Vegetable oils-based polyols prepared by epoxidation-hydroxylation often have the phenomenon of the coexistence of epoxy and hydroxyl groups due to different ring-opening degrees. The acylation method recommended by the American Society of Testing Materials (ASTM) standard (D1957-86) and the Association of Official Analytical Chemists (AOAC) standard (965.32) is applicable only to fatty alcohols in oils and fats and their derivatives but not to vegetable oils-based polyols since the residual epoxy groups in vegetable oils-based polyols lead the tested hydroxyl value (OHV) to be higher than the actual OHV. A method combining ring-preopening of residual epoxy groups, ether extraction of ring-preopened vegetable oils-based polyols, and subsequent acetylation by acetic anhydride-acetic acid was established for OHV determination of vegetable oils-based polyols. The accuracy of the method was verified by the known theoretical OHVs of short-chain alcohols and simulated vegetable oils-based polyols. The absolute values of relative deviations for OHVs of short-chain alcohols and simulated vegetable oils-based polyols were within 1.0% and 3.1%, respectively, which indicates the feasibility of the established method in eliminating the negative effects of residual epoxy groups in vegetable oils-based polyols on OHV determination as well as accurately determining and evaluating the OHV of vegetable oils-based polyols. The method can broaden the range of OHV determination up to 1800 mg KOH/g. The ratio of acetic anhydride and acetic acid and reaction time are key factors affecting the complete degree of acetylation, which can be regulated mutually in accurately determining the OHV of vegetable oils-based polyols according to the practice. It is the first time, to our best knowledge, to establish a method to eliminate the negative effects of residual epoxy groups in vegetable oils-based polyols on OHV determination. The established method provides a feasible method for polyol industry to accurately evaluate the product quality of vegetable oils-based polyols.

中文翻译：

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预开环溶剂萃取乙酰化法测定植物油多元醇羟值

环氧化-羟基化制备的植物油基多元醇由于开环程度不同，常出现环氧基和羟基共存的现象。美国材料试验协会（ASTM）标准（D1957-86）和官方分析化学家协会（AOAC）标准（965.32）推荐的酰化方法仅适用于油脂及其衍生物中的脂肪醇，不适用于油脂中的脂肪醇。植物油基多元醇，因为植物油基多元醇中残留的环氧基团导致测试的羟值（OHV）高于实际OHV。建立了残余环氧基团预开环、预开环植物油基多元醇的醚萃取和随后的醋酐-乙酸乙酰化相结合的植物油基多元醇的OHV测定方法。通过已知的短链醇和模拟植物油基多元醇的理论 OHV 验证了该方法的准确性。短链醇和模拟植物油基多元醇的OHV相对偏差绝对值分别在1.0%和3.1%以内，表明该方法消除植物油中残留环氧基团负面影响的可行性基于植物油的多元醇的 OHV 测定以及准确测定和评估基于植物油的多元醇的 OHV。该方法可将 OHV 测定范围拓宽至 1800 mg KOH/g。醋酐与乙酸的比例和反应时间是影响乙酰化完全程度的关键因素，可以根据实际情况相互调节，以准确测定植物油基多元醇的OHV。据我们所知，这是第一次建立一种方法来消除植物油基多元醇中残留环氧基团对 OHV 测定的负面影响。所建立的方法为多元醇行业准确评价植物油基多元醇的产品质量提供了可行的方法。