*2.3. Mechanical Properties*

A universal tester (AGS-X autograph, Shimadzu, Kyoto, Japan) was used to conduct mechanical tests on polymer filaments using a 1 kN load cell. All tests were conducted at 22 ◦C. Filaments were subjected to a 5 N pre-load, the gauge length was 300 mm and materials were tested in triplicate. Additionally, 30 mm/min was used for the displacementbased test and termination was at the point of material failure or 300 mm displacement.

Creep tests were also carried out on filaments using the universal tester and a 1 kN load cell. A displacement loading rate of 10 mm/min was applied to the specimens until a load of 40 N was reached, then held for a duration of 3 h or until the sample reached a maximum displacement of 0.5 m. The initial gauge length was again 300 mm, with tests carried out in triplicate. The change in displacement for each polymer sample for the test duration was evaluated by calculating a steady state creep rate (.*ε*):

$$
\dot{\varepsilon} = \frac{\varepsilon\_{8000}}{\varepsilon\_{50}} \tag{1}
$$

where *ε*8000 and *ε*50 were the strains measured after 8000 and 50 s, respectively.

#### *2.4. Attenuated Total Reflectance—Fourier Transform Infrared (ATR-FTIR)*

An FT-IR Spectrometer (Spectrum Two, Perkin Elmer) was used for chemical analysis. Spectra were recorded from 4000 to 500 cm<sup>−</sup><sup>1</sup> and 16 scans per specimen (spectral

resolution 4 cm<sup>−</sup>1). All output data were baseline corrected and normalised using Spectrum Quant software (Perkin Elmer).

## *2.5. Differential Scanning Calorimetry (DSC)*

Differential scanning calorimetry (DSC823e, Mettler Toledo) was used to assess the thermal profile of the materials. A heating rate of 10 ◦C/min was applied in the range of 25–240 ◦C. Aluminium crucibles were used as the reference and sample holder which contained a known weight of polymer prior to analysis. Material crystallinity was calculated using Equation (2) [33]:

$$\text{Crystallimity } \left( \% \right) = \left( \frac{\Delta H\_m - \Delta H\_{\text{cc}}}{\Delta H\_{m100\%}} \right) \tag{2}$$

where Δ*Hm* is the melting enthalpy, Δ*Hcc* is enthalpy of cold crystallisation and Δ*Hm*100% is the enthalpy of melting for 100% crystalline polymer being investigated. For PLLA, PCL and PHBV, Δ*Hm*100% is reported in the literature as 93.7 J/g, 139 J/g and 146.6 J/g, respectively [6,34,35]. For polymer blends, the crystallinity for each polymer in the blend was calculated according to the relative weight of that polymer in the blend and these quantities added together to give the total polymer crystallinity.

## *2.6. Rheological Assessment*

Rheological analyses were conducted on three samples for each material using a DHR-2 controlled stress rotational rheometer (TA Instruments, New Castle, DE, USA) equipped with an environmental test chamber for temperature control during testing. Analysis was conducted using a 25 mm parallel plate geometry, keeping a constant temperature of 210 ◦C. Frequency sweep tests were performed to observe the variation in the storage modulus (G') and loss modulus (G") with increasing angular frequency (from 1 to 600 rad/s). The values obtained from the frequency sweep analysis were used to obtain the material flow ramps by applying the Cox–Merz equation, where the variation in the material viscosity was obtained for increasing shear rates (1–600 s<sup>−</sup>1).
