@article{salem_kasera_rahman_jameel_habibi_eichhorn_french_pal_lucia_2023, title={Comparison and assessment of methods for cellulose crystallinity determination}, volume={8}, ISSN={["1460-4744"]}, DOI={10.1039/d2cs00569g}, abstractNote={The degree of crystallinity in cellulose significantly affects the physical, mechanical, and chemical properties of cellulosic materials, their processing, and their final application. Measuring the crystalline structures of cellulose is a challenging task due to inadequate consistency among the variety of analytical techniques available and the lack of absolute crystalline and amorphous standards. Our article reviews the primary methods for estimating the crystallinity of cellulose, namely, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), Raman and Fourier-transform infrared (FTIR) spectroscopy, sum-frequency generation vibrational spectroscopy (SFG), as well as differential scanning calorimetry (DSC), and evolving biochemical methods using cellulose binding molecules (CBMs). The techniques are compared to better interrogate not only the requirements of each method, but also their differences, synergies, and limitations. The article highlights fundamental principles to guide the general community to initiate studies of the crystallinity of cellulosic materials.}, journal={CHEMICAL SOCIETY REVIEWS}, author={Salem, Khandoker Samaher and Kasera, Nitesh Kumar and Rahman, Md. Ashiqur and Jameel, Hasan and Habibi, Youssef and Eichhorn, Stephen J. and French, Alfred D. and Pal, Lokendra and Lucia, Lucian A.}, year={2023}, month={Aug} }
 @article{peresin_vesterinen_habibi_johansson_pawlak_nevzorov_rojas_2014, title={Crosslinked PVA nanofibers reinforced with cellulose nanocrystals: Water interactions and thermomechanical properties}, volume={131}, ISSN={0021-8995}, url={http://dx.doi.org/10.1002/APP.40334}, DOI={10.1002/app.40334}, abstractNote={Acid-catalyzed vapor phase esterification with maleic anhydride was used to improve the integrity and thermo-mechanical properties of fiber webs based on poly(vinyl alcohol), PVA. The fibers were produced by electrospinning PVA from aqueous dispersions containing cellulose nanocrystals (CNCs). The effect of esterification and CNC loading on the structure and solvent resistance of the electrospun fibers was investigated. Chemical characterization of the fibers (FTIR, NMR) indicated the formation of ester bonds between hydroxyl groups belonging to neighboring molecules. Thermomechanical properties after chemical modification were analyzed using thermal gravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. An 80% improvement in the ultimate strength was achieved for CNC-loaded, crosslinked PVA fiber webs measured at 90% air relative humidity. Besides the ultra-high surface area, the composite PVA fiber webs were water resistant and presented excellent mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40334.}, number={11}, journal={Journal of Applied Polymer Science}, publisher={Wiley}, author={Peresin, Maria Soledad and Vesterinen, Arja-Helena and Habibi, Youssef and Johansson, Leena-Sisko and Pawlak, Joel J. and Nevzorov, Alexander A. and Rojas, Orlando J.}, year={2014}, month={Jan}, pages={n/a-n/a} }
 @article{lin_zhan_liu_habibi_fu_lucia_2013, title={RAFT synthesis of cellulose-g-polymethylmethacrylate copolymer in an ionic liquid}, volume={127}, ISSN={["1097-4628"]}, DOI={10.1002/app.38071}, abstractNote={We demonstrate for the first time the feasibility in conducting the graft copolymerization of methylmethacrylate (MMA) with cellulose by the means of the reversible addition-fragmentation chain transfer (RAFT) polymerization in an ionic liquid [1-N-butyl-3-methylimidazolium chloride] (BMIMCl). Cellulose was first converted to a macromolecular chain transfer agent to which MMA was grafted by RAFT in BMIMCl. The success of the occurrence of different reactions was validated by elemental analyses, Fourier transform infrared and nuclear magnetic resonance spectroscopies. The results demonstrate that the MMA polymer chains were grafted onto the cellulose while the use of the ionic liquid as a reaction medium enhanced the polymerization rate to a moderate extent. Gel permeation chromatography analysis of poly(MMA) chains cleaved from the cellulose by acidic hydrolysis indicated low polydispersity indices (ca. 1.3) that were consistent with the “living” nature of the RAFT. