Surface Esterification Research Articles

Study on Surface Esterification of Cellulose Nanocrystals Their and Lipid-Lowering Effect

ABSTRACT With the rapid development of the economy and changes in dietary structure, there is an excessive intake of high sugar and high-fat foods. To address this issue, in this study, we grafted palmitic acid onto CNC in the form of ester groups and evaluated its adsorption performance. Research had found that among these three methods, the CDI catalytic method can successfully obtain esterification modified CNC while also taking into account its environmentally friendly and pollution-free characteristics. Compared with CNC, its adsorption capacity for oil had increased, with the maximum adsorption capacity increasing from 35.80 g/g to 46.91 g/g. Meanwhile, the degree of esterification substitution of esterification modified CNC was measured, and the result was 0.03. Especially, after adding CNC-PA, the hydrolysis of fat was significantly reduced during the simulated digestion in vitro, whilst the absorption of fat in the intestine was significantly inhibited. In vivo testing also confirmed that consuming a diet containing CNC-PA significantly reduced elevated levels of triglycerides (TG) compared to the high-fat control group while long-term feeding of a diet containing CNC-PA reduced weight and fat accumulation.

Ultrafast surface esterification of cellulosic materials in aqueous media at room temperature

Ultrafast surface esterification of cellulosic materials in aqueous media at room temperature

Regioselective surface esterification of softwood mechanical pulp fines as hydrophilic paper strength additives

Regioselective surface esterification of softwood mechanical pulp fines as hydrophilic paper strength additives

Development of a beverage carton closure cap based on 100% wood pulp fibres

Single-use plastic products have been identified as an environmental challenge. When such products are not recycled, they may end up in nature and thus cause, e.g., marine littering. Thermoformed wood pulp fibre products are gaining more interest to replace fossil plastic products. However, beverage caps made of wood pulp fibres are challenging due to the hygroscopic nature of wood fibres, i.e., they absorb water, deform and loose functionality. Hence, the purpose of this study was to develop a fibre-based beverage cap that could replace plastic tethered cap systems. Both unbleached and bleached Kraft pulp and chemo-thermo-mechanical pulp (CTMP) fibres were tested in thermoforming trials, using tailor-made metal moulds. The results showed that Kraft pulp fibres formed denser structures, with more limited water absorption, compared to CTMP. The mechanical properties of thermoformed specimens were suitable for the application, i.e., the strength, modulus and elongation were between 32 and 36 MPa, 4–4.9 GPa and 1.6–1.9%, respectively, depending on the type of pulp fibre. Additionally, in order to secure that the caps were functional in relevant conditions in contact with liquids (water or milk), the caps were surface modified by silylation and esterification to increase the liquid barrier. The results indicate that surface esterification increased the contact angle to 95°. On the other hand, the surface-modified caps could not entirely limit the liquid absorption over longer periods of time (>∼1 h) when the caps were directly exposed to liquid. However, the liquid barrier was satisfactory when the products were exposed to increased relative humidity in refrigerated conditions (relative humidity >76% and temperature <7 °C).

Hydrophobic enzymatic cellulose nanocrystals via a novel, one-pot green method

Cellulose nanocrystals (CNCs) are a rapidly growing bionanomaterial with remarkable properties that have been harnessed in various applications, including mechanical reinforcement, biomedical materials, and coatings. However, for non-water-based applications, hydrophobization of CNCs while preserving their integrity is crucial. In this study, we propose a new eco-friendly, one-pot surface esterification method for hydrophobizing enzymatic CNCs in aqueous suspension without solvent exchange. By establishing an appropriate set of reaction conditions, it was possible to create a miscibility gradient that enabled a low-cost, and renewable fatty acid to be utilized as an acyl donor and solvent, allowing direct hydrophobic modification of the as-produced aqueous suspension of enzymatic CNC. FT-IR and AFM-IR analyses confirmed the formation of ester groups, while 13C NMR confirmed the emergence of carboxyl groups. XPS revealed a high degree of surface substitution (0.39) in the modified CNC, while a substantial increase in contact angle (from 40 to approximately 90°) quantitatively confirmed the high efficiency of the enzymatic CNC's hydrophobic modification. Additionally, important properties such as morphology remained practically unchanged, except for a slight increase in thermal stability and crystallinity of the CNCs. Therefore, hydrophobic enzymatic CNCs were successfully produced via a simple, scalable, and environmentally friendly approach without compromising their properties. These hydrophobic CNCs have the potential to enhance nanocomposite compatibility, improve packaging performance for electronics and foods, optimize adhesion in coatings, and offer advancements in cosmetics and drug delivery. However, comprehensive studies are needed to confirm their applicability across these sectors.

