Shift In Tg Research Articles

COMPATIBILITY STUDY OF HYDROCARBON RESINS WITH RUBBER COMPOUNDS FOR TIRE APPLICATIONS

ABSTRACT The addition of hydrocarbon resins to rubber compounds has a significant impact on their properties such as wet grip and rolling resistance. These performance characteristics have a strong correlation with the compatibility of the resin with the rubber matrix. Incompatible resins can cause excessive broadening of the damping curve, which results in poor rolling resistance. Compatibility, however, allows maximization of wet grip while minimizing the effect on rolling resistance. Compatibility is promoted by lower resin molecular weight and structural similarity to the polymers being blended. In this study, a method based on the Fox equation has been developed to quantitatively characterize the compatibility between resin and natural rubber (NR), a binary system. The dynamic shear rheometer (DSR), a tool new to the tire industry, is used to investigate the interaction between resin and two rubbers (i.e., a ternary system of NR–butadiene rubber [BR]–resin and solution polymerized styrene–butadiene rubber [SSBR]–butadiene rubber [BR]–resin), with a specific emphasis on resin partitioning among rubber blends. In addition, the DSR is applied to assess the Tg shift and tangent delta peak height, providing insight into the compatibility between rubbers and resin. A curve-fitting model was developed for the SSBR–BR–resin system to depict the relationship between these two parameters and the physical and chemical properties of resins, with the selection of resins featuring different degrees of aromaticity, Tg, and molecular weight. The findings indicated that higher Tg increased aromaticity and that lower molecular weight of the resin resulted in an elevated Tg shift in the blend, while lower molecular weight led to an increase in the tangent delta peak height. Our findings supply insight into the performance of rubber–resin blends and introduce a new screening tool for characterizing these blends in their green state.

Dynamical mechanical and impact strength behavior of 3D‐printing testing specimens manufactured by fused filament fabrication of isotactic polypropylene/functionalized titania nanotubes nanocomposites: Influence of β‐crystal promoting

AbstractThermomechanical and impact properties of isotactic polypropylene nanocomposites reinforced with titania nanotubes (TiNTs) at weight distributions of 0.5, 1, and 1.5 wt% were investigated. The goal of this study was to create a novel iPP‐based nanocomposite filament fused filament fabrication (FFF) with improved thermo‐mechanical and impact properties to enable the creation of more customized geometries. First, TiNTs were chemically functionalized with pimelic acid (PA) to promote the β‐crystalline phase using Ca as anchoring. FTIR results revealed the presence of new bands at 1575 and 1413 cm−1, which were attributed to the anchoring of the PA molecule on the TiNT surface. TEM images of the TiNTs confirmed its tubular morphology before and after the functionalization, while the SEM/EDS analysis showed the good dispersion of carbon which can only come from the organic molecule employed in the functionalization. The nano‐reinforcements were incorporated by extrusion generating a filament to produce 3D‐printed specimens. The efficacy of the modified reinforcement as a β‐crystalline phase promoter was evaluated by wide‐angle x‐ray diffraction. The nanocomposite with 1% modified TiNTs showed the highest β‐crystal promotion with a kβ‐index of 89% while the nanocomposites reinforced with unmodified TiNTs reached only 15%. Furthermore, the thermomechanical and impact properties were characterized by dynamic mechanical analysis and Izod. In the first, the storage modulus (E′) was higher than the raw iPP for all nanocomposites, with an increase of about 148% and 107%, while the nanocomposite with a high percentage of β‐crystal showed an increase of 183% in the impact strength properties. A shift of Tg to higher temperatures was attributed to better interfacial interactions polymer/nano‐reinforcement because of the functionalization. The modified nano‐reinforcement was able to generate a 3D‐printed nanocomposite with higher stiffness and impact strength properties than the raw iPP.

