Supramolecular Polymer Nanocomposites Derived from Plant Oils and Cellulose Nanocrystals

Multiple hydrogen bonding driven supramolecular architectures and their biomedical applications

Supramolecular chemistry combines the strength of molecular assembly via various molecular interactions. Hydrogen bonding facilitated self-assembly with the advantages of directionality, specificity, reversibility, and strength is a promising approach for constructing advanced supramolecules. There are still some challenges in hydrogen bonding based supramolecular polymers, such as complexity originating from tautomerism of the molecular building modules, the assembly process, and structure versatility of building blocks. In this review, examples are selected to give insights into multiple hydrogen bonding driven emerging supramolecular architectures. We focus on chiral supramolecular assemblies, multiple hydrogen bonding modules as stimuli responsive sources, interpenetrating polymer networks, multiple hydrogen bonding assisted organic frameworks, supramolecular adhesives, energy dissipators, and quantitative analysis of nano-adhesion. The applications in biomedical materials are focused with detailed examples including drug design evolution for myotonic dystrophy, molecular assembly for advanced drug delivery, an indicator displacement strategy for DNA detection, tissue engineering, and self-assembly complexes as gene delivery vectors for gene transfection. In addition, insights into the current challenges and future perspectives of this field to propel the development of multiple hydrogen bonding facilitated supramolecular materials are proposed.

Tailoring an Effective Interface between Nanocellulose and the Epoxidized Linseed Oil Network through Functionalization

Sustainable nanocomposite materials based on different functionalized nanocellulose (NC) structures embedded in epoxidized linseed oil (ELO) were developed as foundation toward a greener approach for anticorrosive coating evolution. The work leans on functionalization with (3-aminopropyl) triethoxysilane (APTS), (3-glycidyloxypropyl)trimethoxysilane (GPTS), and vanillin (V) of NC structures isolated from plum seed shells, evaluated as potential reinforcing agents for the increase of thermomechanical properties and water resistance of epoxy nanocomposites from renewable resources. The successful surface modification was confirmed from the deconvolution of X-ray photoelectron spectra for C 1s and correlated with Fourier transform infrared (FTIR) data. The secondary peaks assigned to C-O-Si at 285.9 eV and C-N at 286 eV were observed with the decrease of the C/O atomic ratio. Compatibility and efficient interface formation between the functionalized NC and the biobased epoxy network from linseed oil were translated as decreased values for the surface energy of bio-nanocomposites and better dispersion imaged through scanning electron microscopy (SEM). Thus, the storage modulus of the ELO network reinforced with only 1% APTS-functionalized NC structures reached 5 GPa, an almost 20% increase compared with that of the neat matrix. Mechanical tests were applied to assess an increase of 116% in compressive strength for the addition of 5 wt % NCA to the bioepoxy matrix.

Fully biobased sustainable elastomers derived from chitin, lignin, and plant oil via grafting strategy and Schiff-base chemistry

With the dramatically increased environmental problems, the rational design of sustainable polymers from renewable feedstocks opens new avenues to reduce the huge pollution impact. The major challenge for sustainable polymers is the decreased mechanical performance compared to that of petroleum-based materials. In this work, fully biobased sustainable elastomers were developed by integrating renewable chitin, lignin, and plant oil into one macromolecule, in which chitin was chosen as the rigid backbone, while a lignin-derived monomer vanillin acrylate (VA) and a plant oil-based monomer lauryl acrylate (LA) were selected as the hard and soft segments for the grafted side chains. A series of Chitin-graft-poly(vanillin acrylate-co-lauryl acrylate) (Chitin-g-P(VA-co-LA)) copolymers with varied feed ratios and chitin contents were synthesized by using reversible addition-fragmentation chain transfer (RAFT) polymerization as an effective grafting strategy. In addition, a dynamic cross-linked network was incorporated via Schiff-base reaction to improve the macroscopic behavior of such kind of chitin graft elastomers. These sustainable elastomers are mechanically strong and show excellent reprocessablity, as well as outstanding UV-blocking property. This strategy is versatile and can inspire the further development of fully biobased sustainable materials from natural resources.

