Showing papers on "Thermogravimetry published in 2021"

Physicochemical Properties and Thermal Stability of Microcrystalline Cellulose Isolated from Esparto Grass Using Different Delignification Approaches

Abstract: Esparto grass, known as alfa, is a renewable biomass widely distributed in southern and western Mediterranean basin The present work focused on the isolation of pure cellulose from alfa stems, via different approaches, ie, acidified sodium chlorite (NaClO2), totally chlorine free (TCF) or their combination, followed by the preparation of microcrystalline cellulose (MCC) using acid hydrolysis method The obtained samples were characterized using infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TGA) and differential scanning calorimeter (DSC) The FTIR spectroscopy exhibited the removal of lignin and hemicellulose after the delignification and alkaline treatments The XRD data showed that all of the MCCs have higher crystallinity indexes (Alfa-MCC 73–82%) and belong to cellulose I type From SEM images, it is clear that the different MCC particles presented rough surface and micro-sized particles The DSC/TGA analyses revealed that MCC samples present better thermal stability than their respective cellulose ones, with higher temperature of decomposition (more than 350 °C) Moreover, the use of a combined process yields to MCC with higher crystallinity and better thermal stability Consequently, based on these findings, the delignification with combined method can be considered as a promising approach to extract MCC from alfa fibers with outstanding features

Effect of stabilizers and nitrogen content on thermal properties of nitrocellulose granules

Abstract: The granules containing nitrogen of various content (12.2–13.3%) and stabilizers (centralite I, centralite II, akardite II, triphenylamine) were obtained in laboratory scale, and the study of their physicochemical and thermal properties was conducted. It has been observed that the helium density of granules depends on the degree of gelling of nitrocellulose by the stabilizer as well as the lack of effect of the stabilizer type on the heat of combustion value. In turn, the heat of combustion depends on the content of nitrogen in nitrocellulose. Granules of 13.3% N nitrocellulose were characterized by a more rapidly developing thermal decomposition than the granules containing 12.2 and 12.9% N nitrocellulose. The maximum temperature of decomposition shifts toward higher temperatures (from 207.6 to 209.8 °C) with decreasing nitrogen content in nitrocellulose for granules containing triphenylamine as a stabilizer. All values of heat generation rate obtained for granules with triphenylamine were lower than the respective rates for granules with centralite I. Thermal properties and chemical stability of granules containing triphenylamine have better properties, when compared to other examined stabilizers. On the basis of differential scanning calorimetry and thermogravimetry, kinetic parameters were calculated by means of Ozawa–Flynn–Wall analysis. The effect of stabilizers and nitrogen content on kinetic parameters was determined. The kinetic model of thermal decomposition of granules was adjusted—the best fit was nth-order reaction with autocatalysis. The activation energy of thermal decomposition process according to the adopted chemical reaction model increases from 190 to 239 kJ mol−1 with increasing nitrogen content in the granulate.

Synthesis and Thermo-Mechanical Study of Epoxy Resin-Based Composites with Waste Fibers of Hemp as an Eco-Friendly Filler.

Abstract: The synthesis, thermal, and mechanical properties of epoxy resin composites incorporating waste fibers of hemp were studied Five different systems with increasing quantity of the eco-filler were obtained For the synthesis of polymeric materials, the commercial epoxy resins Epidian® 5 and triethylenetetramine (TETA) were applied as crosslinking agents The composites were obtained based on the polyaddition reaction of an amine group with an epoxide ring ATR/FT-IR (Attenuated Total Reflection-Fourier Transform Infrared) analysis was used to confirm the chemical structure of the composites and the course of curing processes Moreover, the influence of the eco-friendly components on the mechanical properties was determined, while thermal properties of the materials were investigated by thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) Dynamic mechanical studies (DMA) and Shore hardness tests of the obtained polymers were also carried out The DSC curves and DMA analysis revealed that all materials were characterized by a similar glass transition range Furthermore, the DMA and hardness measurements of the composites demonstrated an increasing elasticity with the increase in the amount of eco-filler present in the compositions

