Existing Scenario and Environmental Significance of Biodegradable Plastics: A Review for a Sustainable Future

Cellulose-based bioplastics

Cellulose-based bioplastics are derived from cellulose, a linear polysaccharide consisting of 𝛽-(1 → 4)-linked D-glucose units, making it the most abundant biopolymer on Earth [17]. The transformation of cellulose into a plastic material requires chemical modifications to overcome its rigid, crystalline structure and insolubility in common solvents. Key processes include acetylation (producing cellulose acetate), esterification, or the formation of cellulose derivatives such as cellulose ethers and esters, which introduce thermoplasticity by disrupting hydrogen bonds and decreasing crystallinity. Few studies have explored cellulose modification via acetylation, esterification, and etherification, emphasizing structural alterations that reduce hydrogen bonding and crystallinity, thereby enhancing solubility and imparting thermoplastic properties for sustainable polymer applications in industrial and biomedical fields [18]. Importantly, cellulose-based bioplastics exhibit good mechanical strength, thermal stability, and oxygen barrier properties, which are critical for applications in packaging and biomedical fields. Their environmental benefits are further amplified by their ability to degrade under composting conditions, unlike traditional plastics, which persist in ecosystems for centuries. However, challenges such as the high cost of production, processing limitations, and achieving properties comparable to petrochemical plastics still need to be addressed for their widespread adoption [19].

Starch-based bioplastics

Starch-based bioplastics are derived from starch, a naturally occurring polysaccharide composed primarily of amylose (linear chains of 𝛼-(1 → 4)-linked D-glucose) and amylopectin (branched chains with 𝛼-(1 → 6) linkages). The conversion of starch into bioplastics typically involves the disruption of its semi-crystalline structure via plasticizers such as glycerol or sorbitol, which lower its glass transition temperature and increase flexibility. During the process, heat and shear forces cause gelatinization of starch, breaking down intermolecular hydrogen bonds and transforming the starch granules into an amorphous, moldable material. Depending on the ratio of amylose to amylopectin and the type of plasticizer used, the mechanical properties of the resulting bioplastic can be tailored, with higher amylose content generally resulting in stronger, more rigid bioplastics due to increased hydrogen bonding. Few studies have examined the influence of amylose-to-amylopectin ratio on starch-based bioplastics. It has been demonstrated that higher amylose content enhances thermal stability and mechanical strength due to extensive hydrogen bonding and molecular alignment. This increases gelatinization temperature and results in bioplastics with improved rigidity and lower water permeability. These findings support tailoring starch formulations based on amylose levels to optimize bioplastic performance for specific applications [20]. Starch-based bioplastics find use in packaging, disposable products, and agricultural films, with ongoing research focusing on enhancing their water resistance and structural properties through cross-linking and the incorporation of nanoparticles, broadening their applicability as a sustainable alternative to petroleum-based plastics [21].

Protein-based bioplastics

Protein-based bioplastics are derived from natural proteins such as soy protein, casein, whey, gluten, and zein, which possess unique structural properties due to their complex polypeptide chains made up of amino acids. These proteins can be transformed into bioplastics through various denaturation processes, including heat, pH adjustment, or enzymatic treatments, which disrupt the native protein structure, allowing intermolecular interactions like hydrogen bonding, hydrophobic interactions, and disulfide linkages to form a network. The plasticization of proteins often requires additives like glycerol or sorbitol to improve flexibility and reduce brittleness. Depending on the protein source and processing conditions, protein- based bioplastics exhibit a range of mechanical properties, from rigid, strong materials (e.g., soy protein) to more flexible films (e.g., gelatin-based bioplastics). The key advantages of protein-based bioplastics include their renewable origin, inherent biodegradability, and potential for functionalization due to the reactive side groups on amino acid residues, which enable chemical modifications to tailor properties like water resistance, mechanical strength, and thermal stability [22].

