Effect of exfoliating agent on rheological behavior of β-chitin fibrils in aqueous suspensions and on mechanical properties of poly(acrylic acid)/β-chitin composites.

Chitin whiskers are promising reinforcing filler for composites due to their mechanical properties, renewable nature and low cost. A new method for preparation of β-chitin fibrils from squid pens in ascorbic acid aqueous solutions (AscA) was developed. Stirring of the solution with 2 g/l AscA for 2 h disperses the swollen chitin to individualized fibrils with an aspect ratio > 250. The optimal conditions of β-chitin exfoliation in acrylic acid (AcrA) aqueous solution were found (0.75-2 g/l, 3-4 h). TEMPO-oxidized β-chitin fibrils were chosen as a reference sample for comparison of different methods. 0.1% chitin suspensions exfoliated in AscA and AcrA solutions show similar gel-like behavior with a storage modulus (G') of 98 ± 23 and 34 ± 12 Pa, respectively, whereas G' of 0.1% dispersion of the TEMPO-oxidized β-chitin fibrils was 0.015 ± 0.005 Pa only. Composites based on poly(acrylic acid) comprising 1-3 wt% of β-chitin fibrils were fabricated by polymerization filling. Mechanical properties of the composites were investigated in dry state in the temperature range of 25-250 °C and at controlled relative humidity in the range from 53.6% to 100%. It was revealed that the maximum reinforcing effect is achieved at high temperature (>120 °C) and high relative humidity (≥75.3%RH).