Change In Transition Temperature Research Articles

Time, temperature and water aging failure envelope of thermoset polymers

Epoxies and epoxy-based fiber reinforced polymers (FRP) are significantly affected by environmental impacts during their service life. Exposures to water, humidity, temperature and UV radiation are known to substantially influence the (thermo-) mechanical properties and durability of the materials. Design-relevant characteristics like strength, stiffness, or the glass transition temperature change with time. Therefore, expensive test campaigns are often necessary in advance of a structural design. Prediction models based on physical relations or phenomenological observations are typically required to reduce costs and increase reliability. Consequently, a combined methodology for fast prediction of long-term properties and accelerated aging purposes is presented in this work for a common DGEBA-based epoxy. Therefore, master curves are obtained by creep and constant-strain-rate tests under temperature and moisture impact. A combined time–temperature–water superposition and the Larson–Miller parametrization demonstrate that time-saving CSR tests and modeling can replace long-lasting creep testing. Resulting, the presented methodology allows to determine a polymer’s entire (environmental) failure envelope in a relatively short time and with low testing effort.

Study of Morphology, Rheology, and Dynamic Properties toward Unveiling the Partial Miscibility in Poly(lactic acid)-Poly(hydroxybutyrate-co-hydroxyvalerate) Blends.

The purpose of the present work was to gain a fundamental understanding of how the composition and physico-chemical properties affect the rheology, morphology, miscibility, and thermal stability of poly(lactic acid) (PLA)-poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) biopolymer blends obtained by melt mixing. First, restricted processing conditions were chosen, due to the inherent thermal degradation of PHBV, as proven by rheological dynamic time sweep (DTS) measurements and size-exclusion chromatography (SEC). Based on this, the composition dependence of the blends was investigated using small-amplitude oscillatory shear rheology (SAOS), and the results were confirmed by scanning electron microscopy (SEM) analysis. Subsequently, the changes in glass transition temperatures (Tgs) from the molten to the solid state, as observed by DMA and DSC, were verified by coupling SAOS to dielectric relaxation spectroscopy (DRS). Herein, the thermo-rheological complexity of PLA/PHBV blends in the melt was revealed, especially for PLA-rich blends. Irregularly structured morphologies, caused by highly mismatched viscoelastic properties, illustrated the degree of partial miscibility. Moreover, the thermo-rheological complexity appeared in the molten state of the asymmetric PLA-rich phases could be correlated to the crystal-amorphous interfacial MWS polarization, because of the locally-induced phase separation and heterogeneity, and owing to the differences in their crystallization properties during cooling. The miscibility also suffered from the lower thermal stability of PLA and the even more unstable PHBV. Nevertheless, the melt-induced degradation process of the PLA/PHBV blends seemed to be responsible for some of the in situ self-compatibilization and plasticization mechanisms. As a result, the miscibility and thermo-rheological simplicity were improved for the intermediate and PHBV-rich compositions at low temperatures, since their properties were, to a large extent, governed by the significant degradation of PHBV. The present findings should increase the understanding of morphological changes in PLA/PHBV blends and help control their micro/nanostructure.

Preparation and characterization of a novel luminescence nano-sillenite (Bi12SiO20) glass ceramic within Bi2O3–ZnO–SiO2 system

Bismuth silicate with sillenite structure (Bi12SiO20) nanophase was prepared via melt–quenching technique in the Bi2O3–ZnO–SiO2 glass system. The effect of replacement ZnO by Bi2O3 was studied. Their thermal behavior showed the change of glass transition temperature (Tg) from 577 °C in the Bi2O3-free glass to 438 °C in ZnO-free glass. In addition, the crystallization temperatures were not only changed from two to one peak, but also decreased from 927 to 476 °C in the same order. According to the heat treatment regimes, willemite, sillenite, tetragonal Bi2O3, cubic Bi2O3 and traces of ZnO were crystallized with different ratios depending on the change in composition and temperature. Sillenite was enhanced with increase heat treatment temperature and/or Bi2O3 additions. Heat treatment at 650 °C/10 h revealed the best regime, where higher degree of crystallization was achieved. The microstructure at 700 ℃/30 min showed nano-scale oriented parallel rod crystals with hexagonal making at their end, whereas clusters of irregular nano-size crystals was appeared at 650 °C/10 h. Transmission spectra of the glasses in UV–Vis–midIR region were increased with Bi2O3 addition reaching 74% in 100B. Photoluminescence properties of both glasses and their corresponding glass–ceramics showed luminescence nature since the blue and green colors were clearly appeared. Calculation of optical bandgap (Eopt) revealed 3.2–2.19 eV with increasing Bi2O3; these values are located in the semiconducting range. The prepared samples can be utilized in electro-optical instruments, also the high transmission in mid-IR nominate it for IR transmitting windows.