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013}, number={6}, journal={JOURNAL OF APPLIED POLYMER SCIENCE}, author={Lin, Chunxiang and Zhan, Huaiyu and Liu, Minghua and Habibi, Youssef and Fu, Shiyu and Lucia, Lucian A.}, year={2013}, month={Mar}, pages={4840–4849} }
 @article{fonseca silva_habibi_colodette_elder_lucia_2012, title={A fundamental investigation of the microarchitecture and mechanical properties of tempo-oxidized nanofibrillated cellulose (NFC)-based aerogels}, volume={19}, ISSN={["0969-0239"]}, DOI={10.1007/s10570-012-9761-x}, number={6}, journal={CELLULOSE}, author={Fonseca Silva, Teresa Cristina and Habibi, Youssef and Colodette, Jorge Luiz and Elder, Thomas and Lucia, Lucian A.}, year={2012}, month={Dec}, pages={1945–1956} }
 @book{habibi_lucia_2012, title={Polysaccharide building blocks: a sustainable approach to the development of renewable biomaterials}, publisher={Hoboken, New Jersey: John Wiley & Sons, Inc.}, year={2012} }
 @article{spence_venditti_rojas_habibi_pawlak_2011, title={A comparative study of energy consumption and physical properties of microfibrillated cellulose produced by different processing methods}, volume={18}, ISSN={0969-0239 1572-882X}, url={http://dx.doi.org/10.1007/s10570-011-9533-z}, DOI={10.1007/s10570-011-9533-z}, number={4}, journal={Cellulose}, publisher={Springer Science and Business Media LLC}, author={Spence, Kelley L. and Venditti, Richard A. and Rojas, Orlando J. and Habibi, Youssef and Pawlak, Joel J.}, year={2011}, month={Apr}, pages={1097–1111} }
 @article{cao_habibi_magalhaes_rojas_lucia_2011, title={Cellulose nanocrystals-based nanocomposites: fruits of a novel biomass research and teaching platform}, volume={100}, number={8}, journal={Current Science}, author={Cao, X. D. and Habibi, Y. and Magalhaes, W. L. E. and Rojas, O. J. and Lucia, L. A.}, year={2011}, pages={1172–1176} }
 @article{fonseca silva_habibi_colodette_lucia_2011, title={The influence of the chemical and structural features of xylan on the physical properties of its derived hydrogels}, volume={7}, ISSN={["1744-6848"]}, DOI={10.1039/c0sm00868k}, abstractNote={Xylan polysacccharides, both with and without acetyl substituents, were obtained from the specific hardwood Eucalyptus urograndis by controlled extraction processes and eventually post-acetylated. They were subsequently functionalized with well-defined levels of methacrylic monomers to thereby provide different degrees of substitution of the functional group. These modified xylans were the basis to successfully prepare for the first time xylan/poly(2-hydroxyethyl methacrylate)-based hydrogels via the radical polymerization of HEMA, used as a crosslinking agent. The tuning of the crosslinking density of the hydrogel network was accomplished by preparing hydrogels that had two composition ratios of xylan to HEMA (60 : 40 and 40 : 60) and was also done by varying the degrees of substitution. The resulting hydrogels were characterized according to their morphology, swelling and rheological properties by field emission scanning electron microscopy (FE-SEM), gravimetric measurements after immersion in water, and dynamical mechanical analysis. Surprisingly, the presence of acetyl moieties leads to stiffer hydrogels which have a reduced capacity for water uptake. A natural extension to the synthesis and characterization of the novel-based xylan hydrogels is examining one of their primary functionalities: encapsulation and release. This functionality was one of the drivers of this work when it was conceived given the inherent ability of hydrogels to act as cargo carriers. Therefore, a representative anticancer drug doxorubicin was loaded into these hydrogels and its release in different media was studied. Acetylated xylans showed high delivery ratios while non-acetylated samples leveled off at half the level of the acetylated samples.}, number={3}, journal={SOFT MATTER}, author={Fonseca Silva, Teresa Cristina and Habibi, Youssef and Colodette, Jorge Luiz and Lucia, Lucian A.}, year={2011}, pages={1090–1099} }
