Dynamic Mechanical Analysis Tests Research Articles

Effect of dodecafluoroheptyl methacrylate (DFMA) on the comprehensive properties of acrylate emulsion pressure sensitive adhesives

Fluorinated acrylate emulsion pressure sensitive adhesives (PSA) based on butyl acrylate (BA), fluorine monomer dodecafluoroheptyl methacrylate (DFMA), acrylic acid (AA) and 2-hydroxyethyl acrylate (HEA) were synthesized via a monomer-starved seeded semi-continuous emulsion polymerization process. The influences of DFMA on the resultant latex and PSA properties were comprehensively investigated. FTIR analysis indicated that DFMA could be successfully introduced into the latex PSA copolymer through emulsion polymerization. DSC and TG analyses showed that Tg and thermal stability of the PSA were both improved as DFMA content increased. XPS analysis indicated that fluoroalkyl groups had a tendency to enrich on the surface of the film, and the more DFMA added the more F content on the film surface. Moreover, the surface roughness and contact angle of the acrylate latex PSA film were both increased with the introduction of DFMA. Dynamic mechanical analysis (DMA) and adhesive property tests showed that the storage modulus (Gʹ) and shear holding power were improved with DFMA content while at the sacrifice of loop tack. Finally, 180° peel strength of fluorinated acrylate latex PSAs on different substrates (PP, SS) as a function of DFMA content was evaluated.

The effects of modified zinc oxide nanoparticles on the mechanical/thermal properties of epoxy resin

AbstractCharacterized by its strength, durability, and thermal properties, epoxy resin has been widely used as an adhesive, paint, and coating in many applications in the aerospace, civil and automotive industries. Despite this, the thermoset polymer resin has been known for its brittleness and low fracture resistance. This study focuses on the reinforcement of an epoxy resin system (diglycidyl ether of bisphenol A) with zinc oxide (ZnO) nanoparticles in their pristine form and a further modified form. The modification took place in two ways: coating with polydopamine (PDA) and covalently functionalizing them with (3‐aminopropyl)triethoxysilane (APTES) and (3‐glycidoxypropyl)trimethoxysilane (GPTMS). Therefore, four different types of nanoparticles were used: pristine ZnO, ZnO/PDA, ZnO/GPTMS, and ZnO/APTES aiming to improve the interfacial bonding between the polymeric matrix and the reinforcement. Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy, and scanning electron microscopy characterization and imaging techniques were used to prove that the ZnO nanoparticles were successfully modified prior to manufacturing the epoxy composites. While tensile testing showed that using pristine ZnO increases the composite's strength by 32.14%, the fracture toughness of the resin was improved by 9.40% when reinforced with ZnO functionalized with APTES. TGA showed that the addition of functionalized nanoparticles increases the material's degradation temperature by at most 7.31 ± 4.9°C using ZnO/APTES. Differential scanning calorimetry and dynamic mechanical analysis testing proved that the addition of any type of nanoparticles increases the resin's glass transition temperature by as much as 7.83°C (ZnO/APTES).

Coupling Dynamic Covalent Bonds and Ionic Crosslinking Network to Promote Shape Memory Properties of Ethylene-vinyl Acetate Copolymers.

Dynamic crosslinking networks based on Diels–Alder (DA) chemistry and ionic interactions were introduced to maleic anhydride modified ethylene-vinyl acetate copolymer (mEVA) via in situ melt processing. The dual dynamic crosslinking networks were characterized by temperature-dependent FTIR, and the effects on the shape memory properties of mEVA were evaluated with dynamic mechanical thermal analysis and cyclic tensile testing. A crosslinking density was achieved at 2.36 × 10−4 mol·cm−3 for DA-crosslinked mEVA; as a result, the stress at 100% extension was increased from 3.8 to 5.6 MPa, and tensile strength and elongation at break were kept as high as 30.3 MPa and 486%, respectively. The further introduction of 10 wt % zinc methacrylate increased the dynamic crosslinking density to 3.74 × 10−4 mol·cm−3 and the stress at 100% extension to 9.0 MPa, while providing a tensile strength of 28.4 MPa and strain at break of 308%. The combination of reversible DA covalent crosslinking and ionic network in mEVA enabled a fixing ratio of 76.4% and recovery ratio of 99.4%, exhibiting an enhanced shape memory performance, especially at higher temperatures. The enhanced shape memory and mechanical performance of the dual crosslinked mEVA showed promising reprocessing and recycling abilities of the end-of-life products in comparison to traditional peroxide initiated covalent crosslinked counterparts.

