From Cellulose Nanospheres, Nanorods to Nanofibers: Various Aspect Ratio Induced Nucleation/Reinforcing Effects on Polylactic Acid for Robust-Barrier Food Packaging

Conductive cellulose nanofibers tailored poly(propylene carbonate) island structure and synergistic reinforcement-toughening mechanism of high-performance poly(lactic acid) composites

Biodegradable poly(lactic acid) (PLA) based composites have broad application prospects in replacing common polyester-based composites, but poor toughness and low thermal stability of PLA composites is still unsatisfactory for practical applications. Herein, a new preparation method of PLA composites by doping rigid conductive cellulose nanofibers (CNFene) and tough poly(propylene carbonate) (PPC) to tailor island structure and synergistic reinforcement-toughening mechanism is presented. Moreover, the composite films and paper-based coated beverage straws prepared from these composites has excellent thermal stability, high-strength, and high-toughness. Compared to pure PLA film, the tensile strength, elastic modulus, and elongation at break of the best PLA80P20C3 were increased by 25.3%, 17%, and 17.5 times respectively. And the strength of PLA80P20C3 coated straws reached up to 49.4 MPa, which was 12.7 times higher than untreated paper-based straws and 70% higher than PLA-coated straws. The high-performance PLA-based composites expanded the application areas of bio-packaging and hot drink straws.

Synergistic enhancement of high-barrier polylactic acid packaging materials by various morphological carbonized cellulose nanocrystals

The environmental challenges linked to petroleum-based polymers have accelerated the search for alternative materials like polylactic acid (PLA). Diverse nanofillers, ranging from inorganic to organic and hybrid inorganic/organic varieties, are employed to bolster PLA performance. Yet, non-synergistic nanofillers often underperform due to inadequate dispersion and singular functionality within the PLA matrix. This work introduces carbonized cellulose nanocrystals (GCNC) with rod-like (R-GCNC) and spherical structures (S-GCNC), as synergistic reinforcements for PLA matrix. Unlike traditional nanofillers, the highly graphitized carbon layer on GCNC effectively mitigates CNC agglomeration while preserving cellulose morphology, fostering improved interfacial interactions and hydrogen bonding within PLA matrix. Moreover, GCNC acts as a nucleating agent, boosting the crystallization rate of PLA and enhancing its mechanical properties. Remarkable synergistic reinforcing effects of GCNC on PLA performances were observed. Particularly, the tensile strength of R-GCNC 5 % and S-GCNC 5 % composites surged by 93 % and 76 %, elongation at break increased by 29.4 % and 33.3 %, Young's modulus rose by 37 % and 18 %, and cold crystallization temperature decreased by 11.5 °C and 12.9 °C. Additionally, the GCNC/PLA composites exhibited exceptional thermal stability, UV resistance, and water vapor permeability reduced by 46 % for R-GCNC, and 35 % for S-GCNC, making them promising for industrial and sustainable packaging.

Cellulose Nanomaterials Functionalized with Carboxylic Group Extracted from Lignocellulosic Agricultural Waste: Isolation and Cu(II) Adsorption for Antimicrobial Application

In this study, we reported the isolation of COOH-functionalized nanocrystal cellulose from agricultural waste, particularly dragon fruit foliage (DFF), by two methods, the citric acid/HCl acid (CA) method and the (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-mediated oxidation method. Chemical component quantification and physiochemical characterization techniques, such as FT-IR spectroscopy, XRD, TGA, XPS, and AFM, were employed to analyze DFF, bleached cellulose, and extracted CNs. We determined the contents of lignin and hemicellulose removed, while the signals for the cellulose contents remain the same for DFF-CA and DFF-TEMPO. The DLS, AFM, and SEM results indicated that the DFF-CA sample has a smaller average particle size (250 ± 50 nm) with a rod-like shape, compared to the DFF-TEMPO sample (600 ± 100 nm) with a fiber-like shape. Importantly, CNs extracted from DFF, including DFF-TEMPO, DFF-CA, and DFF-bleached, exhibited excellent properties for Cu (II) adsorption with a maximum adsorption of 227 mg·g-1 (for DFF-CA samples), and the adsorption is almost independent of the -COOH content. Notably, we were also able to prepare Cu-containing cellulose gels showing promising antimicrobial activity. Our work opens new possibilities for the use of unexplored cellulosic byproducts in the agricultural industry as well as potential applications of Cu-containing cellulose gels as antimicrobials.

Cellulose nanocrystal based electrospun nanofiber for biomedical applications-A review

Electrospinning has become a revolutionized technique for nanofiber fabrication by offering versatile procedures to precisely regulate the nanofibers' properties suitable for a wide range of advanced applications. Nanofibers are utilized as carriers for delivering medications and other health supplements as well as their ability to discharge their contents can be easily programmed and tailored in a specific manner, while serving as tissue engineering scaffolds or medical devices. Cellulose nanocrystals (CNC) are one of the most significant natural biopolymers incorporated as reinforcing agents for nanostructured fibrous frameworks. The integration of electrospinning technology and CNC offers a viable method for manufacturing nanostructured porous substances with favorable functionality, a high ratio of surface area to volume, a tunable crystal structure along with non-toxicity and cytocompatibility, outstanding mechanical properties, flexibility, sustainability, and biodegradable properties. This article offers a thorough summary of the latest progress in the application of CNC based electrospun nanofibers in various biomedical fields such as drug delivery, tissue engineering, and wound healing. It covers the techniques and parameters used for their fabrication, the different types of raw materials employed, and their application criteria. The review concludes by discussing the prospects and challenges in this rapidly evolving research domains.