 @misc{habibi_lucia_rojas_2010, title={Cellulose Nanocrystals: Chemistry, Self-Assembly, and Applications}, volume={110}, ISSN={["1520-6890"]}, DOI={10.1021/cr900339w}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTCellulose Nanocrystals: Chemistry, Self-Assembly, and ApplicationsYoussef Habibi†, Lucian A. Lucia*†, and Orlando J. Rojas†‡View Author Information Department of Forest Biomaterials, North Carolina State University, Box 8005, Raleigh, North Carolina 27695-8005, and Department of Forest Products Technology, Faculty of Chemistry and Materials Sciences, Helsinki University of Technology, P.O. Box 3320, FIN-02015 TKK, Espoo, Finland†North Carolina State University.‡Helsinki University of Technology.Cite this: Chem. Rev. 2010, 110, 6, 3479–3500Publication Date (Web):March 4, 2010Publication History Received12 October 2009Published online4 March 2010Published inissue 9 June 2010https://doi.org/10.1021/cr900339wCopyright © 2010 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views47757Altmetric-Citations3898LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (3 MB) Get e-AlertsSUBJECTS:Cellulose,Hydrolysis,Nanocomposites,Polymers,Suspensions Get e-Alerts}, number={6}, journal={CHEMICAL REVIEWS}, author={Habibi, Youssef and Lucia, Lucian A. and Rojas, Orlando J.}, year={2010}, month={Jun}, pages={3479–3500} }
 @article{habibi_hoeger_kelley_rojas_2010, title={Development of Langmuir-Schaeffer Cellulose Nanocrystal Monolayers and Their Interfacial Behaviors}, volume={26}, ISSN={["0743-7463"]}, DOI={10.1021/la902444x}, abstractNote={Model cellulose surfaces based on cellulose nanocrystals (CNs) were prepared by the Langmuir-Schaeffer technique. Cellulose nanocrystals were obtained by acid hydrolysis of different natural fibers, producing rodlike nanoparticles with differences in charge density, aspect ratio, and crystallinity. Dioctadecyldimethylammonium bromide (DODA-Br) cationic surfactant was used to create CN-DODA complexes that allowed transfer of the CNs from the air/liquid interface in an aqueous suspension to hydrophobic solid substrates. Langmuir-Schaeffer horizontal deposition at various surface pressures was employed to carry out such particle transfer that resulted in CN monolayers coating the substrate. The morphology and chemical composition of the CN films were characterized by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Also, their swelling behavior and stability after treatment with aqueous and alkaline solutions were studied using quartz crystal microgravimetry (QCM). Overall, it is concluded that the Langmuir-Schaeffer method can be used to produce single coating layers of CNs that were shown to be smooth, stable, and strongly attached to the solid support. The packing density of the films was controlled by selecting the right combination of surface pressure during transfer to the solid substrate and the amount of CNs available relative to the cationic charges at the interface.}, number={2}, journal={LANGMUIR}, author={Habibi, Youssef and Hoeger, Ingrid and Kelley, Stephen S. and Rojas, Orlando J.}, year={2010}, month={Jan}, pages={990–1001} }
