利用小核磁法测定聚乙烯密度

Determination for density of polyethylene by desktop NMR method

考察了小核磁法测定聚乙烯密度的重复性及准确性,并分别采用小核磁法与密度梯度柱法测试了高密度聚乙烯、低密度聚乙烯和线型低密度聚乙烯的密度。结果表明,采用小核磁法与密度梯度柱法测定聚乙烯密度值之差为:线型低密度聚乙烯粒料≤0.000 1 g/cm^3,线型低密度聚乙烯粉料≤0.000 2 g/cm^3;低密度聚乙烯粒料≤0.000 1 g/cm^3,低密度聚乙烯粉料≤0.000 2 g/cm^3,高密度聚乙烯粒料≤0.000 1 g/cm^3,高密度聚乙烯粉料≤0.000 4 g/cm^3。确定小核磁法测定聚乙烯密度满足密度梯度柱法要求的精密度及准确度,两种方法可以互相替换。小核磁法测定聚乙烯密度的主要影响因素有试样含水、沾油或混入其他杂质,试样预热时间不足30 min或磁体衰减,同时提出了相应的解决措施。

The repeatability and accuracy of desktop nuclear magnetic resonance(NMR)method for determination of polyethylene density were investigated.The densities of high density polyethylene(HDPE),low density polyethylene(LDPE)and linear low density polyethylene(LLDPE)were determined by desktop NMR and density gradient column methods respectively.The results show that the differences between the testing results obtained by two methods are as follows:that of LLDPE pellets is less than 0.000 1 g/cm^3,that of LLDPE powder is less than 0.000 2 g/cm^3,that of LDPE pellets is less than 0.000 1 g/cm^3,that of LDPE powder is less than 0.000 2 g/cm^3,that of HDPE pellets is less than 0.000 1 g/cm^3,and that of HDPE powder is less than 0.000 4 g/cm^3.The precision and accuracy of desktop NMR method for determining polyethylene density are identical to those of the gradient column density method required which means two methods can be replaced with each other.The factors that affect the density of polyethylene measured by desktop NMR include water,oil or other impurities in samples,the sample is preheated for less than 30 minutes as well as attenuation of magnet.The solutions are offered as well.