Effects of Plasticizers on the Surface Structure and Properties of Cellulose Membranes (2)

2.3 Infrared Analysis

The infrared spectrum of the regenerated fiber membrane and the plasticized membrane is shown in Figure 2. From the IR of the regenerated cellulose membrane, it can be seen that the plasticized cellulose membrane and the unplasticized cellulose membrane are significantly different at about 2900 cm, which is due to the vibration absorption of methyl and methine groups. After washing, the concentration of glycerol in the fiber membrane is significantly reduced. Glycerol has a good plasticizing effect, but it has a large water solubility. When the regenerated cellulose membrane is exposed to water, glycerol dissolves into the water rapidly, and the plasticizing effect deteriorates.


3 Results and Discussion

Cellulose is a long-chain macromolecule composed of glucosyl groups. Each base ring has two secondary hydroxyl groups and a primary hydroxyl group. The cellulose supramolecular structure theory generally believes that cellulose is a crystalline and amorphous region intertwined. In one system, there is no clear boundary between crystalline and amorphous regions, and it gradually transitions. In the crystallization zone, the hydroxyl groups of the macromolecules mostly form hydrogen bonds between the molecular chains and the molecular chains, so that the cellulose has high stability, while the amorphous regions have a small amount of free hydroxyl groups that do not form hydrogen bonds.

When the cellulose membrane without plasticization loses moisture during drying, the water present at the edges of the amorphous and crystalline regions rapidly evaporates, and the macromolecules of the cellulose gradually move closer to each other under the influence of hydrogen bonds and van der Waals forces. The long chain of cellulose One or more layers of water molecules in the gap contact each other. As the moisture content further decreases, the hydrogen bonds directly formed between the cellulose molecules gradually increase, the intermolecular forces are greatly enhanced, and the large molecular chain internal rotation is generated. The increase in activation energy is required to make deformation difficult, and macroscopically exhibits the hard brittleness in the production and use of cellulose films. In order to reduce the visibility of the film and increase the flexibility and flexibility, the film needs to be plasticized. The glycerin plasticized cellulose membrane surface is smooth, glossy, and has good flexibility. Plasticizer can plasticize, the key is that its addition can reduce the interaction between macromolecule chains. Under this premise, the plasticizer has a principle, that is, polar plasticizer plasticized polar polymer, not Polar plasticizers plasticize non-polar polymers. The plasticization mechanism is to replace hydrogen bonds between some macromolecules by using hydrogen bonds formed between small molecules and macromolecules, destroying physical cross-linking points and hydrogen bonds that have formed between macromolecules, and enabling the movement of segments to be achieved. Increases fluidity between polymer segments. The smaller molecular weight glycerol and water are polar molecules that penetrate into the film and form new hydrogen bonds with the cellulose macromolecules. Instead of hydrogen bonds between some macromolecules, the number of hydrogen bonds between macromolecules is reduced, and the relative mobility between the chains is increased when external forces are applied, thereby changing the physicochemical properties of the cellulose membrane. The following conclusions are drawn from testing and analysis:

(1) The fibrous surface of the fibrous membrane of glycerol plasticized fiber is smooth, glossy, and has good flexibility; (2) the mechanical properties of the nitrocellulose plasticized cellulose film are deteriorated, and the elongation at break increases; (3) ) With the increase of plasticizing time, the rejection rate of the membrane becomes significantly larger, but the water flux does not change significantly; (4) After the plasticized membrane is washed with water, part of the glycerin is lost, and the plasticizing effect is deteriorated; (5) Glycerol It is not an ideal plasticizer for cellulose membranes.

4 Conclusion

Environmentally friendly materials are one of the key directions in the development of materials. In the field of film materials, no-wraps are packaging materials, agricultural plastic films, separation films, etc. Currently, plastic films that are not easily degraded are still commonly used. These synthetic polymer films cause severe white pollution to the environment. The cellulose film does not cause harm to the human body and the environment throughout the entire life cycle, and has become a trend in the field of film development. However, the method for plasticizing cellulose film is still glycerol solution. If the plasticized film is used for packaging foods, medicines, garbage, etc., it is exposed to moisture in the environment, glycerin is easily lost, the plasticizing effect is deteriorated, and the performance of the packaging film deteriorates. , may not play a very good protective effect on the contents. Therefore, finding a plasticizer with good effect becomes a key issue in the application of cellulose film.

Zeng Fengcai Wu Jun Beijing Institute of Graphic Arts Source: "Packaging Engineering"

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