 @article{peresin_habibi_vesterinen_rojas_pawlak_seppala_2010, title={Effect of Moisture on Electrospun Nanofiber Composites of Poly(vinyl alcohol) and Cellulose Nanocrystals}, volume={11}, ISSN={["1526-4602"]}, DOI={10.1021/bm1006689}, abstractNote={The effect of humidity on the morphological and thermomechanical properties of electrospun poly(vinyl alcohol) (PVA) fiber mats reinforced with cellulose nanocrystals (CNs) was investigated. Scanning electron microscopy (SEM) images revealed that the incorporation of CNs improved the morphological stability of the composite fibers even in high humidity environments. Thermal and mechanical properties of the electrospun fiber mats were studied by using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and large deformation tensile tests under controlled humidity and temperatures. The balance between the moisture-induced plasticization and the reinforcing effect of rigid CN particles was critical in determining the thermomechanical behaviors of the electrospun fiber mats. Results indicated that the stabilizing effect of the CNs in the PVA matrix might be compromised by water absorption, disrupting the hydrogen bonding within the structure. The amount of this disruption depended on the surrounding humidity and the CN loading. The reduction in tensile strength of neat PVA fiber mats as they were conditioned from low relative humidity (10% RH) to high relative humidity (70% RH) was found to be about 80%, from 1.5 to 0.4 MPa. When the structure was reinforced with CNs, the reduction in strength was limited to 40%, from 2 to 0.8 MPa over the same range in relative humidity. More importantly, the CN-loaded PVA fiber mats showed a reversible recovery in mechanical strength after cycling the relative humidity. Finally, humidity treatments of the composite PVA fiber mats induced significant enhancement of their strength as a result of the adhesion between the continuous matrix and the CNs.}, number={9}, journal={BIOMACROMOLECULES}, author={Peresin, Maria S. and Habibi, Youssef and Vesterinen, Arja-Helena and Rojas, Orlando J. and Pawlak, Joel J. and Seppala, Jukka V.}, year={2010}, month={Sep}, pages={2471–2477} }
 @article{peresin_habibi_zoppe_pawlak_rojas_2010, title={Nanofiber Composites of Polyvinyl Alcohol and Cellulose Nanocrystals: Manufacture and Characterization}, volume={11}, ISSN={["1526-4602"]}, DOI={10.1021/bm901254n}, abstractNote={Cellulose nanocrystals (CN) were used to reinforce nanofibers in composite mats produced via electrospinning of poly(vinyl alcohol) (PVA) with two different concentrations of acetyl groups. Ultrathin cross-sections of the obtained nanocomposites consisted of fibers with maximum diameters of about 290 nm for all the CN loads investigated (from 0 to 15% CN loading). The electrospinning process did not affect the structure of the PVA polymer matrix, but its degree of crystallinity increased significantly together with a slight increase in the corresponding melting temperature. These effects were explained as being the result of alignment and enhanced crystallization of PVA chains within the individual nanofibers that were subjected to high shear stresses during electrospinning. The strong interaction of the PVA matrix with the dispersed CN phase, mainly via hydrogen bonding or bond network, was reduced with the presence of acetyl groups in PVA. Most importantly, the elastic modulus of the nanocomposite mats increased significantly as a consequence of the reinforcing effect of CNs via the percolation network held by hydrogen bonds. However, this organization-driven crystallization was limited as observed by the reduction in the degree of crystallinity of the CN-loaded composite fibers. Finally, efficient stress transfer and strong interactions were demonstrated to occur between the reinforcing CN and the fully hydrolyzed PVA electrospun fibers.}, number={3}, journal={BIOMACROMOLECULES}, author={Peresin, Maria S. and Habibi, Youssef and Zoppe, Justin O. and Pawlak, Joel J. and Rojas, Orlando J.}, year={2010}, month={Mar}, pages={674–681} }