The effect of water sorption on the calorimetric signature of aging in DGEBA epoxies

Epoxies hygrothermally aged in the relatively benign environment of a climate controlled experimental laboratory display a broad endothermic signature which extends from as much as 40 °C below the glass transition temperature, Tg, to over 100 °C above Tg upon an initial DSC heating ramp of an open pan. This is in addition to a shift in Tg to lower temperature associated with plasticization and the relatively sharp endothermic peak just above Tg that is characteristic of physical aging. All of these features are erased by the first heating to well above Tg and are not seen in subsequent heating ramps. The association of the broad endothermic peak with desorption of water from the polymer is demonstrated through systematic investigations of hydrothermally aged samples. The area of the desorption peak is proportional to the absorbed mass of water with a cumulative specific heat equal to the heat of vaporization of water (40 ± 4 kJ/mol). For typical equilibrium water saturation in epoxy (∼ 0.04 g water/g epoxy at room temperature and 100% relative humidity), this amounts to ∼80 J/g epoxy and is many times the enthalpy of the physical aging peak in the laboratory aged samples (∼2 J/g). Consequently, moisture desorption is a major contributor to calorimetric thermograms of aged epoxies, and disentangling desorption endotherms from other aging signatures is key to quantifying the role of each mechanism at play. Similarly, plasticization associated with moisture sorption must be considered when aging environments are not dry in order to avoid mis-associating observed Tg depressions with other mechanisms such as chain scission.

Autonomous Adaption of Intelligent Humidity‐Programmed Hydrogel Patches for Tunable Stiffness and Drug Release

AbstractIntelligent humidity‐programmed hydrogel patches with high stretchability and tunable water‐uptake and ‐release are prepared by copolymerization and crosslinking of N‐isopropylacrylamide and oligo(ethylene glycol) comonomers. These intelligent elastomeric patches strongly respond to different humidities and temperatures in terms of mechanical properties which makes them applicable for soft robotics and smart skin applications where autonomous adaption to environmental conditions is a key requirement. It is shown that beyond using the hydrogel in the conventional state in aqueous media, new patches can be controlled by relative humidity. This humidity programming of the patches allows to tune drug release kinetics, opening potential application fields such as skin wound therapy and personalized medication. In situ dynamic‐mechanical measurements show a huge dependence on temperature and humidity. The glass transition temperature Tg shifts from around 60 °C at dry conditions to below 0 °C for 75% r.h. and higher. The storage modulus is tunable over more than four orders of magnitude from 0.6 up to 400 MPa. Time‐temperature superposition in master curves allows to extract relaxation times over 14 orders of magnitude. With strains at break of over 200% the patches are compliant with human skin and therefore patient‐friendly in terms of adapting to movements.

Mechanical Response of Glass-Epoxy Composites with Graphene Oxide Nanoparticles.

Graphene-based fillers possess exceptional properties that encourage researchers toward their incorporation in glass-epoxy (GE) polymer composites. Regarding the mechanical and wear properties of glass-epoxy composites, the effect of graphene oxide (GO) reinforced in glass-epoxy was examined. A decrease in tensile modulus and increase in tensile strength was reported for 1 wt. % of GO. A shift in glass transition temperature Tg was observed with the addition of GO. The cross-link density and storage modulus of the composite decreased with the addition of GO. The decrease in dissipation energy and wear rate was reported with the increase in GO concentration. A simple one-dimensional damage model of nonlinear nature was developed to capture the stress-strain behavior of the unfilled and filled glass-epoxy composite. Tensile modulus E, Weibull scale parameter σo, and Weibull shape parameter β were considered to develop the model. Finally, to understand the failure mechanisms in GO-filled composites, a scanning electron microscopic (SEM) examination was carried out for tensile fractured composites.

