Dynamic thermomechanical and tensile properties of chain-extended poly(ethylene terephthalate)

A series of chemically modified poly(ethylene terephthalate) (PET) samples was received after chain extension of a virgin sample at different reaction times with a new diepoxide as chain extender. These samples showed different intrinsic viscosity and degrees of branching or crosslinking. The effect of this differentiation on thermal properties was studied by dynamic mechanical thermal analysis and the determined T_g values were found to be in good agreement with those obtained by differential scanning calorimetry and thermomechanical analysis. Also, the branching or crosslinking exhibited significant improvement in tensile mechanical properties, which were studied, and the results are discussed. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 797–803, 1998     

Study of jute fiber reinforced polyester composites by dynamic mechanical analysis

Cyanoethylation of jute fibers in the form of nonwoven fabric was studied, and these chemically modified fibers were used to make jute–polyester composites. The dynamic mechanical thermal properties of unsaturated polyester resin (cured) and composites of unmodified and chemically modified jute–polyester were studied by using a dynamic mechanical analyzer over a wide temperature range. The data suggest that the storage modulus and thermal transition temperature of the composites increased enormously due to cyanoethylation of fiber. An increase of the storage modulus of composites, prepared from chemically modified fiber, indicates its higher stiffness as compared to a composite prepared from unmodified fiber. It is also observed that incorporation of jute fiber (both unmodified and modified) with the unsaturated resin reduced the tan δ peak height remarkably. Composites prepared from cyanoethylated jute show better creep resistance at comparatively lower temperatures. On the contrary, a reversed phenomenon is observed at higher temperatures (120°C and above). Scanning electron micrographs of tensile fracture surfaces of unmodified and modified jute–polyester composites clearly demonstrate better fiber–matrix bonding in the case of the latter. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1505–1513, 1999     

Dynamic mechanical properties of particle‐reinforced EPDM composites

The dynamic mechanical property of particle‐reinforced ethylene–propylene–diene monomer (EPDM) matrix composites has been studied by using a dynamic mechanical thermal analyzer (DMTA). The individual composite has been reinforced with the various reinforcing particles as follows: silicon carbide particles (SiCps) of 60 μm in average diameter with various volume fractions (i.e., 10–40%); copper (Cu) and aluminum (Al) particles with 20 vol %; and SiCps with 6 and 36 μm in different average diameters with 20 vol % over the total composite volume. It is shown from the experimental results that the dynamic elastic modulus values increase and the composites with 40 vol % SiCps exhibit higher tan δ values through the entire rubbery phase after the glass transition region compared with the composites with lower particle volume percentages. This shows that the composites with 20 vol % Cu particles have the higher dynamic elastic modulus but the lower peak tan δ value than the composites with other particles of 20 vol % do. Scanning electron microscopy results show that the effective particle volume in the composite with Cu particles is higher than the other composites, although the same particle volume fraction of 20% has been used. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1595–1601, 2003     

联苯型液晶聚氨酯/环氧体系的动态力学性能

采用动态热力学分析方法(DMA),研究了联苯液晶聚氨酯(DLCP)/环氧树脂(E-51)固化体系的储能模量、损耗模量和力学损耗因子随温度的变化情况。在玻璃化转变温度(Tg)下,通过改变振动频率求出链段运动的活化能并探讨聚合物分子链段的运动情况。结果表明:DLCP可降低材料的内耗,提高材料的Tg。加入质量分数5%的DLCP,复合材料的储能模量可达2 700 MPa,Tg比纯树脂提高10～30℃。     

Dynamic mechanical analysis on highly thermally stable polybenzoxazines with an acetylene functional group

Dynamic mechanical analysis is performed on polybenzoxazines from acetylene-terminated benzoxazine monomers, and glass transition temperatures of these polybenzoxazines are found in the range of 329–368°C. It has been identified that the high glass transition temperature and high thermal stability are due to polymerization of the acetylene terminal group, in addition to oxazine ring polymerization through a comparison study with analogous polybenzoxazines that are obtained from monomers without an acetylene functional group. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 857–862, 1999     

