Thermoplastic starches: Properties, challenges, and prospects

Investigation of film Physical properties under various starch thermal treatments with emphasis on Retrogradation effects

This study investigated the changes in the physical properties of cornstarch-based films as they were retrogradely aged at different temperatures. Using a casting method, the films were fabricated, and their effects on the mechanical properties, thermal stability, barrier properties, and essential properties were analyzed. With prolonged aging and retrogradation periods, reductions in film thickness, solubility, water content, and water vapor permeability of 5.35%, 9.92%, 29.61%, and 20.94%, respectively, were observed. In addition, the surface roughness decreased by 44.46% for Rq (root-mean-square roughness) and 45.61% for Ra (arithmetic average roughness), while the elongation at break decreased by 72.64%. Conversely, the tensile strength, maximum degradation rate, and maximum degradation temperature increased by 116.98%, 99.5%, and 3.21%, respectively. These results provide a fundamental understanding of the changes that occur in the properties of cornstarch-based films during aging and retrogradation.

Reactive extrusion fabrication of thermoplastic starch with Ca2+ heterodentate coordination structure for harvesting multiple-reusable PBAT/TPS films

Creating multiple-reusable PBAT/TPS (PT) films presents a novel solution to reduce carbon emissions from disposable packaging, addressing challenges like the high creep of PBAT and the glycerol migration of TPS. Consequently, adopting reactive extrusion to fabricate reversible cross-linking TPS with high shape memory performance, low migration, and homogeneous dispersion in PBAT matrix was a fascinating strategy. Herein, starch, glycerol and CaCl2 (calcium chloride) were extruded to fabricate TPS-Ca with Ca2+ heterodentate coordination structure and confirmed by XPS, 1H NMR and temperature-dependent FTIR. The results of DMA, dynamic rheology, flow activation energy and SEM revealed that TPS-Ca exhibited significant temperature-sensitive reversible properties and robust melt flow capability, enabling micro-nano scale dispersion in PBAT. Noteworthy, PBAT/TPS-Ca (PT-Ca) would recover 100 % length within 20 s by microwave heating after being loaded under the hygrothermal environment. Meanwhile, the migration weight of glycerol decreased from 2.5 % to 1.2 % for the heat-moisture-treated PBAT/TPS (HPT) and PBAT/TPS-Ca (HPTCa). Remarkably, the tensile strength and elongation at the break of HPT-Ca increased to 20.0 MPa and 924 %, respectively, due to reduced stress concentration sites in the phase interface. In summary, our study provides a streamlined strategy for fabricating multiple-reusable PT, offering a sustainable solution to eliminate carbon emissions linked to disposable plastic.

Ultrasound-Assisted Extrusion Compounding of Nano Clay/Polypropylene Nano Compounds

The incorporation of nanoparticles can significantly enhance the properties of polymers. However, the industrial production of nanocomposites presents a technological challenge in achieving the proper dispersion of nanoparticles within the polymer matrix. In this work, a novel device is presented that can be seamlessly integrated with standard twin-screw extruders, enabling the application of ultrasonic vibration to molten polymeric material. The primary objective of this study is to experimentally validate the effectiveness of this technology in improving the dispersion of nanoparticles. To accomplish this, a comparative analysis was carried out between nanocomposites obtained through conventional compounding extrusion and those processed with the assistance of ultrasonic vibrations. The nanocomposites under investigation consist of a polypropylene (PP) matrix reinforced with nano clays (Cloisite 20A) at a target loading ratio of 5% by weight. To comprehensively evaluate the impact of the ultrasound-assisted compounding, various key properties were assessed, such as the melt flow index (MFI) to characterize the flow behavior, mechanical properties to evaluate the structural performance, oxygen barrier properties to assess potential gas permeability, and microstructure analysis using Scanning Electron Microscopy (SEM) for detailed morphology characterization. The results suggested an improvement in nanoparticle dispersion when using the ultrasound device, particularly when the intensity was adjusted to 60%.

Preparation and properties of thermoplastic starch under the synergism of ultrasonic and elongational rheology

Thermoplastic starch, as an eco-friendly alternative to petroleum-based plastics, possesses numerous advantages, including cost-effectiveness, complete biodegradability, and renewable sourcing. Nevertheless, the plasticizer dispersion and starch plasticization efficiency are poor via the processing method dominate by shear deformation. Thus, the aim of this study is proposing a new approach combining ultrasonic treatment and elongational rheology to prepare thermoplastic starch and evaluate its properties. This innovative approach facilitated the production of thermoplastic starch with glycerol as the plasticizer at varying rotor speeds. Furthermore, this study was carried out by using a self-developed ultrasonic-assisted vane mixer (UVM) based on elongational flow. The samples were analyzed using FTIR, WAXD, polarized optical microscope, dynamic rheometer, universal testing machine and thermogravimetric analysis. FTIR and dynamic rheological analysis showed that elongational rheology and ultrasonics stimulate hydrogen bond formation between starch and glycerol, elevating starch thermoplasticity. Tensile tests and thermogravimetric analysis highlighted that high-intensity elongational field improved the mechanical properties and thermal stability of the thermoplastic starch. Additionally, the incorporation of ultrasonic treatment yielded further improvements, yielding remarkable tensile strength (6.09 MPa) and elongation at break (139.3 %). This synergistic interplay between ultrasonics and elongational rheology holds immense potential for advancing thermoplastic starch manufacturing.

