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Abbreviation (ISO4): Prog Chem      Editor in chief: Jincai ZHAO

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Progress in Chemistry >

2025 , Vol. 37 >Issue 5: 698 - 714

DOI: https://doi.org/10.7536/PC240615

Review

Biodegradable Synthetic Fiber

  • Jizhi Ai ,
  • Siyuan Li ,
  • Change Wu ,
  • Shuanjin Wang , * ,
  • Yuezhong Meng
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  • The Key Laboratory of Low-carbon Chemistry & Energy Conservation of Guangdong Province/State Key Laboratory of Optoelectronic Materials and Technology，Sun Yat-sen University，Guangzhou 510275，China
*

Received date: 2024-06-25

  Revised date: 2024-12-31

  Online published: 2025-04-30

Supported by

National Natural Science Foundation of China(22179149)

Special Funds for Basic Scientific Research Operations of Central Universities(171gjc37)

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Abstract

The rapid development of biodegradable plastics manufactured by chemical and biological processes，including the use of enzymes and microorganisms，makes it possible to reduce "white pollution" in specific areas by substituting biodegradable plastics with non-biodegradable ones. One type of one-dimensional material is fiber material，which is created by processing regular material in a particular way. The use of biodegradable materials in textiles，bio-medicine，and fiber-reinforced composites is extremely important. This paper reviews the biodegradable mechanism of materials，methods of manufacturing for biodegradable synthetic fiber，research status，and composite materials made of biodegradable synthetic fiber. It also describes the spinning molding techniques of materials and explains the relationship that some biodegradable plastics have with conventional fiber molding techniques. The challenges and prospects in the development of biodegradable synthetic fiber materials are also pointed out.

Contents

1 Introduction

2 Biodegradable mechanism

3 Method for preparing biodegradable synthetic fibers

3.1 Melt spinning

3.2 Solvent spinning

3.3 Electrostatic spinning

3.4 Centrifugal spinning

4 Research status of biodegradable synthetic fibers

4.1 PLA fiber

4.2 PGA fiber

4.3 PHA fiber

4.4 PBAT fiber

4.5 PCL fiber

4.6 PBS fiber

5 Biodegradable fiber composite materials

6 Conclusion and outlook

Key words： biodegradable; fiber; spinning; composite material

Cite this article

Jizhi Ai , Siyuan Li , Change Wu , Shuanjin Wang , Yuezhong Meng . Biodegradable Synthetic Fiber[J]. Progress in Chemistry, 2025 , 37(5) : 698 -714 . DOI: 10.7536/PC240615

1 Introduction

Fiber materials are a class of materials composed of continuous or discontinuous fine filaments obtained by special processing of ordinary materials, and have become an indispensable part of daily life[1]. The structure of solid substances can be simple or complex; for example, uniform and simple structured materials such as glass, metal, and plastic are usually man-made. Among them, the structure of fiber is quite complex, composed of basic structural units stacked and mixed at several hierarchical levels, which determines the properties of the fiber. Orientation refers to the degree to which macromolecules align with the fiber axis direction, and it is the key factor that gives fiber materials their unique properties. Compared to general materials, fiber materials possess various performance advantages due to their highly oriented structures. For instance, when fibers have a high orientation degree, the tensile strength along the molecular chain orientation direction is generally higher, while their elongation capability is lower. However, in the direction perpendicular to the molecular chain alignment, the strength is relatively low, making them more susceptible to damage. In addition, fiber materials can also serve as filling materials to reinforce other matrices. Fiber fillers can effectively improve the strength and stiffness of plastics. In the reinforced composites formed by the combination of both, fibers bear significant load stress, and the matrix resin transfers the external load to the supporting fibers through shear stress on the fiber interface, thereby greatly enhancing the plastic material. According to the morphological structural characteristics of chemical fibers, they are usually divided into two major categories: filament and staple fiber. Filament chemical fibers can be further classified into monofilament, multifilament, twisted yarn, cabled yarn, tire cord yarn, and textured yarn, with different types determined by distinct processing methods. For example, textured yarn is a kind of long filament whose original chemical fiber yarn has been subjected to texturing processes, giving it crimped, helical, or looped appearances, thus exhibiting bulkiness and elasticity. However, if chemical fiber products are cut into lengths ranging from several centimeters to dozens of centimeters, these fibers are referred to as staple fibers. Depending on the cutting length, staple fibers can be categorized into cotton-type, wool-type, and medium-length-type fibers. Cotton-type fibers have a length of 30-40 mm and a linear density of approximately 1.67 dtex, being finer and similar to cotton. Wool-type fibers have a length of 70-150 mm and a linear density of 3.3-7.7 dtex, being coarser and resembling wool. Medium-length fibers range from 51-65 mm in length with a linear density of 2.2-3.3 dtex, falling between cotton-type and wool-type fibers in terms of both fineness and length. Chemical filament fibers have found extensive applications across various fields of the national economy (e.g., textile, industrial, and medical fields), whereas staple fibers are primarily used for spinning into yarns, filling applications, and nonwoven production[2-3].
Fiber materials can be divided into biodegradable and non-biodegradable fibers according to their degradation properties. Common non-biodegradable fibers include polyester, nylon, acrylic, vinylon, and polypropylene. These fibers have advantages in tensile strength, elastic modulus, and elongation at break that are unmatched by biodegradable fibers. In addition, each has its own characteristics: for example, polyester fibers possess high molecular crystallinity and orientation, good elasticity, resistance to wrinkling, shape retention, lightfastness, thermal stability, and quick-drying and wrinkle-free properties after washing; nylon fibers have a smooth longitudinal surface and excellent durability, as well as good water- and wind-resistant performance; acrylic fibers exhibit unique thermal extension properties, a soft and full hand feel, ease of dyeing, and vibrant colors. However, non-biodegradable fibers cause irreversible harm to the environment, so biodegradable fibers have gradually become a research and development focus[4]. Biodegradable fibers can be categorized into natural and synthetic fibers based on their primary components. Currently studied biodegradable fibers mainly include cellulose, chitin, starch, protein, polylactic acid (PLA), polybutylene succinate (PBS), polyglycolic acid (PGA), and poly(butylene adipate-co-terephthalate) (PBAT) fibers, among which only cellulose, starch, and PLA fibers have achieved large-scale commercial applications. Natural fibers are fibrous materials existing and growing in nature with textile value and represent one of the important sources of textile industry raw materials. Biodegradable natural fibers can be classified primarily by composition into cellulose fibers, chitin fibers, starch fibers, and protein fibers. Among these, cellulose is one of the most abundant natural polymers on Earth. Due to its stereoregular syndiotactic polymer structure and highly ordered molecular and supramolecular architecture, cellulose fibers not only have a large specific surface area and inherent hydrophilicity but also demonstrate high strength, toughness, and strong acid- and alkali-resistance, offering numerous advantages. Therefore, cellulose and its derivatives in fibrous form find diverse applications (Figure 1), such as in food packaging, drug delivery, biomedical materials, sensors, and filtration membranes[5]. Additionally, chitin, starch, and protein fibers are also widely used in food packaging and biomedical fields. However, natural fibers do not process well and cannot be melt-spun; most are obtained via solution spinning or electrospinning[6-8]. Despite their advantages, natural fibers alone cannot meet all societal needs, making biodegradable synthetic fibers indispensable. For instance, the wide application of PLA synthetic fiber is attributed to its good moisture absorption, thermal insulation, flame retardancy, antibacterial properties, and resilience, with sufficient strength for practical use, although its insufficient toughness limits its applications. Other biodegradable fibers are also limited due to deficiencies in various performance aspects—for example, PBAT fibers lack sufficient strength, while PGA degrades too rapidly. Moreover, PBS fibers are considered to have great commercial potential because they outperform PLA in mechanical and thermal properties, and offer better processability and biodegradability[9].
图1 纤维素的各种应用[5]