Water-Resistant Poly(vinyl alcohol)/ZnO Nanopillar Composite Films for Antibacterial Packaging

To solve the problems that poly(vinyl alcohol) (PVA) easily breeds bacteria and swells in a humid environment, PVA and ZnO nanopillar (ZnO NP) components were composed to generate PVA/ZnO NP composite films via a simple combination process of blending and heat treatment in this study. Here, ZnO NPs endowed composite films with good antibacterial properties, and the etherification and dehydration of hydroxyl groups between PVA molecular chains induced by heat treatment resulted in the composite films having excellent water-swelling resistance. Most importantly, PVA/ZnO NP composite films revealed excellent tensile strength in both humid (52.85 MPa) and dry (74.63 MPa) environments. In addition, PVA/ZnO NP composite films showed good antibacterial and antisepsis abilities as well as preservation functions in the packaging test of half-cut apples. The current work disclosed an easy strategy for producing a PVA-based antibacterial film for packaging materials that are water-resistant and highly strong, making them suitable for applications in humid environments.

Production of Cellulose Nanoparticles from Cashew Apple Bagasse by Sequential Enzymatic Hydrolysis with an Ultrasonic Process and Its Application in Biofilm Packaging

Cellulose nanostructures obtained from lignocellulosic biomass via enzymatic processes may offer advantages in terms of material properties and processing sustainability. Thus, in this study, cellulose nanoparticles with a spherical morphology were produced through the enzymatic hydrolysis of cashew apple bagasse (CAB). CAB was previously subjected to alkaline and acid-alkali pretreatment, and the pretreated solids were labeled as CAB-PTA and CAB-PT-HA, respectively. The enzymatic hydrolysis was carried out using two different enzymatic loadings (7.5 and 12 FPU/gcellulose) of the Trichoderma reesei cellulase complex, and the formation of nanostructures occurred only at 7.5 FPU/gcellulose. The results indicated the production of nanocellulose using only CAB-PT-HA as the precursor, obtaining nanosphere structures with a yield of 65.1 ± 2.9% and a diameter range of 57.26-220.66 nm. The nanocellulose showed good thermal and colloidal stability and was subsequently used for biofilm production. Biofilms were prepared using different percentages of nanocellulose (5 and 7% w/v), and they showed a greater water retention capacity and higher biodegradability compared to the control film, indicating potential for application in food packaging and cosmetic masks. Thus, it highlights the potential for developing new biodegradable plastics incorporated with nanocellulose obtained from CAB through a more sustainable process.

Nanocellulose and microcrystalline cellulose from citrus processing waste: A review

Used since decades to produce pectin, citrus processing waste poor in lignin and rich in hemicellulose obtained from lemon and orange juice industrial manufacturing is ideally suited also as microcrystalline cellulose and nanocellulose raw material. The study merges the outcomes of chemistry and bioeconomy research between 2007 and early 2024 with technology and economic insight, to reach five conclusions that will hopefully inform practice-oriented work of researchers and bioeconomy company's managers interested in the sustainable manufacturing of these important biomaterials.

An enzymatic hydrolysis-based platform technology for the efficient high-yield production of cellulose nanospheres

This study evaluates the feasibility of using enzymatic technology to produce novel nanostructures of cellulose nanomaterials, specifically cellulose nanospheres (CNS), through enzymatic hydrolysis with endoglucanase and xylanase of pre-treated cellulose fibers. A statistical experimental design facilitated a comprehensive understanding of the process parameters, which enabled high yields of up to 82.7 %, while maintaining a uniform diameter of 54 nm and slightly improved crystallinity and thermal stability. Atomic force microscopy analyses revealed a distinct CNS formation mechanism, where initial fragmentation of rod-like nanoparticles and subsequent self-assembly of shorter rod-shaped nanoparticles led to CNS formation. Additionally, adjustments in process parameters allowed precise control over the CNS diameter, ranging from 20 to 100 nm, highlighting the potential for customization in high-performance applications. Furthermore, this study demonstrates how the process framework, originally developed for cellulose nanocrystals (CNC) production, was successfully adapted and optimized for CNS production, ensuring scalability and efficiency. In conclusion, this study emphasizes the versatility and efficiency of the enzyme-based platform for producing high-quality CNS, providing valuable insights into energy consumption for large-scale economic and environmental assessments.

Mussel-inspired polydopamine modified mica with enhanced mechanical strength and thermal performance of poly(lactic acid) coating

Polylactic acid (PLA), as a green functional polymer, has been useful in various coating applications. However, due to the low mechanical strength and thermal stability of PLA, it needs to be improved in order to expand its application areas. In this work, a series of polylactic acid (PLA) nanocomposite films were prepared through introducing polydopamine-modified mica (PDA@MICA) as a self-assemble nanofiller to enhance its mechanical and thermal properties. The results demonstrated that PLA/PDA@MICA shows excellent mechanical properties. Tensile tests showed that PLA/PDA@MICA exhibits a 58.3 % increase in tensile strength and a 16.8 % increase in Young's modulus compared to pure PLA. Meanwhile, thermal performance testing shown the introduction of PDA@MICA led to an increase in crystallinities (Xc = 24.78 %). And the thermal decomposition temperature of PLA/PDA@MICA film (374 °C) was slightly higher than that of PLA film (367 °C). The simultaneous improvement of the mechanical and thermal properties was attributed to the formation of hydrogen bonds between PLA and PDA@MICA. In addition, the parallel arrangement of PDA@MICA and PLA macromolecular chains forms a unique "brick and mortar" structure in the coating, which enhances the mechanical properties of PLA/PDA@MICA composite coatings. This study reports a successful approach to simultaneously address the drawbacks of PLA, specifically its low thermal stability and mechanical strength, thereby promoting its widespread application in the coatings industry.

Jahim J, Sajab MS, Ibrahim Z. Synergistic sequential oxidative extraction for nanofibrillated cellulose isolated from oil palm empty fruit bunch

This research presents a comprehensive study of sequential oxidative extraction (SOE) consisting of alkaline and acidic oxidation processes to extract nanocellulose from plant biomass. This proposed process is advantageous as its operation requires a minimum process with mild solvents, and yet successfully isolated high-quality nanofibrillated cellulose (NFC) from raw OPEFB. The SOE involved ammonium hydroxide (NH4OH, 2.6 M) and formic acid (HCOOH, 5.3 M) catalyzed by hydrogen peroxide (H2O2, 3.2 M). This approach was used to efficiently solubilize the lignin and hemicellulose from Oil Palm Empty Fruit Bunch (OPEFB) at the temperature of 100°C and 1 h extraction time, which managed to retain fibrous NFC. The extracted solid and liquor at each stage were studied extensively through physiochemical analysis. The finding indicated that approximately 75.3%dwb of hemicellulose, 68.9%dwb of lignin, and 42.0%dwb of extractive were solubilized in the first SOE cycle, while the second SOE cycle resulted in 92.3%dwb, 99.6%dwb and 99.8%dwb of solubilized hemicellulose, lignin, and extractive/ash, respectively. High-quality NFC (75.52%dwb) was obtained for the final extracted solid with 76.4% crystallinity, which is near the crystallinity of standard commercial NFC. The proposed process possesses an effective synergy in producing NFC from raw OPEFB with less cellulose degradation, and most of the degraded hemicellulose and lignin are solubilized in the liquor.

