Chitin and Cellulose Processing in Low-Temperature Electron Beam Plasma

Plasma Treatment of Cellulose as the First Step in the Synthesis of Second-Generation Biofuel

Cellulosic ethanol has been an attractive biofuel for over a century. Despite the large scientific interest, the first step of treating cellulose before enzymatic hydrolysis is still inadequate, so the scientific community seeks innovative solutions. Among them, plasma treatment of raw cellulose represents an interesting approach. The literature on approaches to treat cellulose with gaseous plasma is surveyed, and the results reported by different authors are interpreted. Reactive gaseous particles like ions, electrons, metastables, and radicals interact chemically with the surface but do not cause significant depolymerization of bulk cellulose. Such depolymerization results from bond scission in the bulk cellulose by energetic plasma species capable of penetrating deep into the cellulose. Among them, photons in the range of vacuum ultraviolet radiation (photon energy above the threshold for bond scission) are the most suitable plasma species for the depolymerization of cellulose and the formation of water-soluble fragments, which are suitable for further treatment by enzymatic hydrolysis.

Effects of chemically reactive species generated in plasma treatment on the physico-chemical properties and biological activities of polysaccharides: An overview

Plasma technology as an advanced oxidation technology, has gained increasing interest to generate numerous chemically reactive species during the plasma discharge process. Such chemically reactive species can trigger a chain of chemical reactions leading to the degradation of macromolecules including polysaccharides. This review primarily summarizes the generation of various chemically reactive species during plasma treatment and their effects on the physico-chemical properties and biological activities of polysaccharides. During plasma treatment, the type of chemically reactive species that play a major role is related to equipment, working gases and types of polysaccharides. The primary chain structure of polysaccharides did not changed much during the plasma treatment, other physico-chemical properties might be changed, such as molecular weight, solubility, hydrophilicity, rheological properties, gel properties, crystallinity, elemental composition, glycosidic bonding, and surface morphology. Additionally, the biological activities of plasma-treated polysaccharides including antibacterial, antioxidant, immunological, antidiabetic activities, and seed germination promotion activities in agriculture could be improved. Therefore, plasma treatment has the potential application in preparing polysaccharides with enhanced biological activities.

Plasma-activated water improves the accessibility of chitinase to chitin by decreasing molecular weight and breaking crystal structure

Chitooligosaccharides, the hydrolysis products of chitin, have superior biological activities and application value to those of chitin itself; however, the ordered and highly crystalline structure of chitin renders its degradation by chitinase difficult. Herein, the effects of plasma-activated water (PAW) pre-treatment on the physicochemical properties, crystal structure, and enzymatic hydrolysis of chitin were investigated. The hydrolysis of PAW-pre-treated chitin (PAW activation time of 5 min) using chitinase from Vibrio harveyi (VhChit2) yielded 71 % more reducing sugar, compared with that from untreated chitin, with the degree of chitin hydrolysis increasing from 13 % without pre-treatment to 23 % post-treatment. Moreover, the amount of VhChit2 adsorbed by chitin increased from 41.7 to 58.2 mg/g. Fourier transform infrared spectrometry revealed that PAW could break the β-1,4-glycosidic bonds of chitin (but had no effects on the hydrogen and amido bonds), thereby decreasing the molecular weight and crystallinity of the polysaccharide, which caused its structural damage and enhanced its enzymatic hydrolysis by chitinase. Consequently, PAW pre-treatment can be considered a simple, effective, and environmentally-friendly method for the biotransformation of chitin as its easier hydrolysis yields high-value products.

Chitosan Plasma Chemical Processing in Beam-Plasma Reactors as a Way of Environmentally Friendly Phytostimulants Production

A novel technique of phytoactive water-soluble chitooligosaccharide (COS) production in low-temperature plasma is described. Design, operation, and control of plasma chemical reactors used to produce COS from the powder of high molecular weight chitosan are presented. The electron beam plasma is strongly non-equilibrium and chemically active; plasma was excited by injecting the scanning electron beam into reaction volume filled with aerosol, containing oxygen and chitosan powder. Plasma chemical processes, responsible for the raw chitosan destruction and techniques of these processes to obtain control of products of optimal molecular weight, are considered. COS, in amounts sufficient for laboratory tests with some plants, were produced. Tests showed that the addition of COS into the liquid growing medium at 0.25 and 1 mg/mL stimulates root growth in Arabidopsis thaliana seedlings (Col-0) by up to 40%, with respect to control plants. Foliar application of these COS formulations at 0.25 mg/mL on tomato plants (cv. Micro-Tom) also resulted in increases between 11.9% and 36% in two important plant productivity indicators (flower and fruit numbers) compared to the control plants. Being environmentally friendly (and resource saving) the electron beam plasma technology of renewable natural biopolymer processing can be considered as a competitive way to produce biostimulants for commercial agriculture.

