Characterization of Type-II Acetylated Cellulose Nanocrystals with Various Degree of Substitution and Its Compatibility in PLA Films

Biocomposites of Poly(Lactic Acid) and Microcrystalline Cellulose: Influence of the Coupling Agent on Thermomechanical and Absorption Characteristics

In this study, poly(lactic acid) (PLA) and microcrystalline cellulose (MCC)-based green biocomposites were developed using a solution casting technique. Essentially, the bonding between PLA and MCC is quite feeble; therefore, the current study is conducted to strengthen the bonding by incorporating a coupling agent, thereby enhancing the overall quality of the biocomposites. Thus, the present study aimed to examine the influence of combined coupling agents-maleic anhydride (MAH) and maleic acid (MA) (MAH-MA)-on the properties of polylactic acid (PLA)/microcrystalline cellulose (MCC) biocomposites. The investigation also encompassed an examination of the impact of MCC loading (2, 3, and 5% w/w) into a PLA matrix. The Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) examination revealed the interfacial interaction and adhesion among MCC, PLA, and coupling agents and the formation of biocomposites. The incorporation of MAH-MA led to improved mechanical properties of the PLA/MCC biocomposites. Furthermore, the incorporation of MAH-MA into the PLA/3 wt % MCC composite exhibited enhancements in both the tensile strength and tensile modulus, accompanied by a reduced elongation at break. In addition, it is worth noting that the thermogravimetric analysis (TGA) curve of the PLA composite with 3% w/w of MCC and MAH-MA displayed a significant decrease in weight beyond a temperature threshold of 492.65 °C. The water absorption demonstrates that the incorporation of MAH-MA into the PLA/MCC composite led to advantageous water barrier characteristics. The observed improvements were attributed to the efficient dispersion of MCC at the most favorable amount of coupling agents, along with the chemical interactions involving grafting and esterification between MCC and the MAH-MA coupling agent. Furthermore, the incorporation of MAH-MA into the PLA/3% (w/w) MCC composite exhibited enhancements in both the tensile strength and tensile modulus, accompanied by a reduction in the elongation percentage at break. The experimental results about water absorption demonstrate that the incorporation of MAH-MA into the PLA/MCC composite led to advantageous water barrier characteristics. These improvements were attributed to good MCC dispersion and the chemical interactions involving grafting and esterification between the MCC and the MAH-MA coupling agent.

Acetic acid as a protic solvent for reducing sulphuric acid concentrations in the production of cellulose nanocrystals alongside transition metal co-catalysts

Cellulose nanocrystals (CNC) conventionally involve highly concentrated sulphuric acid, which typically resulted in the formation of undesirable by-products. Although less corrosive mineral acids have been explored as alternatives, high concentrations are still required. In this study, CNC was successfully isolated from Leucaena leucocephala wood using mild sulphuric acid with acetic acid as protic solvent, and it was further studied with the addition of Lewis acids in the form of multivalent transition metal salts as co-catalyst. Selected divalent and trivalent transition metal salts including (Cr(NO3)3, Fe(NO3)3, Co(NO3)2, and Ni(NO3)2) were investigated. The morphology, chemical structure, particle size, and physicochemical properties of the CNCs were determined. Controlled depolymerization of cellulose was observed using transmission electron microscopy (TEM). Rod-like morphology for all CNCs was obtained during the hydrolysis process with the smallest CNC particles found at an average length of 278.1 ± 35.1 nm and a diameter of 13.4 ± 3.0 nm. The results showed that higher valence state metal ions resulted in better cellulose hydrolysis efficiency. In addition, the use of transition metal salt as a co-catalyst improved production efficiency and minimised carbonization of CNC while maintaining desired crystallinity and thermal properties.

Grafting natural nicotinamide on tempo-oxidized cellulose nanofibrils to prepare flexible and transparent nanocomposite films with fascinating mechanical strength and UV shielding performance

Light pollution from ultraviolet (UV) radiation is gaining growing concerns, as the emissions and burning of fossil fuels destroyed the ozone layer. Seeking a solution against skin exposure to excessive radiation is an urgent requirement. In this study, nicotinamide (NA), the main component of vitamin B3, was introduced as a new modifier into Tempo-oxidized cellulose nanofibrils (TOCNFs) together with the physical cross-linking with tannin acid (TA) to improve anti-UV performance of the nanocomposite films. Incorporation of NA into the films presents distinguished UV shielding capability UVB wavelength range from 200 nm to 320 nm (NTA1-5) due to the introduced functional groups like CO and benzene rings. Moreover, mechanical properties were notably enhanced, which overcome the low strength of common nanocellulosic materials. The stress increased from 69.8 MPa to 116.3 MPa, and the toughness can reach 131.58 MJ/m³ by tuning the additional amount of NA. Meanwhile, TGA and DTG analysis demonstrated that the incorporation of amide bonds and TA into the composite films greatly improved the thermal stability. Thus, the proposed materials fabricated from natural biomolecules show great potential in serving as new kinds of UV-resistant products in the application areas of sunscreen, protective clothing, and building materials.

