The emergence of 3D printing technologies is revolutionizing the way that industry, consumers, and academic entities approach product design. In 2016 the worldwide market share for 3D printing was ~$5 billion USD, which has now surpassed to over $7 billion USB as of 2018. The market for 3D printing is expected to grow, with projections reaching over $26 billion USD in as little as 3-years (by 2021). To this end, it is necessary to develop a more diverse library of 3D printable polymer filaments that are low-cost, available in abundance, and recyclable. Thermoplastics such as semi-crystalline polypropylene and polyethylene meet all of these criteria but are susceptible to warping due to their inherent crystallization kinetics. Thus, the overarching objective of the project proposal is to employ chemical or physical methods to greatly reduce or eliminate warping in semi-crystalline thermoplastics following filament formation and printing. Filaments and printed semi-crystalline thermoplastics that have low crystallite ordering will be less susceptible to warping. Presented are 3 modes of modification (2 physical, 1 chemical) known to influence the degree of crystallization: (i) cooling rate, (ii) addition of filler(s), and (iii) the molecular architecture in terms of the polymer’s tacticity. (i) cooling rate that is even throughout printed material will have less warping. If the cooling rate is homogeneous and fast, then less shrinkage also occurs. (ii) talc is a common additive to improve bulk polymer properties; the degree of warp is evaluated as a function of 0.1 wt% - 25 wt% talc. (iii) decreasing the isotacticity of the polyolefin (or increasing the branching in the case of polyethylene) will reduce crystallization, but will also reduce the material’s modulus making filament extrusion and printing quality poor. The later may be solved through the introduction of optimized talc from approach (ii). Outcomes will be discussed based on data collected from differential scanning calorimetry, dynamics mechanical analysis, scanning electron microscopy, and 3D printed samples.

Low crystallite phase ordering in semi-crystalline polymer filaments: A low-cost, translational route to reduce warp in fused deposition modeling 3D printing applications

2019 Spring National Meeting

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