Characterization of modulus and glass transition phenomena in poly(L-lactide)/hydroxyapatite composites

• Published in: Polymer composites 2003-02, Vol.24 (1), p.100-108
• Main Authors: Fambri, Luca, Kesenci, Kemal, Migliaresi, Claudio
• Format: Article
• Language: English
• Subjects: Applied sciences; Composites; Exact sciences and technology; Forms of application and semi-finished materials; Polymer industry, paints, wood; Technology of polymers
• ISSN: 0272-8397; 1548-0569
• DOI: 10.1002/pc.10010

In order to study the dynamic‐mechanical properties of Poly(L‐lactide)/Hydroxyapatite (PLLA/HA) composites, two different molecular weight (inherent viscosity (ηinh): 4.0 (dL/g), and 7.8 (dL/g)) poly(L‐lactide) (PLLA) were synthesized by bulk polymerization and filled with 10%, 30%, and 50% (w/w) with medical grade HA (size range: 25–45 μm and Ca/P = 1.69). The plain PLLA polymers and PLLA/HA composites were compression molded and machined to yield 50 × 3 × 2 mm3 specimens. The composites were investigated by dynamic mechanical thermal analyzer (DMTA) of imposed bending load on rectangular specimens over a temperature range from 30 to 120°C using multiple frequencies (0.3–50 Hz). The results showed that the bending storage modulus (E′) of the composites increased linearly with the percentage of the filler, reaching at 37°C and 0.1 Hz about 2.5, 3.7 and 5.0 GPa with 10, 30 and 50% of HA respectively. The glass transition temperature, evaluated at the tan δ peaks, were in the range 70–80°C and 50–70°C for PLLA matrix and PLLA composites respectively. The activation energies at the glass transition temperature were calculated from the Arrhenius plot in the range of 102–111 Kcal/mol for the composites, whereas 132 and 148 Kcal/mol were found for low and high molecular weight of PLLA respectively. The content of amorphous phase was evaluated from the intensity of tan δ peak. Results showed that HA causes an amorphous phase with a greater mobility with respect to the pure PLLA.