Dynamic Mechanical Thermal Analysis Tests Research Articles

Investigation of mechanical properties of compatibilized polyvinyl chloride/polylactic acid nanocomposites

AbstractPolymer alloying is particularly important due to the possibility of choosing a wide range of materials and the ability to design a product with desired properties. In case of incompatibility between the components, the resulting alloy cannot meet the set of desired properties and shows poor performance. In this research, alloys of polyvinyl chloride and polylactic acid were prepared in an internal mixer and nanoclay and maleic anhydride‐grafted styrene‐ethylene/butylene‐styrene (SEBS‐g‐MAH) compatibilizer were used to improve the properties. In order to investigate the morphology and phase distribution of polylactic acid, scanning electron microscope images were taken. Tensile and dynamic mechanical thermal analysis tests were performed to evaluate the properties of the samples. The scanning electron microscope test images show the improvement of system uniformity by adding compatibilizer to the alloy. Adding nanoclay to the alloy increased the storage modulus and uniformity of the system. An increase in glass transition temperature and storage modulus was observed in the samples containing compatibilizer, and the uniformity of the system was also improved. The tensile test results showed that by adding nanoclay up to 3 % by weight, the tensile strength and Young′s modulus increase. Addition of compatibilizer up to 5 % by weight increased the physical and mechanical properties.

Comprehensive investigation into the thermal rheological behavior and relaxation characteristic of single/composite polymers in laminated glass

Polymeric interlayers are of significance for the structural capability of thin-walled laminated glass members both before and after glass fracture. Polymers present evident temperature and time dependence, which should be carefully assessed in the design process. To improve mechanical properties dependent on the temperature and time, novel interlayers including modified ethylene-vinyl acetate (PVE®) and composite PVE/PC (SGE®), have been developed along with the sound resistance of the interfacial adhesion to aging. In this work, dynamic mechanical thermal analysis tests were carried out to investigate the thermal rheological behavior and relaxation characteristic of polyvinyl butyral (PVB), ionomer (SentryGlas®, SG), PVE, PC and SGE. The results show that PVE and SGE follow the complex thermal rheological behavior as a result of the existence of two different types of relaxation transitions, whilst PVB, SG, and PC are thermorheologically simple materials. The arctangent function was introduced to describe the temperature dependence of PVB and SG. The relaxation modulus of polymers was subsequently derived based on the approximation equation and inverse Fourier transform. The results of the inverse Fourier transform indicate that vertical shift might need to be considered for PVE and SGE. The application of the approximation equation was assessed and its limitation was discussed. Finally, the relaxation characteristics of five polymers were described using the generalized Maxwell model based on the weighted least squares method.

Investigation of Dynamic-Mechanical-Thermal Analysis of Innovative Hybrid Carbon/Glass Fibers Reinforced by GNPs and Al2O3 for Marine Structures

AbstractMarine structural applications face numerous challenges related to environmental load, corrosion, and fatigue under varying time and temperature conditions. One of the major challenges faced by marine structural applications is dynamic mechanical thermal analysis (DMTA). In this study, innovative hybrid carbon/glass fibers (CGF) reinforced with different contents (1.5 wt. % and 3 wt. %) of dual nano-powders, including graphene nanoplatelets (GNPs) and aluminium oxide (Al2O3), were developed as reinforcements inside the epoxy matrix. The nanocomposites were fabricated using a hand lay-up technique, resulting in a nanocomposite sheet with dimensions of 300 mm length, 200 mm width, and 2.3 mm thickness. DMTA test specimens were prepared with dimensions of 50 mm length, 10 mm width, and 2.3 mm thickness. To ensure accuracy, three replicates were conducted for each condition, and the average values were calculated for analysis. Before DMTA, the prepared nanocomposites were analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDAX) to compare the influence of incorporating dual nano-powders. DMTA was carried out at different temperature values (ranging from 10 °C to 105 °C) and times (ranging from 5 to 575 min) at 1 Hz frequency with a heating rate of 4 °C/min and a nitrogen flow rate of 20 ml/min. The main objective of this study was to investigate the influence of incorporating dual nano-powders such as GNPs and Al2O3on various dynamic mechanical properties including storage modulus, loss modulus, damping factor (DF), and glass transition temperature (Tg) of the hybrid carbon/glass fiber-reinforced epoxy composites. The fabricated hybrid CGF composite with 1.5% wt. GA nanoparticles exhibited higher values for the DF of 0.68 and the Tg of 73.4 °C. However, increasing the nanoparticle content to 3% wt. GA led to a deterioration in the DF (0.54) and a reduction in Tg (27.8 °C) due to decreased bonding between the carbon fibers (CF) and glass fibers (GF) caused by the higher nanoparticle concentration. The complex modulus (E*) values demonstrated expected trends with temperature and time for the CGF-1.5% wt. GA composite, indicating acceptable behaviour. In contrast, the CGF-3% wt. GA composite exhibited lower E* values, indicating a decrease in stiffness and mechanical properties compared to the CGF-1.5% wt. GA composite. Microstructural observations after DMTA revealed a uniform scattering of nanoparticles in the CGF-1.5% wt. GA sample, while the CGF-3% wt. GA sample demonstrated improved scattering of Al2O3nanoparticles on the surface. The microstructural analysis further indicated a brittle nature with high resistance to crack initiation and propagation in the CGF-1.5% wt. GA composite.

