Higher Dynamic Modulus Research Articles

Mechanical and acoustic frequency responses in flat hot‐compacted polyethylene and polypropylene panels

AbstractA range of flat hot‐compacted single‐polymer composite panels made from oriented polypropylene and polyethylene with differing dynamic modulus and damping capacity were freely suspended and subjected to mechanical excitation, allowing their acoustic frequency response over the audio bandwidth to be measured. The audio response over selected bands was correlated with the dynamic modulus and damping capacity measured in bending in these materials and compared with the response of a traditional composite material, namely, carbon‐fiber‐reinforced epoxy resin. Low damping and high dynamic modulus were found to result in relatively high output levels from the hot‐compacted flat panels, which contrasted with the results previously measured on a traditional cone‐shaped speaker made from a hot‐compacted polypropylene material, which found high damping to be advantageous. The results of the current study on flat panels are explained in terms of mechanical impedance of the panels and their corresponding efficiency. It was concluded that the best flat‐panel audio response came from compacted polyethylene sheets, which combined high stiffness, low density, and a low level of damping. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

A preliminary study of reactive powder concrete as a new repair material

This study aims to use reactive powder concrete (RPC) as a new repair material and evaluate its bond durability to existing concrete. One accelerated aging environment, namely a freeze–thaw cycle acceleration deterioration test, was selected for the evaluation of bond durability of the repair materials. Before and after aging, the samples were evaluated by the compressive strength, bond strength (slant shear test), steel pull out strength, and relative dynamic modulus NDT tests. The test results show that the RPC displays excellent repair and retrofit potentials on compressive and flexure strengthening and possesses high bond strength, dynamic modulus and bond durability as compared with other concretes. The adhesion between the RPC and the steel is also much greater than that for the other concretes. It would be interesting to verify the consequences of this improved adhesion and repair in reinforced concrete structures.

The Study of Bond Strength and Bond Durability of Reactive Powder Concrete

Abstract This research project aims to use reactive powder concrete, RPC, as a new repair material and evaluate its bond strength and bond durability to existing concrete. One accelerated aging environment, namely a freeze-thaw cycle acceleration deterioration test, was selected for the evaluation of bond durability of the repair materials. Before and after aging, the samples were evaluated by the compressive strength, bond strength (slant shear test), steel pull out strength, and relative dynamic modulus NDT tests. The test results show that the RPC possesses high bond strength, dynamic modulus, and bond durability as compared with other concretes. The adhesion between the RPC and the steel is also much greater than that for the other concretes. It would be interesting to verify the consequences of this improved adhesion in reinforced concrete structures. Test results revealed that RPC was still in good condition after 1000 cycles of freezing and thawing in accordance with ASTM C 666-97. After 1000 cycles, the nonshrinkage high strength mortar showed a reduction in compressive strength, slant shear strength, steel pull out strength, and dynamic modulus by 17, 21, 24, and 25 %, compared with the corresponding values of 6, 7, 5, and 10 %, respectively, for RPC. Specimens of normal strength concrete were used as reference specimens. The 5 cm × 10 cm slant shear cylinders made of normal strength concrete had deteriorated severely after 600–700 freeze-thaw cycles. For the normal strength concrete, the average values of relative dynamic modulus of elasticity based on resonant frequencies after 300 and 600 freeze-thaw cycles were 75 and 55%, compared with the corresponding values of 96 and 92%, respectively, for RPC.

Synthesis and rheological properties of polystyrene/layered silicate nanocomposite

Exfoliated polystyrene (PS)/organo-modified montmorillonite (MMT) nanocomposites were synthesized through in situ free radical bulk polymerization by dispersing a modified reactive organophilic MMT layered silicate in styrene monomer. The original MMT was modified by a mixture of two commercial cationic surfactants, [2-(acryloyloxy)ethyl](4-benzoylbenzyl)dimethylammonium bromide (ADAB) and cetyltrimethylammonium bromide (CTAB), with the former containing a polymerizable vinyl group. The exfoliating and intercalating structures were probed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Comparing with pure PS, the nanocomposites show much higher decomposition temperature, higher dynamic modulus, stronger shear thinning behavior and a smaller die swell ratio. The leveling-off of the storage modulus at low frequencies in the oscillatory shear measurements, as well as the observed yield like behavior, implies that the formation of a percolating nanoclay network is the origin of the enhanced viscoelasticity in these composites.

