Bio based chemical fiber is a fiber made of biomass as raw material or polymers containing biomass derived monomers. The product has the properties of ecological environment protection, human affinity, bacteriostatic comfort, and biodegradable waste. It has been widely used in underwear, shirts, socks, home textiles and other products. The launch of the science popularization knowledge series of bio based fibers is to enable industry professionals and consumers to have a more comprehensive understanding of bio based fibers.

Oil is the main raw material of synthetic fiber. As a disposable resource, oil is facing the dilemma of increasingly depletion. At the same time, the traditional synthetic fiber is not easy to degrade, and the harm caused by "white pollution" has been highly concerned by people. In order to meet the needs of green environmental protection and sustainable development, research and development of new bio based chemical fibers has become a strategic plan of developed countries. In recent years, bio based fiber production technology has been emerging. Bio based fiber has been widely used in clothing, home textiles and other products.

What is bio based chemical fiber?

What are the varieties of bio based chemical fibers? What are the characteristics?

Are all bio based chemical fibers degradable?

……

Let's learn about it

All aspects of bio based chemical fiber.

1. What is bio based chemical fiber?

Bio based fiber refers to a fiber made from renewable organisms or biological extracts. Fiber produced from non renewable petrochemical resources such as coal and oil.

There are many kinds of bio based fibers. For the convenience of research and use, they can be classified from different angles:

1) According to biological properties, it can be divided into animal fiber, plant fiber and micro material fiber;

2) According to the industrial classification, it can be divided into agricultural by-product material fiber and marine by-product material fiber;

3) According to the production process, bio based fibers can be divided into three categories:

▲ bio based primary fiber, animal and plant fiber directly used after physical processing;

▲ bio based regenerated fiber, that is, the fiber made from natural animals and plants through physical or chemical methods into spinning solution, and then prepared through appropriate spinning process;

▲ bio based synthetic fiber is a fiber made of biomass as raw material, which is chemically prepared into high-purity monomers, then polymerized to obtain high molecular weight polymers, and then processed by appropriate spinning process.

Bio based regenerated fibers and bio based synthetic fibers are collectively referred to as bio based chemical fibers. So what is the difference between these two types of fibers? Bio based regenerated fiber does not change the original chemical structure of biomass macromolecules. The spinning process is the reconstruction of its physical form, which only changes the aggregate structure. The chemical and physical properties of bio based synthetic fibers depend on the monomer used, which is independent of the monomer source. In other words, synthetic fibers can be made of bio based monomers or petroleum based monomers, and the fibers made of the same monomers have the same performance. Bio based synthetic fiber emphasizes that its monomers are derived from organisms.

2. What are the characteristics of bio based chemical fiber?

Bio based chemical fiber has been considered as "green fiber", "ecological fiber" and "environmental fiber". What are the characteristics of bio based chemical fiber?

First, raw materials are by-products of plants and animals, which are renewable and can achieve sustainable development.

Secondly, bio based chemical fibers have a low carbon footprint: all or part of the carbon atoms contained in bio based chemical fibers come from biomass. Taking plant biomass as an example, plants absorb CO2 in the earth's atmosphere and synthesize new carbon containing natural macromolecules through photosynthesis. No matter whether it is biodegraded in the environment or converted to CO2 by combustion, it will not generate additional carbon emissions from the whole life cycle. Therefore, bio based chemical fiber has the characteristics of overall carbon reduction or no carbon increase.

Thirdly, most of the bio based chemical fibers can exhibit excellent biodegradability and biocompatibility: according to the specific chemical structure, some bio based chemical fibers can be degraded in compost, natural environment and organisms, and have good biocompatibility, which can be used in biomedical fields.

3. What is the relationship between bio based synthetic fiber and biodegradable fiber?

In recent years, with the global concern about the serious environmental pollution caused by traditional plastics and other difficult degradation in the natural environment, and the increasingly serious micro plastic pollution problem, the development of biodegradable plastics and fiber products has become particularly important. In particular, with the gradual implementation of the "plastic prohibition order" in various countries, some products with potential to cause micro plastic pollution will be banned. However, bio based chemical fiber mainly refers to its raw materials containing renewable plant biomass or animal biomass components, and biodegradable fiber can be derived from both bio based and petroleum based, so

Bio based synthetic fiber ≠ biodegradable fiber

Which bio based synthetic fibers are also biodegradable fibers?

Which biodegradable fibers are not bio based synthetic fibers?

Are petroleum based polymer materials or fibers biodegradable?

