Development of Polylactic Acid Films with Alkali- and Acetylation-Treated Flax and Hemp Fillers via Solution Casting Technique.

This study aims to enhance value addition to agricultural byproducts to produce composites by the solution casting technique. It is well known that PLA is moisture-sensitive and deforms at high temperatures, which limits its use in some applications. When blending with plant-based fibers, the weak point is the poor filler-matrix interface. For this reason, surface modification was carried out on hemp and flax fibers via acetylation and alkaline treatments. The fibers were milled to obtain two particle sizes of <75 µm and 149-210 µm and were blended with poly (lactic) acid at different loadings (0, 2.5%, 5%, 10%, 20%, and 30%) to form a composite film The films were characterized for their spectroscopy, physical, and mechanical properties. All the film specimens showed C-O/O-H groups and the π-π interaction in untreated flax fillers showed lignin phenolic rings in the films. It was noticed that the maximum degradation temperature occurred at 362.5 °C. The highest WVPs for untreated, alkali-treated, and acetylation-treated composites were 20 × 10-7 g·m/m2 Pa·s (PLA/hemp30), 7.0 × 10-7 g·m/m2 Pa·s (PLA/hemp30), and 22 × 10-7 g·m/m2 Pa·s (PLA/hemp30), respectively. Increasing the filler content caused an increase in the color difference of the composite film compared with that of the neat PLA. Alkali-treated PLA/flax composites showed significant improvement in their tensile strength, elongation at break, and Young's modulus at a 2.5 or 5% filler loading. An increase in the filler loadings caused a significant increase in the moisture absorbed, whereas the water contact angle decreased with an increasing filler concentration. Flax- and hemp-induced PLA-based composite films with 5 wt.% loadings showed a more stable compromise in all the examined properties and are expected to provide unique industrial applications with satisfactory performance.

Comparative study of the structure and mechanical properties of starch aerogels fabricated from air-classified and isolated pulse starches.

Significant amounts of starch and protein are generated as co-products during fractionation of pulse seeds. While pulse proteins (PP) have garnered a lot of interest in numerous applications, little attention is shown to pulse starch (PS). The creation of novel materials such as bioplastics could revolutionize the use of pulse starches. In this study, we investigated the prospects of air-classified and isolated pea, lentil, and faba bean starches as a precursor for fabricating pulse starch bioaerogels (PSBs) via freeze-drying technique. The results evidenced ultra-low densities (<0.1 m2/g), mesopore sizes (2-50 µm), high porosities (∼99 %), low surface areas (SBET = âˆ¼4-18 m2/g) for all the aerogels. The adsorption isotherm showed typical Type II and III profiles, while the thermogravimetric analysis showed more weight loss (74.39-78.12 %) in aerogels mostly developed from isolated starches. Microstructural studies showed a unique distribution of pores within the developed aerogels. FTIR and XPS studies confirmed the presence of an amide (I, II, III) at different absorption bands range (∼1600-1200 cm-1) and functional groups (carboxylic group and the amide group), respectively. All the PSBs became stiffer with a corresponding increase in load, and a reversible deformation in the linear region was identified at <5 % strain. Comparatively, saturated PSBs from air-classified starch at a relative humidity of 95 % showed a drastic reduction in their compressive moduli (CM), while PSBs from isolated starch experienced markedly high CM. Moisture saturation was achieved at 72 h for all the samples. This study provides crucial information that could spark a keen interest in the use of non-conventional starch for the creation of novel and sustainable biobased products with expanded applications.

Cellulose nanocrystals in the development of biodegradable materials: A review on CNC resources, modification, and their hybridization.

The escalating demand for sustainable materials has propelled cellulose into the spotlight as a promising alternative to petroleum-based products. As the most abundant organic polymer on Earth, cellulose is ubiquitous, found in plants, bacteria, and even a unique marine animal-the tunicate. Cellulose polymers naturally give rise to microscale semi-crystalline fibers and nanoscale crystalline regions known as cellulose nanocrystals (CNCs). Exhibiting rod-like structures with widths spanning 3 to 50 nm and lengths ranging from 50 nm to several microns, CNC characteristics vary based on the cellulose source. The degree of crystallinity, crucial for CNC properties, fluctuates between 49 and 95 % depending on the source and synthesis method. CNCs, with their exceptional properties such as high aspect ratio, relatively low density (≈1.6 g cm-3), high axial elastic modulus (≈150 GPa), significant tensile strength, and birefringence, emerge as ideal candidates for biodegradable fillers in nanocomposites and functional materials. The percolation threshold, a mathematical concept defining long-range connectivity between filler and polymer, governs the effectiveness of reinforcement in nanocomposites. This threshold is intricately influenced by the aspect ratio and molecular interaction strength, impacting CNC performance in polymeric and pure nanocomposite materials. This comprehensive review explores diverse aspects of CNCs, encompassing their derivation from various sources, methods of modification (both physical and chemical), and hybridization with heterogeneous fillers. Special attention is devoted to the hybridization of CNCs derived from tunicates (TCNC) with those from wood (WCNC), leveraging the distinct advantages of each. The overarching objective is to demonstrate how this hybridization strategy mitigates the limitations of WCNC in composite materials, offering improved interaction and enhanced percolation. This, in turn, is anticipated to elevate the reinforcing effects and pave the way for the development of nanocomposites with tunable viscoelastic, physicochemical, and mechanical properties.

