Hydrophilic modification of cellulose using sulfamic acid for optical fiber humidity sensor fabrication

Cellulose as a moisture sensing material had been successfully used in preparation of fiber optic relative humidity sensors (FORHSs) to monitor the humidity of external environment. However, the sensitivity of cellulose to humidity response needs to be further improved. Based on it, sulfamic acid esterified cellulose (SAEC) was fabricated to be a moisture sensitive material for FORHS preparation. The produced SAEC exhibited a good hygroscopicity and dehumidification stability (the standard deviation of weight changes, σ = 0.0035) and high moisture absorption (121% of its own weight). After coating the SAEC hydrogel on the end face of optical fiber, a FORHS was fabricated and its humidity response performance and stability were measured. The results showed that the FORHS displayed a relatively high humidity response (the interference fringe contrast, 3.84 dB), small humidity hysteresis error ( r H = ± 0.07%), high sensitivity (0.16 dB/%RH), and a good stability ( R 2 = 0.9642, the confidence factor) within a relative humidity (RH) range from 45 to 80% and a temperature range between 25 and 45 °C. Therefore, this study provided a new preparation method of FORHS based on biomass material. Graphical abstract