Papers by Keyword: Glass Transition Temperature

Abstract: Corn husks, containing 50-55% cellulose, offer a sustainable source of cellulose nanocrystals (CNCs) with high thermal stability, tensile strength, and biocompatibility, making them ideal for reinforcing Shape-Stabilized Phase Change Materials (SSPCMs). In this study, CNCs were extracted from corn husks and integrated into polyethylene glycol (PEG) composite films to enhance their thermal and structural properties. The extraction process, verified through functional group analysis, thermogravimetric analysis (TGA), and X-ray diffraction, involved alkali treatment and bleaching. CNC-PEG composite films with varying CNC concentrations (0%, 2.5%, 5%, and 10% by weight) were fabricated via solvent casting and analyzed using TGA and differential scanning calorimetry (DSC). DSC revealed exothermic and endothermic peaks indicating crystallization and glass transition, with CNC addition increasing the melting temperature (T_m) by 2.4°C at 2.5% CNC loading. While CNC slightly lowered the decomposition temperature, the improved thermal properties, particularly at 2.5% CNC, show great potential for enhancing the stability and performance of SSPCMs, making them more efficient for thermal energy storage applications.

Abstract: The thermal stability of composite materials based on basalt fibers is determined by the strength of fibers under thermal stress. The decrease in strength occurs due to the crystallization of the original fibers and the development of microcrystalline nuclei in them during heating. Experimental studies of the influence of the processing temperature of continuous basalt fibers on their strength have been carried out. It has been established that the strength of fibers during their heat treatment up to 400^оС decreases by 25 % from the initial one. At the temperature of approximately 500^оС, the strength of the fibers is almost half. At 600^оС, the fiber strength is 20 % of the initial strength. At a processing temperature of 700^оС, the fiber is completely destroyed. The main reasons for the decrease in fiber strength are the development of microcrystalline nuclei that have formed in the fibers at the drawing stage in the crystallization zone. From above, this zone is determined by the temperature of the upper limit of melt crystallization, and from below it is limited by the glass transition temperature. The residence time of the melt in this range is the crystallization time. Calculations the speed of movement and the cooling rate of the melt stream during fiber drawing were carried out, which made it possible to determine the temperature zone and time of crystallization. The results of theoretical studies have shown that for the production of fibers used in composites, it is necessary to select such basalts and conditions for the fiber drawing, under which the values of the temperature zone and time of crystallization will be the smallest.

Abstract: A major function of resin is to provide defense against external attacks by releasing the resin flow on the attacked or damaged area. Nonetheless, the leakage of the resin on the surface can have a negative aesthetic and economic impact on wood material. The aim of this study is to investigate which treatments affect the chemo-physical properties of the resin in order to hinder the exudation on wood surface during service. To achieve a thickening of the resin, it is necessary to remove the volatile turpentine, and several studies have been carried out in this direction, providing useful information about this process. The heat treatment at different temperatures, 60°C, 100°C and 150°C, respectively, gives different mass losses, thus confirming that the turpentine can remain for long time in the resin, and the changes in structural, morphological, and chemical properties are affected by the temperature. FTIR spectroscopy, before and after thermal treatment, does not show major changes in chemical structures. However, from the samples analyzed with UHPLC-DAD-MS significant differences of the ratios of 20 compounds were observed, which characterize possible chemical reactions, such as decomposition, dehydrogenation, oxidation and isomerization. After heat treatment, the glass transition temperature of resin increased. Color changes are evident: resin becomes darker with increasing the temperature of treatment, apart from the resin heated at 100°C. The chemical changes in the composition of the resin caused by heat treatment need further investigation.

Abstract: The current investigation deals with the utilization of the Differential Scanning Calorimetric (DSC) experimental data of Se-Te-Sn Chalcogenide materials at various heating rates, 10,15,20, and 25 Kmin^-1. With the help of glass transition temperatures, T_g, fragility index, m is evaluated using Starink and Vogel-Flutcher-Tammanni (VFT) models. m is also correlated with mean coordination number (Ω) and the conclusions are derived. Sreeram et al. (modified Gibbs-DiMarzio) expression is scrutinized, which relates a verifiable link between T_g and Ω .