Enhancing the Potential of Polymer Composites Using Biochar as a Filler: A Review.

This article discusses the scope biochar's uses; biochar is a sustainable organic material, rich in carbon, that can be synthesized from various types of biomass feedstock using thermochemical reactions such as pyrolysis or carbonization. Biochar is an eco-friendly filler material that can enhance polymer composites' mechanical, thermal, and electrical performances. In comparison to three inorganic fillers, namely carbon black, carbon nanotubes (CNT), and carbon filaments, this paper explores the optimal operating conditions for regulating biochar's physical characteristics, including pore size, macro- and microporosity, and mechanical, thermal, and electrical properties. Additionally, this article presents a comparative analysis of biochar yield from various thermochemical processes. Moreover, the review examines how the surface functionality, surface area, and particle size of biochar can influence its mechanical and electrical performance as a filler material in polymer composites at different biochar loads. The study showcases the outstanding properties of biochar and recommends optimal loads that can improve the mechanical, thermal, and electrical properties of polymer composites.

Crosslinked poly (vinyl alcohol) composite reinforced with tunicate, wood, and hybrid cellulose nanocrystals: Comparative physicochemical, thermal, and mechanical properties.

The development of sustainable and biodegradable composites has gained increasing attention in recent years. Effective interaction and adhesion between polymers and fillers are crucial. In this study, the effect of different aspect ratios of cellulose nanocrystals (CNCs) and their hybrid within a crosslinked poly (vinyl alcohol) (PVA) nanocomposite has been investigated to develop biodegradable materials. The physicochemical, thermal, and mechanical properties of the specimens have been studied. SEM images indicate that the addition of CNC reduced the porosity of the films. The XPS results confirmed the significant formation of covalent bonds for all composites except those reinforced with wood-CNC, which showed a lower amount of crosslinking and CC formation. EDS maps reveals that the dispersity of the CNCs could be different depending on the aspect ratio of the CNCs. Results from the solubility in water (SW) tests indicated that the use of hybrid-CNC in a crosslinked system decreased the SW significantly. The crosslinking and addition of CNC to the PVA composite led to improved mechanical properties. Elongation at break (EB) decreased significantly for the crosslinked hybrid-CNC nanocomposite. Overall, the results of this study indicate that the aspect ratio of CNCs as fillers in nanocomposites may contribute to their physicochemical, mechanical, and thermal properties for the development of biodegradable materials.

Valorization of Starch to Biobased Materials: A Review.

Many concerns are being expressed about the biodegradability, biocompatibility, and long-term viability of polymer-based substances. This prompted the quest for an alternative source of material that could be utilized for various purposes. Starch is widely used as a thickener, emulsifier, and binder in many food and non-food sectors, but research focuses on increasing its application beyond these areas. Due to its biodegradability, low cost, renewability, and abundance, starch is considered a "green path" raw material for generating porous substances such as aerogels, biofoams, and bioplastics, which have sparked an academic interest. Existing research has focused on strategies for developing biomaterials from organic polymers (e.g., cellulose), but there has been little research on its polysaccharide counterpart (starch). This review paper highlighted the structure of starch, the context of amylose and amylopectin, and the extraction and modification of starch with their processes and limitations. Moreover, this paper describes nanofillers, intelligent pH-sensitive films, biofoams, aerogels of various types, bioplastics, and their precursors, including drying and manufacturing. The perspectives reveal the great potential of starch-based biomaterials in food, pharmaceuticals, biomedicine, and non-food applications.

Comparison of Protein Content, Availability, and Different Properties of Plant Protein Sources with Their Application in Packaging.

