Shift In Glass Transition Temperature Research Articles

Impact of hydrothermal aging on microstructure transformation in Poly(L‐lactide) nonwovens under tension in condition close to a living organism

AbstractThe analysis of mechanical properties and structure of bioresorbable polymer nonwoven materials is an important area of research in the medical industry, the properties and structure of which directly affect the processes of cellular activity. In this work, the processes of reorganization of the fibrous microstructure of poly(l‐lactide) nonwoven materials under uniaxial tension in a water environment were investigated. The study which included volumetric ultrasound imaging, mechanical testing, differential scanning calorimetry, X‐ray diffraction, and melting rate measurements was the first attempt to identify correlations between the mechanical behavior of fibrous meshes and changes in the supramolecular structure of the polymer during 3 months of hydrothermal aging T = 37°C. An increase in crystallinity by 4%, a shift of glass transition temperature by 4°C, and a 2 times increase in melt flow rate under hydrolysis were indicated degradation of the amorphous phase. Local degradation of the amorphous phase of fibers led to the formation of surface cracks, an increase in the number of microcracks during hydrothermal aging resulted in a decrease in the mobility of fibers in the volume of the nonwoven material and a decrease in the elasticity of the entire nonwoven material, which was revealed using the volume ultrasound imaging and optical microphotographs.

Enhancing performance: insights into the augmentation potential of acrylonitrile butadiene styrene/boron nitride composites

Abstract This work aims to investigate the morphological, mechanical and thermal characteristics of boron nitride (BN)-reinforced acrylonitrile-butadiene styrene (ABS) composites. ABS and ABS/BN composites with a maximum BN loading up to 8 wt% were developed using two-roll mill followed by compression molding. Scanning electron microscopy (SEM) images presented interlinking of BN flakes in the dimple texture of ABS. A modest decrease in tensile properties was observed for the composites. The tensile strength and impact strength for the ABS/BN8 specimen were lowered by 4.7 and 81.7 %, respectively. On the other hand, hardness increased by 3.39 % for ABS/BN8 composite. The interaction effect of BN in the ABS matrix on the thermal properties was assessed using thermo-gravimetric analysis (TGA). An enhancement in the thermal-stability was observed for BN incorporated ABS. There is a modest shift in glass transition (T g) temperature to a higher value for the ABS/BN composites.

Facile purification of glass fiber powder by sedimentation for enhanced epoxy resin composites

Glass fiber powder contains two distinct forms: crumb-shaped and rod-shaped glass fiber powder particles. The shape and size of the particles in glass fiber powder have a great influence on its application. In order to separate rod-shaped glass fiber, the effects of different dispersants, such as SHMP, NaOL, and Na2SiO3 on them were investigated by settling experiments. Zeta potential, X-ray photoelectron spectroscopy (XPS), optical microscope, and other methods were used to analyze the adsorption behavior and settling mechanism. Three-point bending experiment and dynamic mechanical analysis (DMA) were used to evaluate the performance of epoxy resin composites reinforced with the raw glass fiber powder and the rod-shaped glass fiber powder. The results show that SHMP can effectively separate crumb-shaped glass fiber powder and rod-shaped glass fiber powder, leading to a notable increase in sedimentation recovery difference, up to Δ=51.08%. A preferential sedimentation separation mechanism is proposed to elucidate the settling mechanism. When the content of glass fiber powder and rod-shaped glass fiber is 5%, the glass transition temperature shifts significantly towards higher values, leading to the optimum comprehensive mechanical properties of the composites. Compared with the original epoxy resin, the flexural strength increased by 10.38% to 95.18 MPa and by 20.11% to 103.57 MPa. Similarly, the storage modulus increased by 14.14% to 2083 MPa and by 21.64% to 2220 MPa.