Aliphatic polyesters bioplastics

Aliphatic polyesters are a prominent class of biodegradable bioplastics, synthesized from monomers linked by ester bonds in a repeating sequence of aliphatic (non-aromatic) chains. These bioplastics, which include polymers like PLA, PHA, PBS and polycaprolactone are widely valued for their biodegradability, biocompatibility, and relatively low environmental impact. Their structure, dominated by ester linkages, allows them to undergo hydrolytic and enzymatic degradation, making them suitable for applications requiring biodegradation, such as packaging, agricultural films, and medical implants [23]. The mechanical and thermal properties of aliphatic polyesters vary depending on their specific chemical structure. PLA for instance, exhibits high stiffness and good transparency, but is brittle, requiring plasticization or blending with other polymers to enhance flexibility. PHA produced by microbial fermentation, has better mechanical properties and flexibility but is costlier to produce [24]. PBS and polycaprolactone on the other hand, offer greater flexibility and superior thermal stability but may degrade more slowly under certain environmental conditions. Aliphatic polyesters also possess tunable degradation rates, which can be adjusted by altering their chemical composition or copolymerizing with other monomers, allowing control over their lifespan in various applications [25].

PLA (Polylactic acid) bioplastics

PLA (polylactic acid) is a widely used bioplastic derived from renewable resources such as corn starch, sugarcane, or cassava, and is synthesized through the polymerization of lactic acid monomers. PLA is produced via two primary methods: direct condensation of lactic acid or ring-opening polymerization of lactide, a cyclic dimer of lactic acid, the latter being more commercially favoured due to better control over molecular weight and properties. PLA’s structure consists of repeating units of lactide, and its stereochemistry (D- and L- isomers) influences its crystallinity and mechanical properties. For instance, PLA with high L-content tends to be semi-crystalline, which enhances its strength and thermal resistance, whereas amorphous PLA is more transparent and flexible but has lower mechanical performance [26]. PLA exhibits several desirable properties, such as good tensile strength, transparency, and processability, making it suitable for applications in packaging, textiles, and biomedical devices like sutures and drug delivery systems. It is also compostable under industrial conditions, where high temperatures and microbial activity facilitate its degradation into CO₂, water, and biomass. However, hydrolytic degradation of PLA is relatively slow in natural environments, particularly in marine or soil settings, where conditions including low ambient temperatures, limited moisture, and reduced microbial activity are suboptimal and less favourable for biodegradation. PLA requires elevated temperatures (above 50 °C) and sufficient humidity for effective hydrolysis, conditions typically found in industrial composting facilities. Additionally, natural environments lack the specific thermophilic microorganisms necessary to break down PLA efficiently. Factors like neutral pH and limited surface area exposure further hinder microbial colonization and water penetration, collectively resulting in the slower degradation of PLA outside controlled settings [27].

PHB (Poly 3-hydroxybutyrate) bioplastics

PHB (poly 3-hydroxybutyrate) is a biopolymer belonging to the PHA family, produced naturally by various microorganisms, such as Ralstonia eutropha, as an intracellular carbon and energy storage material under nutrient-limited conditions with excess carbon. Structurally, PHB is a semi-crystalline polymer composed of repeating 3-hydroxybutyrate monomers connected via ester linkages. Its biodegradable and biocompatible nature makes PHB highly attractive for environmental and biomedical applications, including packaging, agricultural films, and tissue engineering scaffolds. PHB is synthesized through microbial fermentation, where bacteria accumulate it in granules, which can be harvested and purified after fermentation. The microbial production process, while sustainable, is often limited by the high cost of substrates and processing compared to petroleum-derived plastics. PHB is often blended with other polymers, such as polyhydroxybutyrate-co-valerate or polycaprolactone (PCL) which introduce flexibility and toughness which are limited in pure PHB due to its brittleness and high crystallinity. Polyhydroxybutyrate-co-valerate, being a copolymer, lowers the melting point and enhances processability, making it more suitable for packaging and biomedical applications. PCL adds elasticity and improves impact resistance, expanding the use of PHB blends in areas like controlled drug delivery, biodegradable films, and agricultural mulch. These modifications make PHB-based materials more adaptable to diverse practical applications where durability and mechanical resilience are essential. Moreover, PHB production can be optimized by genetic engineering of microbial strains and metabolic pathways to increase yields and reduce costs [28].

