树脂酸组成和松香结晶

<正>马尾松松脂的树脂酸部分包括:海松酸,山达海松酸,异海松酸,左旋海松酸,长叶松酸,枞酸,新枞酸和脱氢枞酸。松脂在加工过程中、海松酸型酸变化不大,枞酸型酸则发生较大的变化。在140°—200℃煮炼松香时,左旋海松酸不断减少,长叶松酸,新枞酸和枞酸不断增加。在松香冷却过程中,枞酸型酸继续异构化,长叶松酸和新枞酸逐渐减少而导致枞酸自始至终不断增加,这是马尾松松脂在现有生产工艺条件下树脂酸异构变化的客观规律。 利用树脂酸的异构规律,树脂酸组成与比旋值和结晶趋势的关系,控制松脂蒸馏(温度和时间)和冷却的工艺条件,可以得到比旋值在适宜范围内,结晶趋势最低的优质松香。松香的比旋值是松香结晶趋势的有效指标。以福建尤溪松香为例,长叶松酸与枞酸含量比在1:1.5～1.8时,比旋值+4°～+12°,结晶趋势接近于0％。各地松香均有一结晶趋势最低和最佳比旋值范围。 防止松香结晶现象,除了控制树脂酸组成的主要内因外,尚须注意外界气温、晶种、水份、添香、震动等引起松香结晶的外在因素。

THE COMPOSITION OF RESIN ACIDS AND CRYSTALLIZATION OF ROSIN

The resin acid fractions of Oleoresin of Pinus mossoniana consist of pimaric acid, sandaracopimaric acid, isopimeric acid, levcpimaric acid, plustric acid, abietic acid, neoabietic acid and dehydroabietic acid. During processing of the Oleoresin, the acids of pimaric acid type do not change verg much, while the acids of abietic type undergo a lot of changes. When the gum rosin is processed at temperatures between 140℃ and 200℃. there is a gradual decrease in levopimaric acid, while the plustric, neoabietic and abietic acids continue to increase. In the cooling process of rosin, the acids of abietic acid type continue to isomerize, and plustric acid and neoabietic acid decrease gradually, with the result that the content of abietic acid increases steadily from beginning fo. end.This shows the objective law cf isomerization of resin acids for the oleoresin of Pinus mossoniana under the existing processing conditions. According to the law of isomerization of resin acids, wa can make use of the relationships between the resin acid composition, the optical rotation and the tendency to crystallize. JHence, rosin of tine quality, i. e, rosin with optical rotation within suitable range and with a lower tendency of crystallization can be obtained by controlling distillation (its temperature and time) and cooling process conditibns. The optical rotation of rosin serves as an indicator of its tendency to crystallize. Fox example, when the ratio between the plustric acid and abietic acid contents of the rosin produced in Youxi, Fujian is 1:1.5~l.8, the optical rotation range will be from +4° to +12°, and the tendency to crystallize near 0%. Rosins from; any place can have a best range of optical rotation, which will result in the minimum tendency to crystallize.To prevent rosin crystallization, except for controlling the main internal factors of resin acid composition, attention must be paid to the external factors, such as temperature of the environment, crystalline seed, moisture content, addition of hot rosin, shaking, etc., any of which can cause crystallization of rosin.