Isolation and characterization of cellulose nanocrystals from garlic skin Jeevan Prasad Reddy, Jong-Whan Rhim n Q1 Department of Food Engineering and Bionanocomposite Research Institute, Mokpo National University, 61 Dorimri, Chungkyemyon, Muangun, Jeonnam 534-729, Republic of Korea article info Article history: Received 20 January 2014 Accepted 3 May 2014 Keywords: New cellulose source Garlic skin Microfiber Nanocrystals Agricultural by-product abstract For the value-added utilization of underutilized agricultural by-products, garlic skin obtained abun- dantly in the food processing industry has been tested as a new source of cellulosic materials. Cellulose microfibers (CMF) and cellulose nanocrystals (CNC) were isolated from garlic skin fibers by alkali treatment and acid hydrolysis. The crude fiber, CMF, and CNC of garlic skin were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Transmission electron microscopy (TEM). Most of the lignin and hemicellulose was removed after the chemical treatment, and the degree of crystallinity of the CMF and CNC was increased compared with the crude fiber. The degree of crystallinity was 35%, 45%, and 63% for the crude fiber, CMF, and CNC, respectively. The cellulose nanocrystals exhibited spherical in shape with the size of 58–96 nm. The thermal stability of the CMF increased significantly, but that of CNC decreased slightly due to the introduction of sulfate groups into the cellulose crystals during acid hydrolysis. The nanocrystals had a high potential to be used as reinforcing filler for the preparation of bionanocomposites. & 2014 Published by Elsevier B.V. 1. Introduction Q2 The search for new renewable resources for the production of biodegradable and biocompatible materials has steadily increased in recent years [1]. In particular, non-conventional sources of cellulosic fibers have been extensively studied. There are various unexplored valuable cellulosic materials in the agricultural and food processing industry obtained as waste or by-products. These non-conventional and underexploited renewable materials can be used as an interesting alternative to produce value-added biopo- lymeric materials such as preparation of cellulose nanofibers and other uses [2]. Various agricultural residues and nonwood fibers generated from forestry or agri-food industries have been used to extract cellulose nanofibers, whiskers, and nanocrystals for the value-added utilization [3]. Among such underutilized cellulose resources, garlic skin is one of the promising materials. Garlic (Allium sativum L.) has been widely used due to its culinary and medicinal attributes in various regions of the world such as Asia, the Middle East, northern Africa, southern Europe, and parts of South and Central America. The garlic consumption in 2010 was estimated for 2.3 pounds per person [4]. Accordingly, tre- mendous amount of garlic skin is expected to be discarded as a processing waste in the food processing industry, especially for the production of minimally processed deskinned garlic. Garlic skin has already been used for fruits and vegetable coatings [5], extraction of antioxidants [6] and for removal of Cu 2 þ from the aqueous stream [7].Surface topography and roughness of garlic skin have been studied by atomic force microscopy in order to estimate the surface area for the coating purpose [8]. However, to the best of our knowledge, garlic skin has not been used as a new source of cellulose materials for the production of cellulose micro- and nanofibers. Therefore, the main objective of the present work were extraction and characterization of cellulose micro-fibers and cellulose nanocrystals from garlic skins in order to test their potential for the value- added utilization as a new source of cellulosic fiber materials. 2. Materials and methods Materials: Garlic skin was obtained from a local food processing company. Sodium chlorite, sodium bisulfate, sulfuric acid and ethanol were purchased from Sigma Aldrich (St Louis, MO, USA). Chemical analysis and isolation of cellulose nanocrystals: Garlic skin was washed thoroughly with water to remove dirt and dried in an air oven at 100 1C for 24 h. The dried samples were ground into fine powder using a Waring blender, and used for further analysis and extraction of cellulose microfibers (CMF). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters http://dx.doi.org/10.1016/j.matlet.2014.05.019 0167-577X/& 2014 Published by Elsevier B.V. n Corresponding author: Tel.: þ82 61 450 2423; fax: þ82 61 454 1521. E-mail address: jwrhim@mokpo.ac.kr (J.-W. Rhim). Please cite this article as: Prasad Reddy J, Rhim J-W. Isolation and characterization of cellulose nanocrystals from garlic skin. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.019i Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