PHA (Polyhydroxyalkanoates) plastics

PHA (Polyhydroxyalkanoates) are a family of biodegradable and biocompatible polyesters synthesized by various bacteria as intracellular carbon and energy storage compounds under nutrient-limited conditions with an excess of carbon. PHA is produced through microbial fermentation and consist of various hydroxyalkanoate monomers, resulting in a wide range of material properties. The most well-known PHA, PHB (poly (3-hydroxybutyrate) is highly crystalline and exhibits good tensile strength but suffers from brittleness. Other copolymers, like PHBV (poly 3-hydroxybutyrate-co-3-hydroxyvalerate), introduce greater flexibility and toughness, broadening the potential applications of PHA and the inclusion of 4-hydroxybutyrate (4HB) enhances elasticity, making the polymer suitable for medical applications like sutures. Similarly, monomers like 3-hydroxyhexanoate (3HHx) and 3-hydroxyoctanoate (3HO) produce medium-chain-length PHA with rubber-like flexibility and lower melting points, ideal for films and coatings. These structural variations tailor PHA for specific industrial and biomedical uses. PHBV is preferred over PHB or other PHA types; for instance, PHBV is used in controlled drug delivery systems. Due to its biodegradability and biocompatibility, PHBV is used to create polymer-based drug carriers that gradually release medications over time. This application is particularly beneficial in implantable devices, where PHBV’s controlled degradation ensures sustained therapeutic effects without the need for removal. PHA is synthesized by microbial strains, including Ralstonia eutropha and Pseudomonas species, using renewable feedstocks such as agricultural waste, sugars, or even waste oils, making their production more sustainable than petrochemical-derived plastics. The biodegradability of PHA is its most significant advantage, as they degrade fully in various environments, including marine, soil, and compost, through enzymatic hydrolysis and microbial activity, producing water and carbon dioxide [29]. PHA, including PHB and PHBV, degrade at different rates depending on environmental factors such as temperature, moisture, microbial activity, and oxygen availability. PHA degrades more slowly in soil than in industrial composting, with PHB taking 6–12 months and PHBV 1–2 years, influenced by soil conditions and microbial diversity. In marine environments, PHA degrades within 1–2 years, with PHBV generally degrading faster than PHB due to the presence of diverse marine microorganisms. In composting, PHA breaks down within 6–12 months under optimal conditions of high temperature and moisture. In freshwater, degradation can take 1–3 years, with microbial communities accelerating the process. Read et al. [30] determined the degradation of 150 𝜇m-thick extruded sheets of PHBV submerged in five different natural aquatic environments within the same watershed for nearly 51 weeks. The study aimed to determine and compare the lifetimes and degradation behaviors of PHBV in these environments. The findings provide valuable insights into the degradation rates and mechanisms of PHBV in various natural aquatic settings [30].

PA 11 (Polyamide 11) bioplastic

PA 11 (Polyamide 11) is a bio-based thermoplastic polymer synthesized from 11-aminoundecanoic acid, a monomer derived from castor oil, making it a fully renewable material. PA 11 belongs to the broader class of polyamides (nylons), but unlike petroleum- based polyamides such as nylon 6 or nylon 6, 6; its renewable feedstock significantly reduces its environmental impact. The polymerization of 11-aminoundecanoic acid forms long aliphatic chains with amide linkages, giving PA 11 its excellent combination of mechanical strength, flexibility, and chemical resistance. Its high degree of crystallinity, coupled with its relatively long methylene chain between the amide groups, imparts superior toughness and ductility compared to many other polyamides, alongside low water absorption, which enhances its dimensional stability in humid environments. PA 11 is prized for its thermal stability and good impact resistance, even at low temperatures, making it ideal for demanding applications such as automotive fuel lines, electrical cable sheathing, and high-performance sporting goods [31]. Studies have demonstrated the development of PA 11 nanocomposites reinforced with graphene nanoplatelets (GNPs) for flexible pipeline applications. Results have shown that incorporating 1.0 wt% GNPs into the PA 11 matrix significantly enhanced thermal stability, as evidenced by thermogravimetric analysis (TGA), and improved mechanical properties, including increased storage and loss moduli observed through dynamic mechanical analysis (DMA). Additionally, the nanocomposites exhibited greater hydrophobicity and resistance to hydrothermal aging at 85 °C, maintaining higher corrected inherent viscosity (CIV) values compared to neat PA 11. These findings suggest that low GNP loadings effectively bolster PA 11’s thermal and mechanical performance, making it suitable for demanding applications in the oil and gas industry [32].

