loss of polyester films with time in phosphate buffer (pH 7.2) without and with Rhizopus delemar lipase at 37 °C. The rate of enzymatic degradation of homopolyesters follows the path PPSu > PPAd > PPSe. PPSe did not show significant weight loss in presence of enzyme which may be due to its highest degree of crystallinity and melting point compared to the PPSu, PPAd and copolyesters. In the soil burial degradation polyester sample showed severe surface degradation by the attack of microorganism. 相似文献
In this article, two series of ABA triblock copolyesters composed of poly(l-lactide) A hard blocks and odd-odd aliphatic polyesters as B soft midblock were prepared and compared by various techniques. The results showed that the block structures could be formed without any detectable transesterification, and the composition and molecular weight of the triblock copolyesters could be well controlled by adjusting the feeding ratio of l-lactide monomer to the polyester macroinitiator. It was found that the thermal properties, crystal structure, and spherulitic morphology of the triblock copolyesters depended on the composition and block length. The impact of amorphous and crystalline midblocks on the mechanical properties was compared and discussed. The triblock copolyesters composed of crystalline midblock showed similar ultimate stress and elongation, but higher tensile modulus and yield stress, in comparison with analogous containing amorphous midblock. The triblock copolyester composed of short PLLA hard block and amorphous aliphatic polyester soft midblock displayed typical elastomeric behavior without yield, which is a promising aliphatic polyester thermoplastic elastomer. 相似文献
We present here the first synthesis of cyclic oligo(ethylene adipate)s(COEAs) via pseudo-high dilution condensation reaction of adipoyl chloride with ethylene glycol, and the synthesis of corresponding poly(ethylene adipate)(PEA) via the melt polymerization of COEAs. The structure of COEAs was characterized and proved by 1H-NMR and MALDI-TOF mass measurements. The effects of organic base, reaction temperature and the ratio of adipoyl chloride to ethylene glycol on the yield of COEAs were studied, and the optimum reaction condition was revealed. PEA, a diacid and diol based semi-crystalline green aliphatic polyester, was synthesized by the melt polymerization of COEAs using Ti(n-C4H9O)4 as catalyst and 1,10-decanediol as initiator at 200 °C, which follows the polycondensation-coupling ringopening polymerization method. Our strategy should be applicable to the synthesis of versatile aliphatic polyesters based on diacid and diol monomers, which have potential applications as biocompatible and biodegradable materials. 相似文献
A novel preparation method for the core‐shell type biodegradable polyesters or biodegradable materials grafted with biodegradable polyesters was developed by alkaline surface treatment of biodegradable polyester films and subsequent enzymatic polymerization of aliphatic lactones, one example of which is shown in this study, i.e., the preparation of poly(L ‐lactide) (PLLA) film grafted with poly(ε‐caprolactone). It is revealed that only alkaline surface treatment or the combination of alkaline surface treatment and enzyme‐catalyzed grafting, the former and the latter, respectively accelerating and delaying the enzymatic degradation of PLLA, will give PLLA materials having a wide variety of biodegradability. Also, the specificity of the enzyme used for hydrolysis could be used to confirm the grafted chain species.
The main shortcomings of biodegradable starch/poly(vinyl alcohol) (PVA) film are hydrophilicity and poor mechanical properties. With an aim to overcome these disadvantages, cornstarch was methylated and blend films were prepared by mixing methylated-cornstarch (MCS) with PVA. The mechanical properties, water resistance and biodegradability of the MCS/PVA film were investigated. It was found that MCS/PVA film had higher water resistance than the native starch/PVA film. However, the water resistance of MCS/PVA films did not have significant difference with the increase in the degree of substitution (DS) of the methylated starch from 0.096 to 0.864. Enzymatic, microbiological and soil burial biodegradation results indicated that the biodegradability of the MCS/PVA film strongly depended on the starch proportion in the film matrix. The degradation rate of starch in the starch/PVA film was hindered by blending starch with PVA. Both tensile strength and percent elongation at break of the MCS/PVA film were improved as DS of the methylated starch increased. Conversely, increasing the methylated starch proportion in film matrix deteriorated both tensile strength and percent elongation at break of the film. 相似文献