Abstract
The proper choice of a material system for bioresorbable synthetic bone graft substitutes imposes strict requirements for mechanical properties, bioactivity, biocompatibility, and osteoconductivity. This study aims to characterize the effect of in-mold annealing on the properties of nanocomposite systems based on asymmetric poly(l-lactide) (PLLA)/Poly(d-lactide) (PDLA) blends at 5 wt.% PDLA loading, which was incorporated with nano-hydroxyapatite (HA) at various concentrations (1, 5, 10, 15 wt.%). Samples were melt-blended and injection molded into “cold” mold (50 °C) and hot mold (100 °C). The results showed that the tensile modulus, crystallinity, and thermal-resistance were enhanced with increasing content of HA and blending with 5 wt.% of PDLA. In-mold annealing further improved the properties mentioned above by achieving a higher degree of crystallinity. In-mold annealed PLLA/5PDLA/15HA samples showed an increase of crystallinity by ~59%, tensile modulus by ~28%, and VST by ~44% when compared to neat hot molded PLLA. On the other hand, the % elongation values at break as well as tensile strength of the PLLA and asymmetric nanocomposites were lowered with increasing HA content and in-mold annealing. Moreover, in-mold annealing of asymmetric blends and related nanocomposites caused the embrittlement of material systems. Impact toughness, when compared to neat cold molded PLLA, was improved by ~44% with in-mold annealing of PLLA/1HA. Furthermore, fracture morphology revealed fine dispersion and distribution of HA at 1 wt.% concentration. On the other hand, HA at a high concentration of 15 wt.% show agglomerates that worked as stress concentrators during impact loading.
Highlights
The effect of in-mold annealing on the properties of nanocomposite systems based on asymmetric poly(L-lactide) (PLLA)/Poly(D-lactide) (PDLA) blends at 5 wt.% PDLA
It was noticed that the tensile modulus, crystallinity, and thermal resistance were enhanced with increasing content of HA and blending with 5 wt.% of PDLA
In-mold annealed PLLA/5PDLA/15HA samples show an increase of the tensile modulus by ~28%; Vicat softening temperature (VST) by ~44%; and crystallinity by ~59%, when compared to neat hot molded PLLA
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. As global society continues to grow, sustainability issues concerning our raw material systems arise as well. Sustainability coupled with the rising environmental concerns and fossil resources depletion present considerable challenges for the polymer industry [1]. To alleviate these problems, governments in many countries are enacting laws that encourage the use of recycled, renewable, and biodegradable polymers [2]. In Europe, topics such as greenhouse gas emission, CO2 neutrality, renewability, embodied energy, toxicity, and resource depletion are driven by regulations
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