Effect of fibers treatment on dynamic mechanical and thermal properties of epoxy hybrid composites

Epoxy hybrid composites fabricated by reinforcing 2‐hydroxy ethyl acrylate (2‐HEA) treated oil palm empty fruit bunch (EFB) and jute fibers. It assume that chemical modification of jute and oil palm EFB fibers increased fiber/matrix interfacial bonding and it results in enhanced thermal properties of hybrid composites. Dynamic mechanical and thermal analysis of treated hybrid composites was carried out. Results indicated that chemical modification of oil palm EFB and jute fibers affect the dynamic mechanical and thermal properties of hybrid composites. The storage modulus values of hybrid composites increases with chemical treatment and loss modulus increased with fiber treatment in hybrid composites. Damping factor peak values of treated hybrid composites shifted toward the lower temperature compared to both untreated hybrid composites. Cole–Cole analysis was made to understand the phase behaviour of the hybrid composites. Thermogravimetric analysis indicated an increased in thermal stability of hybrid composite with the incorporation of chemically modified fibers. POLYM. COMPOS., 36:1669–1674, 2015. © 2014 Society of Plastics Engineers     

Thermal conductivity and dynamic mechanical property of glycidyl methacrylate‐grafted multiwalled carbon nanotube/epoxy composites

The well dispersed multiwalled carbon nanotube (MWCNT)/epoxy composites were prepared by functionalization of the MWCNT surfaces with glycidyl methacrylate (GMA). The morphology and thermal properties of the epoxy nanocomposites were investigated and compared with the surface characteristics of MWCNTs. GMA‐grafted MWCNTs improved the dispersion and interfacial adhesion in epoxy resin, and enhanced the network structure. The storage modulus of 3 phr GMA‐MWCNTs/epoxy composites at 50°C increased from 0.32 GPa to 2.87 GPa (enhanced by 799%) and the increased tanδ from 50.5°C to 61.7°C (increased by 11.2°C) comparing with neat epoxy resin, respectively. Furthermore, the thermal conductivity of 3 phr GMA‐MWCNTs/epoxy composite is increased by 183%, from 0.2042 W/mK (neat epoxy) to 0.5781 W/mK. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal degradation kinetics of insulating/conducting epoxy/Zn composites under nonisothermal conditions

This article deals with the nonisothermal degradation kinetics of insulating and conducting epoxy/Zn composites. A comparison of thermal degradation data obtained from epoxy/Zn composites revealed that the addition of zinc content in epoxy significantly increases its degradation rate. However, the zinc content activates the degradation until its melting point (419.5°C) and then it starts stabilizing the matrix due to its higher specific heat in molten state. Kinetics of the phenomena fairly explains this behavior in terms of the comparison of general kinetic equations for epoxy/Zn composites. It is to notice that both the values of effective activation energy and reaction model (Šestâk Berggren/SB‐m, n) for insulator/conductor composite pair have been found almost the same emphasizing upon negligible polymer–metal interactions in both cases. These mechanistic clues derived from comparative kinetic study have been found in good agreement with the results obtained through morphological analysis of samples by scanning electron microscopy and X‐ray diffraction techniques. POLYM. COMPOS., 34:2049–2060, 2013. © 2013 Society of Plastics Engineers     

Thermal and mechanical characterization of amine‐epoxy/Kevlar fibre composites

Experimental results of dynamic‐mechanical measurements and differential scanning calorimetry are compared for a pure diglycidyl‐type epoxy/tetrafunctional aliphatic amine system and for a composite containing Kevlar fibres as reinforcement. The presence of fibres had marked effects on the curing reaction, depending on the curing temperature. At low curing temperatures, the extent of the reaction was lower for reinforced than for neat formulations. For higher curing temperatures, the thermograms shifted to shorter times as the fibre content increased. In dynamic curing, an increase in the fibre content affected the curing kinetics by slightly shifting the heat flow curves to higher temperatures, and resulted also in a reduction of the glass transition temperature of the matrix if postcuring was not applied. The dependence of the dynamic‐mechanical spectra of the samples on fibre content was satisfactorily modelled with the aid of Takayanagi's block model. An analysis of the main relaxation master curve shows that relaxation broadens as fibre content increases. © 1999 Society of Chemical Industry     

