Preparation And Application Of Wood-based Anti-counterfeit Fluorescent Fibers

With the continuous technological development and rapid economic growth, there is an increasing demand of novel and green techniques in the anti-counterfeiting area. Cellulose, as the most abundant natural polymer on earth, is an almost inexhaustible raw material with renewability and biodegradability. In addition, benefiting from their unsurpassed quintessential physical and chemical properties, cellulose-based materials have been widely used for security applications.In this paper, different fluorescent fibers were prepared from natural plant fibers by two methods. In the first method, the fluorescent fiber was prepared by immersing the natural fiber into the fluorescent solution through a simple physical adsorption process. In another method, fibers with controllable aspect ratio were prepared from nanofibrillated cellulose(NFC) via a wet-extrusion process and followed by immersing the fibers into the fluorescent solution and alkylketene dimmer solution. Through physical adsorption and chemical modification, fibers can ultimately obtain both fluorescent and waterproof properties. Herein, the preparation techniques of two methods and the properties of fluorescent fibers were studied in detail. Furthermore, the morphology and fluorescence were characterized by optical microscopy, scanning electon microscopy, atomic force microscopy and laser scanning confocal microscopy. The papermaking performance of fluorescent fibers were also evaluated.1. After treated with fluorescent solution, northwood fiber showed a better fluorescence stability compared to orther cellulose resourses(eucalyptus, cotton and viscose fibers). It was also found that fluorescent agent can be well dissolved in dimethylformamide(DMF). The fluorescent intensity of fibers showed a marked increase as the concentration of fluorescent solution increased. Under the same concentration, however, no significant differences were observed in the fluorescent intensity of fibers that treated with different time. The most suitable condition of direct fluorescent treatment was as follows. northwood fibers were treated with 2.5%(w/w) DMF fluorescent solution at 50°C for 5min followed by hot-air drying.2. Optical microscopy was used to observe the surface morphology of fluorescent fibers, and it showed that no significant differences occurred with the fiber curl and kink index after fiber treated by fluorescent solution. Through scanning electon microscopy, atomic force microscopy, we demonstated that fluorescent agent formed a tight film wrapped around the fiber surface, forming a relatively strong bond after treated.3. The most suitable condition of fluorescent treatment to fibers prepared from nanocellulose was as follows: nanocellulose extruded into ethanol(coagulation bath) for 5mins, then dryed at 50°C by hot-air to obtain fibers, immersed the fibers in 2.5%(w/w) DMF fluorescent solution followed by hot-air drying at 50°C, then treated with 10.0%(w / w) AKD solution for 3s, dried with hot air at 100 ± 5°C, finally fibers with good fluorescence stability were prepared.4. The papermaking performance of fluorescent fibers prepared by two different methods was evaluated, it showed that they both had good dispersibilities in water and fluorescence stability. Observed under UV light, paper sheets with fluorescent fibers of two types emitted obvious red color, and the fluorescent fibers were distributed uniformly in the paper sheets.