Ocean Plastics: Extraction, Characterization and Utilization of Macroalgae Biopolymers for Packaging Applications

Abstract

This review details the extraction, characterization and utilization of seaweed-derived biopolymers for future packaging applications. The review is contextualized within the broader scope of the challenge of plastic pollution and the current urgent need for more sustainable packaging materials. Macroalgae (or seaweed) has been highlighted as a promising source of biopolymers, most commonly sodium alginate, agar and carrageenan, for reasons such as a rapid growth rate and decreased environmental impact when compared with terrestrial plant life. Extraction methods detailed include traditional solvent-based extraction and more sustainable developments such as ultrasound-assisted extraction, microwave-assisted extraction and bead milling. This review additionally presents the characterization techniques most pertinent in determining the applicability of these biopolymers in packaging applications. Properties of key importance to the development of sustainable packaging materials such as thermal properties, mechanical strength, barrier properties and biodegradability are highlighted in comparison to conventional petroleum-based plastics. This review concludes by realistically identifying the challenges faced by implementing seaweed-based biopolymers into packaging structures, such as cost-effectiveness, scalability and performance while suggesting future directions to mitigate these issues and improve the commercial viability of these materials for the packaging industry.

1. Introduction

Humanity currently generates in excess of 350 million metric tons (MMt) of plastic waste annually [1]. Without the effective implementation of additional regulations or alternative materials, this volume is expected to double by 2050 and more than triple by 2100 [2]. Of the approximately 400 MMt of plastic produced annually, 14 MMt ends up in ocean environments, accounting for 80% of all marine debris [3]. The impact of oceanic plastic pollution can be directly observed in its impact on marine life. Marine plastic may injure and kill ocean life, and studies have shown that plastic impacts 44% of seabird species, 56% of marine mammals and up to 100% of sea turtle species [4]. These impacts involve death via ingestion, suffocation, starvation, entanglement and infection [5]. The vast volume of generated plastic waste and improper disposal thereof, particularly with unintentional release into marine environments, has led to a global environmental crisis, with the UN anticipating ocean plastic leakage to triple by 2040 [6,7]. This crisis has driven the ever-accelerating interest in the development and commercialization of more sustainable, environmentally friendly materials. Despite their undoubted versatility and beneficial attributes, synthetic petroleum-derived polymers have been defined as the primary contributor to the ocean plastic crisis because of their non-degradability, persisting for decades in oceanic environments [8]. Though there exists a vast array of sustainable biopolymer sources within the terrestrial realm, their extraction and use may lead to excess land usage, water usage or removal of potential food sources. Macroalgae-derived biopolymers have therefore become promising candidates as they do not require or detract from any of the previously mentioned criteria.

Plastics have long been regarded as the pinnacle of versatility in the context of material applications. While metals still remain a superior option in some cases for their excellent thermal conductivity and durability, this gap is being closed by the introduction of better plastic composites and extensive characterization of traditional polymers. Polymers have become staple materials in modern industry because of their ability to be substantially altered on a molecular level to achieve specific material properties [9]. This versatility has led to plastics being able to fulfill a significant number of prerequisites for both common commercial components for mass production [10] and niche medical applications in drug delivery [11]. While plastics are lauded for their diversity and have evidently benefited from massive market growth since their inception, these materials have had a severe environmental impact. This is an indirect result of these synthetic materials’ centuries-long degradation period [12], and the data show that synthetic polymers will persist in the environment so long as they are not disposed of correctly. It has been a common trend to attribute this material property to the significant environmental consequences that currently dominate the planet; however, it is primarily the consistent and gross mismanagement of these materials on a global scale that has propelled the issue of plastic waste into a global crisis [13]. Plastic waste production has exceeded 400 million tons in recent years [14] and is predicted to surpass 600 million tons in the next decade [15]. The exponential increase in plastic waste is supplemented by poor waste management, with only 12% of plastics being recycled and over 50% going to landfill [16]. The scope and permanence of this issue have resulted in positive innovation and developments in the area of sustainable and renewable biopolymers. These materials offer promising alternatives to traditional synthetics, and their introduction and growth in the commercial market will act to reduce the issue of non-degradable waste significantly by providing fast and effective degradation rates, which have been observed in materials such as PLA, PHB and a wide range of algae-based polysaccharides [17,18].

Macroalgae (commonly referred to as seaweed) are rapidly renewable, sustainable and biopolymer-rich materials. Compared with terrestrial plants, seaweed shows a significantly faster growth rate. Farmed seaweed has displayed a harvested mass of 13.1 kg.m² over a period of 7 months, whereas conventional land plants have shown a harvestable mass of 0.5–4.4 kg.m² over 12 months [19]. An additional benefit regarding the utilization of farmed seaweed for polymer extraction is gained from the fact that seaweed farms do not require fertile land, fertilizers or additional water usage, all of which carry significant economic outlay [20,21]. Seaweed in general is characterized as belonging to one of the following three families, depending on the pigmentation of the seaweed: red (rhodophyta), green (chlorophyta) or brown (phaeophyta) [22]. Predominantly, carrageenan, agar and alginate are the biopolymers extracted from these species of most interest for packaging materials.

The market for biopolymers is still relatively small, accounting for 1–10% of the plastic market [23], although this figure is predicted to rapidly increase as the global demand for sustainability in both materials and processes has seen a notable rise in recent years [24]. A consistent barrier to the full commercialization of these materials is the high cost involved with their production. Feedstocks for biomaterials can contribute to over 50% of the total cost of production and, in many instances, can incur a large cost [25]. This causes biopolymers to cost many times more than traditional synthetics to produce, reducing their viability in the market [26,27]. Seaweed-based biomaterials have been of particular interest in recent times, and they have displayed many distinct advantages in comparison with terrestrial biomaterials. Seaweeds or macroalgae offer extremely abundant and arable materials with growth rates as much as ten times that of terrestrial materials [28]. The polysaccharide and protein contents are also notably high in these materials, ranging from 4–76% to 5–47%, respectively [29], making them ideal candidates for biomaterial production.

Seaweed polysaccharides provide a number of desirable characteristics for commercial use including considerable mechanical properties, impermeability and film-forming abilities [30]. These properties are seen in presently developed agar, alginate and ulvan composites [31]. The primary attraction of these composites lies in their ability to be enhanced to provide unique properties for packaging materials. In many instances, these materials provide additional protection in food packaging applications when compared with traditionally used synthetics. Composite materials created with agar have shown antibacterial properties against E. coli, Salmonella and Staph and enhanced UV barriers while maintaining functional mechanical properties [32,33].

While these materials represent a promising future in sustainable and low-impact processing, there are barriers to production that require further research and development to overcome. Seaweed-based polysaccharides can suffer from poor mechanical and barrier properties when used as a single material [34], as well as historically using extraction techniques that employed toxic non-degradable organic elements [35]. These materials and the methods of processing are still in their infancy and require a multi-faceted approach to be considered a viable alternative to traditional synthetics.