Bio-derived polyethylene

Bio-polyethylene or renewable polythene is derived from ethanol, which converts to ethylene after a dehydration procedure. Ethanol can be obtained from sugar beet, corn, sugar cane and wheat grain. This plastic is non-biodegradable and has the same physical and chemical characteristics as synthetic polythene. It is used in flexible and rigid packaging, bags, closures and various other products. It emits comparatively less CO₂ in its production as compared to petroleum-based polyethylene [33].

Polyhydroxy Urethane plastics

When cyclic carbonates and polyamides are condensed, it produces PHUs (polyhydroxy urethanes). It is used in making foams, sealants, adhesives, and coatings, insulation of refrigerator, mattress, car parts, paints, tires, shoe soles, wood panels, and sportswear and emerging applications of PHUs include their use in biomedical materials, coatings, adhesives, and elastomers. Recent trends highlight their potential in self-healing materials, 3D printing resins, and flexible electronics, driven by their tunable network structures and compatibility with bio-based monomers. Research continues to optimize their performance for high-value, eco-friendly applications [34].

Feedstock sources

Biodegradable plastics are emerging as sustainable alternatives to conventional plastics derived from petrochemicals. The production of biodegradable plastics utilizes a variety of renewable feedstocks that are derived from plant-based sources, microbial processes, and waste materials and these varieties. Feedstock sources of biodegradable plastic are shown in Figure 3. These feedstocks are renewable, bio-based, and are capable of undergoing biological degradation, which significantly reduces the environmental burden associated with plastic pollution. The feedstock categories are plant-based, waste/residue-based, microbial-based, and other renewables highlight diverse, sustainable sources driving bioplastic production through efficient, eco-friendly, and circular bioeconomy pathways. Presently, the production of biodegradable plastics are based on agricultural waste, specifically sugarcane bagasse and wheat straw, as feedstock. The lignocellulosic biomass was pretreated and subjected to microbial fermentation using Cupriavidus necator, a well-known PHA-producing bacterium. The study demonstrated efficient conversion of the biomass into PHA, achieving high yields under optimized conditions. Characterization of the resulting bioplastics revealed favorable mechanical and thermal properties suitable for packaging applications. This approach not only adds value to agricultural residues but also presents a sustainable and circular strategy for bioplastic production, reducing reliance on petrochemical sources [35]. The feedstocks are classified into several categories: plant-based feedstocks, waste and residue-based materials, microbial-based raw materials, and other renewable sources. Each category is summarized in Tables [32] , highlighting the key characteristics along with a flow chart depicting the production processes [36]. Feedstock sources of biodegradable plastic are shown in Figure 3.

Plant-based feedstocks

Starch is a natural polymer that serves as a primary raw material for biodegradable plastics. It is extracted from various crops such as maize (corn) (Zea mays), potato (Solanum tuberosum), wheat (Triticum aestivum), and cassava (Manihot esculenta) and few examples of plant based feedstocks of biodegradable plastic are shown in Table 1 and Table 2. Table 1 also elucidates that starch from crops like maize and cassava produces thermoplastic starch for food packaging, while sugar crops like sugarcane yield PLA for films. Other sources include vegetable oils for PHA, agricultural residues for cellulose acetate, and microalgae for biodegradable packaging. The polysaccharides, amylose and amylopectin present in starch contribute to its thermoplastic properties when subjected to plasticization processes. Maize starch is extensively used due to its availability and cost efficiency. It is chemically or enzymatically modified to produce TPS (thermoplastic starch), which serves as a key component for bioplastic applications. Starch-based bioplastics are also commonly blended with other biodegradable polymers, such as PLA, to improve mechanical and thermal properties. Potato and cassava are also viable sources of starch. They are used particularly in regions where they are produced abundantly, such as Europe and Southeast Asia. These starches are transformed into biopolymers that find applications in food packaging, disposable utensils, and agricultural films. The cost competitiveness of biodegradable plastics in comparison to conventional plastics is presented in Table 3  [37].

