Improving the mechanical and biomaterial properties of the composite

Brief content
In the study, lignin (17% and 29% by weight) was blended with
butyleneadipate-co-terephthalate (PBAT) in an Omega 25 mm twin-screw extruder using standard technology (STD) and fractional geometry technology (FGT). The extruded pellets were used to cast ASTM D-standard samples.

Key findings

1. Addition of lignin to PBAT increased impact strength and flexural modulus, but reduced tensile strength and elongation at break.
2. Fractional geometry technology (FGT) showed advantages over standard (STD): lower melt temperature, lower specific energy consumption, higher impact strength and flexural modulus.
3. Scanning electron microscopy (SEM) analysis confirmed that FGT provides better lignin distribution in the PBAT matrix and no voids, which explains the improved mechanical properties.

Introduction
PBAT is a biodegradable polymer with high flexibility and elongation at break. To reduce the cost, it is modified with bio-fillers such as lignin, a by-product of the pulp and paper industry. However, lignin is poorly compatible with PBAT, which reduces the mechanical properties of the composite. The solution is to use special mixing technologies, such as FGT.

Extrusion process
Equipment: Omega 25 twin-screw extruder (STEER).
Parameters: Cylinder temperature 130-150°C, screw speed 100-800 rpm.
Feeding: PBAT (granules) and lignin (powder) were fed separately through different hoppers.
Mixing: Special elements (DSE, FME) were used for FGT technology to ensure gentle and uniform distribution of lignin without degradation.
Pelletization: The melt was extruded through a die, cooled in water, dried, and cut into 2x3 mm pellets.

Results and discussion

1. Process parameters: FGT allowed to reduce the melt temperature to 145°C (vs. 151°C for STD) and specific energy consumption to 0.38 kWh/kg.
2. Mechanical properties: The sample with 29% lignin, obtained by FGT technology, showed the highest values of impact strength and bending modulus. The tensile strength decreased with the addition of lignin for both methods.
3. Morphology (SEM): Micrographs showed that FGT provides a uniform distribution of lignin and good adhesion to the PBAT matrix without voids. In samples obtained using standard technology, clusters of lignin particles and a weak interfacial boundary were observed.

Conclusion
Fractional Geometry Technology (FGT) when processing the PBAT/lignin composite (29%) on the Omega 25 extruder demonstrates significant advantages over the standard technique:

• Reducing energy consumption and processing temperature.
• Improving key mechanical properties (impact strength, bending modulus).
• Forming a homogeneous microstructure of the composite with good filler distribution.

This makes FGT a promising method for creating cost-effective and environmentally friendly biodegradable materials with improved characteristics.