The degradation and stability of polymer binders in feedstock for metal injection moulding (MIM) have been rarely investigated. Feedstock is a mixture of polymer constituents and metallic powder and is subject to variations in temperature and the complexity of its mechanical effects. The mixture is pressed and squeezed in a mixer with two counter-rotating screws and injected into the mould cavities. This paper investigates the degradation and stability of polymer constituents under the conditions of mixing and injection. The interactions among different constituents were measured and analysed. The methods and application of the equipment are introduced with sufficient detail. The kinetics of decomposition for poly(ethylene glycol) (PEG) are studied to explain the mechanism of its degradation. The measurement of the carbonyl group resulted in a quantitative discussion of the decomposition. The effects of PEG degradation on its behaviour were also investigated and found to show benefits for the metal injection process. Moreover, it is proved that the combination of PEG and polypropylene (PP) is not favourable for a homogenous binder. Thus, other constituents should be found to use instead. The research reveals the degradation and stability of polymer binders under conditions of MIM technologies. It provides a reference for the choice and validation of MIM binder constituents. (C) 2015 Elsevier B.V. All rights reserved.