Probing the effect of post-curing and halloysite nanotube reinforcement on thermo-mechanical properties of lightweight epoxy syntactic foam composites

This paper deals with an investigation of the post-curing effect of halloysite nanotubes (HNTs) reinforced syntactic foam (HRSF) containing cenosphere as hollow inclusion at 0, 20, and 40 vol% in an epoxy matrix. Compression, flexural, and thermal properties of HRSF (1 vol% HNTs) and cenosphere/epoxy syntactic foam (CESF) composites without HNTs are studied under the influence of post-curing. Further, the post-cured HRSF containing 40 vol% cenosphere (NSF40_H) exhibited a compressive modulus of 33.2% higher than room temperature cured neat epoxy due to improved crosslinking. Addition of HNTs in NSF40_H augments the flexural modulus up to 26.9% compared to post-cured neat epoxy. Additionally, the glass transition temperature ( Tg) of CESF composites with 40 vol% cenosphere was increased by 24.3 °C compared to the room temperature cured sample. This positive shift in Tg can be attributed to the beneficial impact of post-curing, as indicated by differential scanning calorimetry study. Thermogravimetric results demonstrated better thermal stability of HRSF relative to CESF and neat epoxy composites. Transmission electron microscopy illustrated the structure-property correlations of nanotube reinforcement. The improved properties of syntactic foams could be viewed as a potential material for lightweight constructions, especially in the marine and automobile industries.

Physicochemical Properties of Milkfish Gelatin-Natural Starch Composite

Halal gelatin sourced from fish can be improved in quality through mixing with other polymers so that it can be an alternative as food, pharmaceutical, and cosmetic ingredient. The purpose of this study was to determine the characteristics of milkfish scale gelatin after the formation of a composite with corn, potato, and cassava starch to be used as a pharmaceutical and food excipient.
 The gelatin composite (FMG) of milkfish scales with corn, potato, and cassava starch (GM, GS, and GC) was made by casting method, using a ratio of gelatin and starch (4,5:0,5). Characteristic assessment includes organoleptic, viscosity, swelling index, FT-IR spectroscopy, and Calorimetry (DSC). Data analysis used a non-parametric One Way ANOVA statistical method (p<0.05).
 The composites produced from mixing FMG with corn starch (GM), potato (GS) and cassava (GC) showed hygroscopic properties, increased viscosity values and decreased swelling index in GM (7.89 cP & 25.0%), GS (8 .36 cP & 21.0%), and GC (8.64 cP & 12.7%), compared to FMG (0.11 cP & 75%) at p < 0.05. The behavior of the composite FT-IR spectrum follows the FMG spectrum pattern with a shift in wavenumber in the typical bands (Amide A, Amide B, Amide I, Amide II, and Amide III) in the gelatin spectrum. There was a shift of Tg to higher values in GM and GS, Tm increased in GM and GC, and all composites showed a decrease in melting enthalpy.
 The spectral pattern of the composite follows the typical spectral pattern of FMG. GM, GS, and GC composites showed increased viscosity, water retention, and thermal stability compared to FMG. GM and GS may be used as pharmaceutical and food excipients.

Nanomechanical and dynamic mechanical properties of rubber–wood–plastic composites

Abstract This article presents the assessment of bulk and in situ mechanical properties of rubber–wood–plastic composites (RubWPC) and their correlations, aiming to obtain a thorough understanding of mechanical behaviour of RubWPC, which is an essential prerequisite in realising their optimal design and applications. Dynamic mechanical analysis results showed that the composites treated with multiple coupling agents (combination of maleic anhydride polyethylene [MAPE] and bis(triethoxysilylpropyl)tetrasulfide and combination of MAPE and vinyltrimethoxysilane) exhibited greater storage modulus than both the untreated and single coupling agent treated composites owing to their superior interfacial bonding quality. The shift of relaxation peak and T g towards higher temperatures observed in the treated composites confirmed the enhancement of interfacial interaction and adhesion. Nanoindentation analysis suggested that the composite with optimised interface (MAPE and Si69 treated) possessed better nanomechanical property (elastic modulus) due to the resin penetration into cell lumens and vessels and the reaction between cell walls and coupling agents.

