Changes of hydrogen bonding and aggregation structure of cellulose fiber due to microwave-assisted alkali treatment and its impacts on the application as fluff pulp

The use of cellulose-based absorbing materials, such as fluff pulp, has attracted extensive attention due to the increasing demands of the hygiene products for the babies, women and seniors in a green and safe way. However, the properties of fluff pulp, mainly including the moisture adsorption and fluff-specific volume, highly depends on the aggregation structure and hydrogen bonding of the feedstock of cellulose fibers. In this study, a microwave-assisted alkali treatment was applied to improve these properties above, and the variations of the hydrogen bonding and aggregation structure of cellulose fiber under the microwave-assisted alkali treatment were investigated. The FTIR results showed that the microwave-assisted alkali treatment not only decreased the inter-molecular hydrogen bonding of inter-fibers, but also increased the intra-fibrillation of single fiber, thus improving the potential moisture adsorption and fluff-specific volume of the fluff pulp. The microwave irradiation facilitated the depolymerization and decrystallization of cellulose fiber during alkali treatment process, which can be confirmed by the decreases of the polymerization degree and crystalline index. The fluff pulp prepared from microwave-assisted alkali treated fiber exhibited higher absorption ability than that of those samples without microwave irradiation. A 10 wt% NaOH concentration in alkali treatment system was optimized to obtain a fluff pulp product with satisfactory fluff-specific volume and burst strength index. Microwave irradiation can be considered as a promising treatment method in the preparing process of cellulose based absorbing material.