台式小核磁共振波谱法测定聚乙烯密度

Determination of polyethylene density by table-top small nuclear magnetite resonance spectroscopy

以密度梯度柱法测得的线型低密度聚乙烯(LLDPE)试样的密度为标准,建立了台式小核磁共振波谱法(简称小核磁法)测试LLDPE密度的标准曲线,分析了试样存放时间、恒温测试温度、存放温度对小核磁法准确度和重复性的影响。实验结果表明,存放时间60~120 d的LLDPE试样可用作标准试样;恒温温度分别为35.0℃和34.5℃时,小核磁法测得的密度与密度梯度柱法得到的密度较吻合。造粒后LLDPE立即在-23℃下冷冻后可用于建立标准曲线。利用标准曲线,对生产装置取出的试样立刻用小核磁法测试密度,结果满足重复性与准确度的要求。小核磁法测密度快速且可批量测试,节省人力和时间,维护简单,健康环保。利用LLDPE粒料存放时间与小核磁法密度的关系表,可通过小核磁法快速准确测定已知生产时间的LLDPE的密度。

Using the density of linear low-density polyethylene(LLDPE)samples tested by density gradient column method as the standard,the standard curve for determining LLDPE density by table-top small nuclear magnetic resonance(NMR)method was established,and the effects of sample storage time,testing constant temperature and sample storage temperature on the accuracy and repeatability of small NMR method were analyzed.The experimental results show that the LLDPE samples stored for 60-120 d can be used as standard samples,and when the constant temperature is 35.0℃and 34.2℃,the density determined by small NMR method is consistent with that obtained by density gradient column method.After granulation,LLDPE is immediately frozen at-23℃and can be used to establish standard curve.Using the standard curve,the density of the samples taken out from the production device was immediately determined using the small NMR method,and the results met the requirements of repeatability and accuracy.Small NMR method for density determination is fast and can be tested in batches,saving manpower and time,simple maintenance and healthy and environmentally friendly.Using the relationship table between the storage time of LLDPE particles and the density by small NMR method,the density of LLDPE with known production time can be determined quickly and accurately by the small NMR method.