The use of water containing TPO/activated carbon in injection molding

In injection molding, cycle time and sink mark are critical factors for process economics and product quality. This work focuses on reducing cycle time and sink part by utilizing water containing polymer/activated carbon pellets. Pellets were prepared by compounding a microparticle, activated carbon (AC) via extrusion, followed by a batch process of pressurizing a small amount of water into the pellets under controlled pressure and temperature. The amount of water, packing pressure and packing time were varied in the injection molding experiment. Preliminary results showed that the cycle time could be reduced to half and part shrinkage substantially decreased at a lower packing pressure without losing mechanical properties when the water content was low (e.g. 0.3 wt %). However, too much water (e.g. 2 wt %) tended to reduce mechanical properties even though the cycle time could be further reduced. We are in the process of tailoring the process conditions for optimized results, as well as evaluating the effect of residual water on the long-term properties of molded parts.