Synthesis and evaluation of poly(propylene fumarate)-grafted graphene oxide as nanofiller for porous scaffolds.

In an effort to obtain porous scaffolds with improved mechanical properties and biocompatibility, the current study discusses nanocomposite materials based on poly(propylene fumarate)/N-vinyl pyrrolidone(PPF/NVP) networks reinforced with polymer-modified graphene oxide (GO@PPF). The GO@PPF nanofiller was synthesized through a facile and convenient surface esterification reaction, and the successful functionalization was demonstrated by complementary techniques such as FT-IR, XPS, TGA and TEM. The PPF/NVP/GO@PPF porous scaffolds obtained using NaCl as a porogen were further characterized in terms of morphology, mechanical properties, sol fraction, and in vitro degradability. SEM and nanoCT examinations of NaCl-leached samples revealed networks of interconnected pores, fairly uniform in size and shape. We show that the incorporation of GO@PPF in the polymer matrix leads to a significant enhancement in the mechanical properties, which we attribute to the formation of denser and more homogenous networks, as suggested by a decreased sol fraction for the scaffolds containing a higher amount of GO@PPF. Moreover, the surface of mineralized PPF/NVP/GO@PPG scaffolds is uniformly covered in hydroxyapatite-like crystals having a morphology and Ca/P ratio similar to bone tissue. Furthermore, the preliminary biocompatibility assessment revealed a good interaction between PPF/PVP/GO@PPF scaffolds and murine pre-osteoblasts in terms of cell viability and proliferation.

Improved mechanical and antibacterial properties of polyvinyl alcohol composite films using quaternized cellulose nanocrystals as nanofillers

Cellulose nanocrystals (CNC) are natural, renewable, and biocompatible materials that have been widely used as new sustainable reinforcing nanofillers in polymer composites. We present polyvinyl alcohol (PVA)/CNC composites with improved mechanical and antibacterial properties using CNC-based nanofillers. The surface esterified CNC (ECNC) was prepared by 6-bromohexanoyl chloride via surface esterification. Subsequently, the alkyl bromide group of the ECNC was transferred to quaternary ammonium groups for preparing quaternized CNC (ECNC-Qn) by introducing tertiary amino groups with different carbon chain lengths (C8–C16). Then, ECNC-Qn were blended with a PVA matrix to prepare PVA/ECNC-Qn nanocomposite films via a solvent casting procedure. Diverse features, including light transmission, mechanical properties, and antibacterial activity against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria were investigated. Compared with pure PVA films, the PVA/ECNC-Qn nanocomposite films had higher tensile strength and higher antibacterial activity. Specifically, the maximum tensile strength and elongation at break of PVA/ECNC-Qn nanocomposite films were 45.4 MPa and 318.4%, respectively, which were 37.2% and 94.3% higher than those of pure PVA film, respectively. Moreover, the ECNC-Q8 exhibited the highest antibacterial efficiency, leading to the best antibacterial activity for PVA/ECNC-Q8 nanocomposite films among all films. This study demonstrates an efficient method for preparing a functional, environment-friendly PVA composite film. The prepared PVA/ECNC-Qn nanocomposite films exhibited considerable application potential in the packaging field, owing to their good mechanical and antibacterial barrier properties.

Electron transfer dynamics and electrocatalytic oxygen evolution activities of the Co3O4 nanoparticles attached to indium tin oxide by self-assembled monolayers.

The Co3O4 nanoparticle-modified indium tin oxide-coated glass slide (ITO) electrodes are successfully prepared using dicarboxylic acid as the self-assembled monolayer through a surface esterification reaction. The ITO-SAM-Co3O4 (SAM = dicarboxylic acid) are active to electrochemically catalyze oxygen evolution reaction (OER) in acid. The most active assembly, with Co loading at 3.31 × 10−8 mol cm−2, exhibits 374 mV onset overpotential and 497 mV overpotential to reach 1 mA cm−2 OER current in 0.1 M HClO4. The electron transfer rate constant (k) is acquired using Laviron’s approach, and the results show that k is not affected by the carbon chain lengths of the SAM (up to 18 -CH2 groups) and that an increase in the average diameter of Co3O4 nanoparticles enhances the k. In addition, shorter carbon chains and smaller Co3O4 nanoparticles can increase the turn-over frequency (TOF) of Co sites toward OER. The Co3O4 nanoparticles tethered to the ITO surface show both a higher number of electrochemically active Co sites and a higher TOF of OER than the Co3O4 nanoparticles bound to ITO using Nafion.