Dynamic mechanical characterization of a soy based epoxy resin system

Epoxidized allyl soyate (EAS), a novel soy based epoxy resin, has been prepared by the process of transesterfication and epoxidation of regular food grade soybean oil. Two types of crosslinking agents were employed in this study. The effects of the concentration of EAS and the type of crosslinking agent on the dynamic mechanical behavior of the soy based resin system have been investigated. The room temperature storage moduli (E′) and the glass transition temperatures (T_g) increased for the anhydride cured and decreased for the amine cured resins. The loss tangent maximum (tan δ)_max decreased for anhydride cured resins and increased for amine cured resins. The effect of frequency on the storage modulus was also studied. Master curves were constructed by the time‐temperature superpositioning technique (TTS) to predict the storage modulus at times and temperatures that are not experimentally feasible. The results indicate that soy based epoxy resins with appropriate concentrations hold great potential as a replacement for petroleum based materials in noise and vibration attenuation applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1772–1780, 2005     

Comparing the dynamic behaviour of several rubbers filled with silanized silica nanofiller

BACKGROUND: The effect of the same amount of precipitated silica nanofiller on the curing and dynamic properties of different rubbers, including natural rubber (NR) without and with the addition of elemental sulfur (NR with S), synthetic polyisoprene (IR), polybutadiene (BR) and poly(styrene‐co‐butadiene) copolymer (SBR), was investigated. The silica surfaces were pre‐treated with bis(3‐triethoxysilylpropyl)tetrasulfane (TESPT) to chemically bond the silica to the rubber. The rubbers were primarily cured by using sulfur in TESPT with the addition of optimum accelerator (TBBS) and activator (ZnO), which helped to form sulfur chemical bonds between the rubber and filler. RESULTS: Cure properties, Mooney viscosity, glass transition temperature, bound rubber and crosslink density along with dynamic properties of the filled rubbers, including tan δ, loss modulus (G″) and storage modulus (G′), were measured as a function of double oscillation amplitude (DSA) from 15 to 1000 µm, temperature from ?130 to 100 °C and frequency from 1 to 100 Hz. The results with emphasis on potential for tyre tread applications are discussed. It emerged that SBR along with BR filled rubbers had the highest rolling resistance while IR filled rubber had the least. Moreover, it was found that SBR filled rubber had the best skid resistance and BR filled rubber the worst. CONCLUSION: Interestingly, the variation of G′ with DSA showed a complicated behaviour for different filled rubbers. It emerged that in some DSA ranges the Payne effect was observed, and in the remaining ranges increments of G′ with DSA were seen. Because the bound rubber of most of the filled rubbers was more than 92%, there should be another predominant mechanism in the systems studied rather than simply de‐agglomeration or filler network breakdown, which is proposed by the Payne model. In addition, the nanoscale of the filler may be effective for this behaviour. Copyright © 2008 Society of Chemical Industry     

Dynamic mechanical analysis of FRP composites based on different fiber reinforcements and epoxy resin as the matrix material

Three-ply composite laminates prepared from E-glass or N-glass chopped strand mats (CSMs) and jute (J) fabrics as reinforcing agents and amine-cured epoxy resin as the matrix material were subjected to dynamic mechanical thermal analysis at a fixed frequency of 1 Hz over a temperature range of 30–180°C. The volume fraction of fibers ranged between 0.21 and 0.25. The reinforcing effect for the three fibers is in the order E-glass > N-glass ≫ jute. Glass-reinforced composites show a higher storage modulus (E′) than that of jute-reinforced composites. The E′ values of glass-jute hybrid composites lie between those of glass-reinforced and jute-reinforced composites. Odd trends in temperature variability of the loss modulus (E′) and the damping parameter, tan δ, and in the glass transition temperature (T_g) for the three different unitary and four different hybrid composites are interpreted and understood on the basis of odd differences in (1) the chemical nature and physical properties of the three different fibers (E-glass, N-glass, and jute), (2) the void content and distribution, (3) the thermal expansion coefficients of the main phases in the composites, (4) the degree of matrix stiffening at or near the fiber-matrix interface, and (5) the extents of matrix softening in the zone next to the interface. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2467–2472, 1997     

