Rheological and mechanical properties of polypropylene composites containing microfibrillated cellulose (MFC) with improved compatibility through surface silylation

초록

We investigated the rheological and mechanical properties of a polypropylene (PP) composite reinforced by microfibrillated cellulose (MFC) fibers, of which the size was fractionated at ca. 24 mu m by removing substances such as lignin or hemicellulose out of natural plants to exert the maximum mechanical performance of cellulose fibers. Due to the poor compatibility of MFC with a non-polar hydrophobic PP matrix, the MFC surface was modified through silylation and acetylation to increase its wetting and dispersion characteristics. The content of silylated-MFC could increase up to 30wt% in the PP composite through large-volume process such as extrusion and injection molding. In addition, all mechanical properties of the silylated-MFC/PP composite were improved compared to untreated MFC/PP, acetylated MFC/PP composite. It was ensured by a strong shear thinning characteristic of the PP composite with silylated MFC content 30wt% exhibiting a 69% lower viscosity (337Pas at 4.7s(-1)) than the neat PP at 180 degrees C. The same 30wt% silylated specimens gave a well-dispersed fibrous MFC in PP, providing a tensile modulus (3.09GPa) and a flexural modulus (3133MPa), which were 64 and 81% higher than the neat PP, and 16 and 15% higher than the untreated-MFC composites, respectively. The flexural strength and the heat distortion temperature were also increased by 10 and 22%, compared to neat PP, respectively. In the acetylation reaction, the fibril structure of MFC was damaged due to full substitution by acetyl groups, and the reinforcing effect was insignificant as a filler in PP matrix. The developed silylated-MFC/PP composites provided excellent mechanical properties and high-loading processability that would be difficult to achieve by other eco-friendly composite systems. [GRAPHICS] .

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