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Research on the Structure and Properties of Biodegradable Polyester Based Nanocomposites

Author: WuYan
Tutor: ZhangLiQun
School: Beijing University of Chemical Technology
Course: Materials Science and Engineering
Keywords: biodegradable polyester nanosilica HA nanocomposites
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 45
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Abstract

Biodegradable polyester elastomers have numerous advantages, such as the flexibility of molecular design, adjustable properties, and excellent biodegradability, however, the mechanical properties and biocompatibility of these materials are not good enough to satisfy various biomedical applications. Thus different nanofillers including nanosilica (SiO2) and nanohydroxyapatite (HA) were utilized to reinforce and modify them. The influence of various preparation conditions and nanofiller loadings on the structure and properties of the resultant composites was characterized and discussed.Nanosilica, which is common and inexpensive, has an outstanding reinforcing effect on elastomers. Also, it has been approved by the US FDA to be applied in foods, cosmetics and biomedicines. In this work, various factors, such as the species of silane coupling agents, citric acid contents and modification methods, were studied in the first place to investigate their effects on the microstructure and mechanical properties of SiO2/PGSC composites, and then the influence of nanosilica loadings (0-20phr) on the structure and comprehensive properties of composites was discussed thoroughly. With the increase of nanosilica loadings, the physical crosslinking densities of composites increased while the chemical crosslinking densities and ordered arrangement degrees decreased. The comprehensive influence of increasing nanosilica loadings on the properties of composites showed decreased swelling degrees and glass transition temperatures, and improved mechanical properties. The composites with 25phr nanosilica exhibited the highest mechanical properties, which tensile strength reached 6.06MPa. Moreover, the addition of nanosilica improved the degradation rates of the elastomers, thus the degradability of the composites could be adjusted to adapt to different requirements of various biomedical applications. HA is the major component of natural bone, which is a bioceramic with good biocompatibility and osteoconductivity, nevertheless, its inherent brittleness and hard processability has limited its broad application to a great extent. To incorporate biodegradable polyesters which have the flexibility of molecular design, elasticity and adjustable properties is supposed to cover the inherent disadvantages of HA, leading to biodegradable nanocomposites with excellent comprehensive properties. The preparation of composites with different loadings of HA was optimized and flat films were achieved through the research on the influence of some experimental conditions on the structure, morphologies and properties of the composites. Such experimental conditions include mold pressing or not, mold pressing T/P/time, mixing methods, curing T/P/time, and so on. Tg of the composites shifted to lower temperatures while increasing the loadings of HA, which indicated that the incorporation of large amounts of HA decreased the crosslinking density and arrangement degree of the polyesters from the aspect of the molecular movements. Yet at the same time, the increase of HA loadings contributed to the enormous increase of physical crosslinking densities of composites, which ultimately led to decreased swelling degrees and sol contents of composites. The combination of in-situ polymerization and Hakke mixing was feasible to achieve good dispersion of HA. Besides, the dispersion of HA became even better with the increase of HA loadings. Results of tensile tests suggested that the tensile strength and Young’s modulus increased continually when the HA loading increased from 20wt% to 60wt%, yet the composites became more brittle and weaker when 70wt% HA was added. The composites with 60wt% HA exhibited the highest mechanical properties, which tensile strength reached 19.4MPa and Young’s modulus reached 179.1MPa. Also, tensile strength and Young’s modulus increased with crosslinking time while elongation at break decreased with it, which meant the elongation of crosslinking time made the composites more brittle but stronger. Besides, the hydrophily, degradability, and cytotoxicity of composites obeyed a similar rule, a consistent decrease followed by a sudden increase. The adjustable properties of composites made them potential candidates for temporary hard tissue replacement materials, and extended to some other biomedical applications of such composites.

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