Synthesis of polyurethane acrylate and application to UV-curable pressure-sensitive adhesive

Synthesis of polyurethane acrylate (PUAs), using dimer acid-based polyester diol and hydrogenated castor oil (HCO), and preparations of the UV-curable pressure-sensitive adhesive (PSA) are reported. The effect of hydroxyl from dimer acid polyester diol/hydroxyl from HCO ratio (OHDiol/OHHCO), hydroxyl from both HCO and DAPD/2-hydroxyethyl acrylate ratio (OHPolyol/OHHEA) and tackifying resin/PUA ratio on the dynamic viscoelastic properties and performance of UV-cured PSA were investigated. The study revealed that, with OHDiol/OHHCO and OHPolyol/OHHEA increased, the storage modulus (G′), the loss modulus (G″) and complex viscosity (η*) of UV-cured PSA increased, and so did the corresponding holding power (HP); Peeling strength, however, decreased. On increasing the tackifying resin/PUA ratio, G′, G″ and η * decreased, as did HP, whereas the peeling strength increased. Catalysts affected the dynamic properties and the performance of PSA. In contrast with PSA corresponding to dibutyltin dilaurate (DBTDL), the PSA corresponding to organic bismuth (OB) had higher dynamic modulus, complex viscosity and holding power, and the converse in case of the peeling strength.

Influence of layer bonding on the prediction of pavement life

It is important to recognise that pavement performance can be seriously compromised by interface problems, even though the performance of an individual layer may be very high. This means that pavements may fail with traffic volumes far less than the design values in spite of the fact that individual layers may exhibit reasonably high dynamic stiffness modulus values, high permanent deformation resistance and high fatigue properties. Material properties and some construction practices can create weak or no interface bonding. Bond failure at one interface can cause a predicted loss of two-fifths to five-sixths, to as low as one sixth of the potential life of the pavement. Pavement analysis based on the assumption that all bound layers work as one single layer is seriously misleading if the bond at one or more layer interfaces is weak or has failed. The fatigue property of a pavement layer above an interface is very sensitive to variations in layer dynamic stiffness modulus, layer thickness and the degree of lateral movement available at the interface.

Influence of layer bonding on the prediction of pavement life

It is important to recognise that pavement performance can be seriously compromised by interface problems, even though the performance of an individual layer may be very high. This means that pavements may fail with traffic volumes far less than the design values in spite of the fact that individual layers may exhibit reasonably high dynamic stiffness modulus values, high permanent deformation resistance and high fatigue properties. Material properties and some construction practices can create weak or no interface bonding. Bond failure at one interface can cause a predicted loss of two-fifths to five-sixths, to as low as one sixth of the potential life of the pavement. Pavement analysis based on the assumption that all bound layers work as one single layer is seriously misleading if the bond at one or more layer interfaces is weak or has failed. The fatigue property of a pavement layer above an interface is very sensitive to variations in layer dynamic stiffness modulus, layer thickness and the degree of lateral movement available at the interface.

Polymer–clay nanocomposites: exfoliation of organophilic montmorillonite nanolayers in polystyrene

A polymerizable cationic surfactant, vinylbenzyldimethyldodecylammonium chloride (VDAC) was synthesized for functionalization of montmorillonite (MMT) and preparation of exfoliated polystyrene–clay nanocomposites. Organophilic MMT was prepared by cationic exchange between inorganic ions of MMT and ammonium cations of VDAC in an aqueous medium. Dispersions of intercalated clay (VDAC–MMT) in styrene monomer formed gels. Shear thinning behavior of the gels was observed via rheological measurements. Polystyrene–clay nanocomposites were prepared by free radical polymerization of styrene containing dispersed organophilic MMT. Exfoliation of MMT in polystyrene matrix was achieved as revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The exfoliated nanocomposites have higher dynamic modulus and higher decomposition temperature than pure polystyrene.

Possibilities to Improve the Properties of Natural Fiber Reinforced Plastics by Fiber Modification – Jute Polypropylene Composites –

The influence of the fiber-matrix adhesion in jute fiber-reinforced polypropylene on the materials behavior under fatigue and impact loadings was investigated throughout this study. It was shown that a strong interface is connected with a higher dynamic modulus and reduction in stiffness degradation with increasing load cycles and applied maximum stresses. The specific damping capacity resulted in higher values for the composites with poor bonded fibers. Furthermore, the stronger fiber-matrix adhesion reduced the loss-energy by non-penetration impact tested composites with roughly 30%. Tests which were performed at different temperatures, showed higher loss energies for cold and warm test conditions compared with room temperature. Post-impact dynamic modulus after 5 impact events was roughly 40% and 30% lower for composites with poor and good fiber-matrix adhesion, respectively.

Synthesis of polystyrene–clay nanocomposites

A reactive cationic surfactant vinylbenzyldimethyldodecylammonium chloride (VDAC) was synthesized for intercalation of montmorillonite (MMT), a smectic type of clay. Organophilic MMT was prepared by ion exchange between Na + ions in the clay and VDAC cations in aqueous medium. VDAC-intercalated MMT particles were easily dispersed and swollen in styrene monomer. Polystyrene–clay nanocomposites were prepared by free radical polymerization of styrene containing dispersed clay. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that exfoliation of MMT was achieved. Polystyrene–clay nanocomposites have higher dynamic modulus than pure polystyrene (PS).