Understanding the influence of in situ produced dextran on wheat dough baking performance: Maturograph, biaxial extension, and dynamic mechanical thermal analysis

Rheological tests performed under conditions relevant to those experienced during proof and oven rise are necessary for understanding the mechanisms of dextran addition on wheat dough baking performance. This study evaluated the effect of a high molecular weight ( Mw ) dextran, produced in situ by Weissella confusa A16 or externally added, on wheat dough rheological properties including, (i) proofing behavior using a maturograph; (ii) bi-axial extensional profile using a dough inflation system; and (iii) viscoelastic characters (proof) and thermo-mechanical properties (simulated baking) by dynamic mechanical thermal analysis (DMA). The externally-added dextran increased dough elasticity, tenacity, and viscoelastic characters, but reduced dough extensibility at bubble rupture. DMA tests of doughs under dynamic heating conditions showed a sharp increase of elastic and loss moduli until maximum between 75 and 95 °C, accompanied by a drastic decrease of Tan δ (dough stiffening). Dextran addition exhibited a weakening effect on the dough thermal properties i.e., decreased peak moduli during heating. On the other hand, the mild acidic conditions during sourdough fermentation favored the activity of in situ produced dextran, conferring significantly improved thermal-mechanical properties and dough extensibility. This may explain the superior ability of in situ produced dextran to improve bread volume and crumb softness compared to the external-added dextran. By analyzing rheological parameters, we showed that the maximum proofing moduli in DMA, fermentation stability, dough level, and elasticity in maturogram were predictors of good baking quality. Overall, our study provides the mechanistic underpinning and optimum of dextran as a natural improver of bread quality. • Rheological properties of doughs are strongly associated with baking performance. • Dextran increases dough elasticity and tenacity but reduces dough extensibility. • Dextran added externally exhibits a thermal weakening effect on wheat dough. • Dextran produced in situ is preferred in improving dough rheology and bread quality. • Favorable effects of in situ -produced dextran are mediated by mild acidification.

Investigating the thermo-mechanical and UV-shielding properties of a nano-porous Zr(IV)-type metal-organic framework (MOF) incorporated epoxy composite coating

In the present work, the effects of UIO-66 nanoparticles on the epoxy-polyamide composite coating thermal resistance, mechanical features, and weathering (UV) resistance were explored. The nanoporous UIO-66 particles were developed by the common solvothermal procedure. The final particles were identified by Brunauer–Emmett–Teller (BET), Fourier transform infrared (FT-IR) spectroscopy, and Raman analysis. Also, the thermal properties, as well as the mechanical characteristics of the epoxy nanocomposites loaded with 0.2, 0.4, 0.8, and 1.2 wt% of the UIO-66 particles were studied by thermal gravimetric analysis (TGA), tensile, and dynamic mechanical thermal analysis (DMTA) methods. Besides, the UIO-66 particles containing composite coatings UV resistance at various loadings were studied after 500 h exposure to UV-A irradiation (320–400 nm range) via spectrophotometer analysis, contact angle test, surface roughness analysis, and micro-hardness investigation. BET surface area analysis illustrated a surface area (SA) of 820 m2 g−1 for the constructed metal-organic framework (MOF) particles. TGA outcome exhibited that the temperature related to the weight loss of 80% in the presence of nanoparticles (NPs) increased up to approximately 60 °C. On the other hand, the tensile analysis outcomes indicated that the toughness and strain values related to the breaking of the film increased about 2.1 and 1.5 times (at 1.2 wt% filler loading), in comparison with the pure (un-filled) epoxy matrix, respectively. The DMTA test outcomes demonstrated significant improvements of the UIO-66 particles loaded epoxy coatings storage modulus in the glassy region (especially at 1.2 wt%) and crosslinking density (especially at 0.8 wt%). Results proved that the thermal and mechanical characteristics of the nanocomposite were promisingly improved compared to the pure epoxy. Results proved significant epoxy film UV-shielding properties enhancement in the presence of 1.2 wt% UIO particles.

