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  • 1.
    Herrera, Martha
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Preparation and characterization of nanocellulose films and coatings from industrial bio-residues2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aim of this work has been to study cellulose nanocrystals (CNC) from bio-residues and their use as green coating materials. In the first part of this work, physical and chemical properties of different types of cellulose nanocrystals, from different raw material sources and different treatments were compared. It was found that all CNC suspensions had similar flow birefringence behavior, and similar diameters of the crystals. The mechanically isolated CNC from bio-ethanol residue had lower crystallinity but higher thermal stability compared chemically isolated CNC. Also the surface charge of these nanocrystals was different, being lower for the mechanically isolated CNC.In the second part, nanocrystals with lower and higher surface charges, were used to spin-coat films. The films were prepared with two different configurations: one with alternating layering of an anchoring polymer and CNC and the other with a single polymer layer coated with multilayers of CNC. The CNC with higher surface charge resulted in a smoother surface and the surface charge impacted the films’ hydrophobicity, being highest for CNC with lower surface charge. The gas permeability coefficient was dependent primarily on the surface charge of the CNC and secondly on the film configuration. The films with lower surface charge CNC were gas barriers for nitrogen and oxygen, and showed gas selectivity with some gas combinations while the films with higher surface charge CNC did not show gas selectivity.In the third part, coatings of CNC were prepared using spin- and dip-coating methods, on porous cellulose substrates. Microscopy studies showed that spin coating technique was suitable for the substrate with smaller pore size, while dip coating was suitable for the substrate with the larger pore size. The coating thickness ranged from some hundreds of nanometers for the spin-coated samples, to some micrometers for the dip-coated ones. The contact angle increased with the coating thickness and roughness. Additionally, the samples showed low oxygen permeability at 23% of relative humidity (RH). It was also seen that eight months storing reduced the barrier properties of the coatings when compared with fresh materials.In the last study, a new coating design as well as sorbitol plasticizer and citric acid crosslinker were used to improve the barrier and mechanical properties. This resulted in a dramatic improvement of the barrier properties and decreased water vapor permeability of more than 60%. Oxygen permeability value as low as 0.7 mL*μm/(m2*day*kPa) at 49% RH was reached when sorbitol was used. Overall, it was seen that the addition of sorbitol increased the thermal stability, barrier properties, and maximum strength of the CNC coatings.This work has demonstrated that nanocellulose films and coating from bio-residues can potentially be used to produce functional barrier coatings, thereby increasing the value of the forest resources.

  • 2.
    Herrera, Martha A.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Barrier and mechanical properties of plasticized and cross-linked nanocellulose coatings for paper packaging applications2017In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, no 9, p. 3969-3980Article in journal (Refereed)
    Abstract [en]

    Barrier, mechanical and thermal properties of porous paper substrates dip-coated with nanocellulose (NC) were studied. Sorbitol plasticizer was used to improve the toughness, and citric acid cross-linker to improve the moisture stability of the coatings. In general, the addition of sorbitol increased the barrier properties, maximum strength and toughness as well as the thermal stability of the samples when compared to the non-modified NC coatings. The barrier properties significantly improved, especially for plasticized NC coating’s, where the oxygen permeability value was as low as 0.7 mL μm day−1 m−2 kPa−1 at 49% RH and the water vapor permeability was reduced by 60%. Furthermore, we found that the cross-linked plasticized NC coating had a smoother surface (50% lower roughness) compared to non-modified ones. This study shows that the environmentally friendly additives sorbitol and citric acid had positive effects on NC coating properties, increasing its potential use in paper-based packaging applications.

  • 3.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Jackson-Etang, Ayuk
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Novel biorefinery: A residue from wood bioethanol production converted into cellulose nanocrystals2010In: International Conference on Nanotechnology for the Forest Products Industry 2010: Otaniemi, Espoo, Finland, 27-29 September 2010, Norcross, GA: TAPPI Press, 2010, p. 1241-1266Conference paper (Refereed)
    Abstract [en]

    The aim of the work was to use an industrial bio-residue as a raw material for the production of cellulose nanocrystals. The used residue, obtained from a bioethanol pilot plant, was purified using chemical extraction and whitening, and separated to nanocrystals by mechanical and chemical treatments such as ultrasonication, high-pressure homogenization and hydrolization. The chemical compositions and characteristics of the bio-residue were studied before and after purification using a TAPPI standard, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The morphology of the isolated nanocrystals was characterized using atomic force microscope (AFM). The chemical composition of the used bio-residue was found to be 49.5 wt-% cellulose, 42.1 wt-% lignin and 8.4 wt-% extractives. The crystallinity of the bio-residue was 14.5% and it increased to more than 73% after the purification process. The AFM study showed that a simple ultrasonication and homogenization processes resulted in nanosized crystals with diameters in the 10-20 nm range.

