| In this article many important injection parameters including melt temperature, mold temperature, injection speed, screw speed, back pressure, holding pressure, holding time, cycle time, dwell time were studied to see their influence on ageing performance and mechanical properties of PA66, PP, and PBT. Argon was used or local used in the injection molding process to get some information about the effect of inert gas on ageing. Also effect of specimens' size and accelerated ageing were investigated. Polarizing microscopy, viscosity number measurement, DSC and tensile test were used to study the micro-morphology, change of average molecular weight and macroscopic mechanical properties.First of all the influence of injection parameters on ageing was investigated. It is concluded that melt temperature plays the most important role in degradation and other properties of polymer materials. With increasing melt temperature, degradation increases known from the results of viscosity number for PP, PA66 and PBT leading to a decrease of mechanical properties. And dwell time has much influence on degradation. It was discovered that smaller specimens are more sensitive to the change of injection conditions and have more ageing degree.As the inert environment to be concerned, it was observed that use of argon can get ride of oxygen to reduce the ageing degree especially for the specimens molded at high melt temperature. Also use of inert injection environment can increase the average molecular weight of aged samples of PA66. It is concluded that drying in argon is a convenient, cheap, and effective method to reduce degradation.It can be known from the results of accelerate ageing that accelerated ageing in an ageing oven can change both the physical and chemical structure of plastics, and decrease the mechanical properties of specimens much. Duo to the coexistence of chains scission and crosslinking, viscosity for PA66 increases to 50%, but for PP and PBT the viscosity number decrease much.
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