Antibacterial Property of Cellulose Acetate Composite Materials Reinforced with Aluminum Nitride

Cellulose acetate (CA) is a synthetic compound that is derived from the acetylation of cellulose. CA is well known as it has been used for many commercial products such as textiles, plastic films, and cigarette filters. In this research, antibacterial CA composites were produced by addition of aluminum nitride (AlN) at different weight percentage, from 0 wt. % to 20 wt. %. The surface characterization was performed using laser microscope, Raman and FTIR spectroscopy. The mechanical and thermal properties of the composite were analyzed. Although the mechanical strength tended to decrease as the concentration of AlN increased and needed to be optimized, the melting temperature (Tm) and glass transition temperature (Tg) showed a shift toward higher values as the AlN concentration increased leading to an improvement in thermal properties. AlN additions in weight percentages >10 wt. % led to appreciable antibacterial properties against S. epidermidis and E. coli bacteria. Antibacterial CA/AlN composites with higher thermal stability have potential applications as alternative materials for plastic packaging in the food industry.

Photoluminescent biocomposite films of chitosan based on styrylbenzothiazolium-g-cellulose nanocrystal for anti-counterfeiting applications

In the present investigation, novel photoluminescent and transparent biocomposite films based on chitosan reinforced with styrylbenzothiazolium-g-cellulose nanocrystal for anti-counterfeiting applications were successfully prepared by casting solvent. Three novel styrylbenzothiazolium derivatives were synthesized by Knoevenagel condensation and characterized by FTIR, ¹H, ¹³C NMR and photoluminescence analysis. These photochromic compounds have been used to functionalize cellulose nanocrystal and the resulting fluorescent photonic materials were characterized by FTIR, ¹³C-CP/MAS NMR as well as photoluminescent analysis to confirm the successful grafting. It can be concluded that the addition of 5 wt% of fluorescent modified CNC to chitosan matrix increase the photoluminescent properties as well as improved the mechanical properties of the Cs/CNC-dye biocomposite films. These photoluminescent biocomposite film hold promising applicative value in anti-counterfeiting material in large-scale.

Cellulose Isolated From Waste Rubber Wood and Its Application in PLA Based Composite Films

Waste rubber wood (RW) is the castoff of rubber plantation with abundant reservation but without high-value utilization. In this study, cellulose with high purity has been efficiently isolated from waste RW and further processed into cellulose nanocrystals. By means of acetylation, more hydrophobic cellulose-based products, namely acetylated rubber wood cellulose (Ac-RWC) and acetylated rubber wood cellulose nanocrystals (Ac-RW-CNC) had been attempted as reinforcing fillers for fabricating two series of PLA-based composite films via spin coating instead of currently prevailing melt compounding technique. To ensure a uniformed dispersion of fillers in PLA matrix, the addition of reinforcing filler should be equal to or less than 5% based on the film dry weight. Compared with pure PLA film, the Ac-RWC reinforced PLA composite films are more thermally stable, while the Ac-RW-CNC reinforced PLA composite films on the other hand exhibit more enhanced performance in mechanical properties and the degree of crystallinity. The highest tensile strength (55.0 MPa) and Young's modulus (3.9 GPa) were achieved for 5%Ac-RW-CNC/PLA composite film.

A Review: Research Progress in Modification of Poly (Lactic Acid) by Lignin and Cellulose

With the depletion of petroleum energy, the possibility of prices of petroleum-based materials increasing, and increased environmental awareness, biodegradable materials as a kind of green alternative have attracted more and more research attention. In this context, poly (lactic acid) has shown a unique combination of properties such as nontoxicity, biodegradability, biocompatibility, and good workability. However, examples of its known drawbacks include poor tensile strength, low elongation at break, poor thermal properties, and low crystallization rate. Lignocellulosic materials such as lignin and cellulose have excellent biodegradability and mechanical properties. Compounding such biomass components with poly (lactic acid) is expected to prepare green composite materials with improved properties of poly (lactic acid). This paper is aimed at summarizing the research progress of modification of poly (lactic acid) with lignin and cellulose made in in recent years, with emphasis on effects of lignin and cellulose on mechanical properties, thermal stability and crystallinity on poly (lactic acid) composite materials. Development of poly (lactic acid) composite materials in this respect is forecasted.