Enhancing shape memory properties of multi-layered and multi-material polymer composites in 4D printing

The shape memory behavior of smart materials is widely used for stimulation or shape-shifting purposes. Shape memory polymers (SMPs) can shape and force recoveries accompanied by attractive attributes such as biocompatibility, biodegradability, and universality. In this paper, a thermoplastic elastomer (TPE) is used as a complementary material for 4D printed polylactic acid (PLA) structures to enhance their shape and force recovery properties and lower the stimulation temperature for more practical implementations. Two approaches are followed to provide SMP composites (SMPCs): multi-layered and multi-material lattices. In multi-layered lattices, specimens are comprised of separate layers and different ratios of SMP and TPE materials. For comparison, PLA-TPE filaments with the same ratios of multi-layered lattices are produced and used to fabricate multi-material lattices. Dynamic mechanical thermal analysis tests showed a reduction in the glass transition temperature of the manufactured PLA-TPE filament. X-ray diffraction test was conducted to prove that the crystallinity of the developed PLA-TPE material increases which explains the better shape memory effect in the multi-material specimens. Phase separation occurred in low ratios of TPE in PLA, discernible in field emission scanning electron microscope (FESEM) images, resultting in low quality in one of the developed PLA-TPE filaments. FESEM images also showed proper miscibility of TPE in PLA in higher ratios. Thermomechanical tests were done on printed specimens to examine and compare the shape and force recovery of the produced SMPCs. While the shape recovery of multi-material samples was not as good as multi-layered samples, both approaches have better shape recovery results than the PLA sample. Due to a lower glass transition temperature in multi-material lattices, their shape recovery process started at lower temperatures widening their potential practical applications. Force recovery of multi-material samples revealed a significant improvement which was due to more oriented crystalline polymer structures.

Effect of layering pattern and fiber hybridization on viscoelastic properties of PALF/COIR hybrid epoxy composites

To design and develop a hybrid biocomposite material for structural applications, it becomes necessary to determine the optimum fibers layering pattern. Therefore, in this research work, the different layered hybrid biocomposite boards i.e. bilayer pineapple/coir (P/C), trilayer (PCP, CPC), and intimately mixed (IM) were developed and characterized for viscoelastic properties. The composites were made by hand lay-up method, keeping the volume ratio of PALF and COIR 1:1 and the total fiber volume fraction is 0.40 volume of composite. Dynamic mechanical thermal analysis test was employed to characterize the viscoelastic behavior in terms of storage modulus, loss modulus, loss damping factor, and the glass transition temperature. Amongst all the different layered hybrid composites, the trilayer CPC has lowest value (0.635) of effectiveness coefficient with highest stiffness and activation energy (40.54 kJ/mole). It confirms the better fiber-matrix interaction at the interfacial region. The glass transition temperature of CF-EP and PF-EP was increased by 8.74% and 13.15% respectively by the synergistic hybridization of cellulosic fibers. The PCP layered composite possesses lowest value of phase transition energy (9.17 kJ/mole) and this was because of the poor fiber-matrix interfacial adhesion.