Fig.1 Various applications of cellulose[5]

This article not only explains the biodegradation mechanism, but also discusses research on the production of fibers from various biodegradable plastics currently available in the market. It summarizes the existing methods for manufacturing fibers, highlighting that different biodegradable plastics require distinct spinning techniques due to variations in their properties. Furthermore, by combining polymer matrices with biodegradable fibers to form fiber-reinforced composites, the application range of fibers can be expanded. Current research primarily focuses on natural fiber-reinforced composites.

2 Biodegradation Mechanism

Polymer biodegradation is described as the deterioration of its physical and chemical properties and a reduction in molecular weight under the influence of microorganisms in aerobic and anaerobic environments, assisted by abiotic chemical reactions such as photodegradation, oxidation, and hydrolysis, leading to the formation of CO2, H2O, and CH4 as well as other low molecular weight products[10-11]. Most importantly, biodegradation often involves microbial enzymes and metabolic activities that break down polymers through biological means. However, in reality, polymer biodegradation results from the synergistic action of both biological and abiotic factors in nature. When biodegradable polymers are exposed to outdoor conditions (e.g., weathering, aging, or burial), they are affected by mechanical, chemical, light, and thermal influences, causing more or less change. These abiotic effects help initiate the biodegradation process[12].
At present, there are three main biodegradation mechanisms of biodegradable polymers: (1) Physical degradation: the polymer is destroyed due to cell growth after being eroded by microorganisms; (2) Chemical biodegradation: polymer chains are corroded and depolymerized under the direct action of microbial enzymes. Polymer biodegradation is catalyzed by microbial enzymes and includes four main stages: i) biodeterioration[13], ii) biofragmentation[14], iii) assimilation[15], and iv) mineralization[16] (Figure 2); (3) The interaction between microorganisms and polymers forms new macromolecules. Polymer degradation usually does not occur through a single mechanism but rather through a complex combination of biophysical, biochemical, and physicochemical mechanisms. Enzymatic action also plays a key role in the biodegradation process. When active enzymes from microorganisms are secreted and penetrate into the active sites of the polymer chains, hydrolysis reactions occur on the macromolecular chains, potentially breaking them into shorter chains or smaller molecules. Research findings indicate that microbial enzymes tend to break down polymer structures such as amide, enamine, ester, urea, and urethane bonds[17].
图2 微生物降解生物塑料的机理综述[18]

Fig.2 Review on mechanism of microbial degradation of bio-plastics[18]

In addition to biodegradation in the natural environment, degradable plastics can also degrade within the human body. The degradation process of biodegradable macromolecules in vivo mainly includes the following stages: initially, hydration occurs, where hydrogen bonds break under the influence of van der Waals forces, initiating the preliminary reaction. Under intermolecular forces, the macromolecules unfold and stretch, making the overall structure more susceptible to subsequent decomposition reactions. Next is loss of strength, wherein substances such as degrading enzymes secreted by decomposing bacteria cause the polymer chains to rupture, breaking the macromolecular chains into shorter segments, thereby reducing the material's strength. Finally, the polymers break down into smaller molecules; as crosslinking strength decreases, the polymer chains further fragment and decompose, ultimately producing harmless small molecules such as water and carbon dioxide. These small molecular products are either absorbed or excreted from the body through metabolic processes.

3 Preparation Method of Biodegradable Synthetic Fibers

3.1 Melt Spinning

Melt spinning is a forming method that uses polymer melt as raw material and is carried out using a melt spinning machine. Any polymer that can melt or transform into a viscous flow state upon heating without undergoing significant degradation can be spun by the melt spinning process. Melt spinning is also a widely used, sustainable, and cost-effective method for producing man-made fibers and filaments from thermoplastic polymers. This process (Fig. 3) involves feeding polymer pellets or powder into a single screw extruder, where they are melted and pressure-mixed. In some cases, masterbatch can be added through a side extruder for specific applications, such as dope-dyed yarns[19]. A melt metering pump ensures consistent throughput. The spinning assembly includes polymer filtration and distribution components along with spinnerets responsible for forming filaments with desired characteristics (e.g., number and cross-section). It is crucial to design the extrusion and spinning line in a way that prevents melt stagnation, which could lead to polymer degradation and intermittent discharge. After exiting the spinneret plate, the extruded melt filaments either directly enter a quench chamber or a water bath for solidification. The filaments are cooled and then drawn to induce or enhance crystallinity. Drawing performance can be improved by heated godet rolls or via hot plates or drawing ovens. Finally, the filaments are wound onto bobbins using a winder or collected as staple fibers.
图3 传统熔融-纺丝-拉拔-缠绕（SDW）试验线示意图[20]

Fig.3 Diagram of the traditional fusion-spinning-drawing-winding（SDW）test line[20]

Melt spinning imposes certain requirements on the melt strength, melt viscosity, and viscoelasticity of polymers. Generally, the polymer's melt strength is required to be around 0.1–1 N, and its melt viscosity should range between 100–1000 Pa·s. For polymers with lower melt strength, special attention must be paid to stretching conditions during spinning. Because low-melt-strength polymers are prone to breakage under stretching, the stretching speed should be appropriately reduced, while simultaneously considering an appropriate increase in melt temperature to enhance flowability, allowing the filament to stretch uniformly under lower stretching stress. For example, some low-molecular-weight polyesters require careful control of the draw ratio during melt spinning to prevent filament breakage. High-viscosity melts require higher pressure to pass through the spinneret during spinning; therefore, it is necessary to ensure that the pressure supply system of the spinning equipment meets the requirements. Additionally, to prevent excessive accumulation of the melt at the spinneret, the orifice diameter of the spinneret can be appropriately increased, and uniform temperature across the spinneret must be maintained to avoid local viscosity variations that may lead to uneven filament thickness. For low-viscosity melts, care must be taken to prevent excessive flow after extrusion from the spinneret, which could hinder proper shaping. This can be addressed by reducing the temperature or increasing the drafting device to control filament shape. Furthermore, there are specific requirements for the viscoelastic properties of the polymer. In general, within the frequency range typical of melt spinning (usually related to spinning speed and spinneret vibration frequency), the storage modulus G' should fall between 10–1000 Pa, and the loss modulus G'' should range from 5–500 Pa. Melts with stronger elasticity exhibit a certain degree of elastic recovery after extrusion through the spinneret. In the spinning process, an appropriate cooling zone can be set below the spinneret to allow the filament to initially set its shape within this region, thereby reducing elastic recovery. Meanwhile, the drafting process must account for the effects of elastic recovery. The draft ratio should be determined based on the elastic modulus of the melt to avoid excessive elastic deformation caused by over-drafting, which could negatively impact fiber quality.
Compared with other spinning methods (such as dry and wet spinning), melt spinning is considered a more economical and sustainable approach. During melt spinning, a higher draw ratio allows molecular chains of the fiber to align along the axial direction, thereby enhancing tensile strength, modulus, and elongation at break. For example, in melt spinning of polyester fibers, increasing the draw ratio enables macromolecular chains inside the fiber to fully extend and arrange orderly, resulting in significantly improved tensile strength. Dry and wet spinning operate at lower production speeds and involve the use of chemical solvents, which are environmentally unfriendly. Moreover, these methods can lead to surface pores and voids. Therefore, melt-spun fibers hold great potential to replace traditional fibers across various applications where biodegradability is important. However, challenges remain in melt spinning of biodegradable polymers, including low crystallization rates, thermal degradation, and limited processing temperature windows during extrusion that still need addressing. Recent studies have focused on melt spinning of these biodegradable polymers and characterization of the spun fibers. For instance, Nishimura et al.[21] obtained PLLA fibers with a tensile strength of 810 MPa through melt spinning combined with a two-step stretching process using a specific draw ratio in hot water. Even after being exposed to the environment for one year, the fiber surfaces remained smooth without significant reduction in tensile strength. Hydrolysis experiments indicated that the fibers were not prone to non-enzymatic hydrolysis after immersion in buffer solution at 37 °C for one month, but rapid hydrolysis occurred above 60 °C, highlighting the effectiveness beyond Tg. Scanning electron microscope observations revealed regularly spaced cracks perpendicular to the fiber axis, indicating the development of a highly ordered structure aligned with the fiber axis.