This body of work aims to provide a comprehensive review of common seaweed polysaccharides, namely, agar, carrageenan and alginate, with reference to additional data relating to ulvan and fucoidan. This overview reviews a significant range of the literature with the purpose of exploring the commercial viability of polysaccharide-based films through analysis of extraction, purification and formulation techniques as well as extensive data on characterization and the development of new applications through these channels. Many of the challenges faced with the commercialization of algae polysaccharides are discussed and analyzed, while the physiological benefits, future directions and impact of these polysaccharides as a sustainable and renewable alternative to traditional synthetics are considered in detail.

2. Extraction and Characterization of Seaweed Biopolymers

2.1. Extraction Methods

The extraction process used to obtain biopolymers from seaweed biomass is a pivotal selection as it may influence both the purity and yield of the biopolymer in question. So too may it impact the applicability and functionality of the material, especially as it pertains to packaging materials. Pertaining to phytophytae, dependent on the specific species utilized and extraction solvents used, the yield of alginate may range from 8% (Colpomenia peregrina) to 52% (Laminaria digitata) [36,37]. Conventional extraction methods for seaweed biopolymers have been criticized for their reliance on toxic solvent use, timeframe and energy usage [38], which, in combination, muddy the concept of a sustainable material. The focus of research in recent years has been a shift towards more sustainable, time-efficient and environmentally friendly extraction methods. This section provides an overview of the most prevalent extraction methodologies used today.

2.1.1. Traditional Methods

The traditional extraction process for biopolymers from seaweed, solvent extraction (SE), involves the following four steps: (i) pre-treatment, (ii) dissolution, (iii) filtration and (iv) purification, recovery and drying. Though these are generally the four steps involved, the exact manner by which they are performed differs depending on whether agar, carrageenan or sodium alginate is the biopolymer in question, as outlined in Figure 1.

Agar

Agar (Figure 2) is a polysaccharide found within the cell walls of certain species of rhodophytae [40]. Agar is derived predominantly from rhodophyta, primarily the species Gelidium, Gracilaria and Pterocladia [40]. It is a versatile biopolymer with excellent gel-forming ability, stabilization and thickening properties and has found use in industries ranging from culinary to microbiological [41]. Because of its gelling and thickening properties, agar is extracted and used as a food-safe additive [42]. Composed of agarose and agaropectin, both fractions possess a similar galactose backbone; however, agaropectin possesses a more complex structure owing to the many variants possible [43].

Agar extraction from red seaweed primarily consists of alkali pre-treatment, extraction, filtration, concentration and drying. The specific conditions of alkali pre-treatment differ according to species. If Gelidium is the chosen species, the pre-treatment occurs with a mild concentration alkali solution, whereas if Gracilaria is used, a sodium hydroxide solution (0.05–7%) at elevated temperatures (85–90 °C) for 1–2 h is required. The treated biomass is subsequently washed in water prior to undergoing acidic extraction at a pH range of 6.3–6.5. Following filtration, the concentration of the extracted agar is carried out through several rounds of freeze–thawing or using a syneresis method.

Carrageenan

Carrageenan (Figure 3) is a high-molecular-weight sulphated galactan found in the cell walls of rhodophyate. It is composed of alternating units of 3,6 anhydro-galactose and D-galactose joined by α-1,3, and β-1,4-glycosidic linkages [44]. Although initially used in the food industry as a thickening ingredient, its gelation, emulsifying and stabilizing properties have allowed carrageenan to find current usage in a diverse array of fields [45].

The extraction of carrageenan from red seaweed occurs primarily using two methods, both utilizing alkaline solutions for extraction. In the first method, carrageenan is recovered via precipitation using an alcohol (e.g., IPA). The second method, known as the gel-press process, involves the formation of a carrageenan gel with potassium chloride (KCl). The first method, alcohol precipitation, is applicable to all varieties of carrageenan, whereas the gel-press process is only applicable to the extraction of κ-carrageenan [46,47].

Sodium Alginate

Alginate (Figure 4) forms naturally as a cell wall polysaccharide in phytophytae (brown seaweeds). The presence of alginate within the cell walls allows for the plant to possess flexibility and maintain a strong overall structure to prevent injury when exposed to tidal forces [48].

The extraction of sodium alginate (NaAl) involves the alkaline treatment of phaeophyta, typically with sodium carbonate (NaCO₃), which leads to the solubilization of NaAl [49]. Subsequent acidification precipitates the alginate as alginic acid [50]. Neutralization of this solution further leads to the formation of NaAl. The extraction process may be varied and tailored to obtain NaAl with various molecular weights (M_w) and compositions depending on the requirements of NaAl [38].

2.1.2. Enzyme-Assisted Extraction

Though the conventional method, SE, is effective at extracting biopolymers from seaweed strains, it is not without its limitations, chief amongst them being the reliance on heavy solvent usage and the overall time-consuming manner of the extraction method. As such, over the years, more sustainable methods have been sought out. One promising alternative is enzyme-assisted extraction (EAE). EAE (shown schematically in Figure 5) is a promising, eco-friendly alternative to SE owing to its lack of solvents, high efficiency and gentle extraction conditions [38]. Though this method utilizes enzymes that are food-safe and suitable for large-scale production, certain enzymes are cost-prohibitive, which has limited their widespread industrial usage [51]. Primarily, proteases and cellulases are used in order to disrupt the structural integrity of the cell wall. Various factors such as pH, enzyme concentration and time may influence both the specificity and selectivity of the enzymes. These factors must, therefore, be considered prior to commencing the extraction process in order to optimize the enzymatic reaction [51]. As the enzymes have a specific affinity for substrates, they may be used to effectively target and subsequently release the biopolymer in question, thereby increasing yield. Though EAE has shown such advantages compared with conventional extraction methodologies, it is increasingly being used as a pre-treatment method prior to extraction via ultrasound, microwave, or subcritical water extraction [52,53,54].

2.1.3. Microwave-Assisted Extraction

A further developed sustainable extraction method is that of microwave-assisted extraction (MAE) (Figure 6). As the name implies, this method utilizes microwave energy, commonly in frequencies of 915 MHz or 2.45 GHz, to heat the solvent and seaweed biomass in a rapid and uniform manner, which in turn leads to an accelerated extraction of biopolymers [53,55]. In principle, this method relies on the interaction between microwaves and molecules found within the seaweed matrix via ionic conduction and dipole rotation [56,57]. The electromagnetic microwaves result in a homogenous distribution of heat that accelerates cell wall degradation and allows the biopolymeric compounds to diffuse into the extraction solvent [58,59]. In general, compounds extracted from seaweed via MAE tend to display higher yields and use less energy, time and solvents compared with conventional methods, thus presenting a more eco-friendly approach to biopolymer extraction [60,61].