Effect of moisture absorption on the wear and dynamic mechanical behavior of polymer composites

The present study focuses on the effect of moisture uptake of jute/epoxy, hemp/epoxy, flax/epoxy and hybrid composites (jute/hemp/epoxy, hemp/flax/epoxy and jute/hemp/flax/epoxy) on the dynamic mechanical and tribological properties. Composite specimens were developed using hand lay-up compression technique. The developed composites were dipped in normal tap water at room temperature for the span of one year. Three parameters were used to analyze the results of dynamic mechanical analysis (damping capability, storage modulus and loss modulus), and three parameters (friction force, coefficient of friction and specific wear rate) were used to analyze the wear test results. Results of dynamic mechanical analysis and wear analysis after one year of moisture absorption were compared with already published results for specimens without moisture absorption. Substantial changes were observed in each parameter of dynamic mechanical analysis and tribology test performed after one year of water immersion. Water-saturated hybrid composite jute/hemp/epoxy achieved highest reduction of 16.03% in damping capability as compared to its dry specimens. Water-immersed jute/epoxy composite achieved highest increment of 763.2% and 589.8% in the value of storage modulus and loss modulus, respectively, as compared to its dry specimen. Hybrid composite jute/hemp/flax/epoxy achieved the highest increment of 13.5% and 19.9% in the value of coefficient of friction as compared to its dry specimen at 3 and 5 m/s sliding speed, respectively. Water-immersed hemp/flax/epoxy achieved the highest increment of 228.9% and 51.56% in the value of specific wear rate at 1 and 3 m/s sliding speed, respectively, as compared to its dry specimen.

Enhancing fatigue performance of damaged metallic structures by bonded CFRP patches considering temperature effects

This paper reports an experimental and theoretical investigation on the fatigue performance enhancement of damaged steel structures by bonded carbon fiber reinforced polymer (CFRP) systems considering the temperature effects. First, thermomechanical properties of the epoxy adhesive and CFRPs were examined via dynamic mechanical analysis (DMA) and tensile tests. The appropriate curing procedure for the structural adhesive was obtained. Next, the fatigue behavior of notched steel plates strengthened by bonded CFRPs was investigated at different temperatures. During the fatigue tests, beach marking and back-face strain techniques were used to monitor the fatigue crack growth on steel components and the damage evolution within the bonding interface. The results show that the high-temperature resistance of the epoxy adhesive can be effectively improved by increasing the curing temperature and duration. The properly cured bonded CFRP patches can effectively enhance the fatigue performance of damaged steel structures. However, and the elevated temperatures significantly degrade the fatigue behavior of the CFRP-strengthened steel components.

Novel chemically cross-linked chitosan-cellulose based ionogel with self-healability, high ionic conductivity, and high thermo-mechanical stability

Developing flexible electrochemical devices with high-performance electrolytes by using natural renewable polymer is of great significance for meeting green and sustainable energy requirements. Here, a new type of chemically cross-linked ionogel based on natural chitosan and cellulose with good self-healability has been designed by a two-step method in ionic liquid. The rheological and dynamic mechanical analysis tests revealed that the as-prepared ionogel exhibited excellent thermo-mechanical stability even when the temperature was as high as 150 °C. Furthermore, the obtained ionogels showed good frost resistance, and still could maintain excellent flexibility even when the temperature was as low as − 20 °C. More importantly, the ionogel showed superior room temperature ionic conductivity (up to 2.1 mS/cm) and retained high electrical performance over a temperature range from − 50 to 120 °C. Additionally, the ionogel was used as electrolyte for preparing flexible supercapacitors and showed good performance under high temperature and harsh mechanical conditions. Such an ionogel, based on natural polymers with robust mechanical properties, high ionic conductivity, self-healability, and wide working temperature range, could be very useful for next-generation sustainable electrochemical devices.

