# Sustainable 3D-printed cellulose-based biocomposites and bio-nano-composites: Analysis of dielectric performances

Morgan Lecoubllet, Mohamed Ragoubi, Nathalie Leblanc, Ahmed Koubaa

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Morgan Lecoubllet, Mohamed Ragoubi, Nathalie Leblanc, Ahmed Koubaa. Sustainable 3D-printed cellulose-based biocomposites and bio-nano-composites: Analysis of dielectric performances. Industrial Crops and Products, 2024, 221, pp.119332. 10.1016/j.indcrop.2024.119332. hal-04840835

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# Sustainable 3D-printed cellulose-based biocomposites and bio-nano-composites: Analysis of dielectric performances

Morgan Lecouplet<sup>a, b</sup>, Mohamed Ragoubi<sup>a, *</sup>, Nathalie Leblanc<sup>a</sup>, Ahmed Koubaa<sup>b</sup>

## ARTICLE INFO

**Keywords:**

Nanocellulose

3D-printing

Dielectric properties

Microstructural properties

Electrical insulation applications

## ABSTRACT

The development of cellulose-reinforced biomaterials appears to be an attractive approach for the production of sustainable materials with good mechanical properties. Although 3D printing of cellulose-reinforced biomaterials has become popular, there is very little feedback regarding their use in electrical insulation applications. This study aims to propose bio-nano-composites containing polylactic acid (PLA), microcrystalline (MCC) and nanocrystalline (NCC) cellulose by fused filament fabrication (FFF) for electrical insulation applications. The influence of the 3D printing process, cellulose content and filler size on dielectric properties was investigated. The addition of cellulosic fillers, and considering their high polarity, increased the dielectric constant (ε'), dielectric loss (ε''), as well as the AC electrical conductivity (σAC) of the composites. Cellulosic fillers also increased the crystallization rate of the materials. At equivalent content, the highest polarization potential were observed for NCC-based composites and were attributed to the nanofiller's better dispersion and available specific surface area. Finally, the 3D printing process affects all the measured properties, due to a combined effect (lower crystalline content and voids presence). The porosity rate was measured at 2.5 % for the neat PLA and increased progressively from 3.1 % to 5.8 % for the cellulose-based composites. These findings showed the benefits provided by the FFF technology in the production of cellulose-based biocomposites with good electrical insulation properties, while noting some needed feedback on the thermomechanical properties of such materials.

## 1. Introduction

The market for dielectric materials is demanding more and more advanced performances. In 2022, the market size of the dielectric materials industry was estimated at $61.5 billion, with a market forecast for 2030 of $89.7 billion (Zion Market Research, 2022). To ensure the sustainability of the dielectric industry, we need to identify viable alternatives to conventional petroleum-based dielectric materials. Bio-based materials can represent this alternative, offering numerous advantages in terms of sustainability, compostability and biodegradability. In 2023, the *European Bioplastic* association noted a biobased polymer production for electronic application of 87.2 kT (*European Bioplastics*, 2023a). Recent reports aimed to promote the use of bio-based polymers in dielectric applications (Jin et al., 2022; Pei et al., 2020; Spinelli et al., 2020), but several limitations still exist. For example, PLA, the most widely produced biobased polymer by 2023 (*European Bioplastics*, 2023b), significantly loses its mechanical rigidity when the applied temperature exceeds 60 °C. Gregorova et al. (2009)

have determined that the PLA's storage modulus between 20 and 80 °C decreased from 2.9 GPa to 0.1 GPa, due to the transition from a glassy to a rubbery state, which limits its suitability for high temperature applications. Improving mechanical performance could be achieved by incorporating fillers such as cellulose to create a biocomposite, maintaining the philosophy of a 100 % sustainable material and preserving the matrix's potential biodegradability.