2.1.4. Ultrasound-Assisted Extraction

Ultrasound waves are mechanical waves that propagate through media, be it gas, liquid or solid, above frequencies detectable by the human ear, i.e., >20 kHz [62,63]. The mode of propagation, compression and rarefaction leads to the creation of areas with negative pressure within a liquid. When the pressure exceeds the tensile strength of the surrounding liquid, vapor bubbles are formed, and when exposed to strong ultrasound fields, they implode in a phenomenon called cavitation [64]. This process of cavitation, when occurring near the liquid/solid interface, forces a high-pressure stream of liquid through the open cavity at surface level, thus leading to peeling, erosion and particle breakdown, thereby allowing for biopolymer release from the seaweed matrix [64]. The use of UAE for biopolymer extraction can reduce the overall timeframe of extraction, prevent excess solvent usage and lower the process cost. Martínez-Sanz et al. demonstrated that implementing UAE (Figure 7) can significantly reduce the extraction time of agar from red seaweed with no significant effect on the yield of agar [65]. Though UAE presents such benefits, it is not without its limitations, with additional studies showing reduced yields compared with conventional methods. Goméz Barrio et al. compared the conventional extraction method to UAE for the extraction of agar from Gelidium sesquipedale. The conventional method provided a total yield (extraction and re-extraction) of 37.7%, whereas, the UAE method provided a total yield of 28.16% [66]. Promising work has been performed using a combination of UAE as a pre-treatment method followed by EAE for biopolymer extraction in order to overcome the limitations of the two methods. Li et al. found that utilizing these methods in combination can increase the agar yield 2–6-fold compared with a non-enzymatic extraction, while the incorporation of ultrasonication reduced the processing time to below one hour [67].

2.1.5. Supercritical Fluid Extraction

Supercritical fluids are liquids exposed to temperatures and pressures exceeding the critical point. As the temperature increases, the density of the liquid decreases owing to thermal expansion; meanwhile, as the pressure increases, so too does the density of the gas. The point at which these densities are identical is termed the critical point, and at this point, the distinction between the liquid and gaseous phases disappears [68]. For the majority of applications involving the extraction of natural compounds (>90%), supercritical carbon dioxide (Sc-CO₂) is used as the solvent for supercritical fluid extraction (SFE) (Figure 8) [69]. The use of Sc-CO_s as the solvent of choice is due to its wide abundance, non-toxicity and low critical conditions in addition to being both non-flammable and non-explosive [70,71,72].

Previous extraction techniques have posed several disadvantages, chiefly being time-consuming, having low selectivity and requiring large volumes of high-purity organic solvents. In response to these disadvantages, sub- and supercritical fluid extraction (SFE) using supercritical CO₂, or subcritical water as the solvents were developed. As a process, SFE can be described in two steps as follows: (i) single extraction and fractional separation. By decreasing pressure in the separation devices, the bioactive compounds extracted in a single step may be fractionated. (ii) Sequential extraction involving progressively increased severity. In the initial steps, mild conditions are enhanced through the further extraction of the solid residues.

Supercritical fluid extraction, particularly with carbon dioxide (CO₂), offers a green alternative to traditional solvent-based methods. At supercritical conditions, CO₂ possesses unique solvent properties that can efficiently extract biopolymers from seaweed. This method eliminates the need for toxic organic solvents and reduces energy consumption by operating at lower temperatures than conventional extraction processes. Supercritical CO₂ extraction is also known for its high selectivity and ability to produce biopolymers of exceptional purity and quality.

2.1.6. Subcritical Water Extraction

As discussed, the heavy use of organic solvents is seen as a major disadvantage of conventional extraction techniques owing to the non-sustainability of the chemicals. The ideal extraction solvent from both the environmental and toxicity perspectives is water, though water at low temperatures presents poor extraction efficiency [73]. Water that is maintained in the liquid state at temperatures between 100 °C (boiling point) and 374 °C (critical point) at pressures below 1–22.1 MPa (critical pressure) is referred to as subcritical water [74]. To enhance the yield of extracted biopolymers, an ionic liquid (IL) catalyst may additionally be used. ILs have gained recognition as an environmentally benign alternative to traditional organic solvents as they possess the ability to dissolve a wide array of both organic and inorganic substances, show low vapor pressure and display high thermal stability [75]. This is shown schematically in Figure 9.

2.1.7. Bead Milling

Bead milling (Figure 10) offers a sustainable and effective method for polysaccharide extraction. This method of extraction uses mechanically agitated beads in a circular vessel, which collide with solid particles to form nanoparticulate powders. The process is commonly aided with a solvent or liquid such as KCl and ethanol and is referred to as “wet beading”. Bead milling is a promising method as it offers a fast and efficient extraction of proteins, lipids and carbohydrates (polysaccharides) from the seaweed [76]. Recent studies by Postma et al. and Firdayanti et al. explored the potential advantages of bead milling as an extraction method with positive results. In both studies, polysaccharide yields were as high as 67%, 62%, 46% and 40% for carrageenan, Chlorella vulgaris, Tetraselmis suecica and Neochlori oleoabundans, respectively [76,77]. The total time taken for a 99% protein release was relatively quick at 400 [s] in the study by Postma et al., and a maximum polysaccharide yield was recorded at 50 [mins] in the study by Firdayanti et al. The fast processing times and relatively high yields make bead milling a notable candidate for the larger scale production requirements common to packaging films.

2.2. Characterization Techniques

Within the context of using seaweed-based biopolymers for the development of various packaging structures, the specific characterization techniques employed are an essential selection in order to ascertain applicability to the production processes involved. The overall complexity of the structures requires a comprehensive suite of analytical techniques to determine the physicochemical, mechanical and functional properties of the individual materials. This section provides an overview of the most relevant analytical techniques used to characterize seaweed-derived biopolymers for the purpose of packaging applications.

2.2.1. Molecular Weight Determination

As is the case for conventional petro-derived polymers, the molecular weight (M_w), of seaweed biopolymers directly influences various physical properties such as viscosity, barrier properties and tensile strength [78,79], essential criteria for the development of packaging structures. The literature has reported a variety of methods to determine the M_w of seaweed biopolymers such as gel permeation chromatography (GPC), sedimentation analysis in analytical ultracentrifugation, intrinsic viscosity and light scattering [80,81,82,83]. As mentioned, it is imperative to characterize the M_w of the biopolymer as it directly influences the resultant properties of the polymer. Ureña et al. examined the effect of M_w and the ratio of mannuronic to guluronic acid (M/G) of the properties of aqueous solutions of alginate and the resultant films. The aqueous solutions of high-M_w alginate displayed a greater apparent viscosity and shear-thinning effect than the lower-M_w alginates. The resultant films, however, showed no significant difference in regards to either their mechanical (Young’s modulus, tensile strength and elongation at break) or barrier (O₂ and water vapor) properties [84]. Freile-Pelegrín et al. examined the tensile properties of agar films exposed to rural–urban atmospheric conditions over a period of 90-days. The films displayed a progressive deterioration in mechanical properties, with a 50% reduction in tensile strength noted by day 45. This reduction in tensile properties was posited as being due to a reduction in M_w caused by chain scission induced by photodegradation [85].