Molecular dynamics and conduction mechanism of poly(vinyl chloride‐co‐vinyl acetate‐co‐2‐hydroxypropyl acrylate) terpolymer containing ionic liquid

AbstractDielectric spectroscopy (DS) measurements were performed to probe the segmental dynamics and ion mobility of poly(vinyl chloride‐co‐vinyl acetate‐co‐2‐hydroxypropyl acrylate) terpolymer dopped with different amounts of tetrabutylammonium tetrafluoroborate ([TBA] [BF4]) ionic liquid (IL). Differential scanning calorimetry (DSC) was also employed to trace the change in the glass transition temperature (Tg) at different loads of IL. The DSC measurements revealed a remarkable reduction in the PVVH Tg from 344 to 310 K just by adding 20 wt% of IL. The DS measurements revealed three relaxation processes named α, β1, and β2. The α‐process is related to the segmental motion of PVVH while the β1 and β2 are due to the restricted local dynamics of side chains. The segmental relaxation times (α‐relaxation) speed up with increasing the concentration of IL due to the plasticization effect of IL on polymer chains. The temperature dependence of α‐relaxation follows the Vogel‐Fulcher‐Tammann (VFT) relation with dynamic glass transition between 323 and 294 K in agreement with the DSC measurements. The β1 and β2‐relaxations have an Arrhenius temperature dependence. The temperature dependence of ionic conductivity obeys the VFT behavior indicating the coupling between the segmental motion of PVVH chains and ion transport. Polaronic tunneling is the predominant conduction mechanism in PVVH and its composites. The specific capacitance increases with increasing both the temperature and IL concentration.

Influence of Phosphate on Network Connectivity and Glass Transition in Highly Polymerized Aluminosilicate Glasses.

Melt-derived metaluminous (Al/Na = 1) aluminosilicate glasses in the system SiO2-Al2O3-Na2O-P2O5 were prepared with P2O5 and SiO2 contents varying from 0 to 7.5 and 50 to 70 mol %, respectively. The glass structure was investigated by X-ray absorption near edge structure, far- and medium-infrared, and polarized Raman spectroscopic techniques. The results indicate the incorporation of phosphate into the aluminosilicate network not only as partially depolymerized groups but also as fully polymerized groups charge-balanced by aluminate units in Al-O-P bonds. A new analysis method based on polarized Raman spectra in the bending frequency range indicates a preference of phosphate to reorganize the smallest ring structures. Changes in the glass transition temperature with the increase in phosphate content were found to be consistent with the depolymerization of the network structure shown by spectroscopy. By contrast, increasing the silica content by substituting SiO4 for AlO4 tetrahedra, while keeping the phosphate content constant, was found to have a negligible effect on network polymerization. Still, the glass transition temperature decreased and correlated with a far-infrared sodium band shift to higher frequency. This was interpreted as local changes in bond strength caused by complex interactions between the different network formers and sodium ions.

Microscale evaluation of epoxy matrix composites containing thermoplastic healing agent

Among the strategies to produce healable thermosetting systems is their modification by the addition of thermoplastic particles. This work investigates the influence of poly(ethylene-co-methacrylic acid) (EMAA) on fiber-matrix interfacial properties of a glass fiber reinforced epoxy matrix composite. Epoxy-EMAA interactions were evaluated using differential scanning calorimetry (DSC) and infrared spectroscopy. The effects of EMAA on the epoxy network formation were evidenced by changes in glass transition temperature, cure kinetics and alteration of chemical groups during cure. Interfacial shear strength (IFSS) measurements obtained by single fiber pull-out tests indicate similar interfacial properties for pure and EMAA modified epoxy. Additionally, the potential for self-healing ability of an EMAA modified epoxy was demonstrated. However, IFSS after a healing cycle for the EMAA modified epoxy was lower as compared to the pure epoxy, because of the lower fiber-EMAA interfacial shear strength. So, thermoplastic healing agents has not only to fill cracks in the matrix material, but also have to be optimized regarding its interface properties to the reinforcing fibers.

