Producing nanofibres from natural fibers

Natural materials such as spider silk, collagen and cotton could be a cheap and abundant source of materials for nanofibers, according to Chinese and American scientists.

Xi-Qiao Feng (Tsinghua University, Beijing) and colleagues at Brown University (Providence, USA) have shown that nanofibers with diameters from 25 to 100 nm can be extracted from material sources. This nature by ultrasound technique. This simple technique can even be deployed on an industrial scale.

Nanofiber materials can be used in many applications such as biotechnology, nanocomposite (nanocomposite materials), nanoscale components, being produced by various techniques such as electrospinning. ), photolithography, a technique for molecular self-assembly. However, certain materials have already contained nanofibers. For example, spider silk, silk of worms contains tens of thousands of nanofibers with a diameter of about 30 nm and Feng and colleagues succeeded in extracting them with ultrasound (20 kHz frequency). .

Initially, the researchers dipped about 0.05 g (50 mg) of spider silk into 100 ml of water. Next, they placed this mixture into an ultrasonic transmitter that normally contained an ultrasound transmitter and held for 45 minutes at a capacity of 900 to 1000 W. After the ultrasonic mixing, the mixture was made cold to room temperature and recover the fibers gathered at the bottom of the tank. This method is carried out simultaneously on both other types of fibers such as deep cocoons, collagen in fish scales, chitin fibers of shrimp, fish, or cellulose from bamboo, wood, hemp .

Figure 1. The separation of different natural fibers at the beginning of ultrasound.

Using the scanning electron microscope, Feng and colleagues observed that these natural materials separated themselves into fibers with diameters from 25 to 60 nm (see figure). Furthermore, the researchers found that the size of fibers from 20 nm to 100 nm can be controlled by changing the time and power of ultrasound.

The team believes that these nanofibers are produced by the foaming effect of sound waves. High-frequency sound waves when transmitted through the solution will create micro-bubbles, these bubbles gradually develop and "collapse" intensely. This collapse creates shock waves at the surface of natural fibers and cuts them along the length. Sound waves also effectively break down relatively weak transition layers in nanofibers, which are often linked together by Van der Waals interaction forces. The separation rate of the fibers depends on the frequency of the ultrasound, the intensity of the ultrasound.

Figure 2. Nano fibers formed.

The researchers say the technique has a relatively cheap price and is simple to create natural nanofibers and can easily mass-produce at large scale by increasing the supersonic. These natural nanofibers have many advantages over artificial fibers that are healthier, more supple and have better biocompatibility and biochemical hybridization. The group has just published results in Applied Physics Letter ( Appl. Phys. Lett. 90 073112, 2007 ).

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