紫胶树脂在氨水中的溶解性及其铵盐的理化性质

Solubility of Lac Resin in Aqueous Ammonia and Physico chemical Properties of Its Ammonium Salt

使用化学法对紫胶树脂羧基进行改性,制备水溶性紫胶树脂铵盐。在40℃条件下测定紫胶树脂在氨水中溶解量与可溶性固形物(TDS)含量值和pH值的关系,并对紫胶树脂与氨水反应机理进行研究,对紫胶树脂及紫胶树脂铵盐进行理化性质表征对比分析。结果表明:紫胶树脂与氨水反应实质是RCOOH和NH3·H2O的反应,生成紫胶树脂羧基铵盐。氨水浓度为0.1mol/L、反应温度为40℃时,紫胶树脂的转化率为62.90%。紫胶树脂铵盐膜在pH5.0时溶胀率高达275.03%,pH7.0时溶解率可达67.04%,相对于紫胶树脂膜更易溶于酸性水环境;穿刺强度为未改性前的4.82倍,韧性提高了64.50%。紫胶树脂铵盐软化点提升了10℃以上,耐热性有显著提升。

To improve the hydrophilicity of lac resin and broaden its application in the food industry, a chemical method was used for preparing carboxyl-modified lac resin. Lac resin ammonium salt was prepared to improve the solubility. The relationship between the quantity of dissolved lac resin and either total dissolved solids （TDS） or pH at 40℃ was elucidated as well as the reaction mechanism between lac resin and aqueous ammonia. The physico-chemical properties of lac resin and its ammonium salt were compared. The results indicated that the reaction between them was essentially an acid-base neutralization reaction between RCOOH and NH3 · H2O, leading to generation of water-soluble strong electrolytes. At the ammonia concentration of 0. 1 mol/L, 62.90% of the lac resin was achieved after reaction at 40 ℃. The swelling ratio of lac resin ammonium salt film was as high as 275.03% at pH 5.0, and dissolving ratio was up to 67.04% at pH 7.0. In addition, it was more soluble in acidic water than lac resin. The puncture intensity was 4.82-fold higher than that of lac resin, accompanied with a 64.50% increase in toughness. The softening point of lac resin ammonium salt was elevated by over 10 ~C and it had significantly better heat resistance when compared to lac resin.