Cellulose nanofibril/polypropylene composites prepared under elastic kneading conditions

• Published in: Cellulose (London) 2022-06, Vol.29 (9), p.4993-5006
• Main Authors: Niihara, Ken-ichi, Noguchi, Toru, Makise, Takahiko, Kashima, Wataru, Endo, Morinobu, Isogai, Akira
• Format: Article
• Language: English
• Subjects: Agglomeration; Aspect ratio; Bioorganic Chemistry; Cellulose; Ceramics; Chemistry; Chemistry and Materials Science; Composites; Coupling agents; Dispersion; Elongation; Glass; Glues; Maleic anhydride; Natural Materials; Organic Chemistry; Original Research; Physical Chemistry; Polymer matrix composites; Polymer Sciences; Polypropylene; Shear forces; Sheets; Storage modulus; Sustainable Development; Tensile properties; Yield stress
• ISSN: 0969-0239; 1572-882X
• DOI: 10.1007/s10570-022-04584-9

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 (DTMACl) with or without silane coupling agents. The mixture was heated at 40 °C for 1 d to prepare an oven-dried TEMPO-CNF/DEG/DTMACl, which was added to maleic anhydride-modified polypropylene (MA-PP) and kneaded at 165‒175 °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 °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 °C, although the crystallinities and melting behavior of MA-PP/PP in the composite sheets at ~ 160 °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 ~ 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. Graphical abstract