Oxidation of polyvinyl alcohol fibres in the presence of phosphorus-containing compounds

Abstract

The oxidation temperature-time regime that results in carbon fibre materials (CFM) The study of deep thermal transformations of polymer fibres is of both scientific and practical interest. From a scientific point of view, despite the publication of a number of generalizing studies [1][2][3], it must be acknowledged that some characteristics of the processes that take place in thermolysis of polymers have not yet been sufficiently investigated. Such characteristics in particular include the features of the effect of inorganic additives on thermal transformations of the polymer. From a practical point of view, fabrication of carbon fibres (CF) with interesting new properties can in this way be hypothesized [4].Thermal oxidation of polyvinyl alcohol (PVA) fibres in the presence of inorganic salts --mono-and diammonium phosphate -is examined in the present article. Loss of thermoplasficity by the fibre, the yield of CF in carbonization, and the elasticity of the carbon fibre materials (CFM) obtained were the criteria in selecting the parameters of the oxidation process, i.e., the temperature and duration which ensure the most complete occurrence of dehydration and cross-linking of the polymer.The phosphorus-containing compounds were applied on the fibre by impregnation with 2-5 % aqueous solutions of the salts with subsequent wringing out of the fibre in a padding machine to a 100% degree of wringing. After wringing, the fibre was dried in air at room temperature for 24 h. Thermooxidation was conducted while heating from 20"C to the selected temperature at a temperature elevation rate of 2*C/rain and subsequent holding for the def'med time. Before thermooxidation, the fibre samples were dried at 110-115~ for 4-5 h to eliminate the possibility of destructive oxidative processes under the effect of moisture.Carbonization was conducted on a laboratory setup in a nitrogen current with a rate of heating from 20 to 450~ of 3~ and from 450 to 900~ at the rate of 10*C/rain. The holding time at 900"C was 30 rain. The thermal properties of the oxidized fibres were investigated by differential thermal (DTA) and thermogravimetric (TGA) analysis while heating the sample in air medium and the characteristic products of decomposition at a temperature elevation rate of 10*C/min on a Paulik-Paulik-Erdey derivatograph and by elemental analysis on an EA 1108 CHNS-0 instrument from Carlo Erba Instruments.The IR spectra were made on a Specord M 80 Carl Zeiss Jena spectrophotometer in the 200-4000 era-1 spectral range. The concentration of double bonds in the polymer was determined by the chemical method based on the "bromine number."As indicated in [3], PVA fibres are oxidized beginning at a temperature of --180"C. The data in Fig. 1 show that in the presence of phosphorus-containing compounds, significant weight loss of the polymer begins at 170"C and becomes more intense when the temperature is increased to 200"C. A comparison of curves 2 and 3 indicates that diammonium phosphate is a more effective agent in this case, since it cause...

Synthesis of poly(1‐oxodimethylene) via oxidation of poly(vinyl alcohol) with a hydrogen peroxide/hydrobromic acid system and metal complexation behavior of poly(1‐oxodimethylene)

“…Because ketenes are very toxic and unstable, oxidation of PVA is more accessible. The reported methods for oxidation of PVA are enzymatic oxidations with enzymes such as pseudomonas vesicularis , chemical oxidations with Ce, Cr, [NH 4 ] 2 HPO 4 , oxoammonium salt (1‐oxo‐4‐methoxy‐2,2,6,6‐tetramethylpiperidinium chloride), and permanganate oxidants, and electrochemical oxidation using a RuO 2 /Ti anode . These reported oxidations involved some disadvantages.…”