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Cellulose nanofibers (CNFs) have exceptional mechanical and thermal properties, but the use of these materials to reinforce polyolefins is challenging. In the present study, ethanol, acetone, isopropyl alcohol (IPA) and water were used as dispersion media for alkenyl succinic anhydride-modified CNFs (ACNFs). Masterbatches were prepared from these ACNFs wetted in the various liquids and then melt-compounded with high-density polyethylene (HDPE) using a twin-screw extruder, followed by injection-molding. The morphologies of the resulting HDPE/ACNF composites were characterized using optical and electron microscopy, and the rheological and mechanical properties of these composites were also evaluated. The results showed that the storage and loss moduli as well as the tensile moduli and strength of the composites produced using the organic liquids were higher than those of the composite made using water, owing to the better dispersion of ACNFs in the HDPE matrix in the former. This improved dispersion would be expected to increase the contact area between the ACNFs and the matrix and to enhance the orientation of the HDPE molecules. IPA was found to give the highest tensile modulus and strength among the organic liquids used in this study. The tensile modulus and strength of the composite containing ACNFs produced from IPA were, respectively, four times and two times higher than those of the neat HDPE. IPA is a relatively non-toxic, inexpensive compound, and so could be readily adopted for industrial scale processing.

Because of their high mechanical performance, high specific surface area, and high aspect ratio, there is a strong interest in cellulose nanofibers (CNFs) as a reinforcing material for plastics. Although three hydroxyl groups per repeating unit exposed on the surface is a unique characteristic of CNFs, an effective chemical treatment to improve the reinforcing efficiency of CNFs for hydrophobic thermoplastic resin has not yet been reported. In this study, six systematically designed aliphatic ester groups with linear, cyclic and branched structures, were incorporated on the surface of CNFs using the hydroxyl groups with a degree of substitution of 0.4. The melt compounding of the esterified CNFs and HDPE was performed at 140 °C using a twin screw extruder followed by injection molding at 160 °C and investigated the CNF dispersibility in HDPE and the CNF reinforcing efficiency in injection-molded HDPE samples. Incorporation of linear long chains results in the best dispersion of CNFs in HDPE compared with cyclic and branched chains, but the latter chains give higher reinforcing efficiencies in Young’s modulus and tensile strength. Especially, the bulky t-butyl group gave the highest reinforcing efficiency. Thus, the structure of ester groups incorporated on the CNFs very much affects on the dispersibility in HDPE, Young’s modulus and tensile strength, and coefficient of thermal expansion (CTE) of the esterified CNFs-reinforced HDPE composites. Addition of pivaloylated CNFs increases the Young’s modulus of HDPE from 1.20 to 3.32 GPa, and the tensile strength from 23.4 to 51.2 MPa. The CTE is 72.5 ppm/K, which is less than one-third that of the HDPE. The high reinforcing efficiency of these composites is partly explained by the formation of the double shish–kebab crystal structure during injection molding identified by the TEM observation.

The gradient structure was observed for the sectional layer of the poly(2-ethylhexyl acrylate-co-acrylic acid-co-vinyl acetate); P(2EHA-AA-VAc)/poly(vinylidene fluoride-co-hexafluoro acetone); P(VDF-HFA) (30/70) blend thin film using SEM. The elipsoidal domain corresponded to P(2EHA-AA-VAc) particle was observed and its size increased from surface to bottom. In the bottom side, P(2EHA-AA-VAc) layer having ∼10μm thickness was formed. The characteristic gradient domain morphology was reduced by adding the micrograin silica into P(2EHA-AA-VAc)/P(VDF-HFA) (30/70) blend. Finally, pressure sensitive adhesive; PSA properties (180° peel adhesion and probe tack) were evaluated in these blends on account of confirming the effect of the micrograin silica on the gradient structure.