  • 4.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Cellulose nanocrystals: extraction from bio-residues2013In: Production and Applications of Cellulose Nanomaterials, TAPPI Press, 2013, p. 13-16Chapter in book (Refereed)
    Abstract [en]

    The aim of this study is to explore the utilization of industrial bio-residues as a source of raw material, for the industrial production of cellulose nanocrystals. For this purpose, cellulose nanocrystals have been isolated from bio-residues from ethanol and specialty cellulose production, to analyze their properties.

  • 5.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Characterization of cellulose nanowhiskers: a comparison of two industrial bio-residues2012In: 6th EEIGM International Conference Advanced Materials Research: 7th and 8th November, 2011 EEIGM, Nancy, France, Bristol: IOP Publishing Ltd , 2012Conference paper (Refereed)
    Abstract [en]

    Cellulose nanowhiskers separated from two different industrial residues, sludge from cellulose production (CNWSL) and lignin residue from ethanol production (CNWER), were compared in order to evaluate their characteristics and their potential as a source for the production of cellulose nanowhiskers (CNWs). It was found that CNWSL and CNWER suspensions exhibited flow birefringence when they were studied through cross-polarized filters. Transmission electron microscopy (TEM) study showed that the CNWSL were longer (377 nm) than CNWER (301 nm). It was also demonstrated that most CNWSL had nanowhiskers between 375-449 nm and CNWER between 300-374 nm. The UV/Vis spectroscopy showed a stronger interference in the UV and visible region for the CNWSL films. The crystallinity, obtained by X-ray analysis, was higher for CNWSL (86%) than for CNWER (78%). Finally, the thermal stability appeared to be slightly higher for the CNWER than for CNWSL. Both studied residues seem to be suitable sources for large-scale production of CNWs.

  • 6.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Comparison of cellulose nanowhiskers extracted from industrial bio-residue and commercial microcrystalline cellulose2012In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 71, no 1, p. 28-31Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to compare the physical and chemical properties of cellulose nanowhiskers extracted from industrial bio-residue (CNW-BR) by homogenization, and microcrystalline cellulose (CNW-MCC) by acid hydrolysis. CNW-MCC showed a higher surface charge than CNW-BR when analyzed using conductometric titration. Both CNW-suspensions showed flow birefringence, indicating the presence of individualized whiskers. Morphology study confirmed that the whisker diameters were less than 10 nm for both materials, and atomic force microscope images showed somewhat more aggregated BR nanowhiskers. UV/Vis spectroscopy of the CNW-films showed transparency in visual light. The relative crystallinity obtained from X-ray diffraction was 77% for the CNW-BR, and 85% for the CNW-MCC. It was demonstrated, by thermal analysis, that the CNW-BR was more thermally stable than the CNW-MCC, having a higher degradation onset temperature (218 °C and 155 °C) as well as maximum degradation temperature.

  • 7.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gas permeability and selectivity of cellulose nanocrystals films (layers) deposited by spin coating2014In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 112, p. 494-501Article in journal (Refereed)
    Abstract [en]

    Cellulose nanocrystals (CNC) were extracted from a cellulose residue using two different acid hydrolysis procedures. CNC extracted with sulfuric acid (CNCS) showed higher surface charge (339 μmol/g) compared with crystals extracted with hydrochloric acid (CNCHCl). Spin-coated films with two different configurations were prepared; the first with alternate layers of poly(allylamine hydrochloride) (PAHCl) and CNC, and the second with a single layer of PAHCl coated with multilayers of CNC. Film characteristics such as roughness, thickness, contact angle, orientation, gas permeability and gas selectivity were studied. Optical microscopy showed more homogeneous films of CNCS compared to CNCHCl. The surface charge of the crystals impacted the films’ hydrophobicity, being highest for 25 alternate layers of PAHCl and CNCHCl. The gas permeability coefficient was different for each film, depending primarily on the surface charge of the crystals and secondly on the film configuration. The films made with CNCHCl displayed gas barriers with nitrogen and oxygen, and gas selectivity with some gas combinations. CNCS films did not show gas selectivity. These results indicate that CNC with low surface charge can be further developed for gas separation and barrier applications.