EFFECT OF FLUORINATED TRIETHYLENE GLYCOL DIMETHACRYLATE ON THE PROPERTIES OF UNFILLED, LIGHT-CURED DENTAL RESINS

ABSTRACT The fluorinated triethylene glycol dimethacrylate (FTEGDMA) was used to improve the properties of Bisphenol A glycol dimethacrylate (BisGMA)/triethylene glycol dimethacrylate (TEGDMA) based dental resin system. Physical properties such as contact angle, polymerization shrinkage and water sorption, thermal properties such as glass transition temperature, dynamic modulus and thermal expansion, and mechanical properties such as compressive and diametral tensile strengths of the experimental neat resins and conventional controls were investigated and compared, using methods described in the text. Results showed that the FTEGDMA modified neat resins exhibited significant less water sorption and lower polymerization shrinkage and the 2,2'-bis(4-methacryloxy ethoxy phenyl) propane (BisEMA) also contributed significantly towards reducing water sorption. The resin containing FTEGDMA and BisEMA(10:90 molar ratio) (or F1E9) showed the highest values in mechanical strengths, due to its higher glass transition temperature (Tg), while the F5E5 (50:50) showed the least water sorption, based on the results of contact angle tests and water sorption measurements. The F5E5 resin exhibited the highest dynamic modulus. The F3E7 (30:70) resin showed the lowest polymerization shrinkage.

A study on the properties of epoxy resin toughened by a liquid crystal-type oligomer

A series of novel reactive toughening agents (LCEUPPG) containing both a flexible spacer and rigid liquid crystalline unit were synthesized to modify the bisphenol epoxy resin/dicyandiamide curing system. The curing reactivity, apparent activation energy, curing mechanism, dynamic mechanical behavior, and impact strength of the modified system were systematically studied. Compared with the unmodified system, the results indicate that LCEUPPG have greatly accelerated the curing reaction between epoxy resin and dicyandiamide, reduced the apparent activation energy of the curing reaction, enhanced the impact strength 3–7 times, and maintained high dynamic modulus and good thermal properties. In addition, SEM observation of the fracture surfaces showed a two-phase microstructure in the modified systems. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 177–184, 1999

Electrical and dynamic mechanical behavior of carbon black filled polymer composites

The effect of processing conditions on the electrical and dynamic behavior of carbon black (CB) filled ethylene/ethylacrylate copolymer (EEA) composites was investigated. The compounds were prepared by two methods, solution blending and mechanical mixing. Compared with the solution counterpart, the mechanical composites have a strong positive temperature coefficient (PTC) effect and a high dynamic elastic modulus, which results from the good dispersion state of carbon black in EEA, i.e. the strong interaction between carbon black and EEA. It can be concluded that the strong interaction between polymer and carbon black is essential for composites to have a high PTC intensity, good electrical reproducibility and high dynamic elastic modulus.

Mechanical and wear properties of poly(vinyl alcohol) hydrogels

AbstractPoly(vinyl alcohol)(PVA) hydrogels with low water contents were prepared by low temperature crystallization of PVA solution from a dimethyl sulfoxide/H2O mixed solvent, followed by high‐temperature annealing after drying and the subsequent re‐swelling with water. The tensile strength and dynamic modulus of PVA hydrogels increased upon annealing, irrespective of the degree of polymerization (DP) of PVA, but always at the sacrifice of the water content of hydrogel. In addition to the mechanical strength, the hardness of PVA hydrogels was improved by lowering the water content. The highest tensile strength(20 MPa) and the highest dynamic modulus(180 MPa) were obtained when hydrogel was prepared from PVA with DP of 11 000 and annealed at 140°C for 24 h. The wear resistance strongly depended on the mechanical strength and coefficient of friction of PVA hydrogels. The wear volume of the hydrogel prepared from PVA with DP of 8 800 decreased with the decreasing coefficient of friction and the increasing mechanical strength of PVA hydrogel except for the 25 wt% PVA hydrogel at 2.5 MPa. Furthermore, any wear particles were not detected for the 45 wt% PVA hydrogel at 2.5 MPa and the 25 wt% PVA hydrogel at 2.0 and 2.5 MPa.