Sugar crops, including sugarcane (Saccharum officinarum) and sugar beet (Beta vulgaris), are widely used for the production of lactic acid—a key monomer in the synthesis of PLA. Sugarcane is a preferred feedstock for lactic acid fermentation in tropical and subtropical regions, while sugar beet is cultivated in cooler climates. PLA is produced through the fermentation of sugars to lactic acid, followed by polymerization. Sugarcane-based PLA is popular in countries like Brazil, India, and Thailand, which have substantial sugarcane cultivation [38].

Vegetable oils, such as soybean (Glycine max), palm oil (Elaeis guineensis), and castor oil (Ricinus communis), serve as carbon feedstocks for microbial production of PHA, which are biodegradable polyesters synthesized by bacteria under nutrient-limiting conditions. Soybean and palm oils are enzymatically hydrolyzed into fatty acids, which are subsequently metabolized by specific bacterial strains, such as Cupriavidus necator, to produce PHA. Palm oil, due to its high yield, is predominantly used in Southeast Asia. Non-edible castor oil is utilized for the synthesis of bio-based polyamides and polyesters, which are suitable for applications requiring enhanced mechanical properties and chemical resistance [40].

Waste and residue-based feedstocks

Agricultural residues such as rice husk, wheat straw, and corn stover are abundant sources of cellulose and hemicellulose. These residues are pre-treated to extract cellulose, which can then be transformed into cellulose acetate, a biodegradable polymer suitable for making films, fibers, and composites. Rice husk and wheat straw contain high amounts of cellulose, which is extracted via chemical or enzymatic processes. The extracted cellulose is used to produce biodegradable materials, such as cellulose acetate and cellulose-derived composites [41]. Food waste, including fruit and vegetable peels and spent grain from brewing industries, is a valuable resource for biodegradable polymer production. Pectin, starch, and other polysaccharides present in food waste can be processed to produce bioplastics. By-products from breweries, such as spent grain, are used to produce biodegradable polymers, contributing to value-added recycling. Waste cooking oils and fats, which are discarded from households and restaurants, are repurposed as substrates for microbial PHA synthesis. These oils are hydrolyzed into fatty acids, providing a carbon source for bacterial fermentation [42].

Microbial-based raw materials

Microalgae are considered as efficient feedstock due to their high biomass productivity and ability to grow on non-arable land and wastewater. Microalgae produce lipids, proteins, and carbohydrates, which can be utilized for biopolymer synthesis. Lipids derived from microalgae can be utilized as carbon substrates for producing PHA. The carbohydrate fraction mainly composed of starch and polysaccharides can be fermented to produce PLA and other bioplastics [43]. Certain bacterial species, such as Cupriavidus necator, accumulate PHA under nutrient-limiting conditions, using various carbon sources. These bacteria can metabolize sugars, fatty acids, and even industrial waste substrates for PHA production. Bacteria such as (Halomonas bluephagenesis) are grown in fermentation reactors with excess carbon and limited essential nutrients to induce PHA synthesis, which is then extracted and processed into biodegradable materials [44]. The fermentation of different carbon sources significantly affects both the yield and the physicochemical properties of PHA. Simple sugars like glucose and sucrose are easily metabolized by microbes such as Cupriavidus necator, often resulting in high yields of short-chain-length PHA (scl-PHA) like PHB, which are stiff and brittle due to their high crystallinity. Fatty acids and plant oils, being more energy-dense, can produce medium-chain-length PHA (mcl-PHA) with flexible, elastomeric properties, ideal for applications requiring ductility. Industrial wastes such as crude glycerol or waste cooking oil offer low-cost alternatives but may introduce impurities that reduce yield or alter polymer composition, depending on microbial tolerance and metabolic versatility [45].