Lightweight and robust cellulose/MXene/polyurethane composite aerogels as personal protective wearable devices for electromagnetic interference shielding

The increasing electromagnetic pollution is urgently needed as an electromagnetic interference shielding protection device for wearable devices. Two-dimensional transition metal carbides and nitrides (MXene), due to their interesting layered structure and high electrical conductivity, are ideal candidates for constructing efficient conductive networks in electromagnetic interference shielding materials. In this work, lightweight and robust cellulose/MXene/polyurethane composite aerogels were prepared by mixing cellulose nanofiber (CNF) suspensions with MXene, followed by freeze-drying and coating with polyurethane. In this process, CNF effectively assembled MXene nanosheets into a conductive network by enhancing the interactions between MXene nanosheets. The prepared aerogel exhibited the shielding effectiveness of 48.59 dB in the X-band and an electrical conductivity of 0.34 S·cm-1. Meanwhile, the composite aerogel also possessed excellent thermal insulation, infrared stealth, mechanical and hydrophobic properties, and can be used as a wearable protective device to protect the human body from injuries in different scenarios while providing electromagnetic interference shielding protection.

Micromorphology reformation of regenerated cellulose nanofibers from corn (Zea Mays) stalk pith in urea solution with high-speed shear induced

Nanocellulose is a kind of renewable natural polymer material with high specific surface area, high crystallinity, and strong mechanical properties. RC nanofibers (RCNFs) have attracted an increasing attention in various applications due to their high aspect ratio and good flexibility. Herein, a novel and facile strategy for RCNFs preparation with high-speed shear induced in urea solution through "bottom-up" approach was proposed in this work. Results indicated that the average diameter and yield of RCNF was approach to 136.67 nm and 53.3 %, respectively. Meanwhile, due to the regular orientation RC chains and arrangement micro-morphology, RCNFs exhibited high crystallinity, strong mechanical properties, stable thermal degradation performance, and excellent UV resistance. In this study, a novel regeneration process with high-speed shear induced was developed to produce RCNFs with excellent properties. This study paved a strategy for future low-energy production of nanofibers and high value-added conversion applications of agricultural waste.

Carboxyl-modified nanocellulose (cNC) enhances the stability of cNC/pullulan bio-nanocomposite hard capsule against moisture variation

The quality of polysaccharide-based films and hard capsules is often affected by changes in relative humidity, manifesting as unstable water content, and changes in mechanical strength that make them brittle or soft. Herein, carboxyl-modified nanocellulose (cNC) was prepared and used as a new component to successfully improve the moisture resistance of cNC/pullulan/high-acyl gellan bio-nanocomposite hard capsules (NCPGs). Homogenously dispersed cNC in the pullulan/high-acyl gellan matrix could render the formation of more hydrogen bonds that provided additional water-binding sites and limited the free movement of pullulan and high-acyl gellan molecular chains within NCPGs. This contributed to a decreased amount of pooling adsorption water and an increased amount of Langmuir adsorption water in NCPGs, as compared to pullulan/high-acyl gellan hard capsules (PGs) without cNC. Therefore, the equilibrium moisture content (EMC) values of NCPGs decreased at 83 % relative humidity and increased at 23 % relative humidity compared to those of PGs. Together with enhanced mechanical and barrier properties, NCPGs effectively protected encapsulated amoxicillin and probiotic powder from changes in the outside humidity. Additionally, NCPGs exhibited faster drug release. This study presents a new mechanism and strategy for fabricating films and hard capsules with enhanced stability against moisture variation.

Extraction and characterization of cellulose nanoparticles from palm kernel meal for potential application in active food packaging

The research aimed to explore the potential of palm kernel meal (PKM) as a sustainable source of cellulose nanoparticles (CNPs) for active food packaging. The CNPs were isolated using a combination of chemical techniques, such as alkaline treatment, bleaching, and acid hydrolysis. The characterization of the CNPs was analysed using various techniques, including scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and UV-visible spectroscopy. The findings revealed that chemical processing effectively removed lignin and hemicellulose from PKM. The SEM morphology confirmed the separation of the CNPs, resulting in the production of 40-100 nm spherical cellulose nanoparticles, while XRD and FTIR analyses confirmed their purity and composition. Moreover, the UV-visible spectroscopy exhibited high transmittance rates, indicating the potential of CNPs as reinforcing agents for polymer matrices. The significance of utilising PKM as a valuable fibre source for extracting CNPs can be recommended for developing active food packaging.

Effects of hydrolysis conditions on the morphology of cellulose II nanocrystals (CNC-II) derived from mercerized microcrystalline cellulose

The properties of cellulose nanocrystals with allomorph II (CNC-II) vary with the sources and the treatments received. In this work, the influences of hydrolysis time, temperature, and the applied acid concentration on the crystal size of CNC-II were investigated by the surface response experimental design. The results showed that temperature was the most significant factor affecting the crystal size of CNC-II during hydrolysis from mercerized cellulose. Then the morphology and colloidal properties of CNC-II were revealed by dynamic laser scattering (DLS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), etc. XRD results indicated that CNC-II had slightly lower crystallinity (80.89 % vs 82.7 %) and larger crystallite size (5.21 vs. 5.13 nm) than CNC-I. TEM and AFM results showed that the morphology of CNC-II were disc-like and rod-like particles, with an average diameter of 14.6 ± 4.7 nm (TEM) and a thickness of 4- 8 nm (AFM). TG and XPS revealed the reduced thermal stability was due to the introduced sulfate groups in CNC-II during hydrolysis. This investigation has addressed the features of CNC-II derived from mercerized cellulose, and it would be promising in fabricating advanced materials.

