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

Abstract

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 DCPinduced 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.

Surface and Interface Engineering for Nanocellulosic Advanced Materials

“…This method is also applicable to nanocelluloses, although only CNC‐based composites have been reported. [ 112–117 ] In 2016, Dhar et al. reported a PLA‐grafted CNC (CNC‐g‐PLA) film via reactive extrusion (Figure 8c).…”

“…[ 113 ] Recently, several biodegradable polymers, including poly(butylene adipate‐ co ‐terephthalate) (PBAT) and poly(3‐hydroxybutyrate‐hydroxyvalerate) (PHBV), were reinforced with CNCs via reactive extrusion. [ 114,116,117 ] Zheng et al. compared three processes: direct compounding, reactive extrusion using a coupling agent, and reactive extrusion using a peroxide free‐radical initiator.…”

“…compared three processes: direct compounding, reactive extrusion using a coupling agent, and reactive extrusion using a peroxide free‐radical initiator. [ 116 ] It was concluded that only the last process resulted in an improvement in strength by 13%. [ 116 ] This result reminds us that nanocellulose reinforcement provides more than interfacial compatibility and this mechanism requires further exploration.…”

“…Additional features were obtained via these interfaces or surface engineering, including an improved wet strength, [ 102,134 ] oil/water separation, [ 132,133,135 ] CO 2 adsorption, [ 122 ] water barrier, [ 102,113,125,126 ] oxygen barrier, [ 113 ] flame‐resistance, [ 128 ] charge‐storage capacity, [ 127 ] self‐healing, [ 100 ] and shape memory. [ 100 ] Because surface modification does not guarantee an enhanced reinforcement, [ 82,116 ] a theoretical study is required to reveal the structure–property relationship. [ 115,116 ] A prediction of the properties prior to material formation would be of great interest.…”

“…[ 100 ] Because surface modification does not guarantee an enhanced reinforcement, [ 82,116 ] a theoretical study is required to reveal the structure–property relationship. [ 115,116 ] A prediction of the properties prior to material formation would be of great interest.…”