Nano-enabled smart and functional materials toward human well-being and sustainable developments.

Fabrication and operation on increasingly smaller dimensions have been highly integrated with the development of smart and functional materials, which are key to many technological innovations to meet economic and societal needs. Along with researchers worldwide, the Waterloo Institute for Nanotechnology (WIN) has long realized the synergetic interplays between nanotechnology and functional materials and designated 'Smart & Functional Materials' as one of its four major research themes. Thus far, WIN researchers have utilized the properties of smart polymers, nanoparticles, and nanocomposites to develop active materials, membranes, films, adhesives, coatings, and devices with novel and improved properties and capabilities. In this review article, we aim to highlight some of the recent developments on the subject, including our own research and key research literature, in the context of the UN Sustainability development goals.

Sulfur Free Crosslinking of EPDM Composites via Silane Grafting and Silica Incorporation.

This study aims at evaluating and developing an environmental-friendly and sulfur-free cured ethylene propylene diene monomer (EPDM) composites. Silane grafted EPDM (SiEPDM) composites incorporated with silica is prepared via a solvent-free, one-step reactive mixing process. The silane grafting and silica filler bonding are characterized using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The mechanical properties of the developed composites are examined. The fracture morphology is observed using an environmental scanning electron microscopy. The rheology and thermomechanical properties are evaluated by using a rotational rheometer and dynamic mechanical analyzer. Notably, a robust bonding between silica and the grafted silane is established, yielding a crosslinking network within the composite structure. This phenomenon is substantiated by the observed gel efficiency and rheology behavior. Consequently, a pronounced augmentation of up to 75% in tensile strength and 29% in tear strength are observed in the optimized SiEPDM-silica composites, distinguishing them from their EPDM-silica counterparts. The introduction of paraffin oil contributes to enhanced processability; however, it is concomitant with a reduction in gel efficiency and associated mechanical properties. Furthermore, subsequent UV weathering test unveils that the SiEPDM-silica composites exhibit the highest levels of residual tensile strength and modulus, indicative of their exceptional UV stability.

Fabrication of Triblock Elastomer Foams and Gelation Studies for Oil Spill Remediation.

Polymeric foamed materials are among the most widely utilized technologies for oil spill accidents and releases of oil-contaminated wastewater oil due to their porosity to absorb and separate oil/water effectively. However, a major limitation of traditional polymeric foams is their reliance on an ad/absorption mechanism as the sole method of oil capture, leading to potential oil leakage once their saturation point is exceeded. Tri-block polymer styrene-ethylene-butylene-styrene (SEBS) is a fascinating absorbent material that can bypass this limitation by both capturing oil and providing a sealing mechanism via gelation to prevent oil leakage due to its unique chemical structure. SEBS foams are produced via simultaneous crosslinking and foaming that results in an impressive expansion ratio of up to 15.2 with over 93% porosity. Most importantly, the SEBS foams show great potential as oil absorbents in spill remediation, demonstrating rapid and efficient oil absorption coupled with superhydrophobic properties. Moreover, the unique interaction between the oil and SEBS enables the formation of a physical gel, acting as an effective barrier against oil leakage. These findings indicate the potential for commercializing SEBS foam as a viable option for geotextiles to mitigate oil spill concerns from infrastructures.

Production of polyhydroxyalkanoate (PHA) copolymer from food waste using mixed culture for carboxylate production and Pseudomonas putida for PHA synthesis.

Production of polyhydroxyalkanoates (PHAs) with high concentration of carboxylate, that was accumulated from solid state fermentation (SSF) of food waste (FW), was tested using Pseudomonas putida strain KT2440. Mixed-culture SSF of FW supplied in a high concentration of carboxylate, which caused a high PHA production of 0.56 g PHA/g CDM under nutrients control. Interestingly, this high PHA fraction in CDM was almost constant at 0.55 g PHA/g CDM even under high nutrients concentration (25 mM NH4+), probably due to high reducing power maintained by high carboxylate concentration. PHA characterization indicated that the dominant PHA building block produced was 3-hydroxybutyrate, followed by 3-hydroxy-2-methylvalerate and 3-hydroxyhenxanoate. Carboxylate profiles before and after PHA production suggested that acetate, butyrate, and propionate were the main precursors to PHA via several metabolic pathways. Our result support that mixed culture SSF of FW for high concentration carboxylate and P. putida for PHA production enables sustainable production of PHA in cost-effective manners.

Oleic acid decorated kraft lignin as a hydrophobic and functional filler of cellulose acetate films.

