*3.2. Analyses*

1H, 13C, and 29Si Nuclear Magnetic Resonance (NMR) spectra were recorded at 25 ◦C on a Bruker Ascend 400 and Ultra Shield 300 spectrometers using CDCl3 as a solvent. Chemical shifts are reported in ppm with reference to the residual solvent (CHCl3) peaks for 1H and 13C.

MALDI-TOF mass spectra were recorded on a UltrafleXtreme mass spectrometer (Bruker Daltonics), equipped with a SmartBeam II laser (355 nm) in the 500–4000 *m*/*z* range. 2,5-Dihydroxybenzoic acid (DHB, Bruker Daltonics, Bremen, Germany) served as matrix. Mass spectra were measured in reflection mode. The data were analysed using the software provided with the Ultraflex instrument—FlexAnalysis (version 3.4).

Fourier Transform-Infrared (FT-IR) spectra were recorded on a Nicolet iS 50 Fourier transform spectrophotometer (Thermo Fisher Scientific) equipped with a diamond ATR unit with a resolution of 0.09 cm<sup>−</sup>1.

Contact angle analyses were performed by the sessile drop technique at room temperature and atmospheric pressure, with a Krüss DSA100 goniometer (Hamburg, Germany). Three independent measurements were performed for each sample, each with a 5 μL water drop, and the obtained results were averaged to reduce the impact of surface nonuniformity.

Thermogravimetry (TG) was performed using a NETZSCH 209 F1 Libra gravimetric analyser (Selb, Germany). Samples of 5 ± 0.2 mg were cut from each granulate and placed in Al2O3 crucibles. Measurements were conducted under nitrogen (flow of 20 mL/min) in the range of 30–800 ◦C and a 20 ◦C/min heating rate. Differential scanning calorimetry (DSC) was performed using a NETZSCH 204 F1 Phoenix calorimeter Samples of 6 ± 0.2 mg were cut from each granulate and placed in an aluminium crucible with a punctured lid. The measurements were performed under nitrogen in the temperature range of −20–290 ◦C and at a 20 ◦C/min heating rate, and Tg was measured from the second heating cycle.

The effect of the modifier addition on the mass flow rate (MFR) was also determined. The measurements were made using a Instron plastometer (Norwood, MA, USA), model Ceast MF20 according to the applicable standard ISO 1133. The measurement temperature was 190 ± 0.5 ◦C, while the piston loading was 2.16 kg.

For flexural and tensile strength tests, the obtained materials were printed into type 1B dumbbell specimens in accordance with EN ISO 527:2012 and EN ISO 178:2006. Tests of the obtained specimens were performed on a universal testing machine INSTRON 5969 with a maximum load force of 50 kN. The traverse speed for tensile strength measurements was set at 2 mm/min, and for flexural strength was also set at 2 mm/min. Charpy impact test (with no notch) was performed on a Instron Ceast 9050 impact-machine according to ISO 179−1. For all the series, 6 measurements were performed.

Hardness of the composite samples was tested by the Shore method using a durometer Bareiss Prüfgerätebau GmbH.

A scanning electron microscope (SEM 3000, Hitachi, Japan) was used to analyse the microstructure and quality of the produced composite samples after 3D printing and injection moulding. Additionally, the effect of SS-Limonene addition on the microstructure of composite materials was investigated. Before the measurement, samples' cross-sections were coated with a thin layer of Au-Pd. The applied voltage for SEM observations was 15 kV.

Surface structure and breakthroughs were analysed under Digital Light Microscope Keyence VHX 7000 with 100× to 1000× VH-Z100T lens (Osaka, Japan). All of the pictures were recorded with a VHX 7020 camera.

#### *3.3. The Procedure for Synthesis of Octaspherosilicate Limonene Derivative (SS-Limonene)*

Octahydrospherosilicate was prepared according to a literature procedure [36]. The hydrosilylation reaction was performed accordingly to a previous report [31].

In a typical procedure, a 500 mL three-neck, round-bottom flask was charged with 25 g of Octahydrospherosilicate, 250 mL of toluene and 26.77 g of limonene, and a magnetic stirring bar was added. A thermometer and condenser equipped with an argon inlet and oil bubbler were attached, the flask placed in a heating mantle and the system was purged with argon. The reaction mixture was set on 110 ◦C and before reaching boiling, 25 μL of Karstedt's catalyst solution was added, which resulted in quick increase of temperature and the system starting to reflux. The reaction mixture was kept at reflux and samples were taken for FT-IR control until full Si-H group consumption was observed. Then, the solvent was evaporated under vacuum to dryness to obtain an analytically pure sample.

#### *3.4. Fabrication of Filaments*

#### 3.4.1. Preparation of Granulates

The polymer and the filler were homogenized using a laboratory two-roll mill ZAMAK MERCATOR WG 150/280. A portion of 500 g PLA Ingeo™ 2003 D was mixed with SS-Limonene, until the final concentration of the additive of 5.0% *<sup>w</sup>*/*<sup>w</sup>*. The mixing was performed at the rolls temperature of 200 ◦C for 15 min., getting to full homogeneity of the concentrates. Masterbatch was granulated by a grinding mill WANNER C17.26 sv. The granulates were diluted with pure PLA up to the final filler concentrations of 0.25, 0.5, 1.0, 2.5 and 5.0% *w*/*w* upon extrusion moulding of a stream with consequent cold granulation on the twin-screw extrusion setup line HAAKE Rheomex OS, and then dried for 24 h at 40 ◦C.

#### 3.4.2. Extrusion of Filaments

The granulates obtained as above were used for moulding of filaments of 1.75 mm in diameter by a single-screw extrusion setup HAAKE Rheomex OS.

#### 3.4.3. 3D Printing (FDM)

Using a 3D printer FlashForge Finder two types of samples were printed by FDM: oars and bars, according to PN-EN-ISO 527-2. Parameters of printing are given in Table 4.


**Table 4.** Process parameters for sample printing.

#### *3.5. Injection Moulding*

To compare the mechanical properties of composite materials made by 3D printing, the samples were produced by the injection moulding method. Specimens for static tensile, three-point bending, and impact tests were in accordance with the dimensions of the following standards: PN-EN ISO 527, PN-EN ISO 178, and PN-EN ISO 179, respectively. HAAKE Minijet Pro Piston Injection Moulding System (ThermoScientific, Bremen, Germany) equipped with a set of moulds was used to produce test samples. Parameters of the injection process are presented in Table 5

**Table 5.** Injection process parameters.