2.2.2. Spectroscopic Analysis

Materials can be identified with a unique “fingerprint” based on the visual spectra produced in spectroscopy, many of which are commercially available for reference and comparison with lab results. Fourier transform infrared spectroscopy (FTIR) works by measuring the absorbance of infrared light on the y-axis versus the infrared spectrum (intensity) on the x-axis. Materials are typically identified through the analysis of their absorbance bands or peaks at certain ranges in the spectra. These can be either group frequencies or fingerprint frequencies seen at ranges of >1500 cm⁻¹ and <1500 cm⁻¹, respectively [86]. Functional groups represent specific ranges of infrared used to identify the presence of particular covalent bonds such as esters, ethers and alcohols, which all have unique absorption frequencies [87].

Spectroscopic analysis of algae provides a non-invasive, non-destructive method of characterization. A study carried out by Pereira et al. used both FTIR-ATR and FT-Raman spectroscopy to identify polysaccharides and characterize a broad range of algae through the analysis of their functional groups. Vibrational spectroscopic results of ι-carrageenan produced strong Raman bands at 845 cm⁻¹ and 930 cm⁻¹. This identified the backbone molecule for carrageenan–galactose-4-sulphate and the molecule 3,6-anhydro-D-galactose, consistent with the commercially available κ-carrageenan spectra. An additional peak occurred at 805 cm⁻¹, which verified the presence of sulphate esters, which is characteristic of the ι-carrageenan used in the experimental procedure [88]. Similarly, Lopez et al. reported on the characteristic spectroscopic fingerprint of agar via both FTIR and Raman spectroscopy, whilst Milivojević et al. presented similar identification for alginate compounds. A comparison of these spectroscopic analyses displaying the most prominent characteristic bonds found in these compounds is presented in

Table 1. Characteristic spectral wavelengths of algal biopolymers quantified via FTIR or Raman spectroscopy.

Biopolymer	Technique	Wavelengths (cm−1)	Identification	Ref.
Agar	FTIR	600; 800–1200; 890, 934, 1162; 1350–1500; 1648, 1671; 2926	Liberation of residual water molecules; C-O stretching; glycosidic linkage vibration; δCH2 vibrations; δH-O-H and δC = C vibrations; asymmetrical and symmetrical νCH	[89]
	Raman	2914; 2977; 2954; 1495; 1375; 1276; 1104	νs(CH2); ν(CH); νas(CH2); δCH2; ωCH2; τCH2; δCOH
Alginate	FTIR	3410; 1635; 1419; 1050	(-OH); asymmetric stretching vibration of COO groups; symmetric stretching vibration of COO groups; elongation of C-O groups	[90,91,92]
	Raman	807, 888 and 954; 1098;1300; 1413; 1625	δ C–O–H, skeletal (ν C–C, ν C–O, δ C–C–H, δ C–C–O); glycosidic ring breathing mode; carboxylate stretching vibration: symmetric stretching or C–O single bond stretching vibration; symmetric carboxylate stretching vibration; asymmetric carboxylate stretching vibration
Carrageenan	FTIR	3000–3600; 1643; 1241; 1069; 922; 847; 701	(–OH) stretching vibration; polymer-bound water; asymmetric stretching of O=S=O; glycosidic bond; ether group in 3,6-anhydrogalactose; C4–O–S sulphate ester bonding	[93]
	Raman	845; 930	D-galactose-4-sulphate G4S; 3,6-anhydro-D-galactose	[94]

. Spectroscopic analysis remains an important tool to analyze the molecular makeup of materials, identifying functional groups and the presence of unexpected elements and to characterize materials based on these functional groups.

2.2.3. Thermal Analysis

Seaweeds continue to be a promising bio-alternative to synthetic polymers; however, to understand the full capabilities and limits of algae-based polysaccharides, their thermal properties must be fully investigated. Data has shown that algae could function as a promising biomass for use as feedstock and presents as a viable biofuel [95].

A study carried out by Das et al. investigated thermochemical methods for the conversion of algal biomass to energy through torrefaction, pyrolysis and gasification. Fossil fuel reserves continue to be diminished, and as they begin to become dangerously finite, research into biofuel alternatives is essential, which was the primary driver of their study. Biofuel was created as a by-product of these thermochemical processes in liquid, solid and gas form, where it was concluded that supercritical water gasification was the most economically viable and energy efficient method from a range of pyrolysis, torrefaction and gasification methods. Gasification eliminated the drying process using samples of up 70 wt.% moisture [96]. Paired with the low environmental impact it provided the highest yields of tar, biochar and bio-oils [97].

A dominant focus of seaweed-based polysaccharides is their ability to be formed into films. The glass transition (T_g) and additional thermal transition temperatures of the materials are key parameters for this process and have been documented in a number of studies. Research completed in 2020 by El-Naggar et al. on the algae Chlorella vulgaris gave a comprehensive review of both differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), which showed exothermic transition crystallization temperature peaks of 144.1 °C, 162.3 °C and 227.7 °C as well as a thermostability maximum temperature of 240 °C. The ability to study these parameters is essential for both understanding and setting processing conditions for commercial use.

3. Properties of Seaweed Biopolymers

In order to integrate seaweed-derived biopolymers as successful sustainable packaging materials, a thorough understanding of the materials’ intrinsic properties is required. These seaweed biopolymers possess unique characteristics that only differentiate them from synthetic petro-polymers but also display their potential for usage as packaging materials. The packaging industry as a whole is one of, if not the most, informed industry in terms of material requirements, two of the most critical being barrier properties (food packaging) and mechanical properties (food and non-food packaging). This section places emphasis on the properties of seaweed biopolymers, namely, their mechanical and barrier properties, biodegradation and compatibility with conventional polymers, underlying their attractiveness for packaging applications. A summary of the main advantages and disadvantages of the primary seaweed-derived biopolymers is shown in

Table 2. Summary table of the major advantages and disadvantages pertaining to agar, sodium alginate and carrageenan.

Biopolymer	Applications	Advantages	Disadvantages	Ref.
Agar	Gelling agent (food), culture medium for bacteria, packaging films, drug delivery systems	Gelling ability, transparent gels, biocompatible, good film forming properties, antimicrobial	Brittle, poor mechanical properties, high permeability	[98,99,100,101]
Alginate	Wound healing, drug delivery, tissue engineering, bone healing, packaging film, active packaging	Gelling ability, biocompatible, good film forming properties, cross-linking activity, 3D scaffolding material (hydrogels, microcapsules, etc.)	Poor mechanical properties when not part of 3D scaffold, hydrophilic, poor barrier properties	[84,102,103,104,105]
Carrageenan	Gelling agent, packaging films, edible coatings, 3D printing, drug delivery	Biocompatible, good film forming properties, antimicrobial	Poor mechanical properties, hydrophilic, low thermal resistance	[106,107]

.

