Impact strength of nylon 6 and 66 in the dry and moist states

Abstract

The impact strength of nylon was determined by the modified Charpy test with double-V notches described in DIN 53753, because it cannot be reliably assessed by the notched Charpy and Izod tests. This test was adjusted to obtain a sensitive, accurate and reproducible method for the determination of impact strength in the dry and moist states. In the light of the criterion thus gained, it is shown that the dry “as-moulded” state is unstable and that the impact strength decreases exponentially with storage timE. Therefore, comparison tests are not valid unless the measurements are performed within a restricted period of time after the specimens had been demoulded. If the age of the specimens is unknown, a reproducible “as-moulded” state can be regenerated by an annealing procedure. The state of “conventional” moisture content that is taken as a reference for comparing data obtained on moist nylon is the equilibrium moisture content in a standard laboratory atmosphere. Various methods are discussed for attaining this state rapidly by accelerated conditioning. An atmosphere of 70‡ C and 62% relative humidity allows accurate adjustment to the “conventional” moisture content but does not result in a stable reference state; for instance, the impact strength decreases within several weeks after conditioning.