Effect of surface structure of porous silica microballoons on dynamic mechanical properties of amine cured epoxy resin composites

Dynamic mechanical properties were studied for epoxy resin filled with porous silica microballoons with varying surface area, pore radius, pore volume and adsorbed water. The glass transition temperature (T_g) of the composites is 12–14°C lower than the T_g of the unfilled epoxy resin. This T_g depression is attributed to the preferential adsorption of curing agents on the porous silica microballoons. Tg of the composite increases with increase in the adsorbed water on fillers. The storage modulus has a distinct correlation with the Hg-surface area of silica microballoons, which corresponds to the sum of the surface area of pores with radii larger than about 4 nm. Tan δ_c tan δ_m decreases with increasing Hg-surface area.     

Preparation of epoxy resin/silica hybrid composites for epoxy molding compounds

Phenolic novolac/silica and cresol novolac epoxy/silica hybrids were prepared through in situ sol‐gel reaction of tetraethoxysilane (TEOS). The formed hybrids were utilized as a curing agent and an epoxy resin in epoxy curing compositions, respectively. Via the two‐step preparation route, the resulting epoxy resin/silica hybrid nanocomposites exhibited good thermal stability, high glass transition temperatures, and low coefficients of thermal expansion. High condensation degree of the condensed silica was observed with a high content of siloxane bridges, p > 85%, measured by ²⁹Si NMR. The two‐step route also provides feasibility of preparation of epoxy resin/silica hybrid nanocomposites compatible with the current processes of manufacturing of epoxy molding compounds. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4047–4053, 2003     

Polyhedral oligomeric silsesquioxane/silica/polydimethylsiloxane rubber composites with enhanced mechanical and thermal properties

Composites of polydimethylsiloxane (PDMS) rubber modified by three kinds of polyhedral oligomeric silsesquioxanes (POSSs) as well as fumed silica were prepared through solution blending and then open two‐roll mill blending with curing agent. Subsequently, the influences of POSS on mechanical and thermal properties of the resulting composites were investigated in detail. The addition of POSS significantly enhanced the tensile strength and elongation at break of the composite but lowered the tensile modulus, which could be ascribed to the interruption of silica–silica and silica–PDMS interactions. Octamethylsilsesquioxane (OMS)/silica/PDMS and octaphenylsilsesquioxane (OPS)/silica/PDMS composites did not show desirable mechanical and thermal properties. Nevertheless, heptaphenylvinylsilsesquioxane (VPS)/silica/PDMS composite with 5 wt % VPS exhibited enhanced glass transition temperature (T_g), mechanical properties, and thermal stability. Further studies revealed that more VPS unfavorably affected properties of the composite. Scanning electron microscope and X‐ray diffraction demonstrated that owing to the grafting reaction, 5 wt % VPS in the rubber matrix could form microcrystal domains the most effectively. Thus, the improved mechanical properties and thermal stability just resulted from the the formation of microcrystal domains and the increase in stiffness of PDMS chains because of the graft of VPS onto PDMS. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42173.     

Thermal and insulating properties of epoxy/aluminum nitride composites used for thermal interface material

We synthesized an epoxy matrix composite adhesive containing aluminum nitride (AlN) powder, which was used for thermal interface materials (TIM) in high power devices. The experimental results revealed that adding AlN fillers into epoxy resin was an effective way to boost thermal conductivity and maintain electrical insulation. We also discovered a proper coupling agent that reduced the viscosity of the epoxy‐AlN composite by AlN surface treatment and increased the solid loading to 60 vol %. For the TIM sample made with the composite adhesive, we obtained a thermal conductivity of 2.70 W/(m K), which was approximately 13 times larger than that of pure epoxy. The dielectric strength of the TIM was 10 to 11 kV/mm, which was large enough for applications in high power devices. Additionally, the thermal and insulating properties of the TIM did not degrade after thermal shock testing, indicating its reliability for use in power devices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal and dynamic mechanical investigations on fiber-reinforced polypropylene composites