Response Surface Optimization of Lipase‐Catalyzed Surface Esterification for Modification of Cassava Starch with Rosin Acid

The rosin acid starch (RAS) is prepared under the catalysis of lipase, by esterification on the starch particles' surface in a two-phase reaction system, using rosin acid and native cassava starch as starting materials. The effects of reaction time, solvent types, substrate ratio, reaction temperature, and lipase dosage on the degree of substitution (DS) of RAS are investigated. Based on the single factor experiments, the reaction conditions are optimized according to the principle of the combination Box-behnken centered design and response surface methodology analysis. The mathematical model of the influence of reaction temperature, material ratio, and enzyme addition amount on DS is established. The optimum synthesis conditions are determined as follows: solvent, trichloromethane; reaction time, 10 h; reaction temperature, 59 °C; substrate ratio (mRosin acid:mstarch), 4.1; and lipase dosage, 264 µL. Under these conditions, it is found that the DS is 0.0608. The analysis of variance and verification experiments show that the mathematical model has good fit degree and high credibility. Compared with the native cassava starch, RAS has improved contact angle, emulsion capacity, and emulsion stability.

Intracellular Delivery of Functional Proteins

Leveraging proteins as therapeutics has revolutionized the way we treat diseases. Recent advances in protein biologics and antibody engineering represent promising new treatment strategies for addressing complex etiologies. Thus far, these advances have been restricted to only accessible extracellular proteins, leaving a significant portion of the proteome undruggable. Efficient intracellular delivery of proteins would reveal uncharted therapeutic avenues and cell surface engineering opportunities. This presentation describes combinatorial strategies towards delivering proteins to the cytosol. By modifying a protein of interest through surface esterification or functionalization with a cell penetrating peptide we have observed robust intracellular delivery. In this presentation, I will first describe the development of a functional assay using a model protein to assess the efficacy and localization of delivery agents. Applying these findings to HaloTag has demonstrated the generality of our approach. I will show that our delivery strategy has enabled stable cell surface engineering. This study highlights that multiple intracellular delivery strategies can be used synergistically to enable cytosolic access with functionally active protein/biologic cargo.

Efficient and portable cellulose-based colorimetric test paper for metal ion detection

Fabrication of metal ion detection materials generally involved problems such as high cost and complicated processes of pretreatment and operation. Herein, a novel colorimetric test paper for metal ions detection was developed based on functionalized cellulose fibers. Acetoacetyl groups were introduced on cellulose fibers by a surface esterification process. The obtained cellulose acetoacetate (CAA) fibers were made into CAA paper via a paper-making process. The CAA paper possessed robust mechanical property, thermal stability selectivity and rapid response to Fe3+ and Cu2+ ions, with an obvious naked-eye color change within 5 s. The mechanism of this visual recognition for metal ions due to that the acetoacetyl groups coordination chelated with metal ion to form six-membered ring structure, further leading to the color change of the materials. It provided a facile and universal method to prepare efficient and portable cellulose-based test paper, which has great potential in metal ion detection field.

Plasma-assisted fibrillation and surface-modification of microfibrillar cellulose

The combination of microcrystalline cellulose (MCC) with maleic anhydride (MA) allowed for in-situ fibrillation and surface modification during pulsed plasma polymerization. Under optimized plasma parameters, the microfibrillated cellulose (MFC) morphology could be tuned according to the positioning in the reactor from small and short fibrils towards more elongated and crystallite structures in relation to the complex interactions between activated species. The chemical surface esterification was verified and resulted in good dispersion and higher water contact angle of the fibrils. The proposed route is an attractive ‘green’ and low-energy alternative for traditional mechanical processing and modification of nanocelluloses.