Cellulose is the most widely available renewable polymer on Earth (Xiao et al., 2024). This abundant resource is an invaluable opportunity for rethinking the design of materials, with sustainable development in mind. In the materials field, cellulose is mainly presented in two forms. After chemical reactions, cellulose can be used as a thermoplastic polymer in polymer blends (Coltelli et al., 2021; Lecouplet et al., 2024). Cellulose can also be used as a mechanical reinforcement (Bonardd et al., 2018; Ten et al., 2012; Wang et al., 2023). These can be divided into three different types. Firstly, cellulosic fillers can be used as long fibers (e.g. hemp, flax, ramie), highly suitable for advanced technical applications (Rahman, 2021). Short cellulosic fillers, such as Kraft or

<footnote><sup>a</sup> UniLaSalle, Unité de Recherche Transformations et Agro-Ressources (ULR 7519 UniLaSalle - Université d'Artois), Mont-Saint-Aignan, France</footnote>

<footnote><sup>b</sup> UQAT, Campus de Rouyn-Noranda, 445, boul. de l'Université, Rouyn-Noranda, QC J9X 5E4, Canada</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: mohamed.ragoubi@unilasalle.fr (M. Ragoubi).</footnote>
microcrystalline cellulose (MCC), are more suitable for thermoplastic matrix, as they can easily be processed by extrusion or injection molding. New nanoscopic fillers such as nanocellulose are becoming increasingly popular with their very high specific surface area and their functionalization capabilities (Ten et al., 2012; Vidakis et al., 2022; Wang et al., 2023; Xiang et al., 2023). However, the presence of cellulosic fillers has been reported in the literature to have a slight negative effect on the electrical insulation performance. Badia et al. (2017) found an increase in the dielectric constant by adding hydrogen bonds to the resulting biocomposites when sisal fillers were added into the PLA matrix. In addition, by hindering chain mobility, an interaction between the hydrogen bonds of sisal and PLA increased the latter's "fragile" behavior. Regarding the use of nano-sized cellulose, Ten et al. (2012) characterized the dielectric and mechanical performances of nano-crystalline cellulose (NCC):PHBV bio-nano-composites. The dielectric constant and electrical conductivity increased with the weight content of NCC ($W_f_{NCC}$). However, mechanical and dielectric properties showed an optimum NCC content between 2% and 2.3%. At $W_f_{NCC} > 2.3\%$, the authors suspected the presence of nanofiller aggregation, which decreased the available specific surface area and thus the benefits provided by the nanofiller.

From a technological view, 3D printing process can also be an invaluable vector for innovation by the wide range of adjustable parameters. Fused filament fabrication (FFF) is the most common 3D printing technique, a suitable technology to print biobased polymer (Bajwa et al., 2021; Senthil and Kumar, 2021). TheFFF process consists of the extrusion of molten materials with a heated nozzle and deposited layer-by-layer to obtain a 3D object, previously designed with a CAD software (Bajwa et al., 2021). For 3D printing applications in the dielectric field, Spinelli et al. (2020) improved the electrical conductivity of 3D-printed PLA by adding carbon nanotubes (CNT) and graphene nanoplatelets (GNP). At 100 Hz and a $W_f = 6\%$, the electrical conductivity of PLA was 1000 times higher for CNT-based nanocomposites than for GNP-based nanocomposites, due to the CNT form factor, favoring the percolation point of CNT-based nanocomposites. The dielectric properties of 3D-printed PLA parts and their processing parameters were also evaluated by Kuzmanić et al. (2023). Dielectric constant was strongly influenced by the infill ratio, increased from 1.78 to 2.81 as example for a corrugated infill pattern, and for an infill ratio of 33–100% respectively. Furthermore, the infill pattern also played a role on the dielectric constant at low electrical frequency. This result demonstrates the possibility of controlling the dielectric constant through keen material design.

Although 3D printing, as well as biocomposites for electrical insulation are becoming increasingly popular, to our knowledge they is no experience of combining these two methods to produce new electrical insulating materials. So, we propose an analysis of the dielectric and microstructural properties of sustainable 3D-printed cellulose-based biocomposites and bio-nano-composites. PLA was chosen as a matrix for the composite elaboration because of its wide availability and good 3D printing capacity. We also propose a comparative study of micro-crystalline cellulose (MCC) and nanocrystalline cellulose (NCC) based PLA biocomposites to investigate the effect of cellulosic filler on the dielectric properties of blends, as well as the influence on the filler content. For the process effect, a comparison between 3D printing process and conventional process was also conducted.

