Mei-Chun Li

Morphological influence of cellulose nanoparticles (CNs) from cottonseed hulls on rheological properties of polyvinyl alcohol/CN suspensions

The present work describes the isolation of cellulose nanoparticles (CNs) with different morphologies and their influence on rheological properties of CN and CN-poly (vinyl alcohol) (PVA) suspensions. Cottonseed hulls were used for the first time to extract three types of CNs, including fibrous cellulose nanofibers, rod-like cellulose nanocrystals and spherical cellulose nanoparticles through mechanical and chemical methods. Rheology results showed that the rheological behavior of the CN suspensions was strongly dependent on CN concentration and particle morphology. For PVA/CN systems, concentration of PVA/CN suspension, morphology of CNs, and weight ratio of CN to PVA were three main factors that influenced their rheology behaviors. This research reveals the importance of CN morphology and composition concentration on the rheological properties of PVA/CN, providing new insight in preparing high performance hydrogels, fibers and films base on PVA/CN suspension systems.

Preparation and Properties of Electrospun Poly (Vinyl Pyrrolidone)/Cellulose Nanocrystal/Silver Nanoparticle Composite Fibers

Poly (vinyl pyrrolidone) (PVP)/cellulose nanocrystal (CNC)/silver nanoparticle composite fibers were prepared via electrospinning using N,N′-dimethylformamide (DMF) as a solvent. Rheology, morphology, thermal properties, mechanical properties, and antimicrobial activity of nanocomposites were characterized as a function of material composition. The PVP/CNC/Ag electrospun suspensions exhibited higher conductivity and better rheological properties compared with those of the pure PVP solution. The average diameter of the PVP electrospun fibers decreased with the increase in the amount of CNCs and Ag nanoparticles. Thermal stability of electrospun composite fibers was decreased with the addition of CNCs. The CNCs help increase the composite tensile strength, while the elongation at break decreased. The composite fibers included Ag nanoparticles showed improved antimicrobial activity against both the Gram-negative bacterium Escherichia coli (E. coli) and the Gram-positive bacterium Staphylococcus aureus (S. aureus). The enhanced strength and antimicrobial performances of PVP/CNC/Ag electrospun composite fibers make the mat material an attractive candidate for application in the biomedical field.

Soy Protein Isolate As Fluid Loss Additive in Bentonite-Water-Based Drilling Fluids.

Wellbore instability and formation collapse caused by lost circulation are vital issues during well excavation in the oil industry. This study reports the novel utilization of soy protein isolate (SPI) as fluid loss additive in bentonite-water based drilling fluids (BT-WDFs) and describes how its particle size and concentration influence on the filtration property of SPI/BT-WDFs. It was found that high pressure homogenization (HPH)-treated SPI had superior filtration property over that of native SPI due to the improved ability for the plugging pore throat. HPH treatment also caused a significant change in the surface characteristic of SPI, leading to a considerable surface interaction with BT in aqueous solution. The concentration of SPI had a significant impact on the dispersion state of SPI/BT mixtures in aquesous solution. At low SPI concentrations, strong aggregations were created, resulting in the formation of thick, loose, high-porosity and high-permeability filter cakes and high fluid loss. At high SPI concentrations, intercatlated/exfoliated structures were generated, resulting in the formation of thin, compact, low-porosity and low-permeability filter cakes and low fluid loss. The SPI/BT-WDFs exhibited superior filtration property than pure BT-WDFs at the same solid concentraion, demonstrating the potential utilization of SPI as an effective, renewable, and biodegradable fluid loss reducer in well excavation applications.

Mechanical and thermal properties of toluene diisocyanate-modified cellulose nanocrystal nanocomposites using semi-crystalline poly(lactic acid) as a base matrix

Although chemical modifications (grafting ‘onto’) of CNCs have been successfully adopted to enhance their dispersibility in apolar matrices and solvents, the problem of the dispersion level of mCNCs (chemically modified CNCs) in apolar matrices above a certain loading of nanoparticles remains an issue. CNCs were successfully modified using toluene diisocyanate, and the effects of the molar mass (Mw) and crystallinity (Xc) of semicrystalline poly(lactic acid) (PLA) on the mechanical and thermal properties of mCNC filled PLA nanocomposites were investigated. An increase in the mechanical properties of the PLA nanocomposites with mCNCs implied that Mw and Xc of PLA can be key factors to improve the dispersion level of mCNCs. In our solvent dilute polymer system, despite a reduction in the crystallinity of PLA with increasing mCNC loading level, the melting temperature of the PLAs remained constant due to the mCNC effect, which hinders the chain mobility of the PLAs. The results demonstrated that a fundamental understanding of the crystallinity and molar mass of polymers as well as surface modification of CNCs can be a reasonable approach to take full advantage of the potential usage of CNCs as reinforcements.

