Cellophane is made by turning opaque fiber pulp into a shiny film. There are generally two methods in production, viscose method and copper ammonium method, and their quality is basically similar.
The viscose method is similar to the viscose fiber (rayon) production method in the textile industry. Generally, the pulp is first treated with 17.5~18% sodium hydroxide solution (alkali immersion) to make the fiber swell. In the case of excessive alkali, the pulp is pressed out, broken into small pieces, and stored for a period of time (humidity adjustment). When the original long molecular chain is partially broken, treat it with carbon disulfide to obtain sodium cellulose xanthate, and then dissolve it in dilute sodium hydroxide solution to obtain orange-yellow mucus, then remove impurities by pressure filtration, and vacuum Take off the air. Store it for a while longer to "mature".
This viscous (glue) liquid is squeezed out of a slit and passed through an acid bath (composed of sulfuric acid, sodium sulfate, zinc sulfate, etc.) to form a film. There are two stages in the formation of fiber membrane, that is, coagulation occurs after the viscose enters the acid, and then the so-called regeneration occurs (the name of the so-called regenerated fiber comes from this). The sodium cellulose xanthate complex is broken to obtain cellulose and a certain amount of simple compounds. At this time, the film produced is dark yellow and opaque, and then it is treated with different chemical solutions to remove impurities, and then bleached. If the film is dried at this time, its properties are too brittle and unsuitable for printing, so it must be softened or plasticized with a hygroscopic substance (such as glycerin, ethylene glycol, urea, etc.), and then dried. In other words, make the moisture content between 7 and 10%.