In-situ polymerization of polythiophene/silicon carbide nanocomposites for gas sensing and optoelectronic devices

Silicon carbide (SiC)-reinforced polythiophene (PTh) nanocomposites were synthesized by oxidative in-situ polymerization. The successful inclusion of SiC nanoparticles into the PTh was confirmed by the characteristic peak of Si–C bond around 865 cm−1 in the Fourier transform infrared (FT-IR) spectra. The X-ray diffraction (XRD) patterns demonstrate that the amorphous nature of PTh reduces with the addition of SiC. The intensity of UV–Vis absorbance increased proportionally with filler loading, indicating improved optical properties for PThSiC7 (polythiophene/silicon carbide 7 wt%) nanocomposite compared to pristine PTh. Field emission scanning electron microscopy (FE-SEM) images illustrate the changes in surface morphology of PTh with the addition of SiC and uniform dispersion was observed in PThSiC7. The formation of spherical-shaped moieties was confirmed using transmission electron microscopy (TEM). The shifts in degradation and glass transition temperatures towards higher values were attributed to the enhanced thermal properties of the nanocomposites. Temperature-dependent studies on the electrical and dielectric properties of the samples underscored the excellent conductivity exhibited by PThSiC7 (7 × 10−3 S/cm) with a low activation energy of 0.058 eV. In response to the growing demand for gas sensors, samples were tested to sense ammonia gas, demonstrating that PThSiC nanocomposites were more sensitive than PTh. The controllable optical properties, thermal stability, electrical characteristics, and gas sensing performance of the PThSiC nanocomposites suggest their potential as a promising material for the development of advanced energy storage systems, sensors, and optoelectronic devices.

Sustainable Materials with Improved Biodegradability and Toughness from Blends of Poly(Lactic Acid), Pineapple Stem Starch and Modified Natural Rubber.

Poly(lactic acid) (PLA), derived from renewable resources, plays a significant role in the global biodegradable plastic market. However, its widespread adoption faces challenges, including high brittleness, hydrophobicity, limited biodegradability, and higher costs compared to traditional petroleum-based plastics. This study addresses these challenges by incorporating thermoplastic pineapple stem starch (TPSS) and modified natural rubber (MNR) into PLA blends. TPSS, derived from pineapple stem waste, is employed to enhance hydrophilicity, biodegradability, and reduce costs. While the addition of TPSS (10 to 40 wt.%) marginally lowered mechanical properties due to poor interfacial interaction with PLA, the inclusion of MNR (1 to 10 wt.%) in the PLA/20TPSS blend significantly improved stretchability and impact strength, resulting in suitable modulus (1.3 to 1.7 GPa) and mechanical strength (32 to 52 MPa) for diverse applications. The presence of 7 wt.% MNR increased impact strength by 90% compared to neat PLA. The ternary blend exhibited a heterogeneous morphology with enhanced interfacial adhesion, confirmed by microfibrils and a rough texture on the fracture surface. Additionally, a downward shift in PLA's glass transition temperature (Tg) by 5-6 °C indicated improved compatibility between components. Remarkably, the PLA ternary blends demonstrated superior water resistance and proper biodegradability compared to binary blends. These findings highlight the potential of bio-based plastics, such as PLA blends with TPSS and MNR, to contribute to sustainable economic models and reduce environmental impact for using in plastic packaging applications.

Improved miscibility and toughness of biological poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/poly(lactic acid) blends via melt-blending-induced thermal degradation

Polymer blending has been a facile method to resolve the brittle issue of poly(lactic acid) (PLA). Yet, miscibility becomes the primary concern that would affect the synergy effect of polymer blending. This study aimed to improve the miscibility of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) and PLA by lowering their molecular weights via a melt-blending-induced thermal degradation during mechanical mixing to form m-P34HB/PLA blends. The molecular weight of the P34HB was significantly reduced after blending, thereby improving the miscibility of the blends, as evidenced by the shift of glass transition temperatures. Also, simulation based on Flory-Huggins theory demonstrated increased miscibility with decreasing molecular weight of the polymers. Moreover, the thermal gravimetric analysis revealed that the PLA provided a higher shielding effect to the P34HB in the blends prepared by melt-blending than those by solution-blending, that the addition of PLA could retard the chain scission of P34HB and delay its degradation. The addition of m-P34HB at 20 wt% in the blend contributed to a 60-fold enhancement in the elongation at break and an increment of 4.6 folds in the Izod impact strength. The enzymatic degradation using proteinase K revealed the preferential to degrade the PLA in the blends and followed the surface erosion mechanism.