Undoped tetragonal ZrO2 obtained by the Pechini method: thermal evaluation of tetragonal–monoclinic phase transition and application as catalyst for biodiesel synthesis

Abstract: Zirconia (ZrO2) is a well-known polymorphic material, and the monoclinic phase of this compound is the most stable phase at room temperature. Nevertheless, tetragonal zirconia has been obtained at room temperature without doping using chemical synthesis methods. In the present work, tetragonal undoped ZrO2 was obtained by the Pechini method, and the tetragonal–monoclinic phase transition was evaluated by thermogravimetry, differential thermal analysis (DTA) and in situ high-temperature X-ray diffraction (HT-XRD). The tetragonal phase was obtained as the major phase after calcination at and below 800 °C, while most of the transition to the monoclinic phase took place during cooling at temperatures below 500 °C, as indicated by DTA and HT-XRD. The pure monoclinic phase was obtained after calcination at 1000 °C. Samples calcined at 600 and 1000 °C were sulphated and applied in the ethylic transesterification of soybean oil. No meaningful difference was observed in the activity, and high efficiency was attained for both catalysts for the reaction performed at 100 °C for 2 h.

Vegetable Oil-Based Thiol-Ene/Thiol-Epoxy Resins for Laser Direct Writing 3D Micro-/Nano-Lithography.

Abstract: The use of renewable sources for optical 3D printing instead of petroleum-based materials is increasingly growing. Combinations of photo- and thermal polymerization in dual curing processes can enhance the thermal and mechanical properties of the synthesized thermosets. Consequently, thiol-ene/thiol-epoxy polymers were obtained by combining UV and thermal curing of acrylated epoxidized soybean oil and epoxidized linseed oil with thiols, benzene-1,3-dithiol and pentaerythritol tetra(3-mercaptopropionate). Thiol-epoxy reaction was studied by calorimetry. The changes of rheological properties were examined during UV, thermal and dual curing to select the most suitable formulations for laser direct writing (LDW). The obtained polymers were characterized by dynamic-mechanical thermal analysis, thermogravimetry, and mechanical testing. The selected dual curable mixture was tested in LDW 3D lithography for validating its potential in optical micro- and nano-additive manufacturing. The obtained results demonstrated the suitability of epoxidized linseed oil as a biobased alternative to bisphenol A diglycidyl ether in thiol-epoxy thermal curing reactions. Dual cured thermosets showed higher rigidity, tensile strength, and Young’s modulus values compared with UV-cured thiol-ene polymers and the highest thermal stability from all prepared polymers. LDW results proved their suitability for high resolution 3D printing—individual features reaching an unprecedented 100 nm for plant-based materials. Finally, the biobased resin was tested for thermal post-treatment and 50% feature downscaling was achieved.

Morphology, Structural, Thermal, and Tensile Properties of Bamboo Microcrystalline Cellulose/Poly(Lactic Acid)/Poly(Butylene Succinate) Composites.

Abstract: The present study aims to develop a biodegradable polymer blend that is environmentally friendly and has comparable tensile and thermal properties with synthetic plastics. In this work, microcrystalline cellulose (MCC) extracted from bamboo-chips-reinforced poly (lactic acid) (PLA) and poly (butylene succinate) (PBS) blend composites were fabricated by melt-mixing at 180 °C and then hot pressing at 180 °C. PBS and MCC (0.5, 1, 1.5 wt%) were added to improve the brittle nature of PLA. Field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscope (FTIR), thermogravimetric analysis (TGA), differential thermogravimetry (DTG), differential scanning calorimetry (DSC)), and universal testing machine were used to analyze morphology, crystallinity, physiochemical, thermal, and tensile properties, respectively. The thermal stability of the PLA-PBS blends enhanced on addition of MCC up to 1wt % due to their uniform dispersion in the polymer matrix. Tensile properties declined on addition of PBS and increased with MCC above (0.5 wt%) however except elongation at break increased on addition of PBS then decreased insignificantly on addition of MCC. Thus, PBS and MCC addition in PLA matrix decreases the brittleness, making it a potential contender that could be considered to replace plastics that are used for food packaging.