MECHANOCHEMICAL ACTIVATED AND FUNCTIONALIZED CELLULOSE POWDERS AND THEIR REINFORCED PLASTIC COMPOSITES

LANG HUANG

Cellulosic fibers have the potential for serving as lightweight and biobased reinforcement in many applications but they suffer from difficulties in obtaining adequate dispersion and a strong interface in many polymers. The hydrophilic and aggregating nature of the cellulose fiber usually lead to poor processability, incompatibility, and high moisture sensitive when compounded with hydrophobic plastics. Here we proposed that cellulose fibers be subjected to mechanochemical activation and functionalization to prepare surface modified cellulose powders for improved use in composite materials. Specifically, mechanochemical ball milling was used to simultaneously and cost-effectively pulverize, activate, and functionalize wood pulp fibers to produce a series of property-tuned cellulose powders for polypropylene (PP) composite. Ball milling was effective for preparing micronized ellipsoid cellulose particles with low aspect ratios and high specific surface area. The milling destroyed the highly ordered crystal structure of cellulose, decreasing the degree of crystallinity. For the ball milled cellulose particles reinforced PP composites, smaller particles with higher specific surface areas and lower aspect ratio increased the melting processability, promoted the matrix crystallizing at a higher temperature, improved the tensile property and reduced the water absorption of the composite compared with those of pulp fiber reinforced one. The mechanochemical esterification of the cellulose particle with acetic/oleic mixed anhydrides was successful conducted in ball milling at room temperature. Results showed that sodium hypophosphite catalyst was effective on accelerating the mechanochemical reaction. Higher mixed anhydrides molar fractions and longer milling time led to higher yields cellulose esters. The modification increased the hydrophobicity of the cellulose sample, and the surface esterified cellulose particles reinforced composites showed increased melting processability, toughness property and water repellency. To improve the matrix crystallization, polypropylene β form nucleating sites were introduced to the cellulose powder through ball milling. The results indicated the nucleating agent was synthesized during mechanochemical reaction. β form PP crystals, with small spherulite size and good toughness behavior, were induced in the filled PP composites. The nucleating functionalized powder reinforced composites presented better mechanical behavior and higher crystallization rate and temperature than the untreated ones.

MECHANOCHEMICAL ACTIVATED AND FUNCTIONALIZED CELLULOSE POWDERS AND THEIR REINFORCED PLASTIC COMPOSITES

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