Modelling changes in glass transition temperature in polymer matrices exposed tolow molecular weight penetrants.

Polymer matrices, when placed in contact with a fluid phase made of low molecular weight compounds, undergo a depression of their glass transition temperature (Tg) determined by the absorption of these compounds and the associated plasticization phenomena. Frequently, this effect is coupled with the mechanical action of the compressive stress exerted by the pressure of the fluid phase that, in contrast, promotes an increase in the Tg. This issue is relevant for technological and structural applications of composites with high-performance glassy polymer matrices, due to their significant impact on mechanical properties. We propose an approach to model and predict rubbery-glassy states maps of polymer-penetrant mixtures as a function of pressure and temperature based on the Gibbs-Di Marzio criterion. This criterion establishes that a 'thermodynamic' glass transition does occur when the configurational entropy of the system vanishes. Although questioned and criticized, this criterion constitutes a good practical approach to analyse changes of Tg and, in some way, reflects the idea of an 'entropy catastrophe' occurring at the glass transition. Several polymer-penetrant systems have been analysed modelling configurational entropy by means of the Non-Random Hydrogen Bond lattice fluid theory, able to cope with possible non-random mixing and occurrence of strong interactions. This article is part of the theme issue 'Ageing and durability of composite materials'.

Structural length-scale of β relaxation in metallic glass.

Establishing the structure-property relationship is an important goal of glassy materials, but it is usually impeded by their disordered structure and non-equilibrium nature. Recent studies have illustrated that secondary (β) relaxation is closely correlated with several properties in a range of glassy materials. However, it has been challenging to identify the pertinent structural features that govern it. In this work, we show that the so-called polyamorphous transition in metallic glasses offers an opportunity to distinguish the structural length scale of β relaxation. We find that, while the glass transition temperature and medium-range orders (MROs) change rapidly across the polyamorphous transition, the intensity of β relaxation and the short-range orders (SROs) evolve in a way similar to those in an ordinary reference glass without polyamorphous transition. Our findings suggest that the MRO accounts mainly for the global stiffening of the materials and the glass transition, while the SRO contributes more to β relaxation per se.

Study of temperature fields in samples of polymer materials using dynamic mechanical analysis

The goal of the study is to reveal the dependence of the glass transition temperature on conditions of its determination. We present the results of studying temperature fields in the samples of polymer materials by the method of dynamic mechanical analysis. Changes in the glass transition temperature of the poly­mer casting VSE-34 and the temperature profile in the polymer matrix ED-20/DAFS were analyzed. Stan­dard melting samples were used to correct the test results using the correction function. It is shown that the most significant temperature deviations are observed when measured in argon and helium media with heating rates of 1, 2, 5, and 5 K/min. The temperature distribution over the polymer casting sample is highly non-uniform. The difference between the temperature in the middle and at a distance of 1/4 from the edge of the sample equals 16°C (medium — argon, heating rate — 5 K/min). Moreover, at a heating rate of 1 K/min, abnormally low values of the glass transition index were marked. The results obtained can be used to improve the measurement procedure, reduce test duration and refine the results of tests in various gaseous media.

The influencing factors of evaporation residue of emulsified modified asphalt to optimize the environmental adaptability

Compared with traditional asphalt, emulsified asphalt occurs to be a better low-temperature usability and environmental adaptability, which can reduce environmental pollution and energy consuming during road construction. The low-temperature ductility is a very important indicator to evaluate the environmental adaptability of emulsified asphalt. However, the relevance between microstructure and low-temperature ductility of modified asphalt is still rarely reported. Herein, we reported the first successful unfolding of the microscopic mechanism of ductility attenuation of the modified emulsified asphalt by combining experiments and characterization: Emulsifiers and additives had greater influence on the low-temperature ductility. Anionic and cationic emulsifiers had the similar ductility loss. Adding a non-ionic emulsifier OP-10 could be a solution to improve the ductility. The effect of the temperature change occurred less significant compared to the pH evolution of surfactant solution. The grey relation entropy (GRE) analysis revealed that the emulsifier structure (C/H ratio) would be the most important factor to affect the low-temperature ductility. The macro, micro and nano scales of modified emulsified asphalt were correlated, revealing in-depth that the aggregation and inter-chains interaction of styrene-butadiene-styrene (SBS) were the internal mechanism leading to the ductility loss. The change of glass transition temperature (Tg) was proposed to correlate the microstructural factor with the ductility. Moreover, the combination of ductility test and bending beam rheometer (BBR) test could be an effective way to evaluate the low-temperature performance of asphalt.

