Surface Wettability and Young's Moduli in Blends of Poly(L‐Lactide) and Poly(3‐Hydroxybutyrate‐Co‐3‐Hydroxydecanoate) Produced From Brewer's Spent Grains Fermented by Recombinant E. coli Co‐Fed Fatty Acid

ABSTRACT We report on the behavior of surface wettability and Young's moduli of poly(L‐lactide) (PLLA)/poly(3‐hydroxybutyrate‐co‐3‐hydroxydecanoate) (PHBD) blends, in which the PHBD is produced from second‐generation feedstocks. PHBD is biosynthesized from brewer's spent grains using recombinant E. coli and blended with PLLA via solvent casting at compositions of 100/0, 90/10, 75/25, 50/50, 25/75, 0/100 (PLLA/PHBD). We found that the incorporation of 25 wt% PHBD yields the highest mechanical performance, with tensile stress (44.5 MPa) and strain at break (10.7%) exceeding the values exhibited by neat PLLA. These results indicate partial miscibility and suggest that PHBD reinforces the PLLA matrix by promoting intermolecular interactions within the amorphous phase. An increase in the PHBD wt% results in lower Young's moduli values due to crystalline phase separation. Attenuated total reflectance‐Fourier transform infrared spectroscopy and microscopy, X‐ray diffraction, and differential scanning calorimetry confirm the crystalline phase separation. We performed surface wettability measurements with water, coffee, and cooking oil. The results indicate improved surface hydrophobicity and oleophobicity with increasing PHBD content. The 25/75 (PLLA/PHBD) blend exhibits a water contact angle (CA) of 125.9°, higher than that of neat PLLA (78°). We believe that these results are the first to demonstrate the chemical and mechanical tunability of PLLA/second‐generation PHBD blends and the potential of these blends in biopolymer packaging applications that require hydrophobicity and oleophobicity.