 @article{zoppe_habibi_rojas_venditti_johansson_efimenko_österberg_laine_2010, title={Poly(<i>N</i>-isopropylacrylamide) Brushes Grafted from Cellulose Nanocrystals via Surface-Initiated Single-Electron Transfer Living Radical Polymerization}, volume={11}, ISSN={1525-7797 1526-4602}, url={http://dx.doi.org/10.1021/bm100719d}, DOI={10.1021/bm100719d}, abstractNote={Cellulose nanocrystals (CNCs) or nanowhiskers produced from sulfuric acid hydrolysis of ramie fibers were used as substrates for surface chemical functionalization with thermoresponsive macromolecules. The CNCs were grafted with poly(N-isopropylacrylamide) brushes via surface-initiated single-electron transfer living radical polymerization (SI-SET-LRP) under various conditions at room temperature. The grafting process was confirmed via Fourier transform IR spectroscopy and X-ray photoelectron spectroscopy and the different molecular masses of the grafts were quantified and found to depend on the initiator and monomer concentrations used. No observable damage occurred to the CNCs after grafting, as determined by X-ray diffraction. Size exclusion chromatography analyses of polymer chains cleaved from the cellulose nanocrystals indicated that a higher degree of polymerization was achieved by increasing initiator or monomer loading, most likely caused by local heterogeneities yielding higher rates of polymerization. It is expected that suspension stability, interfacial interactions, friction, and other properties of grafted CNCs can be controlled by changes in temperature and provide a unique platform for further development of stimuli-responsive nanomaterials.}, number={10}, journal={Biomacromolecules}, publisher={American Chemical Society (ACS)}, author={Zoppe, Justin O. and Habibi, Youssef and Rojas, Orlando J. and Venditti, Richard A. and Johansson, Leena-Sisko and Efimenko, Kirill and Österberg, Monika and Laine, Janne}, year={2010}, month={Sep}, pages={2683–2691} }
 @article{spence_venditti_habibi_rojas_pawlak_2010, title={The effect of chemical composition on microfibrillar cellulose films from wood pulps: Mechanical processing and physical properties}, volume={101}, ISSN={0960-8524}, url={http://dx.doi.org/10.1016/j.biortech.2010.02.104}, DOI={10.1016/j.biortech.2010.02.104}, abstractNote={Films of microfibrillated celluloses (MFCs) from pulps of different yields, containing varying amounts of extractives, lignin, and hemicelluloses, were produced by combining refining and high-pressure homogenization techniques. MFC films were produced using a casting-evaporation technique and the physical and mechanical properties (including density, roughness, fold endurance and tensile properties) were determined. Homogenization of bleached and unbleached Kraft pulps gave rise to highly individualized MFCs, but not for thermo-mechanical pulp (TMP). The resulting MFC films had a roughness equivalent to the surface upon which the films were cast. Interestingly, after homogenization, the presence of lignin significantly increased film toughness, tensile index, and elastic modulus. The hornification of fibers through a drying and rewetting cycle prior to refining and homogenization did not produce any significant effect compared to films from never-dried fibers, indicating that MFC films can potentially be made from low-cost recycled cellulosic materials.}, number={15}, journal={Bioresource Technology}, publisher={Elsevier BV}, author={Spence, Kelley L. and Venditti, Richard A. and Habibi, Youssef and Rojas, Orlando J. and Pawlak, Joel J.}, year={2010}, month={Aug}, pages={5961–5968} }
 @article{spence_venditti_rojas_habibi_pawlak_2010, title={The effect of chemical composition on microfibrillar cellulose films from wood pulps: water interactions and physical properties for packaging applications}, volume={17}, ISSN={0969-0239 1572-882X}, url={http://dx.doi.org/10.1007/s10570-010-9424-8}, DOI={10.1007/s10570-010-9424-8}, number={4}, journal={Cellulose}, publisher={Springer Science and Business Media LLC}, author={Spence, Kelley L. and Venditti, Richard A. and Rojas, Orlando J. and Habibi, Youssef and Pawlak, Joel J.}, year={2010}, month={May}, pages={835–848} }
