Dispersion and reinforcing effect of carrot nanofibers on biopolyurethane foams Xiaojian Zhou a , Jatin Sethi a , Shiyu Geng a , Linn Berglund a , Nikolina Frisk a , Yvonne Aitomäki a , Mohini M. Sain a,b , Kristiina Oksman a,b, ⁎ a Division of Materials Science, Luleå University of Technology, 971 87 Luleå, Sweden b Centre of Biocomposite and Biomaterials Processing, Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto M5S 3B3, Canada HIGHLIGHTS • Semirigid castor oil based PU foams with very low bulk density (b 50 kg/m 3 ) were successfully prepared. • Carrot nanofibers were used as rein- forcement to improve cell wall rigidity. • Prepared nanocomposite foams are performing in the level of commercial PU foams. • Foams were shown to be excellent core for biocomposite laminates. GRAPHICAL ABSTRACT abstract article info Article history: Received 8 July 2016 Received in revised form 1 August 2016 Accepted 9 August 2016 Available online 10 August 2016 In this study, carrot nanofibers (CNF) were used to enhance the performance of biobased castor oil polyol poly- urethane nanocomposite foams. A method of dispersing CNF in the polyol was developed and the foam charac- teristics and CNF reinforcing effect were studied. Co-solvent-assisted mixing resulted in well-dispersed CNF in the polyol, and foams with 0.25, 0.5 and 1 phr CNF content were prepared. The reinforced nanocomposite foams displayed a narrow cell size distribution and the compressive strength and modulus were significantly el- evated and the best compressive strength and modulus were reached with 0.5 phr CNF. Similarly, the modulus of the solid material was also significantly increased based on theoretical calculations. When comparing the foam performance, compressive strength and stiffness as a function of the density, the nanocomposite foams performs as commercial rigid PU foam with a closed cell structure. These results are very promising and we believe that these foams are excellent core materials for lightweight sandwich composites. © 2016 Elsevier Ltd. All rights reserved. Keywords: Polyurethane foam Castor oil polyol Cellulose nanofibers Dispersion Compressive mechanical properties 1. Introduction During the past 10–15 years, the utilization of bioresources to pre- pare polyurethane (PU) foams has attracted attention because of the increasing concerns about environmental problems, replacement of fos- sil resources and the low price and abundant supply of natural vegetable oils and biomass by-products [1–7]. However, the prepared biobased polyurethane (BPU) foams are not yet suitable for commercial applica- tions because they do not meet the industrial standard requirements for compression strength (≥ 180 kPa) [1,4]. Therefore, enhancing the prop- erties of BPU foam has been and continues to be of interest. Many differ- ent strategies have been used to improve the properties of the foams. Materials and Design 110 (2016) 526–531 ⁎ Corresponding author at: Division of Materials Science, Luleå University of Technology, 971 87 Luleå, Sweden. E-mail address: kristiina.oksman@ltu.se (K. Oksman). http://dx.doi.org/10.1016/j.matdes.2016.08.033 0264-1275/© 2016 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes