Green Nanocomposites Based on Thermoplastic Starch: A Review

Dynamic imine crosslinking for waterproof starch plastic with tunable mechanical properties

Starch-based plastics offer a potential solution to environmental pollution and can reduce the dependence on petroleum-based plastics. However, effectively preparing starch-based plastics with moisture resistance and high strength remains challenging. Herein, dialdehyde starch (DAS) with different degrees of oxidation was first synthesised. The molecular weight and crystallinity of DAS decreased depending on the aldehyde content, as determined through scanning electron microscopy, X-ray diffraction and molecular weight analyses. Subsequently, a sustainable starch plastic (DAS-DA) was prepared via the dynamic imine crosslinking of DAS with diamines. The influence of the degree of oxidation of DAS on the structure and properties of DAS-DA was systematically investigated. No linear relationship was observed between the tensile strength of DAS-DA and the aldehyde content of DAS. When the aldehyde content was 41.1 %, the resulting DAS41-DA exhibited optimal mechanical strength (27.8 MPa), exceeding that of most reported starch-based plastics. In addition, owing to the presence of imine crosslinking networks, DAS41-DA exhibited excellent water and solvent resistance (>60 days), good thermal stability (456 °C-462 °C) and excellent reprocessability and biodegradability. These findings provide a theoretical basis for the preparation of high-performance bioplastics from aldehyde-containing polysaccharides.

Extraction and characterization of cellulose microfibers from cornhusk for application as reinforcing agent in biocomposite

This study aims to extract and characterize cellulose microfibers from cornhusk, an agricultural by-product. The extracted fibers will then be used as a reinforcing agent in a biocomposite made of thermoplastic corn starch. The process of extracting cellulose microfibers involved two treatments: sequential alkali treatment (using sodium hydroxide at 120 °C for 120 min) and peroxide bleach treatment (using hydrogen peroxide at 90 °C for 60 min). Various techniques such as Fourier transform infrared (FTIR), X-Ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were employed to characterize the extracted fibers. The properties of the composite were examined through tensile strength tests, contact angle measurements, and UV-Vis spectrophotometry. The study found that cellulose microfibers were successfully extracted from cornhusks, with a diameter of 7 to 30 μm and a crystallinity of 65 %. The treated fibers showed gradual degradation between 150 °C and 350 °C, indicating a lower amount of non-cellulosic substances compared to untreated cornhusks. Adding 10 % of the microfibers to the thermoplastic starch composite increased the tensile stress at breaking and the Young's modulus, but decreased the contact angle of water droplets and the film's transparency.

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.

Impact of Nanoclays Addition on Chickpea (Cicer arietinum L.) Flour Film Properties

Chickpea flour is an affordable natural blend of starch, proteins, and lipids, which can create films with suitable properties as an eco-friendly packaging material. Nanoclays' incorporation into natural biopolymers enhances the barrier properties of the resulting nanocomposites, so they could improve the properties of flour films. The objective of this work was to assess the influence of three types of nanoclays (halloysite, bentonite, and Cloisite 20A) at two concentrations on the characteristics of chickpea flour films. In general terms, when the lowest dose (5%) was added, no or very slight significant differences with the control were observed in most parameters, except for thermal stability and opacity, which increased, and solubility, which decreased. At the highest concentration (10%), films containing any of the nanoclays demonstrated greater thermal stability, opacity, and rigidity while being less soluble than those without nanofillers. Bentonite exhibited superior film structure distribution compared to other nanoclays. At the highest concentration, it had the most significant impact on modifying the properties of chickpea flour films, increasing their tensile and puncture strengths while decreasing elasticity and water vapor permeability. The incorporation of nanoclays into chickpea flour films could be a useful technique to enhance their properties.

Thermoplastic Starch Biocomposite Films Reinforced with Nanocellulose from Agave tequilana Weber var. Azul Bagasse

In this work, cellulose nanocrystals (CNCs), bleached cellulose nanofibers (bCNFs), and unbleached cellulose nanofibers (ubCNFs) isolated by acid hydrolysis from Agave tequilana Weber var. Azul bagasse, an agro-waste from the tequila industry, were used as reinforcements in a thermoplastic starch matrix to obtain environmentally friendly materials that can substitute contaminant polymers. A robust characterization of starting materials and biocomposites was carried out. Biocomposite mechanical, thermal, and antibacterial properties were evaluated, as well as color, crystallinity, morphology, rugosity, lateral texture, electrical conductivity, chemical identity, solubility, and water vapor permeability. Pulp fibers and nanocelluloses were analyzed via SEM, TEM, and AFM. The water vapor permeability (WVP) decreased by up to 20.69% with the presence of CNCs. The solubility decreases with the presence of CNFs and CNCs. The addition of CNCs and CNFs increased the tensile strength and Young's modulus and decreased the elongation at break. Biocomposites prepared with ubCNF showed the best tensile mechanical properties due to a better adhesion with the matrix. Images of bCNF-based biocomposites demonstrated that bCNFs are good reinforcing agents as the fibers were dispersed within the starch film and embedded within the matrix. Roughness increased with CNF content and decreased with CNC content. Films with CNCs did not show bacterial growth for Staphylococcus aureus and Escherichia coli. This study offers a new theoretical basis since it demonstrates that different proportions of bleached or unbleached nanofibers and nanocrystals can improve the properties of starch films.