The packaging industry has primarily been dominated by single-use, petrochemical-sourced plastic materials despite their short-term use. Their leakage into the ecosystem after their use poses substantial environmental concerns. As a result, compostable and renewable packaging material alternatives are garnering significant attention. Cellulose acetate is a derivative of cellulose that exhibits excellent tensile properties, transparency, melt processability, and intermediate compostability. However, its application in the food packaging industry is limited due to its hygroscopic behavior and lack of dimensional stability. This study investigated using lignin (pristine and esterified) as a functional additive of cellulose acetate. The effect of varying concentrations of pristine kraft and oleic acid functionalized lignin in the cellulose acetate matrix and its effect on the resulting film's mechanical, morphological, viscoelastic, and water barrier properties were explored. Comprehensive characterization of the thermomechanical processed lignin-cellulose acetate sheets revealed reduced moisture absorption, improved UV and moisture barrier, and enhanced tensile properties with melt processability. Overall, the studied films could have appealing properties for food and other packaging applications, thus, serving as eco-friendly and sustainable alternatives to conventional petroleum-derived packing materials.

Chemically tailored graphite oxide nanoparticles for improving material properties of canola protein-based films.

Canola protein obtained from canola meal, a byproduct of the canola industry, is an economical biopolymer with promising film-forming properties. It has significant potential for use as a food packaging material, though it possesses some functional limitations that need improvement. Incorporating nanomaterials is an option to enhance functional properties. This study aims to produce canola protein films by integrating GO exfoliated at several oxidation times and weight ratios to optimize mechanical, thermal, and barrier properties. Oxidation alters the C/O ratio and adds functional groups that bond with the amino/carboxyl groups of protein, enhancing the film properties. Significant improvement was obtained in GO at 60 and 120 min oxidation time and 3% addition level. Tensile strength and elastic modulus increased 200% and 481.72%, respectively, compared to control. Control films showed a 37.57 × 10-3 cm3m/m2/day/Pa oxygen permeability, and it was significantly reduced to 5.65 × 10-3 cm3m/m2/day/Pa representing a 665% reduction.

Rubber-lignin-ammonium polyphosphate bio-composite foams: Fabrication, thermomechanical properties and flame retardancy.

Bio-composite foams based on Epoxidized Natural Rubber (ENR) filled with lignin (LG) and ammonium polyphosphate (APP) were fabricated via batch foaming. The addition of APP accelerated the foaming process at lower temperatures. Pre-mixing induced ionic and hydrogen bonding between the LG and the APP particles, which reduced crosslinking between LG and ENR. The resulting ENR bio-composite foams with LG/APP exhibited a significant increase in compressive strength (up to 700 %) and modulus (up to 600 %) compared to the ENR foam baseline. Furthermore, the LG/APP foams demonstrated lower thermal conductivity than both the ENR foam baseline and foams containing only LG or APP, attributed to optimal thermal conduction in the solid phase and convection within the pore cells. The combination of APP and LG produced synergistic effects, with phosphorus (from APP) and high carbon content (from LG) enhancing flame-retardant efficiency. This study highlights the potential of these sustainable bio-composite foams for applications requiring enhanced thermal insulation and flame retardancy attributes for insulation and other practical applications.

Hybrid Zwitterionic Hydrogels with Encoded Differential Swelling and Programmed Deformation for Small-Scale Robotics.

Stimuli-responsive shape-morphing hydrogels with self-healing and tunable physiochemical properties are excellent candidates for functional building blocks of untethered small-scale soft robots. With mechanical properties similar to soft organs and tissues, such robots enable minimally invasive medical procedures, such as cargo/cell transportation. In this work, responsive hydrogels based on zwitterionic/acrylate chemistry with self-healing and stimuli-responsiveness are synthesized. Such hydrogels are then judiciously cut and pasted to form hybrid constructs with predetermined swelling and elastic anisotropy. This method is used to program hydrogel constructs with predetermined 2D-to-3D deformation upon exposure to different environmental ionic strengths. Untethered soft robotic functionalities are demonstrated, such as actuation, magnetic locomotion, and targeted transport of soft and light cargo in flooded media. The proposed hydrogel expands the repertoire of functional materials for fabricating small-scale soft robots.

Esterification of lignin with long chain fatty acids for the stabilization of oil-in-water Pickering emulsions.