Eco-friendly castor oil-based UV-curable urethane acrylate zinc oxide nanocomposites: Synthesis and viscoelastic behavior

Attention to environmental problems and the importance of maintaining it have caused the researchers to pay more attention in this regard. The production of polymers and resins has increased in recent years and has affected by environmental pollution due to their long-term degradation. An appropriate solution to this problem is the synthesis of degradable and environmentally friendly polymers and resins. Using natural materials in the synthesis of polymers and resins can help them to be environmentally friendly. The purpose of this research is to synthesize urethane acrylate resins using natural resources. For this purpose, the urethane acrylate pre-polymer was synthesized with castor oil. Then, using modified zinc oxide nanoparticles with 1, 3 and 5 wt% urethane acrylate zinc oxide nanocomposites were produced. The use of castor oil as a degradable part and lack of organic solvent in radiation systems led to the creation of an environmentally friendly resin. Subsequently, the viscoelastic behavior of the prepared nanocomposite was evaluated. Spectrometry results confirm the synthesized resin structure. The morphology of nanocomposites confirmed the proper particle size distribution in a 3 wt.% sample. The results of the dynamic mechanical thermal analysis test showed that increasing the amount of modified nano ZnO could increase the glass transition temperature, and the maximum value was observed in 5 wt.% modified nano ZnO (69.7℃).

Viscoelastic Properties of PVB Interlayer for Laminated Glass Structures Used in Building Reconstructions

Laminated glass is a structural element used extensively in a reconstruction of existing building structures because of its transparency and simplicity. When using laminated glass as a glass staircase, balustrades, transparent flooring, facades or other structural elements, it is advisable to consider the shear interaction of individual glass panes in the cross-section. A conservative approach where the glass panes shear interaction is not considered, is uneconomical. This interaction depends on the properties of polymeric interlayers used in lamination process. Various commercial products based on PVB (polyvinyl butyral), EVA (ethylene vinyl acetate), ionomer, or thermoplastic polyurethane (TPU) are used. Stiffness of polymers depends on temperature and duration of a load. Interlayers exhibit the viscoelastic properties and temperature dependency usually described by the generalized Maxwell model and WLF model (Williams-Landel-Ferry). Parameters of these models are the most effectively determined by Dynamic Mechanical Thermal Analysis (DMTA), where the material is cyclically loaded at different frequencies and temperatures. Material parameters were found by DMTA in shear for PVB type of interlayer Trosifol® BG R20. In addition, the experimental quasi-static loading tests in shear were performed at different loading rates and at various temperatures. These experimental stress-strain diagrams were compared to the theoretical stress-strain relations obtained from Maxwell model with material parameters based on DMTA testing. All tests were performed in Klokner Institute CTU in Prague.

An experimental investigation on the viscoelastic properties of CNT reinforced CY 219 epoxy resin, using DMTA and creep tests

The viscoelastic properties of carbon nanotube (CNT) reinforced epoxy resin were researched experimentally, in this study. To this end, single walled CNT with CY 219 epoxy resin and HY 5161 hardener were utilized and dynamic mechanical thermal analysis (DMTA) and creep tests were carried out. The DMTA were performed in several frequencies and the effects of the CNT weight percent and the frequency of the test on the storage and loss moduli were investigated. Additionally, frequency-sweep DMTA at room temperature were carried out to obtain master curve of the mentioned moduli in terms of the frequency. To evaluate viscoelastic properties of the composite in time domain, creep tests at room temperature were conducted. The effect of CNT content on the time dependent results were studied. A combination of molecular structural mechanics and micromechanics modeling was implemented to predict overall viscoelastic properties in time and frequency domains. The effect of CNT length and agglomeration were taken into account in the modeling. Comparison between model prediction and experimental results shows good agreement when the short agglomerated CNTs were considered in the model.

Ageing simulation of a hydraulic engine mount: A data-informed finite element approach

Hydraulic engine mounts are key elements in an automotive vehicle suspension system that typically experience a change of their designed function during their working lifetime due to progressive material ageing, primarily from the elastomeric component. Ageing of the engine mount, resulting from severe and continuous mechanical and thermal loads, can have a detrimental impact on the ride and comfort and long-term customer satisfaction. This paper introduces a new practical methodology for simulating the ageing behaviour of engine mounts resulting from the change in properties of their elastomeric main spring component. To achieve this, a set of dynamic mechanical thermal analysis tests were conducted on elastomeric coupons taken from a set of engine mounts with different service and ageing conditions. These experimental results were used to characterise the change in mechanical response of the elastomer and to build up an empirical elastomer ageing model. Then a finite element model of the main spring was developed that used the elastomer ageing model so that the ageing behaviour of the engine mount could be simulated. The resulting ageing model was verified by using experimental results from a second batch of ex-service engine mounts. The results show an increasing trend of the vertical static stiffness of the engine mounts with distance travelled (or age) up to a certain distance (approximately 95,000 km). The trend is then reversed and a softening effect is observed. Moreover, the results reveal that both the maximum stiffness value and the distance travelled at the peak stiffness decrease as the temperature increases.

