A new research carried out by Enneti et al aims to understand the evolution of shape loss during polymer burnout. Polymers are used as process aids during component shaping from particulates in processes such as die compaction, tape casting, slip casting, injection molding, and extrusion. The polymers provide lubrication between the particles, extend tool life, improve particle packing, assist in flow, and generally increase the handling strength of the compacted powder. Following the shape-forming stage, polymers are typically removed from the components by heating. Polymer burnout is the widely applied method of polymer removal and is commonly termed thermal debinding. This thermal debinding or burnout process is a delicate procedure, since it can be easily cracked, blistered, slumped, or otherwise damaged.
The study, published in the International Journal of Powder Metallurgy, is the first report of shape loss during polymer burnout being observed in situ in the field. The results revealed that shape loss to occurred primarily due to viscous creep during the softening of the polymer. In addition, a recovery of shape loss was observed on burnout of ethylene vinyl acetate (EVA).
The recovery of shape loss was attributed to the burnout characteristics of EVA. During the first stage burnout, EVA degrades to form acetic acid and polyethylene co-polyacetylene. The polyethylene co-polyacetylene forms with a carbon-carbon double bond. The phase change due to the formation of polyethylene co-polyacetylene was attributed to the recovery of distortions during the first stage of polymer burnout. The recovery of shape loss was found to be absent for injection molded samples in which the burn out of the polymers occurred without the formation of double bond products. The research study shows that the shape loss during burnout depends on the degradation behavior of the polymer, and that shape loss during polymer burnout can be minimized by selecting polymers that degrade by yielding carbon-carbon double bond products.
Story provided by Dr Ravi K Enneti.