Synergistic impact of cellulose nanocrystals with multiple resins on thermal and mechanical behavior

The cellulose nanocrystals (CNCs) surface modified with phenolic and acrylic resins were investigated for different properties such as thermally stability and adhesive property, the mechanical properties of CNCs and interactions of the resulting materials at a micro-level are very important. Phenolic resins are of great interest due to their smooth structure, low thermal conductivity and good thermal insulation. However, the high spray rates and poor mechanical properties limit its use for external insulation of buildings. Acrylic resins are used as a matrix resin for adhesives and composites due to their adhesion, mechanical properties, and their good chemical resistance. The brittleness of acrylic resins makes them less attractive than the structural materials, being much harder. For this reason, most of the resins are modified with suitable elastomers, which act as hardeners. Therefore, treatment of these compounds is necessary. In this research paper, the effect of CNCs surface on phenolic and acrylic resins were investigated to obtain an optimized surface using three different weight (wt%) ratios of CNCs. Scanning electronic microscopy (SEM), X-rays diffraction (XRD), Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the structure, and investigate different properties of CNCs. Furthermore, the Zwick/Roell Z020 model was used to investigate the adhesion properties of the phenolic and acrylic resins with CNCs.

Preparation, characterization and evaluation of cellulose nanocrystal/poly(lactic acid) in situ nanocomposite scaffolds for tissue engineering

Cellulose nanocrystal (CNC)/poly(lactic acid) (PLA) in situ nanocomposite scaffolds were fabricated by in situ polymerization of lactic acid and CNC which was directly utilized as aqueous suspension, followed by a process of thermally induced phase separation. The CNC/PLA in situ nanocomposite porous scaffolds were characterized by mechanical test, protein adsorption, hemolysis test, in vitro degradation measurement, TEM, FTIR, SEM and WAXD. Compared to the PLA scaffold, the CNC/PLA in situ nanocomposite scaffolds showed a greatly increased compression modulus, an improved hemocompatibility and protein adsorption capacity. The inclusion of CNCs boosted the in vitro degradation of the in situ nanocomposite porous scaffolds and facilitated the deposition of Ca²⁺, CO₃^2-, PO₄^3- ions in simulated body fluid. Furthermore, cell cultures were carried out on the CNC/PLA in situ nanocomposite porous scaffolds. In comparison with the PLA scaffold, the in situ nanocomposite scaffolds improved cell attachment and enhanced cell proliferation, denoting low cytotoxicity and good cytocompatibility. It can therefore be concluded that such scaffolds with excellent mechanical property, biocompatibility, biomineralization capacity and bioactivity hold great potential for bone tissue engineering.

Nanocomposites of LLDPE and Surface-Modified Cellulose Nanocrystals Prepared by Melt Processing

Cellulose nanocrystals (CNCs) were surface modified by esterification in tetrahydrofuran (THF) at 25 °C using different catalysts and anhydrides bearing different alkyl side chain lengths. Unmodified and acetic anhydride (AcAnh)-modified CNCs were studied as potential nanofillers for linear low-density poly(ethylene) (LLDPE). Nanocomposites were prepared by melt processing. Determination of the size and size distribution of CNCs in the nanocomposites by SEM revealed an enhanced compatibility of the AcAnh-modified CNCs with the LLDPE matrix, since the average size of the aggregates of the modified CNCs (0.5⁻5 μm) was smaller compared to that of the unmodified CNCs (2⁻20 μm). Tensile test experiments revealed an increase in the nanocomposites' stiffness and strain at break-by 20% and up to 90%, respectively-at the CNC concentration of 5 wt %, which is close to the critical percolation concentration. Since the CNC nanofiller simultaneously reduced LLDPE crystallinity, the reinforcement effect of CNCs was hampered. Therefore, the molding temperature was increased to 120 °C, and, in this way, the greatest increase of the Young's modulus was achieved (by ~45%). Despite the enhanced compatibility of the AcAnh-modified CNCs with the LLDPE matrix, no additional effect on the mechanical properties of the nanocomposites was observed in comparison to the unmodified CNC.