Membrane technology has been extensively used in various applications, including but not limited to waste/wastewater treatment, gas separation, hemodialysis, energy production, drug delivery, and the food industry. Polymeric membranes are mainly employed in all those separation processes [1,2]. The production and disposal processes of polymeric membranes result in unsustainable accumulations of waste and several environmental concerns [3,4,5,6,7]. Even though these types of membranes are more prevalent and dominate the membrane market, they are still subject to waste disposal challenges, chemical, mechanical, and thermal stability concerns, as well as the membrane fouling issue [7]. As an environmentally friendly and sustainable approach to solving these problems, biodegradable membranes have been introduced, especially to reduce the amount of waste disposal. Under favorable conditions in the environment in terms of pH, humidity, and temperature, biodegradable membranes are broken down into non-toxic compounds by enzymes and microorganisms in nature [1]. Biodegradable membranes proved to be potential substitutes for conventional membranes in various applications such as oil/water separation, dye removal, tissue engineering, food packaging, fuel cells, etc. [1,8,9,10,11].

Synthetic polymer materials have been developed less than 100 years ago but because of their low ability to be utilized in nature are considered to have serious ecological impact on the environment. The interest in biodegradable plastics is constantly increasing, and their production is forecasted to reach more than 1.3 million tons in 2024 [12]. The main position on the biopolymers market belongs to the Asia-Pacific region, North America, and Europe [13]. All biodegradable polymeric materials considered in this chapter could be divided into two main classes: bio-sourced and synthetic. Synthetic materials, in turn, fall into two categories: petrochemical and made out of renewable sources, which is illustrated on Figure 1.

Bio-sourced materials have been used by humanity since ancient times as materials for construction (wood), tools (wood, bones), cloth (plants, leather, wool, fur), jewelry (bones, wood, amber), and other. Nowadays we also use bio-sourced crude to create new materials, including membranes. The majority of bio-sourced polymers used for membrane fabrication are carbohydrates/polysaccharides and their derivatives. The origin of bio-sourced materials possesses a high degree of biodegradability that makes them attractive as green materials to be used for reducing pollution of the environment with plastic wastes.

Cellulose is one of the first materials used for membrane production. Thus, the first membrane for hemodialysis was produced from cellophane, which is the product of cellulose treatment. Cellulose is one of the most prevalent polysaccharides that occurs in natural sources like trees and plants. Saccharide monomer units in cellulose (see Figure 2A) macromolecules are arranged predominately in a linear manner, which results in its fiber structure and high mechanical properties.

Due to the presence of active hydroxyl groups in the saccharide unit, cellulose is widely used for its modification to obtain new artificial materials with improved properties. Some of the structures that resulted from cellulose modification are presented on Figure 2A.

Thus, the most common cellulose derivative is cellulose triacetate, which is, along with other cellulose derivatives, used as the fabrication material for membranes applied in many industries such as oil-water separation [14,15,16], antifouling improvement [17], virus removal [18], heavy metal adsorption [19,20], desalination [21,22,23], hemodialysis [24], and gas separation [25,26,27].

Chitosan is the second (after cellulose) most abundant biopolymer in nature that can be found in insects, shells, mollusks, shrimps, crabs, fungi etc. It also can be derived from chitin (the exoskeleton of many living creatures, insects in particular) by its deacetylation (see Figure 2B).

Though this biopolymer is widely spread in nature, the research of chitosan began only in the 1980s because of the structure’s features and insolubility in water [28].

Examples of chitin and chitosan membranes applications are ion exchange membranes [29,30,31], wastewater treatment [32,33], oil-water separation [34], dye removal [35], etc.

Carrageenan is a naturally occurred polysaccharide containing sulphate groups. This polymer can be extracted from red algae, particularly from Rhodophyceae [36]. Depending on the degree of sulfanation, there are three classes of carrageenan: kappa, iota, and lambda. The structure of carrageenan is shown on Figure 2C. One carrageenan application example is the super-oleophobic membrane for the removal of dyes and heavy metals [37].

Starch is another example of a polysaccharide. It is one of the most abundant biopolymers in nature and can be found in such common products as potato, corn, and rice. Due to its branched structure, resulting in poor mechanical properties, starch can be hardly used as the main material for membrane production [38]. Thus, starch was reported to be used as an additive to produce membranes for wastewater treatment [39,40,41].

Cyclodextrin (CD) can also be used as an additive for the improvement of hydrophilicity and permeability of membranes used for water treatment [42]. The functionalization of hydroxyl groups to amino, sulphonyl, and other groups resulted in the further improvement of membrane selectivity by enhancing porosity and hydrophilicity [43].

Alginate is a naturally occurring anionic water-soluble linear polysaccharide composed of α-L-guluronic acid and β-D-mannuronic acid (see Figure 2D), typically obtained from brown seaweed (Phaeophyceae), including Laminaria hyperborea, Laminaria digitata, Laminaria japonica, Ascophyllum nodosum, and Macrocystis pyrifera [44]. Alginate-containing membranes were reported to be used for dyes and heavy metal removal [45,46,47,48,49].

Silk fibroin is another natural biopolymer, extracted from insects’ cocoons when treating them with hot alkali solution [50]. This protein is added to membranes to improve their adsorption of heavy metal ions [51,52].

Similar to fibroin, collagen can be extracted from animal connective tissues [53]. Despite being sensitive to pH, temperature, and bacteria, collagen can be used for membrane fabrication, though its application is limited. Due to its protein nature, collagen is perfectly suitable to create fiber-type membranes for oil-water separation [54] and pervaporation [55,56].