Effect of chemical treatment on impact strength and dynamic thermal properties of Jute/PLA composites

The Untreated jute fiber reinforced composite (UTJFRC) and treated jute fiber reinforced composite (TJFRC) have been fabricated using compression molding processes. For chemical treatment of jute fiber mat sodium bicarbonate (NaHCO3) is used. The solution used for treatment has maintained pH of range 7–8 which show the ecofriendly treatment nature of sodium bicarbonate. Jute fiber mats were treated at three different concentration of sodium bicarbonate at 10, 20 and 30% for 4 h of treatment time. The prepared sample were characterized by dynamic mechanical thermal analysis (DMTA) and Izod impact test. All sample were cut according to ASTM standard to measure izod impact strength on impact tester. The composite sample which were treated at 10% concentration appear high impact strength. Even for dynamic mechanical properties treated jute fiber mat 20% concentration achieved maximum storage and loss modulus values. Even the glass transition temperature (Tg) is maximum shift for 20% concentration treated sample of jute/PLA composites. The improvement in properties because of good interfacial adhesion of jute and PLA achieved by sodium bicarbonate treatment of natural fiber.

Influences of processing conditions on mechanical properties of recycled epoxy‐anhydride vitrimers

AbstractThe chemically crosslinked network structures make epoxies, the most common thermosets, unable or hard to be recycled, causing environmental problems and economic losses. Epoxy‐based vitrimers, polymer networks deriving from epoxy resins, can be thermally malleable according to bond exchange reactions (BERs), opening the door to recycle epoxy thermosets. Here a series of experiments were carried out to study the effects of processing conditions (such as particle size distributions, temperature, time, and pressure) on recycling of an epoxy‐anhydride vitrimer. Polymer powders from the epoxy‐anhydride vitrimer with different size distributions were prepared and characterized, and the influence of particle size on the mechanical performance of recycled epoxy‐anhydride vitrimers was investigated by dynamic mechanical analysis and uniaxial tensile test. Experimental results demonstrated that finer polymer powders can increase the contacting surfaces of recycled materials and thus result in high quality of recycled materials. In addition, the influences of other treating parameters, such as temperature, time, and pressure, were also discussed in this study. Adjusting these treating parameters can help the design of an optimized reprocessing procedure to meet practical engineering applications.

Parameters estimation of generalized Maxwell model for SBR and carbon-filled SBR using a direct high-frequency DMA measurement system

Due to their desired physical properties as viscoelastic materials, polymers have attracted the attention of various industrial engineering systems. Accurate examination and measurement of physical properties of polymers is a key step required for their full-scale adoption and integration in industrial settings. Simulation studies, provide a relatively inexpensive and valuable analytical framework for analyzing the physical properties of such systems. Generalized Maxwell Model (GMM) is the standard analytical model used for analyzing viscoelastic materials. The viscoelastic constitutive parameters of the GMM are usually inferred by fitting the model to the master curve obtained from Dynamic Mechanical Analysis (DMA) tests. However, since conventional DMA tests are limited to low-frequency measurements, Williams, Landel and Ferry (WLF) relation is used to predict the high-frequency properties from the tests done at low frequencies. Known limitations and imprecisions of this indirect measurement method result in inaccurate inference of viscoelastic constitutive parameters in the GMM fitting procedure. In the current study, data obtained from a new high-frequency DMA (HFDMA), capable of performing tests at frequencies between 100–7000 Hz, is used to fit GMM equations through numerical optimization techniques. The new HFDMA operates the simple shear test for a double-sandwich specimen, directly at high-frequencies and therefor doesn't suffer from inaccuracies caused by the indirect measurements. The storage moduli, loss moduli and damping factor of Styrene-Butadiene Rubber (SBR) and carbon-black filled SBR (SBR-CB) at the frequency range of 100Hz−5 kHz are measured using the new HFDMA, and compared with the results of a conventional DMA to demonstrate the difference between the direct and indirect measurement methods. It is shown that the direct measurement method is 5%−7% more accurate than the indirect measurement method, at least for the SBR and SBR-CB. Finally, new GMM viscoelastic constitutive parameters for SBR and SBR-CB are presented.

