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. 2021 Aug 23;13(16):2835.
doi: 10.3390/polym13162835.

Effect of In-Mold Annealing on the Properties of Asymmetric Poly(l-lactide)/Poly(d-lactide) Blends Incorporated with Nanohydroxyapatite

Martin Boruvka  1 , Cenek Cermak  1 , Lubos Behalek  1 , Pavel Brdlik  1
Affiliations

Effect of In-Mold Annealing on the Properties of Asymmetric Poly(l-lactide)/Poly(d-lactide) Blends Incorporated with Nanohydroxyapatite

Martin Boruvka et al. Polymers (Basel). .

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.

Keywords: crystallization; heat resistance; impact resistance; mechanical properties; nanocomposites; nanohydroxyapatite; poly(d-lactide); poly(l-lactide); stereocomplex.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
DSC curves of the PLLA a PLLA/HA nanocomposites obtained during the first heating.
Figure 2
Figure 2
DSC curves of the asymmetric PLLA/5PDLA a PLLA/5PDLA/HA nanocomposites obtained during the first heating.
Figure 3
Figure 3
Tensile modulus plots of samples from cold and hot molds.
Figure 4
Figure 4
Tensile strength plots of samples from cold and hot molds.
Figure 5
Figure 5
Elongation at break plots of samples from cold and hot molds.
Figure 6
Figure 6
Impact toughness plots of samples from cold and hot molds.
Figure 7
Figure 7
Heat deflection temperature plots of samples from cold and hot molds.
Figure 8
Figure 8
Vicat softening temperature plots of samples from cold and hot molds.
Figure 9
Figure 9
Fracture morphologies of (a) cold and (b) hot mold PLLA.
Figure 10
Figure 10
Fracture morphologies of (a) cold and (b) hot mold PLLA/5PDLA.
Figure 11
Figure 11
Fracture morphologies of (a) cold and (b) hot mold PLLA/1HA.
Figure 12
Figure 12
Fracture morphologies of (a) cold and (b) hot mold PLLA/5PDLA/1HA.
Figure 13
Figure 13
Fracture morphologies of (a) cold and (b) hot mold PLLA/15HA.
Figure 14
Figure 14
Fracture morphologies of (a) cold and (b) hot mold PLLA/5PDLA/15HA.
See this image and copyright information in PMC

References

    1. Nagalakshmaiah M., Afrin S., Malladi R.P., Elkoun S., Robert M., Ansari M.A., Svedberg A., Karim Z. Green Composites for Automotive Applications. Woodhead Publishing; Sawston, UK: 2019. Biocomposites: Present trends and challenges for the future; pp. 197–215.
    1. Ganapini W. Bioplastics: A Case Study of Bioeconomy in Italy. Edizioni Ambiente; Milan, Italy: 2014.
    1. Watkins E., Schweitzer J.-P. Think 2030. Brussels: Institute for European Environmental Policy (IEEP) IEEP; Brussels, Belgium: 2018. Moving towards a circular economy for plastics in the EU by 2030.
    1. Masutani K., Kimura Y. Synthesis, Structure and Properties of Poly(Lactic Acid) Springer; Cham, Switzerland: 2017. Present situation and future perspectives of poly (lactic acid) pp. 1–25.
    1. Fiorentino G., Ripa M., Ulgiati S. Chemicals from Biomass: Technological versus Environmental Feasibility. A Review. Biofuel. Bioprod. Biorefin. 2017;11:195–214. doi: 10.1002/bbb.1729. - DOI

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