3.2 Solution Spinning

Solution spinning is a technique for preparing fibers, which forms fibrous materials by stretching and solidifying polymers or other active substances dissolved in a solvent. The principle of solution spinning can be simply summarized into three steps: dissolution, stretching, and solidification. First, the polymer or other active substance is dissolved in a solvent to form a uniform solution. The selection of solvent is very important; it must not only be compatible with the solute but also provide sufficient stretching and evaporation capabilities during the spinning process. For stretching, the solution is sprayed or stretched into fibrous form via methods such as spraying, electrospinning, or centrifugal spinning. In this step, the solution undergoes high shear forces, tensile forces, and evaporation, causing the bond energy between polymer chains to be disrupted and the molecules to rearrange. After stretching, the polymer chains are no longer ordered but exhibit a disorganized structural arrangement. Finally, the solidification process, also called fiber formation, occurs. Under the influence of solvent evaporation and temperature changes, the polymer in the solution begins to aggregate and crystallize, forming a fibrous structure. The speed and method of solidification directly affect the morphology and properties of the fiber. Solution spinning requires the viscosity of the spinning solution to be about 2-400 Pa·s. Depending on the curing method, solution spinning is divided into dry spinning and wet spinning. Dry spinning mainly forms fibers in hot air, while wet spinning involves precipitation through a coagulation bath to form fibers. Both have their own advantages and disadvantages. Dry spinning has low cost and simple operation, but during subsequent heat treatment processes, solvent volatilization or thermal decomposition may cause internal defects in the precursor fiber and adhesion between fibers, affecting the quality and application of the fiber product. However, wet-spun fibers have small variations in fineness, stable solidification shaping, low residual solvent content, and easier control of precursor fiber quality, but they require large amounts of solvent, making them less suitable for large-scale production from cost and environmental protection perspectives. Nevertheless, compared with melt spinning, both methods allow polymers to be uniformly dispersed in the solvent and can form more structurally uniform fibers during solidification shaping. This uniformity helps improve the overall performance of the fiber—for example, in solution spinning of cellulose fibers, it enables a more uniform distribution of tensile strength along the length of the fiber.
In recent years, with further in-depth research, new solution spinning methods for preparing nanofibers have also been developed. Solution blow spinning (SBS) is a novel technique for nanofiber preparation, originating from the combination of electrospinning and traditional melt-blown technology. The main theoretical basis of SBS nanofiber production involves the principle of high-speed airflow stretching and Bernoulli's principle. The working principle is illustrated in Figure 4. When the high-pressure airflow P1 exits the outer nozzle, its pressure drops to Patm, causing an increase in jet energy and gas velocity. This, in turn, reduces the central jet pressure P2, forming a driving force that accelerates the polymer solution (Figure 4b). The formation process of the solution jet is shown in Figure 4c. Additionally, the high-speed gas flow generates shear forces at the gas/solution interface, deforming droplets of the polymer solution into cones. Once these shear forces overcome the surface tension of the polymer solution, solution jets are produced. During flight (Figure 4d), the solvent rapidly evaporates, and finally, the polymer fibers deposit onto the collector[22]. Compared with electrospinning technology, SBS offers advantages such as higher productivity, shorter preparation time, and greater practical value. Moreover, a relatively larger number of polymers and spinning solutions can be used in SBS without requiring conductivity, thereby expanding the application scope of polymer solutions. Furthermore, no high-voltage electrostatic field is needed during the solution spinning process, making it relatively safer and less demanding on equipment. Compared with melt-blown technology, SBS provides more abundant raw material sources and broader material applicability, particularly suitable for some polymers that can dissolve in non-toxic and volatile solvents but are unsuitable for melt-blowing[23].
图4 （a）鼓收集示意图；（b）网纱集合示意图；（c）溶液射流的形成过程；（d）溶液射流的运动图象[24]

Fig. 4 （a）Drum collection diagram；（b）mesh collection diagram；（c）formation process of solution jet；（d）motion image of solution jet[24]

Solution spinning technology has a wide range of applications in many fields. In the field of nanotechnology, solution spinning can be used to prepare nanofiber films, nanofiber cell beds, and nanofiber adsorbents. These nanofiber materials possess high specific surface area and porous structures, enabling applications in catalysis, filtration, separation, and sensing. In the textile industry, solution spinning provides a new approach for the preparation of high-performance fibers and specialty functional textiles. By optimizing spinning conditions, fibers with special functionalities such as antistatic, antibacterial, and flame-retardant properties can be produced. Additionally, properties such as hydrophilicity, antimicrobial activity, and moisture absorption of textiles can be regulated through solution spinning techniques. Biomedical applications represent one of the most extensive areas for solution spinning technology. Solution spinning can be employed to fabricate three-dimensional scaffolds, artificial blood vessels, and controlled drug delivery systems. By adjusting the spinning process, the pore structure and crystallinity of the fibers can be controlled, endowing the scaffolds with excellent biocompatibility and biodegradability, thus promoting tissue regeneration and repair. In summary, solution spinning is an important technique for preparing nanofibers. It produces nanofiber materials with diverse morphologies and properties through steps including dissolution, stretching, and solidification. Solution spinning technology finds broad applications in nanotechnology, the textile industry, and biomedical fields, providing novel methods and pathways for research and applications across various domains.

