High cellulose nanowhisker content composites through cellosize bonding† Kazi M. Zakir Hossain, a Latifah Jasmani, b Ifty Ahmed, a Andrew J. Parsons, a Colin A. Scotchford, a Wim Thielemans * bc and Chris D. Rudd a Received 17th August 2012, Accepted 25th September 2012 DOI: 10.1039/c2sm26912k Flexible composite ﬁlms with a high cellulose nanowhisker (CNW) content of up to 75% by weight were produced by casting from aqueous solution with water soluble cellosize (CS). The surface topography of the ﬁlms displayed an aggregated morphology inﬂuencing the surface roughness and light transparency properties of the blends. Using ﬂuorescently labelled CS, we were able to determine the extent of aggregation in the composites which indicated that up to 13% of CNWs can be homogeneously blended with CS, above which larger CNW aggregates occur. However, even in a somewhat aggregated form, the CNWs still form a percolated network and appear to be homogeneously dispersed as larger aggregated entities. The composite CNW–CS ﬁlms further exhibited improved thermal stability compared to both the CNWs and CS alone with decomposition temperatures shifting from 261  C for CNWs and 313  C for CS to 361  C for blends containing 75% CNWs. Surface induced crystallisation of CS by CNWs was also found with higher crystallinity for the composite ﬁlms than for the individual constituents. Due to the reinforcing effect of CNWs within the matrix, an increase in the tensile strength (294%) and modulus (2004%) was observed for the blend containing 75% CNWs compared to the pure CS ﬁlm (tensile strength 12.23 MPa and modulus 0.39 GPa). The storage modulus of all the ﬂexible blends/ﬁlms investigated also revealed an increasing trend with the CNW content across the temperature region explored. The swelling kinetics of the CNW–CS blends in phosphate buffered saline (PBS) media at 37  C were also investigated and CNWs were shown to have a strong inﬂuence on reducing the equilibrium swelling capacity and initial swelling rate of the blends. Introduction Composites based on water soluble biopolymers are of signiﬁ- cant interest due to their biodegradability, biocompatibility and good processability and have already shown their potential for application in the ﬁelds of biomedical materials, 1,2 tissue engi- neering 3,4 and pharmaceuticals. 5,6 Dispersion, interfacial prop- erties and/or miscibility of the biopolymers in the blends signiﬁcantly inﬂuence the mechanical and degradation properties of the composite materials, which can be explained by the pres- ence or absence of interactions and bonding between the constituents and the surface characteristics of the polymers and the ﬁllers. A number of positive interactions between various water-soluble polysaccharides and biopolymers have been reported in the literature. 7–9 For example, the physicochemical properties of hydrophilic polymeric ﬁlms prepared from the blends of hydroxyethylcellulose (HEC) and poly[(methyl vinyl ether)-alt-(maleic acid)] (PMVEMAc) were investigated by Khutoryanskaya et al., 10 who suggested that cross-linking of water-soluble polymers was achieved through the formation of inter-macromolecular hydrogen bonds via thermal treatment of the blends. The glass transition temperature, T g , for HEC was reported to be 97  C and the blend containing 50% PMVEMAc showed an increase in T g to 143  C due to the cross-linking effect on the polymers. Wang et al. investigated a composite hydrogel prepared via graft copolymerisation of HEC, sodium acrylate (NaA) and medicinal stone (MS) and showed that by incorpo- rating 10 and 50 wt% MS into the blends, the swelling capacity increased by 400% (from 162 to 810 g g 1 ) and 117% (from 162 to 352 g g 1 ), respectively. A 7.5-fold improvement in the initial swelling rate constant was also reported for MS incorporated blends over that of MS-free samples. They also conﬁrmed the grafting of NaA on the HEC backbone and improved dispersion of MS in the polymer matrix after preparing the composite hydrogels via a facile free-radical graft copolymerisation. 11 The thermal degradation behaviour of pure HEC was reported by Chen et al. and they found 67% weight loss had occurred at 350  C with their initial (T d ) and maximum (T dm ) decomposition a Division of Materials, Mechanics and Structures, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK b School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. E-mail: wim.thielemans@nottingham.ac.uk c Process and Environmental Research Division, Faculty of Engineering, University of Nottingham, University Park, Nottingham, NG7 2RD, UK † Electronic supplementary information (ESI) available. See DOI: 10.1039/c2sm26912k This journal is ª The Royal Society of Chemistry 2012 Soft Matter Dynamic Article Links C < Soft Matter Cite this: DOI: 10.1039/c2sm26912k www.rsc.org/softmatter PAPER Downloaded by University of Nottingham on 12 October 2012 Published on 12 October 2012 on http://pubs.rsc.org | doi:10.1039/C2SM26912K View Online / Journal Homepage