纸张内部水分存在形式及其干燥特性研究

Study on Existing Forms and Drying Characteristics of Internal Water in Paper Web

中文关键词:  纸张干燥  干燥特性  低场核磁共振技术

Key Words:paper drying  drying characteristics  LF-NMR

中文摘要:

      利用低场核磁共振（LF-NMR）检测技术，对纸张内部水分存在形式及其干燥特性做了初步探索。结果表明，①依据所受束缚力的不同，纸张内部水分存在3种形式，即游离水、毛细管水和结合水；②结合水含量很少（约2%），且在干燥工段基本不发生变化，纸张干燥蒸发的主要是游离水和毛细管水，游离水所受束缚力小，干燥初期就开始大量蒸发，毛细管水所受束缚力大，在游离水蒸发完全时，才迅速蒸发；③依据蒸发水分的不同形式，以临界含水率为界，纸张干燥过程可以分为两个阶段：临界含水率以上为游离水干燥阶段，临界含水率以下为毛细管水干燥阶段。

Abstract:

      In the current study, the existing forms of internal water in paper web and its drying characteristics during drying process were preliminarily explored by using LF-NMR detection technology.The experimental results showed: ①According to the different binding forces, there are three forms of internal water in paper web, i.e. free water, capillary water and bound water.②The bound water is very little (about 2%), and it is basically unchanged during drying process.The main evaporated water during paper drying process is free water and capillary water.Free water has little restraint and it is evaporated largely at the beginning of drying.Capillary water is strongly bound and evaporates rapidly after free water is evaporated completely.③According to the different forms of evaporating water, the drying process of paper can be divided into two stages i.e.free water drying stage (the moisture content of paper is greater than critical moisture content) and capillary water drying stage (the moisture content of paper is less than critical moisture content).