In order to answer these questions, we can divide polymer materials or fibers into four quadrants according to the source of raw materials and whether they can be biodegraded. The main categories are as follows:

▲ petroleum based, non biodegradable fiber (quadrant III):

Traditional petroleum based chemical fibers such as polyester, nylon, polypropylene and spandex are all in this quadrant. These fibers have high melting point, high crystallinity, regular molecular structure, excellent mechanical properties, and good resistance to hydrolysis and chemical corrosion, so they degrade very slowly in the natural environment. For example, in the natural environment, polyolefins can undergo thermal oxygen degradation when exposed to sunlight, but the degradation rate is extremely low. The proportion of low density polyethylene (LDPE) degraded into CO2 within 2.5 years is only 0.35%. Therefore, we generally consider this kind of fiber material as non biodegradable fiber.

▲ bio based and biodegradable fiber (quadrant I):

All bio based primary fibers (natural fibers) and bio based regenerated chemical fibers retain the polysaccharide or protein structure of natural biomass, so their fiber products have complete biodegradability similar to natural biomass. However, in the bio based synthetic fibers, such as polylactic acid (PLA) and polycaprolactone (PCL), mass loss, mechanical property degradation and mineralization into small molecules such as carbon dioxide and water can occur in composting and neutral enzyme degradation solution, so they have good biodegradability. From the whole life cycle analysis, such fibers are eco-friendly fiber materials.

▲ bio based but hardly biodegradable fibers (quadrant IV):

The biodegradability of polymer materials is a complex process, which is closely related to the chemical structure and properties of the materials themselves. Although some chemical fiber materials have bio based properties, their biodegradability is restricted due to their high crystallinity and excellent thermal properties, and they are difficult to degrade. For example:

(1) Bio based PTT fiber:

The diol monomer used in biological PTT polyester is bio 1,3-propanediol (PDO). PDO can be produced from grain by biological method. It is further prepared by direct esterification (direct reaction of terephthalic acid and PDO) or transesterification (transesterification reaction of dimethyl terephthalate and PDO). PTT fiber has better resilience, lower tensile modulus and higher elongation at break than other polyester fibers; It has good dyeing performance; Wrinkle carrying and soft feel. It is a new type of bio based fiber with international leading status in China in recent years. However, bio based PTT polyester fiber is close to polyester fiber and has no biodegradability. Its ecological advantage is that it can effectively reduce the carbon footprint of products, but it is difficult to degrade products through the natural environment after they are discarded.

(2) PEF (poly (ethylene furan dicarboxylate) fiber:

Similar to bio based PTT polyester fiber, PEF polyester fiber is prepared by using bio based binary carboxyl monomer, namely bio furan-2,5-dicarboxylic acid and ethylene glycol. Furan dicarboxylic acid can be prepared from natural biomass such as starch or cellulose by biological fermentation or chemical methods. PEF fiber is similar to polyester PET fiber and has a relatively close melting point and glass transition temperature. Although it is reported that PEF has certain biodegradability, its biodegradation rate is relatively slow. According to the current biodegradable compost standard, it is not a biodegradable fiber.

Other bio based fiber materials such as nylon 56 and bio based PDT fibers also belong to this category.

▲ petroleum based biodegradable polymer materials and fibers (quadrant II):

As mentioned above, the biodegradability of polymer materials is a relatively complex process, which is closely related to the chemical structure and properties of the materials themselves. Although some chemical fiber materials are mainly derived from petroleum based materials, due to their flexible molecular chain structure, ester bonds are easy to be hydrolyzed and degraded by microorganisms or biological enzymes, they exhibit good biodegradability, such as:

Dimethyl oxalate (DMO), an important compound of PGA (polyacetyl alcohol), is prepared from coal by hydrogenation, hydrolysis and polymerization. Although PGA is made from coal, its biodegradability is very good, and it can be completely degraded within 1-3 months. The degradation products are water and carbon dioxide, which are completely non-toxic and harmless. It is often used for absorbable surgical sutures, with high biodegradability and biocompatibility. PGLA (polyglycolide) is prepared by copolymerizing 9 parts of glycolide (PGA) and 1 part of lactide (PLA) in a certain proportion. If lactide is prepared by biological method, PGLA can be called bio based and biodegradable fiber. PGLA has high tensile strength, good biocompatibility and biodegradability, and is also commonly used in absorbable surgical sutures.

Others such as PBAT and PBST are also mainly derived from petroleum. PBAT and PBST are prepared by copolymerization of butylene adipate (PBA), butylene succinate (PBA) and butylene terephthalate (PBT), respectively. Their material properties have the properties of PBA and PBT, with good elongation at break, ductility, heat resistance and impact performance, and excellent biodegradability. The application of fiber is still in the development stage to be used as agricultural film and other film materials.

4. How is bio based chemical fiber processed?

The traditional bio based primary fiber, that is, natural fiber, is represented by cotton fiber and mulberry silk. The history of producing cotton fiber and mulberry silk textiles in China has lasted for thousands of years. "Silk and satin" is used to describe the exquisite and high-grade quality of silk fiber textiles. In ancient times, it was a symbol of power and wealth. The production of cotton fiber and mulberry silk mainly takes cotton and silk as raw materials and is mainly prepared by various physical means. In the early days of liberation, the manual "elastic cotton" which was widely used by the people was the process of physically classifying cottonseeds and cotton fibers and further processing them into fiber products.