Effect of Type and Concentration of Nanoclay on the Mechanical and Physicochemical Properties of Bis-GMA/TTEGDMA Dental Resins.

Bis-GMA/TTEGDMA-based resin composites were prepared with two different types of nanoclays: an organically modified laminar clay (Cloisite® 30B, montmorillonite, MMT) and a microfibrous clay (palygorskite, PLG). Their physicochemical and mechanical properties were then determined. Both MMT and PLG nanoclays were added into monomer mixture (1:1 ratio) at different loading levels (0, 2, 4, 6, 8 and 10 wt.%), and the resulting composites were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and mechanical testing (bending and compressive properties). Thermal properties, depth of cure and water absorption were not greatly affected by the type of nanoclay, while the mechanical properties of dental resin composites depended on both the variety and concentration of nanoclay. In this regard, composites containing MMT displayed higher mechanical strength (both flexural and compression) than those resins prepared with PLG due to a poor nanoclay dispersion as revealed by SEM. Solubility of the composites was dependent not only on nanoclay-type but also the mineral concentration. Dental composites fulfilled the minimum depth cure and solubility criteria set by the ISO 4049 standard. In contrast, the minimum bending strength (50 MPa) established by the international standard was only satisfied by the dental resins containing MMT. Based on these results, composites containing either MMT or PLG (at low filler contents) are potentially suitable for use in dental restorative resins, although those prepared with MMT displayed better results.

Synthesis of physically cross-linked gum Arabic-based polymer hydrogels with enhanced mechanical, load bearing and shape memory behavior

The TiO2 dispersed physically cross-linked polymer hydrogels were synthesized through a single step free radical addition polymerization mechanism based on acrylic acid and gum Arabic (GA) as polymer constituents, and ferric ions (Fe3+) as physical cross-linker. The effect of TiO2 powder was investigated on thermal and mechanical properties of the hydrogels by dispersion of 0.01, 0.02 and 0.03 g of TiO2 in hydrogels. The prepared hydrogels were successfully characterized through FTIR, XRD, SEM and thermogravimetric analysis (TGA). For the mechanical properties, dynamic mechanical analysis and universal testing machine (UTM) were used. The DMA results showed that the storage modulus was increased with the TiO2, while UTM results showed that 0.02 g of TiO2 powder significantly enhanced the fracture stress, elastic modulus, toughness and stretchability by 4514%, 4328%, 4124% and 20%, respectively, compared to the virgin hydrogels. Cole–Cole plot confirmed the homogeneity and viscoelastic behavior of the system, while manual load bearing and shape memory test showed that the hydrogels bear a load of 2.5 kg for a long time and it is recovered within 10 s to its original state. The materials can be applied for the synthesis of artificial body parts in the field of bio-engineering. The use of un-modified GA for the synthesis of hydrogels will open a new window for the researchers working in this field.

Material characterisation of additively manufactured elastomers at different strain rates and build orientations

Material jetting, particularly PolyJet technology, is an additive manufacturing (AM) process which has introduced novel flexible elastomers used in bio-inspired soft robots, compliant structures and dampers. Finite Element Analysis (FEA) is a key tool for the development of such applications, which requires comprehensive material characterisation utilising advanced material models. However, in contrast to conventional rubbers, PolyJet elastomers have been less explored leading to a few material models with various limitations in fidelity. Therefore, one aim of this study was to characterise the mechanical response of the latest PolyJet elastomers, Agilus30 (A30) and Tango+ (T+), under large strain tension-compression and time-dependent high-frequency/relaxation loadings. Another aim was to calibrate a visco-hyperelastic material model to accurately predict these responses. Tensile, compressive, cyclic, dynamic mechanical analysis (DMA) and stress relaxation tests were carried out on pristine A30 and T+ samples. Quasi-static tension-compression tests were used to calibrate a 3-term Ogden hyperelastic model. Stress relaxation and DMA results were combined to determine the constants of a 5-term Prony series across a large window of relaxation time (10 μs–100 s). A numerical time-stepping scheme was employed to predict the visco-hyperelastic response of the 3D-printed elastomers at large strains and different strain rates. In addition, the anisotropy in the elastomers, which stemmed from build orientation, was explored. Highly nonlinear stress-strain relationships were observed in both elastomers, with a strong dependency on strain rate. Relaxation tests revealed that A30 and T+ elastomers relax to 50 % and 70 % of their peak stress values respectively in less than 20 s. The effect of orientation on the loading response was most pronounced with prints along the Z-direction, particularly at large strains and lower strain rates. Moreover, the visco-hyperelastic material model accurately predicted the large strain and time-dependent behaviour of both elastomers. Our findings will allow for the development of more accurate computational models of 3D-printed elastomers, which can be utilised for computer-aided design in novel applications requiring flexible or rate-sensitive AM materials.

