Preparation of monolithic polycaprolactone foams with controlled morphology Ozgun Can Onder, Emel Yilgor, Iskender Yilgor * Chemistry Department, KUYTAM Surface Science and Technology Center, Koç University, Istanbul, Turkey article info Article history: Received 4 October 2017 Received in revised form 20 December 2017 Accepted 21 December 2017 Available online 26 December 2017 Keywords: Polycaprolactone Foam Thermally induced phase separation abstract Polycaprolactone (PCL) foams were produced by thermally induced phase separation. Tetrahydrofuran/ methanol (THF/MeOH) (solvent/non-solvent) mixture was used for the induction of liquid-liquid phase separation of PCL solutions at three different temperatures. Subsequent solvent exchange followed by vacuum drying yielded polymeric foams with different morphologies. Characterization of foams was obtained by scanning electron microscopy, x-ray diffractometry, mercury intrusion porosimetry and compression tests. Influence of polymer concentration (8, 10 and 12 wt%), quench temperature (4, 20 and 80  C), and THF/MeOH ratio from (42/58) to (54/46) (wt/wt) on the foam formation, morphology and properties were investigated systematically. Lower PCL concentration, lower THF content and higher quench temperature lead to larger pore sizes in the foams obtained. Detailed discussions of the influence of processing parameters on foam structure and porosity, foam density, percent crystallinity and compressive properties are provided. By selectively tuning the process parameters, foams with controlled pore sizes (10e450 mm), porosity (83e91%) and morphology (cellular, bead-like, micro- spherical) were obtained. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction Polymeric foams find uses in variety of applications including packaging, thermal and acoustic insulation, energy dissipation, shock protection, filtration and separation [1]. Growing use of plastic foams, reliance on oil based starting materials and ongoing concerns on the accumulation of plastic waste globally have driven scientists to develop bio-based and/or biodegradable polymeric foams. Production of biosafe polymeric foams is especially impor- tant for biomedical applications such as protein fractionation filters [2], gas and liquid filtration matrices [3], drug delivery systems [4] and scaffolds for tissue engineering and regeneration [5]. Polycaprolactone (PCL) is a semicrystalline aliphatic thermo- plastic polyester. It is produced by the ring opening polymerization of e-caprolactone, a monomer that can be derived from natural resources [6]. PCL has glass transition temperature (T g ) of 54  C and melting temperature between 55 and 60  C[7]. Due to its low T g , PCL chains are found in the rubbery state at room temperature. However, PCL crystallites, which act as reinforcing scaffolds, provide mechanical strength, rendering PCL as a flexible and tough material. PCL is a biocompatible, bioresorbable, and biodegradable polymer. It can be degraded in human body and biotic environ- ments through the hydrolysis of its aliphatic ester linkages. Degradation products of PCL can be metabolized in tricarboxylic acid cycle and are not harmful to the environment [8]. PCL is an FDA approved polymer along with poly(lactic acid) (PLA), poly(glycolic acid) (PGA) and their copolymers [9]. Compared to its counterparts, PCL has very desirable combination of proper- ties. Its low T g gives it an exceptional flexibility compared to rigid PLA and PGA. Furthermore, owing to its greater hydrophobicity, PCL has shown longer in vivo degradation times. This makes it a suit- able material especially for the preparation of long-term implants [7]. Currently, PCL based materials find biomedical applications as sutures [10], delivery agents [11], adhesion barriers [12], dental fillings [13], biodegradable coatings for optoelectronic systems [14]. Porous PCL based materials have been shown to be promising scaffold candidates for various tissue engineering applications [15e17]. Sufficient porosity, appropriate pore size, and inter- connectivity of pores are required for enabling diffusion of nutri- ents and cellular ingrowth throughout the scaffold. Scaffold pore size is important especially in cell binding, migration and ingrowth. Depending on tissue type, there exists an optimum pore size range. * Corresponding author. Tel.: þ90 212 338 1418; fax: þ90 212 338 1559. E-mail address: iyilgor@ku.edu.tr (I. Yilgor). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer https://doi.org/10.1016/j.polymer.2017.12.054 0032-3861/© 2018 Elsevier Ltd. All rights reserved. Polymer 136 (2018) 166e178