Green Synthesis of Bioplastics from Microalgae: A State-of-the-Art Review

The synthesis of conventional plastics has increased tremendously in the last decades due to rapid industrialization, population growth, and advancement in the use of modern technologies. However, overuse of these fossil fuel-based plastics has resulted in serious environmental and health hazards by causing pollution, global warming, etc. Therefore, the use of microalgae as a feedstock is a promising, green, and sustainable approach for the production of biobased plastics. Various biopolymers, such as polyhydroxybutyrate, polyurethane, polylactic acid, cellulose-based polymers, starch-based polymers, and protein-based polymers, can be produced from different strains of microalgae under varying culture conditions. Different techniques, including genetic engineering, metabolic engineering, the use of photobioreactors, response surface methodology, and artificial intelligence, are used to alter and improve microalgae stocks for the commercial synthesis of bioplastics at lower costs. In comparison to conventional plastics, these biobased plastics are biodegradable, biocompatible, recyclable, non-toxic, eco-friendly, and sustainable, with robust mechanical and thermoplastic properties. In addition, the bioplastics are suitable for a plethora of applications in the agriculture, construction, healthcare, electrical and electronics, and packaging industries. Thus, this review focuses on techniques for the production of biopolymers and bioplastics from microalgae. In addition, it discusses innovative and efficient strategies for large-scale bioplastic production while also providing insights into the life cycle assessment, end-of-life, and applications of bioplastics. Furthermore, some challenges affecting industrial scale bioplastics production and recommendations for future research are provided.

Biodegradable Biocomposite of Starch Films Cross-Linked with Polyethylene Glycol Diglycidyl Ether and Reinforced by Microfibrillated Cellulose

Biopolymers are biodegradable and renewable and can significantly reduce environmental impacts. For this reason, biocomposites based on a plasticized starch and cross-linker matrix and with a microfibrillated OCC cardboard cellulose reinforcement were developed. Biocomposites were prepared by suspension casting with varied amounts of microfibrillated cellulose: 0, 4, 8, and 12 wt%. Polyethylene glycol diglycidyl ether (PEGDE) was used as a cross-linking, water-soluble, and non-toxic agent. Microfibrillated cellulose (MFC) from OCC cardboard showed appropriate properties and potential for good performance as a reinforcement. In general, microfiber incorporation and matrix cross-linking increased crystallization, reduced water adsorption, and improved the physical and tensile properties of the plasticized starch. Biocomposites cross-linked with PEGDE and reinforced with 12 wt% MFC showed the best properties. The chemical and structural changes induced by the cross-linking of starch chains and MFC reinforcement were confirmed by FTIR, NMR, and XRD. Biodegradation higher than 80% was achieved for most biocomposites in 15 days of laboratory compost.

Hard Carbon Derived From Different Precursors for Sodium Storage

Due to the almost unlimited resource and acceptable performance, Sodium-ion batteries (SIBs) have been regarded as a promising alternative for lithium-ion batteries (LIBs) for grid-scale energy storage. As the key material of SIBs, hard carbon (HC) plays a decisive role in determining the batteries' performance. Nevertheless, the micro-structure of HCs is quite complex and the random organization of turbostratically stacked graphene layers, closed pores, and defects make the structure-performance relationship insufficiently revealed. On the other hand, the impending large-scale deployment of SIBs leads to producing HCs with low-cost and abundant precursors actively pursued. In this work, the recent progress of preparing HCs from different precursors including biomass, polymers, and fossil fuels is summarized with close attention to the influences of precursors on the structural evolution of HCs. After a brief introduction of the structural features of HCs, the recent understanding of the structure-performance relationship of HCs for sodium storage is summarized. Then, the main focus is concentrated on the progress of producing HCs from distinct precursors. After that, the pros and cons of HCs derived from different precursors are comprehensively compared to conclude the selection rules of precursors. Finally, the further directions of HCs are deeply discussed to end this review.

Unveiling the Future of Meat Packaging: Functional Biodegradable Packaging Preserving Meat Quality and Safety

Meat quality and shelf life are important parameters affecting consumer perception and safety. Several factors contribute to the deterioration and spoilage of meat products, including microbial growth, chemical reactions in the food's constituents, protein denaturation, lipid oxidation, and discoloration. This study reviewed the development of functional packaging biomaterials that interact with food and the environment to improve food's sensory properties and consumer safety. Bioactive packaging incorporates additive compounds such as essential oils, natural extracts, and chemical substances to produce composite polymers and polymer blends. The findings showed that the incorporation of additive compounds enhanced the packaging's functionality and improved the compatibility of the polymer-polymer matrices and that between the polymers and active compounds. Food preservatives are alternative substances for food packaging that prevent food spoilage and preserve quality. The safety of food contact materials, especially the flavor/odor contamination from the packaging to the food and the mass transfer from the food to the packaging, was also assessed. Flavor is a key factor in consumer purchasing decisions and also determines the quality and safety of meat products. Novel functional packaging can be used to preserve the quality and safety of packaged meat products.

Biocomposites Based on Wheat Flour with Urea-Based Eutectic Plasticizer and Spent Coffee Grounds: Preparation, Physicochemical Characterization, and Study of Their Influence on Plant Growth

In this study, we conducted the first plasticization of wheat flour (WF) with the addition of choline chloride:urea (1:5 molar ratio) eutectic mixture as a plasticizer and spent coffee grounds (cf) as a filler. Thermoplastic wheat flour (TPWF) films were obtained via twin-screw extrusion and then thermocompression. Their physicochemical characterization included mechanical tests, dynamic mechanical thermal analysis (DMTA), and sorption tests. XRD analysis revealed that the eutectic plasticizer led to a high degree of WF amorphization, which affected the physicochemical properties of TPWF. The results indicated that it was easy for the TPWF biocomposites to undergo thermocompression even with a high amount of the filler (20 pph per flour). The addition of the cf into TPWF led to an increase in tensile strength and a decrease in the swelling degree of the biocomposites. Biodegradation tests in soil revealed that the materials wholly degraded within 11 weeks. Moreover, a study of cultivated plants indicated that the biocomposites did not exhibit a toxic influence on the model rowing plant.