Bio-based monomers for amide-containing sustainable polymers

The field of sustainable polymers from renewable feedstocks is a fast-reviving field after the decades-long domination of petroleum-based polymers. Amide-containing polymers exhibit a wide range of properties depending on the type of amide (primary, secondary, and tertiary), amide density, and other molecular structural parameters (co-existing groups, molecular weight, and topology). Engineering amide groups into sustainable polymers via the "monomer approach" is an industrially proven strategy, while bio-based monomers are of enormous importance to bridge the gap between renewable sources and amide-containing sustainable polymers (AmSPs). This feature article aims at conceptualizing the monomer-design philosophy behind most of the reported AmSPs and is organized by discussing di-functional monomers for step-growth polymerization, cyclic monomers for ring-opening polymerization and amide-containing monomers for chain-growth polymerization. We also give a perspective on AmSPs with respect to monomer design and performance enhancement.

A rapid synthesis of nanofibrillar cellulose/polystyrene composite via ultrasonic treatment

A new method of the synthesis of nanofibrillar cellulose/polystyrene composite based on ultrasonic treatment of styrene emulsion in cellulose-water solution was elaborated. A new approach does not require additional heating and proposes a significantly faster synthesis (15 min, 45 °C) of the target composite compared to the methods described previously. A comprehensive analysis did not reveal any significant differences between mechanical, physical and biodegradable properties of the composite obtained by ultrasonic method and that one obtained by conventional thermal method, which requires much higher temperature (above 75 °C) and reaction duration (from 3 h).

Dispersibility Characterization of Cellulose Nanocrystals in Polymeric-Based Composites

Cellulose nanocrystals (CNCs) are hydrophilic nanoparticles extracted from biomass with properties and functions different from cellulose and are being developed for property-oriented applications such as high stiffness, abundant active groups, and biocompatibility. It has broad application prospects in the field of composite materials, while the dispersibility of the CNC in polymers is the key to its application performance. Many reviews have discussed in-depth the modification strategies to improve the dispersibility of the CNC and summarized all characterization for the CNC, but there are no reviews on the in-depth exploration of dispersion characterization. This review is a comprehensive summary of the characterization of CNC dispersion in the matrix in terms of direct observation, indirect evaluation, and quantified evaluation, summarizing how and why different characterization tools reveal dispersibility. In addition, "decision tree" flowcharts are presented to provide the reader with a reference for selecting the appropriate characterization method for a specific composite.

Recent Advances in Chemically Modified Cellulose and Its Derivatives for Food Packaging Applications: A Review

The application of cellulose in the food packaging field has gained increasing attention in recent years, driven by the desire for sustainable products. Cellulose can replace petroleum-based plastics because it can be converted to biodegradable and nontoxic polymers from sustainable natural resources. These products have increasingly been used as coatings, self-standing films, and paperboards in food packaging, owing to their promising mechanical and barrier properties. However, their utilization is limited because of the high hydrophilicity of cellulose. With the presence of a large quantity of functionalities within pristine cellulose and its derivatives, these building blocks provide a unique platform for chemical modification via covalent functionalization to introduce stable and permanent functionalities to cellulose. A primary aim of chemical attachment is to reduce the probability of component leaching in wet and softened conditions and to improve the aqueous, oil, water vapor, and oxygen barriers, thereby extending its specific use in the food packaging field. However, chemical modification may affect the desirable mechanical, thermal stabilities and biodegradability exhibited by pristine cellulose. This review exhaustively reports the research progress on cellulose chemical modification techniques and prospective applications of chemically modified cellulose for use in food packaging, including active packaging.

Rheological Percolation of Cellulose Nanocrystals in Biodegradable Poly(butylene succinate) Nanocomposites: A Novel Approach for Tailoring the Mechanical and Hydrolytic Properties

Although biodegradable plastics are gradually emerging as an effective solution to alleviate the burgeoning plastic pollution, their performance is currently trivial for commercialization. A proposed two-pronged strategy to overcome this limitation includes (1) preparation of the nanocomposites from biorenewable nano-fillers to preserve their biodegradability and (2) tailoring their properties to meet the diverse demands in various applications. Herein, we report the preparation of biodegradable nanocomposites composed of poly(butylene succinate) (PBS) and cellulose nanocrystals (CNCs) (loading of 0.2-3.0 wt%) and propose a rheological strategy to tailor their performances. Depending on the shear frequencies, the rheological evaluation revealed two percolation thresholds at approximately 0.8 and 1.5 wt%. At high shear frequencies, the disappearance of the first threshold (0.8 wt%) and the sole persistence of the second one (1.5 wt%) indicated the collapse of the immature network of partially interconnected CNCs. The tensile and hydrolytic properties of the nanocomposites were found to undergo drastic changes at the thresholds. The tensile strength increased by 17% (from 33.3 to 39.2 MPa) up to 0.8 wt% CNC loading. However, the reinforcing efficiency of CNC decreases sharply with further incorporation, reaching nearly zero at 1.5 wt%. On the other hand, hydrolytic degradation of the nanocomposites was rapidly accelerated above 1.5 wt% CNC loading. Therefore, a thorough understanding of the rheological properties of nanocomposites is essential for the design and development of materials with tailored properties.

