Comparative Study of Direct Compounding, Coupling Agent-Aided and Initiator-Aided Reactive Extrusion to Prepare Cellulose Nanocrystal/PHBV (CNC/PHBV) Nanocomposite

Three compounding methods were compared to determine their effects on the organization of the interphase in nanocomposites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV) and cellulose nanocrystals (CNCs) processed via (1) direct compounding, (2) reactive extrusion using a coupling agent (PHBV-g-GMA), or (3) reactive extrusion using a peroxide free-radical initiator (dicumyl peroxide, DCP). Tensile testing showed that only the peroxide-aided extrusion resulted in improvement in strength by 13%. Analyzing the interphases via DSC, WAXRD, SAXS, ATR-FTIR, and XPS helped relate the compounding methods to mechanical performance. Distinct PHBV-CNC graft configurations were found by analyzing CNCs isolated from each of the three composite types. Use of DCP led to polymer grafting, incomplete coverage of PHBV on the CNC surface, and many interpolymer cross-links. The result was robust matrix-CNC interfacial interaction and alignment of the CNCs, which yielded the best mechanical properties. Conversely, adding a coupling agent led to less actual PHBV grafts but greater coverage of the CNC surface relative to DCP-induced grafting. Although the CNCs were more dispersed, the lower PHBV grafting limited interfacial stress transfer and, consequently, reinforcement. While the direct compounding led to the less-dispersed CNC particles in the matrix with higher polymer coverage of flexible polymeric chain.