In January 5th, the reporter learned from the Qingdao Institute of bioenergy and process, China Academy of Sciences, that the research group of the metabolomics group led by Cui ball researcher, using boron ion crosslinking strategy, combined with the synergistic effect of chitosan and a small amount of cationic polyacrylamide (CPAM), developed a high strength, fire-resistant, antibacterial pulp foam.
Porous materials with high porosity, low density and light weight have a wide application prospect in the fields of packaging, construction, medical and health care, chemical industry and so on. With the enhancement of people’s awareness of environmental protection and the demand of “double carbon” strategy, the preparation of porous materials from renewable and biodegradable cellulose has become a research hotspot in recent years.
Pulp foam is a cheap and environment-friendly new porous material. It takes pulp fiber as raw material, and the forming mechanism is to use fast agitated surfactant to foam in pulp fiber dispersion, prevent fiber flocculation, and form a uniform porous structure. After filtering and drying, foam is produced. However, the foam materials made from pulp fibers alone are of poor strength, flammable and easily contaminated, which can not meet the requirements of practical application.
In fact, the self-supporting effect of plant cell wall is related to the firm interlocking structure between its components. Among them, trace boron ions enhance the support of cell wall by covalent bonding with oxygen-containing groups of wood fiber components. On the other hand, borate is also a common flame retardant.
Inspired by this, researchers carried out a conceptual verification experiment in the early stage. During the molding process of pulp foam, the mechanical strength of the pulp foam was greatly improved by means of the crosslinking action between boron ions and pulp fibers, and its compressive strength was 28 times higher than that of boron ion pulp foam, giving it certain flame retardant and self extinguishing properties.
In order to further enhance the mechanical strength and flame retardancy of pulp foam materials, endow them with good antibacterial properties and increase their practicality. Based on the boron ion crosslinking in the pulp forming process, the researchers continued to introduce appropriate amount of chitosan and a small amount of CPAM. The study confirmed that boron ions can form a strong covalent bond with the hydroxyl groups of cellulose and chitosan. There are electrostatic bonding and intermolecular hydrogen bonding between cellulose, chitosan and CPAM. The synergy between these components makes the mechanical strength of the pulp foam further increase. The compressive strength under the 50% strain condition is 6 times that of the boron ion crosslinking but not the chitosan and CPAM pulp foam, and is higher than most of the cellulose based porous materials reported. It is worth noting that CPAM with a dosage of only 0.5% (relative to the absolute dry weight of pulp) can replace 30% of the chitosan dosage and obtain pulp foam with the same mechanical strength, which greatly reduces the preparation cost of pulp foam. At the same time, due to the synergistic effect of boron ions, chitosan and CPAM, the pulp foam has excellent fire protection, heat insulation, antibacterial and sound absorption. Its low density (52.65 mg/cm3), high mechanical strength and good thermal insulation (thermal conductivity 0.068 W/ (M. K)) have been compared with commercial fire resistant mineral wool, porous inorganic materials and foam glass products. In addition, the filtrate produced in the process of foam preparation can be completely recycled to ensure that the process is clean and has the potential of large-scale application.
It is reported that the high performance pulp foam prepared in this study is expected to be applied in the fields of high quality packaging, heat insulation, photothermal conversion and sound absorption. The relevant research results were published in the journal carbohydrate polymers. The first author of the paper is Dr. Wu Meiyan of the Institute, and the corresponding authors are Dr. Liu Chao and associate researcher Li Bin of the Institute.
(Science and technology daily)
