Cellulose nanofibril/polypropylene composites prepared under elastic kneading conditions

An aqueous dispersion of 2,2,6,6,-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibrils (TEMPO-CNFs) was mixed with diethylene glycol (DEG) and dodecyltrimethylammonium chloride (DTMAC1) with or without silane coupling agents. The mixture was heated at 40 degrees C for 1 d to prepare an oven-dried TEMPO-CNF/DEG/DTMAC1, which was added to maleic anhydride-modified polypropylene (MA-PP) and kneaded at 165-175 degrees C with high shear forces to prepare TEMPO-CNF/MA-PP master batches. Various amounts of TEMPO-CNF/MA-PP master batch pieces were mixed with PP to prepare TEMPO-CNF/MA-PP/PP composite sheets. The yield stress and storage modulus at 25 degrees C of the composite sheets increased almost linearly with an increase in TEMPO-CNF content. However, the elongation at break decreased clearly with TEMPO-CNF content because of partial formation of TEMPO-CNF aggregates in the composites. The presence of TEMPO-CNFs restricted flow behavior of the MA-PP/PP components above 160 degrees C, although the crystal-linities and melting behavior of MA-PP/PP in the composite sheets at similar to 160 degrees C were unchanged. The apparent aspect ratios of TEMPO-CNF components in the composite sheets were 5-13 by partial aggregation of TEMPO-CNFs in the PP matrix, although the aspect ratio of the original TEMPO-CNFs dispersed in water was similar to 183. The aggregation behavior of TEMPO-CNFs in the PP matrix may have resulted in brittle tensile properties of the composite sheets. The TEMPO-CNF-containing PP sheets have better printability and adhesion performance between sheets using glues. These results indicate that the oven-dried TEMPO-CNFs can be used as fillers for improvement of mechanical, thermal, and printing properties of recycled and low-quality PP and for quantitative expansion of recycled PP. [GRAPHICS] .

Automated summary

An aqueous dispersion of TEMPO-CNFs was used to prepare TEMPO-CNF/MA-PP/PP composite sheets, which showed increased yield stress and storage modulus with increasing TEMPO-CNF content but decreased elongation at break. The presence of TEMPO-CNFs restricted the flow behavior of the MA-PP/PP components but did not affect the crystallinities and melting behavior of the composite sheets. Aggregation behavior of TEMPO-CNFs in the PP matrix may have resulted in brittle tensile properties of the composite sheets.