Green composites based on thermoplastic starch reinforced with micro- and nano-cellulose by melt blending - A review

Starch is a biodegradable biopolymer, a sustainable material that can replace conventional petrochemical-based plastics. However, starch has some limitations, as it must be processed by heating and treated mechanically with a plasticizer to become thermoplastic starch (TPS). Different variables such as mixing speeds, amount, and kind of plasticizers play a vital role in preparing TPS by melting. Despite this, the properties of the TPS are not comparable with those of traditional plastics. To overcome this limitation, microcellulose or nanocellulose is added to TPS by melt mixing, including the extrusion and internal mixing process, which enables large-scale production. This review aims to compile several studies that evaluate the effect of plasticizers, as well as the relevance of incorporating different cellulosic fillers of different dimensions on the properties of TPS obtained by melt mixing. Potential applications of these materials in food packaging, biomedical applications, and other opportunities are also described.

Thermoplastic starch (TPS) bioplastic, the green solution for single-use petroleum plastic food packaging - A review

Plastic throughout the years is now one of the biggest world commodities and also the largest pollution to have an environmental impact, accumulating in landfills and also leaching into water systems and oceans. Especially with the shift to single-use disposable plastic, evermore positions plastics as the number one novel entity that pollutes the earth. This shift is also consistent in the food packaging industry. Managing plastic waste is still an issue at large, while the process of pyrolysis incineration still requires an obscene amount of energy that also does not resolve the problems with its environmental impact, the cost of mechanical-chemical degradation even outweighs the cost of producing the materials, and biodegradation process is a very slow and long process. Converting to bioplastics is one of the potential solutions to the global plastic issue. This review covers the potentials, limitations, challenges, progress and advancements of bioplastics, especially thermoplastic starch (starch-based bioplastic) in their efforts to replace petroleum plastics in food packaging and smart food packaging, especially for single-use (disposable) food packaging.

Development and characterization of starch‑sodium alginate-montmorillonite biodegradable antibacterial films

The biodegradable antibacterial composite film blended with starch and sodium alginate was developed by solution casting method, using montmorillonite as the fortifier and star anise oil as the bacteriostat. Infrared analysis showed that montmorillonite and star anise oil were successfully incorporated into starch and sodium alginate to form a stable composite film. The addition of 6 wt% montmorillonite could enhance several properties of the films, including barrier properties, optical properties, thermal stability and mechanical properties. Meanwhile, the incorporation of star anise oil made the composite films have antibacterial properties to resist E. coli. Packing cherry tomatoes with starch‑sodium alginate-montmorillonite-star anise oil composite film could reduce the weight loss rate and decay rate of fresh cherry tomatoes. Soil burial experiments showed that the composite films exhibited a continuous biodegradation process. The starch‑sodium alginate-montmorillonite-star anise oil films decomposed into little pieces and were completely mixed in the soil within 22 days, which offered an application foreground for the development of biodegradable food packaging film with bacteriostatic activity.

Wheat thermoplastic starch composite films reinforced with nanocellulose

The rising costs of non-renewable plastic and environmental concerns with their industrial usage have encouraged the study and development of renewable products. As an alternative, biological-based materials create a huge opportunity for a healthy and safe environment by replacing non-renewable plastic in a variety of applications. Wheat is one of the world’s most widely cultivated crops. Due to its mechanical and physical properties, wheat starch is vital in the biopolymer industry. Wheat thermoplastic starch exhibits useable properties when plasticizers, elevated temperatures and shear are present. Thus, make it very suitable to be used as packaging material. However, this material suffers from low mechanical properties, which limit its applications. Several studies looked at the feasibility of using plant components which is nanocellulose as a reinforcing agent in wheat starch thermoplastic composites. Overall, the addition of nanocellulose can improve the performance of wheat thermoplastic starch, especially for its mechanical properties. It can potentially be used in several areas of packaging and biomedical. The objective of this review is to discuss several achievements regarding wheat starch/nanocellulose-based composites. Several important aspects of the mechanical performance and the thermal properties of the composites were evaluated. The discussion on wheat starch and nanocellulose was also tackled in this review.