Comparative assessment of cellulose nanofibers and calcium alginate beads for continuous Cu(II) adsorption in packed columns: the influence of water and surface hydrophobicity

While water is indispensable for life, around 785 million people do not have access to basic drinking water. Heavy metals present high toxicity at low concentrations, are non-biodegradable and easy to accumulate in living organisms such as human body, causing serious diseases or even death. Copper is usually found at high concentrations in wastewater due to its extensive use in several industrial applications, and effective copper removal systems must be developed. The present work aims at developing effective TEMPO-oxidized cellulose nanofibers (CNFs) based systems able to adsorb Cu(II) in adsorption columns. CNFs were partially modified with alkyl ketene dimer (AKD) to avoid regelation during flowing through the column, as it was experienced for those unmodified. Calcium alginate beads were used as reference, as there is extensive literature on their use as Cu(II) adsorbent. Breakthrough curves were obtained and modelled according to Bohart-Adams, Yoon-Nelson and Thomas models, concluding that the adsorption rate of CNFs was significantly higher than in the case of calcium alginate beads due to the negative effects of highly charged water and diffusion through the beads. In addition, CNF-based adsorption systems demonstrated to be effective, especially at the beginning of the tests, as they exhibited a well-defined sigmoidal behavior, which was not observed in the case of the calcium alginate beads. On the contrary, the adsorption capacity was higher in the case of the alginate-based system, mainly due to the higher carboxyl content and ion exchange capacity. Overall, the present work shows the feasibility of using a high-performance bio-based and nanostructured cellulose material as Cu(II) adsorbent by means of a fast, simple, and effective chemical modification based on surface esterification.

The Application of Cellulose Nanocrystals Modified with Succinic Anhydride under the Microwave Irradiation for Preparation of Polylactic Acid Nanocomposites

The aim of this work was to use cellulose nanocrystals that were obtained by hydrolysis in phosphoric acid solution and further modified with succinic anhydride in the microwave field for PLA reinforcement. A series of all-bionanocomposites containing unmodified and surface modified cellulose nanocrystals with CNC content in the range of 1–3 %w.t. were obtained by melt blending and tested by XRD, SEM, DSC and DMA to investigate the effect of surface esterification of CNCs on the structure, morphology, dynamic mechanical properties of bionanocomposites, as well as phase transitions of PLA in the presence of cellulosic nanofiller. DMA investigations showed the highest increase of storage modulus by ca. 7% (335 MPa at 25°C) in the glassy state of PLA for 2 %w.t. of unmodified CNC. Though, addition of 2 %w.t. of succinylated CNCs caused the highest increase of the onset of glass transition temperature (by 6.2°C) thus widening the temperature range of biocomposite application. The increase of glass transition temperature indicates the strongest interfacial interactions due to improved miscibility of surface modified nanocrystals and thus good dispersion of additive in PLA matrix providing high interface.

Regioselective and water-assisted surface esterification of never-dried cellulose: nanofibers with adjustable surface energy.

A new regioselective route is introduced for surface modification of biological colloids in the presence of water. Taking the case of cellulose nanofibers (CNFs), we demonstrate a site-specific (93% selective) reaction between the primary surface hydroxyl groups (C6-OH) of cellulose and acyl imidazoles. CNFs bearing C6-acetyl and C6-isobutyryl groups, with a degree of substitution of up to 1 mmol g−1 are obtained upon surface esterification, affording CNFs of adjustable surface energy. The morphological and structural features of the nanofibers remain largely unaffected, but the regioselective surface reactions enable tailoring of their interfacial interactions, as demonstrated in oil/water Pickering emulsions. Our method precludes the need for drying or exchange with organic solvents for surface esterification, otherwise needed in the synthesis of esterified colloids and polysaccharides. Moreover, the method is well suited for application at high-solid content, opening the possibility for implementation in reactive extrusion and compounding. The proposed acylation is introduced as a sustainable approach that benefits from the presence of water and affords a high chemical substitution selectivity.

Correction: Regioselective and water-assisted surface esterification of never-dried cellulose: nanofibers with adjustable surface energy

Correction for ‘Regioselective and water-assisted surface esterification of never-dried cellulose: nanofibers with adjustable surface energy’ by Marco Beaumont, Caio G. Otoni, Bruno D. Mattos et. al., Green Chem., 2021, DOI: 10.1039/D1GC02292J.