Multiple noncovalent interactions tailored crystallization and performance reinforcement mechanisms of Biopolyester Composites with functional Cellulose Nanocrystals

The slow crystallization and weak mechanical features of poly (butylene adipate-co-terephthalate) (PBAT) have become a severe industrial problem in food packaging. Inspired by principle of bionic structure, functional cellulose nanocrystals (CNC) modified with hexamethylene diisocyanate (HMDI) and toluene diisocyanate (TDI) can enhance the crystallization ability and mechanical properties of PBAT nanocomposites. Significantly, CNC-T (CNC modified by TDI) showed a stronger reinforced effect on PBAT properties than unmodified CNCs and CNC-H (CNC modified by HMDI) nanofillers due to hydrogen bonds, π-π interaction between PBAT matrix and CNC-T nanofillers with benzene ring structure. Thus, compared with pure PBAT, PBAT/5CNC-T composites displayed an enhancement of 34.5 % on the tensile strength and exhibited the most robust nucleation ability on PBAT crystallization than CNC and CNC-H. Meanwhile, the possible nucleation, crystallization, and performance reinforcement mechanisms of PBAT nanocomposites have been presented, which is very beneficial for designing robust PBAT nanocomposites with functional cellulose nanocrystals for potential green packaging.

Deep insights into biodegradability mechanism and growth cycle adaptability of polylactic acid/hyperbranched cellulose nanocrystal composite mulch

The widespread use of petroleum-based plastic mulch in agriculture has accelerated white and microplastic pollution while posing a severe agroecological challenge due to its difficulty in decomposing in the natural environment. However, endowing mulch film with degradability and growth cycle adaptation remains elusive due to the inherent non-degradability of petroleum-based plastics severely hindering its applications. This work reports polylactic acids hyperbranched composite mulch (PCP) and measured biodegradation behavior under burial soil, seawater, and ultraviolet (UV) aging to understand the biodegradation kinetics and to increase their sustainability in the agriculture field. Due to high interfacial interactions between polymer and nanofiler, the resultant PCP mulch significantly enhances crystallization ability, hydrophilicity, and mechanical properties. PCP mulch can be scalable-manufactured to exhibit modulated degradation performance under varying degradation conditions and periods while concurrently enhancing crop growth (wheat). Thus, such mulch with excellent performance can reduce labor costs and the environmental impact of waste mulch disposal to replace traditional mulch for sustainable agricultural production.

In situ preparation and properties of polyvinyl alcohol/synthetic ribbon-like nanocellulose composites

This study presents a novel approach in which a dual network (DN) composite, comprising polyvinyl alcohol (PVA) and ribbon-like nanocellulose (RC), was synthesized in one step using the volume exclusion effect involved in enzyme-catalyzed cellulose synthesis. Additionally, the impact of PVA as a crowding reagent during enzymatic catalysis on the in situ formation of nanocellulose and its resulting aspect ratio was explored. In contrast, the other two composites were created by incorporating enzyme-catalyzed synthetic block cellulose (BC) and its acid-hydrolyzed regenerated disc-shaped cellulose (DC) into the PVA. Subsequently, the mechanism by which three distinct types of nanocellulose, varying in morphology and size, was explored to elucidate their contributions to enhancing the properties of PVA. The results demonstrated that PVA/RC outperformed PVA/BC and PVA/DC. The elevated aspect ratio and intricate network structure of RCs not only significantly bolster the mechanical robustness of PVA/RC, leading in an 86.40 % surge in tensile strength and a remarkable 277.03 % rise in tensile modulus in comparison to pure PVA, but also induce a slight enhancement in elongation at break. Moreover, the thermal stability and biodegradability of PVA/RC was enhanced. Collectively, this study introduces an innovative strategy for the efficient fabrication of biodegradable composites with enhanced properties.

Multi-functional nanocellulose based nanocomposites for biodegradable food packaging: Hybridization, fabrication, key properties and application

Nowadays, non-degradable plastic packaging materials have caused serious environmental pollution, posing a threat to human health and development. Renewable eco-friendly nanocellulose hybrid (NCs-hybrid) composites as an ideal alternative to petroleum-based plastic food packaging have been extensively reported in recent years. NCs-hybrids include metal, metal oxides, organic frameworks (MOFs), plants, and active compounds. However, no review systematically summarizes the preparation, processing, and multi-functional applications of NCs-hybrid composites. In this review, the design and hybridization of various NCs-hybrids, the processing of multi-scale nanocomposites, and their key properties in food packaging applications were systematically explored for the first time. Moreover, the synergistic effects of various NCs-hybrids on several properties of composites, including mechanical, thermal, UV shielding, waterproofing, barrier, antimicrobial, antioxidant, biodegradation and sensing were reviewed in detailed. Then, the problems and advances in research on renewable NCs-hybrid composites are suggested for biodegradable food packaging applications. Finally, a future packaging material is proposed by using NCs-hybrids as nanofillers and endowing them with various properties, which are denoted as "PACKAGE" and characterized by "Property, Application, Cellulose, Keen, Antipollution, Green, Easy."

Molecular-Scale Exploration of Mechanical Properties and Interactions of Poly(lactic acid) with Cellulose and Chitin

Poly(lactic acid) (PLA), one of the pillars of the current overarching displacement trend switching from fossil- to natural-based polymers, is often used in association with polysaccharides to increase its mechanical properties. However, the use of PLA/polysaccharide composites is greatly hampered by their poor miscibility, whose underlying nature is still vastly unexplored. This work aims to shed light on the interactions of PLA and two representative polysaccharide molecules (cellulose and chitin) and reveal structure-property relationships from a fundamental perspective using atomistic molecular dynamics. Our computational strategy was able to reproduce key experimental mechanical properties of pure and/or composite materials, reveal a decrease in immiscibility in PLA/chitin compared to PLA/cellulose associations, assert PLA-oriented polysaccharide reorientations, and explore how less effective PLA-polysaccharide hydrogen bonds are related to the poor PLA/polysaccharide miscibility. The connection between the detailed chemical interactions and the composite behavior found in this work is beneficial to the discovery of new biodegradable and natural polymer composite mixtures that can provide needed performance characteristics.