Electrospun Nanofibers Made of Silver Nanoparticles, Cellulose Nanocrystals, and Polyacrylonitrile as Substrates for Surface-Enhanced Raman Scattering

Nanofibers with excellent activities in surface-enhanced Raman scattering (SERS) were developed through electrospinning precursor suspensions consisting of polyacrylonitrile (PAN), silver nanoparticles (AgNPs), silicon nanoparticles (SiNPs), and cellulose nanocrystals (CNCs). Rheology of the precursor suspensions, and morphology, thermal properties, chemical structures, and SERS sensitivity of the nanofibers were investigated. The electrospun nanofibers showed uniform diameters with a smooth surface. Hydrofluoric (HF) acid treatment of the PAN/CNC/Ag composite nanofibers (defined as p-PAN/CNC/Ag) led to rougher fiber surfaces with certain pores and increased mean fiber diameters. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results confirmed the existence of AgNPs that were formed during heat and HF acid treatment processes. In addition, thermal stability of the electrospun nanofibers increased due to the incorporation of CNCs and AgNPs. The p-PAN/CNC/Ag nanofibers were used as a SERS substrate to detect p-aminothiophenol (p-ATP) probe molecule. The results show that this substrate exhibited high sensitivity for the p-ATP probe detection.

Synthesis-Free Phase-Selective Gelator for Oil-Spill Remediation

A new deep eutectic solvent (DES) was developed as a phase-selective gelator for oil-spill remediation. The newly designed nonionic DES is based on a combination of an amide (N-methylacetamide) and a long chain carboxylic acid (lauric acid) and does not require any synthetic procedure besides mixing. Our studies show that the DES works as gelator by forming a gel between lauric acid and the hydrocarbon, whereas the amide serves to form the DES and dissolves in water during the gelation process. In addition, the DES material has gelation properties comparable to those considered as state-of-the-art. Overall, the newly developed material shows a promising future in oil recovery methodologies.

Grafting polycaprolactone diol onto cellulose nanocrystals via click chemistry: Enhancing thermal stability and hydrophobic property

Hydrophobic and thermally-stable cellulose nanocrystals (CNCs) were synthesized by polycarpolactone diol (PCL diol) grafting via click chemistry strategy. The synthesis was designed as a three-step procedure containing azide-modification of CNCs, alkyne-modification of PCL diol and sequent copper(I)-catalyzed azide-alkyne cycloaddition reaction. The structure of azide-modified CNCs and alkyne-modified PCL diol, the structure, hydrophobic ability and thermal stability of click products CNC-PCL were characterized. FTIR, XPS and H1 NMR results indicated a successful grafting of the N3 groups onto the CNCs, synthesis of PCL diol-CCH, and formation of the CNC-PCL material. CNC-PCL had enhanced dispersion in the non-polar solvent chloroform owing to the well-maintained microscale size and PCL-induced hydrophobic surface. The thermal stability of CNC-PCL was largely increased due to the grafting of thermally-stable PCL. This work demonstrates that click chemistry is an attractive modification strategy to graft CNCs with polyester chains for further potential application in polymer composites.

Synergistic influence of halogenated flame retardants and nanoclay on flame performance of high density polyethylene and wood flour composites

High density polyethylene and wood flour (HDPE/WF) composites containing three flame modifiers (FMs) (i.e., two fire retardants: 1,2-bis(pentabromophenyl) and ethylene bis(tetrabromophthalimide), and one nanoclay), maleic anhydride grafted polyethylene (MAPE) and other processing aids were prepared through twin-screw extrusion, and their properties were characterized. The addition of FMs lowered the composite strength, but composite modulus did not change in a systematic manner. The fiber-polymer interfacial adhesion became increasingly deteriorated with the FM addition, and the use of MAPE coupling agent in the composites helped improve the interfacial adhesion. There was a synergistic effect of the fire retardants, nanoclay and MA-g-PE, especially for 1,2-bis(pentabromophenyl)–clay–MAPE system, on thermal stability and fire retardancy with lowered heat release rate and total heat release of the composites, leading to significantly improved flame performance.

Cellulose Nanocrystals (CNCs) from Corn Stalk: Activation Energy Analysis

Cellulose nanocrystals (CNCs) were isolated from corn stalk using sulfuric acid hydrolysis, and their morphology, chemical structure, and thermal stability properties were characterized. The CNCs had an average length of 120.2 ± 61.3 nm and diameter of 6.4 ± 3.1 nm (L/D = 18.7). The degree of crystallinity of the CNCs increased to 69.20% from the 33.20% crystallinity of raw corn stalk fiber, while the chemical structure was well kept after sulfuric acid hydrolysis. Thermal stability analysis showed that the degradation temperature of the CNCs reached 239.5 °C, which was higher than that of the raw fiber but lower than that of the extracted cellulose. The average activation energy values for the CNCs, evaluated using the Friedman, Flynn-Wall-Ozawa (F-W-O) and Coats-Redfern methods, were 312.6, 302.8, and 309 kJ·mol−1 in the conversion range of 0.1 to 0.8. The isolated CNCs had higher values of activation energy than did the purified cellulose, which was attributed to the stronger hydrogen bonds present in the crystalline domains of CNCs than in those of cellulose. These findings can help better understand the thermal properties of polymer/CNC composites.