Compariosn of drying bacterial cellulose nanofiber film using jet drier, vaccuum oven and oven

Background and objectives
Bacterial cellulose nanofiber (BCN) with diameter size of 30 to 60 nm is naturally produced in film form. After purification, a semi-transparent film is prepared with water absorption of 99 folds its dry weight; hence it is classified as super absorbent material. The BCN film is completely bio-based and biodegradable, safe, edible material with high specific surface area, high mechanical and reinforcing properties. Based on these promising characteristics, it found wide variety of applications such as nanocomposite, aerogel and foam, filter, paper making, packaging, medical, biomedical, pharmaceutical, cosmetics, food, textile, agriculture, electronics, magnetics, aerospace, automotive, defence, building, etc. Based on the promising properties and wide variety of application, it is worth to research on removing the drawbacks of BCN film to develop its applications at industrial scale production. One of these important research topics is drying BCN film. Because, drying BCN film has several advantages including film lightening (99 fold), decrease in transportation cost, long term storage, increase in biological deterioration, simpler storage, increase in mechanical properties and developing area of applications. On the other hand, BCN film is super absorbent material because of high amount of available OH-groups and having 3-D network structure, which prepare high capillary forces. Because of these, removing water from this super absorbent nano-biopolymer needs high energy, time and cost compared to drying ordinary micro-scale cellulose fiber film like paper. This motivated us to compare different drying methods including jet drier, vacuum oven and oven to dry BCN film.
Materials and methods
Bacterial cellulose nanofiber film was prepared from Nano Novin Polymer Co. (Iran). After primary dewatering step, the BCN film was dried using jet drier, vacuum oven and oven at 50 ᵒC. The drying methods were evaluated and compared in regard to dewatering speed, minimum drying time and drying energy. Also, the dried BCN film were compared through physical and mechanical testing.

Results
Results showed that the primary dewatering could decrease the water content of BCN film by 50 wt%. The dewatering speed in jet drier was higher than that of vacuum oven and oven. The minimum drying time of jet drier, vacuum oven and oven was 10, 25 and 45 min, respectively. The corresponding values for energy consumption were 0.25, 0.67 and 1.1 KW/h, respectively. The BCN film dried in jet drier had higher wrinkle and less transparency compared to those dried in vacuum oven and oven. The density of dried BCN film in jet drier was slightly higher than those dried in vacuum oven and oven. Also, its tear and burst indexes were less than those of dried in other methods. Generally, jet drier with minimum drying time and less energy consumption could decrease the weight of BCN film 99 fold which can have several advantages to develop the commercialization of BCN film.