Fibre tessili artificiali - viscosa - parte 3

Summary

This script explores the fascinating journey of viscose, an artificial cellulose fiber derived from the canes of *Arundo donax*. It delves into its production process, from harvesting and transforming the canes into cellulose, to its chemical treatment and eventual spinning into thread. The video also highlights the historical significance of viscose production in Italy during the Fascist era, the materials used, and the chemical reactions involved. Additionally, it touches on other cellulose-derived fibers such as modal and cellophane, as well as the process of opacifying viscose for different applications.

Takeaways

• 😀 Viscose is the most successful artificial cellulosic fiber, widely used due to its low cost and versatile applications in clothing, furniture, and industrial purposes.
• 😀 The process of making viscose starts with harvesting and processing giant reed (Arundo donax) into cellulose, which undergoes multiple chemical treatments.
• 😀 The raw material for viscose production is high-quality cellulose, which is extracted primarily from cotton linters in the US and from wood or reed in Europe.
• 😀 The viscose production process involves turning cellulose into sodium cellulose, which is then treated with carbon disulfide to create cellulose xanthate.
• 😀 The cellulose xanthate is dissolved in sodium hydroxide to form a viscous solution that is filtered and extruded into filaments.
• 😀 These filaments solidify when immersed in a sulfuric acid bath, transforming into regenerated cellulose fibers.
• 😀 The viscose fibers are then treated, washed, and bleached before being wound into large spools or 'cakes'.
• 😀 Viscose fibers are highly hygroscopic and degrade at high temperatures, losing their strength and softening at 140°C and 200°C respectively.
• 😀 In terms of combustion, viscose behaves similarly to cotton, burning easily with a paper-like smell and leaving light ash.
• 😀 Modal is a variant of viscose that has higher crystallinity and improved mechanical properties, with higher tenacity and lower hygroscopicity.
• 😀 Cellophane, made from viscose, is a transparent sheet material obtained by compressing viscose and treating it with plasticizers to make it impermeable.
• 😀 To reduce the shine of viscose, opacifying agents like titanium dioxide (TiO2) or sodium carbonate can be added to create matte fibers.

Q & A

What is viscose and why is it the most successful artificial cellulose fiber on the market?

Viscose, also known as rayon viscose, is the most successful artificial cellulose fiber due to its low cost and versatility in various applications. It is used extensively in clothing, furniture, and industrial purposes, covering 80% of the artificial fiber production market.

What role does 'Arundo donax' play in the production of viscose?

Arundo donax, a plant commonly known as giant reed, is harvested and processed to extract cellulose for viscose production. The process involves boiling the plant, treating it with chemicals, and refining it into a cellulose paste before further processing into viscose fibers.

How is the transformation of cellulose into viscose fibers achieved?

The transformation of cellulose into viscose involves several chemical steps. Initially, cellulose is treated with sodium hydroxide to form sodium cellulose. Then, carbon disulfide is added, turning the sodium cellulose into cellulose xanthate, which is soluble in diluted sodium hydroxide. This solution is then extruded, coagulated, and solidified into fibers, which are further processed into viscose.

What are the primary differences between modal and viscose fibers?

Modal is a variant of viscose with improved properties. It is produced using a slower chemical process, which minimizes cellulose degradation, resulting in higher crystallinity and mechanical strength. Modal fibers have double the tensile strength and lower hygroscopicity compared to regular viscose fibers.

What are the applications of viscose beyond clothing?

In addition to its widespread use in clothing, viscose is also used in home furnishings, industrial products, and for various decorative purposes. Its versatility makes it suitable for many different industries.

How does the production of viscose relate to Italy's historical context during the fascist era?

During the fascist era, Italy faced shortages in raw materials, including cotton, due to trade restrictions. This led to the development of a process for producing cellulose from 'Arundo donax' to make viscose, which was crucial for Italy’s self-sufficiency in fiber production.

What are the key chemical processes involved in the production of viscose?

The key processes include the transformation of cellulose into sodium cellulose, followed by treatment with carbon disulfide to create cellulose xanthate. This is then dissolved in sodium hydroxide, filtered, and extruded through a spinneret, where it solidifies in an acidic bath to form solid fibers.

What physical properties distinguish viscose fibers from other cellulose fibers?

Viscose fibers are characterized by a smooth, shiny surface, and a cylindrical shape with deep grooves visible under a microscope. They are highly absorbent but have lower strength, particularly when wet. They also have a low melting point, softening at 140°C.

How does viscose behave when exposed to heat and flame?

Viscose behaves similarly to cotton when exposed to heat and flame. It burns easily with a bright flame, emits the odor of burning paper, and leaves a light, fluffy ash residue due to its cellulose content.

What is cellophane, and how is it produced?

Cellophane is a transparent film made from viscose, but instead of being extruded into fibers, it is processed into sheets. These sheets are then treated with plasticizers to make them impermeable and to improve their durability.