Concluding Remarks by Prof. Linda Wang
AIChE Annual Meeting
Tuesday, November 12, 2019 - 10:20am to 10:30am
Fused filament fabrication (FFF) of polymers is a 3D additive manufacturing technique that places filaments or tracks one on top of each other to build a three dimensional object. The challenge is two-fold; the weld strength is low resulting in poor mechanical properties and speed of manufacture is dictated by melt flow instabilities such as sharkskin. Sharkskin appears at a critical stress level and is the result of stress relief at the exist of a die. We have used processing aids to reduce sharkskin allowing faster manufacture for poly(lactic acid) or PLA. Contemporary aids are used with polyolefins and these were found to be effective with PLA and in the presentation optimization of their utility will be discussed. Low weld strength can be overcome by thermal annealing of a printed part to induce macromolecular diffusion across the interface, however, this can lead to warping and sagging of the part in general. One could print at higher temperatures to promote diffusion, yet, this leads to a poor part either due to polymeric degradation or the features are simply not as sharp due to sagging during printing. To overcome this limitation, we print two different polymers together, by using two hot ends, simultaneously printing a low temperature polymer (LTP) and a high temperature polymer (HTP). The LTP is the majority of the printed part and constitutes the integrity while the HTP is strategically printed to heat up deposited LTP tracks promoting annealing during the print. This process is called in process thermal annealing and dramatically improves part strength. In addition, a functional material of unique properties is manufactured being a composite of two chemically distinct materials.