Performance of nitrogenous polybutylene succinate/polylactic acid materials and their degradation effects on physiological indicators of lettuce

Nitrogenous polybutylene succinate (N-PBS) was synthesized herein by melt polycondensation with a 10% molar content of the third monomer, N-methyldiethanolamine (N-MDEA). The chemical structure of the synthesized N-PBS was characterized, and its crystallinity and relative molecular mass were tested. Then the N-PBS was modified by blending with polylactic acid (PLA) in different proportions, and the crystal morphology, thermodynamic properties, water contact angle, degradation properties, and plant nutritional properties of the resulting composites were studied. The results confirmed that the N-PBS copolymer was successfully synthesized. Polarizing microscope (POM)and differential scanning calorimetry tests revealed defects in the crystallization of the N-PBS in the composite, while the crystallinity also declined. Thermogravimetry tests revealed an overall enhancement of the thermal properties of the composite, with mass loss occurring above 300 °C. When the N-PBS content is 60%, the overall mechanical properties of the composites are optimal. The water contact angle of the N-PBS was also lower than that of the PLA, indicating higher hydrophilicity in the N-PBS than the PLA. The composite degraded in the soil supernatant for six months, reaching a degradation rate of up to 40%, and grooves and holes on the surface of the material were observed clearly by scanning electron microscopy. By identifying the components in the degradation solution, it was found that most of the small nitrogen-containing molecules were oligomers of succinic acid, butanediol, and N-MDEA. With the degradation of N-PBS in the composites, nitrogen was released, facilitating lettuce growth.