Bacteria for Bioplastics: Progress, Applications, and Challenges

Bioplastics are one of the answers that can point society toward a sustainable future. Under this premise, the synthesis of polymers with competitive properties using low-cost starting materials is a highly desired factor in the industry. Also, tackling environmental issues such as nonbiodegradable waste generation, high carbon footprint, and consumption of nonrenewable resources are some of the current concerns worldwide. The scientific community has been placing efforts into the biosynthesis of polymers using bacteria and other microbes. These microorganisms can be convenient reactors to consume food and agricultural wastes and convert them into biopolymers with inherently attractive properties such as biodegradability, biocompatibility, and appreciable mechanical and chemical properties. Such biopolymers can be applied to several fields such as packing, cosmetics, pharmaceutical, medical, biomedical, and agricultural. Thus, intending to elucidate the science of microbes to produce polymers, this review starts with a brief introduction to bioplastics by describing their importance and the methods for their production. The second section dives into the importance of bacteria regarding the biochemical routes for the synthesis of polymers along with their advantages and disadvantages. The third section covers some of the main parameters that influence biopolymers' production. Some of the main applications of biopolymers along with a comparison between the polymers obtained from microorganisms and the petrochemical-based ones are presented. Finally, some discussion about the future aspects and main challenges in this field is provided to elucidate the main issues that should be tackled for the wide application of microorganisms for the preparation of bioplastics.

A Review of Natural Polysaccharides: Sources, Characteristics, Properties, Food, and Pharmaceutical Applications

Natural polysaccharides, which are described in this study, are some of the most extensively used biopolymers in food, pharmaceutical, and medical applications, because they are renewable and have a high level of biocompatibility and biodegradability. The fundamental understanding required to properly exploit polysaccharides potential in the biocomposite, nanoconjugate, and pharmaceutical industries depends on detailed research of these molecules. Polysaccharides are preferred over other polymers because of their biocompatibility, bioactivity, homogeneity, and bioadhesive properties. Natural polysaccharides have also been discovered to have excellent rheological and biomucoadhesive properties, which may be used to design and create a variety of useful and cost-effective drug delivery systems. Polysaccharide-based composites derived from natural sources have been widely exploited due to their multifunctional properties, particularly in drug delivery systems and biomedical applications. These materials have achieved global attention and are in great demand because to their biochemical properties, which mimic both human and animal cells. Although synthetic polymers account for a substantial amount of organic chemistry, natural polymers play a vital role in a range of industries, including biomedical, pharmaceutical, and construction. As a consequence, the current study will provide information on natural polymers, their biological uses, and food and pharmaceutical applications.

Effect of cellulose nanofiber-montmorillonite hybrid filler on the melt blending of thermoplastic starch composites

This study investigated the impact of cellulose nanofibers (CNFs) on montmorillonites (MMTs) exfoliation within thermoplastic starch (TPS) nanocomposites during the melt blending process. TPS nanocomposite films were manufactured using an internal mixer with a controlled ratio of CNFs and MMTs to evaluate the effect of individual and hybrid fillers on the material interactions and characteristics of the TPS composites. The incorporation of hybrid fillers resulted in notable enhancements in torque values and rheological properties, suggesting interactions between the starch, CNFs, and MMTs. The degree of MMT intercalation, obtained via X-ray diffraction analysis, decreased with the addition of CNFs, indicating that CNFs positively impacted MMT exfoliation. Scanning electron microscopy (SEM) images of cryo- and tensile-fractured samples highlighted the effectiveness of CNFs in facilitating MMT exfoliation and reinforcing interactions between the MMTs and TPS matrix. These interactions enhanced the tensile strength and Young's modulus by up to 95.8 % and 278.2 %, respectively, with a 1:1 weight ratio of CNFs to MMTs. Additionally, well-dispersed MMTs within the TPS matrix caused passivation and created tortuous paths, improving the water contact angle and decreasing the water vapor sorption. These synergistic effects of the hybrid filler, achieved through a melt blending process, indicate the potential use of TPS nanocomposites as an eco-friendly packaging material.

Effects of glycerol content on structure and molecular motion in thermoplastic starch-based nanocomposites during long storage

Thermoplastic starch-based nanocomposites with varying glycerol content and montmorillonite as a nanofiller were studied using dynamic-mechanical analysis (DMA), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) during one-year storage. DMA results showed that starch-rich and glycerol-rich domains were present in the samples and during storage for up to one year the content of the amorphous phase decreased and molecular mobility changed. 13C NMR and XRD measurements confirmed that ordered structures were formed during storage and its content was larger for samples with higher glycerol content and increased with the storage time. The data obtained from deconvolutions of 1H broad line NMR spectra indicate increased overall molecular mobility in the samples up to four months of storage, while after nine months the trends were opposite. Lower free water content compared to the total water content in the samples determined according to deconvoluted 1H MAS (magic-angle spinning) NMR spectra indicated that a part of water molecules was immobilized in the ordered structures.

Facile fabrication of reusable starch sponge with adjustable crosslinked networks for efficient nest-trap and in situ photodegrade methylene blue

The fabrication of reusable natural polysaccharide sponges with nanoscale dispersed photocatalysts to achieve robust photocatalytic efficiency is desirable yet challenging. Herein, inspired by the nesting behavior when fishing, we designed reusable starch sponge with chemically anchored nano-ZnO into carboxylated starch matrix by thermoplastic interfacial reactions and solvent replacement for absorbing and photodegrading methylene blue (MB) in situ. The plasticization and interfacial reactions promoted a simultaneous increase in the reactivity of the starch hydroxyl/carboxyl groups and the specific surface area of ZnO. Meanwhile, the crosslinked networks of starch sponge could be adjusted by varying the ZnO and carboxylic groups contents. The results of photodegradation experiments revealed the recyclable closed-loop process of attraction-trapping-photodegradation of MB was successfully realized, achieving the effect of killing three birds with one stone. The reusable starch sponge with homogeneous dispersion of nano-ZnO by constructing three-dimensional porous channels possessed the high enrichment capacity and the remarkable photocatalysis efficiency with 150 mg/L ZnO. Under UV irradiation, the starch sponge degraded 97 % of MB with 1.67 × 10-3 min-1 photodegradation rate constant even after five cycles, which exceeded most existing photocatalytic systems. Overall, the reusable starch sponge with adjustable structure provided new insights for multifunctional bio-based photocatalyst loading systems.