SYNTHESIS AND STUDY OF THE PROPERTIES OF EPOXYCYCLOCARBONATES BASED ON ACRYLATE-VINYL COPOLYMERS

A method of synthesis of acrylate-vinyl copolymers based on glycidyl methacrylate and styrene at different molar ratios and epoxy cyclocarbonates based on them was developed. Synthesis of styrene-glycidyl methacrylate (СP GMA/St) copolymers was carried out by the method of thermally initiated radical polymerization in steel reactors in the presence of 1% azo-bis-isobutyronitrile initiator at a temperature of 65 °C for 10 hours. The number of epoxy groups in the synthesized СP GMA/St, determined by the potentiometric titration method, naturally decreases with a decrease in the molar ratio of GMA/styrene. The synthesis of СP GMA/St epoxycyclocarbonates was carried out in a high-pressure autoclave by passing CO2 through the reaction mixture of a solution of KP in toluene with a catalyst (tetrabutylammonium bromide 5%) with stirring at a temperature of 110–120 °C, a pressure of (4-5) atm. The structure of СP and ECC was confirmed by IR spectroscopy. No bands of double bonds are observed in the IR spectra of СP GMA/St, there are vibration bands characteristic of oligostyrene and vibration bands of C=O, C–O–C and epoxy groups. During the formation of ECC, new vibration bands of cyclocarbonate groups with a maximum of 1802 cm-1 appear, changes are observed in the absorption region of C–O–C groups (1100–1300) cm-1, and the vibration bands of epoxy groups with a maximum of 843 cm-1 decrease. The study of relaxation transitions in acrylate-vinyl copolymers GMA/St and epoxy cyclocarbonates based on them using the DSC method showed that all samples are amorphous single-phase polymers. After changing the background, the excessive enthalpy observed during the first heating disappears, and the glass transition temperature shifts towards higher temperatures, which indicates the formation of a denser and thermodynamically balanced structure. The thermostability of the synthesized GMA/St copolymers and epoxy cyclocarbons was investigated by the method of thermogravimetry. It was established that all the obtained substances have one stage of weight loss and are heat resistant, since weight loss begins at a temperature above 240 °C. In the future, the obtained epoxycyclocarbonates will be used for the synthesis of polyurethanes by the non-isocyanate method.

Effect of boehmite nanoparticles on structural, optical, thermal, mechanical and electrical properties of poly (methyl methacrylate) nanocomposites for flexible optoelectronic devices

The structural, optical, morphological and thermal properties of poly (methyl methacrylate) (PMMA)/boehmite nanocomposite films were studied by Fourier transform infrared spectroscopy (FT-IR), UV-Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies. The FT-IR spectra of composites showed the characteristic band of boehmite nanoparticles at 518 cm−1 indicating an effective interaction between PMMA and boehmite. The UV-visible measurements showed that the optical energy gaps for the direct permitted transitions decreased as boehmite content increased. The orientation of nanoparticles observed from XRD revealed that the addition of boehmite increases the crystallinity of PMMA. The SEM analysis showed the uniform distribution of boehmite in the PMMA matrix. The shift in glass transition and melting temperatures to higher temperature domains were revealed by DSC analysis. From the TGA studies, the reinforcement of PMMA with boehmite nanoparticles increases thermal stability. The electrical conductivity was measured using the impedance technique, and it was studied as a function of nanoparticles loading, applied frequency ranging from 100 to 106 Hz and at different temperatures. The AC conductivity of the composite increases with frequency and temperature. The activation energy was also measured for all samples at various applied frequencies, and it was observed that it decreased with increasing nanoparticle loading. The dielectric constant of PMMA increases with nanoparticle concentration up to 7 wt%. The modulus, tensile strength, hardness, and impact properties of the PMMA/boehmite nanocomposite films were significantly enhanced by the reinforcement of nanoparticles into the polymer matrix. The excellent optical properties, mechanical strength and electrical properties obtained for 7 wt% loaded nanocomposite films enable them to be used in the construction of electromagnetic induction shielding materials, conducting adhesives, and flame-resistant flexible optoelectronic devices.