Investigation on gradient dielectric characteristics of bamboo (Dentroclamus strictus)

Dependence of dielectric constant (ε′) and dielectric dissipation factor (tan δ) on distance from outermost skin to the center of bamboo has been determined. Dielectric measurements have been done in the temperature range of 24–120°C and in the frequency range, 4–100 kHz. Gradient behavior in ε′ and tan δ has been found in bamboo. It has also been observed that ε′ and tan δ increase with increasing temperature and decrease with increasing frequency. Relaxation times have been calculated for the four samples at 80, 90, and 100°C temperatures, which show that relaxation time decreases with the increase of temperature because of the increased molecular mobility. A continuous increase in the hardness from center (48) to outer surface (70) and density from 0.45 to 0.80 g/cc has been observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 380–386, 2006     

Investigation on gradient dielectric characteristics of bamboo (Dendrocalamus strictus)

Dielectric constant (ε′) and tan δ dependence on distance from the outer most skin to the center of bamboo has been determined. Dielectric measurements have been done in the temperature range from 24 to 120°C and in the frequency range from 4 to 100 kHz. Gradient behavior in dielectric constant (ε′) and tan δ has been found in bamboo. It has also been observed that the dielectric constant (ε′) and tan δ increase with the increasing temperature and decrease with the increasing frequency. Relaxation times have been calculated for the four samples at 80, 90, and 100°C temperatures, which show that relaxation time decreases with the increase of temperature due to the increased molecular mobility. A continuous increase in the hardness from the center 48 to the outer surface 70 and density from 0.45 to 0.80 g/cc has been observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3489–3494, 2006     

Determination of dynamic mechanical properties of engineering thermoplastics at wide frequency range using Havriliak–Negami model

Using Havriliak–Negami (HN) model of time–temperature superposition, dynamic mechanical properties for two thermorheologically simple engineering thermoplastics, viz., polyether ether ketone (PEEK) and polycarbonate (PC) were determined. Calculations have been made with respect to (i) temperature‐independent HN parameters from dynamic mechanical analysis (DMA) and (ii) activation energies of the deformation processes involved. Viscoelastic properties, over a wide frequency range, were predicted from the HN model, which were further correlated with the experimentally determined quantities and chemical structure of the polymers. The mathematical calculations were done using Matlab® software. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 677–683, 2006     

Investigation of accelerated aging behaviour of high performance industrial coatings by dynamic mechanical analysis

Dynamic mechanical analysis (DMA) represents one of the most important methods for understanding mechanical behaviour of surface coatings providing a valuable link between chemistry, morphology, and performance properties. In this work, dynamic mechanical properties of several high performance industrial coatings were studied extensively. Four commercially available topcoats namely alkyd modified polyurethane (PU), economy aliphatic PU, high performance aliphatic PU and epoxy modified polysiloxane were selected based on their cure chemistries, volume solids, and overall performance. DMA was used to determine elastic modulus, glass transition temperature (T_g), crosslink density and creep behaviour of these coatings. DMA data were substantiated with mechanical and performance properties. Among the coatings, epoxy modified polysiloxane showed the highest T_g of 65.6 °C as well as crosslink density value of 2.24 × 10⁻³ mol/cc which was attributed to its superior mechanical and performance properties. In addition, topcoats were also subjected to artificial aging process in accelerated cyclic corrosion cabinet and QUV-weatherometer, respectively. The consequent changes in their physico-mechanical properties post exposure were also evaluated using DMA and correlated with other performance properties. After aging, the T_g increased substantially for all the coatings irrespective of their exposure type. For example, T_g of economy aliphatic PU increases from 38.4 °C to 52.9 °C and 51 °C after cyclic corrosion and UV-B weathering, respectively. However, crosslink densities either increased or decreased depending on the type of exposure and cure chemistries. These changes were corroborated using the Fourier transform infrared spectroscopy findings. The outcome of this study is expected to generate new insights into the behaviour of these coatings under dynamic mechanical stress and its relation with long term performance properties.     