Replacing Harmful Flame Retardants with Biodegradable Starch-Based Materials in Polyethylene Formulations

The addition of toxic flame retardants to commercially available polymers is often required for safety reasons due to the high flammability of these materials. In this work, the preparation and incorporation of efficient biodegradable starch-based flame retardants into a low-density polyethylene (LDPE) matrix was investigated. Thermoplastic starch was first obtained by plasticizing starch with glycerol/water or glycerol/water/choline phytate to obtain TPS-G and TPS-G-CPA, respectively. Various LDPE/TPS blends were prepared by means of melt blending using polyethylene graft maleic anhydride as a compatibilizer and by varying the content of TPS and a halogenated commercial flame retardant. By replacing 38% and 76% of the harmful commercial flame retardant with safe TPS-G-CPA and TPS-G, respectively, blends with promising fire behavior were obtained, while the limiting oxygen index (LOI ≈ 28%) remained the same. The presence of choline phytate improved both the charring ability and fire retardancy of starch and resulted in a 43% reduction in fire growth index compared to the blend with commercial flame retardant only, as confirmed by means of cone calorimetry. Standard UL 94 vertical tests showed that blends containing TPS exhibited dripping behavior (rated V2), while those with commercial flame retardant were rated V0. Overall, this work demonstrates the potential of starch as a natural flame retardant that could reduce the cost and increase the safety of polymer-based materials.

A Biodegradable, Waterproof, and Thermally Processable Cellulosic Bioplastic Enabled by Dynamic Covalent Modification

The growing environmental concern over petrochemical-based plastics continuously promotes the exploration of green and sustainable substitute materials. Compared with petrochemical products, cellulose has overwhelming superiority in terms of availability, cost, and biodegradability; however, cellulose's dense hydrogen-bonding network and highly ordered crystalline structure make it hard to be thermoformed. A strategy to realize the partial disassociation of hydrogen bonds in cellulose and the reassembly of cellulose chains via constructing a dynamic covalent network, thereby endowing cellulose with thermal processability as indicated by the observation of a moderate glass transition temperature (T_g  = 240 °C), is proposed. Moreover, the cellulosic bioplastic delivers a high tensile strength of 67 MPa, as well as excellent moisture and solvent resistance, good recyclability, and biodegradability in nature. With these advantageous features, the developed cellulosic bioplastic represents a promising alternative to traditional plastics.

Study on Physicochemical Properties of Biocomposite Films with Spent Coffee Grounds as a Filler and Their Influence on Physiological State of Growing Plants

The aim of the study was to plasticize corn starch with two selected urea (U)-rich plasticizers: choline chloride (CC):U or betaine (B):U eutectic mixtures at a molar ratio of 1:5 with a presence of spent coffee grounds as a filler. The biomaterials were prepared via a solventless one-step extrusion method and then extrudates were thermoformed using compression molding into sheets. The materials were characterized using mechanical and sorption tests, TGA, DMTA and FTIR. Additionally, a study on the biodegradation and remaining nitrogen content in soil was conducted. For the first time, an influence on physiological state of growing plants of the materials presence in soil was investigated. The addition of the coffee filler slightly increased the mechanical properties and decreased the swelling degree of the materials. The DMTA results indicated that biocomposites were easily thermoformable and the high filler addition (20 pph per polymer matrix) did not affect the processability. According to the biodegradation test results, the materials disappeared in soil within ca. 70 days. The results from this study on the physiological state of growing plants revealed that the materials, especially plasticized with CCU, did not exhibit any toxic effect on the yellow dwarf bean. The percentage of total nitrogen in the soil substrate in comparison with the control increased indicating an effective release of nitrogen from the TPS materials into the substrate.

Exploring the roles of starch for microbial encapsulation through a systematic mapping review

Microorganism encapsulation protects them from stressful conditions and assists in maintaining their viability, being especially beneficial when the carrier material is a renewable and biodegradable biopolymer, such as starch. Here, a systematic mapping was performed to provide a current overview on the use of starch-based systems for microbial encapsulation. Following well-established guidelines, a systematic mapping was conducted and the following could be drawn: 1) there was a significant increase in publications on microbial encapsulation using starch over the past decade, showing interest from the scientific community, 2) ionotropic gelation, emulsification and spray drying are the most commonly used techniques for starch-based microbial encapsulation, and 3) starch play important functions in the encapsulation matrix such as assisting in the survival of the microorganisms. The information gathered in this systematic mapping can be useful to guide researchers and industrial sectors on the development of innovative starch-based systems for microbial encapsulation.

Characterization of Thermoplastic Starch Plasticized with Ternary Urea-Polyols Deep Eutectic Solvent with Two Selected Fillers: Microcrystalline Cellulose and Montmorillonite

The aim of the study was to prepare and characterize composite materials based on thermoplastic starch (TPS)/deep eutectic solvent (DES). Potato starch was plasticized with ternary DES: urea:glycerol:sorbitol and modified with the selected fillers: microcrystalline cellulose and sodium montmorillonite. Films were prepared via twin-screw extrusion and thermocompression of the extrudates. Then, the physicochemical properties of the TPS films were examined. The ternary DES effectively plasticized the polysaccharide leading to a highly amorphous structure of the TPS (confirmed via mechanical tests, DMTA and XRD analyses). An investigation of the behavior in water (swelling and dissolution degree) and water vapor transmission rate of the films was determined. The introduction of the two types of fillers resulted in higher tensile strength and better barrier properties of the composite TPS films. However, montmorillonite addition exhibited a higher impact than microcrystalline cellulose. Moreover, a cone calorimetry analysis of the TPS materials revealed that they showed better fire-retardant properties than TPS plasticized with a conventional plasticizer (glycerol).