Long-term effects of low and high temperatures on the mechanical performance of hybrid FRP composite laminates: Experimental and model assessment

The present paper investigates the long-term effects of low and high temperatures on the mechanical performance of hybrid composite laminates applicable to the structural design of spar caps of the blade. The top and bottom layers of hybrid laminates were specified as carbon fibre-reinforced polymer and the middle layer as glass fibre-reinforced polymer. Hybrid laminates were prepared using resin transfer molding methods. Compressive strength, tensile strength, and stiffness parameters such as storage modulus, loss modulus, and damping factors of hybrid laminates were tested under low and high temperatures. The experimental results confirmed that the compressive and tensile properties of the hybrid laminates were not affected significantly at low temperatures. This may be due to the closely compacted epoxy chain segments that delay the elastic deformation of the materials. Additionally, degradation in the storage and loss modulus of the laminates was observed in the glass transition regions due to the mobilization of the epoxy molecules. The relationships between glass transition temperature and frequency were assessed. The glass transition temperature shifts to higher temperatures as the frequency increases due to a reduction in the gaps between the crosslinking of the epoxy network. The accuracy of the storage modulus results was compared with the empirical models. The model developed using the Arrhenius law provided the closest correlation. The model developed by Gibson et al. [1] needs further research to be used to predict when gamma and beta relaxation occur before the glass transition temperature of the epoxy matrix turns into a glassy state.

Reactive compatibilization of PLA/PBS bio‐blends via a new generation of hybrid nanoparticles

AbstractPoly(butylene succinate) (PBS) is a worthy biodegradable thermoplastic polyester for blending along with other biopolymers, especially with poly (lactic acid) (PLA), to overcome its inadequacies in mechanical and thermal characteristics. Since binary blends of PLA and PBS showed that they are incompatible, compatibilization is required. In this work, multi‐epoxide polyhedral oligomeric silsesquioxane (Glycidyl POSS) was added to PLA and PBS using the melt blending method to make them compatible. The blends were prepared at different weight ratios having different amounts of compatibilizer. SEM analysis showed that the Glycidyl POSS impacted the interfacial adhesion and other properties of PLA and PBS blends. Noticeable improvements in mechanical properties were revealed by tensile and impact test results. Tensile strength and Young's modulus were improved when epoxy‐POSS was added up to 1 and 3 wt% into ternary blends, but further increasing POSS concentrations resulted in lower values. FTIR analysis showed a strong interaction between the epoxide group of POSS and the end groups of PBS or PLA. The thermal properties of samples were analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The shifts in glass transition temperatures of the PLA phase towards lower values appeared in DSC, confirming the enhanced compatibility of PLA and PBS. Also, the reinforcing ability of the POSS inorganic core structure impacted the thermal stability of the blends.

The Impact of Isocyanate Index and Filler Functionalities on the Performance of Flexible Foamed Polyurethane/Ground Tire Rubber Composites.

The structure and performance of polyurethane (PU) foams are strongly driven by the stoichiometry of the polyaddition reaction, quantitatively described by the isocyanate index. It determines the balance between isocyanate and hydroxyl groups in the reacting system and is affected by the introduction of additional functionalities originated, e.g., from applied fillers. Nevertheless, this issue is hardly taken into account in research works. Herein, the structure and performance of PU/ground tire rubber (GTR) composites differing in their isocyanate index (from 0.8 to 1.2) and prepared with and without considering the GTR functionalities in formulation development were investigated. Incorporating GTR into the PU matrix led to a reduction in average cell diameter (from 2 to 30% depending on the isocyanate index) compared to unfilled foams. However, formulation adjustments did not show a significant impact on cellular structure. The only decrease in open cell content was noted, from 10% for the 0.9 index to 40% for 1.2. Such changes were related to the increasing strength of the PU cellular structure able to maintain inside the increasing amount of carbon dioxide. On the other hand, considering hydroxyl values of GTR noticeably affected the thermomechanical performance of composites. The shift of glass transition temperature (Tg), even by 10 °C for 1.2 isocyanate index, enhanced the performance of materials, which was expressed in an 8-62% drop in the composite performance factor, pointing to the enhanced reinforcing effect resulting from filler incorporation. The stiffening of foams, related to the variations in PU segmental structure, also caused minor changes in the course of thermal degradation of PU/GTR composites due to the inferior thermal stability of hard segments. The obtained results provide important insights into the development of formulations of PU composites filled with materials containing reactive functional groups able to disrupt the stoichiometric balance of the polyaddition reaction.