3.1. Biodegradability

Of vast concern to modern-day life is the effective disposal of plastic waste produced by our consumer-heavy lifestyle. In order to offset the growing environmental hazards caused by plastic pollution and incineration of conventional petroleum-based plastics, much interest is focused on polymers, which may biodegrade into non-harmful, inert compounds in the environment. These biodegradable plastics, composed of natural materials or chemically derived from non-petroleum sources, are being designed in order to achieve a minimal carbon footprint and recyclability or be entirely biodegradable with no potential to cause harm [108].

A leading factor in the accelerating interest in seaweed-derived biopolymers is their inherent biodegradability. The increased demand for sustainable packaging solutions driven by environmental concern and new legislation surrounding the use of petroleum-plastics is making the market accelerate rapidly. It has been demonstrated that while seaweed-derived bioplastics are biodegradable, the specific extraction methodology can affect the resultant biodegradation. Ling et al. prepared bioplastic films composed of agar extracted from Malaysian red seaweed (Gracilaria salicornia) via two methods as follows: alkali extraction (AE) and photo bleaching (PB). When buried in three different soil types for a period of 30 days, the AE films presented a mass loss of 61.51%, whilst the PB-extracted agar displayed a mass loss ranging from 25.78 to 43.27%. The rationale posited is that the PB extraction method yielded a denser molecular structure, which, in turn, led to a reduced capacity for water absorption and subsequent microbial growth [109]. Sari et al. similarly displayed the biodegradation of red seaweed (Kappaphycus alvarezii) in combination with glycerol. The biodegradation of the developed films, buried in soil, could be tailored by varying the ratio of seaweed/glycerol, with a 1:3 ratio displaying the highest degree of biodegradation (81.8%) over the testing period [110]. It is evident that though biodegradability may be tailored, this alone does not quantify seaweed as a sufficient packaging material, and this property must be balanced with sufficient mechanical and barrier properties.

3.2. Mechanical Strength

Petroleum plastics have become the undoubted packaging material for a variety of reasons, one of the main being tailorable mechanical strength, an essential criterion to ensure adequate protection of the contained product. In order for a seaweed-based biopolymer to be implemented as an alternative packaging material, it needs to display comparable mechanical properties to these conventional materials. The mechanical properties most relevant to packaging materials are the materials’ tensile strength and elongation at break [111]. Within the packaging industry, the most commonly employed materials are polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). An overview of these materials’ mechanical properties is shown in

Table 3. Packaging-specific mechanical properties of conventional petro-polymers.

Polymer	Elongation at Break (%)	Tensile Strength (MPa)	Ref.
HDPE	2131.1	27.93	[112]
LDPE	349.0	9.93	[112]
PP	690	22.3	[113]
PS	3.35	20.64	[114]
PVC	180.37	30.33	[115]
PET	1.87	40.02	[116]

.

As is evident in Table 3, there is a diverse array of mechanical properties available to packaging manufacturers and seaweed-derived biopolymers must be comparable in order to retrofit the existing packaging equipment. Though seaweed-based biopolymers display excellent film-forming characteristics with moderate tensile strength, the resultant films are predominantly brittle, which has hindered their widespread deployment in packaging applications [117]. To counteract this brittleness, methods such as plasticization, reinforcement, compounding or other alteration methods are employed in order to meet the high standards of petroleum plastics. Giz et al. demonstrated that the plasticization of sodium alginate with increasing proportions of glycerol and calcium increased tensile strength from 71.1 to 134.8 MPa (0% Ca) and 60.6 to 146.5 MPa (0.5% Ca) [118]. Similarly, Bhatia et al. showed that the tensile strength of carrageenan films can be improved from 65.2 MPa to 98.21 MPa through the incorporation of grapefruit essential oil (GFO) [119]. Hernández et al. likewise studied alterations of the tensile properties of agar for packaging applications. Utilizing a formulation containing 1% agar and 0.31% glycerol yielded an ultimate tensile strength of 22.69 MPa. Such studies show that seaweed-derived polymers, much like petro-polymers, display tunable and tailorable mechanical properties.

A common methodology in polymer processing to improve mechanical properties is to reinforce the base polymer with fillers or additional additives. For the purpose of enhancing the mechanical properties of seaweed-biopolymers, cellulose nanofibers (CNFs) have been the most studied reinforcement material. It has been shown that the addition of up to 15% CNFs can significantly improve the tensile properties of carrageenan polymers owing to the formation of hydrogen bonds between the CNFs and carrageenan, thus increasing the polymeric crosslinkages formed. Above 15%, the CNFs tend to form agglomerates, incompatible with the carrageenan matrix, thus leading to a reduction in tensile strength [120]. A comparison of the mechanical properties of various seaweed biopolymer/filler composites is shown in

Table 4. Mechanical properties of seaweed-based composite materials [121].

Material	Filler/Additive	Elongation at Break (%)	Tensile Strength (MPa)	Ref.
Seaweed	Cellulosic pulp fiber	2.5–5.4	45–81	[122]
Seaweed	Microcrystalline cellulose	13.57–19.17	20.21–29.76	[123]
Seaweed/Starch	−	6.17–18.4	41.37–65.73	[124]
Seaweed	Oil palm shell nanofiller	2.08–3.30	31.4–44.8	[125]
Seaweed	Neem leaves	17.64-20.73	34.55-39.95	[126]

.

3.3. Barrier Properties

The term “barrier properties” refers to the ability of a packaging material to prevent the migration of low-molecular-weight compounds (such as organic aromas, water vapor or gasses) through the packaging. Within the food packaging sector, this is of critical importance in order to maintain food safety and quality. Exposure to the aforementioned compounds may lead to lipid oxidation, microbial spoilage and deterioration of organoleptic properties [127]. Typically, the gasses of interest, and indicative markers of food spoilage, are water vapor, oxygen (O₂) and carbon dioxide (CO₂). Thus, the barrier properties of packaging materials are commonly quantified by the permeability rates of these gasses.

Within the packaging industry, it has been difficult to obtain singular materials that meet all demands with respect to barrier properties, thus leading to the growth in multilayer films in recent decades. In general, these structures tend to have defined layers that impart a water vapor barrier or O₂ barrier with subsequent layers, resulting in additional properties such as increased tensile strength, puncture resistance, tear strength, etc. As seaweed-derived biopolymers are themselves generally water-soluble, they commonly display a good barrier to O₂ but poor water vapor barrier properties. Sodium alginate films prepared by Kaczmarek displayed promising values for O₂ impermeability; however, it was noted that the water vapor transmission rate (WVTR) was much higher than that of petro-plastics and, as such, would be inapplicable with dry foods or fresh meat [128]. Carrageenan too displays moderate barrier properties though not sufficiently comparable to conventional materials. Carrageenan, as a linear polysaccharide film-forming material, has also been shown to be an effective barrier to O₂ and CO₂, thus decreasing loss of food quality during storage and transport. As films composed of carrageenan are swellable when exposed to water they display poor barrier to water vapor thus limiting its use [129,130]. Carrageenan may be obtained as a base material, semi-refined or refined though with each additional refinement step there is additional cost. Semi-refined is now the preferred option for the development of edible packaging films because, as compared with the refined form, it presents a lower economic output, whereas, compared with the base form, it displays improved physicochemical and barrier properties [131].