Fully bio-based hydroxy ester vitrimer synthesized by crosslinking epoxidized soybean oil with doubly esterified starch

Catalyst-free fully bio-based hydroxyester (BHE) vitrimers were synthesized by crosslinking and plasticizing epoxidized soybean oil with synthesized acetylated starch succinate monoesters to investigate the effects of different starch structures on the properties of the BHE vitrimers. The BHE vitrimers possessed a lower glass transition temperature as well as better solvent resistance and reprocessing performance compared to traditional starch-based materials. Owing to dynamically covalent bonds, the migration and exudation of plasticizers were avoided. A maximum strain of 230 % was achieved to prevent the retrogradation and brittleness of starch-based materials. Furthermore, the mechanical properties remained unchanged after three reprocessing cycles. Consequently, the obtained BHE vitrimers are eco-friendly and sustainable.

Deep Eutectic Solvents for Biotechnology Applications

Deep eutectic solvents (DESs) are an alternative to traditional organic solvents and ionic liquids and meet the requirements of "green" chemistry. They are easy to prepare using low-cost constituents, are non-toxic and biodegradable. The review analyzes literature on the use of DES in various fields of biotechnology, provides data on the types of DESs, methods for their preparation, and properties. The main areas of using DESs in biotechnology include extraction of physiologically active substances from natural resources, pretreatment of lignocellulosic biomass to improve enzymatic hydrolysis of cellulose, production of bioplastics, as well as a reaction medium for biocatalytic reactions. The aim of this review is to summarize available information on the use of new solvents for biotechnological purposes.

The development of recycling methods for bio-based materials - A challenge in the implementation of a circular economy: A review

This review focuses on the characteristics of the most widely used biopolymers that contain starch, polylactic acid, cellulose and/or polybutylene succinate. Because worldwide production of bio-based materials has grown dynamically, their waste is increasingly found in the existing waste treatment plants. The development of recycling methods for bio-based materials remains a challenge in the implementation of a circular economy. This article summarizes the recycling methods for bio-based materials, which, in the hierarchy of waste management, is much more desirable than landfilling. Several methods of recycling are available for the end-of-life management of bio-based products, which include mechanical (reuse of waste as a valuable raw material for further processing), chemical (feedstock recycling) and organic (anaerobic digestion or composting) ones. The use of chemical or mechanical recycling is less favourable, more costly and requires the improvement of systems for separation of bio-based materials from the rest of the waste stream. Organic recycling can be a sustainable alternative to those two methods. In organic recycling, bio-based materials can be biologically treated under aerobic or anaerobic conditions, depending on the characteristics of the materials. The choice of the recycling method to be implemented depends on the economic situation and on the properties of the bio-based products and their susceptibility to degradation. Thus, it is necessary to label the products to indicate which method of recycling is most appropriate.

Improving Properties of Starch-Based Adhesives with Carboxylic Acids and Enzymatically Polymerized Lignosulfonates

A novel strategy for improving wet resistance and bonding properties of starch-based adhesives using enzymatically polymerized lignosulfonates and carboxylic acids as additives was developed. Therefore, lignosulfonates were polymerized by laccase to a molecular weight of 750 kDa. Incorporation of low concentrations (up to 1% of the starch weight) of 1,2,3,4-butanetetracarboxylic acid (BTCA) led to further improvement on the properties of the adhesives, while addition of greater amounts of BTCA led to a decrease in the properties measured due to large viscosity increases. Great improvements in wet-resistance from 22 to 60 min and bonding times (from 30 to 20 s) were observed for an adhesive containing 8% enzymatically polymerized lignin and 1% BTCA. On the other hand, the addition of citric acid (CA) deteriorated the properties of the adhesives, especially when lignosulfonate was present. In conclusion, this study shows that the addition of the appropriate amount of enzymatically polymerized lignosulfonates together with carboxylic acids (namely BTCA) to starch-based adhesives is a robust strategy for improving their wet resistance and bonding times.

Green synthesis of oxidized starch with a novel catalyst based on Fe3O4 nanoparticles and H2O2 reagent to form thermoplastic as a stable gel coating on the cardiovascular stents

Oxidation of starch is one of the most commonly used approaches to improve its properties in the thermoplastic (TP) reactions. Iron oxide nanoparticle (IONP) (8.2 ± 1.5 nm) was used as a novel catalyst for this reaction. The functional groups of the carbonyl (COH) and the carboxyl (COOH) were obtained about of 7-12.2 % and 0.03-0.3 %. TP reaction and then electrospray technique of oxidized starch were used for the thin-film coating. The swelling ratio of the gelled thermoplastic structure with IONP (198 ± 9 % at 180 min) was lower than the sample without NP (193 ± 8 % at 90 min). The results from fourier transform infrared spectroscopy (FTIR), hydrogen nuclear magnetic resonance (HNMR), X-ray diffraction (XRD), and transmission electron microscopy (TEM) reveal desirable chemical and crystalline changes. Scanning electron microscopy (SEM) analysis was used to determine the thickness of the thin film (1.4 ± 0.2 μm) and the size of the electrosprayed droplets (172 ± 45 nm). Cytotoxicity studies of HUVEC and L929 cell lines against the extracts have shown appropriate biocompatibility. The blood compatibility analysis demonstrated proper results for (nanocomposite) NC. The results show that NC coated on metal surfaces can be used in medical approaches with drug delivery capability.

