Accuracy measurement of grafting degree of radiation-induced surface graft polymerization by weighing

Abstract

Weighing by an electron analytical balance is one of the simple and direct methods to measure the grafting degree of a polymer, usually defined as: where G m, w a, and w b represent the grafting degree, the weights of sample after and before grafting, respectively. However, the measured grafting degree by weighing is not accurate due to omission of the weight losses during radiation and surface-graft copolymerization in the reaction media. In this paper, corona discharge-induced surface graft copolymerization of acrylic amide (AAM) onto biaxial oriented polypropylene (BOPP) was studied. The results show that the weight losses during corona-discharge treatment and copolymerization in the AAM solution are quite high compared to the measured grafting degree. The weight loss increases with treatment time, AAM concentration, reaction time, and temperature. The measured grafting degrees according to Eq. 1 are all less than zero and decrease with the reaction time and AAM concentration in the reaction solution, conflicting with the x-ray photoelectron spectroscopy (XPS) and infrared (IR) spectra of our previous work [1]. After adding the weight losses, the true grafting degree increases with reaction time and AAM concentration, in agreement with the rule of common graft polymerization. The true grafting degree must be described as: where G t, G m, G i, and G s represent the true grafting degree, measured grafting degree as described in Eq. 1, weight loss during irradiation, and weight loss in the reaction media in wt% based on the initial weight, respectively.