As is the case with enhancing the mechanical performance of seaweed biopolymers, the barrier properties may be further enhanced through the manufacture of composite materials or through the use of additives. For the improvement of WVTR, essential oils of various descriptions are commonly used. For example, Praseptiangga et al. prepared ι-carrageenan impregnated with cinnamon essential oil (CEO). It was demonstrated that increased proportions of CEO had a direct effect on the WVTR of the films, decreasing from 23.61 ± 0.85 g/m²h to 21.45 ± 0.63 g/m²h by incorporating a 0.5% or 1.0% loading of CEO respectively [132].

3.4. Compatibility with Other Materials

Because of the stringent requirements on food packaging materials in terms of mechanical, optical and barrier properties, seaweed-derived biopolymers may not be sufficient as a standalone packaging material. As a result, the manufacturing of polymeric composites or reinforced seaweed biopolymers has allowed for tailorable properties in these regards. Seaweed biopolymers have displayed a wide array of compatibilities with natural and synthetic polymers, fillers, fibers and additives. Such compatibility and development of biopolymer composites allows for tailored functionalities such as improved mechanical strength and barrier properties as well as imparting antimicrobial activity. Data have shown that polysaccharide composites have had success in both food packing with agar and nano clay [133] and drug delivery with alginate and montmorillonite [134].

Composites using seaweeds and other biomaterials are of particular interest because of the natural abundance of seaweeds their abilities to be blended with more expensive commercial biopolymers such as PLA as a form of cost reduction. While the data are not significant, some studies have been carried out. Adli et al. characterized a PLA/Algae powder composite for use in the packaging industry where optimal material performance in mechanical and thermal was found to be 3 wt% algae loading. A more comprehensive study carried out by Bulota and Budtova tested red, brown and green seaweeds at concentrations of 2–40% wt.% and particle size between <50 μm and 200–400 μm. Their results indicated that further improvements were required to overcome poor stress transfer in most of the test samples; however, it was found that at 40 wt% with large particles of green seaweeds, the modulus was superior to neat PLA [135]. The compatibility of different biomaterials can be beneficial for cost reduction and, in some cases, material performance. While studies on material interactions with PLA are limited, further characterization of PLA/algae and other biocomposites may be beneficial for the commercialization of these materials.

4. Applications in Packaging

4.1. Food Packaging

On an annual basis, roughly 30% of all produced food is wasted at each step along the supply chain and disposed of into landfills, a volume of food worth in excess of USD one trillion [136,137]. To mitigate this loss of otherwise perfectly edible food, the importance of effective food packaging cannot be understated. Because of their lightweight nature and broad versatility, petroleum-based plastics have become the dominant packaging material for the preservation of food produce. The inherent lack of sustainability of these materials along with legislation aiming to limit the usage and wastage of these materials and increased consumer demand for more sustainable options have driven the growth in biodegradable and bio-based packaging structures. Seaweed-derived polymers have emerged as a frontrunner in the development of these new packaging structures because of their abundance, unique physico-chemical characteristics and tailorable mechanical properties. This section discusses the application of these seaweed-derived biopolymers in food packaging, placing an emphasis on performance, innovations and consumer perceptions.

4.1.1. Innovations in Seaweed Biopolymer-Based Food Packaging

Traditionally, conventional packaging structures simply acted as a mechanical barrier to prevent contaminating or damaging the contained produce; however, over time, there has been a desire enhance the functionality of the packaging structure into so-called smart packaging. Smart packaging is broadly categorized as either active or intelligent packaging [138]. The differentiation arises based on whether additives are incorporated into the structure of the packaging to enhance or improve shelf-life (active) [139] or if the packaging possesses the capability to carry out functions such as sensing, tracing or communicating without interacting with the product (intelligent) [140].

Technological developments in recent years have led to seaweed-based biopolymers being examined for various food packaging applications. Carrageenan, agar and alginate have been extensively studied for their capability to develop edible and biodegradable films and coatings for fresh fruit, dairy and meat products [141,142,143]. Such developments not only contribute to enhanced sustainability by reducing packaging but also improve food preservation by providing an additional barrier to moisture, O₂ and microbial contamination. Additional innovations such as the incorporation of natural bioactive compounds such as antimicrobial agents or antioxidants allow for further extending the shelf-life of the contained good and improving the overall safety of the packaging [144,145].

One notable innovation is the development of intelligent packaging systems utilizing seaweed biopolymers. These systems can interact with food or the environment to provide real-time information about the food’s condition, such as pH changes indicating spoilage. By integrating natural pH indicators into alginate-based films, researchers have created packaging that changes color in response to microbial growth, offering a visible signal of food quality and safety to consumers. Han et al. prepared a dual function smart-active composite film based on carrageenan with nanoparticles of curcumin–zein–EGCG–carrageenan to improve the shelf-life of fresh fish. As the process of fish spoilage occurs, high levels of total volatile basic nitrogen (TVB-N) are produced, which causes a pH increase within the packaging structure. The carrageenan films produced undergo a color change in response to pH changes and so can act as an early indicator of spoilage to the consumer. Additionally, carrageenan films displayed lower TVB-N values than those of the control group after a 3-day period. As such it, was concluded that carrageenan-based composite films showed the capability to simultaneously monitor and control the freshness of the produce [146].

4.1.2. Performance Evaluation

Biomaterials offer a sustainable and greener alternative to synthetic petrochem processing, and many of their attributes are directly beneficial to human physiology with an extensive range of benefits including anti-cancer, anti-inflammatory and anti-bacterial properties [147]. Although biomaterial production only accounts for 0.5–2% of the annual plastic production, their status as fully renewable resources has led to positive predictions for exponential growth in the coming years [148]. Seaweed-based polysaccharides overcome some common issues prevalent with other biopolymers, namely, their ability to be cultivated and harvested much faster and cheaper than bio alternatives such as PLA and PHB [149]. For these materials to be considered as total replacements for synthetic polymers, they must have adequate performance comparable to the most commonly used commercial materials. Many biomaterials including seaweed polysaccharides suffer from poor material performance when exposed to adverse conditions. Evaluating the performance of these materials requires an understanding of the scope of their applications in a given setting and the purpose those applications. These details allow for the performance criteria of the material to be fully considered, and, in the context of packaging films, these are commonly associated with mechanical, barrier, rheological and optical properties [150]. This characterization of properties and performance of polysaccharide packing materials is essential for the development of reliable films that conform to industry standards and has been successful in the creation of many seaweed polysaccharide composites and mixtures for film applications [151,152,153].