A novel UV-curable waterborne polyurethane-acrylate coating based on green polyol from hydroxyl telechelic natural rubber

A novel UV-curable waterborne polyurethane-acrylate (WPUA) was firstly prepared based on hydroxyl telechelic natural rubber (HTNR) via sequential emulsion polymerization. The WPUA was composed of HTNR, Hexamethylene diisocyanate (HDI), 2-hydroxyethyl acrylate (HEA), and the content of hydroxymethyl propionic acid (DMPA) was studied for effects on particle size, stability, and morphology of the new series of WPUA dispersions. The WPUA had a good stability at a total solids content of about 20%. Particle size and dispersion stability slightly decreased with DMPA content. The WPUA gave a good film formation and can provide good wettability with high surface free energy. The mechanical and thermal properties of WPUA film were improved by UV-curing. The effects of photoinitiator (Darocur1173) content were investigated. The UV-cured WPUA films showed better mechanical properties and less water absorption than the not cured WPUA film. Also, the surface wetting was the improvement in the water resistance of the coating on the substrate. In addition, the thermal properties by TGA and the dynamic properties by DMTA slightly increased with photoinitiator dose level due to the higher crosslink density and decreasing the molecular weight between crosslink (Mc) caused the Tg shift to a higher temperature.

Large T g Shift in Hybrid Bragg Stacks through Interfacial Slowdown.

Studies of glass transition under confinement frequently employ supported polymer thin films, which are known to exhibit different transition temperature Tg close to and far from the interface. Various techniques can selectively probe interfaces, however, often at the expense of sample designs very specific to a single experiment. Here, we show how to translate results on confined thin film Tg to a “nacre-mimetic” clay/polymer Bragg stack, where periodicity allows to limit and tune the number of polymer layers to either one or two. Exceptional lattice coherence multiplies signal manifold, allowing for interface studies with both standard Tg and broadband dynamic measurements. For the monolayer, we not only observe a dramatic increase in Tg (∼ 100 K) but also use X-ray photon correlation spectroscopy (XPCS) to probe platelet dynamics, originating from interfacial slowdown. This is confirmed from the bilayer, which comprises both “bulk-like” and clay/polymer interface contributions, as manifested in two distinct Tg processes. Because the platelet dynamics of monolayers and bilayers are similar, while the segmental dynamics of the latter are found to be much faster, we conclude that XPCS is sensitive to the clay/polymer interface. Thus, large Tg shifts can be engineered and studied once lattice spacing approaches interfacial layer dimensions.

Strain‐induced post‐curing of acrylate networks

AbstractThe mechanical properties and network structure of photocurable polymers are strongly dependent on processing conditions. Here it is reported that highly crosslinked acrylate systems undergo unexpected additional post‐curing during DMTA measurements, resulting in an increase in glass‐transition temperature (Tg). A detailed study of the conditions under which this increase in Tg takes place unequivocally shows that a small (0.1%) oscillatory strain applied above Tg is responsible for additional cross‐linking reactions. The effect of strain‐induced post‐curing is confirmed by applying post‐curing treatments under oscillatory shear strain in rheological tests. Different acrylate systems were characterized and the results show that the strain induced post‐curing depends on the network structure of the polymer. In polymer networks with an initial high crosslink density the effect is pronounced while in polymers with an initial lower crosslink density no shift in Tg is observed.