Poly(Vinyl Alcohol) Fiber Reinforced High Density Poly(Ethylene) Composites: Dynamic Mechanical Thermal Analysis

In the present work, high density polyethylene (HDPE)/poly (vinyl alcohol) (PVA) fiber composites with four different PVA fiber loadings (i.e. 0, 5, 10, 20 wt%) have been prepared via melt compounding method using a twin-screw extruder. The composites were characterized for their morphology by using a scanning electron microscopy (SEM). Whereas, the dynamic mechanical thermal analysis (DMTA) was carried out by using an oscillatory rheometer. The DMTA test was carried out under torsion mode using temperature sweep test on rectangular composites samples. The DMTA results showed that the storage modulus (G¢) of the composites were higher than that of the neat HDPE and increased with increasing PVA fiber loadings. This indicated that there was a considerable stiffness enhancement of the composites. For example, at temperature of 60°C, the increases of stiffness (i.e. storage modulus) of the composites were approximately 3, 31, and 54% for PVAC-5, 10, and 20, respectively. Whereas, at higher temperature (i.e. 120°C), the increases were about 4, 50, and 98% for PVAC-5, 10, and 20, respectively. These results indicated that even at higher temperatures, the enhancement of storage modulus of the composites was still high.

Evaluation of highly filled epoxy composites modified with walnut shell waste filler

Epoxy composites modified with ground walnut shell used as organic waste fillers were prepared and examined. Post-agricultural waste materials after grinding were characterized by evaluation of grain size distribution and structure observations realized using scanning electron microscope (SEM). The influence of filler addition on the mechanical properties of epoxy-based composites was determined by: static tensile test, Charpy impact test, and ball indentation hardness measurements. Composite samples containing 20, 30, 40, and 50 wt% of walnut shell were characterized by increased stiffness and hardness in comparison to the unmodified resins. Moreover, the incorporation of the filler resulted in a decrease of composite material tensile strength and impact resistance. Thermo-mechanical properties of the composites were investigated by dynamic mechanical thermal analysis (DMTA). Results obtained from DMTA tests showed a growth in the composites’ stiffness at elevated temperatures as a function of the increasing natural filler content. The material characterization was supplemented by thermal stability evaluation realized by thermogravimetric analysis (TGA). It was found that the incorporation of ground walnut shell led to an improved thermal stability of composite materials. The analysis of the change in composite material properties, caused by natural filler incorporation, was complemented by material microstructure observations.

Influence of SEBS-MA and SBS compatibilizers on properties and morphology of blends of polystyrene/rubber residue (SBRr) from the footwear industry

Abstract The reuse of rubber waste is very important today, both to reduce the harm-ful effects on the environment, and to reduce the cost of new material development. Considering that most of the studies reported in literature refer to the reuse of tire waste, this article aims to evaluate the influence of styrene-butadiene-styrene (SBS) and styrene-(ethylene-butylene)-styrene grafted with maleic anhydride (SEBS-MA) compatibilizers on the blend performance of polystyrene (PS)/styrene-butadiene rub-ber residue (SBRr), which come from the footwear industry. The blends were prepared in a co-rotating twin screw extruder and then were molded by injection. They were analyzed by impact and tensile tests, heat deflection temperature (HDT), ductile-brittle transition temperature, dynamic mechanical thermal analysis (DMTA) and transmis-sion electron microscopy (TEM). The results evidenced that the use of any of the com -patibilizers on the PS/SBRr blend significantly increased the impact strength, while the tensile properties and HDT were lower when compared to the polymer matrix. The ductile-brittle transition temperature remains at approximately 25°C range for all the blends. In general, it has been proved that the SBS was the most effective compatibiliza -tion process in the PS/SBRr system. The DMTA test shows the presence of two distinct temperature peaks. The morphologies obtained by TEM of binary and ternary blends were quite different and typical of immiscible blend. The results show a good perspec -tive regarding the use of industrial waste (SBRr), since it may enhance a material that would be discarded.