Other renewable feedstocks

Lignocellulosic biomass, including wood chips, miscanthus (Miscanthus giganteus), and switchgrass (Panicum virgatum), is composed of cellulose, hemicellulose, and lignin. The cellulose and hemicellulose fractions are pretreated and hydrolyzed to release fermentable sugars that can be converted to PLA and PHA. The lignocellulosic feedstock is subjected to chemical, physical, or enzymatic pretreatment to deconstruct its complex structure. The released sugars are subsequently fermented to yield biodegradable plastics [46]. Chitin is a natural polysaccharide found in the exoskeletons of crustaceans, such as shrimp and crab. It can be processed into chitosan, which is used in the manufacture of biodegradable films and coatings. Chitosan exhibits antimicrobial properties, making it suitable for food packaging applications. Extracting chitin from crustacean shell waste also provides an opportunity to repurpose seafood by-products into high-value biopolymers [47].

Fermentation-based production

Fermentation-based production is a biochemical process that employs microorganisms to convert biomass into biodegradable polymers. Two prominent biodegradable plastics produced through fermentation are PLA and PHA. PLA is synthesized by fermenting carbohydrate-rich feedstocks, such as glucose or starch, using lactic acid bacteria, notably Lactobacillus. The fermentation process converts sugars into lactic acid, which is subsequently polymerized into lactide and finally into PLA via ring-opening polymerization. This method offers several advantages, including the utilization of renewable resources, biocompatibility, and versatile applications in packaging and medical devices [49]. In contrast, PHA is a family of biodegradable polyesters synthesized by various bacteria, including Cupriavidus necator, which metabolize organic substrates such as plant oils, glucose, or fatty acids to produce PHA granules. The bacteria store these granules as energy reserves, which can be harvested and processed into usable plastic. Studies have investigated the optimization of PHA production using a newly isolated strain, Ensifer sp. HD34. Response surface methodology (RSM) was used to optimize key fermentation parameters, including carbon source concentration, pH, and incubation time. Through this statistical approach, a significant increase in PHA yield was achieved while reducing experimental trials. Studies have also highlighted the effectiveness of RSM in fine-tuning bioprocess conditions for enhanced microbial biopolymer production, offering a cost-effective and scalable solution for industrial applications [50]. The fermentation process allows for high biodegradability in diverse environments, making PHA a highly attractive alternative to conventional plastics. Moreover, advancements in metabolic engineering are enhancing the yields of these biopolymers by optimizing bacterial strains and fermentation conditions, thus improving the feasibility of large-scale production [51].

Chemical synthesis

Chemical synthesis involves the polymerization of monomers derived from renewable or petrochemical sources to produce biodegradable polyesters such as PCL (polycaprolactone) and PBS (polybutylene succinate). PCL is synthesized through the ring- opening polymerization of 𝜀-caprolactone in the presence of a catalyst, resulting in a flexible polymer with excellent biodegradability. This synthetic pathway allows for precise control over molecular weight and crystallinity, leading to tailored material properties for specific applications. PCL’s mechanical characteristics make it suitable for use in various fields, including drug delivery systems and biodegradable packaging [52].

PBS is produced through the polycondensation of succinic acid and butanediol, both of which can be sourced from renewable biomass or synthesized through fermentation. The process involves heating the monomers at elevated temperatures to facilitate the formation of polyester chains. PBS exhibits favorable mechanical properties, including good thermal stability and flexibility, making it suitable for applications in agricultural films and food packaging. The ability to synthesize these polyesters from renewable resources significantly contributes to their environmental appeal and aligns with the principles of green chemistry [53].

Blending and compounding

Blending and compounding techniques are employed to enhance the properties of biodegradable plastics by mixing them with other materials. This method often involves combining biodegradable polymers with natural fibers, plasticizers, or other biodegradable materials to improve mechanical strength, flexibility, and processing characteristics. For instance, the incorporation of starch into PLA during the melt blending process can enhance its biodegradability and reduce production costs, making it a more sustainable option for various applications [54].

Natural fibers, such as jute or hemp, can also be blended with PHA to improve their mechanical properties while maintaining environmental benefits. The use of plasticizers, such as glycerol, in the production of PCL can significantly enhance flexibility and processability. These compounding techniques not only improve the performance of biodegradable plastics but also expand their potential applications in consumer goods, automotive parts, and construction materials [55]. García-García et al. (2024) investigated the life cycle assessment (LCA) of PLA/starch biocomposites, exploring the environmental impacts of varying starch contents (0–50 wt%) through melt blending and 3D printing applications. The LCA revealed that incorporating starch into PLA reduced the overall environmental impact, primarily by decreasing the carbon footprint compared to pure PLA. The study emphasized that renewable, biodegradable fillers like starch can improve the sustainability of bioplastics, making them more eco-friendly without significantly compromising material properties [56].

