Feng Jiang

Escalating plastic waste and the limited property retention of mechanically recycled polymers motivate the development of bio-based reinforcements that enable higher-value reuse. This thesis targets reinforcing recycled polyethylene terephthalate glycol (R-PETG) and addresses the incompatibility between the hydrophobic matrix and hydrophilic cellulose nanocrystals (CNCs). CNCs were esterified with dodecenylsuccinic anhydride (DDSA) to introduce aliphatic succinyl chains at controllable grafting levels. The modified CNCs (mCNCs) were then incorporated into R-PETG via solution blending and film casting to develop biocomposite. Chemical modification was verified by Fourier-transform infrared spectroscopy. Colloidal stability and nanoparticle dispersion were examined by dynamic light scattering in aqueous and ethanolic media and by transmission electron microscopy in chloroform. The thermal property of the biocomposite was evaluated by thermogravimetric analysis and differential scanning calorimetry. The optical performance of the mCNCs suspension and the biocomposite was quantified by UV-Vis spectroscopy, and the mechanical properties were investigated using tensile testing.DDSA grafting increased CNC hydrophobicity, improved dispersion in semi-polar media and in R-PETG, and reduced aggregation relative to pristine CNCs at comparable contents (wt%). As a result, mCNCs/R-PETG films maintained higher visible transmittance than their unmodified counterparts, while providing effective reinforcement. Meanwhile, mCNCs incorporation converts R-PETG from brittle to ductile, maintaining comparable strength while markedly increasing the extensibility and toughness. Thermal analyses indicated that incorporating mCNCs did not compromise stability within the processing window and preserved the glass-transition characteristics of R-PETG. Overall, this work demonstrates a tunable, chemistry-guided route to compatibilize CNCs with R-PETG, delivering optically clear, mechanically robust, and potentially re-recyclable biocomposites. The findings support circular-economy pathways by coupling waste-plastic valorization with renewable nanofillers and provide design principles for next-generation sustainable polymer composites.

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The objective of this work was to develop a path to create a plastic film alternative in packaging applications using cellulose materials. It was expected that a small amount of chemical and energy are needed during the process to align with the principles of eco-friendly development and sustainable development. It was also anticipated that the product of this work should have favorable optical properties and good mechanical performance comparable to ordinary plastic film products.In this study, without going through dissolution or nanofibrillation, Northern Bleached Softwood Kraft (NBSK) cellulose pulp is treated with a 10% NaOH solution at a subzero temperature (-10 °C) and mechanical disintegration using a domestic blender to create a substitute that resembles plastic films. The kraft pulp can be converted into a stable fibrous slurry that can then be processed into a translucent and hazy film using vacuum filtration. The prepared cellulose film demonstrated high transmittance (89% at 650 nm with integrated sphere), excellent biodegradability (completely degrade in 19 days when buried in soil), high mechanical strength (99.7 MPa tensile strength in the dry state and 17.2 MPa after being immersed in water for 30 days), and high thermal stability (Tmax of 350 °C). In sum, in this study a translucent, hazy, and strong cellulose film was developed through a simple chemical-saving and energy-saving fabrication method which involves treatment in 10% NaOH solution at -10 °C, blending and vacuum filtration, showing great promise as plastic alternative for packaging applications.

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To address the increasing environmental concerns related to solid waste disposal, specifically non-biodegradable electronic sensors laden with heavy metals, this thesis investigates an environmentally friendly substitute. We delve into the potential of cellulose, the most abundant natural polymer, in developing biodegradable and flexible 3D sensing materials. In the first part, we create a super-stretchable and self-healing all-cellulose hydrogel. Our technique involves molecular engineering of cellulose chains and their hydrogen bonding network through periodate oxidation ring-opening reactions, followed by borohydride reduction. This innovative approach alleviates chain rigidity, enhances chain mobility, and leads to the production of hydrogels that showcase record-breaking stretchability, quick self-healing properties, and non-Newtonian behavior. The hydrogels are further tested as human motion sensors and ECG electrodes, marking significant strides in wearable technology.The second part of this work presents a super-elastic Carbon Black (CB) coated cellulose sub-micron fiber aerogel sensor, which is developed through ice-templating and electrostatic assembly. By controlling temperature, the 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNF) assembles into a 3D sub-micron fiber (SMF) network, achieving elasticity in the aerogel. The CB forms a conductive network structure on the TOCNF SMF surface through electrostatic adsorption. This unique strategy results in a SMF/CB aerogel with super-elasticity, high sensitivity, fast response and recovery times, which opens new avenues for wearable sensor applications.In summary, this thesis advocates for the potential of cellulose in developing eco-friendly, high-performance sensors, offering key insights into cellulose-based hydrogel and aerogel that manifest extraordinary properties, with potential applications in wearable technology and human health monitoring.

