Influence of hygrothermal conditioning on the chemical structure and thermal mechanical properties of aliphatic polyketone Harrison Lin a , Adam Pearson a , Yasamin Kazemi a , Adel Kakroodi b , Ahmed Hammami b , Marcus Heydrich b , Bo Xu b , Hani E. Naguib a, * a Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada b Shawcor Ltd., Corporate Research & Development Toronto, Ontario, Canada article info Article history: Received 10 September 2019 Received in revised form 22 April 2020 Accepted 6 June 2020 Available online 19 June 2020 Keywords: Polyketone Thermoplastic Hygrothermal degradation Thermal degradation Chemical degradation Mechanical properties FTIR abstract Hygrothermal conditioning on the chemical, thermal and mechanical properties of aliphatic polyketone terpolymer, ethylene-propylene-carbon monoxide (EPCO), were investigated under high temperature fluid transport conditions. The DSC results suggest the effect of hygrothermal treatment and exposure time on the advancement of chain scission leading to an increase in crystallinity induced by chemi- crystallization, which was confirmed by FTIR results. TGA results of EPCO correspond to reductions of thermal stability with decreases in T 5% and T max characteristic temperatures by 19% and 10%, respectively. The yield stress, stiffness and dynamic storage modulus increased with degradation time. However, decreases in the elongation at break were observed after prolonged periods of degradation due to the embrittlement resulting from polymer chain scission. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Aliphatic polyketones (PK) are a relatively new class of semi- crystalline polymers known for their enhanced chemical, thermal and mechanical properties. Polyketones are high-performance thermoplastics obtained from perfectly alternating olefins with carbon monoxide (CO) to form a copolymer of ethylene-CO (ECO) or terpolymerization of ethylene-propylene-CO (EPCO). Polyketones have excellent barrier performance, heat resistance, friction and wear characteristics, and good impact behavior compared to semi- crystalline polyethylene and polypropylene [1 ,2]. The versatile combination of properties gives polyketone an advantage over other semi-crystalline polymers and makes it a promising candi- date for use in engineering, fiber reinforcement, barrier and pack- aging applications [3e5]. Compared to other aliphatic polymers such as polyethylene with a melting temperature around 140  C[6,7], polyketone copolymers of ethylene-CO origin have relatively higher melting point (up to 255  C) [1]. This increase of around 115  C in the melting temperature is a result of strong interactions between the highly polar carbonyl groups of adjacent polymer chains. It is known that during processing, polyketone copolymers are relatively sensitive to thermal degradation [8], which can lead to intermolecular and intramolecular reactions limiting the allowable processing time. Therefore, polymerisation of terpolymers, through introduction of propylene monomers, is often employed to lower the melting temperature, making it more stable for processing [9]. There are several papers which deal with aliphatic polyketones, most of which focus on permeation barrier applications and toughening of the material using microparticles. Cho et al. fabri- cated a blend of EPCO with 1 wt% graphene nanoplatelets using aminopyrene to significantly improve the barrier performance [10]. Nobile et al. found EPCO permeation properties, above the glass transition temperature, and to be comparable to nylon-6, poly (ethylene terephthalate) and poly carbonates [11]. Zuiderduin et al. demonstrated improvements to the toughness of polyketone after the incorporation of calcium carbonate and rubber particles, [12, 13]. Additionally, studies on the crystallization behavior of polyketone have also been a subject of interest recently. Holt and Spruiell studied the melt crystallization of polyketone show that lamellae thickness increases with increasing crystallization * Corresponding author. E-mail address: naguib@mie.utoronto.ca (H.E. Naguib). Contents lists available at ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab https://doi.org/10.1016/j.polymdegradstab.2020.109260 0141-3910/© 2020 Elsevier Ltd. All rights reserved. Polymer Degradation and Stability 179 (2020) 109260