All‐cellulose composites prepared by partially dissolving cellulose using NaOH /thiourea aqueous solution

Sustainable All-Cellulose Biocomposites from Renewable Biomass Resources Fabricated in a Water-Based Processing System by the Vacuum-Filtration-Assisted Impregnation Method

The increasing awareness of global ecological concerns and the rising sustainability consciousness associated with the manufacturing of non-renewable and non-biodegradable composite materials have led to extensive research on product and process developments of more sustainable, environmentally friendly, and fully biodegradable biocomposites for higher-value end-use applications. All-cellulose composites (ACCs) are an emerging class of biocomposites, which are produced utilizing solely cellulose as a raw material that is derived from various renewable biomass resources, such as trees and plants, and are assessed as fully biodegradable. In this study, sustainable ACCs were fabricated for the first time based on the full dissolution of commercially available sulfite dissolving (D) pulps as a matrix with concentrations of 1.5 wt.% and 2.0 wt.% in an aqueous NaOH-urea solvent, and they were then impregnated on/into the pre-fabricated birch (B), abaca (A), and northern softwood (N) fiber sheets as reinforcements by the vacuum-filtration-assisted impregnation approach. This research aimed to investigate the effects of the impregnated cellulose matrix concentrations and types of the utilized cellulose fiber reinforcements (B, A, N) on the morphological, crystalline, structural, and physio-mechanical properties of the ACCs. The highest degrees of improvements were achieved for tensile strength (+532%, i.e., from 9.24 MPa to 58.04 MPa) and strain at break of the B fiber-reinforced ACC B1.5 (+446%, i.e., from 1.36% to 4.62%) fabricated with vacuum impregnation of the 1.5 wt.% cellulose matrix. Noticeably, the greatest improvements were attained in strain at break of the A and N fiber-reinforced ACCs A2.0 (+218%, i.e., from 4.44 % to 14.11%) and N2.0 (+466%, i.e., 2.59% to 14.65%), respectively, produced with vacuum impregnation of the 2.0 wt.% cellulose matrix. The study highlights the diverse properties of the all-cellulose biocomposite materials that could, expectedly, lead to further development and research for upscaled production of the ACCs.

Direct dissolution of unbleached pulp from corncob and wheat straw in N-methylmorpholine-N-oxide

Lignocellulose, as a kind of abundant natural resource, continuously developed to convert high value-added biological products is of great significance. Herein, we report a N-methylmorpholine-N-oxide (NMMO) solvent system to completely dissolve unbleached pulp to prepare a renewable lignin-containing cellulose film. The viscosity of the completely dissolved cellulose solution was measured using a high-pressure rotary rheometer. The shear viscosity exceeded 85 Pa·s at a shear rate of 1.62 s-1. It exhibited shear-thinning non-Newtonian fluid behavior with increasing shear rate. CF-WS had excellent tensile strength (>73 MPa), and exhibited unique optical properties of high transmittance in the visible region and high shielding performance in the ultraviolet region. When the thickness is only 0.016 mm, the UV shielding rate exceeds 75 % (λ < 380 nm). The structure of the bioplastic was revealed by SEM, XPS, and Raman spectroscopy. Directly dissolving lignocellulose in NMMO aqueous solution is expected to yield bioplastics with high strength and biodegradability. It is a potential substitute for petrochemical plastics and provides a possible way for the utilization of agricultural waste.