The thermal behavior and dynamic mechanical properties of isotactic polypropylene (PP) and reactor blend PP/ethylene-propylene copolymer (EPM), reinforced with different amounts of short glass fibers (GF) and/or polyester fibers (PETF), were investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermoanalysis (DMTA) of imposed tensile load on rectangular film specimens. DSC measurements exhibited an increase of the crystallization temperature of PP in the presence of fibers, but indicated no change in its percentage of crystallinity. DMTA spectra revealed an increase in the stiffness and a decrease of the damping with increasing GF content. The positions of the primary relaxations of PP and EPM did not change, but a significant broadening of the α-relaxation in the crystalline phase was observed, due to the induced reinforcement and interfacial interactions. The addition of PETF to PP enhanced its damping values at low temperatures and promoted the α-transition. The DMTA behavior was studied in dependence on the preconditioning and the frequency excitation. Heat treatment changed the characteristics of the β-relaxation of PP, due to enhanced molecular motion of the polymer segments. The variation of frequency affected the secondary relaxations considerably and, in the presence of GF, the glass transitions. For the different relaxations, activation energies from peak shift and loss peak areas were determined. Experimental data of loss peaks were fitted to phenomenological equations. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1143–1154, 1997     

A dynamic mechanical thermal analysis on allylester polymers and composites filled with alumina

A dynamic mechanical thermal analysis (DMTA) was performed on allylester polymers and composites filled with alumina. We determined the glass transition temperatures and the values of the storage moduli in both the glassy and rubbery states in each system and compared the mechanical-thermal behavior of pristine allylester polymers with that of composites filled with alumina. To supplement the result of DMTA, we also carried out viscometry, gel permeation chromatography, and differential scanning calorimetry. The molecular structures had an influence on the viscosity, the glass transition temperature, and the storage modulus. Allylester composite filled with 20 phr alumina showed peculiar mechanical—thermal behavior. © 1996 John Wiley & Sons, Inc.     

In situ growth of multilayered crystals in amorphous matrix: Thermal,dynamic mechanical,and morphological analysis of nylon‐6/epoxy composites

A new procedure for processing of epoxy/polyamide blend was explored via solution polymerization of ε‐caprolactam in N‐methylpyrollidone (NMP), which resulted in a suspension of nylon‐6 in solvent at room temperature. The suspension was blended with water based epoxy resin using mechanical stirring at room temperature. Several films were prepared from blend by varying the amount of nylon‐6 without curing agent. All films were fully characterized for thermal and dynamic mechanical properties using differential scanning calorimetry and dynamic mechanical analysis. The addition of nylon‐6 had a plasticizing effect on epoxy evident by decrease in glass transition temperature (T_g). The reaction between nylon‐6 and epoxy was studied using Fourier transform infrared spectroscopy by following the characteristic epoxy peak (914 cm^?1). The growth of nylon‐6 crystals in epoxy matrix lead to spherulitic multiphase morphology, which was observed under scanning electron microscope. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3319–3327, 2013     

Fungal degradation of wood‐plastic composites and evaluation using dynamic mechanical analysis

Small samples of two wood–polyethylene (HDPE) composite formulations were incubated with either the white‐rot fungus Trametes versicolor or the brown‐rot fungus Gloeophyllum trabeum for 24 and 77 days in an agar‐block test. Noninoculated, side‐matched controls were employed in the tests to serve as references, and solid wood samples of yellow‐poplar (Liriodendron tulipifera L.) inoculated with T. versicolor were included as positive controls. Potential changes in storage and loss moduli because of fungal colonization and moisture were determined using dynamic mechanical analysis, whereas weight loss and visual observation served as indicators of fungal decay. Severe losses in storage modulus (E′) and loss modulus (E″) following incubation of yellow‐poplar with T. versicolor were observed. However, the E′ of the two wood–plastic composite (WPC) formulations increased after 24 days of incubation with T. versicolor. The same effect was observed for G. trabeum, but only in one formulation. The increase of E′ was attributed to a reinforcing effect of the fungal hyphae present in the interfacial gaps between the wood filler and the polymer matrix. Dynamic temperature scans revealed a peak in E″ between 30°C and 63°C, depending on the frequency and fungal treatment. The peak temperature of E″ represents the α‐transition of HDPE. Increased activation energies were required for the α‐transition in WPC samples incubated with T. versicolor for 77 days as compared to controls. This observation confirmed that incubation of WPC with T. versicolor improved interfacial adhesion and reinforced the composite under the assay conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3138–3146, 2006     