Physical Properties and Biodegradability Evaluation of Vulcanized Epoxidized Natural Rubber/Thermoplastic Potato Starch Blends

The sustainable material-thermoplastic potato starch (TPS)-was blended with modified natural rubber-epoxidized natural rubber (ENR). The poor mechanical properties of the ENR/TPS blends limited the application. Sulfur vulcanization is a common and economical method to improve the mechanical properties in the rubber industry. To fully understand the relationship between vulcanization systems and ENR/TPS blends and the sustainability of the developed material, the effects of a vulcanization accelerator (N-cyclohexylbenzothiazole-2-sulphenamide (CBS), 2-mercaptobenzothiazole (MBT), N-tert-butylbenzothiazole-2-sulphenamide (TBBS)) and a system type (conventional vulcanization (CV), semi-efficient vulcanization (SEV) and efficient vulcanization (EV)) on curing characteristics, mechanical and thermal properties, water absorption and biodegradability were systematically evaluated. The results indicate that vulcanization significantly improves the mechanical properties of ENR/TPS blends. The performance optimization of the CBS-CV vulcanization system is the best for improving the mechanical properties and reducing the water absorption. The CBS-CV curing system makes ENR/TPS less biodegradable (12-56% of mass loss) than other accelerators and systems. TBBS-CV makes the material more biodegradable (18-66% of mass loss). The low rubber content enables the rapid biodegradation of the vulcanized blend. This has implications for research on sustainable materials. The material can be applied for eco-friendly packaging and agricultural films, etc. The investigation on performance by using common accelerators and systems provides ideas for industries and research.

Corn: Its Structure, Polymer, Fiber, Composite, Properties, and Applications

Biocomposite materials have a significant function in saving the environment by replacing artificial plastic materials with natural substances. They have been enrolled in many applications, such as housing, automotive engine components, aerospace and military products, electronic and circuit board components, and oil and gas equipment. Therefore, continuous studies have been employed to improve their mechanical, thermal, physical properties. In this research, we conduct a comprehensive review about corn fiber and corn starch-based biocomposite. The results gained from previous studies were compared and discussed. Firstly, the chemical, thermal, and mechanical properties of cornstarch-based composite were discussed. Then, the effects of various types of plasticizers on the flexibility of the cornstarch-based composite were addressed. The effects of chemical treatments on the properties of biocomposite using different cross-linking agents were discussed. The corn fiber surface treatment to enhance interfacial adhesion between natural fiber and polymeric matrix also were addressed. Finally, morphological characterization, crystallinity degree, and measurement of vapor permeability, degradation, and uptake of water were discussed. The mechanical, thermal, and water resistance properties of corn starch and fibers-based biopolymers show a significant improvement through plasticizing, chemical treatment, grafting, and cross-linker agent procedures, which expands their potential applications.

Struvite-based composites for slow-release fertilization: a case study in sand

Struvite (St) recovered from wastewaters is a sustainable option for phosphorus (P) recovery and fertilization, whose solubility is low in water and high in environments characterized by a low pH, such as acidic soils. To broaden the use of struvite in the field, its application as granules is recommended, and thus the way of application should be optimized to control the solubility. In this study struvite slow-release fertilizers were designed by dispersing St particles (25, 50, and 75 wt%) in a biodegradable and hydrophilic matrix of thermoplastic starch (TPS). It was shown that, in citric acid solution (pH = 2), TPS promoted a steadier P-release from St compared to the pure St pattern. In a pH neutral sand, P-diffusion from St-TPS fertilizers was slower than from the positive control of triple superphosphate (TSP). Nevertheless, St-TPS featured comparable maize growth (i.e. plant height, leaf area, and biomass) and similar available P as TSP in sand after 42 days of cultivation. These results indicated that St-TPS slow P release could provide enough P for maize in sand, achieving a desirable agronomic efficiency while also reducing P runoff losses in highly permeable soils.

Microbial biodegradation of plastics: Challenges, opportunities, and a critical perspective

The abundance of synthetic polymers has increased due to their uncontrolled utilization and disposal in the environment. The recalcitrant nature of plastics leads to accumulation and saturation in the environment, which is a matter of great concern. An exponential rise has been reported in plastic pollution during the corona pandemic because of PPE kits, gloves, and face masks made up of single-use plastics. The physicochemical methods have been employed to degrade synthetic polymers, but these methods have limited efficiency and cause the release of hazardous metabolites or by-products in the environment. Microbial species, isolated from landfills and dumpsites, have utilized plastics as the sole source of carbon, energy, and biomass production. The involvement of microbial strains in plastic degradation is evident as a substantial amount of mineralization has been observed. However, the complete removal of plastic could not be achieved, but it is still effective compared to the preexisting traditional methods. Therefore, microbial species and the enzymes involved in plastic waste degradation could be utilized as eco-friendly alternatives. Thus, microbial biodegradation approaches have a profound scope to cope with the plastic waste problem in a cost-effective and environmental-friendly manner. Further, microbial degradation can be optimized and combined with physicochemical methods to achieve substantial results. This review summarizes the different microbial species, their genes, biochemical pathways, and enzymes involved in plastic biodegradation.

Isosorbide plasticized corn starch filled with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) microparticles: Properties and behavior under environmental factors

In this work, new green and fully biodegradable composites, based on corn starch, plasticized with two different amounts of isosorbide and filled by poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) microparticles, were obtained by melt processing. The analysis of their morphologies, crystallinity, structural interactions and dynamomechanical properties as well as the evaluation of their moisture resistance and biodegradability in soil, were performed in function of the plasticizer and/or microparticle amount. The analysis of morphology, crystallinity and structural interactions showed that the plasticization process was completed under the melting processing conditions used. The microparticles were homogeneously dispersed in the thermoplastic starch matrix without suffering any deformation or breaking during the processing. Biocomposites with adequate storage modulus values were obtained, especially the TPS plasticized with 35% of isosorbide and filled with 5 wt% of PHBV microparticles. The incorporation of PHBV microparticles leads to biocomposites with higher moisture resistance. All the biocomposites were completely biodegraded in soil in a short period of time. The performed study demonstrated that these biocomposites could be used for applications in the packaging industry.