Extrusion and molding techniques

Extrusion and molding are critical techniques for shaping biodegradable plastics into final products. The extrusion process involves melting the polymer and forcing it through a die to create films, sheets, or other continuous shapes. This method is widely used in the production of biodegradable packaging films and agricultural films, where thin, flexible materials are required. Extrusion allows for efficient mass production and can be easily adapted to various polymer formulations [39].

Injection molding is another prevalent technique, whereby molten biodegradable polymers are injected into molds to create intricate shapes and structures. This method is particularly suitable for producing disposable items such as cutlery, containers, and automotive components. The ability to produce complex geometries with high precision makes injection molding a valuable technique in the biodegradable plastics industry. Blow molding, which involves inflating a molten plastic tube into hollow shapes, is also utilized for producing containers and bottles, thereby expanding the range of biodegradable products available on the market [57].

Extrusion

Extrusion is a commonly employed processing technique for biodegradable polymers, particularly in the fabrication of films, sheets, and profile products. In this process, polymer granules are introduced into the extruder and subjected to controlled thermal and mechanical energy. As the material progresses through the barrel under shear and elevated temperatures, it transitions into a molten state and is subsequently forced through a die to form a continuous profile. Upon exiting the die, the extrudate is cooled and solidified, followed by cutting or shaping to desired specifications. While extrusion offers advantages such as high throughput, versatility across polymer types, and efficient raw material usage, it presents technical challenges, including the necessity for stringent temperature regulation to avoid thermal degradation and ensuring homogeneous dispersion of additives [59].

Injection molding

Injection molding is a widely utilized manufacturing process for fabricating biodegradable plastic components with complex geometries and high dimensional accuracy. This technique involves the thermal softening of polymer pellets within a heated barrel, followed by high-pressure injection of the molten material into a precision-engineered mold cavity. The process sequence encompasses polymer feeding, melting, injection, mold cooling for solidification, and subsequent part ejection. Injection molding is well-suited for large-scale production due to its high repeatability and capability to produce intricate structures. Nevertheless, it presents challenges such as high capital expenditure for mold fabrication and processing limitations associated with the viscosity and thermal sensitivity of certain biodegradable polymers [60].

Blow molding

Blow molding is an established thermoplastic processing technique employed for the fabrication of hollow structures such as bottles and containers. The process commences with the formation of a preform, which is subsequently heated to its viscoelastic state and subjected to pressurized air within a mold cavity, enabling it to conform to the mold’s geometry. This is followed by cooling and ejection of the finished product. The method is characterized by high production efficiency and the capability to produce lightweight yet mechanically robust components. However, its application with biodegradable polymers is constrained by their rheological limitations and sensitivity to thermal and shear conditions [61].

Thermoforming

Thermoforming is a widely utilized processing technique wherein a biodegradable plastic sheet is heated to a pliable forming temperature, positioned over a mold, and shaped using vacuum or pressure. This method is extensively employed in the fabrication of packaging components such as trays, blisters, and containers. The process encompasses sequential steps: thermal softening of the polymer sheet, molding under applied force, cooling to solidify the structure, and subsequent trimming of excess material. Thermoforming offers high production efficiency and design flexibility across a range of geometries. However, it is constrained by sheet thickness limitations, which may lead to non-uniform wall thickness in the final products [62].

Film casting

Film casting is a widely utilized technique for producing thin films of biodegradable polymers, particularly for applications in packaging and barrier materials. This method enables precise control over film thickness and physicochemical properties. The process involves the extrusion of polymer granules, which are melted and subsequently cast onto a cooled casting surface. The molten polymer undergoes controlled solidification, followed by film collection onto rolls for storage or further processing. Film casting facilitates the fabrication of uniform, high-quality films with tailored characteristics. Nonetheless, achieving optimal cooling rates remains critical, as inadequate thermal regulation may lead to structural defects such as warping or thickness irregularities [63].