Thermal and mechanical properties of poly(urethane‐imide)/epoxy/silica hybrids

Improving properties of polyurethane (PU) elastomers have drawn much attention. To extend the properties of the modified PU composite, here a new method via the reaction of poly(urethane‐imide) diacid (PUI) and silane‐modified epoxy resin (diglycidyl ether of bisphenol A) was developed to prepare crosslinked poly (urethane‐ imide)/epoxy/silica (PUI/epoxy/SiO₂) hybrids with enhanced thermal stability. PUI was synthesized from the reaction of trimellitic anhydride with isocyanate‐terminated PU prepolymer, which was prepared from reaction of polytetramethylene ether glycol and 4,4′‐diphenylmethane diisocyanate. Thermal and mechanical properties of the PUI/epoxy/SiO₂ hybrids were investigated to study the effect of incorporating in situ SiO₂ from silane‐modified epoxy resin. All experimental data indicated that the properties of PUI/epoxy/SiO₂ hybrids, such as thermal stability, mechanical properties, were improved due to the existence of epoxy resin and SiO₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal treatment and dynamic mechanical thermal properties of polyaniline

Thermal transitions of polyaniline in the emeraldine base form (Pani-EB) were studied by DMTA using two series of thermally treated samples. In the first series the specimens were annealed at 70 °C for 5, 15 min, 1 and 3.5 h. In the second they were submitted to annealing at 100 °C during the same periods of time plus a 24 h treatment. Two transitions were observed at sub-zero temperatures and were attributed to the motion of solvated water and solvent (NMP). The glass transition and the highest temperature relaxation, assigned to crosslinking depended on the degree of solvation resulting from the thermal treatment. A linear contraction of Pani-EB films with residual water evaporation was reported for the first time.     

High-performance composite from epoxy and glass fibers: Morphology,mechanical, dynamic mechanical,and thermal analysis

Diglycidyl ether of bisphenol-A type epoxy resin cured with diamino diphenyl sulfone was used as the matrix for fiber-reinforced composites to get improved mechanical and thermal properties for the resulting composites. E-glass fiber was used for fiber reinforcement. The morphology, tensile, flexural, impact, dynamic mechanical, and thermal properties of the composites were analyzed. The tensile, flexural, and impact properties showed dramatic improvement with the addition of glass fibers. Dynamic mechanical analysis was performed to obtain the T_g of the cured matrix as well as the composites. The improved thermal stability of the composites was clear from the thermogravimetric analysis. Scanning electron micrographs were taken to understand the interfacial adhesion between the fiber and the matrix. The values of mechanical properties were compared with modified epoxy resin composite system. Predictive models were applied using various equations to compare the mechanical data obtained theoretically and experimentally. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Grafting of epoxy chains onto graphene oxide for epoxy composites with improved mechanical and thermal properties

