Mechanical Loss Tangent Research Articles

Shape fixation of compressed wood by steaming: a mechanism of shape fixation by rearrangement of crystalline cellulose

Japanese cedar wood specimens were compressed radially using saturated water vapor at 160 °C. Their shape recovery in hot water, cellulose crystallinity, and dynamic viscoelastic properties were measured. The compressed shape of the wood was fixed completely with 120 min of steam compression. In addition, the tensile strain of the elongated steam-compressed wood specimens was recovered almost completely upon immersion in hot water. The crystallinity and crystal width of cellulose in the compressed wood increased with increasing steaming duration, corresponding to the fixation of the compressed shape and the recovery of tensile strain. These results suggested that the recrystallization or co-crystallization of cellulose, i.e., the reformation of elastic members in the wood cell walls, caused shape fixation by steam compression. When a wood specimen was compressed at 25 °C, its dynamic Young’s modulus in the radial (R) direction (ER) decreased, while its mechanical loss tangent (tan δR) increased remarkably. However, upon subsequent steaming, the reduced ER began increasing and the enhanced tan δR began decreasing. These changes were explained by a hypothetical slip–cure model in which microfractures and slippage between or within microfibrils were cured by the rearrangement of cellulose under steaming.

Thermal Properties of Salt and Base Forms of Chitosan

The temperature dependences of elastic and relaxation properties of films of salt and base forms of chitosan were obtained by methods of dynamic mechanical analysis. It was estimated that the presence of two maxima on the temperature dependence of mechanical loss tangent tanδ at T1 = 150–160°C and T2 = 250–270°C is typical of the salt form of chitosan. The maximum at 150–160°C on tanδ curves is reduced or even eliminated after thermal or alcohol–alkali treatment of chitosan acetate films, while the high-temperature maximum is preserved. The results of IR spectroscopy and thermogravimetric analysis allow supposing that the low-temperature maximum of molecular mobility in films of chitosan salt form is related to the removal of absorbed water and residues of acetic acid as well as to dehydration of macromolecules. The maximum at 259°C determines the glass transition temperature of the chitosan base form.

The Effect of the Functionalisation of Low-Dispersion Carbon Black of the OMCARB Series by Hydrogen Peroxide on the Properties of Filled Composites

The aim of this work was to produce a new filler for polymers in which a low surface activity is combined with a high degree of structure and functionalisation of the surface, which will bring the processing properties of filled rubber mixes closer to the properties of rubber mixes with channel carbon black. The oxidation of specimens of low-dispersion, highly structured carbon black of grade OMCARB S820 was carried out using aqueous solutions of hydrogen peroxide of different concentration. Using a combination of methods, including X-ray diffraction analysis (D8 Advance diffractometer; Bruker, Germany) and transmission electron microscopy (JEM 2100 electron microscope; JEOL, Japan), we assessed the physicochemical properties and the form and the number of oxygen-containing groups (carboxyl, phenolic, lactone) on the surface of a particle of oxidised S820 in comparison with carbon black K354 (produced by the Khazar Chemical Plant, Turkmenistan) and semi-active furnace black N550 (produced by Omsktekhuglerod). The rheological characteristics (MDR 3000 vibrorheometer and MV 3000 viscometer; MonTech, Germany) and the physicomechanical characteristics (tensometer; Shimadzu, Japan) of rubber mixes filled with these blacks and of rubber compounds based on natural rubber were determined. The dynamic properties of the rubber compounds and the glass transition temperatures were determined on a DMA 242D instrument (Netzsch, Germany). Comparative data on the temperature dependence of the mechanical loss tangent (tg δ)of the rubber compounds showed that at temperatures of −60 and +60°C the greatest differences are possessed by rubber compounds with K354. At intermediate temperatures, the tg δ values for rubber compounds with the different fillers are similar. The new carbon black was advantageous with respect to the strength properties and dynamic characteristics of the rubber compounds, retaining the unique properties of composites filled with channel black.