Esterification of cellulose using carboxylic acid-based deep eutectic solvents to produce high-yield cellulose nanofibers

Deep eutectic solvents (DESs), as emerging green solvents, provide a new opportunity for the biorefinement of biomass, component extraction, and cellulose nanofibrillation. Herein, different carboxylic acid-based DESs were applied for preparation of cellulose nanofibers (CNFs) from cellulose raw materials accompanied by simultaneous esterification modifications of CNFs. The results showed that pretreatment of DESs combined with mechanical treatment can swell and esterify the cellulose materials, producing CNFs with widths less than 100 nm. The DES pretreatment temperature played important roles in the esterification modifications and nanofibrillation of cellulose. The esterification modifications of cellulose prevented the over-hydrolysis and dissolution of cellulose during the DES pretreatment, guaranteeing CNFs with high yields of 72 %–88 % and maintaining the cellulose I crystal structure. Moreover, the esterified CNFs were used as a reinforcement to prepare CNF-strengthened polylactic acid (PLA) composites. The surface esterification of the CNFs improved their dispersibility and interfacial compatibility with PLA, thereby achieving the mechanical enhancement of CNF/PLA composites.

Interphase Design of Cellulose Nanocrystals/Poly(hydroxybutyrate-ran-valerate) Bionanocomposites for Mechanical and Thermal Properties Tuning

Poly[(3-hydroxybutyrate)-ran-(3-hydroxyvalerate)] (PHBV) is a bacterial polyester with a strong potential as a substitute for oil-based thermoplastics due to its biodegradability and renewability. However, its inherent slow crystallization rate limits its thermomechanical properties and therefore its applications. In this work, surface-modified cellulose nanocrystals (CNCs) have been investigated as green and biosourced nucleating and reinforcing agent for PHBV matrix. Different ester moieties from the CNCs were thereby produced through a green one-pot hydrolysis/Fisher esterification. Beyond the improved dispersion, the CNCs surface esterification affected the thermal and thermomechanical properties of PHBV. The results demonstrate that butyrate-modified CNCs, mimicking the PHBV chemical structure, brought a considerable improvement toward the CNCs/matrix interface, leading to an enhancement of the PHBV thermomechanical properties via a more efficient stress transfer, especially above its glass transition.

Conversion of a low value industrial waste into biodiesel using a catalyst derived from brewery waste: An activation and deactivation kinetic study

In this study, biodiesel was produced by using a heterogeneous acid catalyst made from brewer’s spent yeast (BSY). BSY was initially activated by phosphoric acid followed by carbonization in inert atmosphere and sulfonation process to prepare the catalyst. It is completely characterized using sophisticated instruments to determine its physical and chemical properties. Subsequently, the effectiveness of the catalyst was analyzed by subjecting it to sonochemical esterification of an industrial low value waste product, palm fatty acid distillate (PFAD). The reactions were performed in the presence of ultrasound at a constant frequency of 25 kHz. An optimum methyl ester conversion of 87.8% was achieved at 8 wt% of catalyst, 21:1 methanol to PFAD molar ratio, 65 °C and 180 min of reaction time. The catalyst displayed a high catalytic stability up to four cycles due to firm SO3H functional group attached onto the surface. Furthermore, a novel sonochemical kinetic model was proposed for surface esterification reaction on the catalyst. The reaction rate was found and it followed a pseudo-first-order reaction mechanism. Furthermore, a deactivation model was also proposed to account for the loss of activity upon catalyst reuse during sonochemical reaction.

Direct esterification of reinforced papers by immersion method and evaluation of their properties

Today, the use of biodegradable packaging materials is very noteworthy. They are one of the most used materials in the packaging industries. These materials require proper barrier and mechanical strength properties. Cellulose nanofibril (CNF) can improve the mechanical strength and air resistance of paper, but it is not able to improve its water barrier property. In this study, modification of the water barrier property of CNF-reinforced papers was evaluated using the esterification process. Handsheets were made by adding CNF to the pulp fibers. After drying, the handsheets were esterified using the liquid-phase acetylation process without any catalyst for different reaction times (0.5, 1, and 3 h). Infrared spectroscopy confirmed a successful chemical modification. The mechanical properties and air resistance of the paper sheet were significantly increased by adding CNF to the pulp. The esterification led to a decrease in the water absorption of the unmixed and mixed papers of about 24.5 and 48%, respectively. Therefore, the addition of CNF to the pulp and surface esterification of the mixed paper caused simultaneous improvement in the barrier and mechanical strength properties of paper.