Effects of Molecular Weight and Thermal Treatment on Wear Behavior of Polyamide 6

Abstract A series of polyamide 6 (PA 6) samples varying in their molecular weight (between 10000 and 50000) were annealed for 6 h in vacuum at various temperature (between 100 and 220°C) in order to create different morphological structures. The samples have been characterized with respect of their density, melting and crystallinity (from DSC), thermal expansion coefficient, humidity, predomination α- or γ-crystalline modification (from IR), shear melt viscosity and their tribological behaviour (the specific wear rate Ws ). It is found that density increases with increasing annealing temperature Ta but decrease with the rise of molecular weight (m.w.). The thermal expansion coefficient is more sensitive to Ta than to m.w. Contrary, shear-viscosity increases from 35 MPa for PA 6 with a m.w. of 10000 to 7200 MPa for samples with a m.w. of 50000. Concerning wear behavior it is concluded that the observed tendency for a decrease of Ws with an increase of Ta , particularly for samples with low m.w. is attributed to the formation of a more stable physical structure during annealed. This well defined tendency (except samples annealing at highest Ta ) is related to the observed drastic increase of shear melt viscosity with an increase of m.w.