Magnetostructural phase transitions and magnetocaloric effect in Mn-Fe-Ni-Ge-B alloys

The search for room-temperature high-performance magnetocaloric materials is highly stimulated towards magnetic refrigeration techniques. Here we report the boron doping effect on the magnetostructural transition and magnetocaloric effect of the Mn 0.89 Fe 0.11 NiGe alloy. Our studies reveal that the addition of only 0.2 at% boron induces a large magnetic entropy change (∆ S m ) of − 69.4 J kg −1 K −1 at 298.5 K under μ 0 H up to 7 T, which is ~ 34.0% higher than that of − 51.8 J kg −1 K −1 in the host alloy Mn 0.89 Fe 0.11 NiGe obtained at a much lower temperature of 267.5 K. With the increase of boron content, the phase transition temperature M s showed a nonlinear change that first increased and then decreased. The investigation of the microstructure by transmission electron microscopy suggests that the minor B atoms will get into the interstitial site of Mn 0.89 Fe 0.11 NiGe alloy, increase the cell volume, and stabilize the orthorhombic structure of the alloy. This could be the main reason for the increase in magneto-structural transition temperatures. Otherwise, the excessive B atoms will introduce precipitates, and cause the reduction of the magnetostructural transition temperature. It suggests that proper doping point defects are effective to tailor magneto-structural transition toward achieving the magnetocaloric effect. • B causes a nonlinear change of the magneto-structural transition temperature of Mn 0.89 Fe 0.11 NiGe. • Adding 0.2 at% B enhances magnetic entropy change by~ 34.0%. • The minor boron atoms will increase the cell volume and stabilize the martensitic phase. • Nano-precipitates at high B contents hinder the phase transition and decrease the transition temperature.

Investigation on the morphology and the permeability of biomimetic cellulose triacetate (CTA) impregnated membranes (IM): In-situ synchrotron imaging, experimental and computational studies

The goal of the present study is to ascertain the controlled permeability of the biomimetic cellulose triacetate (CTA) membranes at different temperatures and salt concentrations by investigating the electrical oscillatory behaviour across the impregnated membranes (IM). The novel biomimetic CTA membranes were infused with a capric fatty acid to induce the electrical oscillatory behavior, and hence, to ensure the controlled permeability. In-situ synchrotron-based X-ray tomography (SR-μCT) at BioMedical Imaging and Therapy (BMIT) Beamline at the Canadian Light Source (CLS) was used to evaluate the main impregnated membrane morphology compared to neat CTA to ensure the fatty acid penetration inside membrane pores along membrane matrices. This study has revealed changes in phase transition temperatures of the impregnated CTA membrane at the melting temperature of the fatty acid. The pulsations of measured voltages were observed to be related to changes in the KCl concentration in the vicinity of the Ag/AgCl electrode. In this study, amplitudes and frequencies of voltage pulsations were dependent on the temperature and concentration of the KCl solution to control the permeability of the biomimetic membrane membranes. Increasing the KCl concentration led to a higher frequency of oscillation which reflects a higher permeability. In addition, no mechanical stirring or disturbance of the system was required for the electrical oscillatory phenomenon to occur. Nevertheless, for the average waveforms, the peak-to-peak value obtained was doubled when stirring was performed, while for the higher amplitude waveforms, the amplitude increased by 5 times. In addition, interactions at the molecular level between water molecules and the fragments of infused membranes at different temperatures and their effect on controlling permeability was investigated using pair interaction energy decomposition analysis (PIEDA) as part of the fragment molecular orbital (FMO) method's framework. Those results opened new frontiers for facilitation and regulation of active transport and permeability through biomimetic smart membranes for a variety of biomedical and drug delivery applications.