Epoxy composites filled with both graphene oxide (GO) and diglycidyl ether of bisphenol-A functionalized GO (DGEBA–f–GO) sheets were prepared at different filler loading levels. The correlations between surface modification, morphology, dispersion/exfoliation and interfacial interaction of sheets and the corresponding mechanical and thermal properties of the composites were systematically investigated. The surface functionalization of DGEBA layer was found to effectively improve the compatibility and dispersion of GO sheets in epoxy matrix. The tensile test indicated that the DGEBA–f–GO/epoxy composites showed higher tensile modulus and strength than either the neat epoxy or the GO/epoxy composites. For epoxy composite with 0.25 wt% DGEBA–f–GO, the tensile modulus and strength increased from 3.15 ± 0.11 to 3.56 ± 0.08 GPa (∼13%) and 52.98 ± 5.82 to 92.94 ± 5.03 MPa (∼75%), respectively, compared to the neat epoxy resin. Furthermore, enhanced quasi-static fracture toughness (K_IC) was measured in case of the surface functionalization. The GO and DGEBA–f–GO at 0.25 wt% loading produced ∼26% and ∼41% improvements in K_IC values of epoxy composites, respectively. Fracture surface analysis revealed improved interfacial interaction between DGEBA–f–GO and matrix. Moreover, increased glass transition temperature and thermal stability of the DGEBA–f–GO/epoxy composites were also observed in the dynamic mechanical properties and thermo-gravimetric analysis compared to those of the GO/epoxy composites.     

Thermal modification of amine cured epoxy resins - thermal and mechanical studies

Mechanical test data are reported on lap joints and tensile test specimens which have been subjected to a defined post cure cycle. The mechanical properties exhibited an apparently systematic variation with temperature. Inspection of the resins indicated that chemical modification does not appear to occur to a significant extent below 433K. The change in the strength of the joints tensile test samples are discussed in terms of the relative importance of physical and chemical changes on the mechanical properties. It is evident that in the presence of oxygen considerable chemical modification can occur and this is observed both in terms of a change in colour of the resin and the appearance of voids.     

The influence of carbon spheres on thermal and mechanical properties of epoxy composites

In order to improve the properties of epoxy resion, a reinforcement addictive of carbon spheres (CSs) was successfully synthesized by hydrothermal methods and CSs/Epoxy composite was prepared using in-situ polymerization technique. The morphology and structure of CSs and CSs/Epoxy composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that CSs distributed homogeneously in epoxy matrix and the integrating state of interface between CSs and epoxy is good. TGA and DMA analysis showed that the thermal stability of CSs/Epoxy composite in air and the glass transition temperature (T_g) increased with the addition of CSs. DMA results show that the creep recovery property also improved. Additionally. The impact fracture strength of EP composites increased after the addition of CSs compared to pure EP, it means the toughness of epoxy improved effectively, which attribute to the effective dissipation of the crash energy. Finally, the mechanism for the improvement of mechanical properties by the CSs is also discussed.     

Fabrication of graphene/epoxy resin composites with much enhanced thermal conductivity via ball milling technique

Ball milling is selected to prepare composites of graphene nanoplatelets (GNPs) and epoxy. Much enhanced thermal conductivity was recorded with higher GNP loading, which varied between 5 and 25 wt %. A maximum thermal conductivity of 2.67 W/m·K was found. The prepared composites were characterized by scanning electron microscopy, transmission electron microscopy, and Raman. It was found that KNG180, a commercially available kind of natural graphite, with a thickness of 30 ～ 80 nm were mainly exfoliated into GNPs (<10 layers) with high quality, which were in turn uniformly dispersed in the composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40565.     

Thermal and mechanical properties of epoxy composites reinforced by a natural hydrophobic sand

If a low weight percentage of crude fine fillers can improve properties of polymer materials directly without complicated chemical treatment process involved, it will be significant for many industrial applications. Our previous study indicated that a kind of Cancun natural sand could be an effective filler material for polymer composites. In this current work, the epoxy composites reinforced by this kind of natural sand particles were prepared and thermal and mechanical properties of the composites containing up to 5 wt % of the sand particles were characterized. Results showed that the highest flexural strength appears in the epoxy composite containing 1 wt % sand particles. A damage model was used to interpret the flexural properties, which showed an acceptable agreement with the experimental results. The glass transition temperature, high temperature storage modulus, and dimensional stability of the sand/epoxy composites monotonically increased with the addition of the sand particles. The sand particle/epoxy composites also displayed a noticeable enhancement in thermal conductivity. Theoretical analysis showed that in addition to conduction, other heat transport mechanisms played roles in the improved heat transmission through the composites. As a natural porous micron-scale material, Cancun sand has the potential for applications in cost-effective composites with enhanced mechanical and thermal properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008