Dynamic mechanical properties of cotton/polypropylene commingled composite systems

The dynamic mechanical properties of cotton/polypropylene (PP) commingled composite system was studied with reference to the fiber content, chemical treatments with potassium permanganate and maleic anhydride modified PP, processing conditions and applied frequency. Side by side commingling of matrix and reinforcing fibers was adopted for the fabrication of composite laminates as they provide the shortest melt flow distance during the melting of matrix fibers. This method can also be used for the recycling of textile wastes. The storage modulus was found to increase with the fiber content across a range of temperatures. The loss factor was found to decrease with the increase in fiber content while the glass transition temperature increases. The chemical treatments increase the value of storage modulus. A master curve was constructed and also made a comparison between the experimental results and the theoretically predicted values. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Unsaturated polyester–poly(ε‐caprolactone) hybrid nanocomposites: Thermal–mechanical properties

This paper reports on the thermal behavior and mechanical properties of nanocomposites based on unsaturated polyester resin (UP) modified with poly(ɛ‐caprolactone) (PCL) and reinforced with an organically modified clay (cloisite 30B). To optimize the dispersion of 30B and the mixing of PCL in the UP resin, two different methods were employed to prepare crosslinked UP–PCL‐30B hybrid nanocomposites. Besides, two samples of poly(ɛ‐caprolactone) of different molecular weight (PCL2: M_n = 2.10³g.mol⁻¹ and PCL50: M_n = 5.10⁴g.mol⁻¹) were used at several concentrations (4, 6, 10 wt%). The 30B concentration was 4 wt% in all the nanocomposites. The morphology of the samples was studied by scanning electron microscopy (SEM). The analysis of X‐ray patterns reveals that intercalated structures have been found for all ternary nanocomposites, independently of the molecular weight, PCL concentration and the preparation method selected. A slight rise of the glass transition temperature, T_g, is observed in UP/PCL/4%30B ternary nanocomposites regarding to neat UP. The analysis of the tensile properties of the ternary (hybrid) systems indicates that UP/4%PCL2/4%30B nanocomposite improves the tensile strength and elongation at break respect to the neat UP while the Young modulus remains constant. POLYM. COMPOS., 35:827–838, 2014. © 2013 Society of Plastics Engineers     

Preparation and dynamic mechanical properties of polyurethane‐modified epoxy composites filled with functionalized fly ash particulates

Fly ash (FA) is a porous ceramic, which has proved to have some favorable functions. In this article, we have prepared a series of fly ash filled composites, where the polyurethane‐(PU) modified epoxy (EP) was acted as the matrix. With the purpose of characterizing the effect of the content of PU in the matrices and the surface‐treatment (ST) of fly ash particulates on the dynamic mechanical properties of composites, Fourier transform infrared spectral analysis (FTIR), microstructure observation, impact property test as well as dynamic mechanical analysis (DMA) were systematically investigated. With FTIR test, it can be found that the chemical reactions occur, and new chemical structures are formed between EP and PU, and the functionalized groups existing on the surface of fly ash particulates can also be detected. In fractographs observation of composites, it can be seen that the silane coupling agent improves the interfacial bonding conditions between fly ash particulates and the matrix. Impact property test result reveals that PU improves the toughness of EP. Dynamic mechanical analysis of the composites is carried out from ?40 to 150°C using a tension‐compression mode. Results show that the composites, whose matrices are with 10 and 20 wt % PU, may possess better dynamic mechanical properties as compared with the other composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Glass transition temperatures of hydrocarbon blends: Adhesives measured by differential scanning calorimetry and dynamic mechanical analysis