Copper alumina reinforced poly(aniline-co-indole) nanocomposites for optoelectronic devices

ABSTRACT Copper alumina (Cu-Al2O3) reinforced poly(aniline-co-indole) (PANI-co-PIN) nanocomposites were prepared and characterised by UV-vis spectroscopy, FE-SEM and DSC. The bandgap energy decreased with the addition of Cu-Al2O3 to PANI-co-PIN. The FE-SEM confirms the uniform dispersion of nanoparticles in the copolymer. The DSC showed a shift in glass transition temperatures to higher regions with Cu-Al2O3 concentrations. The frequency-temperature-dependent dielectric parameters and electrical conductivity of nanocomposites were investigated. Activation energy calculated from Arrhenius equation decreases with increasing frequency. The real and imaginary part of electric modulus implies the thermally activated dielectric relaxations. The decreasing radius of semicircles in Nyquist plot with increasing temperatures indicates the existence of thermally activated conduction mechanisms. Different theoretical models were used to predict the DC conductivity mechanism in copolymer nanocomposites.

High Performance of Titanium Dioxide Reinforced Acrylonitrile Butadiene Rubber Composites

Recently, dielectric elastomer actuators (DEA) have emerged as one of the most promising materials for use in soft robots. However, DEA needs a high operating voltage and high mechanical properties. By increasing the dielectric constant of elastomeric materials, it is possible to decrease the operating voltage required. Thus, elastomeric composites with a high dielectric constant and strong mechanical properties are of interest. The aim of this research was to investigate the effect of titanium dioxide (TiO2) content ranging from 0 to 110 phr on the cure characteristics, and physical, dielectric, dynamic mechanical, and morphological properties of acrylonitrile butadiene rubber (NBR) composites. The addition of TiO2 reduced the scorch time (ts1) as well as the optimum cure time (tc90) but increased the cure rate index (CRI), minimum torque (ML), maximum torque (MH), and delta torque (MH - ML). The optimal TiO2 content for maximum tensile strength and elongation at break was 90 phr. Tensile strength and elongation at break were increased by 144.8% and 40.1%, respectively, over pure NBR. A significant mechanical property improvement was observed for TiO2-filled composites due to the good dispersion of TiO2 in the NBR matrix, which was confirmed by scanning electron microscopy (SEM). Moreover, incorporating TiO2 filler gave a higher storage modulus, a shift in glass transition temperature (Tg) to a higher temperature, and reduced damping in dynamic mechanical thermal analysis (DMTA). The addition of TiO2 to NBR rubber increased the dielectric constant of the resultant composites in the tested frequency range from 102 to 105 Hz. As a result, TiO2-filled NBR composite has a high potential for dielectric elastomer actuator applications.

Generating crosslinking network in XNBR based on copper (I)–carboxylate interaction

AbstractCarboxylated nitrile rubber (XNBR) is crosslinked via metal–ligand coordination bond by simple mixing and compounding as an alternate to chemically rich traditional vulcanization route. Basis of the generation of reversible non‐covalent crosslinks, in the rubber matrix, is copper (I)–carboxylate metal–ligand interaction that is evidenced by XPS, FTIR, and rheological studies. At low copper content (5 phr), self‐healing property is exhibited by the composite while adequate mechanical strength is obtained at higher copper content (20 phr). For 20 phr filled composite (XNBR–Cu20), the tensile strength reaches up to 5.41 ± 0.28 MPa, which is almost 19 times higher than that of pure XNBR (0.29 ± 0.02 MPa). On the other hand, tensile strength is not so high (1.95 ± 0.20 MPa) for composite XNBR–Cu5, however, this one shows the self‐healing efficiency of around 75% for the first cycle, 71% for second cycle, and 56% for the third cycle. The positive shift of glass transition temperature (Tg) takes place with the increasing content of copper (I)–carboxylate crosslinking that is caused by the lowering in segmental mobility of the rubber chains. Reversible nature of the metal–ligand coordination, recoverability, and hysteresis in the XNBR–Cu (I) composite are studied by cyclic stress–strain loading. The CuCl content greatly influences the inherent crosslinking nature of the elastomeric network and the ultimate properties of the composites.

Insights into Stoichiometry Adjustments Governing the Performance of Flexible Foamed Polyurethane/Ground Tire Rubber Composites.