High-temperature fast pyrolysis of coal: An applied basic research using thermal gravimetric analyzer and the downer reactor

The study explored the influence of temperature and particle size on the high-temperature fast pyrolysis behaviors of Shenmu(Yulin) coal through thermal gravimetric analyzer and the downer reactor. Results of TG-FTIR show that the thermal hysteresis causing by high heating rate make TG and DTG curves shift to high-temperature zone. The infrared spectra reveal that the release characteristics of typical products and functional groups are consistent with the weight loss curve. Moreover, experimental results of the downer reactor reveal that the content of coal-char and coal-tar decreased and coal-gas increased with the increment of temperature. Better syngas can be obtained at 900 °C. The yield of coal-char firstly increases and then decreases with the decrease of particle size and the coal-tar is opposite. More importantly, during the pyrolysis process of 35–60 mesh coal, the largest amount of coal-char and the smallest amount of coal-tar are not only obtained, but high-quality syngas is also obtained. Through the characterization of coal-tar, it is found that coal-tar is mainly composed of aromatic compounds, and the content can reach more than 50%. Moreover, the change of infrared absorption intensity of O–H, CO and C–O groups in coal-char varies with the change in pyrolysis parameters.

Application of the Hofmeister series to the structure and properties of poly(vinyl alcohol) films containing metal salts

The effects of ions on the structures and properties of poly(vinyl alcohol) films were systematically studied using various metal salts. Although cations play an important role, the data obtained in this study demonstrated that the strong ion–dipole interactions between anions and poly(vinyl alcohol) chains also have a significant impact on crystallinity and glass transition temperature. For the first time, the study revealed that the impact of the added salts follows the Hofmeister series. Investigations of various bromine salt cations revealed that Li+ is more effective at disrupting the water structure than either Na+ or K+. Further experiments using lithium salts with various anion species verified that lithium salts play an important role in determining the crystallinity and hydrogen bonding within aqueous poly(vinyl alcohol) and therefore affect the dynamic mechanical properties of films. This phenomenon clearly follows the order LiClO4 > LiI > LiBr > LiNO3 > LiCl, which corresponds to the Hofmeister series. The salt addition affects the structure and properties of poly(vinyl alcohol) films as it reduces the hydrogen bonding in PVA chains and decreases the crystallinity. Consequently, the Tg shifts to low temperatures, and the modulus beyond Tg decreases markedly. This study confirmed that the impact of bromine salts on the structure and properties followed the order of Hofmeister series, i.e., Li+ > Na+ > K+. Although cations play an important role, the data obtained also demonstrated that the strong ion–dipole interactions between anions and PVA chains have a significant impact on the crystallinity and Tg.

Conductivity–modulus–Tg relationships in solvent‐free, single lithium ion conducting network electrolytes

AbstractA model system of single‐ion conducting network electrolytes with acrylic backbone, ethylene oxide (EO) side chains, tethered fluorinated anions, and mobile Li cations was designed and synthesized to investigate structure–property relationships. By systematically tuning four molecular variables, one at a time, we investigated how crosslinker length, mol% of crosslinker added, Li:EO ratio and side‐chain length affect conductivity, Tg, and modulus. Ionic conductivity at 90 °C varied by two orders of magnitude (and by three orders of magnitude at room temperature) depending on the molecular details, while a 70 °C span in glass transition temperature (Tg) was observed. The range of crosslinking, which can be achieved without impacting conductivity was also elucidated, and the modulus of the electrolyte can be increased by a factor of 8, up to 2.4 MPa, without impacting ion transport. Changes in conductivity due to crosslink density and crosslinker length are fully explained in terms of Tg shifts, while comonomer length cannot be accounted for by such a shift. The best performing network exhibited 10−5 S/cm at high temperature, which is comparable to other single‐ion conductors reported in the literature, while the modulus is higher due to crosslinking. Adding 10 wt% propylene carbonate further increased this value to 10−4 S/cm. This work provides insights into the structure–property relationships of solid‐state polymer electrolytes, which retain conductivity but can potentially help suppress dendrites.