3.3 Electrospinning

Due to the rapid demand for fiber applications, electrospinning has increasingly gained attention as an important technique for preparing micro- and nano-scale materials. Electrospinning is a process in which a polymer solution is stretched into nanofibers by applying a high-voltage electric field. Gilbert[29] proposed the concept of electrospinning as early as 1600, observing in a study that polymer solutions could form conical droplets under an electric field. In 1882, Taylor[30] published a series of groundbreaking papers, showing that as the electric field intensity increases to a critical level, spherical droplets gradually transform into cones (commonly known as "Taylor cones") and emit liquid jets. Taylor's discovery significantly accelerated the development of electrospinning. Recently, electrospun fibers have found new applications in soft electronic devices, biomedical engineering, energy harvesting, conversion, and storage[31-33]. Therefore, increasing attention has been focused on electrospinning composite and ceramic nanofibers using novel materials.
The schematic diagram of electrospinning for preparing nanofibers, as shown in Figure 5, includes strategies such as direct mixing, in situ growth, and inorganic NC assembly. The electrospinning setup generally consists of three components: a spinneret, a high-voltage power supply, and a collecting device[34]. Typically, the electrospinning process can be divided into the following four steps: (i) formation of a Taylor cone under the action of an electric field; (ii) linear extension of the charged jet under the electric field; (iii) thinning of the jet due to the electric field and increasing bending instability (also known as whipping instability); (iv) solidification of the jet into fibers, which are then collected on a grounded collector[35]. Among these steps, the formation of the Taylor cone is the most critical step, as it determines fiber quality and is closely related to the viscosity of the spinning solution. Generally, the viscosity of the polymer solution used in electrospinning should range between 1000 and 6000 Pa·s. Electrospinning also has various types, including solution electrospinning, melt electrospinning, near-field electrospinning, and derivative electrospinning techniques, each with its own advantages and disadvantages. Different electrospinning methods should be selected based on specific spinning conditions and materials.
图5 纳米纤维静电纺丝及其直接混合、原位生长和无机NCs组装示意图[36]

Fig.5 Diagram of nanofiber electrospinning and its direct mixing，in-situ growth and inorganic NCs assembly[36]

Electrospun fibers possess high specific surface area and porosity, which reduces the actual load-bearing area of the fibers and decreases their tensile strength to some extent. However, this unique structure provides advantages in applications such as adsorption and filtration, leading to extensive research. Specifically, electrospun nanofibers that are non-toxic, biocompatible, and biodegradable are considered promising candidates for biomedical applications[37-39], as they offer tunable properties including drug release, wound dressing, tissue engineering, and trauma repair. By direct mixing, Erick et al. incorporated Ag NPs into PCL electrospun nanofibers to enhance their antibacterial properties[40]. Qian et al.[41] developed a novel Ag-modified/collagen-coated electrospun PLGA/PCL scaffold (PP-pDA-Ag-COL) with improved antibacterial and osteogenic properties. The scaffold was fabricated by electrospinning a basic PLGA/PCL matrix, followed by in situ reduction, polydopamine coating, and collagen I impregnation to incorporate Ag NPs.

3.4 Centrifugal Spinning

Centrifugal spinning is an alternative method for producing nanofibers from various materials at high speed and low cost. In centrifugal spinning, the spinning fluid is placed in a rotating spinneret. When the rotational speed reaches a critical value, the centrifugal force overcomes the surface tension of the rotating fluid, ejecting liquid jets from the tip of the nozzle on the rotating head. Subsequently, the jets undergo a stretching process and finally deposit onto a collector, forming solidified nanofibers[42]. Centrifugal spinning is very simple, based on the same mechanism as a cotton candy machine (Fig. 6), enabling rapid fabrication of nanofibers for various applications. Compared to conventional methods for producing nanofibers, such as electrospinning, melt blowing, phase separation, and template synthesis, centrifugal spinning is a simple and scalable process that avoids the use of high voltage and can be used to produce nanofibers from many different materials for various applications. Additionally, its viscosity requirement is similar to that required for electrospinning polymer spinning solutions, ranging from 1000 to 8000 Pa·s.
图6 （a）由空心储层构成的离心纺丝装置；（b）通过离心纺丝、聚合物射流（i）引发、（ii）拉伸和（iii）溶剂蒸发形成纳米级纤维的机制[45]

Fig.6 （a）A centrifugal spinning device consisting of a hollow reservoir.（b）A mechanism for the formation of nanoscale fibers by centrifugal spinning，polymer jet（i）initiation，（ii）stretching，and（iii）solvent evaporation[45]

Centrifugal spinning has become a promising manufacturing method due to its advantages in low-cost, large-scale production of nanofibers. However, up to now, centrifugal spinning is still less popular than electrospinning. First, from the perspective of academic research, the setup of centrifugal spinning equipment is complicated, especially in selecting appropriate motors and spinneret geometries. Second, compared with electrospinning, centrifugal spinning typically uses polymer solutions with higher concentrations, resulting in slightly thicker fibers. Third, the fibrous mats collected from laboratory-scale centrifugal spinning setups are loosely packed; such loosely packed fibrous mats may be less desirable for certain applications when compared with densely packed fibrous mats prepared via electrospinning. Fourth, most centrifugally spun nanofibers reported currently are based on simple solid structures. Certainly, these issues will have corresponding solutions when centrifugal spinning is scaled up for industrial production. For example, the issue of loosely packed fibrous mats can be addressed through post-treatments after fiber collection, such as hot pressing and calendering.
Centrifugal spun nanofibers are generally applicable to the same applications as those fabricated by conventional nanofiber production methods. To date, the most studied application of centrifugal spun polymer nanofibers is tissue engineering. Compared with electrospinning, centrifugal spinning can produce reproducible and biocompatible three-dimensional scaffolds with large pore sizes, which enhances cell infiltration and structural integrity over time, thus enabling the development of biocomposite matrices for various tissue repair and replacement processes. Such 3D scaffolds have been used for cell infiltration, migration, adhesion, and growth[43]. Badrossamay et al.[44] prepared PLA nanofiber scaffolds using the centrifugal spinning method. To evaluate the feasibility of using centrifugal spun polylactic acid nanofibers as scaffolds for tissue engineering, they cultured chemically isolated neonatal rat ventricular cardiomyocytes on the prepared fibrous structures. The results showed that the cardiomyocytes spontaneously attached to and aligned along the fibers. Their work demonstrated that centrifugal spinning is a simple and convenient method for producing anisotropic, biodegradable nanofiber scaffolds.