Tough and strong sustainable thermoplastic elastomers nanocomposite with self-assembly of SI-ATRP modified cellulose nanofibers

The ingenious design of sustainable thermoplastic elastomers (STPEs) is of great significance for the goal of the sustainable development. However, the preparation of STPEs with good mechanical performance is still complicated and challenging. Herein, to achieve a simple preparation of STPEs with strong mechanical properties, two biobased monomers (tetrahydrofurfuryl methacrylate (THFMA) and lauryl methacrylate (LMA)) were copolymerized into poly (THFMA-co-LMA) (PTL) and grafted onto TEMPO oxidized cellulose nanofiber (TOCN) via one-pot surface-initiated atom transfer radical polymerization (SI ATRP). The grafting modified TOCN could be self-assembled into nano-enhanced phases in STPEs, which are conducive to the double enhancement of the strength and toughness of the STPEs, and the size of nano-enhanced phases is mainly affected by TOCN fiber length and molecular weight of grafting chains. Especially, with the addition of 7 wt% TOCN, tensile strength, tensile strain, toughness, and glass transition temperature (Tg) of TOCN based STPEs (TOCN@PTL) exhibited 140 %, 36 %, 215 %, and 6.8 °C increase respectively, which confirmed the leading level in the field of bio-based elastomers. In general, this work constitutes a proof for the chemical modification and self-assembly behavior of TOCN by one-pot SI ATRP, and provides an alternative strategy for the preparation of high-performance STPEs.

Crystallization behaviors regulations and mechanical performances enhancement approaches of polylactic acid (PLA) biodegradable materials modified by organic nucleating agents

Polylactic acid (PLA) has attracted much attention because of its good biocompatibility, biodegradability, and mechanical properties. However, the slow crystallization rate of PLA during molding leads to its poor heat resistance, which limit its diffusion for many industrial applications. In this review, the relationship between PLA crystallization and its molecular structure and processing conditions is summarized. From the perspective of the regulation of PLA crystallization by organic nucleating agents, the research progress of organic micromolecule (e.g., esters, amides, and hydrazides), organic salt, supramolecular, and macromolecule nucleating agents on the crystallization behavior of PLA is mainly introduced. The nucleation mechanism of PLA is expounded by organic nucleating agents, and the effect of the interaction force between organic nucleating agents and PLA molecular chains on the crystallization behavior of PLA is analyzed. The effects of the crystallization behavior of PLA on its mechanical properties and heat resistance are discussed. It will provide a theoretical reference for the development and application of high-efficiency nucleating agents.

Probing into the nucleation and reinforcing effects of poly (vinyl acetate) grafted cellulose nanocrystals in melt-processed poly (lactic acid) nanocomposites

Blending poly (lactic acid) (PLA) with cellulose nanocrystals (CNCs) to fabricate nanocomposites is a valuable strategy to improve the properties of PLA without sacrificing its biodegradability. However, the nucleation and reinforcing mechanisms of CNCs for semi-crystalline PLA matrix are still elusive in melt-processed PLA/CNC nanocomposites. Herein, poly (vinyl acetate) (PVAc) chains were grafted onto the surface of CNCs via an efficient radical polymerization in an aqueous medium, making CNCs suitable for conventional melting processing techniques. It is found that the dispersion state of CNCs in the PLA matrix and the interface interaction between PLA and CNCs can be tailored by varying the PVAc grafting density. Further studies show that well-dispersed CNCs play a positive role in reinforcing PLA. But unexpectedly, the nucleation effect is suppressed even though the homogeneous dispersion of CNCs is achieved with higher PVAc grafting density because the rich PVAc chains at the interface dilute the PLA chains, thus hindering the nucleation and spherulite growth of PLA. This research sheds light on the nucleation and reinforcing mechanisms of polymer grafted CNCs, and will provide theoretical guidance for the industrialization of high-performance bio-based nanocomposites.

Using celluloses in different geometries to reinforce collagen-based composites: Effect of cellulose concentration

Cellulose is frequently used to strengthen biocomposite films, but few literature systematically deliberates the effects of concentration of celluloses in different geometries on the reinforcement of these composites. Here we prepared three types of celluloses, including rod-like cellulose nanocrystalline (CNC), long-chain cellulose nanofiber (CNF) and microscopic cellulosic fines (CF). The effect of concentration of the three celluloses was examined on the barrier properties to water and light, thermostability, microstructure, and mechanical properties of collagen (COL) films. The addition of celluloses increased the watertightness and thermostability of composite films. Besides, FTIR showed a increased hydrogen bonding for COL/CNF and COL/CNC composite films, but decrease for COL/CF composites. As the concentration of CF and CNF increased, the strength of composites improved. The TS for COL/CNF (124 MPa) and COL/CF composites (113 MPa) were largely increased, compared with that of collagen ones (90 MPa). Considering the factors of crystallinity, hydrogen bonding, and interfacial tortuosity, COL/CNF composites possessed better mechanical behaviors than that of COL/CF and COL/CNC composites. Furthermore, Halpin-Kardos and Ouali models well predicted the modulus of COL/CNF composites when CNF was below and above percolation threshold (2.7 wt%), respectively.