Molecular-weight dependence of simulated glass transition temperature for isolated poly(ethylene oxide) chain

ABSTRACT Molecular dynamics simulations have been performed with chemically realistic coarse-grained potentials to assess the effects of molecular weight on the glass transition temperatures (Tg ) of single-chain particle of poly(ethylene oxide) in a vacuum. It is found that all the long isolated chains form impact globule like configurations, and higher molecular weight and lower temperature lead to more perfect sphericity. With increasing molecular weight, the simulated Tg of the isolated chain tends to increase whereas the Tg of the bulk undergoes a slight change. The confinement effects are associated with localisation of chain ends at the surface and specific surface areas. More importantly, the Tg shift can be quantified by the solubility parameter that includes the contribution of conformational change. As compared to the conventional definition that only sums intermolecular interactions, such solubility parameter is a better metric in simulations to explain the confinement effects since it does not depend upon the degree of equilibration as the Tg . These results can be quite valuable to clarifying glass transition behaviour of polymers films.

Hydrophilic modification and cross-linking of polystyrene using the synthesized N,N′-(hexane-1,6-diyl)diacrylamide

The aim of this work was to synthesize a novel hydrophilic structure based on polystyrene (PS) cross-linked by using N,N′-(hexane-1,6-diyl)diacrylamide (HDBPA). FT-IR was carried out for chemical structure characterization of HDBPA and cross-linked samples. In addition to FT-IR, 1H NMR was also applied on HDBPA for more investigations. The results showed that HDBPA was synthetized through a condensation reaction, and consequently, it could successfully cross-link PS structure. Moreover, the determination of nitrogen content in HDBPA within PS network was investigated by means of elemental analysis. Afterward, the reactivity ratios between HDBPA and styrene were calculated via Fineman–Ross equation in which the obtained values were 0.66 and 0.23, respectively. On the other hand, by adding the HDBPA to PS the water contact angle was decreased from 73.6° to 57.4°, thereby proving the indispensable role of the cross-linking agent on hydrophilicity of the samples. Finally, the thermal behavior of the samples was studied using DSC and TGA analyses. According to DSC thermograms, there was a shift in Tg up to 30 °C for the samples with cross-linking densities ranging from 2.5 to 20 mol.%. In regard to the thermal stability of the cross-linked samples, the TGA curves revealed a reduction in this property owing to the presence of amide groups in HDBPA through the PS structure.

Solid and microcellular polylactide nucleated with PLA stereocomplex and cellulose nanocrystals

Blending polylactide (PLA) with poly(d-lactide) (PDLA) and cellulose nanocrystals (CNC)-based stereocomplex (SC) nanohybrids presents practical approach to produce fully biobased blends and nanocomposites with enhanced properties. This paper investigated the nucleation effect of PLA/PDLA and PLA/PDLA-g-MAH/CNC nanohybrids at low loading levels on the non-isothermal crystallization, morphology, as well as thermal and thermo-mechanical properties of PLA-based samples. Neat PLA, blends and nanocomposites were produced by conventional and microcellular injection molding. Nitrogen (N2) in a supercritical state was used as the physical blowing agent for preparation of microcellular samples. CNC-based SC showed superior nucleating efficiency compared to SC nucleating agents. However, low mold temperature resulted in relatively low degree of crystallinity (~ 15%). In addition, decrease in cell size and increase in cell density of microcellular samples have been observed after introduction of both nucleating agents. Slight increase in mechanical properties of nucleated samples compared to neat PLA has been ascribed to the higher degree of crystallinity. Despite these, decrease in all mechanical properties of microcellular samples has been noticed when compared to solid counterparts. Furthermore, dynamic mechanical analysis (DMA) reveals subsequent foaming and dramatic decrease in dimensional stability of microcellular samples above glass transition temperature (Tg). The storage modulus in a glassy region has been improved in both solid blends and nanocomposites. In addition, shift of Tg due to restricted chain mobility of PLA due to retarded relaxation of amorphous regions due to SC interactions has been observed.