  • 8.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Moisture and Gas Barrier Properties of Cellulose Nanocrystals in Thin Films2014In: Handbook of Green Materials: Processing Technologies, Properties and Applications, Singapore: World Scientific and Engineering Academy and Society, 2014Chapter in book (Refereed)
  • 9.
    Herrera, Martha
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sirviö, Juho A.
    Fibre and Particle Engineering Laboratory, University of Oulu.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Environmental friendly and sustainable gas barrier on porous materials: Nanocellulose coatings prepared using spin- and dip-coating2016In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 93, p. 19-25Article in journal (Refereed)
    Abstract [en]

    In this study, environmental friendly and sustainable coatings of nanocellulose (NC) were prepared using spin- and dip-coating methods, on two different porous cellulose substrates. Microscopy studies showed that spin-coating technique was suitable for the substrate with smaller pore size, while the dip-coating was suitable for the substrate with larger pore size. The coating thickness ranged from some hundreds of nanometers for the spin-coated layers, to some micrometers for the dip-coated ones. It was also seen that the contact angle increased with the coating thickness and roughness. NC coating resulted in low oxygen permeability (between 0.12 and 24 mL ∗ μm/(m2 ∗ 24 h ∗ kPa)) at 23% RH, but at 50% RH the oxygen permeability was too high to be measured, except for the dip-coated sample with 23 μm thickness. Also, it was seen that eight month storing reduced the barrier properties of the coatings when compared with fresh materials. These results indicate that NC coatings have a great potential as sustainable alternative coating on paperboard.

  • 10.
    Rodríguez, Martha Herrera
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nanostructured materials isolated from bio-residues, and their characterization2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The use of natural components in nanocomposites has continuously increased, due to environmental problems that are growing day by day. The use of bio-residues from forest industries to develop new materials will not only alleviate ecological problems but also affect the economy of forest industries positively.The aim of this work was to characterize cellulose nanowhiskers isolated from two different industrial bio-residues, one from bioethanol production and another from specialty cellulose production. Furthermore, the structure and permeability of thin films made of these nanowhiskers were studied. In the first study, the characteristics of nanowhiskers isolated from bioethanol residue were compared with nanowhiskers from microcrystalline cellulose (MCC). The nanowhiskers from ethanol residue had lower surface charge compared with whiskers obtained from MCC when analyzed by conductometric titration. The AFM microscopy showed that both cellulose nanowhisker suspensions presented individualized whiskers with diameters less than 10 nm. Nanowhiskers from ethanol residue showed higher relative crystallinity than the nanowhiskers from MCC, and the films made from both whiskers showed transparency in visual light. In addition, the nanowhiskers extracted from bio-residue were more thermally stable than the whiskers extracted from MCC, having a higher degradation onset temperature and maximum degradation temperature.In the second study, nanowhiskers isolated from two different bioresidues were compared. It was seen that both nanowhiskers suspensions (reject cellulose and ethanol residue) exhibited flow birefringence. Transmission electron microscopy study showed that the nanowhiskers extracted from the reject cellulose were slightly longer (377 nm) than the ones extracted from the ethanol residue (301 nm). The casted films of nanowhiskers from reject cellulose showed a stronger interference in the UV and visible region, compared with the other films. The comparative crystallinity was higher for reject cellulose nanowhiskers than for ethanol residue whiskers. Moreover, the thermal stability was slightly higher for the ethanol residue whiskers than for the reject cellulose whiskers. In the last study, cellulose nanowhiskers were isolated from the reject cellulose using hydrochloric and sulphuric acid hydrolysis processes with a aim to obtain different surface characteristics. Sulfuric acid whiskers had higher surface charge than the hydrochloric acid whiskers. Thin spin-coated films with two different configurations were prepared; one with alternate layers of poly(allylamine hydrochloride) (PAHCl) and cellulose nanowhiskers, and the second one with a single layer of PAHCl coated with 25 layers of whiskers. In addition, the film roughness, and surface charge of the whiskers was shown to increase the hydrophilic behavior of the films, being highest for a single layer of PAHCl coated with cellulose nanowhiskers. The gas permeability was measured and the coefficient was highest for hydrogen (H2) followed by helium (He), oxygen, (O2) and carbon dioxide (CO2) and nitrogen (N2). It was observed that the surface charge did not affect the gas permeability of the films and did not display selective gas barrier. The results showed that CNW can be extracted from ethanol residue and reject cellulose, and that these whiskers had similar characteristics as nanowhiskers obtained from other non-residual sources. This work has demonstrated that bio-residues can potentially be used as a source of new nanosize materials, thereby increasing the value of the forest resources.

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