Cellulose fiber | properties, types, manufacturing process | advantages

Cellulose fiber

Cellulose fibers are fibers made from ethers or esters cellulose, obtained from tree bark, wood or leaves, or other plant-based materials. In addition to cellulose, fibers may also contain hemicellulose and lignin, a percentage of these elements altering the mechanical properties of fibers. The main applications of cellulose fibers are in the textile industry, as chemical filters, and as fiber-reinforcement composites, due to the similar properties of engineered fibers, another alternative to biocomposite and polymer composites.

Cellulose fiber properties

i. Cellulose fiber has good absorbency.

ii. It has a good conductor of heat.

iii. It has the ability to withstand high temperatures.

iv. It has a low resiliency.

v. It has a low loft, and good compressibility.

vi. It has a good conductor of electricity.

vii. These are heavy fibers.

viii. It is damaged by mineral acids, with minimal damage by organic acids.

Cellulose fiber chemical structure

Cellulose is a polymer made up of repeating glucose molecules that attach from end to end. A cellulose molecule can be several hundred to 10,000 glucose units long. Cellulose is similar in form to complex carbohydrates such as starch and glycogen. These polysaccharides are also made up of multiple subunits of glucose. The difference between cellulose and other complex carbohydrate molecules is how glucose molecules combine. In addition, cellulose is a straight-chain polymer, and each cellulose molecule is long and rod-like. It is different from starch, which is a coiled molecule. As a result of this difference in composition, cellulose cannot be broken down into its glucose subunits by an enzyme produced by animals compared to starch and other carbohydrates.

Cellulose fiber types

There are two types of Cellulose fiber, such as-

i. Natural cellulose fibers

Natural cellulose fibers originate from one of the three parts of a plant such as flowers or seeds, stems, or leaves, and are differentiated based on their origin. Seed fiber is the fiber that comes from the flower or seed of a plant; Bast fiber comes from the stems of plants. Cotton comes from the flowers of the cotton plant, which belongs to the genus Gossypium of the mallow family Malvaceae. Kapok is a seed fiber (like cotton) derived from the fruit of a tree. Poplar fiber is another type of seed fiber; They were brought to the attention of the public over the last decade by German scientists who declared it the Fiber of the Year in 2006 for its sustainable growth. Bast fibers such as flax, nettle, ramie, hemp, and jute have similar morphological properties and are therefore difficult to distinguish under a microscope.

ii. Manufactured/regenerated cellulose fibers

Regenerated cellulose is a class of materials that convert natural cellulose into soluble cellulosic derivatives and subsequent regeneration, usually forming a fiber or a film. Rayon is a general term for any regenerated cellulose fiber, including viscose, modal, and lyocell. The most common type of rayon is viscose rayon.

With the explosion of the world's population, the demand for textile materials has increased, as clothing is one of the basic needs of human beings. Thus, in addition to natural fibers, with limited resources, and since synthetic fibers harm the environment during their processing, cellulose fibers regenerated from cellulose have emerged as a great resource to meet the demands of the modern age. Based on the fiber requirements, regenerated cellulosic fibers are made by different methods to achieve the desired properties and on this basis, they are classified into different classes. Modern manufacturing methods and their evolution are dedicated to reducing problems with sustainability in all aspects. Huge amounts of research have been done to achieve the maximum output of regenerated fiber without compromising the environment and ecosystem while optimizing the process.

Cellulose fiber manufacturing process

To liberate cellulose fibers from wood, mechanical or chemical treatment must be applied. Wood treatment ​involves steam treatment before separation into fibrous material by refining or grinding capable of abrasion in the mechanical pulp. Chemical pulping is mainly based on chemical reactions and thermal energy to dissolve the lignin and other substances of plant material, then mechanical refining to separate the fibers. Both processes are mainly used to produce industrially fiber material, paper grade pulp which is reassembled as a structural network for paper making.

For cellulose shaping and production of cellulose derivatives, the high-purity pulp must be applied. Dissolved grade pulp represents a special pulp that is chemically refined by bleaching and is composed of more than 90% pure cellulose. The main processes for making dissolved pulp are the sulfite process (α-cellulose content is about 90-92%; α-cellulose is 17.5% insoluble in aqueous NaOH) and prehydrolysis Kraft pulp process (α-cellulose content up to 94-96%). Special alkaline treatment can even produce pulp up to 98% with α-cellulose content; alkali-soluble hemicelluloses are removed, i.e., alkali-soluble degraded cellulose and heteropolysaccharides such as degraded xylan and mannan. Cellulose obtained from wood is responsible for about 85-88% of dissolved pulp; The rest are cotton linters.

In the sulfite process, wood chips are treated with hydrogen sulfite (Ca₂ ⁺, Mg₂ ⁺, Na ⁺ or NH₄ ⁺ salts) and sulfur dioxide at high temperatures (cooking process) under pressure. The degree of de-lignification depends on the concentration of [H ⁺] × [HSO3^-], whereas [H ⁺] concentration affects the rate of cellulose hydrolysis. Cooking progress determines the composition of both binding SO₂ (HSO₃^-) and protons in equilibrium:

SO₂ + H₂O ↔ H₂SO₃ ↔ HSO₃^- + H⁺

Depending on the detailed condition, sulfonation of lignin (under acidic conditions) dissolves the biopolymer in the cooking liquor. Furthermore, hydrolysis of the link between lignin and carbohydrate and inter lignin bonds is performed although somewhat slower than sulfonation.

Cellulose fiber biodegradable

The biodegradability of cellulose fabrics was assessed using a soil burial test, an active sewage sludge test, and enzyme hydrolysis. Surface changes after biodegradation were observed by optical microscopy. From X-ray diffraction analysis (XRD), internal structures resulting from crystal changes and degradation were also investigated. It was shown that the biodegradability decreased in the following order: Rayon> Cotton ≫ Acetate. Rayon fiber, which has low crystallinity and a low degree of adaptation, shows the highest biodegradability in most cases. However, despite its low crystallinity, acetate fibers exhibited very low biodegradability, probably due to the presence of hydrophobic groups in their structure. Linen, on the other hand, showed an inconsistent behavior that it had the highest biodegradability in soil burial tests, but less biodegradability than cotton in the active sewage sludge test. XRD analysis showed that the crystallization of linen, cotton, and rayon fabrics increased slightly in the early stages, but then continued to decline. From the correlation analysis, it was revealed that the biodegradability of cellulose fabrics was closely related to the moisture recovery of the fibers, which at the same time reflected the hydrophilicity and internal structure of the fibers.

Cellulose fiber advantages

i. Cellulose fibers are known to possess special properties because they can absorb moisture. That's why it eliminates bacterial growth with respect to synthetic fabrics.

ii. Currently, fabrics made from cellulose fiber are hypoallergenic substances that, due to their ability to inhibit bacterial growth, cellulose fiber is used in the manufacture of medical clothing and cosmetics.

iii. In addition to being environmentally friendly and renewable, clothing articles based on cellulose fiber are unique and durable. In addition to the above advantages, garments made with cellulose fiber are smooth and soft.

iv. The ability of cellulose fibers to absorb moisture is much better than the quality of conventional cotton, so the fabric is suitable for everyday clothes.

v. Some cellulose fibers exhibit tensile strength which is higher than that of steel wire, although highly flexible, a highly desirable combination of properties. Ramie has the strongest plant fiber and is currently used to make parachutes and notes.