Enhancement of tensile, electrical and thermal properties of epoxy nanocomposites through chemical hybridization of polypyrrole and graphene oxide

This paper presents the properties of epoxy nanocomposites, prepared using a synthesized hybrid Polypyrrole-Graphene Oxide (PPy-GO) filler, via in-situ chemical polymerization, at various filler loadings (i.e., 0.5–2 w. t %). The microstructures and properties of the PPy-GO hybrids and epoxy nanocomposites were studied via Fourier transform infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), mechanical (Tensile Properties), electrical, Dynamic mechanical thermal analysis (DMTA) and thermogravimetric analyses (TGA). Morphological study demonstrated that varying the nanofiller nature (PPy-GOs, PPy or GO) lead to different states of dispersion. Mechanical, electrical and thermal analysis demonstrated that the hybrid concentration and its architecture (PPy:GO ratio) are interesting factors significantly affected the properties of the epoxy based nanocomposites. On the other hand, the mechanical performance of the cured nanocomposites outperformed the PPy-GO, with enhancements of 78% and 51% of Young's modulus and strength, respectively. Here it has been established that the embedding of PPy-GO hybrids into pristine epoxy endows optimum dispersion of PPy and GO as well as better interfacial adhesion between the fillers and matrix, which results in a significant improvement in load transfer effectiveness. Electrical conductivity measurements showed that conductivity of epoxy filled nanocomposites increased up 10−4 S/cm for Epoxy/PPy-GO nanocomposites. DMTA test indicated that incorporation of PPy-GO resulted in a significantly increase in Tg of the resultant nanocomposites, which is attributed to the highly exfoliation structure and the stronger interfacial interaction. The PPy-GO particles enhanced electrical, thermal and mechanical properties of nanocomposites, confirming the synergistic effect of PPy-GO as multifunctional filler.

Hyperbranched polyesters urethane acrylate resin

In the present study, response surface methodology is used to synthesize hyperbranched polyesters based on variables reaction time, ratio of monomer to core, and type of catalyst. Then, the synthesized polyesters were used for preparing hyperbranched urethane acrylates in two steps. In order to characterize these polymers, infrared spectroscopy and proton nuclear magnetic resonance is used. Hyperbranched urethane acrylates were formulated and cured by ultraviolet irradiation. Finally, dynamic mechanical thermal analysis (DMTA) test is used to investigate the viscoelastic properties of the coatings. The results of DMTA test were shown that the higher molar mass distribution of hyperbranched polyester is associated with less uniformity of cross-link network of cured samples. Also by increasing the molar mass of hyperbranched polyester, glass transition temperature of cured urethane acrylate resins was increased. The samples produced by using methane sulfonic acid catalyst show higher strength and more uniform cross-link network than the those made by sulfuric acid catalyst.

Synthesis of a novel phosphorus-containing curing agent and its effects on the flame retardancy, thermal degradation and moisture resistance of epoxy resins

A novel phosphorus-containing compound diphenyl-(1, 2-dicarboxylethyl)-phosphine oxide defined as DPDCEPO was synthesized and used as a flame retardant curing agent for epoxy resins (EP). The chemical structure of the prepared DPDCEPO was well characterized by Fourier transform infrared spectroscopy, and 1H, 13C and 31P nuclear magnetic resonance. The DPDCEPO was mixed with curing agent of phthalic anhydride (PA) with various weight ratios into epoxy resins to prepare flame retardant EP thermosets. The flame retardant properties, combustion behavior and thermal analysis of the EP thermosets were respectively investigated by limiting oxygen index (LOI), vertical burning tests (UL-94), cone calorimeter measurement, dynamic mechanical thermal analysis and thermogravimetric analysis (TGA) tests. The surface morphologies and chemical compositions of the char residues for EP thermosets were respectively investigated by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS). The water resistant properties of the cured EP were evaluated by putting the samples into distilled water at 70°C for 168 hr. The results revealed that the EP/20 wt% DPDCEPO/80 wt% PA thermosets successfully passed UL-94 V-0 flammability rating and the LOI value was as high as 33.2%. The cone test results revealed that the incorporation of DPDCEPO effectively reduced the combustion parameters of the epoxy resin thermosets, such as heat release rate and total heat release. The dynamic mechanical thermal analysis test demonstrated that the glass transition temperature (Tg) decreased with the increase of DPDCEPO content. The TGA results indicated that the incorporation of DPDCEPO promoted the decomposition of epoxy resin matrix ahead of time and led to a higher char yield and thermal stability at high temperatures. The surface morphological structures and analysis of the XPS of the char residues of EP thermosets revealed that the introduction of DPDCEPO benefited the formation of a sufficient, compact and homogeneous char layer with rich flame retardant elements on the epoxy resin material surface during combustion. The mechanical properties and water resistance of the cured epoxy resins were also measured. After water resistance tests, the EP/20 wt% DPDCEPO/80 wt% PA thermosets retained excellent flame retardancy, and the moisture adsorption of the EP thermosets decreased with the increase of DPDCEPO content in EP thermosets because of the existence of the P–C bonds and the rigid aromatic hydrophobic structure in DPDCEPO. Copyright © 2015 John Wiley & Sons, Ltd.

