Biodegradable polyhydroxyalkanoate (PHA) composites with biochar ratios optimized for the additive manufacturing method of material extrusion: engineering, rheological, and morphological insights†

Naturally derived poly(hydroxyalkanoate) (PHA) and biochar from agricultural residues were combined to develop an environmentally friendly, completely biodegradable composite with improved thermal and mechanical properties. Six filler concentrations (0.0, 0.5, 1.0, 1.5, 2.0, and 2.5 wt%) were prepared to extrude into filaments and subsequently manufacture the respective 3D printed composites through material extrusion (MEX) additive manufacturing (AM). The samples discussed here are bio-originated composites, and as a consequence, they can potentially be a revolutionary replacement for environmentally harmful, industrially produced polymeric materials, at the appropriate and desired applications. 3D printed PHA/biochar composites have potential for use across a range of industrial applications such as packaging, agriculture, prototyping, and environmental monitoring, where sustainability and biodegradability are requirements. Still, their industrialization involves several challenges, such as the brittleness of PHA, the interaction with the biochar, and possible printability issues that need to be addressed. The samples were subjected to several tests to assess their rheological, thermal, and mechanical properties, as well as their structure and morphology. Thermogravimetric analysis, dynamic mechanical analysis, differential scanning calorimetry, tensile tests, bending tests, microhardness, and Charpy impact tests were conducted. In addition, the porosity and dimensional accuracy were evaluated, while scanning electron microscopy and, by extension, energy dispersive spectroscopy were used to assess microstructure formation. The obtained results indicated enhanced performance in the biochar 0.5 wt% compound in terms of tensile (17.7% increase) and bending toughness (3.1% increase), bending strength (32.8 MPa, 15.3% increase), and Charpy (1.9% increase) impact strength, and for PHA/1.0 wt% biochar composites regarding tensile strength (22.1 MPa, 15.3% increase), Young's modulus (131.5 MPa, 25.4% increase), dimensional accuracy (better by 11.2%), and porosity (reduced by 23.3%).