Linda Vecbiškena

Preparation of Nanocellulose Using Ammonium Persulfate and Method’s Comparison with other Techniques

Cellulose nanocrystals (CNCs) have generated increasing attention in the past few years as potential sources of innovative bionanomaterials. This study focuses on an alternative method of nanocellulose particle preparation, using ammonium persulfate, and compares this to existing techniques. Nanoparticles were prepared using 4 different methods: thermocatalytic method, TEMPO oxidation, the acid hydrolysis and oxidation with ammonium persulfate. With the ammonium persulfate method, the grinding time of the oxidised cellulose is reduced drastically to only 0.5h, and results in an average nanoparticles size of 404.5 nm, zeta potential of -26.4 and crystallinity degree of 80%. Based on comparison of these parameters to results from existing techniques, oxidising cellulose using ammonium persulfate appears to be a promising alternative.

Nanocelluloses obtained by ammonium persulfate (APS) oxidation of bleached kraft pulp (BKP) and bacterial cellulose (BC) and their application in biocomposite films together with chitosan

Abstract Bleached birch kraft pulp (BKP, Södra Cell AB, Sweden) and unmodified bacterial cellulose (BC) pellicles, biosynthesized by the bacterium Komagataeibacter rhaeticus, were converted to cellulose nanofibers via ammonium persulfate (APS) oxidation. Fiber dimensions were investigated in an atomic force microscope, and the crystallite size was calculated by Rietveld analysis. Saos-2 osteosarcoma cell line served to assess the in vitro cytocompatibility of the biocomposite films. Results showed that individual cellulose nanofibers with an average width of 80±15 nm and a length between 600 and 1200 nm are formed by APS oxidation. The obtained BC nanofibers can be promising constituents in nanocellulose films and in chitosan-matrix films with improved physical-mechanical and biological properties. Good cellular biocompatibility was found for chitosan/oxidized cellulose films; the viability of Saos-2 osteosarcoma cells was higher on chitosan/oxidized BC films compared to chitosan/oxidized BKP films.

Nanostructured Calcium Phosphates for Biomedical Applications

This work is focused on the phase transformation from amorphous calcium phosphate (ACP) to nanostructured hydroxyapatite (HA) or tricalcium phosphate (TCP). Amorphous calcium phosphates with Ca/P molar ratio near 1.67 and 1.5 were synthesized by wet-chemical precipitation method and treated with ethanol. Upon thermal treatment, ACP clusters about 50 nm create a nanostructured HA or TCP. The highlights of this research: The precipitate treatment with ethanol provided a pure α-TCP that was found to be stable up to 1000 °C. HA is obtained from the ACP precursor synthesized using also ammonium dihydrogen phosphate.

Crystallized nano-sized alpha-tricalcium phosphate from amorphous calcium phosphate: microstructure, cementation and cell response

New insight on the conversion of amorphous calcium phosphate (ACP) to nano-sized alpha tricalcium phosphate (α-TCP) provides a faster pathway to calcium phosphate bone cements. In this work, synthesized ACP powders were treated with either water or ethanol, dried, crystallized between 700 and 800u2009°C, and then cooled at different cooling rates. Particle size was measured in a scanning electron microscope, but crystallite size calculated by Rietveld analysis. Phase composition and bonding in the crystallized powder was assessed by x-ray diffraction and Fourier-transform infrared spectroscopy. Results showed that 50u2009nm sized α-TCP formed after crystallization of lyophilized powders. Water treated ACP retained an unstable state that may allow ordering to nanoapatite, and further transition to β-TCP after crystallization and subsequent decomposition. Powders treated with ethanol, favoured the formation of pure α-TCP. Faster cooling limited the growth of β-TCP. Both the initial contact with water and the cooling rate after crystallization dictated β-TCP formation. Nano-sized α-TCP reacted faster with water to an apatite bone cement than conventionally prepared α-TCP. Water treated and freeze-dried powders showed faster apatite cement formation compared to ethanol treated powders. Good biocompatibility was found in pure α-TCP nanoparticles made from ethanol treatment and with a larger crystallite size. This is the first report of pure α-TCP nanoparticles with a reactivity that has not required additional milling to cause cementation.