# 2. Materials & methods

## 2.1. Raw materials

PLI-005 supplied by Natureplast (Montdeville, FRA) was used in pellet form. The MFI given by the technical data sheet was 25–35 g·10 min⁻¹ (ISO 1133 @ 190 °C). To study the influence of cellulosic filler size on dielectric and mechanical properties, micro-crystalline and nanocrystalline cellulose (MCC and NCC respectively)

were selected in powder form. MCC was supplied by J. Rettenmaier (Fosston, USA), obtained from bleached kraft pulp. The density given by the suppliers was 0.27–0.33 g·cm⁻³. NCC (DextraCel Nano HP) was supplied by Anomera (Montreal, QC, CAN). The bulk density given by suppliers was 0.3–0.7 g·cm⁻³.

## 2.2. Filler silanization and masterbatch processing

Silanization was carried out on MCC and NCC fillers, following the protocol proposed by Dammak (2022), by magnetic stirring, at room temperature and in 1 L Erlenmeyer flasks. (3-aminopropyl) triethoxysilane (APTES) was used, supplied by Sigma Aldrich. The protocol consisted of a preliminary hydrolysis of 2% by mass of APTES in a 1:1 solution of ethanol (95% by volume) and distilled water for 1 h at room temperature. In the second step, acetic acid is added to obtain a pH between 4 and 5. For 1 L of solution, 20–22 ml of acetic acid (99.7%) was found to achieve a pH of 4.5. After 15 minutes, the fillers are added and left in solution for 3 hours. Once the reaction is completed, the fillers were filtered and washed, then dried in an oven at 60 °C for 24 hours. Infrared analysis, conducted on a IRTracer-100 (Shimadzu, Kyoto, JAP) between 500 cm⁻¹ and 4000 cm⁻¹, confirmed the presence of compatibilizer on MCC and NCC, with a decrease in the peak associated with adsorbed water, and the presence of a new peak associated with the Si–O–C binding. TGA analysis showed that silanized fillers demonstrated improved thermal stability, potentially associated with a reduction in the hydroxyl groups, and thus attenuating oxidation phenomena at high temperatures. Once silanized, microscopic analysis of the MCC gave a median and a mean length of 34.1 and 51.9 µm respectively, and a median and a mean width of 16.6 and 22.9 µm respectively.

The masterbatch pre-processing was carried out for NCC bio-nano-composites before the extrusion processing. The melt route was chosen for industrial purposes and achieved on a Haake Minilab II (Thermo Scientific, Massachusetts, USA). This microcompounder operated by batch extrusion of 5 g of PLA:NCC blend. The raw material was conditioned at 60 °C until the moisture content of the components fell below 1%. Preliminary tests showed that a temperature of 180 °C was sufficient to fully melt the PLA, while limiting the thermal degradation of the extrudate. The protocol used consisted of a screw speed of 70 RPM at 180 °C for 1 minute. Once obtained, the extrudate was finally granulated.

## 2.3. Extrusion processing

The Coalia company (Thetford Mines, QC, CAN) extruded and granulated the materials. A twin-screw extruder was used with a temperature of 190 °C and a rotational speed between 70 and 100 RPM. Die pressure was measured between 22 and 24 bars. Table 1 shows the different conditions produced. The maximal MCC content by weight has been fixed at 15% according to previous laboratory results, while the maximal NCC content by weight has been fixed at 5% to avoid excessive aggregates.

<table><caption>**Table 1**
PLA biocomposites and bio-nano-composites conditions.</caption><thead><tr><th></th><th>PLA (g)</th><th>MCC (g)</th><th>Masterbatch (g) ($W_f_{NCC}$ = 20 %)</th><th>$W_{MCC}$ (%)</th><th>$W_{NCC}$ (%)</th></tr></thead><tbody><tr><td>PLA</td><td>1200</td><td>0</td><td>0</td><td>0</td><td>0</td></tr><tr><td>M5</td><td>950</td><td>50</td><td>0</td><td>5</td><td>0</td></tr><tr><td>M10</td><td>900</td><td>100</td><td>0</td><td>10</td><td>0</td></tr><tr><td>M15</td><td>850</td><td>150</td><td>0</td><td>15</td><td>0</td></tr><tr><td>N1</td><td>950</td><td>0</td><td>50</td><td>0</td><td>1</td></tr><tr><td>N3</td><td>850</td><td>0</td><td>150</td><td>0</td><td>3</td></tr><tr><td>N5</td><td>750</td><td>0</td><td>250</td><td>0</td><td>5</td></tr></tbody></table>
## 2.4. 3D printing and hot-pressing processing