A Comprehensive Review of Self-Healing Polymer, Metal, and Ceramic Matrix Composites and Their Modeling Aspects for Aerospace Applications

Composites can be divided into three groups based on their matrix materials, namely polymer, metal and ceramic. Composite materials fail due to micro cracks. Repairing is complex and almost impossible if cracks appear on the surface and interior, which minimizes reliability and material life. In order to save the material from failure and prolong its lifetime without compromising mechanical properties, self-healing is one of the emerging and best techniques. The studies to address the advantages and challenges of self-healing properties of different matrix materials are very limited; however, this review addresses all three different groups of composites. Self-healing composites are fabricated to heal cracks, prevent any obstructed failure, and improve the lifetime of structures. They can self-diagnose their structure after being affected by external forces and repair damages and cracks to a certain degree. This review aims to provide information on the recent developments and prospects of self-healing composites and their applications in various fields such as aerospace, automobiles etc. Fabrication and characterization techniques as well as intrinsic and extrinsic self-healing techniques are discussed based on the latest achievements, including microcapsule embedment, fibers embedment, and vascular networks self-healing.

A Review on Fully Bio-Based Materials Development from Polylactide and Cellulose Nanowhiskers

This review covers the development of eco-friendly, bio-based materials based on polylactide (PLA) and cellulose nanowhiskers (CNWs). As a biodegradable polymer, PLA is one of the promising materials to replace petroleum-based polymers. In the field of nanocomposites, CNWs offer many advantages; they are made from renewable resources and exhibit beneficial mechanical and thermal properties in combination with polymer matrix. A wide range of surface modifications has been done to improve the miscibility of CNW with the PLA homopolymer, which generally gives rise to hydrophobic properties. PLA–CNW nanocomposite materials are fully degradable and sustainable and also offer improved mechanical and thermal properties. Limitations pertaining to the miscibility of CNWs with PLA were solved through surface modification and chemical grafting on the CNW surfaces. Further development has been done by combining PLA-based material via stereocomplexation approaches in the presence of CNW particles, known as bio-stereo-nanocomposite PLA–CNW. The combination of stereocomplex crystalline structures in the presence of well-distributed CNW particles produces synergetic effects that enhance the mechanical and thermal properties, including stereocomplex memory (melt stability). The bio-based materials from PLA and CNWs may serve as eco-friendly materials owing to their sustainability (obtained from renewable resources), biodegradability, and tunability properties.

Synthesis of cellulose II-based spherical nanoparticle microcluster adsorbent for removal of toxic hexavalent chromium

Since natural cellulose is mostly cellulose I and has a fibrous form, most cellulose-based adsorbents are fibrous/rod-shaped and exhibit the cellulose I crystal structure. This study reports a cellulose II-based spherical nanoparticle microcluster adsorbent (SNMA), synthesized from biomass by a bottom-up approach, for removing toxic hexavalent chromium (Cr(VI)). The basic structure of SNMA was investigated. Notably, the prepared adsorbent was a microcluster composed of spherical nanoparticles, while exhibiting cellulose II crystal structure, resulting in higher thermal stability and significantly enhanced adsorption performance. The adsorption process and mechanism of SNMA on Cr(VI) were studied in detail. The SNMA achieved a high adsorption capacity (225.94 mg/g) and receptor site density. The SNMA is expected to be used as a bio-based spherical nanoparticle microcluster adsorbent platform for the adsorption of different toxic substances by changing the surface functional groups of its components, spherical nanoparticles.

Facile dispersion strategy to prepare polylactic acid/reed straw nanofiber composites with enhanced mechanical and thermal properties

The challenge of dispersing nanocellulose in hydrophobic polymers such as polylactic acid (PLA) still obstacles the further application of cellulose nanocomposites. An environment-friendly and facile wet-shearing pretreatment strategy without using any organic solvent was developed in this work. Silane modified lignocellulose nanofiber (SLCNF) was pre-dispersed into PLA by wet-shearing pretreatment, followed by extrusion process and the SLCNF could be dispersed extremely well in PLA matrices. SLCNF formed a crosslinked network and had an improved compatibility, which improved the mechanical and thermal properties of PLA composites. The tensile strength, elongation at break and thermal deformation temperature of the composites were increased by 12.6 %, 32.4 % and 9.1 °C, respectively. Moreover, SLCNF promoted the crystallization of PLA as a heterogeneous nucleating agent and the crystallinity was increased by about 40 %. This study provides an effective way to disperse nanocellulose in polymer matrix with high efficiency to enhance polymer-based composites.

Cosmetic-Derived Mannosylerythritol Lipid-B-Phospholipid Nanoliposome: An Acid-Stabilized Carrier for Efficient Gastromucosal Delivery of Amoxicillin for In Vivo Treatment of Helicobacter pylori

Helicobacter pylori infection is a leading cause of gastritis and peptic ulcer. Current treatments for H. pylori are limited by the increase in antibiotic-resistant strains and low drug delivery to the infection site, indicating the need for effective delivery systems of antibiotics. Although liposomes are the most successful drug delivery carriers that have already been applied commercially, their acidic stability still stands as a problem. Herein, we developed a novel nanoliposome using cosmetic raw materials of mannosylerythritol lipid-B (MEL-B), soy bean lecithin, and cholesterol, namely, LipoSC-MELB. LipoSC-MELB exhibited enhanced stability under the simulated gastric-acid condition, owing to its strong intermolecular hydrogen-bond interactions caused by the incorporation of MEL-B. Moreover, amoxicillin-loaded LipoSC-MELB (LipoSC-MELB/AMX) had a particle size of approximately 100 nm and exhibited sustained drug release under varying pH conditions (pH 3-7). Besides, LipoSC-MELB/AMX exhibited significantly higher anti-H. pylori and anti-H. pylori biofilm activity as compared with free AMX. Furthermore, LipoSC-MELB was able to carry AMX across the barriers of gastric mucus and H. pylori biofilms. Remarkably, in vivo assays indicated that LipoSC-MELB/AMX was effective in treating H. pylori infection and its associated gastritis and gastric ulcers. Overall, the findings of this study showed that LipoSC-MELB was effective for gastromucosal delivery of amoxicillin to improve its bioavailability for the treatment of H. pylori infection.