Nanocomposites based on natural rubber, organoclay and nano-calcium carbonate: Study on the structure, cure behavior, static and dynamic-mechanical properties

In this work, natural rubber (NR) based nanocomposites, using different amounts (0, 5, 10 and 15 parts per hundred rubber, phr) of nano-calcium carbonate (nano-CaCO3) with and without organoclay (OC) are prepared by melt mixing process. The prepared samples are characterized, performing X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FE-SEM), dynamic-mechanical thermal analysis (DMTA), swelling resistance in chemicals and tensile test. The tensile test results show that by the simultaneous using of 5phr OC and 10phr nano-CaCo3 the tensile strength is improved about 350%. The other tests such as XRD, FE-SEM, DMTA and swelling resistance tests as well as the theoretical investigation and calculating some thermodynamic parameters such as filler activity, activation enthalpy and Gibbs free energy reveal a considerable improvement of properties for the NR with OC and nano-CaCO3 in comparison to corresponding nanocomposites containing either one. The optimized sample in spite of having high elasticity exhibits high loss modulus which is very important in rubber product application.

Flexible fiber-reinforced composites with improved interfacial adhesion by mussel-inspired polydopamine and poly(methyl methacrylate) coating

To obtain a kind of light-curable fiber-reinforced composite for dental restoration, an excellent interfacial adhesion between the fiber and the acrylate resin matrix is quite essential. Herein, surface modification on glass fibers were carried out by coating them with poly(methyl methacrylate) (PMMA), polydopamine (PDA), or both. The PMMA or PDA coating was performed by soaking fibers in PMMA/acetone solution or dopamine aqueous solution. PDA/PMMA co-coated glass fibers were obtained by further soaking PDA-coated fibers in PMMA/acetone solution. These modified fibers were impregnated with bisphenol A glycidyl methacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) (5:5, w/w) dental resin at a volume fraction of 75%, using unmodified fibers as reference. Light-cured specimens were submitted to evaluations including flexural properties, morphological observation, dynamic mechanical thermal analysis (DMTA) and pull-out test. In comparison with unmodified glass fibers, all the modified glass fibers showed enhancements in flexural strength and modulus of Bis-GMA/TEGDMA resin composites. Results of DMTA and pull-out tests confirmed that surface modification had significantly improved the interfacial adhesion between the glass fiber and the resin matrix. Particularly, the PDA/PMMA co-coated glass fibers displayed the most efficient reinforcement and the strongest interfacial adhesion due to the synergetic effects of PDA and PMMA. It indicated that co-coating method was a promising approach in modifying the interfacial compatibility between inorganic glass fiber and organic resin matrix.

Drying of calcium-silicate-hydrates: regeneration of elastic modulus

Dynamic mechanical thermal analysis (DMTA) measurements for layered calcium silicate systems (1·4 nm tobermorite, jennite, synthetic calcium-silicate-hydrate and hydrated Portland cement paste) are reported. Elastic modulus results were obtained for samples initially conditioned to 11% relative humidity (RH) and dried during the DMTA test and for samples subjected to prolonged vacuum and thermal drying prior to a DMTA test. Decreases in elastic modulus relative to the 11% RH starting condition typically observed during a DMTA test were recovered subsequent to the prolonged thermal treatment. A possible ‘regeneration' mechanism for the elastic modulus is discussed. The ‘regeneration' occurs for all the calcium silicate systems studied. The results are consistent with the notions expressed for nanostructural models of calcium-silicate-hydrate in cement paste that comprise structural units based on 1·4 nm tobermorite and jennite.