To print pelletized extrudates, an intermediate filament-making step was carried out on a 3DEVO filament maker (3DEVO, Utrecht, NLD). A temperature profile of 170–185–185–180 °C was applied, with a screw speed of 3.5 RPM and a cooling power of 40 %. 3D printing was performed on a CR-10 Max (Creality, Shenzhen, CHN) (Fig. 1a)). Fig. 1b) shows the used parameters for the 3D printing. These parameters have been selected via preliminary tests, giving the best printing quality for all the different produced conditions. No printing problems was noted for neat PLA, but the bed had to be sprayed with lacquer to improve adhesion and prevent delamination during printing of the high-filled biocomposites. Furthermore, the filaments were dried at 60 °C just before use to remove any traces of moisture that might alter the print quality. 25 mm-diameter disks were produced for dielectric analyses (Fig. 1c)).

To study the influence of the 3D printing, the hot-press process was chosen as the conventional process and realized with a LabEcon series (Fontjine Presses, Rotterdam, NDL). After drying the material at 60 °C, the material was hot-pressed at 180 °C for 3 minutes at 100 kN to form homogeneous sheets. The sheets were cut with an ml-W1290 150 W laser cutter (MLlaser, Pont-à-Mousson, FRA) to obtain the desired shapes.

## 2.5. Methods used

### 2.5.1. Scanning Electronic Microscopy (SEM) analysis

SEM analyses were performed with a Jeol JSM IT200 (Jeol, Akishima, JAP) to characterize the microstructure of the prepared composites. Tests were carried out on specimens obtained by hot-press. Samples were cryofractured with liquid nitrogen to obtain a clean cross-section, and the selected specimens were all carbon-coated. Tests were made at 5 kV with a x200 magnification.

### 2.5.2. Differential scanning calorimeter (DSC) analysis

DSC analyses were performed on a DSC Q20 (TA Instruments, New Castle, USA) with 15 mg of material, inserted in Al pans. The used protocol consisted of one heating and one cooling ramp between 20 and 200 °C with a heating/cooling rate of 10 K·min⁻¹ and an argon flow of 20 ml·min⁻¹. The crystallinity degree (Xcr) determination was determined by setting the melting enthalpy of 100 % crystalline PLA at 93 J·g⁻¹ (Kang et al., 2018).

### 2.5.3. Rheological analysis

To characterize the viscoelastic behavior of composites in the melt state, rheological analysis tests were conducted on hot-pressed sample

<figure><img src="image_4.png" /><figcaption>Fig. 1. a) Creality CR-10 Max 3D printer, b) 3D printing parameters applied, c) 3D-printed dielectric samples.</figcaption></figure>

using an MCR 302 plane rheometer (Anton Paar, Graz, AUT). Disk samples with a diameter of 25 mm and a thickness of 2 mm were subjected to a temperature of 180 °C under nitrogen. All tests were performed in the Linear Viscoelastic Range (LVE), with a shear rate range between 0.1 and 628 rad·s⁻¹.

### 2.5.4. Broadband dielectric spectroscopy (BDS) analysis

BDS analyses were carried out a low-frequency dielectric spectrometer Keysight E4980A Precision LCR Meter (Agilent Technologies, Santa Clara, USA). The frequency range was 20 Hz-2 MHz. Analyses are performed at 20 °C and the results were triplicated. To determine the porosity of 3D-printed samples, a method derived from the measured permittivity was applied (Eq. 1):

$$ \text{Porosity}(\%) = 100 - \left( \frac{\varepsilon_{3D-printed} - \varepsilon_{air}}{\varepsilon_{hot-pressed} - \varepsilon_{air}} \right) \times 100 \quad (1) $$

Where ε₃D-printed corresponds to the dielectric constant of hot-pressed sample; εₚhot-pressed corresponds to the dielectric constant of 3D-printed sample; and εₐir corresponds to the dielectric constant of air and fixed at 1.