Abstract: Multifunctional materials refer to the types of materials that possess enhanced mechanical, electrical, and thermal properties. In this work, nano silica and Carbon Black (CB) are added to epoxy polymer as an effort to improve the thermomechanical and dielectric properties of the composites. Filler loadings are varied from 0.1 wt.%, up till 5 wt.%. The thermomechanical properties are measured from Dynamic Mechanical Thermal Analysis (DMTA) while the dielectric properties are measured from Vector Network Analyser (VNA). The synergistic effects of combining both fillers (keeping them at 1:1 wt.% ratio) are also assessed. It was found that the value of glass transition temperature (T_g) increased from 56.85°C (neat epoxy) to 59.8°C (5 wt.% CB). The T_q values further increased to 64.7°C, for 5 wt.% hybrid fillers (2.5 wt.% silica + 2.5 wt.% CB), demonstrating the synergistic effects by employing dual fillers. By adding single and dual fillers, the values of storage Modulus, E’ remains almost constant for both glassy (40°C) and rubbery region (100°C), regardless of the loadings employed. The values of real permittivity, e_r’ was also measured for dual fillers in the frequency range between 300 kHz to 18 GHz. The highest value of e_r’ was 5.5 F/m, which was measured for both 1.5 mm and 2.0 mm sample thickness of 5 wt.% hybrid fillers (2.5 wt.% silica + 2.5 wt.% CB). This study highlights the thermomechanical and dielectric properties improvement of epoxy composites by incorporating dual fillers.

Abstract: In the present study, Polylactic acid/ silicon dioxide (SiO₂)/ alumina (Al₂O₃) composite films were produced by a casting method. Thermal, morphological, optical and structural properties of obtaining samples investigated. The addition of aluminum monoxide and silicon dioxide fillers in PLA matrix increases the glass transition temperature significantly, and the Al₂O₃ and SiO₂ particles behave as good nucleating agents with PLA matrix. A homogeneous distribution of SiO₂ and Al₂O₃ particles was observed in the composite films. XRD results revealed that the addition of SiO₂ particles improved the crystallinity of PLA, knowing that the degree of crystallinity increase from 2.75% to 31.63% by adding the nucleating agents. The DSC results showed that the glass transition temperature increases by 12 °C in the composites than the pure PLA.

Abstract: Co-Pоly (Urethane-Imide) s (CPUI) based on pоly (diethyleneglycol) adipate diol, tolylenediisocyanate, multinucleate dianhydrides and diamines were synthesized. The films and moldings from CPUI were processed and their mechanical characteristics were evaluated. Distinctions of specifications of the films formed from polymer solutions and the moldings formed from melt polymers are indicated when using the same starting CPUI. It appears that films and moldings possess typical properties of elastomers. The reprocessing of studied copolymers by using the injection molding method allows to assign CPUI to the thermoplastic elastomers or so-called thermoelastoplasts.

Abstract: In this work, we investigated the influence of physical aging on polylactic acid (PLA) films using thermal and optical techniques; Differential Scanning Calorimetry (DSC), Thermally Stimulated Depolarization Current (TSDC), and Attenuated Total Reflection Spectroscopy (ATR). The PLA films were aged for different periods: 60, 90, and 120 minutes at a temperature T_a = 43 °C. The result obtained by DSC showed that the effect of physical aging appeared as an endothermic peak, which increased with increasing aging time and evolved towards higher temperatures. TSDC results showed a thermal current peak located between 30 and 80 ° C, which represented the main relaxation mode (α relaxation) of the dielectric manifestation of the glass transition. The intensity of this peak decreased and was shifted to higher temperatures when aging time increased, this result can be explained by a decrease in the molecular mobility of macromolecular chains due to the decrease in the free volume. The effect of physical aging on the PLA by the ATR technique showed a gradual decrease in all absorption bands during the aging period. In particular, the wide absorption band between 3000 and 3700 cm^-1 attributed to the hydroxyl group (OH), which disappeared after two hours of aging

Abstract: The present paper is aimed to investigate the effect of modifiers, such as poly (phenylene sulfone) and poly (aril ether ketone), on physico-mechanical and thermophysical properties of heat-resistant epoxy-anhydride binder based on EHD epoxy resin. It was found that the addition of poly (phenylene sulfone) and poly (aril ether ketone) can improve mechanical and impact strength characteristics of the binder with no reduction in heat resistance and thermal stability.

Abstract: Copolyarylates based on a mixture of 2,2-bis (4'-hydroxyphenyl) propane, 3,3-bis (4'-hydroxyphenyl) phthalide, terephthalic and isophthalic acid chlorides and 3,5-dibromo-p-hydroxybenzoic acid chloride were synthesized by low-temperature acceptor-catalytic polycondensation. To study the structure of the obtained polyesters and study the physical and mechanical properties, infrared spectroscopy, elemental, thermogravimetric, X-ray structural and thermomechanical analyzes were used. The obtained polymers have high values ​​of strength characteristics, thermal and heat resistance, good fire resistance.