Plant-based proteins are considered to be one of the most promising biodegradable polymers for green packaging materials. Despite this, the practical application of the proteins in the packaging industry on a large scale has yet to be achieved. In the following review, most of the data about plant protein-based packaging materials are presented in two parts. Firstly, the crude protein content of oilseed cakes and meals, cereals, legumes, vegetable waste, fruit waste, and cover crops are indexed, along with the top global producers. In the second part, we present the different production techniques (casting, extrusion, and molding), as well as compositional parameters for the production of bioplastics from the best protein sources including sesame, mung, lentil, pea, soy, peanut, rapeseed, wheat, corn, amaranth, sunflower, rice, sorghum, and cottonseed. The inclusion of these protein sources in packaging applications is also evaluated based on their various properties such as barrier, thermal, and mechanical properties, solubility, surface hydrophobicity, water uptake capacity, and advantages. Having this information could assist the readers in exercising judgement regarding the right source when approving the applications of these proteins as biodegradable packaging material.

Multilayer photonic films based on interlocked chiral-nematic cellulose nanocrystals in starch/chitosan.

In this study, a new approach to employ and control cellulose nanocrystal (CNC) chiral nematic structure as a biodegradable, intelligent material was investigated. Tuned CNC self-assembled films were interlocked between two layers of citric acid, cross-linked starch/chitosan (1:1) films through the solvent casting process. This method increased the mechanical properties of produced films and created a selective reflection band from UV to near-IR depending on the helical pitch of the chiral nematic CNC layer. The features of these intelligent films have potential for different applications, from UV protective packaging to biomedical uses. The water vapor permeability (WVP) of the produced films decreased considerably by adding a CNC layer into the cross-linked starch/chitosan structure. Also, the WVP was different for the different helical pitches of the CNC layer. The starch/chitosan (outer layer) also showed a remarkable antibacterial property against E. coli, P. fluorescens, S. Enteritidis, and S. aureus which could be useful for biomedical applications or antibacterial packaging.

Humidity-Responsive Photonic Films and Coatings Based on Tuned Cellulose Nanocrystals/Glycerol/Polyethylene Glycol.

It has been extensively reported that cellulose nanocrystals (CNCs) can represent structural colors due to their unique chiral-nematic self-assembly. However, the application of this remarkable structure does need further investigation. It has been challenging to keep the selective reflection band (SRB) resulting from the CNC structure in the visible spectrum. Herein, composition of CNC colloidal suspensions with polyethylene glycol (PEG) and glycerol (Gly) have been studied to develop humidity-responsive sensors in the form of coatings and films. The fabricated samples were characterized for their mechanical properties, optical properties, water uptake capacity, water contact angle, and surface roughness. Additionally, the chemical structure of the samples was studied with FTIR spectroscopy. The produced humidity indicators on microbial glass slides were maintained and tested in a different relative humidity range from 20% to 98% with a different color response from blue to red, respectively. The color change of the humidity sensors was reversible for several cycles. It should be noted that the color change can be detected easily by the naked eye. The water uptake test showed that pure CNC and CNC/Gly had the lowest (34%) and highest (83%) water absorption levels. The mechanical tests for CNC/PEG composites showed the highest tensile strength (40.22 MPa). Moreover, microstructural characterizations confirmed the CNC pitch formation in all the samples. Addition of the fillers increased the CNC pitch, resulting in a mesoporous film formation. These produced humidity sensors are promising candidates in food and drug packaging due to their biodegradability, biocompatibility, and cost-effectiveness.

Antimicrobial Biodegradable Food Packaging Based on Chitosan and Metal/Metal-Oxide Bio-Nanocomposites: A Review.

Finding a practical alternative to decrease the use of conventional polymers in the plastic industry has become an acute concern since industrially-produced plastic waste, mainly conventional food packaging, has become an environmental crisis worldwide. Biodegradable polymers have attracted the attention of researchers as a possible alternative for fossil-based plastics. Chitosan-based packaging materials, in particular, have become a recent focus for the biodegradable food packaging sector due to their biodegradability, non-toxic nature, and antimicrobial properties. Chitosan, obtained from chitin, is the most abundant biopolymer in nature after cellulose. Chitosan is an ideal biomaterial for active packaging as it can be fabricated alone or combined with other polymers as well as metallic antimicrobial particles, either as layers or as coacervates for examination as functional components of active packaging systems. Chitosan-metal/metal oxide bio-nanocomposites have seen growing interest as antimicrobial packaging materials, with several different mechanisms of inhibition speculated to include direct physical interactions or chemical reactions (i.e., the production of reactive oxygen species as well as the increased dissolution of toxic metal cations). The use of chitosan and its metal/metal oxide (i.e., titanium dioxide, zinc oxide, and silver nanoparticles) bio-nanocomposites in packaging applications are the primary focus of discussion in this review.

Digital holographic microscopy for real-time investigation of 3D microstructural dynamics of starch-kefiran-based nanocomposite.