The efficacy and safety of cold atmospheric plasma as a novel therapy for diabetic wound in vitro and in vivo

Cold atmospheric plasma (CAP) is a group of various chemical active species, such as ozone and nitric oxide, generated by working gas. CAP was demonstrated to have an effect on tissue regeneration and wound healing. We conducted this study to evaluate the efficacy and safety of CAP as a novel therapy for diabetic wounds in vitro and in vivo. The plasma consists of ionised helium gas that is produced by a high-voltage and high-frequency power supply. Eight-week-old male db/db mice and C57BL mice were treated with helium gas (control group), 90s' CAP (low-dose group), and 180s' CAP (high-dose group). Mice were treated and observed for 2 weeks. Skin samples from around the wound and blood samples were collected. Our in vitro analysis included scratch wound-healing assays by using human HaCaT immortalised human epidermal cells. After 14 days of treatment, CAP could obviously promote diabetic wound healing. Wound closure rates were significantly higher in the low-dose group and high-dose groups compared with the control group. Meanwhile, compared with the control group, the protein expression of IL-6, tumour necrosis factor-α, inducible nitric oxide synthase, and superoxide dismutase in two CAP groups significantly decreased, while the protein expression of vascular endothelial growth factor and transforming growth factor-β in two CAP groups significantly increased (all P < .05); these data show good agreement with the change in mRNA level (all P < .05). In vitro, scratch wound-healing assays showed that plasma treatment could effectively ensure healing within 3 minutes of exposure (all P < .05). In addition, no difference was found in histological observations of normal skin and the level of serum alanine transaminase, aspartate aminotransferase, blood urea nitrogen, creatinine, and white blood cells among the CAP groups and control group. CAP treatment for 3 minutes every day improves wound healing in diabetic mice by suppressing inflammation, reducing oxidative stress, and enhancing angiogenesis, involving several proteins signalling, and it is safe for the liver and kidney.

Novel chitosan-ethylene glycol hydrogel for the removal of aqueous perfluorooctanoic acid

It is urgent to explore an effective removal method for perfluorooctanoic acid (PFOA) due to its recalcitrant nature. In this study, a novel chitosan-based hydrogel (CEGH) was prepared with a simple method using chitosan and ethylene glycol through a repeated freezing-thawing procedure. The adsorption of PFOA anions to CEGH agreed well to the Freundlich-Langmuir model with a maximum adsorption capacity as high as 1275.9 mg/g, which is higher than reported values of most adsorbents for PFOA. The adsorption was influenced by experimental conditions. Experimental results showed that the main removal mechanism was the ionic hydrogen bond interaction between carbonyl groups (COO^-) of PFOA and protonated amine (NH⁺) of the CEGH adsorbent. Therefore, CEGH is a very attractive adsorbent that can be used to remove PFOA from water in the future.

Influence of Dielectric Barrier Discharge Treatment on Surface Structure of Polyoxymethylene Fiber and Interfacial Interaction with Cement

Polyoxymethylene (POM) fiber was treated with atmospheric dielectric barrier discharge (DBD) plasma to enhance the surface activity of the fiber and interfacial interaction with cement. The physical and chemical properties of samples with different DBD plasma treatment durations were tested and analyzed. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the surface roughness of the sample increased significantly as a result of the DBD plasma treatment. Fourier transform infrared spectrophotometer (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis showed that a large number of ⁻COH and ⁻COOH groups were formed on the surface of the sample after DBD plasma treatment. The hydrophilicity of the POM fiber was greatly improved with the increase in the treatment duration. When the treatment duration was longer than 120 s, the fiber surface contact angle decreased from 90° to 43°. The DBD plasma treatment resulted in a decrease in the tensile strength of the POM fiber, but the increase in the amount of ⁻COH and ⁻COOH on the surface of the POM fiber and the increase in the roughness resulted in an increase in the fiber pull-out bonding strength in cement from 2.15 N to 4.68 N.