ARTICLE Retardation effect of nanohydroxyapatite on the hydrolytic degradation of poly (lactic acid) Juliana Satie Watai 1 | Patrícia Schmid Calv~ ao 1 | Talita Rocha Rigolin 2 | Silvia Helena do Prado Bettini 2 | Adriana Martinelli Catelli Souza 1 1 Department of Materials Engineering, Centro Universitário FEI, S~ ao Bernardo do Campo, SP, Brazil 2 Department of Materials Engineering, Universidade Federal de S~ ao Carlos, S~ ao Carlos, SP, Brazil Correspondence Adriana Martinelli Catelli Souza, Department of Materials Engineering, Centro Universitário FEI, Av. Humberto de Alencar Castelo Branco, 3972, CEP 09850-90, S~ ao Bernardo do Campo, SP, Brazil. Email: amcsouza@fei.edu.br Funding information Coordenaç~ ao de Aperfeiçoamento de Pessoal de Nível Superior, Grant/Award Number: Finance Code 001 Abstract Poly (lactic acid) (PLA) and PLA/nanohydroxyapatite (nHA) composites, con- taining 2 wt% and 5 wt% of nHA were subjected to in vitro hydrolytic degrada- tion tests in saline phosphate solution at different temperatures (37  C, 48  C, 60  C, and 72  C) to accelerate degradation. Samples were characterized by water uptake, weight loss tests, size exclusion chromatography (SEC), differen- tial scanning calorimetry (DSC), and visual analyses. Arrhenius equation was used to describe the behavior of weight loss as a function of time. The PLA activation energy of weight loss showed to be lower than that of the PLA/nHA composites, indicating that the incorporation of nHA retarded the hydrolytic degradation. The rate and percentage of weight loss increased with increasing temperature. All samples presented a decrease in T g and an increase in degree of crystallinity as a function of time. Incorporation of nHA retarded this behav- ior that showed to be more expressive in PLA containing 5 wt% nHA. KEYWORDS in vitro hydrolytic degradation tests, nanohydroxyapatite, poly (lactic acid) 1 | INTRODUCTION Poly (lactic acid) (PLA) is a biodegradable, bioresorbable, and biocompatible aliphatic thermoplastic polyester pro- duced from renewable resources. [1] This polymer has been used in packaging and technical applications and can be processed by sheet and film extrusion, blow mold- ing, injection molding, fiber spinning, and the- rmoforming. [2,3] However, the poor thermal resistance and barrier performance and also inherent brittleness are some disadvantages of PLA restricting its applications. [3,4] A special use of PLA has been in textile and biomedical applications like sutures, stents, tissue engineering, and drug delivery. [4] PLA polymers can be amorphous or semicrystalline depending on their structure (molar mass and the amount of D-enantiomers) [5] and processing conditions (cooling rate and annealing). The physical, mechanical, thermal, and barrier properties of PLA are dependent on its morphology and crystallinity. [6] PLA presents differ- ent crystal structures, which depend on the crystalliza- tion conditions. The α-form crystal is the most common and it occurs under normal crystallization conditions, such as melt and solution crystallization. [7] Another form of α crystal is the α'-form which is similar to α structure, but with less ordered chain packing. The pre- dominance of α'-form occurs at crystallization tempera- tures below 100  C while there is a coexistence of α'e α crystal structures between 100  C and 120  C. [7] The β-form is obtained by high temperature and high draw ratio stretching of α-form, and the γ-form is obtained by epitaxial crystallization of PLA on hexamethylbenzene, with two chains, which are oriented antiparallel in a crystal cell unit. [2,7] Received: 20 April 2020 Revised: 7 June 2020 Accepted: 8 June 2020 DOI: 10.1002/pen.25459 Polym Eng Sci. 2020;1–11. wileyonlinelibrary.com/journal/pen © 2020 Society of Plastics Engineers 1