Enhancing and toughening plant oil-based polymeric materials through synergetic supramolecular and covalent interactions by introducing nucleobase-functionalized celluloses

Renewable plant oil-based polymeric materials were enhanced and toughened through complementary H-bonding interactions by introducing nucleobase-functionalized celluloses.

Cellulose nanocrystal/plant oil polymer composites with hydrophobicity, humidity-sensitivity, and high wet strength

The preparation of high-performance cellulose nanocrystals (CNCs)/plant oil-derived polymer composites is still a challenge, due to their poor compatibility. Here, by designing amide groups and epoxy groups on sunflower oil derived polymers, appropriate interfacial hydrogen bond interactions between the polymers and CNCs were constructed, where CNCs were homogenously dispersed in polymer matrix. Tensile tests and DMA results revealed that the incorporation of CNCs into sunflower oil derived epoxy polymers significantly enhanced the tensile strength and storage modulus. More importantly, nanocomposites with 50 wt% CNCs are still hydrophobic, which not only show a fast and reversible humidity induced modulus switch, but also exhibit high wet strength (19.9 MPa) after equilibrium water adsorption. The present work revealed that proper designed CNCs/plant oil polymer nanocomposites are good candidates for high performance and functional materials, which are able to replace petroleum-based materials in various fields.

Structural insight into the viscoelastic behaviour of elastomeric polyesters: effect of the nature of fatty acid side chains and the degree of unsaturation

Increase in unsaturation of fatty acid side chains results in decrease of zero-shear viscosity, degree of entanglement and resilience of polyesters. Cis double bonds act as kinks that prevent molecular packing of polymer chains.

Temperature and CO2 Dual-Responsive Pickering Emulsions Using Jeffamine M2005-Modified Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) with excellent biodegradability are promising biomaterials for use as responsive Pickering emulsifiers. However, the high hydrophilicity of CNCs limits their emulsification ability. Some existing studies have utilized complicated covalent modification procedures to increase the hydrophobicity of CNCs. To simplify the modification process, we prepared hydrophobically modified CNCs (CNCs-M2005) via simple and controllable electrostatic interactions with thermosensitive M2005. The obtained CNCs-M2005 exhibited temperature and CO₂ dual-responsive properties. Subsequently, stable oil/water Pickering emulsions were prepared using the partially hydrophobic CNCs-M2005 at 20 °C. However, demulsification occurred when the temperature increased to 60 °C. This temperature-induced demulsification resulted from the dehydration of polyethylene oxide and polypropylene oxide, causing the aggregation of the CNCs-M2005, as shown by dynamic light scattering and transmission electron microscopy experiments. In addition, demulsification was also achieved after bubbling CO₂, which was attributed to the dissociation of the partially hydrophobic CNCs-M2005. The temperature and CO₂ dual-responsive biosafe Pickering emulsions open up opportunity for the design of intelligent food, cosmetic, and drug delivery systems.

Core-Shell Nanohybrid Elastomer Based on Co-Deposition Strategy to Improve Performance of Soy Protein Adhesive

Exploitation of a versatile strategy for fabricating a plant protein adhesive with outstanding adhesion and water resistance is a growing concern in the ecofriendly wood industry. Herein, a core-shell nanohybrid elastomer composed of the cellulose nanocrystal (CNC) core and elastic polyurethane shell is prepared via a co-deposition strategy and then used as an efficient reinforcer to improve the performances of soy protein (SP) adhesive. It is found that the core-shell nanohybrid acts as a multiple cross-linker, giving rise to the construction of a stable protein adhesive system. Moreover, owing to the nanohybrid design combining "strong yet tough" qualities, the hard CNC serves to repair the discontinuous protein adhesion layer for a rigid and integrated system, while the elastic polyurethane contributes to energy dissipation, thus endowing the protein adhesive with excellent overall cohesive strength. Given such synergistic effects, the modified SP-based adhesive exhibits a significant improvement in both adhesion and water resistance, particularly achieving a 311.8% increase in wet adhesion strength compared to that of the pristine SP adhesive. This work may provide an effective guide for the preparation and practical application of high-performance plant-protein-based adhesive.

