Chemical modification of nanocellulose with canola oil fatty acid methyl ester.

Cellulose nanocrystals (CNCs), produced from dissolving wood pulp, were chemically functionalized by transesterification with canola oil fatty acid methyl ester (CME). CME performs as both the reaction reagent and solvent. Transesterified CNC (CNCFE) was characterized for their chemical structure, morphology, crystalline structure, thermal stability, and hydrophobicity. Analysis by Fourier transform infrared (FTIR) and FT-Raman spectroscopies showed that the long chain hydrocarbon structure was successfully grafted onto CNC surfaces. After transesterification the crystal size and crystallinity of nanocrystals were not changed as determined by Raman spectroscopy and wide angle X-ray diffraction (XRD). CNCFE showed higher thermal stability and smaller particle size than unmodified CNCs. Water contact angle measurement indicated the CNCFE surface has significantly higher hydrophobicity than unmodified CNCs. The transesterified CNCs could be potentially used as hydrophobic coatings and reinforcing agents to hydrophobic polymer for nanocomposites.

Cell morphology of extrusion foamed poly(lactic acid) using endothermic chemical foaming agent.

Poly(lactic acid) (PLA) was foamed with an endothermic chemical foaming agent (CFA) through an extrusion process. The effects of polymer melt flow index, CFA content, and processing speed on the cellular structures, void fraction, and cell-population density of foamed PLA were investigated. The apparent melt viscosity of PLA was measured to understand the effect of melt index on the cell morphology of foamed PLA samples. The void fraction was strongly dependent on the PLA melt index. It increased with increasing melt index, reaching a maximum value, after which it decreased. Melt index showed no significant effect on the cell-population density of foamed samples within the narrow range studied. A gas containment limit was observed in PLA foamed with CFA. Both the void fraction and cell-population density increased with an initial increase in CFA content, reached a maximum value, and then decreased as CFA content continued to increase. The processing speed also affected the morphology of PLA foams. The void fraction reached a maximum value as the extruder's screw speed increased to 40 rpm and a further increase in the processing speed tended to reduce the void fraction of foamed samples. By contrast, cell-population density increased one order of magnitude by increasing the screw speed from 20 to 120 rpm. The experimental results indicate that a homogeneous and finer cellular morphology could be successfully achieved in PLA foamed in an extrusion process with a proper combination of polymer melt flow index, CFA content, and processing speed.