4.1.3. Consumer and Environmental Benefits

As previously mentioned, seaweed possesses a major benefit compared with terrestrial plant life in that it does not take up excess land or food sources in order to grow. The farming of seaweed allows for controlling the growth of the crop and preventing potential damage to marine ecosystems such as coral reefs. The farming of seaweed thereby increases the rate of primary production via photosynthesis with significant contributions to the carbon, O₂ and nutrient cycles of the earth [154]. This process additionally reduces the rate of eutrophication and the emission of greenhouse gases [155]. Seaweeds may reduce eutrophication by removing excess nutrients from marine systems and releasing O₂ as a by-product [156]. The two major environmental impacts provided by seaweed farming are the sequestration of environmental carbon dioxide (CO₂) and deacidification of marine systems. CO₂ is far and above the greatest contributing gas to global warming, totaling 37.1 billion metric tons (GtCO₂) in 2022 [157]. Owing to the rapid economic development of developing nations, CO₂ emissions are expected to continue to rise; as such, it is imperative to implement measures to mitigate atmospheric CO₂ in order to offset and prevent environmental damage [158]. The farming of seaweed species is a promising route to mitigate global warming as seaweeds have the potential to fix higher carbon and more effectively remove atmospheric CO₂ than both microalgae and terrestrial plant life [159].

4.2. Edible Films and Coatings

Seaweed-derived biopolymers (agar, carrageenan and alginate) have found most use within the field of edible film and coating development owing to their excellent film-forming abilities and non-toxicity. It is worthwhile to note that though carrageenan is non-toxic, it may impart an inflammatory response when ingested; therefore, the development of edible films utilizing this biopolymer may have severe health implications for sufferers of Crohn disease, ulcerative colitis and inflammatory bowel disease [160]. The promising aspects in the development of edible films and coatings are threefold and include the following: (a) post-use, the “packaging” can be safely eaten by humans or animals with no hazardous health implications, thus facilitating a significant reduction in waste generation, (b) the film/coating facilitates easier product transportation by providing an effective barrier to outside contaminants and (c) edible films prevent food loss/waste by promoting an extended shelf-life compared with non-coated goods [161,162,163,164]. The rapid film-forming capabilities of these biopolymers allow for rapid packaging of the product with total conformation to the product’s shape with no material waste, thus providing an effective physical barrier to microbial spoilage. Sodium alginate films possess qualities such as high gloss, resistance, imparting no taste or odor to the produce and low permeability to O₂ [165]. Sodium alginate plasticized by glycerol has been used extensively as a film-forming coating for fresh fruit and vegetables, delaying spoilage and microbial contamination. Additionally, this coating allows for the preservation of color by preserving polyphenol and anthocyanin contents, thereby improving the post-harvest quality of produce [166,167,168].

4.2.1. Formulation and Development

The data pertaining to the formulation and development of seaweed-based polysaccharides is continually expanding. Currently, a broad range of composites and mixtures achieve enhanced material performance and specific functionalities. A considerable list of both potential and successful additives has been identified through the research and development of algae materials, with many of them significantly enhancing base materials [169]. While polysaccharides exhibit strong film-forming capabilities, additives or composite materials are often necessary. This comes from polysaccharides’ tendency for hydrolysis. This hydrophilic nature leads to poor barrier properties and, paired with the poor mechanical properties observed in some seaweed polysaccharides, has led to the consideration of other organic additives such as proteins, starches and cellulose fibers [170]. The development of packaging film made from polysaccharides has seen much development in recent years, with increases in strength, permeability and microbial resistance. While the applications of seaweed polysaccharides are still primarily packaging-based, there are still many new and distinct developments within this category. Research has shown applications such as packaging [171], active packaging [172] and coatings [173]. The development of alternative applications for seaweed-based polysaccharides will require further testing and development of these materials so that more versatile characteristics can be incorporated through organic additives or composites.

4.2.2. Properties and Performance

Algae biomass can be considered a third-generation feedstock or one that does not require the presence of arable land to be developed or cultivated [174]. These materials have gained traction because of their renewability and composition, which make them excellent candidates for material production. Seaweed-based materials are known for their high protein and polysaccharide (carbohydrate) contents, with values ranging from 25–77% to 5–43%, and a smaller lipid content of 1–5% [175]. Seaweed polysaccharides are typically anionic because of the presence of sulphate ester groups in their molecular structures [176]. This negative charge allows for a range of property alterations in the presence of oppositely charged (cationic) materials [177]. The tunability of seaweed-based polysaccharides makes them desirable for material processing applications, with particular interest in the previously mentioned packaging industry, and, in recent years, their applications in the medical industry using hydrogels [178,179]. The versatility of algae polymers and the ability to alter their properties to fit a specific or niche roles in industry is not yet fully explored, and much of the data reside primarily in the regions of food packaging applications with some breakthrough studies on hydrogel medical applications. Other studies have posited and explored their applications as nutraceuticals [180] and food additives to stabilize and thicken products [181]; however, the bulk of the data remain in packaging films and the medical industry. Further exploration into the advantageous health-boosting properties of these biomaterials and their application in medicine could lead to a much more diverse range of capabilities in the future.

4.2.3. Commercial Viability and Challenges

Biopolymers are considered to be the most desirable option for long-term sustainability and to replace finite petrochemical-based polymers. Many polysaccharides and biopolymers in general can be broken down into their base monomers through enzymatic degradation or hydrolysis. This characteristic alone generates particular interest in these materials as it promotes circular practices in terms of processing, allowing for large percentages of the materials to be reclaimed and reprocessed into new product [182,183,184]. In recent years, there has been a notable shift in the area of circular practices, with many corporations and countries shifting to more sustainable mindsets [185]. The shift towards more environmentally safer processing and renewability has indirectly increased the commercial viability of biopolymers, and their production is forecast to grow annually by 17% between 2023 and 2028 [186]. While algae-based polysaccharides have become a subject of interest, particularly in the food packaging industry, their commercial viability is restricted by a number of challenges. The data on algae polysaccharides focuses heavily on their applications as food packaging materials, with some data existing in medical applications using hydrogels and drug development [187]. While the packaging industry is significant in terms of scope, it still presents a restriction in terms of versatility for algae-based polysaccharides. A more direct challenges is the lack of suitable extraction and purification methods, as there are thousands of species of algae with different compositions. The many extraction methods and their relative successes can be mutually exclusive depending on the species studied [188]. Extraction and purification methods involving solvents were previously brought into question for their lack of sustainability and have been substituted in favor of greener methods such as bead milling and supercritical extraction. These methods are promising, but an all-encompassing and expandable method of extraction and purification still needs development. The challenges facing seaweed-based polysaccharides can be alleviated by further developing their processing and further research to expand their range of applications in industry.