Ultra-strong long-chain polyamide elastomers with programmable supramolecular interactions and oriented crystalline microstructures

Polyamides are one of the most important polymers. Long-chain aliphatic polyamides could bridge the gap between traditional polyamides and polyethylenes. Here we report an approach to preparing sustainable ultra-strong elastomers from biomass-derived long-chain polyamides by thiol-ene addition copolymerization with diamide diene monomers. The pendant polar hydroxyl and non-polar butyrate groups between amides allow controlled programming of supramolecular hydrogen bonding and facile tuning of crystallization of polymer chains. The presence of thioether groups on the main chain can further induce metal-ligand coordination (cuprous-thioether). Unidirectional step-cycle tensile deformation has been applied to these polyamides and significantly enhances tensile strength to over 210 MPa while maintaining elasticity. Uniaxial deformation leads to a rearrangement and alignment of crystalline microstructures, which is responsible for the mechanical enhancement. These chromophore-free polyamides are observed with strong luminescence ascribed to the effect of aggregation-induced emission (AIE), originating from the formation of amide clusters with restricted molecular motions.

Gels without Vapor Pressure: Soft, Nonaqueous, and Solvent-Free Supramolecular Biomaterials for Prospective Parenteral Drug Delivery Applications

The engineering advantages of soft, nonaqueous, solvent-free supramolecular materials have resulted in their emerging transition and adoption from a predominantly food, cosmetics, and paint industry-driven technology to biocompatible matrices for parenteral drug delivery. Factors that have contributed to this trend are the drastic increase of hydrophobic and combination drugs in the pharmaceutical pipeline and the limitations of hydrated drug delivery materials with regard to poorly soluble drugs and biologics. This review highlights examples of nonaqueous, soft supramolecular materials, illustrates molecular engineering principles that may give rise to novel structures and unique properties, and explores emerging opportunities of application of these materials in parenteral drug delivery.

A facile approach to thermomechanically enhanced fatty acid-containing bioplastics using metal–ligand coordination

Dynamic metal–ligand coordination creates physical crosslinking and thus improves chain entanglements for enhancing the thermomechanical properties of biobased polymers.

Recent Advances in Nanocellulose Composites with Polymers: A Guide for Choosing Partners and How to Incorporate Them

In recent years, the research on nanocellulose composites with polymers has made significant contributions to the development of functional and sustainable materials. This review outlines the chemistry of the interaction between the nanocellulose and the polymer matrix, along with the extent of the reinforcement in their nanocomposites. In order to fabricate well-defined nanocomposites, the type of nanomaterial and the selection of the polymer matrix are always crucial from the viewpoint of polymer⁻filler compatibility for the desired reinforcement and specific application. In this review, recent articles on polymer/nanocellulose composites were taken into account to provide a clear understanding on how to use the surface functionalities of nanocellulose and to choose the polymer matrix in order to produce the nanocomposite. Here, we considered cellulose nanocrystal (CNC) and cellulose nanofiber (CNF) as the nanocellulosic materials. A brief discussion on their synthesis and properties was also incorporated. This review, overall, is a guide to help in designing polymer/nanocellulose composites through the utilization of nanocellulose properties and the selection of functional polymers, paving the way to specific polymer⁻filler interaction.

High strength gelatin-based nanocomposites reinforced by surface-deacetylated chitin nanofiber networks

In this study, chitin nanofiber (ChNF) was deacetylated on the crystalline surface by NaOH treatment, leading to the fibrillation of mostly individualized nanofibers with high aspect ratio. The small diameter and high strength of chitin nanofibers make them promising reinforcing fillers for composites. Herein by introducing into the gelatin, surface-deacetylated chitin nanofiber (S-ChNF)/gelatin nanocomposites were fabricated in different component ratios using immersion method followed with drying. Due to the reinforcing effect attributed to S-ChNF, mechanical properties of the S-ChNF/gelatin were significantly improved in both stress and Young's modulus while still maintaining high transparency regardless of nanofiber content. Morphology and Fourier-transform infrared characterization revealed that S-ChNF preserved nanonetwork structures in the gelatin matrix and exhibited good compatibility through hydrogen bonding, which further confirmed the improvement in mechanical properties. Therefore, these S-ChNF/gelatin nanocomposites based on biocompatible and biodegradable raw materials have potential applications in biomedical and food packaging industries.