Correlation between mechanical dissipation and improved X-band electromagnetic shielding capabilities of amine functionalized graphene/thermoplastic polyurethane composites

Graphene-based polymer nanocomposites have demonstrated significant promise to create commercially viable electromagnetic interference (EMI) shielding to protect the next-generation of electronic materials from radiative pollution. In the present study, we carry out a systematic analysis of the dynamic mechanical, dielectric, electrical and X-band shielding properties of thermoplastic polyurethane (TPU) elastomer filled with amine functionalized graphene obtained by the rapid thermal expansion of graphite oxide. By preparation of nanocomposites based on modified and unmodified graphene using solution mixing and hot compression moulding, we demonstrate that the modification with 2-aminoethyl methacrylate enhances the EMI shielding from 14 to 25dB. We also show by fracture analysis, cross-sectional transmission electron microscopy and dynamic mechanical analysis that the modification significantly strengthens the interfacial interactions between TPU and the functionalized graphene at the same filler loading. We find that the dominant shielding mechanism is through absorption and discuss the correlation between the viscoelastic mechanical loss tangent and the more effective dissipation of absorbed EM radiation which might account for the discrepancy between the theoretically predicted and experimentally observed EMI SE.

A Biobased Flame‐Retardant Resin Based on Lignin

AbstractThis study focuses on the development of biobased flame‐retardant resins. Lignin and α,ω‐alkanediols are used, which can be obtained from biomass. To introduce intumescent properties, phosphoryl chloride and 3‐amino‐1,2,4‐triazole are introduced into kraft lignin prior to it being resinified with the α,ω‐alkanediols. In simple combustion tests using a gas burner at 1300 °C, the resins prepared exhibit nonburnable properties, producing only a swollen char. According to dynamic mechanical analysis, the glass transition temperature decreases with an increase in the carbon number and amount of the alkanediols introduced. The mechanical loss tangent (tan δ) value of the prepared resins is below 1, indicating that the resins would not drip flaming particles during burning. Indeed, the specimens do not generate particles in the simple combustion tests. According to the results of cone calorimeter testing, the total heat release and the peak heat release rate are significantly smaller than those of a commercial phenol‐formaldehyde‐resin‐containing flame retardant.

Single-wall Carbon Nanotubes in Vulcanisates Based on Different Rubbers: Investigation of the Dynamic Mechanical Characteristics

The dynamic mechanical properties of sulphur vulcanisates based on different rubbers containing single-wall carbon nanotubes (SCNTs) were studied. Components of the dynamic modulus (G′ and G″) and the temperature dependence of the mechanical loss tangent tg δ were obtained on a DMS Ares instrument (Reometrics) at an amplitude of 0.5%, a frequency of 1 Hz, and a heating rate of 1°C/min at temperatures ranging from −80 to +80°C. The glass transition temperature Tg was determined as the temperature of the maximum on the temperature dependence of tg δ. The morphology was studied on transmission and scanning electron microscopes. Rubber compounds based on hydrogenated nitrile butadiene rubber (HNBR Therban 3496), styrene butadiene rubber (Sprintan SLR 4502), and natural rubber (NR of grade SMR CV60) were chosen. SCNTs (1%) were introduced into composite YU-58 containing NR latex (98%) and polyvinylpyrrolidone (1%). This composite was regarded as the filler. The properties of composites containing SCNTs with a carboxylated surface (SCNT-COOH) were also studied. To calculate the parameters of the two-phase ‘rubber (matrix)–filler’ system at temperatures of −70, −30, and +23°C, we used the Kerner equation. There is a notable trend towards an increase in the flexibility of the macromolecules. For NR-based composites containing 0.3% SCNTs, the calculated value of G′ of the boundary layer at −30°C is 10 times higher than the G′ value of the matrix, and 15 times higher at +23°C. Deliberations concerning the nature and properties of the boundary layer are laid out.

