Process for producing refined cotton with high polymerization degree

A process for producing refined cotton with a high polymerization degree, comprising the following steps:

• material selection:
• selecting a cotton linter without impurities of non-cotton fibers, wherein the cotton linter has a fiber length of 13-15 mm and a maturity of more than 80%;
• impurity removal:
• opening and scutching the cotton linter, and removing impurities of sand, stone and cotton hulls by an impurity remover,
• impregnation:
• blending a sodium hydroxide solution with a mass concentration of 1-2.5%, an ethylenediamine tetraacetic acid with a mass concentration of 0.1-0.2%, a cyclic ketone compound with a mass concentration of 0.1-0.2%, sulfur trioxide with a mass concentration of 0.2-0.5% and hydrogen peroxide with a mass concentration of 30% to form a cooking agent, and uniformly spraying the cooking agent into the cotton linter at a liquid ratio of 1:2.5-4.0;
• pretreatment:
• compounding triethanolamine, sodium carbonate, copper sulfate and magnesium oxide in equal proportion to form a cooking compound adjuvant with a mass concentration of 0.2-0.5%, putting the cooking compound adjuvant into a spherical digester together with the cotton linter subjected to the impregnation treatment, heating to 70° C., stopping heating, and subjecting to idling pretreatment for 40-60 min;
• cooking;
• wherein,
• a first stage of temperature rise:
• uniformly raising the temperature of the spherical digester to 100-110° C. for a temperature rise time controlled within 30-40 min;
• a second stage of temperature rise:
• then uniformly raising the temperature of the spherical digester to 120-130° C. for a temperature rise time controlled within 20-30 min, and keeping at this temperature for 20 min;
• cooling of the spherical digester:
• quickly cooling the interior of the spherical digester by pouring condensed water at 10-15° C. into the spherical digester, so that the pressure in the spherical digester drops to zero within 8-15 min and the temperature drops below 60° C., opening a covering cap of the spherical digester to recover alkali liquor and pouring out cotton pulp, and putting the cotton pulp into a container filled with water at a room temperature for cooling;
• formulating a chlorine dioxide bleaching stabilization solution;
• wherein,
• (1) taking 75-90 parts of deionized water, 2-4 parts of aminoalcohol, 1-2 parts of polyaminoamide, 0.5-1.5 parts of polyvinylpyrrolidone, 0.5-1 part of ethylenediamine tetraacetic acid, 5-8 parts of phosphate and 2-3 parts of potassium hydrogen phthalate, mixing them at the aforementioned proportion of parts by weight, adding into a buffer tank and stirring for 15-60 min, and allowing to stand for 1-2 h to formulate a buffer absorption solution;
• (2) preheating a chlorate solution with a mass concentration of 30-40% and a hydrochloric acid solution with a mass concentration of 30-40% to 50-65° C. respectively, and adding the chlorate solution and the hydrochloric acid solution dropwise into a reactor continuously according to a mass ratio of 1:0.8-1.5, to generate a mixed gas of chlorine and chlorine dioxide;
• (3) pumping the generated mixed gas of chlorine dioxide and chlorine into the buffer tank in a manner of negative pressure of 0.05-0.08 MPa, circulating for 30 min-60 min, and fully contacting the generated mixed gas with the buffer absorption solution, so that the mixed gas is completely absorbed by the buffer absorption solution to prepare a stable chlorine dioxide bleaching solution with a pH controlled at 7-8;
• and
• (4) sealing the stable chlorine dioxide bleaching solution for storage at a temperature of 15-25° C.;
• a first stage of bleaching:
• washing the cotton pulp after cooking with water for the first time, and conducting first bleaching of the cotton pulp with ethylenediamine tetraacetic acid with a mass concentration of 99.9% and a chlorine dioxide solution with a mass concentration of 1-2% for a time of 20-30 min,
• alkali treatment:
• washing the cotton pulp with water for the second time, filtering to dryness, controlling a pH value at 10-12, and performing alkali treatment with a sodium hydroxide solution with a mass concentration of 30% and a magnesium carbonate solution with a mass concentration of 0.02-0.5% for a time of 10-20 min;
• a second stage of bleaching:
• washing the cotton pulp with water for the third time, and conducting second bleaching with a chlorine dioxide solution with a mass concentration of 0.1-0.2% for a bleaching time of 10-20 min, wherein 0.05-0.1% of sodium hypochlorite and 0.01-0.5% of amino hydroxy acid are added in the process of bleaching;
• dechlorination:
• washing the cotton pulp with water for the fourth time, conducting dechlorination treatment with a Na2S2O3 solution with a mass concentration of 25-30%, washing the cotton pulp with water for the fifth time, and controlling a pH value between 6.8 and 7.0, so as to form a bleached cotton pulp;
• and
• rolling and drying by baking:
• rolling the bleached cotton pulp for dehydration, and finally drying by baking to obtain a finished product with a polymerization degree up to more than 2,800.