4 Research Status of Biodegradable Synthetic Fibers

4.1 PLA Fiber

PLA is a biodegradable thermoplastic polymer that can be produced from renewable resources such as corn and sugar beets. Due to its excellent strength, modulus, and good processing properties, it has been widely applied in the fields of packaging, medical care, and agricultural production in recent years[46-47]. The chemical properties of polylactic acid involve the processing and polymerization of lactic acid monomers. Lactic acid HOCH3CHCOOH is a simple chiral molecule existing in two enantiomeric forms: L-lactic acid and D-lactic acid (see Figure 7). Polymerization of these two enantiomers subsequently results in three different types of polylactic acid: PLLA, PDLA, and PDLLA[48]. This conformational difference leads to variations in performance among the three. PLLA is a semi-crystalline polymer (favorable for spinning), characterized by high tensile strength, slow degradation rate, and poor toughness. PDLLA is an amorphous polymer with relatively low tensile strength, very fast degradation speed, and better toughness compared to PLLA. Due to synthesis process challenges, PDLA is difficult to obtain and exhibits unstable performance, making it less suitable for industrial applications.
图7 乳酸的光学异构体[49]

Fig.7 Optical isomers of lactic acid[49]

Among the biodegradable plastics that have been commercialized, polylactic acid (PLA) has the widest application and the highest demand. Currently, the global lactic acid industry mainly employs fermentation methods for production, yielding L-lactic acid. PLA is produced by ring-opening polymerization using L-lactic acid as the raw material, resulting in predominantly poly-L-lactic acid (PLLA). The lactic acid produced in the human body is L-lactic acid, and PLLA exhibits superior biocompatibility within the human body, allowing for biodegradation and absorption. Due to its advantages in easier industrial production and better biocompatibility, PLLA has become the dominant product in the global polylactic acid market, with PLA generally referring to PLLA in common market terms. However, PLA also presents several disadvantages. Firstly, PLA has relatively low fracture toughness, which limits its widespread application. Secondly, it possesses poor heat resistance, making it unsuitable for high-temperature applications such as food containers, household appliances, electronic products, and automotive components. Additionally, due to its high cost, PLA finds limited use in civil and industrial applications. Although PLA demonstrates good biocompatibility, it cannot fully meet all clinical requirements[50-51].
There are various methods for producing polylactic acid (PLA), including ring-opening polymerization, polycondensation, azeotropic dehydration, and enzymatic polymerization[52]. Among these methods, direct condensation of lactic acid and ring-opening polymerization are the most commonly used processes (Fig. 8). Cargill Dow LLC, the world's largest PLA manufacturer, has developed a low-cost continuous process for producing lactic acid-based polymers[53]. In this process, PLA synthesis occurs in the melt rather than in solution, and it is a closed-loop cycle (Fig. 9), thereby providing significant environmental and economic benefits. Initially, natural or renewable resources such as corn, sugar beets, potatoes, etc., are converted into glucose, which then produces lactic acid through a fermentation process. In the presence of a catalyst, lactic acid is converted into lactide. The molten lactide is further purified via vacuum distillation and subsequently converted into PLA through polymerization. Any remaining lactide monomer is recycled throughout the process.
图8 聚乳酸的合成[49]

Fig.8 Synthesis of polylactic acid[49]

图9 PLA的循环周期[54]

Fig.9 The cycle of PLA[54]

The conversion of PLA into textile structures is complicated, but due to its semi-crystalline structure, spinning is possible depending on the changes in its crystalline structure during processing. Producing monofilaments and multifilaments from polymers can be achieved through melt spinning, dry spinning, wet spinning, and dry-jet-wet spinning[55]. Each process has different characteristics that subsequently affect fiber properties. Due to PLA's thermoplastic nature, melting the polymer is feasible under appropriate conditions. Melt spinning typically offers advantages over solution spinning by being a solvent-free process, providing a more economical and environmentally friendly route, and generally enabling faster production speeds. However, melt spinning can sometimes be impractical either because the polymer degrades upon melting or because the melt lacks sufficient thermal stability. In dry spinning, the solvent is removed via flash evaporation, diffusion within the spin line, and mass transfer from the spin line surface to the surrounding medium; however, the resulting fibers may exhibit inferior quality with slightly porous and defective surfaces. In wet spinning, polymer solidification occurs in another fluid compatible with the spinning solvent but not itself a solvent for the polymer[56]. Fibers obtained this way have smooth surfaces and uniform texture, but this method consumes large amounts of solvent, leading to higher costs and environmental concerns.
Biodegradable textiles have attracted considerable interest in various fields of significant technological importance. The diversity of applications makes it possible for a single polymer to prove useful in many applications through simple modifications of its physicochemical structure. In many cases, polymers can be blended with other polymers or non-polymer components to achieve the desired behavior. For example, PLA can be modified by blending to provide certain toughness, which is beneficial for obtaining PLA fibers with improved performance. The tensile strength of PLA fibers generally ranges from 3.6 to 5.4 cN/dtex; however, through blending, copolymerization modification, or post-treatment, polylactic acid fibers with a breaking strength higher than 7.2 cN/dtex can be produced. Their elongation at break is close to that of polyester, ranging from 20% to 30%, indicating good extensibility. Polylactic acid possesses unique characteristics such as biodegradability, thermoplastic processability, and ecological friendliness, making it potentially applicable as commodity plastics, packaging, agricultural products, and disposable materials. On the other hand, this polymer shows promising application prospects in the medical, surgical, and pharmaceutical fields. Yuanjin Zhao et al.[57] deposited hydrogel microfibers with hydrophilic properties from microfluidics onto electrospun nanofibers composed of hydrophobic polylactic acid and silver nanoparticles, forming Janus textiles. The hydrophobicity of Janus textiles prevents excess liquid from re-entering the wound, avoids excessive moisture accumulation, and maintains breathability at the wound site. Additionally, the silver nanoparticles contained in the hydrophobic nanofibers endow the textile with excellent antibacterial effects, further promoting wound healing efficiency. The fundamental polymer chemistry of PLA enables control over certain fiber characteristics, making the fibers suitable for a wide range of technical textile applications, particularly in apparel and functional clothing. Low moisture absorption and high moisture absorption offer benefits for sportswear and functional garment products. High UV resistance provides advantages for high-performance clothing as well as outdoor furniture and upholstery applications. Furthermore, low density and low refractive index contribute to lighter weight and superior color characteristics of PLA fibers. PLA can be used in various filament and nonwoven structures, which can be produced using diverse spinning technologies and mechanical processing methods. Fibers can be fabricated into fabrics via bonding, thermal bonding, carding, knitting, and weaving. The versatility of filaments in transforming into various shapes and forms, along with favorable mechanical properties, broadens their range of applications.

4.2 PGA Fiber

In recent years, polyglycolic acid (PGA), also known as polyhydroxyacetic acid, has received significant attention as an important biodegradable plastic product that promotes China's reduction of plastic waste and helps achieve the "dual carbon" goals. PGA is an aliphatic polyester with the fewest carbon atoms in its repeating unit, a completely degradable ester structure, and the fastest degradation rate. Figure 10 presents the proposed crystal structure of PGA, with lattice parameters of italicized a = 5.22 Å, italicized b = 6.19 Å, and italicized c = 7.02 Å. Model A is based on molecular dimensions proposed by Chatani et al. [58], while model B is based on crystallographic unit cell parameters calculated from wide-angle X-ray diffraction measurements conducted in our laboratory (italicized a = 5.00 Å, italicized b = 6.03 Å, italicized c = 6.76 Å). PGA has a structure similar to polylactic acid (PLA) but offers higher heat deflection temperature, excellent mechanical properties, and particularly outstanding gas barrier performance. PGA is a synthetic absorbable polymer with a melting point range of 220–225 °C, a glass transition temperature of approximately 35–45 °C, and a density of 1.5–1.7 g/cm³ [59]. It typically exhibits high crystallinity (45%–55%) and dissolves only in high-fluorine organic solvents. The properties of PGA are positively correlated with its average molecular weight and molecular weight distribution.
图10 PGA的晶体结构[60]