Comprehensively improved mechanical properties of silane crosslinked polypropylene/ethylene propylene diene monomer elastomer blends

AbstractThe properties and structure of silane crosslinked polypropylene (PP)/ethylene propylene diene monomer (EPDM) elastomer blends had been carried out. Fourier transform infrared spectroscopy and gel content tests were employed to evaluate the crosslinking reaction of PP/EPDM blends. Crosslinking efficiency of PP/EPDM blends was investigated using thermogravimetric analysis, differential scanning calorimeter, dynamic mechanical analysis, dynamic rheology, and tensile testing. Tanδcurves of silane crosslinked PP/EPDM blends exhibited an obvious “gel point” originated from the formation of dynamic crosslinking network. The blend corresponding to the “gel point” presented comprehensively improved mechanical properties. These results demonstrated that characteristic rheological parameters showed close correlations with key mechanical properties of silane crosslinked PP/EPDM blends. Scanning electron microscopy images illustrated that crosslinking had remarkably changed the morphologies of PP/EPDM blends. The large deformation mechanism of these blends had been suggested.

Effect of pulse electric field applied to carrot prior to its heating

The tissue of carrot (variety Jereda) was tested using dynamic mechanical analysis (DMA) combined with dielectric thermal analysis (DETA), in air of 90% humidity in temperature scans between 30 and 90 °C. Temperature plots of loss tangent were determined. In DETA, based on alternated current of frequency 20 kHz, both components of impedance were continually determined. Pulsed electric field (PEF) was applied prior to the DMA and DETA tests. Four sets of experiments were performed, without PEF (b), with a single 10 ms long pulse given an alternated field of 500 V/cm (c), with two similar pulses at 0.1 s interval (d) and with two similar pulse at 1 s interval (e). The impedance was recalculated giving parameters of a single model represented by parallel connection of a resistor Re and a capacitor with capacitance ωC. Three stages of the range of temperature, namely subcritical (30–70 °C), critical (70–80 °C), and supercritical (80–90 °C) were considered. For set b, in subcritical stage, the parameter, Re decreased whereas capacitance was nearly constant. Both of these parameters decreased slightly in the supercritical stage but whereas Re is in supercritical stage much lower than in the subcritical stage, the capacitance is in supercritical stage rather higher than it is in subcritical stage. In critical stage, Re sharply decreased and the capacitance showed a sharp peak, both indicating collapse of the cellular membranes. Application of PEF led to little reduction of the capacitance peak and the reduction was more effective after the repeated pulse application (that is in sets d and e). These results at carrot were compared with the previous research at potato and it was shown that PEF effects in critical and supercritical stages significantly differ in the both plant tissues.

Aromatic Hyperbranched Polyester/RTM6 Epoxy Resin for EXTREME Dynamic Loading Aeronautical Applications.

