Minor amounts of monomers or homopolymer of poly(butylene succinate) (PBS) were copolymerized or blended with monomers or homopolymer of poly(ethylene succinate) (PES). PEBSA 95/05 represents a copolymer synthesized from a feed ratio of 95 mol% ethylene glycol and 5 mol% 1,4-butanediol with 100 mol% succinic acid. Copolymers PEBSA 90/10 and 50/50 were also synthesized. Blends of PES and PBS were prepared in solution with ratios of PES/PBS: 98/02, 95/05 and 90/10. Molecular weights of homopolymers and copolymers were measured using capillary viscometer and gel permeation chromatography. The results indicate that polyesters used in this study have high molecular weights. The chemical composition and the sequence distribution of co-monomers in copolyesters were determined using 1H NMR and 13C NMR. The distribution of ES and BS units in these copolyesters was found to be random from the evidence of a single Tg and a randomness value close to 1.0 for a random copolymer. Thermal properties of polyesters and blends were characterized using differential scanning calorimeter (DSC), temperature-modulated DSC (TMDSC) and thermogravimeter. For copolymers, melting point of PES significantly decreases from 100.9 to 94.5 to 89.8 oC with an increasing in BS units from 0 to 5 to 10 mol%. Blends keep the intrinsic melting points of PES and PBS homopolymers. There is no significant difference or no trend about the thermal stability of these polyesters and blends. Wide-angle X-ray diffractograms (WAXD) were obtained for specimens after complete isothermal crystallization. Diffraction peaks indicate that the crystal structure of PES is dominated in PES-enriched copolymers. However, PEBSA 50/50 displays weak diffraction peaks of the characteristic peaks of PBS homopolymer.
Isothermal crystallization of copolyesters and blends were performed using DSC. Their crystallization kinetics and melting behavior after complete crystallization were analyzed. The n1 values of the Avrami exponent for copolyesters increased from 2.54 to 2.84 as the isothermal temperature (Tc) increased. The Hoffman-Weeks linear plots yielded an equilibrium melting temperature of 111.1 and 107.0 oC, respectively, for PEBSA 95/05 and 90/10. Homopolymer PES has an equilibrium melting temperature of 112.7 oC. For blends, the n1 value has a minimum at Tc of 40 oC then it increases with an increase in Tc or in PBS. At the same Tc, n1 increases slightly and the rate constant (k1) decreases when the ratio of PBS in blends increases. All of these blends gave an equilibrium melting temperature of 113.1 oC. Multiple melting behavior involves melting-recrystallization-remelting and various lamellar crystals. As Tc or BS unit in copolymer increases, the contribution of recrystallization slowly declines.
Acetophenone was used a diluent for PES homopolymer. Five concentrations were used to estimate the melting point depression, and the heat of fusion of PES was obtained to have a value of 163.3 J/g according to Flory equation. Spherulitic growth rates of copolymers were measured at Tc between 30 and 80 oC using polarized light microscope (PLM). Maximum growth rates occurred at Tc around 50 oC. It is found that the growth rate of copolymer decreases significantly after randomly incorporating BS units into PES. Non-isothermal method at a cooling rate of 2, 4 or 6 oC/min was used to calculate the isothermal growth rates of copolymers. These continuous data fit very well with the data points measured isothermally. Growth rates data are separately analyzed using the Hoffman-Lauritzen equation. A regime II-III transition is found at 59.4 and 52.4 oC, respectively, for copolyesters PEBSA 95/05 and PEBSA 90/10.
The results of DSC and PLM indicate that blend PES/PBS 98/02 not only retains the melting point and the crystallinity of PES homopolymer, but also increases the nucleation rate of this blend. The effect of blending 2 mol% PBS with PES on the biodegradability of PES is deserved to be investigated furthermore.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0724107-154256 |
| Date | 24 July 2007 |
| Creators | Lu, Hsin-ying |
| Contributors | Ming Chen, Chi Wang, Tien-Wei Shyr, Shih-Jung Bai, |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0724107-154256 |
| Rights | withheld, Copyright information available at source archive |
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