Water or moisture absorption is important in determining the value of industrial laminates as a control of the uniformity of the product, affects the mechanical, electrical and chemical properties of the laminate and has a bearing on a laminate’s appearance and dimensional stability.
Water absorption is tested according to ASTM D 570-57T. A 1” x 3” x thickness test specimen is immersed in water 24 hours @ 23°C. It is weighed before, after the test period and the water absorption rate recorded as a percent of the sample’s original weight.
This method of recording water absorption can lead to false interpretations. Various laminate formulations of different specific gravities will differ in weight and actually represent a considerable difference in percentage increase by weight. An absorption of 1 gram for a test specimen of Lamitex G5 glass melamine weighing 100 grams would be recorded as 1% absorption. A same size test specimen of Lamitex CE weighing 66.5 grams and absorbing the same amount by weight of water, 1 gram, would be reported as a 1.5%.
There are a number of water absorption factors that should be considered. While water absorption measurement is based on 24 hours immersion at 23°C, none of the laminates become fully saturated in that time. Saturation may require immersion for as long as 6 months. Also, the thicker the test specimen, the less water is absorbed in 24 hours as a % by weight and raising the water temperature will increase the rate of absorption but not the quantity of water absorbed. The thicker the wall of a tube or the larger the diameter of a rod, the less water will be absorbed in 24 hours as a % by weight. Therefore, material dimensions and thickness greatly influence the rate of water absorption.
Low or the minimal moisture absorption rate for each laminate formulation, a key property in the material selection process, is accomplished with strict manufacturing process controls. Established resin content, volatile content and % of flow, times, pressures and process temperatures are audited for all laminate productions to ensure they meet published performance expectations.
Low water absorption rates are essential in mechanical applications to insure the lowest possible dimensional changes and least possible insulation degradation for electrical application in high humidity conditions.
Low moisture absorption is equally important to chemical resistance. Generally speaking, the lower the water absorption, the better chemical resistance to acids and alkalizes.