Metallic Nanoparticle Integrated Ternary Polymer Blend of PVA/Starch/Glycerol: A Promising Antimicrobial Food Packaging Material

Advances in food processing and food packaging play a major role in keeping food safe, increasing the shelf life, and maintaining the food supply chain. Good packaging materials that enable the safe travel of food are often non-degradable and tend to persist in the environment, thereby posing a hazard. One alternative is to synthesize biodegradable polymers with an antimicrobial property while maintaining their mechanical and thermal properties. In the present study, biodegradable composites of PVA–starch–glycerol (PSG) incorporated with CuO and ZnO nanoparticles (NPs) were prepared as PSG, PSG–Cu, PSG–Zn, and PSG–CuZn films. Scanning electron microscopy, energy dispersive x-ray analysis, and thermogravimetric analysis were performed to study and characterize these films. The water barrier properties of the films improved significantly as the hydrophobicity of the PSG–CuZn film increased by 32.9% while the water absorptivity and solubility decreased by 51.49% and 60% compared to the PSG film. The Young’s modulus of the films incorporated with CuO and ZnO nanoparticles was lower than that reported for PVA, suggesting that the film possessed higher flexibility. The thermogravimetric analysis demonstrated high thermal stability for films. Biosynthesized CuO and ZnO nanoparticles exhibited antifungal activity against vegetable and fruit spoilage fungi, and hence the fabricated polymers incorporated with nanoparticles were anticipated to demonstrate an antifungal activity. The nanoparticle incorporated films exhibited fungicidal and bactericidal activity, suggesting their role in extending the shelf life of packaged food. The result of ICP-OES studies demonstrated the steady release of ions from the polymer films, however, EDX analysis demonstrated no leaching of CuO and ZnO nanoparticles from the films, thus ruling out the possibility of nanoparticles entering the packaged food. The strawberries wrapped with the fabricated films incorporated with nanoparticles demonstrated improved shelf life and retained the nutritional quality of the fruit. Among the four films, PSG–CuZn was the most promising for food wrapping since it exhibited better water-resistance, antimicrobial, thermal, and mechanical properties.

Molecular insight into the interactions between starch and cuminaldehyde using relaxation and 2D solid-state NMR spectroscopy

The interaction between cuminaldehyde and starch mainly governed the effect of further handling on food applications of cuminaldehyde. However, little information is available about the interactions of these components. We utilized relaxation and heteronuclear correlation (HETCOR) solid-state NMR spectroscopy to investigate the interaction between cuminaldehyde and porous starch at molecular level. We found that the interactions occurred mainly through hydrogen bonds. Cuminaldehyde molecules were restricted by starch, which resulted in the limitation of their movements and the longer ¹H T₁ relaxation time. Furthermore, the well resolved correlated peaks in 2D ¹H-¹³C HETCOR spectrum confirmed the formation of hydrogen bonds. The oxygen atoms at hydroxyl-2,3 of starch were the binding sites, which combined with hydrogens of cuminaldehyde. This present work not only afford a new approach to obtain a molecular understanding of interactions, but also expanded the application of solid-state NMR to investigation of the interaction on functional components.

Biodegradable Thermoplastic Starch/Polycaprolactone Blends with Co-Continuous Morphology Suitable for Local Release of Antibiotics

We report a reproducible preparation and characterization of highly homogeneous thermoplastic starch/pol(ε‑caprolactone) blends (TPS/PCL) with a minimal thermomechanical degradation and co-continuous morphology. These materials would be suitable for biomedical applications, specifically for the local release of antibiotics (ATB) from the TPS phase. The TPS/PCL blends were prepared in the whole concentration range. In agreement with theoretical predictions based on component viscosities, the co-continuous morphology was found for TPS/PCL blends with a composition of 70/30 wt.%. The minimal thermomechanical degradation of the blends was achieved by an optimization of the processing conditions and by keeping processing temperatures as low as possible, because higher temperatures might damage ATB in the final application. The blends’ homogeneity was verified by scanning electron microscopy. The co-continuous morphology was confirmed by submicron-computed tomography. The mechanical performance of the blends was characterized in both microscale (by an instrumented microindentation hardness testing; MHI) and macroscale (by dynamic thermomechanical analysis; DMTA). The elastic moduli of TPS increased ca four times in the TPS/PCL (70/30) blend. The correlations between elastic moduli measured by MHI and DMTA were very strong, which implied that, in the future studies, it would be possible to use just micromechanical testing that does not require large specimens.

Insights into the gelatinization of potato starch by in situ 1H NMR

The gelatinization of potato starch and the effect of NaCl on starch gelatinization were monitored successfully in situ by 1H NMR spectroscopy. Variable temperature (VT) 1H NMR measurement, from 316 K to 340 K, was conducted on a suspension of potato starch and deuterium water as well as a mixture of potato starch, NaCl and deuterium water. The hydration level of starch was determined with the increase of temperature. In the presence of NaCl, the initial gelatinization temperature of potato starch was decreased from 331 to 328 K. Meanwhile, in situ 1H NMR spectroscopy as a function of time was also carried out to monitor the gelatinization with a time resolution of 90 s per spectrum. Furthermore, the effect of using different processing methods during gelatinization, including varying the temperature or time duration, was investigated in detail. It was confirmed that protons from different groups of starch showed different accessibility for water during hydration of starch granules. In comparison with temperature, gelatinization time as the major factor for reaching complete gelatinization was confirmed. We expect that this research, as a continuing effort to apply NMR spectroscopy for characterizing starch, will pave a new way in the structural elucidation of starch.

Starch-Polyvinyl Alcohol-Based Films Reinforced with Chitosan Nanoparticles: Physical, Mechanical, Structural, Thermal and Antimicrobial Properties

The main purpose of the current study was to propose innovative composite films based on a corn starch/polyvinyl alcohol (PVA) blend (starch:PVA 40:60) and loaded with 3 different levels of chitosan nanoparticles (CNPs) (1, 3, and 5% w/v) to strengthen its physical, mechanical, structural, thermal and antimicrobial attributes. The synthesized CNPs were spherical with a particle size of ca. 100 nm as demonstrated by scanning electron microscopy (SEM) micrographs and dynamic light scattering tests. The results showed that the CNPs incorporation within the starch-PVA 40:60 films promoted a uniform surface without any considerable pores. These films were characterized by a homogeneous CNP distribution within the polymer matrix, causing a significant decrease in water vapor permeability (WVP) (e.g., from 0.41 for the control film to 0.28 g·mm/kPa·h·m2 for the composite film loaded with 5% CNPs). The film solubility, transparency, glass transition and melting temperatures, and elongation at break were also reduced by increasing the CNP content from 1% to 5%, while total color and tensile strength parameters increased. The antibacterial effects of CNPs were more effective against Gram-positive bacteria (Staphylococcus aureus) than Gram-negative bacteria (Escherichia coli and Salmonella typhimurium). It can be concluded that the addition of CNPs to the starch-PVA matrix could improve its functional and technological attributes for food packaging applications.