Functionalized graphenes as nanofillers for polylactide: Molecular dynamics simulation study

AbstractThis simulation studied graphene functionalized with methyl (CH3), hydroxyl (OH), carboxyl (COOH), and amine (NH2) groups as potential nanofillers for polylactide (PLA) biodegradable polymers. Key properties including the structure and dynamics of polymer chains, interaction energy and interfacial shear force between the polymer matrix and the filler, and glass transition temperature (Tg) of the nanocomposites were investigated. Results indicated that graphene functional groups play important roles in the interfacial bonding characteristics between polymer matrix and the filler. Among the fillers studied, graphene modified by COOH groups provided the strongest enhancement of interfacial interaction and shear force between the PLA matrix and the filler. The presence of nanofillers resulted in a moderate shift of the composite Tg compared to the unfilled polymer. The system with stronger interfacial interaction possessed higher Tg due to lower mobility of chain segments induced by the interaction strength between the polymer and the filler.

Antibacterial activity of sustainable composites derived from epoxidized natural rubber/silver-substituted zeolite/poly(lactic acid) blends

Sustainable composites derived from epoxidized natural rubber (ENR)/silver-substituted zeolite (AgZ)/poly(lactic acid) (PLA) blends possessing antibacterial activity were reported. ENR, herein, acted as an antibacterial promoter providing more hydrophilicity to the composites and facilitating water diffusion. Two methodologies were used to prepare composites, including solution casting (S) as well as solution casting followed by roll milling (SR). Both composites were compared in terms of morphology, AgZ dispersion, water absorption, and antibacterial activity. The shift of Tg and tan δ toward lower temperature of PLA composites consistently confirmed the compatibility between ENR and PLA by DSC and DMA results, respectively. The good AgZ distribution was observed in composites-SR, as confirmed by SEM/EDX. The results of agar disk diffusion susceptibility test showed that PLA, AgZ/PLA, and even ENR/AgZ/PLA composites-S showed no or less inhibition zone; meanwhile, ENR/AgZ/PLA composites-SR showed the significant inhibition zone against both Escherichia coli and Staphylococcus aureus. Besides, the antibacterial activity of the composites was required at least 5 wt% of AgZ. More than 98% inhibition of S. aureus growth by the composites-SR was observed during 2–24 h of cultivation, whereas AgZ/PLA provided the highest inhibition of only 75% at 24 h of cultivation. Hence, the incorporation of ENR enhances the bactericidal activity of the composites. In terms of mechanical properties, incorporating ENR into the composites decreased tensile modulus and strength, but increased the impact strength significantly. Therefore, the developed composites could be promising materials in food and biomedical fields in which antibacterial and impact resistance properties are required.

Glass transition temperature of nanoparticle-enhanced and environmentally stressed conductive adhesive materials for electronics assembly

In our paper, the characterization of glass transition temperature (Tg) was performed for one- and two-component electrically conductive adhesive used in electronic joining technologies. Both adhesives were of the epoxy type with the silver filler. Dynamic mechanical analysis (DMA) was used to measure the Tg. The adhesives were modified with nanoparticles, namely, carbon nanotubes (concentration of 0.5 and 0.8% by weight) and silver nanoballs (2.5% by weight). The values of Tg were determined from the plot of the Tg δ parameter. Two types of environmental stresses were used for climatic aging: 125 °C/56% RH and 85 °C/85% RH. The aging of the samples at 125 °C and 56% RH caused increase Tg for all formulations. The cause of these changes is additional curing of adhesive. Aging in the combined climate 85 °C/85% RH caused a shift in Tg toward lower values for formulations based on the one-component adhesive modified by CNT and toward higher values for all other formulations. The major cause of the decrease in Tg was that CNT inhered the curing reactions and banned them from completion. In cases where Tg grew, glue hardening take place. DMA was performed to examine Tg of the samples. The DMA measurements were carried out up to 200 °C. Repeated DMA measurement confirmed that this measurement caused additional hardening and increase Tg for all samples. The results will contribute to the use of conductive adhesives with better quality and reliability in electronics manufacturing.