Crystallization kinetics of poly(L‐lactide)/carbonated hydroxyapatite nanocomposite microspheres

Abstract

Microspheres consisting of carbonated hydroxyapatite (CHAp) nanoparticles and poly(L-lactide) (PLLA) have been fabricated for use in the construction of osetoconductive bone tissue engineering scaffolds by selective laser sintering (SLS). In SLS, PLLA polymer melts and crystallizes. It is therefore necessary to study the crystallization kinetics of PLLA/CHAp nanocomposites. The effects of 10 wt% CHAp nanoparticles on the isothermal and nonisothermal crystallization behavior of PLLA matrix were studied, using neat PLLA for comparisons. The Avrami equation was successfully applied for the analysis of isothermal crystallization kinetics. Using the LauritzenHoffman theory, the transition temperature from crystallization Regime II to Regime III was found to be around 120 C for both neat PLLA and PLLA/CHAp nanocomposite. The combined Avrami-Ozawa equation was used to analyze the nonisothermal crystallization process, and it was found that the Ozawa exponent was equal to the Avrami exponent for neat PLLA and PLLA/CHAp nanocomposite, respectively. The effective activation energy as a function of the relative crystallinity and temperature for neat PLLA and PLLA/CHAp nanocomposite under the nonisothermal crystallization condition was obtained by using the Friedman differential isoconversion method. The Lauritzen-Hoffman parameters were also determined from the nonisothermal crystallization data by using the Vyazovkin-Sbirrazzuoli equation. CHAp nanoparticles in the composite acted as an efficient nucleating agent, enhancing the nucleation rate but at the same time reducing the spherulite growth rate. This investigation has provided significant insights into the crystallization behavior of PLLA/CHAp nanocomposites, and the results obtained are very useful for making good quality PLLA/CHAp scaffolds through SLS.

Solidification behavior of PLLA/nHA nanocomposites

“…For T c between 110 and 130°C, N increased significantly with nHA content (by over an order of magnitude in PLLA/5 wt.% nHA, as reflected by Fig. 2, for example), and, although it again levelled off at lower T c , N remained higher in the presence of nHA, indicating a greater density of heterogeneous nucleation sites, consistent with the literature [34]. As shown in Fig.…”

Effect of surface-grafted cellulose nanocrystals on the thermal and mechanical properties of PLLA based nanocomposites

“…Moreover, the presence of an exothermic peak between both previous phenomena reveals that a significant fraction of the amorphous chains were able to crystallize due to a higher molecular mobility above Tg. The physical addition of the CNCs to PLLA only induced a slight reduction in the polymer crystallization temperature as observed for filled macromolecular systems [51][52][53][54][55]. …”

CHAPTER 3. Crystallization of PLA-based Materials

“…If the value is close to 3, this indicates the instantaneous growth of spherulites, a common occurrence in PLAs. 78 Table 3.4 reports a wider range of values fluctuating from 2-3.5 for different types of PLAs. Table 3.5 reports the Avrami fitting parameters for PLA-based blends, where the parameters are based on the crystallization of the PLA matrix.…”