Inhibitory Effect of Lanthanides on Native Lipid Flip-Flop

The influence of ytterbium ions (Yb3+), a commonly used paramagnetic NMR chemical shift reagent, on the physical properties and flip-flop kinetics of dipalmitoylphosphatidylcholine (DPPC) planar supported lipid bilayers (PSLBs) was investigated. Langmuir isotherm studies revealed that Yb3+ interacts strongly with the phosphate headgroup of DPPC, evidenced by the increases in shear and compression moduli. Using sum-frequency vibrational spectroscopy, changes in the acyl chain ordering and phase transition temperature were also observed, consistent with Yb3+ interacting with the phosphate headgroup of DPPC. The changes in the physical properties of the membrane were also observed to be concentration dependent, with more pronounced modification observed at low (50 μM) Yb3+ concentrations compared to 6.5 mM Tb3+, suggesting a cross-linking mechanism between adjacent DPPC lipids. Additionally, the changes in membrane packing and phase transition temperatures in the presence of Tris buffer suggested that a putative Yb(Tris)3+ complex forms that coordinates to the PC headgroup. The kinetics of DPPC flip-flop in the gel and liquid crystalline (lc) phases were substantially inhibited in the presence of Yb3+, regardless of the Yb3+ concentration. Analysis of the flip-flop kinetics under the framework of transition state theory revealed that the free energy barrier to flip-flop in both the gel and lc phases was substantial increased over a pure DPPC membrane. In the gel phase, the trend in the free energy barrier appeared to follow the trend in the shear moduli, suggesting that the Yb3+-DPPC headgroup interaction was driving the increase in the activation free energy barrier. In the lc phase, activation free energies of DPPC flip-flop in the presence of 50 μM or 6.5 mM Yb3+ were found to mirror the free energies of TEMPO-DPPC flip-flop, leading to the conclusion that the strong interaction between Yb3+ and the PC headgroup was essentially manifested as a headgroup charge modification. These studies illustrate that the presence of the lanthanide Yb3+ results in significant modification to the lipid membrane physical properties and, more importantly, results in a pronounced inhibition of native lipid flip-flop.

An experimental study on the mechanical performance of BFRP-Al adhesive joints subjected to salt solutions at elevated temperature

In order to study the mechanical properties of basalt fiber reinforced resin polymers–aluminum alloy (BFRP-Al) single lap joints (SLJ) under different humid and hot conditions. 80 °C/deionized water (DI-water), 80 °C/3.5%NaCl solution and 80 °C/5%NaCl solution were used as the aging conditions of BFRP-Al joints. Through the hygroscopic experiment, the maximum water absorption rate of dumbbell-shaped adhesive in the three environments was 7.15%, 4.12% and 4.96%, respectively. The maximum water absorption of basalt fiber reinforced resin polymers (BFRP) in the three environments was 2.24%, 1.2% and 1.55%, respectively. It is concluded that salt solution inhibits the absorption of water by adhesive and BFRP. The quasi-static tensile test of the joint was carried out. And the result shows that the failure strength of the joint in the three environments increases at first and then decreases with the prolongation of aging time. And the failure strength of the joint in the high-temperature salt solution is better than that in high-temperature DI-water. DSC experiments show that changes in glass transition temperature (T g) reflect changes in failure strength. SEM image analysis of the joint failure mechanism can show that the resin matrix damage in BFRP increases with aging time. The mechanical properties of the joint at the later stage of aging depend on the performance of BFRP.

Fabrication and Characterization of Carbon Nanofibers Coated Expandable Thermoplastic Microspheres-Based Polymer Composites