Tailoring the Barrier Properties of PLA: A State-of-the-Art Review for Food Packaging Applications

It is now well recognized that the production of petroleum-based packaging materials has created serious ecological problems for the environment due to their resistance to biodegradation. In this context, substantial research efforts have been made to promote the use of biodegradable films as sustainable alternatives to conventionally used packaging materials. Among several biopolymers, poly(lactide) (PLA) has found early application in the food industry thanks to its promising properties and is currently one of the most industrially produced bioplastics. However, more efforts are needed to enhance its performance and expand its applicability in this field, as packaging materials need to meet precise functional requirements such as suitable thermal, mechanical, and gas barrier properties. In particular, improving the mass transfer properties of materials to water vapor, oxygen, and/or carbon dioxide plays a very important role in maintaining food quality and safety, as the rate of typical food degradation reactions (i.e., oxidation, microbial development, and physical reactions) can be greatly reduced. Since most reviews dealing with the properties of PLA have mainly focused on strategies to improve its thermal and mechanical properties, this work aims to review relevant strategies to tailor the barrier properties of PLA-based materials, with the ultimate goal of providing a general guide for the design of PLA-based packaging materials with the desired mass transfer properties.

Cellulose nanosphere: Preparation and applications of the novel nanocellulose

Over the past few years, cellulose nanosphere (CNS) has gained growing attention and rapid development. As a new type of nanocellulose materials, CNS can be prepared from native cellulose by using methods which have been adopted extensively to prepare the well-known nanocelluloses, i.e., cellulose nanofiber and cellulose nanocrystal. The particular interest is that the regenerated cellulose and mercerized cellulose can also be used as important feedstocks to produce CNS. In this review, the preparation methods of CNS are described and discussed, via both top-down processes, including chemical, mechanical, and enzymolysis ones, and bottom-up processes by using various cellulose I and II starting materials. This review also highlights the researches relative to cellulose composite nanospheres, and summarizes the applications of spherical cellulose-based nanoparticles. Finally, the future challenges and opportunities of CNS are prospected in this work.

A comprehensive investigation on cellulose nanocrystals with different crystal structures from cotton via an efficient route

The crystal structures of cellulose nanomaterials play an important role in their morphologies and applications, however, there was still lacking systematic research on preparing various crystalline allomorphs of cellulose nanocrystals with high thermal stability. Herein, the efficient synthesis route was presented to design various crystalline allomorphs of cellulose from cotton. And then, cellulose nanocrystals with different crystal structures (CNC-I, CNC-II, CNC-III_II, CNC-IV_II) were prepared by hydrogen peroxide hydrolysis of resultant cellulose. Overall, needle-like CNC-I (length of 180 ± 25 nm, diameter of 12 ± 2 nm), near-spherical CNC-II (diameter of 101 ± 12 nm), and spherical CNC-III_II (diameter of 22 ± 3 nm) and CNC-IV_II (diameter of 21 ± 2 nm) all exhibited remarkable dispersibility and thermal stability (T_max > 357 °C). This work provides a simple and low-cost synthesis route for various crystalline allomorphs of CNCs with high thermal stability from the same raw materials (cotton).

Advanced nanocellulose-based gas barrier materials: Present status and prospects

Nanocellulose based gas barrier materials have become an increasingly important subject, since it is a widespread environmentally friendly natural polymer. Previous studies have shown that super-high gas barrier can be achieved with pure and hierarchical nanocellulose films fabricated through simple suspension or layer-by-layer technique either by itself or incorporating with other polymers or nanoparticles. Improved gas barrier properties were observed for nanocellulose-reinforced composites, where nanocellulose partially impermeable nanoparticles decreased gas permeability effectively. However, for nanocellulose-based materials, the higher gas barrier performance is jeopardized by water absorption and shape deformation under high humidity conditions which is a challenge for maintaining properties in material applications. Thus, numerous investigations have been done to solve the problem of water absorption in nanocellulose-based materials. In this literature review, gas barrier properties of pure, layer-by-layer and composite nanocellulose films are investigated. The possible theoretical gas barrier mechanisms are described, and the prospects for nanocellulose-based materials are discussed.

Impact of the Incorporation of Nano-Sized Cellulose Formate on the End Quality of Polylactic Acid Composite Film

Polylactic acid (PLA) films with good sustainable and biodegradable properties have been increasingly explored recently, while the poor mechanical property of PLA limits its further application. Herein, three kinds of nano-sized cellulose formate (NCF: cellulose nanofibril (CNF), cellulose nanocrystal (CNC), and regenerated cellulose formate (CF)) with different properties were fabricated via a one-step formic acid (FA) hydrolysis of tobacco stalk, and the influence of the properties of NCF with different morphologies, crystallinity index (CrI), and degree of substitution (DS) on the end quality of PLA composite film was systematically compared. Results showed that the PLA/CNC film showed the highest increase (106%) of tensile strength compared to the CNF- and CF-based films, which was induced by the rod-like CNC with higher CrI. PLA/CF film showed the largest increase (50%) of elongation at the break and more even surface, which was due to the stronger interfacial interaction between PLA and the CF with higher DS. Moreover, the degradation property of PLA/CNF film was better than that of other composite films. This fundamental study was very beneficial for the development of high-quality, sustainable packaging as an alternative to petroleum-based products.

Healable, Adhesive, and Conductive Nanocomposite Hydrogels with Ultrastretchability for Flexible Sensors

In recent years, conductive hydrogels have generated tremendous attention in biomedicals and bioelectronics fields due to their excellent physiochemical properties. In this study, a physically cross-linked conducting hydrogel has been designed in combination with cellulose nanocrystalline (CNC), polyacrylic acid (PAA) chains, laurel methacrylate, and sodium dodecyl sulfate. The obtained result shows that the hydrogel prepared is ultrastretchable, mechanically robust, transparent, biocompatible, conductive, and self-healing. The mechanical property of the prepared hydrogel is optimized through variation of the CNC content. The optimal hydrogel (CNC-1/PAA) exhibits an impressive mechanics, including high stretchability (∼1800%) and compressibility, good elasticity, and fatigue resistance. Furthermore, the conductivity of the hydrogel enables tensile strain- and pressure-sensing capabilities. The CNC/PAA-based flexible sensors are successfully designed, which shows high sensitivity, fast response (290 ms), and excellent cycle stability as well as the pressure sensing capability. As a result, the designed hydrogel has the ability to sense and detect diverse human motion, including elbow/finger/wrist bending and speaking, which demonstrates that the designed self-healing conductive hydrogels have significant potential for applications in flexible electronics.