Polyhydroxybutyrate (PHB) is bio-derived polyester (see Figure 3) that is produced by some microorganisms such as Cupriavidus necator, Methylobacterium rhodesianum, or Bacillus megaterium during assimilation of glucose or starch [57].

This polymer has a tensile strength close to polypropylene, making it suitable to manufacture fibers. As a result, PHB has been used to prepare electrospun fibers-based membranes with improved antibacterial properties for medical applications, dye removal, and microfiltration [58,59,60,61].

Polylactic acid (PLA) is a thermoplastic polyester that is produced by polycondensation of lactic acid or ring-opening polymerization of cyclic diester-lactide (see Figure 4). Lactic acid, in turn, is produced from a renewable bio-source, such as sugarcane or starch, [62] by aerobic fermentation [63]. PLA is one of the most researched and mass-produced biodegradable polymers.

PLA belongs to semicrystalline polymers. PLA-application temperatures are limited by its low glass-transition temperature (T_g = 55–60 °C) and melting temperature (T_m = 170–180 °C) [64]. PLA is suitable to prepare membranes based on electro-spun fibers for oil-water separation [65] and tissue regeneration [66]. PLA biodegradation proceeds quite fast to CO₂ and water [67], which meets all the requirements of all standards for biodegradable plastics [68]. PLA is also suitable for decomposition as a part of compost [69].

Polybutylene succinate (PBS) is another (like PLA) example of a biodegradable polyester that is produced by polycondensation of succinic acid and 1,4-butanediol. Succinic acid can be produced through biomass fermentation [70] by further hydrogenation to 1,4-butanediol [71]. The further polycondensation process of succinic acid and 1,4-butanediol proceeds in two steps and requires catalysts to produce a polymeric PBS from its oligomers, obtained in the first step (see Figure 5). The first mass production of this polymer began in 1990s in Japan by the Showa Highpolymer company [72]. PBS are reported to be used for the fabrication of membranes for pervaporation and other applications [73,74,75]. PBS biodegradation in soil was reported to proceed with 65% carbon mineralization (conversion to CO₂) for 425 days [76].

Poly-ε-caprolactone is an aliphatic polyester, produced by ring-opening polymerization of ε-caprolactone (see Figure 6A) [77]. This polymer has a low Tg = −55–60 °C and low melting point of Tm = 60–65 °C and good resistance to oil and water. Examples of using poly-ε-caprolactone for membranes include dye removal [78], wound dressing [79], antifouling [80], treatment blood infections [81], and guided tissue regeneration [82] applications. Furthermore, poly-ε-caprolactone is highly degradable polymer. Thus, Pseudozyma japonica-Y7-09 enzyme, which is present in different microorganisms, results in Poly-ε-caprolactone degradation by 93.3% for 15 days for polymer film and 43.2% for 30 days when the polymer was made as foam plastic [83].

Polypropylene fumarate (PPF) is an aliphatic polyester, containing a double bond in the main chain. This polymer can be produced by multistep synthesis (see Figure 6B) [84]. Because of the presence of double bonds, this polymer can be cross-linked by various methods which, results in the broad mechanical properties of the resultant structures [85]. Although, the mechanical properties are still low and limit the use of PPF for the membrane and other applications. However, some new approaches have been applied by the introduction of nanofillers into PPF to improve its properties [86,87,88]. The in vitro biodegradation of PPF scaffolds revealed nearly 17% mass loss at 6 weeks [89].

Polyethylene glycol (PEG) is a synthetic polyether that can be produced by various ways: from ethylene oxide, ethylene glycol, or ethylene glycol oligomers (see Figure 6C).

PEG production has been reported in 1859 by both A. V. Lourenço and Charles Adolphe Wurtz, independently. PEG membranes are predominately used for drug release systems [90,91,92,93,94]. In addition, PEG is well known to possess sensitivity to oxidative degradation [95]; thus, this material is substantial to oxidative biological degradation by different microorganisms [96,97,98].

Polyvinyl alcohol (PVA), unlike most of other vinyl polymers, cannot be produced by polymerization of its monomer units because vinyl alcohol is thermodynamically unstable. PVA is predominately produced by hydrolysis of polyvinyl acetate (see Figure 7). Hydrolysis reaction is usually proceeded in the presence of ethanol but can be easily done without it.

PVA has been reported to use for membrane preparation for wound dressing applications [99,100]. In addition, PVA is biodegradable in the presence of different microorganisms under two-step metabolic processes, including oxidation and hydrolysis [101].

Polyurethanes (PU) are one of the most produced polymers in the world. Around 25 million tons of this class of polymer was produced in 2019, which is about of 6% of all manufactured polymers [102]. The interest to polyurethanes is determined by the broad chemical variety of monomer units, resulting in a wide range of physical properties–from rigid and strong plastics to flexible elastomers [103]. Linear PU are basically produced during polycondensation reaction between diisocyanates and diols (see Figure 8A, step 2A) with the ability to produce polyurethane urea when a diamine chain extender is used on the second synthesis step (see Figure 8A, step 2B).

Polyurethanes were known for a long time as non-degradable polymers. For the last decades, biodegradable PU were developed by using monomer units with hydrolysable bonds (e.g., ester, amide) groups [104,105]. Examples of oligomeric diols [106,107] used for biodegradable PU synthesis are given on Figure 8B. A broad opportunity to adjust and control PU chemistry and structure makes PU degradable by enzymes, fungi, and bacteria [108].

PU applications include sprayable membranes [109], tissue repair [110], and many other biomedical applications [110].

The biodegradable membranes synthesis routes and main applications are summarized in Table 1.