Pickering emulsions offer numerous advantages over conventional surfactant-stabilized emulsion systems, including lower loading levels and enhanced long-term stability. Through both organic and inorganic Pickering emulsifying particles exist, more efforts are being invested in devising renewable, biodegradable, and non-toxic alternatives to conventional Pickering emulsifiers. In this study, the use of lignin (unmodified and esterified) specimens as an effective alternative to conventional Pickering emulsifiers was investigated. Hexanoyl chloride, decanoyl chloride, and palmitoyl chloride esterified lignin specimens were produced and their employability as Pickering emulsifiers was studied. The effects of varying the concentrations of lignin (unmodified and esterified specimens) and pH of the dispersion medium on the stability of the produced Pickering emulsions were explored. Comprehensive characterization of the esterified lignin stabilized Pickering emulsions exhibited enhanced stability, and smaller average oil droplet size, resulting in stable Pickering emulsions with high zeta potential and better flow properties. Overall, the studied esterified lignin specimens can have appealing applications in various Pickering emulsion systems, as a nontoxic and sustainable alternative to conventional emulsifiers.

Cationic modification of cellulose as a sustainable and recyclable adsorbent for anionic dyes.

There is a dire need to find an efficient, cost-effective, sustainable, and environment-friendly adsorbent for the removal of anionic pollutants such as dyes from waste effluent. In this work, a cellulose-based cationic adsorbent was designed and utilized for methyl orange and reactive black 5 anionic dyes adsorption from an aqueous medium. Solid-state nuclear magnetic resonance spectroscopy (NMR) revealed the successful modification of cellulose fibers, and dynamic light scattering (DLS) evaluations showed the levels of charge densities. Furthermore, various models for adsorption equilibrium isotherm were utilized to understand the adsorbent characteristics, with the Freundlich isotherm model providing an excellent fit for the experimental results. The modelled maximum adsorption capacity was as much as 1010 mg/g for both model dyes. The dye adsorption was also confirmed using EDX. It was noted that the dyes were chemically adsorbed through the ionic interaction that can be reversed using sodium chloride solution. Overall, the cationized cellulose is inexpensive, environment-friendly, nature-driven, and recyclable making it an appealing adsorbent feasible for the dye removal from textile wastewater effluent.

Programmable nanocomposites of cellulose nanocrystals and zwitterionic hydrogels for soft robotics.

Stimuli-responsive hydrogels have garnered significant attention as a versatile class of soft actuators. Introducing anisotropic properties, and shape-change programmability to responsive hydrogels promises a host of opportunities in the development of soft robots. Herein we report the synthesis of pH-responsive hydrogel nanocomposites with predetermined microstructural anisotropy, shape-transformation, and self-healing. Our hydrogel nanocomposites are largely composed of zwitterionic monomers and asymmetric cellulose nanocrystals. While the zwitterionic nature of the network imparts both self-healing and cytocompatibility to our hydrogel nanocomposites, the shear-induced alignment of cellulose nanocrystals renders their anisotropic swelling and mechanical properties. Thanks to the self-healing properties, we utilized a cut-and-paste approach to program reversible, and complex deformation into our hydrogels. As a proof-of-concept, we demonstrated the transport of light cargo using tethered and untethered soft robots made from our hydrogels. We believe the proposed material system introduce a powerful toolbox for the development of future generations of biomedical soft robots.

Cellulose nanocrystals enabled sustainable polycaprolactone based shape memory polyurethane bionanocomposites.

In recent years, shape memory polyurethanes have gained substantial attention and are targeted for a range of smart and functional materials. In this work, the development of nanocrystalline celluloses (CNCs) enabled polycaprolactone-based shape memory polyurethane biocomposite using an in situ one-pot reactions is reported. The incorporation of up to 10 wt% CNCs resulted in a remarkable enhancement in the tensile strength at yield (from 0.2 MPa to 7.2 MPa), tensile strength at break (167% improvement), and modulus of elasticity (from 3.5 to 139.3 MPa) while maintaining the elongation at break. This was attributed to the simultaneous action of CNCs as a nucleating agent for crystallization and highly compatibilized reinforcing agent of the network. Moreover, the in situ incorporation of CNCs enhanced the shape memory capability of polyurethanes, which enables its employment in functional material applications, such as the biomedical sector. The intimate interfacial adhesion between the CNCs and the polymer matrix, which promoted shape fixating and recovery, was confirmed by fractured surface morphology studies. Rheology characterizations provided strong evidence that the addition of CNCs increased the shape fixity attributed to the stiffness of CNCs below the glass transition temperature (Tg) compared to the neat PU in conjuncture with the higher Tg of CNCs. Overall, the developed polymer nanocomposites are appealing materials for biomedical applications.

Sustainable paper coating with enhanced barrier properties based on esterified lignin and PBAT blend.

