Molecular Simulation Study On Oxidation And Hydrolysis Of Amorphous Region Of Cellulosic Insulation Paper In Power Transformer

With the rapid development of UHV power grid in China, the ever higher voltagegrade stress more on power transformer insulation and anti-aging properties. Celluloseinsulation paper is the main solid insulation material in power transformers. In thelong-term run, the mechanical and electrical properties of insulation paper irreversiblydecline when subjecting to electric, thermal field, water, organic acids, oxygen,mechanical force. Thus, jeopardizing the safety of the power transformer. In order toassessing insulating condition,predicting life span of insulation materials and guidingmaterials modification, a better understanding on the degradation mechanism ofinsulating paper is important academically and practically.The oxidation and hydrolysis are two important reactions in the aging process ofcellulose insulation paper. In early stage, the active group in the insulating paper will beoxidized to generate the oxidized cellulose; a synergistic effect between H+ions andwater will lead to glycosidic bond breakage, resulting in decrease in polymerizationdegree and mechanical properties of the insulating paper. In last decades, scholars athome and abroad conducted a wide range of experimental studies on the oxidation andhydrolysis, and gradully realize the important role of oxidation and hydrolysis in theinsulating paper aging, but the study on structural properties,chemical reactions relatedto the physical and chemical disciplines, the experimental techniques have its limitation.The computer simulation technology developed in recent decades provides a new wayto study the aging mechanism.In this paper, molecular dynamics and quantum chemistry method are adopted tocalculate the modeling molecules related to the oxidation and hydrolysis of theinsulating paper, and fully take into account a variety of factors such as temperature,moisture, acid and oxidizer, natural cellulose and oxidized cellulose. Chemical reactiveand active sites, the impact of oxidation on cellulose structure and properties, thehydrolysis of cellulose are analyzed. The research achievements are as follows:1. Quantum chemistry method is utilized to study chemical reactivity and activesites of natural cellulose and oxidized cellulose. The results showed that the stability ofoxidized celluloses decreased resulted from carbonyl group. The primary hydroxyl,secondary hydroxyl groups, which are prone to react with aging factor,are the mostactive sites in cellulose. The ozone, one of partial discharge products, have strong oxidation ability, so does hydrogen peroxide. H ions and hydronium ions,with highcatalytic ability,are likely to obtain electrons from cellulose. This may lead to ruptureof pyran ring or breakage of glycosidic bond, which pose a serious threat to thestructural stability of insulating paper. Formic acid and water molecule have similarreaction ability, and the catalytic effect of copper ions is limited.2. Molecular dynamics method is using to study effects of oxidation on propertiesof amorphous region of cellulose,such as density, mechanical parameters, hydrogenbonds network, and a glass transition temperature.The results show that the density mayincrease or decrease depending on the oxidized cellulose.There is a linear correlationsignificantly between mechanical properties and hydrogen bonds.Besides, mild oxidizedcellulose will produce6-carboxycellulose,with improvement in mechanicalproperties,while deep oxidized cellulose will destroy the mechanical properties ofmaterials. Moreover,oxidation of the cellulosehave low glass transition temperature, itproves the thermal properties of materials become worse.(3) Molecular dynamics method is using to study hydrolysis of natural celluloseand four oxidized cellulose.The presence of water and hydronium promote thehydrolysis of natural cellulose,nor does formic acid. The oxidized cellulose have lowpotential difference,it means oxidation of cellulose make paper less likely to hydrolysis,which have good agreement with experiments. The impact of formic acid, watermolecules, hydronium different on their hydrolysis vary. With increase in watermolecules, Binding capacity between cellulose chain and each water molecule decline,so there a increase infree water and a decrease in the chemically combined water.Theproliferation of small molecules faciliate the hydrolysis reaction of the insulation paper.