Polylactic acid is a biodegradable material and one of the promising fiber materials in the 21st century. Polylactic acid (PLA) does not exist in nature and requires artificial synthesis. The raw material lactic acid is fermented from crops such as wheat, sugar beet, cassava, corn, and organic fertilizers. Polylactic acid fibers, also known as corn fibers, can be obtained by spinning.
The development of polylactic acid fibers
Lactic acid is found in yogurt. Later, scientists discovered that the acid produced by muscle movements in animals and humans is lactic acid. The invention of DuPont Corporation (the inventor of nylon) was the first to use lactic acid polymers to prepare polylactic acid polymer materials in the laboratory.
The research and development of polylactic acid fibers has a history of over half a century. Cyanamid, an American company, developed polylactic acid absorbable sutures in the 1960s. In 1989, Japan’s Zhong Fang and Shimadzu Manufacturing Institute collaborated to develop pure spun polylactic acid fiber (LactonTM) and its blend with natural fibers (Corn FiberTM), which was exhibited at the 1998 Nagano Winter Games; Unijica Corporation of Japan developed polylactic acid filament and spunbond nonwoven fabric (TerramacTM) in 2000. Cargill Dow Polymers (CDP) in the United States (now NatureWorks) released a series of products (IngeoTM) covering polylactic acid resins, fibers, and films in 2003, and licensed Trevira in Germany to produce the IngeoTM series of non-woven fabrics for use in fields such as automobiles, home textiles, and hygiene.
The process and application of polylactic acid fibers
At present, mainstream PLA non-woven fabrics are made from high optical purity L-polylactic acid (PLLA) as raw material, utilizing its high crystallinity and orientation characteristics, and prepared through different spinning processes (melt spinning, wet spinning, dry spinning, dry wet spinning, electrostatic spinning, etc.). Among them, melt spun polylactic acid fibers (long fibers, short fibers) can be used in the fields of clothing, home textiles, etc. The production equipment and process are similar to polyester, with good spinnability and moderate performance. After appropriate modification, polylactic acid fibers can achieve superior flame retardant (self extinguishing) and natural antibacterial properties. However, melt spun PLA fiber still has room for improvement in mechanical strength, high temperature dimensional stability, resilience and aging resistance.
Wet spinning, dry spinning, dry wet spinning, and electrospinning of polylactic acid fibers (membranes) are mainly used in the biomedical field. Representative products include high-strength absorbable sutures, drug carriers, anti adhesion membranes, artificial skin, tissue engineering scaffolds, etc.
With the increasing demand for disposable non-woven fabrics in medical, sanitary, filtration, decoration and other fields, polylactic acid non-woven fabrics have also become one of the research and development hotspots.
In the 1990s, the University of Tennessee in the United States first studied polylactic acid spunbond and melt blown nonwoven fabrics. Japan’s Zhongfang subsequently developed polylactic acid spunbond nonwoven fabrics for agricultural applications, while France’s Fibreweb company developed polylactic acid spunbond, melt blown nonwoven fabrics, and multi-layer composite structures (DepositaTM). Among them, the spunbond nonwoven fabric layer mainly provides mechanical support, while the melt blown nonwoven fabric layer and the spunbond nonwoven fabric layer jointly provide barrier, adsorption, filtration, and insulation effects.
Domestic Tongji University, Shanghai Tongjieliang Biomaterials Co., Ltd., Hengtian Changjiang Biomaterials Co., Ltd. and other units have successfully developed nonwoven fabrics such as spun viscose, spunlaced, hot rolled, hot air, etc. in the development of composite fibers for nonwovens and nonwoven products, which are used for disposable sanitary products such as sanitary napkins and diapers, as well as facial mask, tea bags, air and water filtering materials and other products.
Polylactic acid fiber has been widely promoted and applied in automotive interiors, cigarette bundles, and other areas due to its natural source, biodegradability, and environmental friendliness.
The characteristics of polylactic acid fibers
One of the highly acclaimed advantages of polylactic acid fibers is their ability to biodegrade or absorb in the body. Under standard composting conditions, biodegradability must be measured, and the degradation products are water and carbon dioxide. Conventional polylactic acid fibers hydrolyze slowly or even difficult to detect in normal use or most natural environments. For example, if buried in natural soil for a year, it basically does not degrade, but under normal temperature composting conditions, it degrades for about a week.
The degradation and absorption of polylactic acid fibers in vivo are greatly affected by their crystallinity. Simulation in vitro degradation experiments have shown that high crystallinity polylactic acid fibers still maintain their shape and nearly 80% strength after 5.3 years, and may take 40-50 years to fully degrade.
Innovation and expansion of polylactic acid fibers
As a chemical fiber variety that has been developed and produced for over half a century, the actual usage of polylactic acid fiber is still less than one thousandth of polyester fiber. Although the cost factor ranks first, its performance cannot be ignored. Modification is a way to develop polylactic acid fibers.
China is a major producer and consumer of chemical fibers, and in recent years, research on modified polylactic acid fibers has been given priority. Polylactic acid fibers can be blended with traditional natural “cotton, linen, and wool” to make machine woven and knitted fabrics with complementary performance, as well as with other chemical fibers such as spandex and PTT to make fabrics, reflecting skin friendly, breathable, and moisture wicking effects. They have been promoted in the field of underwear fabrics.
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Post time: Jun-11-2024