Carboxymethyl cellulose (CMC) is obtained from Vietnamese pineapple leaf waste through etherification. By treating pineapple leaf powder with a solution of NaOH then with HNO₃ at 90°C for an appropriate time, cellulose can be efficiently extracted. To obtain CMC, carboxymethylation was performed by reaction of the pineapple cellulose with chloroacetic acid at 60°C for 1.5 h. The optimal conditions for this reaction were established. The resulting CMC had a degree of substitution (DS) of 0.91. The hydrogel was prepared by graft copolymerization of acrylic acid and acrylamide to the synthesized CMC. During that reaction, N,N′methylenebisacrylamide (MBA) served as the crosslinking agent and ammonium persulfate (APS) as the initiator. The maximum hydrogel absorbencies for distilled water and 0.9 wt.% NaCl solution were relatively high, namely, 588.2 g/g and 79.3 g/g, respectively. Additionally, the water swelling and water retention behaviors of the hydrogel in soil were also investigated. The results showed that this hydrogel can be employed as a suitable moisture-holding additive in soil for cultivation purposes.

中文翻译：

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越南菠萝叶废羧甲基纤维素合成水凝胶的研究

羧甲基纤维素（CMC）是从越南菠萝叶废料中醚化获得的。通过先后用NaOH溶液和HNO ₃处理菠萝叶粉在90°C下适当的时间，可以有效地提取纤维素。为了获得CMC，通过使菠萝纤维素与氯乙酸在60°C下反应1.5小时来进行羧甲基化。确定了该反应的最佳条件。所得CMC具有0.91的取代度（DS）。通过将丙烯酸和丙烯酰胺接枝共聚到合成的CMC中来制备水凝胶。在该反应过程中，N，N'亚甲基双丙烯酰胺（MBA）作为交联剂，过硫酸铵（APS）作为引发剂。对于蒸馏水和0.9重量％的NaCl溶液的最大水凝胶吸收能力相对较高，分别为588.2g / g和79.3g / g。此外，还研究了水凝胶在土壤中的水溶胀和保水性能。