Preparation of effective ultraviolet shielding poly (lactic acid)/poly (butylene adipate-co-terephthalate) degradable composite film using co-precipitation and hot-pressing method

Biodegradable poly (lactide) (PLA) and poly (butylene adipate-co-terephthalate) (PBAT) composite films were made by a co-precipitation and hot-pressing method. The property of composite films like the chemical interaction, phase morphology, mechanical properties, and thermal properties were studied. The Fourier transform infrared spectroscopy (FTIR) test manifested that there was a small amount of the transesterifications between the PBAT and PLA during hot pressing, which could improve the compatibility of the two phases. The tensile strength of the film only reduced by 7.4%, while the elongation at break was increased by 119.1% compared with PLA after adding 4%wt PBAT. The composite films showed a high Ultraviolet-visible (UV) light barrier property. The UV blocking rate of the composite after adding 4%wt PBAT was 6.95 times higher than that of pure PLA at 380 nm. The PLA/PBAT composite films with excellent thermal stability, satisfactory mechanical properties and UV-light barrier have high a possibility for an UV screening packaging application.

Comparative Study on Water Vapour Resistance of Poly(lactic acid) Films Prepared by Blending, Filling and Surface Deposit

The polylactic acid (PLA) resin Ingeo 4032D was selected as the research object, with a focus on PLA modification by using polymers such as linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE) and ethylene-propylene-diene monomer grafted with glycidyl methacrylate (EPDM-g-GMA), by using fillers such as nano calcium carbonate and zeolite. In order to characterize the deposition effect of Al2O3 on the film surface by plasma-assisted atomic layer deposition, Bio-oriented PLA (BOPLA) with more uniform thickness than blown film was purchased for study. The mechanical properties, friction coefficient, surface contact angle and water vapour transmission rate of the modified PLA film were compared and discussed. The aim was to find out the most influencing factors of film's water vapour resistance.

Spherical Cellulose Micro and Nanoparticles: A Review of Recent Developments and Applications

Cellulose, the most abundant natural polymer, is a versatile polysaccharide that is being exploited to manufacture innovative blends, composites, and hybrid materials in the form of membranes, films, coatings, hydrogels, and foams, as well as particles at the micro and nano scales. The application fields of cellulose micro and nanoparticles run the gamut from medicine, biology, and environment to electronics and energy. In fact, the number of studies dealing with sphere-shaped micro and nanoparticles based exclusively on cellulose (or its derivatives) or cellulose in combination with other molecules and macromolecules has been steadily increasing in the last five years. Hence, there is a clear need for an up-to-date narrative that gathers the latest advances on this research topic. So, the aim of this review is to portray some of the most recent and relevant developments on the use of cellulose to produce spherical micro- and nano-sized particles. An attempt was made to illustrate the present state of affairs in terms of the go-to strategies (e.g., emulsification processes, nanoprecipitation, microfluidics, and other assembly approaches) for the generation of sphere-shaped particles of cellulose and derivatives thereof. A concise description of the application fields of these cellulose-based spherical micro and nanoparticles is also presented.

Supercritical Carbon Dioxide Isolation of Cellulose Nanofibre and Enhancement Properties in Biopolymer Composites

The physical properties, such as the fibre dimension and crystallinity, of cellulose nanofibre (CNF) are significant to its functional reinforcement ability in composites. This study used supercritical carbon dioxide as a fibre bundle defibrillation pretreatment for the isolation of CNF from bamboo, in order to enhance its physical properties. The isolated CNF was characterised through zeta potential, TEM, XRD, and FT-IR analysis. Commercial CNF was used as a reference to evaluate the effectiveness of the method. The physical, mechanical, thermal, and wettability properties of the bamboo and commercial CNF-reinforced PLA/chitin were also analysed. The TEM and FT-IR results showed the successful isolation of CNF from bamboo using this method, with good colloidal stability shown by the zeta potential results. The properties of the isolated bamboo CNF were similar to the commercial type. However, the fibre diameter distribution and the crystallinity index significantly differed between the bamboo and the commercial CNF. The bamboo CNF had a smaller fibre size and a higher crystallinity index than the commercial CNF. The results from the CNF-reinforced biocomposite showed that the physical, mechanical, thermal, and wettability properties were significantly different due to the variations in their fibre sizes and crystallinity indices. The properties of bamboo CNF biocomposites were significantly better than those of commercial CNF biocomposites. This indicates that the physical properties (fibre size and crystallinity) of an isolated CNF significantly affect its reinforcement ability in biocomposites. The physical properties of isolated CNFs are partly dependent on their source and production method, among other factors. These composites can be used for various industrial applications, including packaging.

Comprehensive Review of Polysaccharide-Based Materials in Edible Packaging: A Sustainable Approach

Edible packaging is a sustainable product and technology that uses one kind of "food" (an edible material) to package another kind of food (a packaged product), and organically integrates food with packaging through ingenious material design. Polysaccharides are a reliable source of edible packaging materials with excellent renewable, biodegradable, and biocompatible properties, as well as antioxidant and antimicrobial activities. Using polysaccharide-based materials effectively reduces the dependence on petroleum resources, decreases the carbon footprint of the "product-packaging" system, and provides a "zero-emission" scheme. To date, they have been commercialized and developed rapidly in the food (e.g., fruits and vegetables, meat, nuts, confectioneries, and delicatessens, etc.) packaging industry. However, compared with petroleum-based polymers and plastics, polysaccharides still have limitations in film-forming, mechanical, barrier, and protective properties. Therefore, they need to be improved by reasonable material modifications (chemical or physical modification). This article comprehensively reviews recent research advances, hot issues, and trends of polysaccharide-based materials in edible packaging. Emphasis is given to fundamental compositions and properties, functional modifications, food-packaging applications, and safety risk assessment of polysaccharides (including cellulose, hemicellulose, starch, chitosan, and polysaccharide gums). Therefore, to provide a reference for the development of modern edible packaging.