Low-loading toughening of Poly(butylene succinate) by cellulose acetate propionate: Crystallization, morphology, and mechanical properties

This study presents the first systematic investigation of cellulose acetate propionate (CAP) as a bio-based toughening modifier for poly(butylene succinate) (PBS) through melt blending. The effects of CAP on the miscibility, crystallization behavior, mechanical performance, thermal stability, and flame retardancy of PBS were comprehensively evaluated. FTIR spectra showed an apparent change in the ester carbonyl region after blending, indicating an altered local ester environment and possible weak intermolecular interactions. However, the nearly unchanged PBS-rich glass-transition temperature and the increasingly heterogeneous fracture morphology demonstrate limited, composition-dependent compatibility rather than complete miscibility. At a cooling rate of 20 °C min -1 , the crystallization temperature of PBS decreased systematically from 71.8 °C for neat PBS to 57.1, 41.4, and 32.9 °C for blends containing 5, 10, and 15 wt% CAP, respectively. Additional scans at 10 and 5 °C min -1 shifted the crystallization peaks to higher temperatures but retained the same composition-dependent trend, confirming that CAP primarily retards PBS crystallization kinetics. The 5 wt% CAP blend exhibited the most favorable mechanical balance: the elongation at break increased from 14.5% to 213.4% and the impact strength increased from 5.5 to 8.5 kJ m -2 , although the strength at break decreased from 45.38 to 36.83 MPa. SEM revealed enhanced plastic flow, tear ridges, and fibrillation, supporting an interfacial-debonding-assisted shear-yielding mechanism rather than classical crazing. In contrast, higher than 10 wt% CAP contents led to interfacial incompatibility reduced stress-transfer efficiency. TGA showed that CAP delayed the onset of measurable mass loss, whereas the main decomposition temperature remained nearly unchanged at 5–10 wt% CAP and decreased to 401.3 °C at 15 wt% CAP; no enhancement in char residue was observed. CAP also produced only a modest change in flammability, increasing the limiting oxygen index from 27.5% to 28.5–29.0 % and changing the UL-94 result from Fail to V-2 while melt dripping and cotton ignition persisted. These findings identify 5 wt% CAP as an effective low-loading toughening composition and clarify the limits imposed by crystallization retardation and phase separation.