REVIEW Designing polymer crystallinity: An industrial perspective Daniela Mileva | Davide Tranchida | Markus Gahleitner Borealis Polyolefine GmbH, Innovation Headquarters, 4021, Linz, Austria Correspondence Markus Gahleitner, Borealis Polyolefine GmbH, Innovation Headquarters, 4021 Linz, Austria. Email: markus.gahleitner@borealisgroup.com Abstract More than 50% of the thermoplastic polymers applied globally are semi-crystalline, making crys- tallization part of the material and component design process for these materials. The mechani- cal and optical performance, but also the long-term stability of the final articles and applications will depend upon three major groups of influence factors: Polymer structure and monomer com- position, additive addition (especially nucleation) and blending with secondary components, and processing parameters. In the present review, we try to establish a connection between these three areas, the resulting combination of crystallinity and morphology, and the final application properties. Examples are drawn from the two major polyolefins, polyethylene and polypropyl- ene, technical polymers like polyamide and polyester, but also polymers from renewable sources like poly(lactic acid). KEYWORDS crystallization, mechanics, morphology, optics, polyethylene, polypropylene, processing 1 | INTRODUCTION A look at the distribution of thermoplastic polymer consumption in Europe 2017 (see Figure 1) gives a first indication why polymer crys- tallization is so important for the polymer production, processing and application industry. The two biggest polymer classes, polyethylene (PE) and polypropylene (PP), both being semi-crystalline, already make up nearly 50% of the market, and poly(ethylene terephthalate) (PET) as polymer with a particular flexibility in terms of crystallinity, adds further 7%. For these major commodity polymers just as well as for engineering thermoplastics like polyamide-6 (PA-6) and novel biopoly- mers like poly(lactic acid) (PLA), crystallization is part of the material and component design process. This means that the mechanical and optical performance of as diverse articles like a packaging film and a car bumper will be affected by crystallization, but also the long-term stability of drinking water pipers or cable insulations. In all these cases, polymer structure and processing conditions need to be considered together when trying to understand the final crystallinity and morphology defining those appli- cation properties. Research on polymer crystallization has fortunately made signifi- cant progress since the pioneering work of Van Krevelen [2,3] and Kel- ler. [4] Studies by standard differential scanning calorimetry (DSC) or hot-stage microscopy with a limited heating and cooling rate range had dominated polymer studies for many years. Meanwhile, creative scientists managed to look far deeper into the process, employing X- ray methods to get an image of the molecular arrangement in the crys- talline structure like Lotz [5,6] or developing innovative setups for processing-like deformation and cooling histories like Janeschitz- Kriegl. [7,8] One major challenge of early crystallization research resolved by the latter group was a routine for measuring high nucle- ation densities and spherulitic growth rates, thus assessing processing-relevant temperature ranges. At the same time, structural analysis of chain structure (eg, by car- bon 13 nuclear magnetic resonance spectroscopy, 13C-NMR [9] ) and polymer composition (eg, by temperature rising elution fractionation, TREF [10] ) allowed both better control and understanding of polymer structure effects on crystallization. In the meantime, however, conversion processes became faster and faster. Characterization methods caught up gradually, using high- speed and later nano-calorimetry achieving better heat transfer (through higher surface-to-volume ratio) and enabling cooling and heating rates up to 10 6 Ks -1 . This allowed studying quenching effects and the development of metastable crystal modifications, as in case of isotactic polypropylene (iPP [11,12] ) or poly(ethylene terephthalate) (PET [11,13] ), with Figure 2 showing a comparison of cooling rate effects on the resulting density of three different polymers. It also turned out Received: 13 March 2018 Revised: 4 May 2018 Accepted: 6 May 2018 DOI: 10.1002/pcr2.10009 Polymer Crystallization. 2018;1:e10009. wileyonlinelibrary.com/journal/pcr2 © 2018 Wiley Periodicals, Inc. 1 of 16 https://doi.org/10.1002/pcr2.10009