Investigating real-time phenomena in bio-polymers has received much attention because of their increasing demands in polymer substitution. The 3D morphometry of polymer surfaces may be very impactful in such studies. Here, digital holographic microscopy (DHM) is applied for quantitative measurement of the rare morphological changes of UV-A and UV-C exposed nanocomposites during their incubation with excess water. By reconstructing the recorded successive digital holograms, the time evolution of the swelled regions of the samples is derived. Our results clearly show that the higher water swelling of UV-A irradiated starch/kefiran/ZnO may be attributed to its higher hydrophilicity.

Effect of magnetic field alignment of cellulose nanocrystals in starch nanocomposites: Physicochemical and mechanical properties.

The magnetic field (MF) induced alignment of cellulose nanocrystals (CNC) within a starch matrix is investigated and its effect on the physicochemical and mechanical properties of the nanocomposites are discussed in the paper. Two different kinds of CNC i.e. plant-CNC and tunicate-CNC and its hybrid combination are studied to understand the effect of aspect ratio of CNC on the properties of nanocomposite. Nanocomposites with tunicate sourced CNC showed higher tensile strength and modulus, and lower water vapor permeability as compared to plant sourced CNC. These properties are higher for nanocomposites prepared under MF. The modulus of starch nanocomposites increased from 0.26 GPa and 0.32 GPa to 0.38 GPa and 0.44 GPa, respectively for plant-CNC and tunicate-CNC when exposed to MF. The improved orientation and alignment of CNC in presence of MF is further supported by Raman and scanning electron micrographs studies.

Production of starch based biopolymer by green photochemical reaction at different UV region as a food packaging material: Physicochemical characterization.

In current study, the functional properties of modified starch solutions by photochemical reactions as a biodegradable food packaging material were investigated. Starch film-forming solutions were exposed to ultraviolet A (UV-A) and C (UV-C) over different time periods (1, 6, 12, and 24 h). A green method was used to prepare the modified starch films. Hydrophobicity, moisture sensitivity, and water vapor permeability of the starch films, decreased after exposure to UV irradiation up to 12 h. Tensile strength and Young's modulus of the specimens decreased by increasing UV exposure time. Elongation at break, and tensile energy to break of the film specimens were increased, simultaneously. Scanning electron microscopy images demonstrated that most of the films' physical properties were affected by their microstructures. UV-Vis spectrum of the specimens confirmed that UV-protective properties of the irradiated specimens in UV-A, UV-B, and UV-C region have changed in comparison with the control sample. According to the results, UV-irradiation could be considered as a green, easy, and accessible process for modification of starch-based films.

Using photo-modification to compatibilize nano-ZnO in development of starch-kefiran-ZnO green nanocomposite as food packaging material.

In this study, the effect of UV-C light on starch-kefiran-ZnO (1%) primary solution in different exposure times (1, 6, and 12 h) was investigated. Starch-kefiran-ZnO (SKZ) solution was modified by UV irradiation in different time periods. Also, nano-ZnO (ZN) was used as a photo-initiator and reinforcement agent, simultaneously. Mechanical properties of the films were affected after the UV treatment. The tensile strength increased because of the enhanced interaction between the biopolymer mixture and nano filler but elongation at break was decreased. WVP decreased about 16% and dwindled to 2.08 × 10-10 g m-1 s-1 Pa-1. Water related properties (i.e. moisture content, moisture absorption, and solubility in water) of the films decreased by UV-C exposure. On the other hand, UV absorption and water contact angle increased because of the better distribution of the ZNs in polymer matrix after the UV exposure. Better compatibility of the ZNs and the biopolymer matrix after UV treatment was confirmed by the SEM micrographs. Comparison of FTIR spectra before and after UV exposure showed slight shifts. It was due to some formed or deformed bonds inside of the nanocomposite matrix. The modified SKZ by UV could be an appropriate process to sanitizing and food packaging concurrently. As well as UV can be used as a nano-ZnO compatibilizer in food packaging materials.

Preparation of ecofriendly UV-protective food packaging material by starch/TiO2 bio-nanocomposite: Characterization.

In this study, ecofriendly starch/TiO2 bio-nanocomposites were produced using with different nano-TiO2 (TiO2) content (1, 3, and 5 (wt%)). Physical, mechanical, thermal, water-vapor permeability (WVP) properties and UV transmittance were investigated. Our results showed that the increasing TiO2 content increased the hydrophobicity of starch/TiO2 films. WVP of the bio-nanocomposites was reduced, simultaneously. With increasing TiO2 content, tensile strength and Young's modulus of the film specimens were reduced while elongation at break and tensile energy to break were increased. The thermal properties of specimens showed that glass transition temperature of the films increased but melting point of the specimen films was decreased by increasing TiO2 content. Scanning electron microscopy observations demonstrated, the most of films' physical properties were in relation to their microstructures. The starch/TiO2 nanocomposites effectively protect goods against UV light, and could potentially be applied as UV-shielding packaging materials.