Background: Thermoplastic expandable microspheres (TEMs) are spherical particles that consist of a polymer shell encapsulating a low boiling point liquid hydrocarbon that acts as the blowing agent. When TEMs are heated at 80-190 °C, the polymer shell softens, and the hydrocarbon gasifies, causing the microspheres to expand, leading to an increase in volume and decrease in density. TEMs are used in food packaging, elastomeric cool roof coatings, shoe soles, fiber and paper board, and various applications in the automotive industry. It is noted that TEMs are known by their brand name ‘Expancel’, which is also used to refer TEMs in this paper. Objective: The objective of this work was to develop and characterize forms prepared from TEMs with/without carbon nanofibers (CNFs) coatings to study the effect of CNFs on structural, thermal, and mechanical properties. Method: Sonochemical method was used to coat TEMs with various weight percentages (1, 2, and 3%) of CNF. Neat foam (without CNF) and composite foams (TEMs coated with various wt.% of CNF) were prepared by compression molding the TEMs and TEMs-CNF composites powders. Thermal and mechanical properties of the neat and composite foams were investigated. Result: The mechanical properties of the composite foam were notably improved, which is exhibited by a 54 % increase in flexural modulus and a 6% decrease in failure strain with the TEMs-(2 wt.% CNF) composite foam as compared to the neat foam. Improvement in thermal properties of composite foam was demonstrated by a 38% increase in thermal stability at 800ºC with the TEMs-( 1 wt.% CNF) composite foam as compared to the neat foam. However, no change in the glass transition of TEMs was observed with the CNF coating. SEM-based analysis revealed that CNFs were well dispersed throughout the volume of the TEMs matrix, forming a strong interface. Conclusions: Straightforward sonochemical method successfully triggered efficient coating of TEMs with CNFs, resulting in a strong adhesion interface. The mechanical properties of composite foams increased up to 2% of CNFs coating and then decreased with the higher coating, presumably due to interwoven bundles and aggregation of CNFs, which might have acted as critical flaws to initiate and propagate cracking. Thermal properties of foams increased with the CNFs coating while no change in glass transition temperature was observed due to coating.

Effect of Thermal Exposure on Residual Properties of Wet Layup Carbon Fiber Reinforced Epoxy Composites.

Ambient cured wet layup carbon fiber reinforced epoxy composites used extensively in the rehabilitation of infrastructure and in structural components can be exposed to elevated temperature regimes for extended periods of time of hours to a few days due to thermal excursions. These may be severe enough to cause a significant temperature rise without deep charring as through fires at a small distance and even high-temperature industrial processes. In such cases, it is critical to have information related to the post-event residual mechanical properties and damage states. In this paper, composites are subjected to a range of elevated temperatures up to 260 °C over periods of time up to 72 h. Exposure to elevated temperature regimes is noted to result in a competition between the mechanisms of post-cure that can increase the levels of mechanical characteristics, and the deterioration of the resin and the bond between the fibers and resin that can reduce them. Mechanical tests indicate that tensile and short beam shear properties are not affected negatively until the highest temperatures of exposure considered in this investigation. In contrast, all elevated temperature conditions cause deterioration in resin-dominated characteristics such as shear and flexure, emphasizing the weakness of this mode in layered composites formed from unidirectional fabric architectures due to resin deterioration. Transitions in failure modes are correlated through microscopy to damage progression both at the level of fiber-matrix interface integrity and through the bulk resin, especially at the inter-layer level. The changes in glass transition temperature determined through differential scanning calorimetry can be related to thresholds that indicate changes in the mechanisms of damage.

Effect of sintering time on the structural and magnetocaloric properties of Mn-Fe-P-Si-Ge-B alloys prepared by spark plasma sintering

Spark plasma sintering (SPS) has some advantages for preparing multifunctional materials, such as fast heating rate, short sintering time, and high compactness of products. In this work, we reported the effect of sintering time on the structural and magnetocaloric properties of Mn1.15Fe0.85P0.65Si0.13Ge0.2B0.02 prepared by SPS. The crystalline structure, microstructure and composition were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The results indicated that all the alloys crystallized in the hexagonal structure with a space group of P6 − 2m. A secondary phase of (Mn,Fe)3(Si,Ge) was not found in SEM but in TEM measurement. Transition temperature and isothermal entropy change were determined from thermal magnetization data measured in different constant magnetic fields. The results showed that the alloys undergo first-order phase transitions at transition temperatures between 248.8 K and 281.9 K. The maximum isothermal entropy change was found in the alloy sintered for 15 min, being 15.6 J ⋅ kg−1 ⋅ K−1 for a magnetic field change of 3 T. It indicated that no less than 15 min sintering time was required to prepare the alloy with good homogeneousness and large magnetocaloric effect. Consequently, SPS is an effective method for synthesizing the Fe2P-type alloys and the resultant alloys are promising magnetocaloric materials for magnetic refrigeration near room temperature.