 @article{kim_montero_habibi_hinestroza_genzer_argyropoulos_rojas_2009, title={Dispersion of Cellulose Crystallites by Nonionic Surfactants in a Hydrophobic Polymer Matrix}, volume={49}, ISSN={["1548-2634"]}, DOI={10.1002/pen.21417}, abstractNote={Cellulose nanoparticles obtained by acid hydrolysis of cellulose paper were used to reinforce polystyrene composite films. The nonionic surfactant sorbitan monostearate was utilized to improve the dispersion properties of the hydrophilic cellulose in hydrophobic matrix and to prevent the formation of aggregates. Turbidity tests were used to measure dispersion stability of the cellulose crystallites in the hydrophobic solvent used in the composite manufacture. A correlation was found between the dispersion stability in solvent and the formation of aggregates in the polymeric composites. Nanocomposite films were processed using a casting/evaporation technique. Thermal and mechanical properties of processed composites were studied by differential scanning calorimetry (DSC) and dynamical mechanical analyses (DMA), respectively. The results showed that the optimum addition of surfactant produced better dispersion of the cellulose particles in the polystyrene matrix and improved the mechanical properties of the resulting composite due to an enhanced compatibility. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers}, number={10}, journal={POLYMER ENGINEERING AND SCIENCE}, author={Kim, Jooyoun and Montero, Gerardo and Habibi, Youssef and Hinestroza, Juan P. and Genzer, Jan and Argyropoulos, Dimitris S. and Rojas, Orlando J.}, year={2009}, month={Oct}, pages={2054–2061} }
 @article{rojas_montero_habibi_2009, title={Electrospun Nanocomposites from Polystyrene Loaded with Cellulose Nanowhiskers}, volume={113}, ISSN={["1097-4628"]}, DOI={10.1002/app.30011}, abstractNote={Composite microfibers from polystyrene and cellulose nanowhiskers were produced by electrospinning. The morphology of the microfibers was examined by using scanning and transmission electron microscopies. Surface porosity, unique ribbon-shapes, and the presence of twists along the fiber axis were observed in the composite microfibers. Thermomechanical properties of processed nanocomposites were studied by differential scanning calorimetry and dynamical mechanical analyses. The reinforcing effect of cellulose nanowhiskers was confirmed as the glassy modulus of electrospun microfibers increased with nanowhisker load. This effect is explained to be the result of mechanical percolation of cellulose nanowhiskers forming a stiff and continuous network held by hydrogen bonding. It is demonstrated that cellulose nanoparticles can be used effectively to reinforce hydrophobic matrices and to produce unique structural properties, enabling new functionalities and properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009}, number={2}, journal={JOURNAL OF APPLIED POLYMER SCIENCE}, author={Rojas, Orlando J. and Montero, Gerardo A. and Habibi, Youssef}, year={2009}, month={Jul}, pages={927–935} }
 @inbook{rojas_lucia_habibi_stubenrauch_2009, title={Interfacial properties of sugar-based surfactants}, ISBN={9781893997677}, booktitle={Bio-based surfactants and detergents: Synthesis, properties, and applications}, publisher={Urbana, IL: AOCS Press}, author={Rojas, O. J. and Lucia, L. A. and Habibi, Y. and Stubenrauch, C.}, year={2009} }
 @article{habibi_mahrouz_vignon_2009, title={Microfibrillated cellulose from the peel of prickly pear fruits}, volume={115}, ISSN={["0308-8146"]}, DOI={10.1016/j.foodchem.2008.12.034}, abstractNote={Cellulose microfibrils were isolated from the skin of Opuntia ficus indica (prickly pear fruits). Defatted skin powder was processed through consecutive extraction steps in order to remove mucilage, pectin and hemicelluloses. The cellulosic residue was made up of disencrusted cell-ghosts, having ovoid or elongated shapes, as revealed by optical microscopy. Transmission electron microscopy showed that, at the ultrastructural level, the cell walls of these cell-ghosts consisted of a loose network of cellulose microfibrils. This residue was subjected to mechanical homogenisation, leading to a stable and non-flocculating suspension by cellulose microfibril individualisation. This cellulosic material was characterised in terms of chemical composition, morphology and crystallinity, using sugar analyses, transmission electron microscopy and X-ray diffraction, as well as solid state NMR 13C spectroscopy.}, number={2}, journal={FOOD CHEMISTRY}, author={Habibi, Youssef and Mahrouz, Mostafa and Vignon, Michel R.}, year={2009}, month={Jul}, pages={423–429} }
