# Towards 4D printed PLA actuators

Fabienne Touchard, Thuy Quynh Truong Hoang, Damien Marchand, Francisca Martinez-Hergueta, Laurane Roumy, C Lingois

► To cite this version:

Fabienne Touchard, Thuy Quynh Truong Hoang, Damien Marchand, Francisca Martinez-Hergueta, Laurane Roumy, et al. Towards 4D printed PLA actuators. ADDFABCOMP-Additive Fabrication of Composite n°2 -Online, Nov 2021, Edimbourg (Ecosse), United Kingdom. hal-04506717

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Submitted on 15 Mar 2024

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# TOWARDS 4D PRINTED PLA ACTUATORS

L. ROUMY¹,²,³, C. LINGOIS¹, F. TOUCHARD¹, D. MARCHAND¹, T. QUYNH TRUONG HOANG², F. MARTINEZ-HERGUETA³

1 : Institut PPRIME, CNRS-ENSMA-Université de Poitiers, Dpt Physique et Mécanique des Matériaux, ENSMA, 1 Av. C. Ader, B.P. 40109, 86961 Futuroscope Cedex, France

2 : ESTACA, Pôle Mécanique des Structures Composites et Environnement, Ecole d'ingénieurs, France

3 : School of Engineering, Institute for Infrastructure and Environment, University of Edinburgh, UK

fabienne touchard@ensma.fr

## Introduction

4D printing enables the use of “smart materials” that can be transformed in a pre-programmed way under an external stimulus. This is known as ‘4D printing’, with the fourth dimension referring to time [1]. Shape Memory Polymers (SMP), specifically thermally activated SMP, have been largely developed in the past decade due to their lightweight, ease of forming, low costs for manufacturing, high deformations and high shape recovery ratios [2]. In particular, self-bending structures made of bilayer composites have been proposed [3]. In this work, preliminary results for the development of a thermo-responsive structure made of a polymer-paper bilayer are presented.

## Materials and methods

In this study, polylactic acid (PLA) filaments from RS PRO with a diameter of 2.85 mm and a density of 1.24 g/cm³ were used. All the samples were manufactured with an Ultimaker 2 Extended + printer. The extruder diameter was 0.6 mm, the nozzle temperature was set at 210 °C and the platform temperature at 60 °C. DSC (Differential Scanning Calorimetry) tests were performed on printed polymer, using a Q20 from TA Instruments. Tensile tests were performed using an INSTRON 5982 machine with a cross-head speed of 0.5 mm/min. Longitudinal strain was measured by a 25 mm gauge length extensometer. Tensile specimens were dog-bone shaped, following the standard NF_T_54-034, with a 60 mm gauge length and a 4 mm thickness, made of 37 PLA layers. Three different orientations of the printed filaments were used: longitudinal (0°), transverse (90°) and crossed (±45°). Bi-layer structures were made of only one layer of PLA deposited on a copy paper of 80 g/m². A heating plate at 100 °C was used as an external stimulus.

## Results

The DSC thermogram made on 3D printed PLA shows that its glass transition temperature ($T_g$) is equal to 59 °C (Figure 1a). It gives its activation temperature as a SMP. A small endothermic peak appears at a temperature situated just above $T_g$, due to the physical ageing of the material. Moreover, an exothermic peak centered near 104 °C can be seen on the thermogram, corresponding to the cold crystallization and finally the melting peak is located around 154 °C. The area values of these two last peaks are similar (20.50 J/g and 17.71 J/g). Using a melting enthalpy of 100% crystalline PLA equal to 93.6J/g [4], it gives a degree of crystallinity of 3%. This result shows that the printed PLA is almost amorphous. Tensile curves obtained for the three different directions are presented in Figure 1b. Results show the strong influence of the filament orientation on the PLA tensile properties. Ultimate strength and Young modulus of 0° samples are higher than ±45° and 90° ones. The Young modulus measured for the 0° samples is very close to the reference value provided by the supplier (3990±44 MPa versus 3860 MPa). Images of the thermo-activated bilayer structures are shown in Figure 2. The self-deployment movement can be observed for the two tested geometries. These structures recover their planar configuration
relatively quickly: after about 35s for the rolled structure, and after about 20s for the origami-type structure.

<figure><img src="image_2.png" /><figcaption>Fig. 1 – a) DSC thermogram on 3D printed PLA material. b) Tensile curves of PLA specimens with different orientations of the filament.</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Fig. 2 – Examples of thermo-activated bilayer structures: a) Unrolling movement. b) Origami-type structure.</figcaption></figure>

## Conclusions

The PLA filament is a good candidate for the development of shape shifting structures: its temperature of glass transition is low (59 °C), its Young modulus is quite high (3990 MPa) and its thermo-activation speed is elevated. After testing self-bending polymer-paper bilayer, future work will involve designing morphing assemblies which integrate different components towards a wide range of applications.

## Acknowledgements

This work was supported by the Defense Innovation Agency (AID) of the French Ministry of the Armed Forces through the grant [AID-2021 65 0045].

## References

[1] A. Mitchell, U. Lafont, M. Hołyńska, C. Semprimoschnig. Additive manufacturing — A review of 4D printing and future applications. Additive Manufacturing 2018; 24:606–626.

[2] I.T. Garces, C. Ayranci. Active control of 4D prints: Towards 4D printed reliable actuators and sensors. Sensors and Actuators 2020; A 301:111717.

[3] W. Wang, C. Y. Yua, P. A. A. Serranoa, S.-H. Ahn. Soft grasping mechanisms composed of shape memory polymer based self-bending units. Composites Part B 2019; 164:198–204.

[4] S. Solarski, M. Ferreira, E. Devaux. Characterization of the thermal properties of PLA fibers by modulated differential scanning calorimetry. Polymer 2005; 46:11187–11192.