Fig.10 Crystal structure of PGA[60]

There are many synthetic pathways for producing PGA polymer (see Figure 11), including direct polycondensation of glycolic acid, ring-opening polymerization (ROP) of ethylene glycol ester, solid-state polycondensation (SSP) of halogenated acetates, and synthesis via reaction of formaldehyde (trioxane) with carbon monoxide (CO). To achieve higher molecular weights, ring-opening polymerization (ROP) of the cyclic dimer of glycolic acid, ethylene glycol ester, is typically employed. The synthesis process starts with CO and H2 as raw materials to first produce methanol, which subsequently undergoes addition and substitution reactions to yield glycolic acid. The key difference from other synthetic methods lies in the requirement to convert glycolic acid into glycolide, a step that increases both energy consumption and process cost. PGA degradation primarily occurs through hydrolysis, during which the number of carboxyl groups increases and pH decreases; the degradation products, such as ethanol, are eventually excreted from the body through the urinary system. Typically, PGA degrades within the body in approximately 1.5 to 3 months[62].
图11 PGA合成路线

Fig.11 Synthesis route of PGA

Currently, the main technologies for producing PGA products include electrospinning and melt spinning[63]. However, PGA is insoluble in most organic solvents, which significantly increases the production costs associated with electrospinning. In comparison, melt spinning offers advantages of lower processing costs and continuous production, making it the most widely used method for forming PGA fibers. Typically, fiber processing involves orientation and annealing processes. The orientation process mechanically stretches polymer chains and microcrystals, thereby increasing crystal orientation and crystallinity. The orientation process is influenced by draw ratio and temperature. Generally, a higher draw ratio results in greater tensile strength but lower elongation at break[64], while thermal annealing tends to improve crystallization but can also cause fiber shrinkage. Li et al.[65] reported similar findings, where at higher stretching temperatures, molecular chain segments have shorter relaxation times and are more prone to lose alignment, making it difficult for them to move in the direction required for crystallization, thus resulting in lower crystallinity. During the hot stretching stage, higher temperatures can reduce internal stress in constrained amorphous chains. In the annealing stage, the crystallinity and microcrystal size of the sample increase significantly, while thermal shrinkage near the glass transition temperature (Tg) decreases notably.
Early studies on PGA fibers mainly focused on biocompatibility and degradation properties. According to related research, the degradation cycle of PGA is closely related to its crystal structure and the arrangement of amorphous molecular chains. Obviously, different structures play a crucial role in material properties; therefore, understanding the relationship between the aggregate state structure of polymer materials and their macroscopic performance is very important. Ward et al.[60,66] demonstrated through solid-state 1H NMR spectroscopy measurements (see Figure 12) that oriented PGA fibers consist of rigid crystalline phase, semi-rigid amorphous phase, and highly mobile amorphous phase. The degradation of the semi-rigid amorphous phase plays a vital role in maintaining fiber strength, while fibers with different initial lamellar structures exhibit similar structures and mechanical properties at later stages of degradation.
图12 （a）固体回波核磁共振脉冲序列；（b）自旋锁定与固体回波探测核磁共振脉冲序列[60]

Fig.12 （a）solid-state echo NMR pulse sequences；（b）spin locking and solid-state echo detection NMR pulse sequences[60]

PGA fibers are commonly used in medical fields, textiles, filtration materials, composites, and 3D printing materials. However, in practice, due to its biocompatibility and rapid biodegradability, PGA is widely utilized in the production of surgical sutures and nonwoven meshes[67]. The nonwoven mesh of PGA fibers is highly porous, allowing nutrient diffusion throughout the scaffold and capable of providing a high cell density. However, this structure lacks structural stability to withstand compressive forces in vivo. To improve its mechanical properties, PGA fibers in these matrices have been physically bonded with PLLA and PLGA. By varying the amount of physical bonding, a wide range of mechanical strengths and degradation rates can be achieved. Additionally, fiber mechanical strength can also be enhanced, and degradation rates slowed, by introducing crosslinking structures, such as common polyester-based crosslinkers or chain extenders like MDI and ADR.

4.3 PHA fibers

Polyhydroxyalkanoates (PHA) are a group of thermoplastic, bio-based, and biodegradable polyesters that exhibit excellent biocompatibility compared to other biopolymers such as polylactic acid (PLA) or polyglycolic acid (PGA), thus holding significant potential in medical applications and tissue engineering. Emerging PHA polymers (PHA family, such as Figure 13) consist of various polymers with greatly differing properties and performance. Many copolymers within the PHA family are composed of chemically linked hydroxybutyrate (HB), hydroxyvalerate (HV), or hydroxyhexanoate (HHx) monomers, which cannot simply replace one another due to their distinct attributes and broad ranges of property indicators. Current research on PHA fibers mainly focuses on PHB and PHBV, which offer numerous advantages over other types of PHA polymers, such as toughness and elasticity. However, the high production cost of PHA—5 to 15 times higher than petroleum-derived polymers—has hindered its development. There are three main pathways for synthesizing PHA polymers (i.e., microbial, enzymatic, and chemical routes [ring-opening polymerization]) (Figure 14)[68]. Each synthesis method has its key influencing factors, leading to differences in the molecular characteristics of PHA, production costs, and the availability of industrial technologies for large-scale production.
图13 一些短链和中链PHAs的化学结构[69]

Fig.13 Chemical structure of some short- and medium-chain PHAs[69]

图14 PHA的主要生产工艺：微生物法、酶法和化学法[68]

Fig.14 Main production processes of PHA： microbial method，enzymatic method and chemical method[68]

PHA-based products are commonly used in the production of packaging and medical materials, with potential biomedical applications including implants for various tissues, sutures, patches, scaffolds, and matrices used in drug delivery systems[70-72]. Regarding PHA fibers, they demonstrate significant potential both in the medical field (tissue engineering scaffolds, plasters, wound healing, drug delivery systems) and in industrial applications (filtration systems, food packaging) (Figure 15)[73]. The breaking strength of PHA fibers is generally about 21.71 cN/dtex, with an elongation at break of 29.55%; however, their mechanical properties can be effectively improved by regulating their crystallization behavior. Currently, major methods for manufacturing PHA fibers include melt spinning, wet spinning, and electrospinning. However, each method has certain drawbacks—for example, the main challenge in melt spinning PHA is controlling their crystallization behavior through various approaches to enable broader application in the industrial textile field. Presently, two primary strategies are employed: one involves adjusting the molecular structure, such as incorporating copolymer segments with lower crystallinity or modifying the molecular weight; the other strategy involves optimizing processing parameters, controlling cooling rates, and implementing annealing treatments to effectively regulate crystallization behavior. In addition, adding nucleating agents is also an effective approach. Wet spinning and electrospinning face challenges related to safety, environmental impact, and cost, making large-scale industrial production difficult, thus limiting their application mainly to the medical field[69]. For instance, PHBV fibers interact with osteoblasts and fibroblasts (Figure 15), and researchers have found that when PHBV fibers are modified, they can provide structures supporting cell adhesion, thereby facilitating bone tissue regeneration. PHBV scaffolds enriched with inorganic HA particles support osteoblast adhesion and attachment, and incorporating HA particles into the fiber structure enhances cell proliferation[74].
图15 SEM显微照片显示（A，B）成骨细胞和（C，D）成纤维细胞在（A，C）3天和（B，D）7天后与纤维相互作用；（E）PHBV纤维和（F）PHBV+HA纤维细胞培养7天后的细胞形态；红色箭头表示丝状伪足与纤维相互作用[74]

