Dual synergistic role of phosphorylated microcrystalline cellulose as organoinitiator and filler for PCL biocomposites.

In the present work, phosphorylated microcrystalline cellulose MCC@P was successfully prepared using phosphorus oxychloride (POCl3) and employed both as an eco-friendly metal-free initiator for the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and as an organic functional filler for the resulting biocomposites. Poly(ε-caprolactone) (PCL) biocomposites were prepared under solvent-free conditions without the use of any metal catalyst. In this system, phosphorylated MCC serves a dual role. The phosphate groups associated with MCC participate in the initiation of ε-CL polymerization, while the remaining hydroxyl groups may serve as potential initiation and grafting sites, leading to the formation of MCC@P-g-PCL biocomposites. The prepared biocomposites were fully characterized using (31P/13C) nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), X-ray diffraction (XRD) and dynamic light scattering (DLS), and a suspension stability test to investigate the formation of the MCC@P-g-PCL biocomposites and provide complementary evidence supporting the proposed grafting of PCL onto MCC@P. The molecular-weight characteristics of the extracted free PCL fraction were determined by SEC, with M n values ranging from 8312 to 21 880 g mol-1 depending on the MCC@P content, while thermal stability of the prepared biocomposites was significantly enhanced compared to the neat PCL as demonstrated by the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). For instance, the thermal degradation temperature at 30% (T d30%) weight loss of MCC@P-g-PCL 1% reached 394 °C instead of 372 °C for PCL used as standard. The DSC results showed higher apparent crystallinity values for the MCC@P-g-PCL biocomposites than for neat PCL, with the highest value obtained for MCC@P-g-PCL 1% (64.8% versus 52.1% for neat PCL). The heat-release parameters measured by microscale combustion calorimetry were reduced for the MCC@P-g-PCL biocomposites, with the largest reduction in HRR observed for the 3 wt% formulation. Overall, these results highlight the potential of phosphorylated MCC as a metal-free initiating and functional-filler strategy for the development of PCL-based biocomposites with modified thermal and heat-release behavior.