Studies On Lac Bleaching Technical Improvement And The Thermal Character Of Bleached Lac

Shellac is an important natural resins, which have widely application in the national defence, paints, medicine, food, cosmetics, electrical appliances, machinery, plastics, paper and other industries because of the unique excellent performance. The application range of lac have shrank because of the impact of synthetic resin since 21st century, but it is still irreplaceable in the food, pharmaceutical, cosmetics and other high-end industrial because of the natural, green, non-toxic and non-irritating inbeing. Among the lac products, bleached lac occupied 50% market share. In this paper, the hydrogen peroxide bleaching process, sodium hypochlorite bleaching process and bleaching process sodium hypochlorite cooperate with with hydrogen peroxide was studied. In the end of paper, the thermal properties of lac resin products are investigated by differential scanning calorimetry in order to more reasonable use of the lac resin. Main contents and results are listed as follows:1 Study of production process of bleached lac(1) Hydrogen peroxide bleaching process:Three kinds of chelating agents (stabilizers), respectively, sodium citrate, sodium silicate and bitter salt, EDTA treat with the bleaching liquid before bleach of different to liquid bleach pretreatment with chelating agents (stabilizers) the amount of hydrogen peroxide dosage, temperature and bleaching time for the bleaching effect factors in a single factor experiment, by comparing the different process conditions on the yield of bleaching shellac and color index of the effects of hydrogen peroxide bleaching to determine the optimal experimental conditions:hydrogen peroxide bleaching process with chelating agent sodium citrate with the amount of sodium citrate,2g, hydrogen peroxide dosage of 10ml, bleachde temperature of 60℃, bleached time of 1h, in this condition the color index of bleached lac products is 17.5, the yield is 86.6%. Hydrogen peroxide bleaching process with chelating agent Sodium + magnesium sulfate, with the amount of the sodium + magnesium sulfate 1.5g respectly, hydrogen peroxide dosage 8ml, bleached temperature of 60℃, bleachied time of 1h, in this condition the color index of bleached shellac products is 17.4, the yield is 85.4%. EDTA chelated hydrogen peroxide bleaching with the EDTA dosage of 1 g, hydrogen peroxide dosage of 1 Oml, bleached temperature of 60℃, bleached time of 1h, in this condition the color index of bleached shellac is 17.3, the yield is 85.3%.(2) Research of Sodium hypochlorite bleaching process:yield as target, three factors, the temperature of the dissolution of shellac, the concentration of shellac resin and sodium carbonate concentration are employed to assess the effect to yield of shellac,respectly. After the single-factor experiment, the optimum conditions for the shellac dissolution is:dissolved temperature is 80℃, the concentration of shellac resin is 20%, sodium carbonate concentration is 3%, under these conditions the yield is 87%; To valued the factor to the yield and color index of bleached shellac, available chlorine content of the sodium hypochlorite, bleached temperature, sodium hypochloritedosage and bleaching time are employed. Based on the single factor experiment,3 factors and 3 levels of response surface optimization design of experiment, results showed that:bleached temperature is 22.5℃, sodium hypochlorite dosage is 109ml, bleached timeis 120min, the theoretical color index is 0.3; Bleached shellac yield and color index as an indicator of shellac phase of the titration end point analysis carried out experiments, the results show that the titration end point at pH=6 the yield can reach over 87% color index of 0.4.(3) Adding hydrogen peroxide 150ml to the shellac solution bleached by sodium hypochlorit, after 4h, the combined chlorine content is 0.38% of the bleaching shellac products.2 Differential scanning calorimetry analysis of lac resin product(1) DSC spectra of stick shellac and shellac shows two peaks, which is the heat absorbed by the lac wax caused; Heat absorption of refined bleached shellac is only one peak.(2) DSC study of shellac resin shows that the softening point of refined bleached shellac top, lac minimum;...