5. Challenges and Future Directions

5.1. Scalability and Cost-Effectiveness

Seaweed-based polysaccharides present the opportunity for large-scale harvesting and high cost-effectiveness. This is due to the lack of time required to grow and the ability to grow in both salt and freshwater depending on the species. Algae is reported to grow up to ten times faster than conventional crops on land [28], giving it a distinct advantage in terms of scalability. While the abundance and easy harvesting of seaweed is a notable positive the process of extracting polysaccharides from them, and purification is a consistent issue, as previously discussed, many traditional methods of extraction used toxic solvents as a form of extraction and removed unwanted elements such as chlorophyll [189]. Over the years, this has seen major improvements, but we still lack consistent and reliable methods that can be upscaled for mass production. Biopolymers suffer from high cost of production, and the cost of feedstock for these materials can amount to as much as 50% of the cost [149,190]. As better methods of extraction become available for polysaccharides, their natural abundances can be fully utilized to generate a large-scale and cost-effective process, which would make them a dominant candidate in the field of biomaterials.

5.2. Performance under Diverse Conditions

With a primary focus on packaging materials, the biodegradable nature of seaweed-based polysaccharides paired with their medicinal and physical benefits gives them an advantage over traditional materials; however, these materials must also exhibit an ability to withstand harsh external factors while retaining an acceptable level of performance [191]. Understanding how polysaccharides will perform under diverse conditions is crucial to developing materials that are acceptable under commercial standards, and a detailed characterization of seaweed polysaccharides will provide a platform for accurate and specific material selection for a range of applications. When used as external packaging, these materials will be expected to exhibit some level of chemical, abrasion and impact resistance as well as good barrier and tensile properties [192]. Many of these characteristics have been studied extensively. Although data relating to UV-resistance [193,194], barrier properties/permeability [195,196] and mechanical properties [197,198] are all readily available, data on the effects of low and high pH elements’ interactions [199], optical properties and other forms of radiation are still lacking. As these materials will be heavily considered in the field of medicine and the food industry, sterilization is necessary. Many forms of sterilization can impact material performance and involve heat, moisture, humidity and radiation; therefore, the full range of effects these phenomena induce in the materials must be identified to understand material performance.

5.3. Regulatory Approval and Consumer Acceptance

For regulatory approval in the EU, packaging must conform to a range of standards set out to ensure the safety of the consumer and provide a framework for producers to avoid contamination and serious health and safety violations. Regulations such as the European framework Regulation NO 1935/2004 outline specific requirements for packaging that is in direct contact with food and incorporate active and intelligent packaging as well as coverings and coatings [200]. Other regulations for recyclability are included in the EU Packaging and Packaging Waste Directive (PPWD), which aims to reduce environmental impacts, and regulations related to labeling and traceability are commonly contained within ISO 9001 (Quality Management System) [201]. Seaweed-based polysaccharides are materials that produce no toxic by-products and can fully degrade in the presence of water; these properties allow for strict adherence to many of the regulations put in place for traditional materials.

Although these materials represent a sustainable and renewable option for packaging film products, the commercial success of these materials will be heavily influenced by consumers’ willingness to purchase and accept these new materials. A study carried out by Uehara et al. explored an important factor of these materials, which was consumer understanding and ability to differentiate categories of materials. Different words such as bioplastic, biodegradable and biomass were presented to a control group of 30,000 Japanese consumers, and it was found that over 50% had little knowledge of the terms. The results of the study showed a relatively lower environmental concern amongst Japanese consumers when compared with similar European studies [202]. A similar meta-analysis by Ruf et al., including over 50 scientific journal articles and papers, suggested that many consumers are not aware of the existence of biobased materials and could not identify their respective labels or brands. It was also noted that many consumers would select non-biomaterial products that were more functional or cheaper when given the option [203].

Seaweed-based polysaccharides present a group of materials that can safely adhere to current regulations while providing greener and renewable sources for producers; however, for these materials to be a commercial success, consumers need to be aware of and understand their benefits. The cost of these products must also compete with traditional prices to have the greatest chance of success on the market.

5.4. Future Directions

Assessing the future directions of seaweed polysaccharides requires an intimate understanding of their benefits, challenges and overall potential as sustainable materials. The necessity of the extensive and complete characterization of these biomaterials has become increasingly important, with much of the observable data pointing to a higher degree of efficacy and material performance when polysaccharides are contained within a polymer blend or composite. This requirement has been a consistent trend in a large portion of the research discussed, and the characterization of seaweed polysaccharides has deemed the base materials to be lacking in mechanical and barrier properties. These materials are extremely promising in the space of biomaterials with many positive attributes. Their abundances and considerable growth rates give seaweeds a distinct advantage over traditional biomaterials, and these properties alone have led labeling them as third-generation feedstocks requiring no terrestrial land to produce. Many studies have also proven the extensive physiological benefits these materials provide, not only for physical health in the context of a nutraceutical but also their medicinal value with anticancer, anticoagulant and antimicrobial properties.

Much of the data pertaining to these materials is biased towards their applications in the food industry as packaging films and coatings; however, some data cover their potential applications in tissue engineering and wound healing [204]. While there is a positive trend in the literature regarding “seaweed packaging film”, with results increasing from 154 entries in 2018 to 529 entries in 2024 based on ScienceDirect, there are still considerable gaps in the current literature that must be addressed. Data relating to these materials’ applications in the food and medical industry lacks any notable entries relating to regulatory measures such as sterilization techniques and their effects on material properties. Sterilization has been known to cause degradation in the form of chain scission and produce unwanted cross-linking in some specimens as well as dulling or complete changing of color, which must be fully understood for the commercialization of these products. Other significant influences on the integrity of the materials themselves are also not fully realized, and large gaps exist in varying external influences. The degradation of these materials in water of varying pH values and chemicals or compounds of varying pH values is not widely investigated. These factors present an opportunity for further characterization of seaweed-based polysaccharides, which has the potential to expand their market applications.

The implementation of these materials on a commercial or industrial scale is still met with significant challenges. Although the abundance and ability to grow seaweed in any environment is advantageous, the lack of reliable and expandable extraction and purification methods is a persistent issue. In addition, while the data are plentiful on extraction techniques, an all-encompassing method has not been developed for all families of seaweeds. The poor mechanical properties and permeability of these materials has also led to their viability being questioned, but many promising composites have since been developed. With advances in biocomposites and nanomaterials, these polysaccharides have been solidified as a notable contender amongst other biomaterials.

This review assessed the extraction, characterization and utilization of seaweed-based polysaccharides in industry through an extensive review of the available data and literature. The analysis and consideration of the future of these materials lies primarily in the development of reliable and efficient techniques for mass extraction. By proxy mass production, it is clear that the extreme variance in organic content across seaweed families and species is a prominent barrier to expandable extraction processes, and the progression of these materials from small scale to large scale production will be heavily influenced by research in this area. A secondary issue faced by these materials has historically been their performance under adverse conditions. Further research is required to obtain a greater degree of characterization and the creation of more durable and resistant materials by blending or composites to alleviate this issue and allow these materials to compete with traditional synthetics and eventually replace them.