## 3. Results and discussion

### 3.1. Analysis of microstructural properties

Fig. 2 shows SEM pictures of biocomposites and bio-nano-composites. The neat PLA (not presented here) showed a brittle and single-component morphology, as expected. The addition of MCC fillers was clearly visible in the MCC-based biocomposites, forming a scattered morphology in the matrix (more visible for M5 and M10). Pictures of the NCC-based bio-nano-composites showed that N1 was free of aggregates. N3 presented few scattered aggregates, demonstrating a relatively good dispersion. For N5, however, several aggregates were noted, indicating that the NCC content may be too high to ensure a proper dispersion. All the cellulose-based composites showed a very rough matrix, demonstrating that the matrix has undergone rearrangement into a new microstructure with the addition of fillers, which could indicate a change in the crystallinity degree of the composites.

Regarding the rheological behavior, Fig. 3 and Fig. 4 show the complex viscosity η* and storage modulus G' of neat PLA, biocomposites and bio-nano-composites. All tested materials presented a shear-thinning behavior, with an increase in storage modulus G' as the shear rate frequencies increased. Regarding the complex viscosity, at high shear rate (f > 10 rad·s⁻¹), PLA also presented a shear-thinning behavior, with a decrease in complex viscosity with an increasing frequency. At medium frequencies (1 > f > 10 rad·s⁻¹) PLA exhibited a Newtonian plateau, where the viscosity was independent of the shear rate, named zero shear viscosity (η₀) (Bakrani Balani et al., 2023).

By applying the Cross equation, the η₀ PLA was found at 246 Pa·s (Fig. 5). At frequencies below 1 rad·s⁻¹, η*(PLA) decreased due to a too-long application of temperature, degrading the PLA (Al-Itry et al., 2012). Whatever the nature of fillers (micro or nano), the addition of cellulosic fillers enhanced the viscoelastic behavior of PLA, with an increase in the storage modulus at low frequencies as well as complex viscosity at all frequencies. The η₀ of M15 showed the greatest increase, rising by 66 % compared to the neat PLA. A slight increase of the PLA viscosity with the addition of MCC filler was also observed in the literature (Joseph et al., 2015). The addition of cellulosic fillers acted as a reinforcement, limiting the mobility of PLA's macromolecular chains and thus increasing its viscosity. Moreover, the viscosity increase may also be due to a good compatibility between the silanized filler and the matrix, resulting in interfacial adhesion hindering the PLA mobility. However, the reduction in filler size resulted in an increase in specific surface area and therefore in interfacial adhesion effects, which limits the fluidity of the bio-nano-composites. Even if the addition of cellulosic
<figure><img src="image_5.png" /><figcaption>Fig. 2. SEM pictures of biocomposites (M5, M10, M15) and bio-nano-composites (N1, N3, N5).</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 3. Complex viscosity η* versus shear rate of biocomposites and bio-nano-composites.</figcaption></figure>

fillers increased the viscosity of cellulose-based composites, this increase remained very limited and mainly depend on the rather low form factor of the used filler.

Regarding the crystallinity degree Xcr, Fig. 6 presents DSC results and shows that the PLA possessed a typical behavior of a low-crystalline PLA. For hot-pressed PLA, glass transition, temperature (Tg heat), cold temperature (Tcc) and melting temperature (Tm) were found at respectively 64.1 °C, 113.6 °C and 180.2 °C. These values were in line with the literature (Kang et al., 2018; Yang et al., 2008). The addition of cellulosic fillers was critical on PLA crystallinity, independently of the type of filler used (Fig. 7). The Xcr rose from 11.8 % to 50.4 % when 5 % of MCC was added. Even at a Wf NCC = 1 %, the crystallinity of PLA was sharply

enhanced. This positive effect was directly attributable to the nucleation role of the fillers, increasing the Xcr (Wang et al., 2020). Whatever the nature of fillers, the filler content contributes to rapid crystallization process of PLA, accelerating the kinetics and lowering the Tcc. Furthermore, no particular effect was observed for Tg and Tm values.