Rheological Behaviour of Wheat Glutens at Small and Large Deformations. Comparison of Two Glutens Differing in Bread Making Potential

Abstract The rheological characteristics of hydrated cv. Obelisk and Katepwa glutens, with poor and good baking potential, respectively, were studied at small and large deformations. Dynamic (oscillatory) measurements at small deformations over a frequency range of 0·03 to 3 rad/s showed that cv. Katepwa gluten had a higher dynamic modulus and a lower loss tangent than cv. Obelisk gluten. Overmixing resulted in increases in the dynamic moduli of both glutens. Measurements at different water contents indicated that the lower dynamic moduli at higher water contents resulted mainly from a concentration effect and were not due to water acting as a plasticiser. The apparent biaxial extensional viscosities of the glutens were determined by uniaxial compression of cylindrically shaped test pieces at various cross-head speeds. This proved to be a very useful method of providing information about the rheological behaviour of glutens at large deformations as a function of different strain rates. At every biaxial strain rate tested, the apparent biaxial extensional viscosity of cv. Katepwa gluten was higher than that of cv. Obelisk gluten. A thin layer of biaxially extended gluten showed a higher resistance to further biaxial extension than a less biaxially extended, thicker layer. Cv. Katepwa gluten exhibited this strain hardening behaviour to a greater extent than cv. Obelisk gluten. Possible consequences for baking performance are discussed.

High strain dynamic modulus and damping of chemically grouted sand

Laboratory resonant column and cyclic triaxial tests are performed to determine the dynamic response (i.e. shear modulus and damping) of chemically grouted sand. The effect of chemical grouting is evaluated as a function of shearing-strain amplitude, confining stress, cycling prestrain, number of cycles, grout type, concentration, and curing time. The test results show that the shearing-strain amplitude, grout type and grout concentration have significant effects on the shear modulus and damping ratio of the test specimens. The increased addition of sodium silicate grout, which produces stiff gels, improved the shear modulus of the test sand. The acrylate (AC-400) and polyurethane (CG5610) grout, which produces flexible (rubber-like) gels, improved the damping capacity of the sand with increasing grout concentration. The addition of chemical grout greatly reduces the effect of cyclic prestraining over untreated sands. In the case of dense sands, the reduction of cyclic prestraining is less pronounced than in loose sands, which have a higher potential for particle movement and reorientation.

Combined processing of polypropylene film by coextrusion and zone‐annealing

AbstractIn order to improve the mechanical properties of polypropylene film, a new processing combining extrusion and zone‐annealing has been applied. It was found that there are suitable conditions for each step in the combined processing. When the coextrusion draw ratio was low, the total draw ratio and modulus could be increased by the zone‐annealing subsequently done. The highest modulus was obtained when the film was coextruded at extrusion draw ratio 4 and then zone‐annealed at 120°C under 7 kg/mm2. The value was 12 GPa in Young's modulus or 17 GPa in dynamic modulus. The peak temperature of αc dynamic dispersion for the combinedly processed film was 109°C, which is higher by 10°C than that for the as‐coextruded film. Four drawing methods were compared in dynamic viscoelasticity. These methods are the coextrusion, zone‐drawing/zone‐annealing, two‐step coextrusion, and the combined processing by coextrusion and zone‐annealing. The highest dynamic modulus for each method was arranged in the above order. The combined processing indicated the most effective improvement in mechanical properties, because it is believed that lamellae in the original film were broken by cooperating interaction of shear stress, compression, and tension on coextrusion and then the superstructure with a high crystallinity and a high molecular orientation was formed on zone‐annealing.

Preparation of ultra‐high modulus polyvinyl alcohol fibers by the zone‐drawing method

AbstractThe zone‐drawing method has been applied to prepare ultra‐high modulus polyvinyl alcohol fibers. First, the suitable temperature for zone‐drawing was decided. In the first zone drawing, when drawing temperature was as high as near melting point, the highest draw ratio and modulus were obtained. The modulus was further increased by repeating zone drawing and heat treatment. In this study, the highest dynamic moduli were 115 GPa at room temperature and 42 GPa at 200°C. The fiber has a sharp melting peak that appeared at 246°C and a small peak at 260°C in the DSC curve.

Flexural fatigue strength of lime-laterite soil mixtures : Bhattacharya, P G; Pandey, B B Trans Res RecN1089, 1986, P86–92

Laterite soils, which are the producs of tropical or subtropical weathering, have been stabilized with lime to evaluate the dynamic modulus and the flexural fatigue strengths of the lime-soil mixtures. Tests have been carried out on four types of laterite soils compaced at three dry density ranges-light, medium, and heavy. Least-squares regression analysis was used to establish relationships betwen stress ratio and the logarithm of the number of stress cycles to failure. Heavily compacted lime-soil specimens were found to have considerably higher dynamic modulus and fatigue life than those having standard Proctor compaction. Increased values of dynamic flexural modulus and strength at the higher dry density favor the use of lime-laterite soil as a road base.

High temperature dynamic modulus measurements by use of ultrasonics: Dunegan, H.L. Materials Evaluation, 22, No. 6, p. 266 (1964)

High temperature dynamic modulus measurements by use of ultrasonics: Dunegan, H.L. Materials Evaluation, 22, No. 6, p. 266 (1964)