In this study, carboxymethyl cellulose (CMC) was synthesized from wheat straw cellulose by a homogeneous reaction. The main process was as follows: wheat straw was cut into 1-2 cm-long pieces, rinsed with water 3-5 times to remove dust and other impurities, and washed first with deionized water for a further 3-5 times and then with boiling distilled water. The wheat straw was then preliminarily treated for 1 h, and dried in an oven. Crushing was then performed using a high-speed grinder with a 40-mesh screen to obtain the wheat straw powder. Sodium hydroxide and hydrogen peroxide were used to treat the wheat straw powder to obtain cellulose. An alkali/urea/thiourea system was used to dissolve ZnO. The extracted wheat straw cellulose was dissolved by freezing and melt circulation, following which the cellulose was stored for 4 h at -20°C, then thawed, and a clear cellulose solution was obtained by rapid stirring in an ice water bath. The optimal composition of the alkali/urea/thiourea aqueous solution was obtained through orthogonal experiments. The orthogonal design were four factors, five levels. The four factors with five levels were sodium hydroxide (5%, 6%, 7%, 8%, and 9%), thiourea (5%, 7%, 9%, 11%, and 13%), urea (5%, 7%, 9%, 11%, and 13%), and zinc oxide (0, 0.05%, 0.1%, 0.15%, and 0.2%). After dissolving wheat straw cellulose with the optimal dissolving system, CMC samples were prepared with sodium chloroacetate. The CMC samples were characterized by Fourier transform-infrared (FTIR) spectroscopy and the degree of substitution (DS). The results can be summarized as follows: first, the wheat straw powder was treated at a solid-liquid (10% NaOH solution) ratio of 1:20 g/mL, at a reaction temperature of 85℃, reflux time of 3.5 h, and with a 10% sodium hydroxide solution, followed by treatment with a 10% hydrogen peroxide solution. For the reaction conditions of a solid-liquid (the wheat straw powder treated with 10% NaOH and 3% H2O2) ratio of 1:30 g/mL, at a reaction temperature of 85℃, and a reflux time of 3 h, the highest proportion of cellulose that can be extracted from the wheat straw was 84.61 %. The removal rate of hemicellulose was 84.44%, while that of lignin was 91.14%. In the orthogonal experiment, we assessed the influence of theR value of each factor on the experimental indicators, with a greaterR value indicating a greater impact. TheRvalues for the dissolution system (NaOH, thiourea, urea, ZnO) were 1.1907, 0.2174, 0.1708, and 0.2199, respectively; thus, the most influential factor was NaOH, followed by ZnO, thiourea, and urea with minimal impact. Variance analysis also showed that NaOH was the most influential factor, followed by ZnO. After comparing NaOH, thiourea, urea, and ZnO at the level of solubility, a comprehensive consideration of the cost and environmental factors can be developed. The optimum values of the mass fraction for the solution components were 7%, 11%, 5%, and 0.05% for NaOH, thiourea, urea and ZnO, respectively, for a total solubility of 2.8801 g. The FTIR spectra of the cellulose straw and cellulose showed characteristic absorption peaks of pure cellulose. The etherification reaction of wheat straw cellulose results in the formation of CMC. The characteristic absorption peaks of wheat straw CMC and pure CMC were very similar. The DS of CMC was dependent on the cellulose dosage, temperature, and the molar ratio of sodium chloroacetate to cellulose AGU. Increased cellulose dosage, molar ratios of sodium chloroacetate to cellulose AGU, and temperature initially increased the DS and then caused it to decrease. For a temperature of 55℃, the amount of cellulose is 2.8 g, the molar ratio of sodium chloroacetate and cellulose AGU is 10.5:1, and the DS is the highest at 0.45.%为了利用小麦秸秆通过均相反应制备羧甲基纤维素(CMC,carboxymethyl cellulose),采用氢氧化钠和过氧化氢回流加热法制备小麦秸秆纤维素.以加入氧化锌的氢氧化钠/尿素/硫脲体系为溶剂,采用冻融循环法溶解小麦秸秆纤维素,利用正交试验获得了该溶解体系的最佳组成.在溶解了小麦秸秆纤维素的氢氧化钠/尿素/硫脲/氧化锌的体系中,以氯乙酸钠为醚化剂制备CMC,并对其进行红外光谱分析和取代度(degree of substitution,DS)测定.结果表明:在固液比为1:20 g/mL,质量分数为10%NaOH,反应温度为85℃,回流3.5 h和固液比为1:30 g/mL,质量分数为3%H2O2,反应温度为85℃,回流3 h处理小麦秸秆,纤维素提取率最高为84.61%,同时能较好的脱除半纤维素和木质素;最佳溶解体系为:质量分数为7%NaOH,11%硫脲,5%尿素,0.05%氧化锌,0℃时,最大溶解度为2.8801 g.红外光谱试验表明小麦秸秆纤维素与微晶纤维素特征吸收峰基本一致,醚化反应生成的CMC与商品CMC的特征吸收峰基本一致.CMC的取代度受纤维素用量、温度和氯乙酸钠与纤维素葡萄糖单元(AGU,anhydroglucose unit)的摩尔比影响,随纤维素用量和氯乙酸钠与纤维素AGU的摩尔比增大而提高,随醚化温度的增加先增大(<55℃)后降低.研究结果为以小麦秸秆为原料,经NaOH和H2O2处理获得纤维素,溶解在加入氧化锌的氢氧化钠/尿素/硫脲体系中,与氯乙酸钠经过均相醚化反应合成取代度较高的CMC提供参考.
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