On the other side, all the 3D-printed MCC-based biocomposites and NCC-based bio-nano-composites showed a crystallization degree lower than the hot-pressed ones (Fig. 7). According to Cuiffo et al. (2017), the 3D printing faster cooling rate can lead to changes in the nature and distribution of the crystalline phases formed, which can explain our findings.
<figure><img src="image_7.png" /><figcaption>**Fig. 6.** DSC curves for hot-pressed samples a) heating ramp of biocomposites, b) cooling ramp of biocomposites, c) heating ramp of bio-nano-composites, d) cooling ramp of bio-nano-composites.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 7.** Crystallinity degree measured by DSC.</figcaption></figure>

important parameter to be kept as low as possible to avoid accelerated degradation of biobased materials. At 1 MHz, the lowest dielectric loss was measured for the 3D-printed PLA at 1.88×10⁻² and the highest was measured for the hot-pressed M15 at 4.67×10⁻². A slight increase of the dielectric loss over the frequency was noticed, which can be linked to the structure rearrangement as shown by DSC. Hot-pressed M15 showed the

highest ε", with a value 96 % higher than for hot-pressed neat PLA. The literature found similar trend and attributed it to the β-relaxation of PLA and interfacial polarization (Badia et al., 2014; Jeszka et al., 2010; Yakubu et al., 2020). Moreover, Yakubu et al. (2020) noted that this effect was more pronounced for smaller fillers, in agreement with our findings. The 3D printing process contributed to reduce the dielectric
<figure><img src="image_9.png" /><figcaption>Fig. 8. Dielectric constant ε' of biocomposites and bio-nano-composites.</figcaption></figure>

<table><caption>**Table 2**
Porosity of the 3D-printed samples measured by permittivity-derived method.</caption><thead><tr><td>Sample</td><td>Porosity (%)</td></tr></thead><tbody><tr><td>PLA</td><td>2.5 ± 0.7</td></tr><tr><td>M5</td><td>3.1 ± 0.7</td></tr><tr><td>M10</td><td>3.5 ± 1.7</td></tr><tr><td>M15</td><td>4.8 ± 1.2</td></tr><tr><td>N1</td><td>3.3 ± 1.5</td></tr><tr><td>N3</td><td>3.1 ± 1.0</td></tr><tr><td>N5</td><td>3.8 ± 1.2</td></tr></tbody></table>

loss, with a 12% decrease in ε" for PLA measured at 1 MHz. This observation could be attributed to the presence of voids caused by the 3D process, as explained previously.

Regarding the electrical conductivity measured at 1 MHz, the lowest σ<sub>AC</sub> was measured for 3D-printed PLA at 7.19 × 10<sup>-7</sup> S·cm<sup>-1</sup>, and the highest σ<sub>AC</sub> was measured for hot-pressed M15 at 2.64 × 10<sup>-6</sup> S·cm<sup>-1</sup>. The values observed for neat PLA are in agreement with the literature (Fal et al., 2021). For all the tested materials, a clear increase in σ<sub>AC</sub> as a function of applied electrical frequency was noted. Hot-pressed neat PLA showed an increase in σ<sub>AC</sub> of 2 × 10<sup>4</sup> between 100 Hz and 1 MHz. Higher electrical frequencies favor the hopping carrier phenomenon, carrying the electrical current into the insulating materials. The addition of cellulosic fillers slightly increased the electrical conductivity. This behavior could be associated with the higher polarity of fillers. No abrupt increase in electrical conductivity with the addition of fillers was observed, showing that even if a percolation threshold may be present, it

does not alter the electrical insulating nature of these materials. The strong frequency-dependent behavior observed is typical of the behavior of an insulating material (Wu et al., 2019). Moreover, the conductivity values were within the electrical insulation range noted by Solazzo et al. (2019), which also suggests that the proposed materials are suitable for the field of electrical insulation.

Regarding the choice of NCC or MCC for the manufacture of low-k materials, we propose a comparison of the dielectric constant of all the produced materials with conventional dielectric materials used in the electrical insulation field, i.e. low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP) and polyvinyl chloride (PVC). ε' values were selected from the literature. Our materials possessed lower ε' than PVC, so they appeared to be relevant candidates to replace PVC for electrical insulation applications. It should be noted that the 3D printing of the M15 condition was not without printing problems, with a high failure rate, requiring a great deal of work and maintenance for an industrial production. NCC-based composites, however, were much easier to print. In view of the results, we recommend using the 3D-printed N3 condition to replace PP and HDPE at the cost of slightly higher polarity. It should be noted that despite a slightly increased ε', such values were still in the apolar materials range according to Dubois (2001). We still need to carry out a mechanical study alongside to determine the contribution of fillers on the mechanical properties in order to fully assess the suitability of our materials for more serious industrial development.