 @article{cao_habibi_lucia_2009, title={One-pot polymerization, surface grafting, and processing of waterborne polyurethane-cellulose nanocrystal nanocomposites}, volume={19}, ISSN={["1364-5501"]}, DOI={10.1039/b910517d}, abstractNote={A series of new waterborne polyurethane (WPU)/cellulose nanocrystal (CN) composites have been successfully synthesized viain situpolymerization. The conditions were optimized to induce the grafting of part of the pre-synthesized WPU chains on the surface of cellulose nanocrystals (CNs) and the corresponding nanocomposites were processed by casting and evaporation. The morphology, structural, thermal, and mechanical properties of the resulting nanocomposite films were evaluated by scanning electron microscopy, wide-angle X-ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, and tensile tests. The success of the grafting was substantiated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and differential scanning calorimetry. Thus, it was demonstrated that the grafted WPU chains formed crystalline domains on the surface of CNs which expedited the crystallization of the polycaprolactone (PCL) soft segment domains in the WPU/CN nanocomposites. This co-crystallization phenomenon induced the formation of a co-continuous phase between the matrix and filler which significantly enhanced the interfacial adhesion and consequently contributed to an improvement in the thermal stability and mechanical strength of the nanocomposites. Although the ductility of the final nanocomposites was slightly reduced, in the CN content range from 0 to 10 wt-%, the Young's modulus and strength were significantly improved as shown by the change from 1.7 to 107.4 MPa and 4.4 to 9.7 MPa, respectively.}, number={38}, journal={JOURNAL OF MATERIALS CHEMISTRY}, author={Cao, Xiaodong and Habibi, Youssef and Lucia, Lucian A.}, year={2009}, pages={7137–7145} }
 @article{zoppe_peresin_habibi_venditti_rojas_2009, title={Reinforcing Poly(ε-caprolactone) Nanofibers with Cellulose Nanocrystals}, volume={1}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/am9003705}, DOI={10.1021/am9003705}, abstractNote={We studied the use of cellulose nanocrystals (CNXs) obtained after acid hydrolysis of ramie cellulose fibers to reinforce poly(ε-caprolactone) (PCL) nanofibers. Chemical grafting with low-molecular-weight PCL diol onto the CNXs was carried out in an attempt to improve the interfacial adhesion with the fiber matrix. Grafting was confirmed via infrared spectroscopy and thermogravimetric analyses. The polymer matrix consisted of electrospun nanofibers that were collected as nonwoven webs. The morphology as well as thermal and mechanical properties of filled and unfilled nanofibers were elucidated by scanning electron microscopy, differential scanning calorimetry, and dynamic mechanical analysis, respectively. The addition of CNXs into PCL produced minimal changes in the thermal behavior of the electrospun fibers. However, a significant improvement in the mechanical properties of the nanofibers after reinforcement with unmodified CNXs was confirmed. Fiber webs from PCL reinforced with 2.5% unmodified CNXs showed ca. 1.5-fold increase in Young’s modulus and the ultimate strength compared to PCL webs. Compared to the case of grafted nanocrystals, the unmodified ones imparted better morphological homogeneity to the nanofibrillar structure. The grafted nanocrystals had a negative effect on the morphology of nonwoven webs in which individual nanofibers became annealed during the electrospinning process and, therefore, could not be compared to neat PCL nonwoven webs. A rationalization for the different effects of grafted and unmodified CNXs in reinforcing PCL nanofibers is provided.}, number={9}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Zoppe, Justin O. and Peresin, Maria S. and Habibi, Youssef and Venditti, Richard A. and Rojas, Orlando J.}, year={2009}, month={Aug}, pages={1996–2004} }