Prehydrolyzed Cellulose as Reinforcing Filler for Thermoplastics

Abstract

Abstract This paper presents the results of an experimental study of the mechanical properties of composites consisting of prehydrolyzed cellulose and thermoplastic matrices. The main feature of prehydrolyzed cellulose fibres is a high degree of brittleness, permitting the fibres to be finely comminuted in the shear field of normal compounding and processing machinery. Such an effect can be anticipated to improve the homogeneity and the mechanical parameters of the moulded samples. In the present work, this has been demonstrated with PP, HDPE and PS containing varying amounts of prehydrolyzed cellulose of different origin (bleached pulps). The tests were done on injection moulded samples. The compounding method (Buss-Kneader vs. twin-screw extruder) had only minor influence on the results. Theoretical assessment of the modulus values using the Tsai–Halpin equation gave somewhat lower values than those recorded on experimental samples. This was interpreted in terms of the disintegration of the cellulose component into submicroscopic fibrillar entities, so-called microfibrils, with a high aspect ratio and high modulus and strength values. In another series of experiments suspensions of microfibrillar cellulose in water were prepared by intense mechanical treatment of prehydrolyzed cellulose. This fibrillar material was then incorporated into a thermoplastic matrix either directly by mixing with a latex (PVAC, PS), or after drying (freeze drying, solvent exchange (PP)). Contrary to what could be anticipated, the modulus and strength values of the composites obtained were inferior to those recorded with the composites prepared by conventional compounding of prehydrolyzed cellulose with the matrix material and subsequent injection moulding. This is interpreted in terms of excessive agglomeration of the fibrils resulting in a loss of the original aspect ratio. The data obtained support the concept that cellulose has a significant potential, hitherto largely unexploited, as a reinforcing filler.