Preparation and Characterization of Microalgae Styrene-Butadiene Composites Using Chlorella vulgaris and Arthrospira platensis Biomass

The food industry is a high consumer of polymer packing materials, sealing materials, and engineering components used in production equipment. Biobased polymer composites used in the food industry are obtained by incorporating different biogenic materials into the structure of a base polymer matrix. Renewable resources such as microalgae, bacteria, and plants may be used as biogenic materials for this purpose. Photoautotrophic microalgae are valuable microorganisms that are able to harvest sunlight energy and capture CO2 into biomass. They are characterized by their metabolic adaptability to environmental conditions, higher photosynthetic efficiency than terrestrial plants, and natural macromolecules and pigments. The flexibility of microalgae to grow in either low-nutrient or nutrient-rich environments (including wastewater) has led to the attention for their use in various biotechnological applications. Carbohydrates, proteins, and lipids are the main three classes of macromolecular compounds contained in microalgal biomass. The content in each of these components depends on their growth conditions. In general, proteins represent 40-70% of microalgae dry biomass, followed by carbohydrates (10-30%) and lipids (5-20%). A distinctive feature of microalgae cells is the presence of light-harvesting compounds such as photosynthetic pigments carotenoids, chlorophylls, and phycobilins, which are also receiving growing interest for applications in various industrial fields. The study comparatively reports on polymer composites obtained with biomass made of two species of green microalgae: Chlorella vulgaris and filamentous, gram-negative cyanobacterium Arthrospira. Experiments were conducted to reach an incorporation ratio of the biogenic material into the matrix in the 5-30% range, and the resulting materials were characterized by their mechanical and physicochemical properties.

The Effect of Montmorillonites on the Physicochemical Properties of Potato Starch Films Plasticized with Deep Eutectic Solvent

In the paper, the method of obtaining the potato starch nanocomposites plasticized with a deep eutectic solvent is described. The deep eutectic solvent based on choline chloride and malic acid (CM, molar ratio 1:1) was used as the plasticizer. The effect of the sodium and calcium montmorillonite (MMTNa, MMTCa respectively) addition on the properties of potato starch films was investigated. The thermal, mechanical, and barrier properties were determined. Moreover, a moisture absorption test was performed. The starch gelatinization temperature increased in the presence of montmorillonite. The values of glass transition determined by DMTA depended on the nanofiller type. For the systems containing MMTCa, they generally decreased with its content (although still lower than reference samples). The obtained nanocomposites showed improved mechanical and barrier properties. The highest values of tensile strength and Young's modulus were noted for the system containing 1% MMTNa. The XRD revealed that only the films with MMTNa exhibited intercalation. The homogeneity of the samples decreased with increasing nanofiller concentration. This was probably due to the occurrence of choline chloride-montmorillonite interactions, which were more favored than clay-starch interactions.

Mater-Bi/Brewers' Spent Grain Biocomposites-Novel Approach to Plant-Based Waste Filler Treatment by Highly Efficient Thermomechanical and Chemical Methods

Thermoplastic starch (TPS) is a homogenous material prepared from native starch and water or other plasticizers subjected to mixing at a temperature exceeding starch gelatinization temperature. It shows major drawbacks like high moisture sensitivity, poor mechanical properties, and thermal stability. To overcome these drawbacks without significant cost increase, TPS could be blended with bio-based or biodegradable polymers and filled with plant-based fillers, beneficially waste-based, like brewers' spent grain (BSG), the main brewing by-product. Filler modifications are often required to enhance the compatibility of such composites. Herein, we investigated the impact of BSG thermomechanical and chemical treatments on the structure, physical, thermal, and rheological performance of Mater-Bi-based composites. Thermomechanical modifications enhanced matrix thermal stability under oxidative conditions delaying degradation onset by 33 °C. Moreover, BSG enhanced the crystallization of the polybutylene adipate terephthalate (PBAT) fraction of Mater-Bi, potentially improving mechanical properties and shortening processing time. BSG chemical treatment with isophorone diisocyanate improved the processing properties of the composites, expressed by a 33% rise in melt flow index. Depending on the waste filler's selected treatment, processing, and rheological performance, thermal stability or interfacial adhesion of composites could be enhanced. Moreover, the appearance of the final materials could be adjusted by filler selection.