Fig.15 SEM micrographs showed that（A，B）osteoblasts and（C，D）fibroblasts interacted with the fibers after（A，C）3 days and（B，D）7 days.（E）Cell morphology of PHBV fiber and（F）PHBV+HA fiber cells cultured for 7 days； red arrows indicate filamentous pseudopods interacting with fibers[74]

4.4 PBAT Fiber

Among chemically synthesized biodegradable polymers, poly(butylene adipate-co-terephthalate) (PBAT) is the most widely used. PBAT is an aliphatic-aromatic copolyester composed of both aliphatic and aromatic units, primarily synthesized from PTA (or DMT), AA, and BDO through direct esterification and polycondensation reactions under catalytic conditions (Figure 16). Due to this structural characteristic, the mechanical properties of PBAT are influenced by the monomer composition and molecular weight. On one hand, Franco et al. and Herrera et al. reported that the Young's modulus increases with higher terephthalate content, while the elongation at break decreases[75]. On the other hand, as molecular weight increases, tensile strength increases but elongation at break decreases[76]. Generally, PBAT exhibits similar mechanical properties, including a tensile strength of approximately 21 MPa, an elongation at break ranging from 670% to 1200%, and a flexural strength of about 7.5 MPa.
图16 PBAT合成示意图[77]

Fig.16 PBAT synthesis diagram[77]

PBAT exhibits mechanical and processing properties similar to LDPE, with good thermal stability, and can be processed through extrusion, blow molding, injection molding, and other methods. Unlike the fully biodegradable plastic PLA, PBAT is a material with good toughness, high elongation, but low strength. However, spinning PBAT faces certain difficulties in both melt spinning and solution spinning processes. When using melt spinning to produce PBAT fibers, the melt strength is insufficient, making it difficult to adjust spinning parameters; while producing PBAT fibers via solution spinning requires meeting stringent requirements for the concentration of the spinning solution. From a material perspective, PBAT fibers possess low strength and excessive elasticity, resulting in poor dimensional stability and susceptibility to creep. To address these issues, blending PBAT with materials possessing higher melt and mechanical strengths can yield improved PBAT fibers. Currently, applications of PBAT fibers are primarily limited to tissue engineering scaffolds, where PBAT's good wettability enhances cell adhesion and proliferation. However, due to manufacturing challenges, its application remains limited[78-79]. In order to expand the application of PBAT fibers in agriculture and medicine, Kikutani et al.[80] aimed to provide insights into PBAT fiber processing and resulting fiber properties by studying the mixed crystalline structure of PBAT (Fig. 17). Through various calculations and WAXD patterns, they found that PBAT possesses a lattice structure similar to α-form PBT. When the tensile strain exceeds 15%, the crystal structure of PBT completely transforms from α-form to β-form, whereas the α-form still dominates in PBAT. This difference results in a much lower modulus in PBAT fibers compared to PBT fibers. The crystal form transition in PBT occurs under stress above a critical value (approximately 75 MPa at room temperature). Therefore, they suggested that PBAT likely requires a similar prerequisite, albeit needing higher strain to achieve it.
图17 拉伸变形过程中记录的PBT和PBAT纤维的WAXD图案[80]

Fig.17 WAXD patterns of PBT and PBAT fibers recorded during tensile deformation[80]

4.5 PCL Fiber

Polycaprolactone (PCL) is a hydrophobic semi-crystalline polymer. Its glass transition temperature (Tg) is -60·C, with a melting point ranging between 59 and 64·C. It is soluble at room temperature in chloroform, dichloromethane, benzene, toluene, carbon tetrachloride, 2-nitropropane, and cyclohexanone. PCL can undergo ring-opening polymerization using various anionic, cationic, and coordination catalysts (Figure 18), and it can also be polymerized via free radicals for the ring-opening of 2-methylene-1,2-dioxolane[81]. The excellent solubility and blending compatibility of PCL have led to its widespread application in biomedical fields[82]. Typically, PCL can be hydrolytically degraded under physical conditions through its ester bonds, as well as by biologically organisms such as bacteria and fungi. However, due to the lack of suitable enzymes in vivo, it cannot be degraded within animals or humans. Because PCL degrades more slowly than other polymers and their copolymers, it is suitable for applications requiring slow degradation. PCL can be blended and modified with other polymers to improve its physical, chemical, and mechanical properties. The tensile strength of PCL fibers is similar to that of nylon, and studies on small-scale spinning of its monofilament fibers indicate that stiffness and toughness increase in a typical manner with increasing draw ratio; for example, the stiffness of microfiber bundles is approximately 1382.5 N/tex, with a maximum load of 30.7 N. The elongation at break of PCL fibers lies between that of LDPE and HDPE, and the presence of ester groups within the molecules endows PCL with good flexibility[83].
图18 PCL的不同合成路线

Fig.18 Different synthesis routes of PCL

PCL fibers have been widely applied in the biomedical field due to their biodegradability and high biocompatibility, especially in tissue engineering and medical implants. PCL can be formed into continuous ultrafine fibers via electrospinning to provide excellent properties such as high porosity and surface area suitable for biomedical applications. Electrospun PCL fiber mats serve as temporary matrices to promote adhesion, proliferation, and differentiation of various types of cultured cells, and are carriers for biologics and wound dressing materials[84-85]. Linhardt et al.[86] prepared polycaprolactone (PCL)-PGS microfiber core-shell mats using coaxial electrospinning (Fig. 1919), where the PCL-PGS core-shell structure provided tunable degradation and mechanical properties. Additionally, anticoagulant heparin was immobilized on the surfaces of these electrospun fiber mats, improving attachment and proliferation of human umbilical vein endothelial cells.
图19 用于组织工程的可生物降解和生物活性PCL-PGS核壳纤维[86]

Fig.19 Biodegradable and Bioactive PCL-PGS core-shell fibers for tissue engineering[86]

PCL fibers produced by melt spinning are rarely addressed in the literature, whereas fiber production via electrospinning is widely reported. Electrospinning, melt spinning, and melt deposition are some techniques used to generate PCL fibers at micro- and nano-scales. Although electrospinning is a convenient method for producing nanometer- or micrometer-sized fibers, it generally requires the use of organic solvents, and the mechanical properties of electrospun fibers have been found to be generally poor[87]. On the other hand, melt spinning is a fundamental technique for fiber fabrication, which has a simple setup and allows continuous drawing of fibers directly from molten polymer, avoiding the use of solvents. However, these fibers cannot be manufactured at the nanoscale using melt spinning, and this technique is not suitable for polymers that are prone to degradation under melt-spinning conditions, such as PCL (when exposed to high temperatures in the presence of air or moisture)[88].