A comparison of calculated and measured glass transition temperatures of a series of three‐component hydrocarbon blends was performed. The blends were prepared as mixtures of an elastomer with different proportions of tackifying resin and oil. Glass transition temperature, T_g, was measured by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) at four measurement frequencies. Most of these blends had pressure‐sensitive adhesive (PSA) properties, and were used to prepare a series of PSA tapes. The adhesion of the PSA tapes was shown to be strongly dependent on T_g. Tack of PSA tapes was measured at two different temperatures, and shown to be directly correlated to the blend T_g. Several predictive methods for blend T_g that are based on individual component T_gs were evaluated. The prediction of blend T_g is far more accurate if the individual component T_g values are determined by DMA instead of DSC. In addition, the Gordon‐Taylor equation gave a significant improvement on predicted blend T_g when compared to the Fox equation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 826–832, 2000     

Relationship between thermal properties and diffusion coefficients of gases for polyimide films

The relationships between the chemical structure, packing density (1/V_F), and cohesive energy density (CED) and the thermal properties of polyimides were investigated. Particularly, the correlation of tan δ measured by stress–strain/thermal mechanical analysis with 1/V_F and CED was found for eight polyimides. We measured the relationship between the apparent diffusion coefficient (D_a) and 1/V_F and CED, respectively, as described in previous articles. From these experiments, we found that the thermal properties, especially tan δ, were correlated with the apparent diffusion coefficient of gas. These results are well explained by use of micro-Brownian motion. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 389–397, 1997     

Dynamic mechanical analysis of fibre‐reinforced plastic composites based on carboxyl terminated poly(ethylene glycol) adipate modified epoxy and E glass fibre

Fibre reinforced plastic (FRP) composites prepared from E glass woven fabrics as reinforcing agent and carboxyl terminated poly(ethylene glycol) adipate (CTPEGA) modified epoxy as a matrix, were subjected to dynamic mechanical thermal analysis at a fixed frequency of 5 Hz. The volume fraction of glass was about 0.45. The concentration of CTPEGA in the matrix was varied gradually from 0 to 40 phr (phr stands for parts per hundred parts of resin), to investigate the effect of CTPEGA concentration on the dynamic properties of the composites. It was found that the tan δ peak temperature and storage modulus gradually decrease with incorporation of CTPEGA. However, the tan δ peak value increases up to 20 phr of CTPEGA concentration and decreases thereafter. The same trend was obtained in the case of impact strength. © 2000 Society of Chemical Industry     

Effect of rubber reactivity on the morphology of polybenzoxazine blends investigated by atomic force microscopy and dynamic mechanical analysis

Atomic force microscopy (AFM) is employed to study the hydroxyl‐terminated polybutadiene (HTBD) rubber‐modified polybenzoxazine resin. The morphology exhibits a submicron phase separation when HTBD with low epoxy contents are used. No distinguishable phase separation appears in the blend modified with high epoxy content HTBD. The rubber and resin phases are identified by the change of nanoscale indentation as a function of external load imposed on the cantilever. The existence of an interphase between the glassy matrix and the rubbery domain is shown by comparing the pulling distances from force–distance (F–d) curve measurements. The extent of rubber cavitation is investigated by the particle analysis on the fracture surface and is found to increase with the particle diameter. The amount of dissolved rubber, estimated by the Fox equation, increases with the rubber reactivity, and the data corroborates well with the observed morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2443–2454, 2006     

Effects of epoxidized sunflower oil on the mechanical and dynamical analysis of the plasticized poly(vinyl chloride)

Epoxidized soybean oil (ESBO), is one of the most commonly used epoxides because of its typical combined roles as a plasticizer and heat stabilizer. In this study, a novel plasticizer of poly(vinyl chloride) (PVC) resins, epoxidized sunflower oil (ESO), was synthesized, and its performance was evaluated. ESO was designed to act as a coplasticizer and a heat stabilizer like ESBO. ESO is used as organic coplasticizer for plasticized PVC containing Ca and Zn stearates as primary stabilizers and stearic acid as lubricant. Di‐(2‐ethylhexyl) phthalate (DEHP), a conventional plasticizer for PVC, was partially replaced by ESO. Mechanical properties (tensile and shore D hardness) were investigated. The performance of ESO to ESB0 (20 g) for comparison, indicated that ESO could be used as secondary plasticizer for PVC in combination with DEHP. All mechanical and dynamical properties of plasticized PVC sheets varied with the oxirane oxygen of the ESO. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008