Sustainable and biodegradable packaging materials are appealing alternatives to the petrochemical-derived and non-biodegradable plastics that currently dominate the market. However, their inferior barrier properties and high cost inhibit their widespread applications. In this work, pristine and esterified lignin were investigated as a functional filler of poly (butylene adipate-co-terephthalate) (PBAT) based bioplastic paper coating formulations. For this, the pristine and esterified lignin (10-50 wt%) were separately dispersed in a solvent and incorporated in PBAT solutions and applied on paper substrates. The effects of varying concentrations of pristine and esterified lignin on the rheology, mechanical, morphology, and barrier properties of the coated paper substrate were investigated. Comprehensive characterization of esterified lignin/PBAT coatings exhibited enhanced dispersion of the lignin fraction in the PBAT, resulting in excellent wet tensile properties and enhanced water, oil, and oxygen barrier performance. Overall, the studied coating formulations have appealing properties for food contact materials, such as paper wraps and paperboard applications, as a sustainable and eco-friendly alternative to the incumbent coating materials, such as petroleum sourced waxes and polyolefin-based coatings.

Green mechano-chemical processing of lignocellulosic biomass for lignin recovery.

Lignin extraction from biomass is heavily dependent on chemical processes that are harmful to the environment and the quality of the recovered lignin. Ionic liquid solvents are some of the latest solutions in green processing; however, their implementation for lignin recovery is limited by their high cost, typically high loadings requirements, and long processing times. To overcome these issues, in this study, high loadings of mixed hardwood flour (MHF) were processed with 1-butyl-3-methylimidazolium chloride (BmimCl) in a batch mixer. The rheological behaviour of the biomass and ionic liquid mixture was studied. The mixture had a high complex viscosity (approx. 107 Pa s) at low shear rates and displayed pronounced shear thinning behavior at 50 wt% MHF loading. A 22 factorial design was also implemented to study the effects of MHF solid loading amount and residence time on lignin extraction yield. A maximum yield of 36.6% was obtained at the maximum solid loading amount and residence time (50 wt% and 45 min, respectively). The extracted lignin samples were also characterized in comparison with commercial Kraft lignin and lignosulfonate. The novelty of this study is the successful lignin extraction at high solid loadings and shorter residence times compared to previous biomass pre-treatments with ionic liquids that employs low solid loading and long processing times.

Biobased and compostable trilayer thermoplastic films based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and thermoplastic starch (TPS).

Food preservation is crucial in safeguarding the global food supply and security. Current regulations do not encourage the use of chemical food preservatives. Therefore, creating a physical barrier in the form of packaging remains a necessary measure to prevent food contact with biological and physical contaminants. This work presents a novel biodegradable thin trilayer assembly of two sandwiching layers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and a core layer composed of thermoplastic starch (TPS), maleated TPS, or their blends with PHBV (80/20). Scanning electron microscope (SEM), and optical microscopy images showed the samples' consistent film formation. The tensile test revealed that the sample with a core layer of a blend of maleated TPS and PHBV was the strongest, with a modulus of 178 MPa. The water vapor transmission rates were as low as 20.2 g/(m2·d). The oxygen permeation rate was below the detection limit of the test. Most importantly, the samples pass the biodegradation (28 °C) disintegration test in less than six weeks. The study confirmed that a trilayer structure with two outer layers of PHBV, and a middle layer of TPS-PHBV blend provides excellent barrier properties in conjuncture with its biodegradability making it an appealing, sustainable food packaging material option.

Thermo-mechano-chemical deconstruction of cellulose for cellulose nanocrystal production by reactive processing.

The commercial production of cellulose nanocrystals (CNCs) requires high concentration of sulfuric or other acids such as hydrochloric, phosphoric, and nitric acids. However, these acids and the involved process are corrosive, toxic, energy-intensive, and not environmentally safe. In this work, a batch mixer reactive process that entails high shear was implemented using 1-butyl-3-methylimidazolium chloride (BmimCl) media and molten oxalic acid dihydrate (OA) to produce CNCs from cellulose. Through this, a maximum CNC yield (59 wt%) was obtained with a mixture composition of 1:0.7:0.075 (Cellulose:BmimCl:OA, w/w/w) and a processing time of 2.5 min. Further investigation revealed that the particle size, degree of crystallinity, and thermal stability of the produced CNCs were found to be competitive with those of a commercial CNC product. This study asserts the potential industrial application of an efficient ionic liquid and molten organic acid treatment for CNC production via reactive processing in a batch mixer.

Sustainable barrier paper coating based on alpha-1,3 glucan and natural rubber latex.