Effective Aging Inhibition of the Thermoplastic Corn Starch Films through the Use of Green Hybrid Filler

Recently, hybrid fillers have been widely used to improve the properties of biopolymers. The synergistic effects of the hybrid fillers can have a positive impact on biopolymers, including thermoplastic corn starch film (TPCS). In this communication, we highlight the effectiveness of hybrid fillers in inhibiting the aging process of TPCS. The TPCS, thermoplastic corn starch composite films (TPCS-C), and hybrid thermoplastic corn starch composite film (TPCS-HC) were stored for 3 months to study the effect of hybrid filler on the starch retrogradation. TPCS-C and TPCS-HC were prepared by casting method with 5 wt% of fillers: nanocellulose (NC) and bentonite (BT). The alteration of the mechanical properties, aging behavior, and crystalline structure of the films were analyzed through the tensile test, Fourier transform infrared (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and water absorption analysis. The obtained data were correlated to each other to analyze the retrogradation of the TPCS, which is the main factor that contributes to the aging process of the biopolymer. Results signify that incorporating the hybrid filler (NC + BT) in the TPCS/4BT1NC films has effectively prevented retrogradation of the starch molecules after being stored for 3 months. On the contrary, the virgin TPCS film showed the highest degree of retrogradation resulting in a significant decrement in the film’s flexibility. These findings proved the capability of the green hybrid filler in inhibiting the aging of the TPCS.

Characterization and Optimization of Real-Time Photoresponsive Gelatin for Direct Laser Writing

There is an abundance of plastic materials used in the widest range of applications, such as packaging, machine parts, biomedical devices and components, etc. However, most materials used today are non-decomposable in the environment, producing a huge burden on ecosystems. The search for better, safer alternatives is still on. Here we present a detailed analysis of a simple, cheap, non-toxic, even edible, eco-friendly material, which can be easily manufactured, laser patterned and used for the fabrication of complex structures. The base substance is gelatin which is made photoresponsive by adding plasticizers and sensitizers. The resulting films were analyzed with respect to their optical, thermal and mechanical properties, which can be modified by a slight variation of chemical composition. The material is optimized for rapid laser-manufacturing of elastic microstructures (lenses, gratings, cantilevers, etc.) without any waste or residues. Overall, the material properties were tailored to increase photothermal responsivity, improve the surface quality and achieve material homogeneity, transparency and long-term stability (as verified using electron microscopy, infrared spectroscopy and differential scanning calorimetry).

Lacerda T. Monomers and Macromolecular Materials from Renewable Resources: State of the Art and Perspectives

A progressively increasing concern about the environmental impacts of the whole polymer industry has boosted the design of less aggressive technologies that allow for the maximum use of carbon atoms, and reduced dependence on the fossil platform. Progresses related to the former approach are mostly based on the concept of the circular economy, which aims at a thorough use of raw materials, from production to disposal. The latter, however, has been considered a priority nowadays, as short-term biological processes can efficiently provide a myriad of chemicals for the polymer industry. Polymers from renewable resources are widely established in research and technology facilities from all over the world, and a broader consolidation of such materials is expected in a near future. Herein, an up-to-date overview of the most recent and relevant contributions dedicated to the production of monomers and polymers from biomass is presented. We provide some basic issues related to the preparation of polymers from renewable resources to discuss ongoing strategies that can be used to achieve original polymers and systems thereof.

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.

Attaining Toughness and Reduced Electrical Percolation Thresholds in Bio-Based PA410 by Combined Addition of Bio-Based Thermoplastic Elastomers and CNTs

Multi-walled carbon nanotubes (CNTs) were added to provide electrical conductivity to bio-based polymer blends with improved toughness (based on commercially available Pebax thermoplastic elastomers and bio-based polyamide 4,10). A preliminary study including three different Pebax grades was carried out to select the grade and the composition that would best improve the impact properties of PA410. Thus, tough multiphasic PA/Pebax/CNT nanocomposites (NCs) with enhanced electrical conductivity were obtained. The CNTs were added either: (1) in the form of pristine nanotubes or (2) in the form of a PA6-based masterbatch. Hence, PA410/Pebax/CNT ternary NCs and PA410/PA6/Pebax/CNT quaternary NCs were obtained, respectively, up to a CNT content of 1 wt%. The ternary and quaternary NCs both showed similar mechanical and electrical properties. The electrical percolation threshold decreased with respect to previously studied corresponding NCs without Pebax, i.e., PA410/CNT and PA410/PA6/CNT, due to the partial volume exclusion effect of Pebax over the CNTs that were dispersed mainly in the PA matrix; materials with percolation concentrations as low as 0.38 wt% were obtained. With respect to mechanical properties, contrary to the NCs without Pebax, all the PA/Pebax/CNT NCs showed a ductile behavior and impact strength values that were from three to five-fold higher than that of the pure PA410.