Vol.:(0123456789) 1 3 Journal of Thermal Analysis and Calorimetry https://doi.org/10.1007/s10973-020-10166-3 Crystallization behavior of zinc oxide/poly(lactic acid) nanocomposites Érica da Cruz Faria 1,2  · Marcos Lopes Dias 1  · Luana Marques Ferreira 1  · Maria Ines Bruno Tavares 1 Received: 17 January 2019 / Accepted: 4 August 2020 © Akadémiai Kiadó, Budapest, Hungary 2020 Abstract In this work, films of commercial PLA Ingeo 4043D with nano-zinc oxide particles (nano-ZnO) with average diameter around 100 nm and ZnO concentrations of 0.1, 0.25, 0.3 and 0.5 mass% were prepared by flat die extrusion. The addition of nano- ZnO had an objective to promote the crystallization of PLA, but it decreased the thermal stability of the films. Both neat PLA and PLA/nano-ZnO composites films did not crystallize during the cooling, but crystallize during a first heating, showing a cold crystallization process, which was significantly influenced by the heating rate. A low chain mobility was evidenced by the values of relaxation time (T 1 H). This low chain mobility avoided the high degree of crystallization of the films which were predominantly amorphous. For all films, an enthalpic relaxation phenomenon was detected during the first heating. The glass transition temperature (T g ) was shifted to higher values as the heating rate and nanofiller content are increased. Addition of nano-ZnO in PLA films did not increase their crystallinity, indicating that it is not an effective nucleating agent for this low-crystallinity PLA grade. Keywords PLA · Nano-zinc oxide · Non-isothermal crystallization · Cold crystallization · Enthalpic relaxation Introduction In the last years, an increasing scientific and industrial inter- est occurred in the use of biopolymers due to a series of factors, including the need of consumption of sustainable environmentally friendly materials, the development of new biobased raw materials and, in special, the increasing restric- tion of the use of polymers with high petrochemical carbon footprint in applications like packaging, automotive, electric and electronic parts. In this context, it is expected that the new technological advances lead biopolymers to a spotlight in the market, not only in traditional sectors as packaging, but also in other sectors [1–3]. Among biodegradable plastics from renewable resources, poly(lactic acid) (PLA) is one of the most promising materi- als, since it is a biodegradable and biocompatible thermo- plastic, with good processability, excellent transparency and relatively low cost. It can contain two enantiomeric units in its structure, the L- and D-units, and its degree of crystal- linity depends on its optical purity, being highly crystalline when rich in one of the enantiomers attaining melting tem- peratures (T m ) up to 180 °C [2, 4, 5]. Generally, commercial PLA is rich in the L-unit (PLLA) with low amount of D-unit which can reduce its optical purity, resulting in the decreasing in the crystallization pro- cess and changes in the mechanical, optical and thermal properties. Depending on the D-unit content, the crystal- lization process cannot take place in ordinary cooling rate conditions and the polymer became a completely vitreous material upon cooling below its glass transition (around 60 °C). In this case, it can show the phenomenon of cold crystallization during a subsequent heating over its glass transition [5]. Although PLLA presents several application advantages, its inherent fragility and low thermal stability restrict its large application. Nevertheless, addition of reinforcing fill- ers to PLLA matrix in the micro or nanoscales can be good ways to improve the mechanical and thermal properties and, in addition, increase barrier properties and promote antimi- crobial activity and ultraviolet protection [6–11]. Incorporation of nanoparticles as fillers in polymers has attracted considerable interest due to the potential * Maria Ines Bruno Tavares mibt@ima.ufrj.br 1 Instituto de Macromoléculas Professora Eloisa Mano – IMA, Universidade Federal do Rio de Janeiro-UFRJ, Rio de Janeiro, RJ 21941-598, Brazil 2 Instituto Federal de Educação, Ciência e Tecnologia do Rio de Janeiro -IFRJ, Rio de Janeiro, RJ 20270-021, Brazil