Thermal properties of wood flour reinforced polyamide 6 biocomposites by twin screw extrusion

Abstract The use of waste wood flour as polymer reinforcements has recently gained popularity because of its environmental benefits. The goal of this research is to determine the thermal properties of a waste wood flour/polyamide 6 composite made via extrusion. The fillers were melt compounded with polyamide 6 at filler concentrations of 5%, 10%, and 15% using a twin screw extruder, followed by compression molding. The processability of waste wood flour/polyamide 6 composite was evaluated using thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), and dynamic thermomechanical analysis (DMA). According to the TGA analysis, the thermal stability of the composites decreases as the natural fiber content increases. The onset temperature of rapid thermal deterioration was reduced somewhat from 425 °C (neat PA6) to 405 °C (15 wt% wood flour). According to the DSC results, the addition of natural fibers resulted in quantify changes in the glass transition (T g), melting (T m), and crystallization temperature (T c) of the PA6 composites. The storage modulus from the DMA study increased from 1177 MPa (neat PA6) to 1531 MPa due to the reinforcing effects of wood flour (15 wt%). Waste wood flour/polyamide 6 composites offer advantageous thermal properties, enabling us to profit from the strengthening potential of such cellulosic reinforcements while remaining recyclable and generally renewable.

Melting Temperature Depression and Phase Transitions of Nitrate-Based Molten Salts in Nanoconfinement.

Hybrids of nitrate-based molten salts (KNO3, NaNO3, and Solar Salt) and anodic aluminum oxide (AAO) with various pore sizes (between 25 and 380 nm) were designed for concentrated solar power (CSP) plants to achieve low melting point (<200 °C) and high thermal conductivity (>1 W m–1 K–1). AAO pore surfaces were passivated with octadecyl phosphonic acid (ODPA), and the results were compared with as-anodized AAO. The change in phase transition temperatures and melting temperatures of salts was investigated as a function of pore diameter. Melting temperatures decreased for all salts inside AAO with different pore sizes while the highest melting temperature decrease (ΔT = 173 ± 2 °C) was observed for KNO3 filled in AAO with a pore diameter of 380 nm. Another nanoconfinement effect was observed in the crystal phases of the salts. The ferroelectric phase of KNO3 (γ-phase) formed at room temperature for KNO3/AAO hybrids with pore size larger than 35 nm. Thermal conductivity values of molten salt (MS)/AAO hybrids were obtained by thermal property analysis (TPS) at room temperature and above melting temperatures of the salts. The highest increase in thermal conductivity was observed as 73% for KNO3/AAO-35 nm. For NaNO3/AAO-380 nm hybrids, the thermal conductivity coefficient was 1.224 ± 0.019 at room temperature. To determine the capacity and efficiency of MS/AAO hybrids during the heat transfer process, the energy storage density per unit volume (J m–3) was calculated. The highest energy storage capacity was calculated as 2390 MJ m–3 for KNO3/AAO with a pore diameter of 400 nm. This value is approximately five times higher than that of bulk salt.

DMA Analysis of Plasma Modified PVC Films and the Nature of Initiated Surface Changes.

The application of DCSBD (Diffuse Coplanar Surface Barrier Discharge) plasma is referred to as the surface modification/activation of materials. The exposure of material surfaces to DCSBD plasma is initiated by changes in their chemical composition, surface wettability and roughness. The given study presents the mentioned plasma application in the context of the modification of the material viscoelastic properties, namely the PVC polymer film. The measurement of viscoelastic properties changes of PVC was primarily examined by a sensitive thermal method of dynamic-mechanical analysis. This analysis allows identifying changes in the glass transition temperature of PVC, before and after DCSBD plasma application, Tangens Delta, supported by glass transition temperatures of Elastic and Loss modulus. The results of the present study prove that DCSBD plasma applied on both sides to PVC surfaces causes changes in its viscoelastic properties. In addition, these changes are presented depending on the variability of the material position, with respect to the winding of the electrodes in the ceramic dielectric generating the DCSBD plasma during modification. The variability of the PVC position holds an important role, as it determines the proportion of filamentous and diffuse components of the plasma that will interact with the material surface during modification. The application of DCSBD plasma must, therefore, be considered a complex modification of the material, and as a result, non-surface changes must also be considered.