Abstract
TEMPO-oxidised cellulose fibres are often explored as nano-reinforcement for polymers. However, it is unclear whether micrometre-sized TEMPO-oxidised cellulose fibres also possess similar reinforcing potential. In this work, we report the mechanical response of polypropylene (PP) composites reinforced with TEMPO-oxidised cellulose (TOC) of different fibre widths. Micrometre-sized TOC fibres (TOCF) containing sodium carboxylate (TOCF-Na) and free hydroxyl (TOCF-H) groups, as well as nano-sized TOC nanofibrils (TOCN) were produced from dissolving pulp and incorporated into PP matrix via melt-extrusion. It was found that model PP composites containing micrometre-sized TOCF-Na and TOCF-H possessed the highest tensile modulus of up to 2.5 GPa; 40% improvement over neat PP and 30% increase over PP/TOCN composite. No significant differences in the tensile strength of PP/TOCF-Na and PP/TOCF-H composites were observed when compared to neat PP. The incorporation of nano-sized TOCN into PP however, led to a 6% decrease in tensile strength. Single-edge notched beam fracture toughness test further showed that PP/TOCN composite possessed the lowest fracture toughness of 2.52 MPa m1/2; a decrease of 18% over PP reinforced with micrometre-sized TOCF-Na and TOCF-H. Our study shows that micrometre-sized TOCFs serve as better reinforcement for polymers compared to nano-sized TOCN. This is attributed to the better dispersion of TOCF in the PP matrix. Furthermore, the presence of surface microfibrillation on TOCFs also enhanced the quality of the TOCF-PP interface through mechanical interlocking and local stiffening of the PP matrix.
Highlights
The publication of Chang and Robyt (1996), as well as the subsequently work by Isogai and Kato (1998) reported one of the first studies describing the selective oxidation of C6 hydroxyl groups of cellulose in water using catalytic amount of 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO), with sodium hypochlorite (NaClO) and sodium bromide (NaBr) as the regenerating oxidants
It was found that the incorporation of dissolving pulp and the micrometre-sized TEMPO-oxidised cellulose fibres (TOCF) into PP led to an improvement in the tensile modulus of the resulting PP/dissolving pulp and PP/TOCF composites by as much as 16% and 35%, respectively, over neat PP
Since wicking measurements showed that both dissolving pulp and TOCFs possessed similar cc, the better reinforcing effect of TOCFs can be attributed to the presence of surface microfibrillation on the fibre surface, which led to improved mechanical interlocking and local stiffening of the PP matrix around the fibres, improving the quality of the fibrematrix interface
Summary
The publication of Chang and Robyt (1996), as well as the subsequently work by Isogai and Kato (1998) reported one of the first studies describing the selective oxidation of C6 hydroxyl groups of cellulose in water using catalytic amount of 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO), with sodium hypochlorite (NaClO) and sodium bromide (NaBr) as the regenerating oxidants. This work discusses the thermal degradation properties and viscoelastic behaviour of the model (TEMPO-oxidised) cellulose reinforced PP composites. Thermal degradation behaviour of (TEMPO-oxidised) cellulose-reinforced PP composites
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