Determination of the lignin content of flax fiber with the acetyl bromide-ultraviolet visible spectrophotometry method

The conventional Klason lignin (KL) method has some shortcomings in the determination of lignin content, such as large sample consumption, long analysis time, and a large number of errors. Therefore, a rapid and accurate method for lignin content determination was studied. In this paper, flax fibers in three forms, namely, flax raw, flax noil and flax rove, were selected for the study, and the acetyl bromide-ultraviolet spectrophotometric lignin (ABUL) method was optimized for quantitative testing of the lignin content in flax fibers. The effect of acetyl bromide concentration, perchloric acid dosage, reaction temperature, and reaction time on the absorbance value was tested systematically. The test results indicated that the maximum characteristic absorption peak of lignin in flax fiber was determined at 276 nm. The optimized reaction conditions were as follows: acetyl bromide concentration of 35%, perchloric acid dosage of 0.3 mL, reaction temperature of 70°C, and reaction time of 80 min. The standard curve of the ABUL method was y = 23.75714 x – 0.00636, R 2 = 0.99913. By comparing the lignin content of flax fiber tested by the KL method and the ABUL method, it was found that the lignin content of flax raw, flax noil, and flax rove tested by the ABUL method was higher than that of the KL method. In addition, the ABUL method has the advantages of simplicity, rapidity, accuracy, and small sample consumption compared with the KL method.