The effects of the addition of an aromatic hyperbranched polyester (AHBP) on thermal, mechanical, and fracture toughness properties of a thermosetting resin system were investigated. AHBP filler, synthesized by using a bulk poly-condensation reaction, reveals a glassy state at room temperature. Indeed, according to differential scanning calorimetry measurements, the glass transition temperature (Tg) of AHBP is 95 °C. Three different adduct weight percentages were employed to manufacture the AHBP/epoxy samples, respectively, 0.1, 1, and 5 wt%. Dynamical Mechanical Analysis tests revealed that the addition of AHBP induces a negligible variation in terms of conservative modulus, whereas a slight Tg reduction of about 4 °C was observed at 5 wt% of filler content. Fracture toughness results showed an improvement of both critical stress intensity factor (+18%) and critical strain energy release rate (+83%) by adding 5 wt% of AHBP compared to the neat epoxy matrix. Static and dynamic compression tests covering strain rates ranging from 0.0008 to 1000 s−1 revealed a pronounced strain rate sensitivity for all AHBP/epoxy systems. The AHBP composites all showed an increase of the true peak yield compressive strength with the best improvement associated with the sample with 0.1 wt% of AHBP.

Studies on the curing behavior, thermal, and mechanical properties of epoxy resin‐co‐amine‐functionalized lead phthalocyanine

AbstractA high performance copolymer was prepared by using epoxy (EP) resin as matrix and 3,10,17,24‐tetra‐aminoethoxy lead phthalocyanine (APbPc) as additive with dicyandiamide as curing agent. Fourier‐transform infrared spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TGA) were used to study the curing behavior, curing kinetics, dynamic mechanical properties, impact and tensile strength, and thermal stability of EP/APbPc blends. The experimental results show that APbPc, as a synergistic curing agent, can effectively reduce the curing temperature of epoxy resin. The curing kinetics of the copolymer was investigated by non‐isothermal DSC to determine kinetic data and measurement of the activation energy. DMA, impact, and tensile strength tests proved that phthalocyanine can significantly improve the toughness and stiffness of epoxy resin. Highest values were seen on the 20 wt% loading of APbPc in the copolymers, energy storage modulus, and impact strength increased respectively 388.46 MPa and 3.6 kJ/m2, Tg decreased 19.46°C. TGA curves indicated that the cured copolymers also exhibit excellent thermal properties.

Studies on dynamic mechanical and thermal properties of boron carbide filled carbon fiber/epoxy composites

This study aims at studying the dynamic mechanical and thermogravimetric properties of boron carbide (B4C) filled carbon fiber (CF)/epoxy composites (BC-CF/Ep composites) using the wet lay-up process assisted by vacuum bagging technique. The B4C fillers were used in varying filler weight percentages (1%, 3% and 5%) in the different CF/Ep composites and are uniformly mixed in epoxy system through ultrasonification process and was used as the matrix. The Toray make bidirectional twill (2 × 2) woven T800CF was used as the reinforcing material. The Dynamic Mechanical Analyzer (DMA) and Thermogravimetric Analysis (TGA) tests are conducted to study the dynamic capacity and thermal degradation behavior respectively. In the DMA, the storage modulus (E1), loss modulus (E11), damping behavior (Tanδ) and glass transition temperature (Tg) of CF/Ep composite specimens are studied with increasing temperature from (25–173)°C. The BC1% composites showed better storage modulus, loss modulus and damping factor, while unfilled CF/Ep and BC3% composites showed better Tg than other CF/Ep composites. As far as TGA is concerned, the BC1% composites exhibited better thermal stability than all other composites. The dynamic tests resulted in the trend of BC1% > unfilled CF/Ep > BC3% > BC5% composites. The TGA tests also followed the trend of BC1% > unfilled CF/Ep > BC3% > BC5% CF/Ep composites.

Study on mechanical and viscoelastic behavior of carbon nanotube (CNT) reinforced Epofine1564 nanocomposite

This paper presents an experimental study to examine the mechanical and viscoelastic characteristics of multi-walled carbon nanotubes (MWCNTs) reinforced epoxy nanocomposite. The nanocomposite samples of varying volume fractions are prepared using solution mixing technique. A two-step mixing procedure with magnetic stir and bath type ultra sonicator is employed to acquire well dispersion of CNTs in epoxy resin. Three-point bending, tensile and impact tests are conducted on the prepared samples to measure the elastic modulus, strength and failure strain respectively. The morphological analysis of fractured samples is carried-out under field emission scanning electron microscopy (FESEM). The dispersion and reinforcing mechanism of CNTs within the polymer matrix are observed. The results show that a small amount of CNTs in a polymer matrix improves the stiffness and strength of the composite considerably. The agglomeration occurs beyond the 0.5 wt% of CNTs. Furthermore, towards thermal stability analysis, the improvement of viscoelastic characteristics with the addition of MWCNTs is studied using dynamic mechanical analysis test. Results are shown in the form of graphs and tables.

