Abstract
The effect of processing conditions during injection on the structure formation and mechanical properties of injection molded polyamide 6 samples was investigated in detail. A large effect of the mold temperature on the crystallographic properties was observed. Also the the effect of pressure and shear flow was taken in to consideration and analysed. The yield and failure kinetics, including time-to-failure, were studied by performing tensile and creep tests at several test temperatures and relative humidities. As far as mechanical properties are concerned, a strong influence of temperature and relative humidity on the yield stress and time-to-failure was found. A semi-empirical model, able to describe yield and failure kinetics, was applied to the experimental results and related to the crystalline phase present in the sample. In agreement with findings in the literature it is observed that for high mold temperatures the sample morphology is more stable with respect to humidity and temperature than in case of low mold temperatures and this effects could be successfully captured by the model. The samples molded at low temperatures showed, during mechanical testing, a strong evolution of the crystallographic properties when exposed to high testing temperature and high relative humidity, i.e., an increase of crystallinity or a crystal phase transition. This makes a full description of the mechanical behavior rather complicated.
Highlights
Injection molding is the most widely used technique to produce polymeric products
The authors have investigated the influence of structural properties, temperature and relative humidity on the yield kinetics and time-to-failure of polyamide 6 processed under quiescent conditions
WAXD experiments were performed on dry samples to understand the influence of mold temperature
Summary
Injection molding is the most widely used technique to produce polymeric products. It is preferred because of advantages such as fast production cycles, cheapness and the large versatility of product shapes. The morphology of injection molded nylon 6 was reported in literature [2,6] These studies led to a common main conclusion: the metastable γ-mesophase (obtainable for moderate cooling rates [7]) is predominant near the surface of the sample, while the most stable α-phase (obtained by slow cooling [7]) takes over towards the center of the sample. The effect of this inhomogeneous morphology distribution on mechanical properties has barely been studied despite this being the most important factor for the end-users. The samples for subsequent mechanical testing were conditioned at different temperatures and different relative humidities
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