<figure><img src="image_10.png" /><figcaption>Fig. 9. Dielectric loss ε" and electrical conductivity σ<sub>AC</sub> of hot-pressed and 3D-printed PLA, M15, and N5.</figcaption></figure>
<table><caption>**Table 3**
Comparison of the dielectric constant of 3D-printed produced materials with the literature.</caption><thead><tr><th>Material</th><th>ε' @ room temperature and 1 MHz</th><th>Reference</th></tr></thead><tbody><tr><td>PLA</td><td>2.61</td><td>present work</td></tr><tr><td>M5</td><td>2.67</td><td></td></tr><tr><td>M10</td><td>2.85</td><td></td></tr><tr><td>M15</td><td>2.99</td><td></td></tr><tr><td>N1</td><td>2.76</td><td></td></tr><tr><td>N3</td><td>2.83</td><td></td></tr><tr><td>N5</td><td>2.89</td><td></td></tr><tr><td>LDPE</td><td>2.3–2.42</td><td>Anh et al. (2016); He et al. (2020); Jiang et al. (2021);</td></tr><tr><td>HDPE</td><td>2.1–2.5</td><td>Vidakis et al. (2024); Wang et al. (2017); Xu et al. (2021);</td></tr><tr><td>PP</td><td>2.2–2.31</td><td>Chen et al. (2021); Izci and Bowler (2019); Mike Chung (2012);</td></tr><tr><td>PVC</td><td>3.5–5</td><td>Elsad et al. (2023); Mansour et al. (2016); Turnhout (2019);</td></tr></tbody></table>

## 4. Conclusion

The proposed study investigated the dielectric and microstructural performances of sustainable cellulose-based materials produced by 3D printing process. Biocomposites based on microcrystalline cellulose (MCC) and bio-nano-composites based on nanocrystalline cellulose (NCC) with different weight content were produced and tested. Samples using a conventional processing method were also included to study the effect of 3D printing itself. A nucleation effect was noted with the incorporation of cellulosic fillers, as well as increased dielectric properties. The increased dielectric properties can be associated with the polarity of the used fillers. Although the tested properties were superior for M15, the enhancement potential was greater for NCC fillers, due to the latter's higher specific surface area available. The 3D printing process showed lower dielectric properties than the reference process, conferring a better suitability for electrical insulation applications. This increased insulating power was associated with the presence of internal voids induced by the processing. The rheological results also highlighted the limited impact of filler content on MCC-based biocomposites and NCC-based bio-nano-composites viscosity, suggesting that it would be possible to increase the filler content or switching to a cellulosic filler with a higher L/d ratio without critically impacting the melt fluidity during the 3D-printing process once the process has been mastered and the failure rate reduced. These observations demonstrated the potential of the proposed material as a sustainable alternative to electrical insulating synthetic materials such as HDPE, PP and PVC. We propose to continue the research by carrying out a mechanical study to understand how the process and the cellulosic fillers will interact positively or negatively on the capacity of our materials to replace the synthetic polymers mentioned above.

### CRediT authorship contribution statement

**Mohamed Ragoubi:** Writing – review & editing, Writing – original draft, Validation, Supervision, Methodology, Formal analysis. **Ahmed Koubaa:** Writing – review & editing, Supervision, Methodology, Funding acquisition. **Nathalie Leblanc:** Supervision, Project administration, Funding acquisition. **Morgan Lecoulet:** Writing – original draft, Methodology, Investigation, Formal analysis, Data curation.

### Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Data Availability

No data was used for the research described in the article.

### Acknowledgements

This work was supported by the Région Normandie (Fr), the Canada Research Chair Program; the NSERC Discovery Grant; MITACS Globalink Program; and TABES Create Program (Grant Number CREATE 554777-2021). Authors acknowledge great help from AGROBIOTECH plateform from UniLaSalle-Rouen for experimental and analytical analysis.

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