Setting Properties of Brushite and Hydroxyapatite Compound Cements

In this work properties of potential brushite (CaHPO4•2H2O) and hydroxyapatite (Ca10(PO4)6(OH)2) compound cements are investigated. Calcium dihydrogenphosphate monohydrate (MCPM) and α-tricalcium phosphate (α-TCP) were the starting materials for investigated cements. Setting time is controlled by adding setting time retarder – citrate ions and initially unreactive filler - monetite (CaHPO4). Some compositions of obtained cements contain both brushite and hydroxyapatite. However a substantial amount of monetite was present even if it is not added as filler. There is a strong evidence of presence of octacalcium phosphate – a precursor phase for hydroxyapatite that lacks long range order.

Wood-Based Biocomposites: Mechanical Processing, Physical and Biological Properties

Wood-based nanoparticles fabricated by different optimized methods – acid hydrolysis, thermocatalytic destruction and TEMPO catalysed oxidation – show the potential to improve the physical-mechanical and biological properties of polymer-matrix biocomposites. In this work, the influence of obtained nanoparticles on physical-mechanical and biological properties of chitosan-matrix biocomposite was investigated. The results showed that wood-based nanoparticles are promising constituents of polymer-matrix biocomposites.

Nanoparticle Gels Obtained from Hardwood and Softwood Bark for Reinforcing of Paper

For reinforcing of paper, nanoparticle gels from black alder, birch and pine bark were obtained. Non-extracted bark and that extracted in biorefinery were used. For producing nanoparticles, the materials were destructed using the thermocatalytic destruction method and then dispersed in water medium in a ball mill. At a sufficient concentration, gel-like dispersions were obtained, which contained nanoparticles with the size ~300 nm. The effect of nanoparticle gels on the properties of paper sheets was investigated by introducing the dissolved gels in paper furnish and by covering both sides of paper sheets with nanoparticle gel coatings. It has been established that the nanoparticle fillers increase the tensile and burst strength. The nanoparticle fillers from extracted bark increase the mechanical indices to a higher extent. The coatings from nanoparticle gels considerably improve the Gurley air resistance of paper and increase the mechanical indices of paper sheets, especially burst strength. The effect of nanoparticle gel coatings is dependent on the coating thickness and gel concentration. The coatings decrease the tensile strength in a wet state.

Nano-Sized Calcium Phosphates: Synthesis Technique and Their Potential in Biomedicine

Nowadays, there is particular interest in nano-sized inorganic crystals for use as calcium phosphate bone substitutes, especially tricalcium phosphate (TCP) and hydroxyapatite (HA). This research takes on the challenge to produce nano-sized TCP and HA by heating amorphous calcium phosphate (ACP) precursors above the crystallization temperature. ACP precursors were synthesized by modified wet-chemical precipitation method. ACP treated with ethanol, favoured the formation of pure α-TCP, as well as others calcium phosphates—β-TCP and HA.

Bio-Based Nanomaterials - Versatile Materials for Industrial and Biomedical Applications

In this work, unmodified bacterial cellulose pellicles, biosynthesized by the bacterium Komagataeibacter rhaeticus, bleached birch Kraft pulp (Sodra Cell AB, Sweden) and birch bark supplied by the plywood industry (JSC Latvijas Finieris, Latvia), were used to obtain the nanoparticles. The results showed that cellulose nanoparticles fabricated by the ammonium persulfate oxidation method, an alternative method developed at the Latvian State Institute of Wood Chemistry, are promising constituents for producing nanopaper. Cellulose and birch bark nanofillers show the potential to improve the physical-mechanical and biological properties of chitosan-matrix films.