So, how is the current bio based chemical fiber processed and prepared from biomass?

(1) Processing process of bio based regenerated fiber

Taking regenerated cellulose fiber as an example, the processing process can be generally divided into two processes: pretreatment of cellulose raw materials and fiber molding:

Pretreatment and processing of cellulose raw materials: the cellulose from the raw materials cannot be directly used, and it can be used to prepare fibers only after purification treatment. The purpose of purification treatment is to remove lignin, hemicellulose and other substances in the raw materials, and then make them into pulp (pulping process). The commonly used treatment methods are chemical treatment, most of which are acid-base hydrolysis. However, this treatment method does great harm to the environment. Many new treatment methods have been gradually developed, such as biological treatment (using fungi and bacteria to remove lignin, cutin and other substances), enzyme treatment, physical treatment (using mechanical force, high-energy radiation, microwave treatment), steam explosion, etc.

At the beginning, the cellulose needed for fiber production mainly came from cotton and wood. However, due to the limitation of arable land and forestry resources in China, the source of raw materials began to transfer to other renewable resources in China, such as bamboo, hemp, banana, sugar cane, etc., especially some agricultural and sideline products, such as bagasse, crop stalks, coconut shells, etc. using these agricultural and sideline products as fiber raw materials can realize the transformation of waste into treasure, Reducing the product cost provides a broad possibility for expanding the output.

Fiber forming processing: after the pretreatment of fiber raw materials, the next step is fiber forming processing. The industrialized spinning technology is solution spinning, of which the most typical are viscose method and direct solvent method.

Viscose method is the most widely used cellulose fiber production method. First, the cellulose is treated with strong alkali to produce alkali cellulose, and then it reacts with carbon disulfide to obtain sodium cellulose sulfonate. Then, the derivative is dissolved in strong alkali to make viscose (spinning solution). The spinning solution is pressed into a coagulation bath composed of sulfuric acid, sodium sulfate and a small amount of zinc sulfate from the fine holes of the nozzle to solidify and regenerate. After stretching, artificial fibers are obtained. The production process includes complex chemical reactions, long process flow and low production efficiency. It also produces waste gas such as CS2 and H2S, waste water containing acid, alkali and Zn2 +, sludge containing CaO, Al2O3, MgO and Fe2O3, and consumes a lot of energy such as water, electricity and coal.

The representative of direct solvent method is the development of new solvent system represented by N-methylmorpholine-N-oxide (NMMO). The NMMO production process is a process of preparing cellulose fiber without chemical reaction. Firstly, the pulp and NMMO containing crystal water are fully mixed and swelled, then most of the crystal water is removed under reduced pressure and dissolved to form a stable, transparent and viscous spinning stock. After filtration and defoaming, the fiber is spun. It has the advantages of short process flow, low pollution and good solubility. The regenerated cellulose fiber produced by NMMO method is called "Lyocell fiber", which is known as the green fiber of the 21st century.

It can be seen from the above that the solvent method can omit a series of chemical treatment processes, shorten the production process and reduce pollution. At present, researchers at home and abroad are working on the development of other solvent systems.

Other solvents include ionic liquids and low-temperature alkali / urea system, among which low-temperature alkali / urea system is a cellulose dissolution system independently developed by China.

The research on the clean processing technology of cellulose fiber also includes the melt spinning method of cellulose ester, that is, the fiber raw material is prepared by derivatization of biomass raw material and then melt spinning. However, due to the complex chemical structure of natural biomass raw materials, including multiple hydroxyl functional groups, it is prone to high-temperature degradation. Although the process has been reported, it has not yet formed a commodity.

(2) Processing process of bio based synthetic fiber

The processing process of bio based synthetic fibers is similar to that of traditional polyester, nylon and other fibers. The chips are mainly prepared by melt polymerization, and then the fibers are prepared by melt spinning. With the further development of the process, melt direct spinning process can also be developed.

Taking polylactic acid as an example, the monomer of polylactic acid is lactic acid, or lactide prepared by dimerization and cyclization of lactic acid can be obtained by biological fermentation from corn, potato, beet and other crops. The output of these crops in China is very large, so the development potential of polylactic acid fiber in China is great. Polylactic acid chips are produced by two-step method. Firstly, lactic acid is polycondensated into oligomer, and then lactide is prepared under the action of catalyst. Then, after distillation and purification in vacuum, polylactic acid is prepared by catalytic ring opening polycondensation. By further using chips and melt spinning process, polylactic acid fibers of various specifications can be prepared for downstream market application. The processing process of bio based synthetic fiber is similar to that of traditional polyester, nylon and other fibers. The chips are prepared by polymerization and then the fibers are prepared by melt spinning. With the further development of the process, melt direct spinning process can also be developed.