Deep Eutectic Solvents for Starch Treatment

In this review, the application of deep eutectic solvents (DESs) as starch solvents, plasticizers and for other treatment has been described. Starch, as one of the most abundant biopolymers, is considered for forming new biodegradable materials. This new approach, referring to applying deep eutectic solvents for dissolving starch, its plasticization and other modifications, was presented. A DES could be a good alternative for common starch plasticizers (e.g., glycerol, urea) as well as recently considered ionic liquids. The high variety of DES component combinations makes it possible to obtain materials with the properties specific for given applications.

Multi-scale reactive extrusion modelling approaches to design polymer synthesis, modification and mechanical recycling

Reactive extrusion (REX) is an important processing and production technique with applications in the field of polymer synthesis, modification and recycling.

Thermoplastic Starch-Based Blends with Improved Thermal and Thermomechanical Properties

This research focused on the development of biomaterials based on cassava starch and corn starch and on the effect of the incorporation of polycaprolactone (PCL) on the thermal and thermomechanical properties of the blends. The results indicated partial compatibility in the blends, especially with cassava starch at a content of 20 wt% as reflected by the maintenance of tensile strength and elongation. In addition, the changes in the crystal quality of PCL and the displacement of the absorption bands of the carbonyl groups of PCL in the infrared (989–1000 cm⁻¹), attributed to the formation of hydrogen bonds between these groups and the hydroxyl groups of starches, were also associated with compatibility. It was observed that the crystallinity of PLC in the presence of cassava and corn starch was 38% and 62%, respectively; a crystallinity greater than that of PCL was related to an improved nucleation at the interface. Based on these properties, the blends are expected to be functional for the manufacture of short-term use products by conventional thermoplastic processing methods.

The effects of cellulose nanocrystal and cellulose nanofiber on the properties of pumpkin starch-based composite films

Pumpkin starch (PS) was extracted from Cucurbita maxima and utilized to prepare films in combination with cellulose nanocrystal (CNC) and cellulose nanofiber (CNF), using a solvent casting strategy. The PS was characterized to contain 26.6% of amylose, exhibiting a "B"-type crystalline structure and high stability against thermal degradation. PS/CNF films showed better thermal stability than PS/CNC films, whereas the CNC was more effective than CNF for enhancing the tensile strength (TS) of the films. The nanocomposite films containing 1% CNC showed the highest TS of 30.32 MPa. Fourier transform infrared spectra revealed stronger hydrogen bonding in the PS/CNC films, likely contributing to the observed high mechanical strength. CNC and CNF both decreased the transparency of PS films, by 5.2% and 13.1%, respectively. Overall, the properties of PS composite films can be effectively modified by incorporating CNC and CNF, as PS/CNC films with high mechanical strength and PS/CNF films with good thermal stability. Our results indicate that PS is a suitable material for CNC/CNF composite film fabrication. These films are expected to be especially useful in food packaging applications.

Deconstruction and Reassembly of Renewable Polymers and Biocolloids into Next Generation Structured Materials

This review considers the most recent developments in supramolecular and supraparticle structures obtained from natural, renewable biopolymers as well as their disassembly and reassembly into engineered materials. We introduce the main interactions that control bottom-up synthesis and top-down design at different length scales, highlighting the promise of natural biopolymers and associated building blocks. The latter have become main actors in the recent surge of the scientific and patent literature related to the subject. Such developments make prominent use of multicomponent and hierarchical polymeric assemblies and structures that contain polysaccharides (cellulose, chitin, and others), polyphenols (lignins, tannins), and proteins (soy, whey, silk, and other proteins). We offer a comprehensive discussion about the interactions that exist in their native architectures (including multicomponent and composite forms), the chemical modification of polysaccharides and their deconstruction into high axial aspect nanofibers and nanorods. We reflect on the availability and suitability of the latter types of building blocks to enable superstructures and colloidal associations. As far as processing, we describe the most relevant transitions, from the solution to the gel state and the routes that can be used to arrive to consolidated materials with prescribed properties. We highlight the implementation of supramolecular and superstructures in different technological fields that exploit the synergies exhibited by renewable polymers and biocolloids integrated in structured materials.

The Food-Materials Nexus: Next Generation Bioplastics and Advanced Materials from Agri-Food Residues

The most recent strategies available for upcycling agri-food losses and waste (FLW) into functional bioplastics and advanced materials are reviewed and the valorization of food residuals are put in perspective, adding to the water-food-energy nexus. Low value or underutilized biomass, biocolloids, water-soluble biopolymers, polymerizable monomers, and nutrients are introduced as feasible building blocks for biotechnological conversion into bioplastics. The latter are demonstrated for their incorporation in multifunctional packaging, biomedical devices, sensors, actuators, and energy conversion and storage devices, contributing to the valorization efforts within the future circular bioeconomy. Strategies are introduced to effectively synthesize, deconstruct and reassemble or engineer FLW-derived monomeric, polymeric, and colloidal building blocks. Multifunctional bioplastics are introduced considering the structural, chemical, physical as well as the accessibility of FLW precursors. Processing techniques are analyzed within the fields of polymer chemistry and physics. The prospects of FLW streams and biomass surplus, considering their availability, interactions with water and thermal stability, are critically discussed in a near-future scenario that is expected to lead to next-generation bioplastics and advanced materials.