Improving aramid pulp dispersion in epoxy resin via the in situ preparation of SiO2 on an aramid pulp surface

AbstractAramid pulp (AP) is a highly fibrillated form of fiber， with excellent heat resistance, wear resistance, size stability, and other beneficial properties, that can be dispersed in rubber or resin matrix systems. Its fibrillation results in a large surface area. However, AP easily tangles and aggregates between fibers because of its large surface area. Consequently, it experiences difficulty in dispersing in matrices, especially when a relatively large amount of pulp is needed to be mixed. In this study, a SiO2 nanoparticle was synthesized on the surface of AP through the hydrolysis of tetraethyl orthosilicate to improve the dispersion of AP in an epoxy matrix. Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, X‐ray photoelectron spectroscopy, and scanning electron microscopy showed that SiO2 nanoparticles coated on the pulp could improve the thermal and mechanical properties. The optimum treatment concentration was 0.15 mol/L. Dynamic mechanical analysis tests indicated when AP modified by SiO2, the E' is higher due to the uniformly diffusion and enhanced interfacial adhesion for load transfer from the epoxy to AP. But Tg is lower as the flexibility chain SiOSi in epoxy. In comparison with the properties of the unmodified AP, the tensile strength and modulus of modified pulp/epoxy composites increased by 53.5% and 160.4%, respectively. Therefore, the dispersion and interface combination of AP modified by SiO2 in the epoxy improved because of the interaction of AP with SiO2 through the hydrogen bonding and crosslinking of SiO2 with epoxy.

An Analysis of Mechanical and Viscoelastic Behaviour of Nano-SiO2 Dispersed Epoxy Composites

The influence of SiO2 nanoparticles dispersion on mechanical and viscoelastic properties of SiO2/epoxy nanocomposites was investigated. In order to develop SiO2/epoxy nanocomposites, SiO2 nanoparticles (≈15 nm) were dispersed in the epoxy resin through ultrasonic mixing. Dynamic mechanical analysis, tensile and fracture tests were performed as per ASTM standards to determine the viscoelastic and mechanical properties. A significant enhancement in viscoelastic, fracture and tensile behaviour was observed in the prepared nanocomposites. With the dispersion of SiO2 nanoparticles in epoxy resin, the value of UTS increases from 34.5 MPa (pristine epoxy) to 49 MPa for 4 wt.% SiO2/epoxy nanocomposite. The average value of fracture toughness (K1C) and fracture energy (G1C) for the pristine epoxy was measured to be 1.09 MN/m3/2 and 2.76 kJ/m2 respectively. However, maximum K1C and G1C were found to be 2.89 MN/m3/2 and 11.54 kJ/m2 respectively for 4 wt.% SiO2 nanoparticles dispersion. The maximum increase in the ultimate tensile strength, toughness, K1C and G1C are observed to be 44%, 144%, 165% and 318% respectively in comparison to pristine epoxy. At room temperature, 5 wt.% SiO2/epoxy nanocomposites have showed maximum increment of about 17% in the storage modulus. The glass transition temperature was found to increase from 62 °C (for pristine epoxy) to 70 °C (for 4 wt.% SiO2/epoxy nanocomposites) whereas, glass transition temperature values start decreasing above 4 wt.% SiO2 nanoparticles dispersion due to the obstruction in cross-linking of polymeric chains. The possible changes in the local structure of epoxy matrix are also indicated by the increase in Tg in ultrasonically processed SiO2/epoxy nanocomposites. Numerical and finite element models were applied to predict Young’s modulus of prepared SiO2/epoxy nanocomposites. The experimental results are in good agreement with the finite element model.