Polyurethanes (PU) are widely applied in the industry due to their tunable performance adjusted by changes in the isocyanate index—stoichiometric balance between isocyanate and hydroxyl groups. This balance is affected by the incorporation of modifiers of fillers into the PU matrix and is especially crucial for PU foams due to the additional role of isocyanates—foaming of the material. Despite the awareness of the issue underlined in research works, the contribution of additives into formulations is often omitted, adversely impacting foams’ performance. Herein, flexible foamed PU/ground tire rubber (GTR) composites containing 12 different types of modified GTR particles differing by hydroxyl value (LOH) (from 45.05 to 88.49 mg KOH/g) were prepared. The impact of GTR functionalities on the mechanical, thermomechanical, and thermal performance of composites prepared with and without considering the LOH of fillers was assessed. Formulation adjustments induced changes in tensile strength (92–218% of the initial value), elongation at break (78–100%), tensile toughness (100–185%), compressive strength (156–343%), and compressive toughness (166–310%) proportional to the shift of glass transition temperatures (3.4–12.3 °C) caused by the additional isocyanates’ reactions yielding structure stiffening. On the other hand, formulation adjustments reduced composites’ thermal degradation onset due to the inferior thermal stability of hard segments compared to soft segments. Generally, changes in the composites’ performance resulting from formulation adjustments were proportional to the hydroxyl values of GTR, justifying the applied approach.

Comprehensive Investigation of Stoichiometry-Structure-Performance Relationships in Flexible Polyurethane Foams.

Polyurethane (PU) foams are versatile materials with a broad application range. Their performance is driven by the stoichiometry of polymerization reaction, which has been investigated in several works. However, the analysis was often limited only to selected properties and compared samples differing in apparent density, significantly influencing their performance. In the bigger picture, there is still a lack of comprehensive studies dealing with the stoichiometry impact on PU foams’ performance. Herein, flexible PU foams with a similar apparent density but differing in the isocyanate index (IIso) (from 0.80 to 1.20) were prepared. The stoichiometry–structure–performance relationships were investigated considering cellular and chemical structure, as well as the static and dynamic mechanical properties, thermal stability, thermal insulation, and acoustic performance. For IIso of 1.00, the biggest cell diameters of 274 µm were noted, which was 21–25% higher compared to 0.80 and 1.20 values. Increasing IIso reduced open cell content from 83.1 to 22.4%, which, combined with stiffening of structure (rise of modulus from 63 to 2787 kPa) resulting from crosslinking, limited the sound suppression ability around five times. On the other hand, it significantly strengthened the material, increasing tensile and compressive strength 4 and 13 times, respectively. Changes in the foams’ performance were also induced by the glass transition temperature shift from 6.1 to 31.7 °C, resulting from a greater extent of urethane groups’ generation and additional isocyanate reactions. Generally, the presented work provides important insights into preparing flexible PU foams and could be very useful for the future development of these materials.

Enhanced dielectric properties, thermal stability and ammonia sensing performance of poly(diphenylamine)/zinc oxide nanocomposites via one step polymerization

AbstractThe structural, morphological, thermal, dielectric and electrical conductivity properties of poly(diphenylamine) (PDPA)/zinc oxide (ZnO) nanocomposites, synthesized by in‐situ chemical polymerization technique, were systematically evaluated and characterized. The ammonia (NH3) gas sensing characteristics of composites were evaluated as a function of ZnO nanoparticle concentration. The Fourier transform infrared (FTIR) spectra of composites showed the characteristic band of ZnO nanoparticles at 418 cm−1indicating an effective interaction between the polymer matrix and filler. The X‐ray diffraction (XRD) studies confirm the increased crystallinity in the PDPA structure when ZnO is incorporated. The uniform distribution of nanoparticles within the polymer matrix is confirmed by transmission electron microscopy (TEM) images. The differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) studies emphasize the shift in glass transition temperatures and enhanced thermal stability of composites relative to bare PDPA, which is further confirmed by the Coat‐Redfern method. Conductivity studies show a significant increase in magnitudes of real part of dielectric permittivity and dielectric loss tangent concerning filler content. The addition of 7 wt% ZnO nanoparticles to PDPA increases the room temperature AC conductivity from 1.058 × 10−5to 7.8 × 10−4 S/cm. Moreover, the room‐temperature NH3gas sensing property of PDPA/ZnO nanocomposites was accelerated by the addition of ZnO nanoparticles.

