Cellulose Nanofibresas Biomaterial for Nano-reinforcement of Poly [styrene- (ethylene-cobutylene) – styrene] Triblock Copolymer
ChandravatiYadav, ArunSaini and Pradip K. Maji*
Department of Polymer and Process Engineering, Indian Institute of Technology Roorkee
Saharanpur Campus, Saharanpur-247001, U.P., India.
Cellulose nanofibres (CNFs) extraction by the chemi-mechanical approach-
Briefly, the cellulose fibres (CFs) with a high cellulose content of 94% with very low lignin content were prepared from raw wood fibres by employing a three step process, i.e., -(i) soxhlet extraction of raw fibres with 2:1 (v/v) mixture of benzene/ethanol for 7 h, 60°C (ii) swelling of fibres in DMSO, (iii) chemical treatment of wet fibres with acidified sodium chlorite (ASC, 2 wt%) and KOH (4 wt%) solutions. The obtained chemically purified CFs were kept in DMSO for 12h and washed repeatedly through centrifugation and DMSO was exchanged with water (pH ~7). The swelled CFs was dispersed in double distilled water at approximately 0.15 wt% (w/w) solid content. To individualize micro-dimensional CFs in nano-dimensional CNFs, themechanical fibrillation of CFs suspension in water (0.15 wt%) was executed with the aid of a common ultrasonic processor for 20 min at an output power of 400 W. The well-fibrillated, slender CNFs were obtained as transparent aliquots after the centrifugation of ultrasonicated suspension at 8000 rpm for 15 min and the final obtained transparent aqueous suspension were freeze-dried (Fig. 1 in manuscript).
Surface characteristics of nanocomposite films
The surface properties of prepared nanocomposite films were scrutinized in terms of water contact angles (CA) to determine the hydrophilic and hydrophobic characteristics of the samples. It is among one of the preliminary techniques to analyze the relationship between solid surface and water (Wu et al. 2014). The initial contact angle measurement and periodic change in the contact angle of water drop on the composite surface are presented in Fig. S1. Table S1 summarizes the average value of contact angles obtained by measuring at different locations. Vogler (1998)have precisely explained the terms related to the quantitative definition of hydrophobic and hydrophilic. They explained 65° to be the differentiating border for the determination of the surface polar characteristics. A completely unexpected behavior of CNFs was seen during contact angle (CA) measurement. As both the matrix and filler are hydrophilic in nature, the CA was supposed to reduce, but, surprisingly with an increase in the loading percent of CNFs, the CA value of prepared composites was increased that indicate the hydrophobic character of nanocomposite films. A similar type of observation was also reported and well explained by (Wu et al. 2014) in the case of nanocellulose and nanoclay platelets composite films. The increment in contact angle of the nanocomposite films can be described on the basis of the increased roughness and entrapped air area fractions. The surface morphology can have very important role in controlling the hydrophobicity of materials (Wu et al. 2014). Nanoscale pins perpendicular to the lauric acid film surface has been reported to increase the CA from 75° to 178° (Hosono et al. 2005). In spite of being covered by hydrophilic lauric acid, the nanopins patterned surface contained an extremely high air fraction of 99% that has resulted in the induction of a very high hydrophobicity (Hosono et al. 2005). Two different kinds of morphologies were analyzed through the FESEM of prepared composite films as shown in Fig. 3in main manuscript. The composite film prepared at a lower concentration, i.e., mSEBS/CNFs-0.001, showed an interwoven thread like structure of CNFs within the matrix material (Fig. 3b) and the mSEBS/CNFs-0.005 and mSEBS/CNFs-0.01 composite films showed a polymer coated network structure (Fig. 3c-d). These morphologies have contributed in attaining a rough microstructure for the prepared nanocomposites. The increment in contact angle of the nanocomposite films can be described on the basis of the increased roughness and entrapped air area fractions. The air fractions can have a significant role in propping up the water droplet from the surface (Wu et al. 2014). The amount of air area fraction seems to be higher in the case of the composite film of mSEBS/CNFs-0.01 (Fig.3d) containing more space within the network structure as compared to the composites of mSEBS/CNFs-0.001 and mSEBS/CNFs-0.005. Hence, these larger voids may also have played a considerable role in entrapping more air and thereby increasing the CA value of composites with higher loadings of CNFs, i.e., mSEBS/CNFs-0.01. The detailed investigation regarding contact angle increment is under study as per various methods described in the literature (Wu et al. 2014; Hosono et al. 2005; Feng et al. Marmur 2013).
Contact angle of mSEBS/CNFs nanocomposite filmsSample / Contact angle (degree)
CNFs / 22 ± 3.6
mSEBS / 62 ± 2.6
mSEBS/CNFs-0.001 / 69 ± 1.8
mSEBS/CNFs-0.005 / 77 ± 1.2
mSEBS/CNFs-0.01 / 84 ± 1.4
Fig. S1 (A) Initial measurement and (B) periodic measurement of contact angle of (a) SEBS-g-MA film (mSEBS), (b) mSEBS/CNFs-0.001, (c) mSEBS/CNFs-0.005, (d) mSEBS/CNFs-0.01, and (e) CNFs.
Fig. S2Histogram obtained for CNFs diameter through image analysis. (The inset shows the processed tiff image of CNFs generated from Fig. 2a (in manuscript).
Fig. S3 Interaction mechanism between surface -OH groups of CNFs and maleic anhydride group of mSEBS.
Fig. S4Figurative representation of fracture mechanism involved in the failure of mSEBS/ CNFs nanocomposite films.
Table S2. Mechanical properties of SEBS/CNFs nanocomposite films.Sample / Young’s modulus
(MPa) / Tensile strength (MPa) / Elongation at break (%) / Work of fracture
mSEBS / 10.4 ± 0.5 / 15.7 ± 0.8 / 636 ± 30.3 / 7.9 ± 0.5
mSEBS/CNFs-0.001 / 12.9 ± 0.3 / 20.3 ± 0.3 / 688 ± 38.2 / 14.5 ± 0.8
mSEBS/CNFs-0.005 / 20.6 ± 0.7 / 26.5 ± 0.7 / 750 ± 29.7 / 23.9 ± 1.1
mSEBS/CNFs-0.01 / 14.6 ± 0.4 / 18.3 ± 0.5 / 696 ± 42.4 / 17.7 ± 0.7
uSEBS / 9.3 ± 0.8 / 12.9 ± 0.9 / 446 ± 39.3 / 6.9 ± 0.9
uSEBS/CNFs-0.005 / 6.0 ± 0.5 / 7.8 ± 0.6 / 364 ± 25.9 / 3.8 ± 0.6
Feng BL, Li SH, Li YS, Li HJ, Zhang LJ, Zhai J, et al (2002) Super-hydrophobic surfaces: From natural to artificial. Adv Mater 14:1857–1860.
Hosono E, Fujihara S, Honma I, Zhou H (2005) Superhydrophobic perpendicular nanopin film by the bottom-up process. J Am Chem Soc 127:13458–13459.
Marmur A (2013) Superhydrophobic and superhygrophobic surfaces: from understanding non-wettability to design considerations. Soft Matter. 9:7900–7904.
Wu CN, Saito T, Yang Q, Fukuzumi H, Isogai A (2014) Increase in the water contact angle of composite film surfaces caused by the assembly of hydrophilic nanocellulose fibrils and nanoclay platelets. ACS Appl Mater Interfaces 6:12707–12712.
Vogler EA (1998) Structure and reactivity of water at biomaterial surfaces. Adv Colloid Interface Sci 74:69–117.