4.6 PBS Fiber

Among aliphatic polyesters, poly(butylene succinate) (PBS) has become one of the fastest-growing varieties due to its excellent comprehensive properties and promising industrialization prospects. It is typically synthesized through a polycondensation reaction between aliphatic diols and dicarboxylic acids (<xref ref-type="fig" rid="F20">Figure 20</xref>), and its raw materials can be derived from crude oil or cellulose<sup>[<xref ref-type="bibr" rid="b89">89</xref>]</sup>. Compared with other biodegradable polyester materials such as polylactic acid (PLA) and polyhydroxybutyrate (PHA), PBS is inexpensive and possesses favorable physical and mechanical properties along with ease of processing and molding. Among other aliphatic polyesters, PBS not only exhibits a high melting point close to that of low-density polyethylene (LDPE), but also demonstrates relatively high glass transition temperature, tensile strength, and hardness (generally between those of PE and PP). Furthermore, PBS displays strength and toughness comparable to LDPE. Currently, it is considered one of the most promising biodegradable polymer materials for industrialization and commercial application.
图20 可持续生物基和石化原料的PBS合成流程图[89]

Fig.20 PBS Synthesis of sustainable bio-based and petrochemical feed-stocks[89]

PBS has a wide range of applications, and its highly transparent surface and rigid structure make it suitable for various uses such as cover films, compostable bags, nonwoven boards and textiles, tableware, and foams[90-91]. PBS fibers are commonly used in monofilaments, filament yarns, biomedical applications, and the textile industry[92]. The production of PBS fibers primarily employs melt spinning and melt electrospinning techniques[93-94], with the former mainly used for textile production and the latter applied in biomedical fields such as tissue engineering and cell regeneration. The tensile strength of obtained PBS fibers generally reaches around 30 MPa, comparable to common plastics like polyethylene and polypropylene, meeting basic strength requirements for everyday use; products such as disposable dry and wet wipes made from PBS fibers exhibit adequate strength. Additionally, through blending modification, the strength of PBS fibers can be enhanced up to 40 MPa. At the same time, PBS fibers demonstrate elongation at break reaching up to 400%, exhibiting excellent flexibility and ductility. This enables them to undergo significant deformation under stress without breaking, making them suitable for applications requiring softness and stretchability. However, there remain certain challenges regarding the industrialization and commercialization of PBS fibers. On one hand, insufficient raw material supply and the need for improved synthesis technologies result in high costs and hinder large-scale production. On the other hand, some performance aspects still require enhancement. For example, compared to other widely used polyester materials, PBS suffers from poor melt strength, which limits its application in film and fiber fields.

5 Biodegradable Fiber Composites

Biodegradable fiber composites are generally materials composed of natural fibers as reinforcing materials and biodegradable plastics as the matrix, and they are also a type of natural fiber polymer composite (NFPC). Typically, embedded reinforcing fibers are high-strength and high-toughness natural fibers such as jute, oil palm, sisal, kenaf, and flax, which are used to compensate for mechanical deficiencies in degradable plastics like PLA, PBAT, and PHA. According to previous studies, the properties of natural fiber composites vary due to differences in fiber types, sources, and moisture conditions. The performance of NFPC depends on several factors, including mechanical composition, microfiber angle, structure, defects, cell size, physical properties, chemical properties, and the interaction between fibers and the matrix[95-101]. Since each product on the market has its drawbacks, natural fiber-reinforced polymer composites also have disadvantages. Due to differences in chemical structures between natural fibers and polymer matrices, the coupling issue between natural fibers and the polymer matrix must be considered. This results in ineffective stress transfer at the NFPC interface. Therefore, chemical treatment of natural fibers is necessary to achieve good interfacial performance.
For natural fiber-reinforced composite materials, there are quite a number of improvements that can be implemented to enhance their mechanical properties, thereby achieving high-strength structures. Once the basic structure becomes robust, polymers can be easily reinforced and improved[102]. Fiber orientation, fiber strength, fiber physical properties, and fiber interfacial adhesion performance are all aspects that can be enhanced[103-104]. Graupner et al.[105] investigated the mechanical properties of polylactic acid (PLA) composites reinforced with natural and man-made cellulose fibers. Various types of natural fiber composites, such as jute, cotton, kenaf, and man-made cellulose fibers with different characteristics, were prepared using compression molding with 40% fiber mass and PLA. Kenaf and hemp/PLA composites exhibited better tensile strength and Young's modulus, whereas cotton/PLA showed superior impact characteristics. Lyocell/PLA composites demonstrated favorable performance. In summary, this study revealed unique properties of the composites that can be applied in various technical applications, each meeting distinct criteria.
Natural fiber-reinforced composites can be applied in fields such as films and hydrogels. In food packaging, for example, PBAT film serves as the matrix material, and the addition of short sugarcane fibers can enhance the crystallinity of the PBAT film, thereby improving its gas barrier properties and effectively preventing the permeation of gases like oxygen and water vapor, thus extending the shelf life of food. Moreover, the incorporation of short fibers itself increases the path length for gas permeation, which is also beneficial to gas barrier performance. In tissue engineering, collagen hydrogel acts as the matrix material; its three-dimensional network structure resembles the extracellular matrix of human tissues, providing a favorable environment for cell growth and proliferation. Due to its high water content, it exhibits good biocompatibility, allowing cells to adhere and migrate within it effectively. The mechanical properties of hydrogels can be adjusted by incorporating fibrous materials such as cellulose or chitosan fibers to meet the requirements of different tissue repairs. Regarding drug delivery, some smart hydrogel matrix materials can also incorporate fibrous materials to slow down drug release, achieving a sustained-release effect.

6 Conclusion and Prospect

In response to the national call for sustainable development, environmental protection has become an inevitable trend, and traditional synthetic plastics will gradually be replaced by biodegradable plastics. The main issue with current biodegradable plastics lies in the development of practical applications, and biodegradable fibers are one example. To date, only polylactic acid (PLA) fibers have achieved widespread application, while most other biodegradable fibers remain at the research stage, encountering various challenges before they can be put into production. The existing problems associated with different types of biodegradable fibers can be briefly summarized as follows: (1) Some biodegradable fibers exhibit good flexibility; however, due to low crystallinity or weak interactions between molecular chains, their strength is insufficient, causing shrinkage after spinning, which is particularly evident in PBAT fibers; (2) Melt spinning is a more suitable method for large-scale industrial production, but materials such as PGA and PCL lack sufficient thermal stability and melt strength, easily degrading during processing and being difficult to shape, thus requiring modification to improve these properties; (3) Besides melt spinning, other spinning methods significantly affect the mechanical properties of the material and are not environmentally friendly, making it important to investigate the causes of these effects and improve the processes accordingly; (4) Compared with PLA, the synthesis processes of other biodegradable plastics still need improvement, particularly regarding cost reduction while maintaining process stability; (5) A common problem hindering the industrial application of all biodegradable fiber materials is the high cost of upstream raw materials and the unstable quality of large-scale production technologies, thus making the development of advanced equipment particularly crucial.
In addition, the properties of biodegradable fibers still lag behind those of commercially available non-biodegradable fibers in aspects such as insufficient tensile strength, inadequate thermal stability, and poor elasticity. Improvements in these properties will require chemical or physical modifications as well as post-spinning treatments, which will be a key focus in the research on biodegradable fibers. Biodegradable fiber composites also represent an effective approach for fiber applications.

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