Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Conductive bacterial cellulose/multiwall carbon nanotubes nanocomposite aerogel as a potentially flexible lightweight strain sensor Hadi Hosseini a , Mehrdad Kokabi a, ⁎ , Seyyed Mohammad Mousavi b a Department of Polymer Engineering, Faculty of Chemical Engineering, Tarbiat Modares University, P.O. Box 14115-114, Tehran, Islamic Republic of Iran b Department of Biotechnology, Faculty of Chemical Engineering, Tarbiat Modares University, P.O. Box 14115-114, Tehran, Islamic Republic of Iran ARTICLE INFO Keywords: Bacterial cellulose Carbon nanotubes Nanocomposite aerogel Electrical conductivity Percolation threshold Strain sensor ABSTRACT In this work, in-situ biosynthesized bacterial cellulose (BC) /multiwall carbon nanotubes (MWCNTs) nano- composite hydrogels converted to the conductive nanocomposite aerogels via the supercritical CO 2 method. A low percolation threshold value of 0.0041 (volume concentration) predicted for BC/MWCNTs nanocomposite aerogels by the proposed modified model. The piezoresistive behavior of the nanocomposite aerogel at perco- lation threshold, evaluated in tension mode. The strain sensing outcomes revealed a linear trend during loading until a critical strain, afterward began to decline with further increasing of strain. Moreover, by applying loading unloading cyclic tension for 10 times at two different strain amplitudes (2% and 8%), the variation of relative resistance was different. This attributed to the rearrangement of MWCNTs at high strain condition. The gauge factor of 21 and response time of 390 ms obtained for flexible lightweight strain sensor. The fabricated strain sensor utilized to monitor human detection motion. 1. Introduction Cellulose aerogels as a third generation of aerogels have attracted a great deal of attention in energy storage devices (Zhang, Zhang, Zhao, & Yang, 2015), water purification (Wan & Li, 2015) and smart magnetic materials (Olsson et al., 2010), due to their high porosity (> 80%), low density (0.004–0.5 g/cm 3 ), flexibility, high specific surface area and three-dimensional interconnected fibrous structure (Demilecamps, Beauger, Hildenbrand, Rigacci, & Budtova, 2015). Generally, resistance-type strain sensors, which convert the external stimuli (stress or strain) to electrical resistance signal, have been ex- tensively used in the electronic skin (Minjeong et al., 2015) and wearable devices (Liu, Cao, Ma, & Wan, 2017). Nevertheless, pivotal requirements for the strain sensing material are including highly flex- ible matrix and efficient conductive nanofiller network. Recently, the utilization of cellulose, as one of the most abundant biopolymers on earth, reported in the field of strain sensing devices. For example, Huang, Liu, Wu, Li, and Wang (2017) fabricated composite aerogels based on graphene/carboxymethylcellulose for compressive strain sensing evaluation and a gauge factor (GF) value of 1.58 obtained (Huang et al., 2017). Yao et al. (2017) reported flexible Ag/cellulose nanofiber aerogel, gained from bamboo, with a maximum GF of 1 up to 20% strain (Yao et al., 2017). Zhuo et al. (2018) introduced a carbon aerogel via carbonization of cellulose nanocrystalline/graphene oxide in compression strain and pressure detection with a GF of 5.81 (Zhuo et al., 2018). It explains that the presence of cellulose plays a critical influence on the viscoelastic properties of the resultant strain sensor. Moreover, the homogeneous dispersion of carbon-based nanofiller within the polymer matrix is vital to improve the performance of sensory materials. BC possesses high purity, crystallinity, and higher flexibility than plant cellulose or other derivatives of cellulose (Ul-Islam, Khan, & Park, 2012). A variety of conductive nanofillers such as carbon nanotube (CNT) and graphene introduced into BC aerogels. Accordingly, the in- situ method suggested as a proper strategy for achieving conductive BC based nanocomposite due to adjusting the shape, structure, and prop- erties of resultant BC along with excellent dispersion of nanofillers during cultivation and biosynthesis process (Erbas Kiziltas, Kiziltas, Blumentritt, & Gardner, 2015). A few works have been reported about the incorporation of MWCNTs into the BC culture medium and char- acterize resultant composites (Park, Kim, Kwon, Hong, & Jin, 2009; Yan, Chen, Wang, Wang, Wang et al., 2008; Yan, Chen, Wang, Wang, & Jiang, 2008), or evaluate bone regeneration (Park et al., 2015) and enzymatic biofuel cell (Lv et al., 2016). No one investigated the elec- trical conductivity and strain sensing behavior of composites. The literature survey clearly illustrates lack of experimental and theoretical works on the electrical conductivity and strain sensing be- havior of in-situ biosynthesized BC/MWCNTs nanocomposite aerogels. https://doi.org/10.1016/j.carbpol.2018.08.054 Received 7 May 2018; Received in revised form 23 July 2018; Accepted 12 August 2018 ⁎ Corresponding author. E-mail address: mehrir@modares.ac.ir (M. Kokabi). Carbohydrate Polymers 201 (2018) 228–235 Available online 13 August 2018 0144-8617/ © 2018 Elsevier Ltd. All rights reserved. T