There is an increasing interest in utilizing more sustainable and inherently biodegradable materials alternatives ideally derived from renewable resources for modern material applications, especially in the area of packaging materials. This work employed the polysaccharide alpha-1,3-glucan derived from an enzymatic polymerization process as a functional additive for natural rubber (NR) latex-based coating films. Coating formulations containing NR and 9-50 wt% alpha-1,3 glucan were prepared and then applied to paper substrates at different thicknesses. The effect of coating formulations on the barrier properties (e.g., oxygen, oil, water vapor barrier), the viscosity, and dry and wet tensile properties were investigated. The NR/glucan coatings exhibited outstanding tensile properties and balanced oxygen and oil barrier performance. However, higher glucan loading could be detrimental to moisture barrier. Overall, this study indicated that the NR/glucan coating films are comparable in performance to commercial coating formulations while providing a renewable, potential to be recycled with paper, and biodegradable alternative.

Fabrication and characterization of bilayer scaffolds - nanocellulosic cryogels - for skin tissue engineering by co-culturing of fibroblasts and keratinocytes.

This study focuses on developing a microarchitectural bilayer structure for stimulating the two top layers of skin tissue (epidermis and dermis) fabricated using a one-step freeze-drying method. Cellulose nanofibers (CNFs) and poly (vinyl) alcohol (PVA) were used as a biocompatible scaffolding material, and the composition was designed in such a way that it provides physical and biological property attributes. In this work, scaffolding materials with integrated layer structures and well interconnected and open pore structures were obtained. This bilayer structure had porosity with a pore size of 19.72 µm and 90.71 µm for the simulation of the epidermis and dermis, respectively. The production and expression of laminin, collagen IV, and keratin 10 proteins in the bilayer cryogel scaffolds obtained from the immunofluorescence study were 49.7 %, 63.8 %, and 49.3 %, respectively. The extracellular matrix (ECM) was produced in each scaffold layer. The observations confirmed that the porosity and pore size of both N1 and N2 layers were appropriate for the fibroblast and keratinocyte cells, respectively. H&E stained cross-sections of bilayer cryogel scaffolds illustrated epidermal and dermal layers produced by co-culturing keratinocytes and fibroblasts. Based on the results, the bilayer CNF/PVA scaffold can be used in skin tissue engineering applications. However, more experiments and in vivo evaluations are needed to express this conclusion more accurately.

Reinforcing canola protein matrix with chemically tailored nanocrystalline cellulose improves the functionality of canola protein-based packaging materials.

Canola protein derived from the canola industry byproduct is a potent biopolymer source to develop sustainable food packaging materials, but it has limitations due to its poor mechanical and barrier properties. Nanomaterials such as nanocrystalline cellulose (NCC) have shown promising potential in improving material properties. The current study aimed to enhance the functionality of canola protein-based films using TEMPO ((2,2,6,6-Tetramethylpiperidin-1-yl)oxyl) modified nanocrystalline cellulose (TM-NCC). TEMPO modification was performed using TEMPO/NaClO/NaBr based oxidation. Modified and unmodified nanocrystalline cellulose (U-NCC) were used at different weight ratios to prepare the films. TEMPO-mediated oxidation converted 19.61 ± 3.53 % of primary -OH groups into -COOH groups. The addition of U-NCC and TM-NCC significantly increased the tensile strength reporting the highest value of 8.36 ± 0.85 MPa for 5% TM-NCC, which was only 3.43 ± 0.66 MPa for control films. Interestingly, both U-NCC and TM-NCC enhanced the films' water barrier and thermal properties compared to control.

Modified cellulose nanofibers aerogels as a novel air filters; Synthesis and performance evaluation.

Nanofilters made with high adsorption freeze-dried modified cellulose nanofiber (CNF) aerogel were produced. The modification was made using functional groups containing phthalimide, and then their ability to adsorb particulate matter (PM) was evaluated and compared with the control filter (HEPA). The results showed that the highest adsorption of PM2.5 (99.95%) belonged to the nanofilters made of 1.5% phthalimide-modified CNF aerogel, and the lowest adsorption (76.66%) was related to the control samples. Moreover, based on the results, the nanofilter produced from freeze-dried phthalimide-modified CNF aerogel showed high filtration efficiency as well as excellent resistance to temperature and humidity. This modification enables the filter to operate in different environmental conditions, especially for particles less than 0.1 µm that are mainly responsible for reducing air quality, human health, air visibility, and climate change. In conclusion, we developed an environmentally friendly biodegradable nanofilter capable of high-performance filtration functions and structural stability in different environmental conditions.