Natural Cellulose Nanofibers As Sustainable Enhancers in Construction Cement

RESEARCH ARTICLE Natural Cellulose Nanofibers As Sustainable Enhancers in Construction Cement Li Jiao1,2, Ming Su2, Liao Chen3, Yuangang Wang4, Hongli Zhu3, Hongqi Dai1* 1 Department of Pulp and Paper Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China, 2 Department of Chemical Engineering, Northeastern University, Boston, United States of America, 3 Department of Mechanical and Industrial Engineering, Northeastern University, Boston, United States of America, 4 Department of Civil Engineering, Nanjing Forestry University, Nanjing, Jiangsu, China * a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Jiao L, Su M, Chen L, Wang Y, Zhu H, Dai H (2016) Natural Cellulose Nanofibers As Sustainable Enhancers in Construction Cement. PLoS ONE 11(12): e0168422. doi:10.1371/journal. pone.0168422 Abstract Cement is one of the mostly used construction materials due to its high durability and low cost, but it suffers from brittle fracture and facile crack initiation. This article describes the use of naturally-derived renewable cellulose nanofibers (CNFs) to reinforce cement. The effects of CNFs on the mechanical properties, degree of hydration (DOH), and microstructure of cement pastes have been studied. It is found that an addition of 0.15% by weight of CNFs leads to a 15% and 20% increase in the flexural and compressive strengths of cement paste. The enhancement in mechanical strength is attributed to high DOH and dense microstructure of cement pastes after adding CNFs. Editor: Varenyam Achal, East China Normal University, CHINA Received: July 13, 2016 Accepted: November 30, 2016 Published: December 22, 2016 Copyright: © 2016 Jiao et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: This work was supported by the Introduction of Advanced International Project of Forestry Science and Technology (Grant number: 2015454), the National Natural Science Foundation of China (Grant Number: 31470599) and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). We thank the Nanjing Forestry University Innovation fund program for the Doctorate Fellowship Introduction Cement composite is one of the mostly used construction materials, but the use of cement based material in dams and long-span bridges is limited due to its brittleness [1–3]. Although a variety of fibers have been added into cement composites to improve their tensile strength, toughness, and energy absorption capacity [4–7], these fibers are limited for poor interface, low corrosion resistance, and high cost, etc. For instance, the bonding of glass fibers to cement is not strong enough, and glass fibers have low alkaline resistance [8,9], and cannot provide flexural, shear, and compressive forces [10,11]. Carbon and polymer fibers made from high energy consumption process are expensive [12]. Natural fibers have also been used to improve the mechanical properties of cement composites. The use of the naturally-derived fibers minimizes carbon footprint of infrastructural materials, -also provide excellent mechanical properties at low cost [13,14]. An addition of 2–16% (mass) millimeter long cellulosic fibers leads to 20–50% enhancement of flexural strength and fracture toughness of cement composites [15– 19]. While, there are some issues related to natural fibers in cement composites. Fiber components such as lignin, hemicelluloses, pectin, and soluble sugars degrade in the alkali cement environment, leading to low durability [20–22]. Micrometer-sized natural fibers can easily aggregate, which creates weak bonding between fiber and cement hydrates, causing stress concentration at interface of fiber and cement [23]. It is reasonable to postulate that the mechanical properties of cement composites will be further improved if the selected natural fibers have PLOS ONE | DOI:10.1371/journal.pone.0168422 December 22, 2016 1 / 13 Nanocellulose As Enhancers in the Cement Composites Foundation and Innovation program KYZZ15-0254 of Jiangsu province for their financial support. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. high mechanical strength but not aggregate when mixed with cement particles. Cao reports that the flexural strength of cement paste increases with the addition of cellulose nanocrystals (CNCs). The degree of hydration of the cement paste increases that the mechanism proposed is steric stabilization and short circuit diffusion [24]. However, cellulose nanocrystals are typically prepared by acid hydrolysis, the most amorphous region of cellulose is removed and the yield of cellulose nanocrystals is only 20–30% [25–27]. Given that, cellulose nanofibers is an alternative, prepared by breaking down organized hierarchically natural cellulose fibers to nanofibers via mechanical and chemical process to break the hydrogen bonds at high yield, as shown in Fig 1(A). Typically technology, cellulose nanofibers are prepared by 2, 2, 6, 6-tetramethylpiperidine1-oxyl radical (TEMPO)-mediated oxidation system and mechanical homogenization, primary hydroxyl groups from the cellulose fibril are oxidized to carboxylate groups on the cellulose fibril surfaces. The introduction of carboxylate groups produce a negative charge on the surface of cellulose fibers, making the cellulose nanofibers suspension uniformly dispersed via the electrostatic repulsion force avoiding aggregation. Cellulose nanofibers not only have active chemical property endowed by the hydroxyl groups and carboxylate groups, but have excellent mechanical properties, for example, the elastic moduli of single microfibers prepared by TEMPO-oxidation is 145.2±31.3 GPa [28], which widely used to improve the mechanical property of polymers, such as chitosan, polylactic acid [29–31]. In this study, we added cellulose nanofibers to cement paste, and the mechanical strength of the cement was effectively enhanced by a low fraction of cellulose nanofibers. The porosity Fig 1. Schematic illustration of the hierarchical structure of a tree and the interaction between cellulose nanofibers and cement particles. (a) The hierarchical structure of celluloses. (b) A network of cellulose nanofibers and cement formed with carboxyl groups and cement hydrates. doi:10.1371/journal.pone.0168422.g001 PLOS ONE | DOI:10.1371/journal.pone.0168422 December 22, 2016 2 / 13 Nanocellulose As Enhancers in the Cement Composites between cement hydrates and degree of hydration play a crucial role in the strength of cement, this work studied the effect of cell (...truncated)