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Phase change materials (PCM) has been increasingly used over the past decades to combat the large amount of energy needed for thermal comfort of human beings. Organic PCM is desired in temperature control, but it suffers from thermal leaking and unstable form during phase transition. This study aimed to develop cellulose nanofibrils (CNF) – phase change mamterials based functional materials for thermal management applications. PCM, using paraffin as an example, is encapsulated into micron-sized emulsions using CNF as interfacial stabilizer. We expected that microencapsulation using CNF can improve the flexibility and thermal stability of PCM, and such emulsion can be used in various applications such as spray coating and 3D printing. Firstly, CNF/PCM Pickering emulsion can be stabilized due to the amphiphilic nature and strong network of CNF with optimized sonication conditions, including sonication time and amplitude, ratio of CNF and PCM, and CNF concentrations. Results indicated uniform PCM emulsion particles of 4.2 ± 2.1 μm could be obtained using 0.8 wt.% CNF suspension sonicated at 100%A and 7 mins with 2:8 paraffin to CNF ratio. The CNF-stabilized paraffin emulsion showed excellent long-term stability with unchanged particle size when stored at 45 °C for 28 days. In addition, differential scanning calorimetry (DSC) results showed high thermal stability after 51 heating-cooling cycles. The CNF-stabilized paraffin Pickering emulsion demonstrated improved thermal stability and versatility for spray-coating application, which can coat a regular polyester-cotton fabric to improve its thermal shielding performance, without sacrificing its flexibility. Secondly, the CNF-stabilized paraffin Pickering emulsion can serve as a gradient to prepare CNF/paraffin printable ink for direct-ink-writing 3D printing. The rheological properties of the inks were characterized in details to demonstrate their printability. Lightweight 3D printed scaffold (35.0 mg/cm³ for pure CNF matrix) endowed the composite monolith with high PCM loading (up to 82% with respect to the composite) and high thermal storage capacity (up to 153 J/g).

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This study aimed to improve the thermal management and mechanical performance of cellulose nanofibrils (CNF) aerogels. We expected that closed-pore structure of CNF aerogel can be gained by Pickering emulsion templating and solvent exchange method, and that paraffin can be encapsulated by CNF to fabricate CNF/Phase change material (PCM) aerogel with excellent stability, super thermal regulation performance, and flexibility. It was also expected that the addition of CNF to prepared emulsion can enhance the structure to further improve the thermal management and mechanical performance. First, CNF aerogels with closed internal pores were successfully fabricated by Pickering emulsion templating and solvent exchange techniques. CNF stabilized oil-in-water Pickering emulsion can be converted into closed pores by sequential solvent exchanging to acetone and tert-butanol, followed by freeze drying from tert-butanol to suppress the formation of large ice crystals. The closed pore was verified by both confocal microscopy and scanning electron microscopy images, and was confirmed to reduce thermal conductivity for aerogel. In addition to the ultra-low thermal conductivity, the CNF/emulsion composite aerogel also demonstrates high performance in properties such as low density, high mechanical properties, superb flexibility, and infrared shielding properties. In addition, robust CNF/PCM aerogels were successfully fabricated with CNF stabilized paraffin by Pickering emulsion templating technique. The CNF/PCM aerogels were ultralight with impressive mechanical properties, which were significantly enhanced by the addition of CNF to the as-formed PCM emulsion. The freeze-dried CNF/PCM aerogels were flexible, and the shape of CNF/PCM aerogel can be well maintained even loaded with a weight of over thousands of times its own weight. The exceptional thermal regulation performance was demonstrated by a series of heating and cooling tests. The CNF/PCM aerogels exhibited excellent shape stability with no leakage after 51 heating-cooling thermal cycles. The latent heat of CNF/PCM aerogel (4:6) can reach approximately 84.4% of that of pure paraffin. In brief, this work fabricated sustainable CNF aerogel with closed-pore structure for the first time, and also obtained CNF/PCM aerogel with high shape stability and energy density. The thermal management and mechanical performance of CNF aerogel were significantly improved.

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