Browsing by Author "Maloney, Thad C."

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  • Absorption of water by pulp fibers
    (2000) Kang, Taegeun
     Helsinki University of Technology | Master's thesis
  • Co-exfoliation and fabrication of graphene based microfibrillated cellulose composites-mechanical and thermal stability and functional conductive properties
    (2018-05-28) Phiri, Josphat; Johansson, Leena Sisko; Gane, Patrick; Maloney, Thad C.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The excellent functional properties of graphene and micro-nanofibrillated cellulose (MNFC) offer plenty of possibilities for wide ranging applications in combination as a composite material. In this study, flexible graphene/microfibrillated cellulose (MFC) composite films were prepared by a simple method of co-exfoliation of graphite in an MFC suspension by high-shear exfoliation. We show that pristine graphene, without any chemical treatment, was homogeneously dispersed in the MFC matrix, and the produced composites showed enhanced thermal, electrical and mechanical properties compared to a non-co-exfoliated control. The film properties were studied by XPS, XRD, Raman, SEM, FTIR, TGA, nitrogen sorption, UV-vis spectroscopy, optical and formation analysis tests. At 0.5 wt% loading, the specific surface area of graphene/MFC composites increased from 218 to 273 m2 g-1 while the tensile strength and Young's modulus for the graphene/MFC composites increased by 33% and 28% respectively. Thermal stability was enhanced by 22% at 9 wt% loading and the composites showed a high electrical conductivity of 2.4 S m-1. This simple method for the fabrication of graphene/MFC composites with enhanced controlled functional properties can prove to be industrially beneficial, and is expected to open up a new route for novel potential applications of materials based largely on renewable resources.
  • Impact of high consistency enzymatic hydrolysis and defibration drying on cellulose fiber pore characteristics
    (2023-08) Dahiya, Deepika; Ceccherini, Sara; Maloney, Thad C.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The purpose of this study is to examine the hornification of enzymatically hydrolyzed high consistency softwood kraft pulp in an experimental defibration dryer. This device dries pulp under turbulent conditions which can prevent interfiber bonding and produce a separated fiber population. This is useful in certain applications, such as composites, which require dry, unbonded pulp fibers. In this study, we examine how fibrillated pulps behave in the dryer with respect to pore expansion in hydrolysis and collapse in drying (hornification). It was found that the endoglucanase cocktail increased the micro-, meso-, and macropore volumes as a function of hydrolysis time. Drying decreased the pore volumes of each size category, with the biggest changes in the macropore region. The pulp with the highest swelling after hydrolysis had the lowest swelling after drying. The mesopores that were formed in hydrolysis were somewhat preserved after drying. After drying, unfibrillated pulp had good fiber separation, while the highly fibrillated samples formed sub-millimeter, spherical particles.
  • Multidimensional Co-Exfoliated Activated Graphene-Based Carbon Hybrid for Supercapacitor Electrode
    (2019-01-01) Phiri, Josphat; Gane, Patrick; Maloney, Thad C.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Herein, a simple route for the fabrication of highly porous-activated few-layer graphene for application in supercapacitors as an electrode material is reported. The process makes use of natural and renewable materials, which is an essential prerequisite, especially for large-scale application. Few-layer graphene is exfoliated in aqueous suspension with the aid of microfibrillated cellulose (MFC), an environmentally benign eco-friendly medium that is low-cost, biodegradable, and sustainable. The exfoliated product is subsequently activated to increase the surface area and to form the desired pore structure. The prepared electrode materials exhibit a high surface area of up to 720 m2 g−1. MFC is also used as a nontoxic environmentally friendly binder in the electrode application. The electrochemical performance is evaluated in a three-electrode system, and the prepared samples show a high specific capacitance of up to 120 F g−1 at a current density of 1 A g−1. The samples also exhibit a high capacity-retentionrate of about 99% after 5000 cycles and 97% after 10 000 cycles. The proposed method for the fabrication of graphene-based supercapacitor electrode materials, based largely on renewable and sustainable materials, offers potential for commercially viable applications.
  • Structural changes induced in pulp fibers from wet pressing from the viewpoint of fiber/water interaction
    (1995) Maloney, Thad C.
     Helsinki University of Technology | Master's thesis
  • Technology roadmap of performance papers
    (2010) Vimeri, Kirmo
     School of Chemical Engineering | Master's thesis