Assessment of recycled PLA based filament for 3D printing

: . This study investigates the possibility to adopt recycled polymers in the additive manu-14 facturing (AM) technology by replacing virgin matrices. At regards, two commercial filaments, made from polylactide acid (PLA), -the second (recycled) obtained from the production waste of the first one (virgin)-, were initially characterized using infrared (IR) spectroscopy, thermogravimetric analysis (TGA) and dynamic rheology. Then, the filaments were extruded in a 3D printer and char-18 acterized by dynamic mechanical analysis (DMA). Despite of a small reduction of intensity in cor-19 respondence of typical absorption bands of PLA polyme, in the case of recycled material compared to virgin one (as attested by IR spectra), the thermal-mechanical results allowed to attest very similar 21 characteristics of recycled and neat filaments. The onset of the thermal degradation was found 22 around 315°C in both systems. Both materials exhibited the same time-dependent trend of complex 23 viscosity, with a reduction of approximately 50% after 900 seconds of testing. When the samples 24 were dried at 80°C under vacuum for 10 hours, the stabilization of the rheological features against 25 time was improved. There is no significant difference in the storage modulus (E') of 3D printed parts 26 made with different types of PLA-based filaments.


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Plastics are extremely useful for a wide range of applications due to their mechanical 32 and chemical properties, as well as their ease of manipulation [1]. Yet, not being biode-33 gradable, plastic materials pose a serious environmental problem due to the accumula-34 tion of products in nature [2]. This aspect has become particularly relevant in the sustain-35 able development of industrial production [3]. 36 Nonetheless, additive manufacturing (AM), well-known as 3D printing, is emerging 37 as a crucial industrial technology for rapid prototyping, to convert a numerical model 38 into material deposition and 3D printed parts [4]. During this cycle, a huge amount of 39 waste products has been developed. In order to reduce plastic waste [5] and limit the 40 environmental impact of AM process [6], bio based and recycled polymers have been 41 considered as alternative perspective to conventional raw materials. taking into account its excellent biocompatibility and environmental sustainability, ab-45 sence of unpleasant odors during handling, and production of final products with fair 46 precision tolerance [7]. 47 In this framework, this study was focused on improving the sustainability aspects 48 of the AM technology by verifying the thermal and mechanical characteristics of recycled 49 polymers, coming from waste products, in comparison with virgin matrices, for devel-50 oping 3D printed parts. 51

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This experiment used commercially available filaments made from poly(lactide) 53 acid (PLA)-based polymer. In particular, a basic PLA, here referred as virgin PLA, and a 54 recycled filament derived from the production waste of the same filaments, here referred 55 as recycled PLA, have been supplied by EUMAKERS (Barletta, Italy). 56 On these filaments, a preliminary characterization was conducted through thermo-57 gravimetric analysis (TGA) to establish the degradation temperature, (IR) infrared spec-58 troscopy to gain information on main constituents, and rotational rheology to understand 59 the thermal stability over time at a given temperature. Samples to be tested through dy-60 namic mechanical analysis (DMA) were obtained by 3D printing machine at temperature 61 of 210°C, by setting, as design parameters: an infill density equal to 70%, a layer thickness 62 of 0.19 mm, and a linear pattern. 63 Thermogravimetric measurements were performed by using Q500 TGA (TA Instru-64 ments, NewCastle-USA). Test were conducted by heating a piece of materials (about 10 65 mg) at a rate of 10 °C/min from room temperature to 600 °C in inert atmosphere. 66 Infrared spectroscopy was conducted in attenuated total reflectance (ATR) modal-

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3.1 Infrared spectroscopy 83 The results of IR spectroscopy are shown in Figure 1, for pristine PLA material 84 (black curve) and waste one (red curve). The absorbance values were normalized in rela-85 tion to an internal standard for the PLA (1455 cm -1 peak [8]).

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During the heating of thermogravimetric analysis, one step of PLA degradation was 97 shown in both samples. This trend was due to the loss of ester group[10] that started at 98 about 310 °C. In table 1, the initial decomposition temperature (Tdec 5%), the temperature 99 in correspondence of the maximum rate of degradation (Tmaxdec) and the final residue at 100 600°C were reported for the two analyzed samples.   Figure 2 depicts the experimental results of time sweep tests in terms of complex viscosity 108 (Pa*s) over time (> 900 s) for investigated systems. Similar to other polyester polymers, 109 PLA is sensitive to hydrolysis under melt processing conditions in the presence of small 110 amounts of water [11]. In fact, as verified from data in Fig.2, a reduction of the rheological 111 signal was attested during time in the case of non dried material; whereas, the stabilization 112 of the complex viscosity over time at temperature of 210°C for over than 900 s was ob-113 tained through sample drying.

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This was a preliminary study devoted to understand the applicability of recycled 125 matrices instead of virgin polymers for 3D printing process. From data, despite a small 126 reduction in ATR spectra, in correspondence of PLA characteristic peaks of the thermal 127 degradation, no substantial differences could be highlighted in terms of thermal degrada-128 tion, rheological behavior and thermo-mechanical properties. In fact, for both materials, 129 the initial degradation temperature was measured around 310°C , the stability of complex 130 viscosity over time was achieved through sample pre-drying, and the storage modulus of 131 3D printed parts made from recycled matrices was very comparable with that of the virgin 132 ones.