Mechanical and Thermal Properties of Wood-Fiber-Based All-Cellulose Composites and Cellulose-Polypropylene Biocomposites

This article explores wood-fiber-based fabrics containing Lyocell yarn in the warp and Spinnova-Lyocell (60%/40%) yarn in the weft, which are used to form unidirectional all-cellulose composites (ACC) through partial dilution in a NaOH-urea solution. The aim is to investigate the role of the yarn orientation in composites, which was conducted by measuring the tensile properties in both the 0° and 90° directions. As a reference, thermoplastic biocomposites were prepared from the same fabrics, with biobased polypropylene (PP) as the matrix. We also compared the mechanical and thermal properties of the ACC and PP biocomposites. The following experiments were carried out: tensile test, TGA, DSC, DMA, water absorption test and SEM. The study found no significant difference in tensile strength regarding the Spinnova-Lyocell orientation between ACC and PP biocomposites, while the composite tensile strength was clearly higher in the warp (Lyocell) direction for both composite variants. Elongation at break doubled in ACC in the Lyocell direction compared with the other samples. Thermal analysis showed that mass reduction started at a lower temperature for ACC, but the thermal stability was higher compared with the PP biocomposites. Maximum thermal degradation temperature was measured as being 352 °C for ACC and 466 °C for neat PP, and the PP biocomposites had two peaks in the same temperature range (340-474 °C) as ACC and neat PP combined. ACCs absorbed 93% of their own dry weight in water in just one hour, whereas the PP biocomposites BC2 and BC4 absorbed only 10% and 6%, respectively. The study highlights the different properties of ACC and PP reference biocomposites that could lead to further development and research of commercial applications for ACC.

All-Cellulose Composite Laminates Made from Wood-Based Textiles: Effects of Process Conditions and the Addition of TEMPO-Oxidized Nanocellulose

All-cellulose composites (ACCs) are manufactured using only cellulose as a raw material. Biobased materials are more sustainable alternatives to the petroleum-based composites that are used in many technical and life-science applications. In this study, an aquatic NaOH-urea solvent system was used to produce sustainable ACCs from wood-based woven textiles with and without the addition of TEMPO-oxidized nanocellulose (at 1 wt.-%). This study investigated the effects of dissolution time, temperature during hot press, and the addition of TEMPO-oxidized nanocellulose on the mechanical and thermal properties of the composites. The results showed a significant change in the tensile properties of the layered textile composite at dissolution times of 30 s and 1 min, while ACC elongation was the highest after 2 and 5 min. Changes in hot press temperature from 70 °C to 150 °C had a significant effect: with an increase in hot press temperature, the tensile strength increased and the elongation at break decreased. Incorporating TEMPO-oxidized nanocellulose into the interface of textile layers before partial dissolution improved tensile strength and, even more markedly, the elongation at break. According to thermal analyses, textile-based ACCs have a higher storage modulus (0.6 GPa) and thermal stabilization than ACCs with nanocellulose additives. This study highlights the important roles of process conditions and raw material characteristics on the structure and properties of ACCs.

Fabrication of lignin-containing cellulose bio-composite based on unbleached corncob and wheat straw pulp

In contemporary life, plastic, a kind of petroleum carbon source, has been produced and used in varieties of applications. However, the vast consumption of petroleum-based plastic and the burning of agricultural wastes make the environmental problems increasingly severe. Furthermore, a large number of lignocellulosic resources (such as corncob and wheat straw) are often wasted and burned, which will aggravate the environmental damage. In this paper, we use unbleached corncob and wheat straw pulp to fabricate the lignin-containing cellulose bio-composites (LCBs) to reduce non-renewable energy consumption and utilize agricultural wastes. The LCBs were obtained by a direct manufacturing process in benzyltrimethyl ammonium hydroxide (BzMe₃NOH) aqueous solution under mild conditions, constituting an entwined composite structure of cellulose micro/nano-fibers. This unique micro/nano-structure provides bio-composites with the outstanding mechanical performance of 96.7 MPa and a high haze of 90.1%. Meanwhile, with the inherent lignin, the LCBs could filter over 81.8% UV-C. As the raw material used is pure natural lignocellulose, the bio-composites prepared have innate environmental friendliness. With exceptional mechanical strength, UV-shielding property, and innate environmental friendliness, the LCBs are possible and potential substitutes for traditional petroleum-based plastic that is easily aging or non-biodegradable.