Effect of post-processing conditions on polyacrylate materials used in stereolithography

Additive manufacturing offers simple and cost-effective production of highly customizable 3D-components. One particularly interesting technology is stereolithography (SLA), which enables the fabrication of micro- and milliscale reactionware using transparent materials. In this work, the influence of 3D-printing settings such as printing angle and layer thickness and post-processing conditions, as well as the size and shape of the test samples, on the mechanical, thermal and physico-chemical properties is determined. Two photocurable acrylate resins were used for 3D-printing: Clear and High Temperature. Post-curing of the test samples was performed using several methods and varying treatment times. The tensile test results show that a higher degree of cure results in a higher tensile strength and smaller elongation. On the other hand, layer thickness and print angle have a stronger influence on the tensile strength than some of the post-curing methods. In particular, the samples printed at 45° angle with the smallest layer thickness of 25 µm were found to be the toughest. When comparing Clear and High Temperature material, it is found that the Clear samples can withstand higher stress and strain, but the samples made of High Temperature resin are more rigid and show higher Young's modulus. Differential scanning calorimerty (DSC) tests show that post-curing reduces curing enthalpy, while the glass transition temperature shifts to higher temperatures, indicating crosslinking of the polymer chains. The swelling test showed that both resins can be considered water resistant with an absorption of less than 2% within 24 h. Regarding ethanol and acetone, High Temperature resin proved to be more resistant compared to the Clear resin. The samples post-cured in the SunTest chamber also showed much lower absorption of ethanol and acetone. The contact angle measurement shows that all samples are hydrophilic, regardless of the degree of post-curing or the printing angle.

A novel bulk metallic glass joining mechanism based on electro pulsive technology

We presented an electro pulsive joining method to join bulk metallic glass and systematically studied the mechanism of the joining process. Zr35Ti30Cu7.5Be27.5 sheets were chosen as the representative BMG, and the experiments were performed in air with electro pulsive energy density ranging from 78.1 J/mm2 to 295.5 J/mm2. The thermodynamic behaviors of the joining process with different pulse currents were analyzed by utilizing X-ray diffraction (XRD) and differential scanning calorimeter (DSC), and it suggests that the glass transition temperature (Tg) and crystallization temperature (Tx) shift distinctly to the high-temperature region as the heating rate increases. Hence, it reveals three different join modes during bonding: supercooled liquid phase joining, crystallization joining, and liquid phase joining. A diagram of temperature versus heating rate obtained by varying the pulse current was drawn, and it further proved that the Zr35Ti30Cu7.5Be27.5 bulk metallic glass could be joined in the liquid phase, crystallization, and supercooled liquid phase. The joint's shearing tests showed that the joint's average strength boned at the three different states were 837 MPa, 1467 MPa, and 1276 MPa, respectively. Furthermore, it proved that the electro pulsive joining method could provide a universal way to join bulk metallic glass.

Mechanical characteristics of epoxy nanocomposites derived through reinforcing carbonaceous fillers

Epoxy nanocomposites (ENCs) were fabricated through reinforcing various carbonaceous fillers (CFs, 3.0 wt%) into epoxy resin followed by curing with polyamine hardener. For this purpose, nanographite (NG), pine needle cone derived biochar (BC), and related graphene oxide (GO) were used as fillers for epoxy modification. Test specimens were fabricated and investigated for their tensile (ASTM D 638-02a), compressive (ASTM D 695-02a) and dynamic mechanical (ASTM E1820-01) behavior with reference to cure epoxy. Effect of chemical identity of CFs on morphology and average roughness of ENCs was investigated through atomic force microscopy. Study reveals that ENCs derived from GO exhibited maximum tensile strength (84.75 MPa) as compare to the other NG and BC derived analogues. ENCs derived through reinforcing NG has exhibited maximum elastic modulus (1307.72 MPa) in compare to their GO and BC derived analogues. ENCs derived through reinforcing BC have exhibited maximum compressive strength (46.93 MPa) and modulus (102.98 MPa) in comparision to their NG and GO analogues. Dynamic mechanical analysis reveals moderate shift in glass transition temperature (Tg, °C) of ENCs derived from GO (77.73) and NG (81.75) ranging to over cured epoxy (66.67).However, reinforcing BC into epoxy has raised the Tg of ENCs to 95.46 °C.