The role of sonication time upon acoustic wave absorption efficiency, microstructure, and viscoelastic behavior of flexible polyurethane/CNT nanocomposite foam

In the present work, acoustic wave absorber nanocomposites based on flexible polyurethane (PU) foam and sonicated multi walled carbon nanotube (CNT) has been fabricated by in-situ solution polymerization of toluene diisocyanate (TDI) and an ether based polyol in the presence of CNT particles. This study provides the influence of sonication time upon the acoustical and dynamic mechanical properties of the prepared composites. Flow resistivity measurement, scanning electron microscopy (SEM), dynamic mechanical thermal analysis (DMTA) and compressive mechanical measurement were performed on the prepared samples. The fabricated PU/CNT foamed nanocomposites were evaluated for their acoustic wave absorbency within a wide range of frequency (400–6300Hz). Nanocomposites originated by highly sonicated CNT exhibited more acoustic absorbency. All CNT filled PU composites showed higher attenuation of the acoustic wave energy than the unfilled reference sample. Results revealed that sound absorbency of the foamed PU/CNT nanocomposites could be effectively enhanced by increasing the sonication time. Dynamic mechanical temperature sweep measurements showed decrease in mechanical loss tangent by enhancing the extent of CNT dispersion state. Results showed that improved sound absorbancy by CNT sonication time is mainly caused by increased CNT interacting surfaces rather than viscous response of the viscoelastic PU/CNT nanocomposites towards the applied dynamic field.

Properties of Elastomeric Composites with Functionalized Carbon Nanomaterial

The influence of two different nanomaterials on the properties of elastomeric composites based on general- and special-purpose rubbers has been investigated. For the elastomeric matrix, we used a combination of synthetic polyisopropene (SKI-3) and stereoregular butadiene (SKD) caoutchoucs in one case and butadiene-nitrile caoutchouc containing 27–30% of bound acrylic acid nitrile (BNKS-28) in the other case. For additives, nanomaterials of two types were used. To determine the degree of interaction of the additives with the elastomeric matrix, complex tests of rubber mixes and vulcanizates based on them were carried out, in which the following indices were determined: the Mooney viscosity, the relaxation and vulcanization characteristics of the mixes, the elastic-strength properties of the vulcanizates before and after thermal ageing, their resistance to thermal ageing, and the mechanical loss tangent.

Mathematical modeling of the multimodal distributions of elastomer relaxation spectra using the family of Pearson curves

An approach to the mathematical modeling of elastomer relaxation spectra obtained via acoustic spectroscopy is presented. The solving of Pearson differential equations is the basis for the calculated dependences. The solutions to the equations describe the frequency and temperature distribution of the mechanical loss tangent. The form of the distribution is estimated from selected statistical moments of the experimental relaxation spectra and the mechanical loss tangent.

Elastic and viscoelastic characterization of inhomogeneous polymers by bimodal atomic force microscopy

The elastic and viscoelastic responses of inhomogeneous polymers upon interacting with an atomic force microscopy (AFM) probe are simultaneously characterized by a bimodal AFM approach namely the amplitude- and frequency-modulation (AM–FM) method. In this approach, the AFM probe is operated in the AM mode at the first flexural frequency and in the FM mode at a higher flexural frequency. The AM mode provides information about the viscoelasticity of polymers in terms of the mechanical loss tangent, whereas the modulus of polymers is obtained as a function of the frequency shift of flexural frequencies in both modes. For a glassy polymer blend, the AM–FM method provides a consistent result in both the elastic modulus and loss tangent in comparison with those obtained by other methods. Moreover, a significant improvement of the contrast and lateral resolution in the AM–FM modulus image can be observed. However, the current approach shows a substantial increase in the modulus of rubbery polymers.

Effect of a Reinforcing Layer on the Mechanical Loss Tangent of Vibration-Absorbing Materials

An investigation was made of the mechanical loss tangent (tg δ) of vibration-absorbing material VTP-1V in the form of a vibration-absorbing coating and with reinforcing layers of different chemical nature – metal and composite – based on glass and carbon fabrics. It was shown that the presence of a reinforcing layer leads to an increase in damping properties.

Effect of the electrical loading on forced vibrations of transversely po-larized piezoceramic bars

This article analyzes the experimental and computational results obtained in the study of the longitudinal vibrations of thin piezoceramic bars with transverse polarization depending on the electrical load such as the given constant amplitude current or voltage. Calculations of the admittance, coupling coefficients, mechanical and piezoelectric loss tangents were made on the basis of a new simple iterative method. The idea of alternate measuring the voltage drop in the modernized Mason scheme was further developed, and the phase shifts between the components of admittance were determined. The experimental data are in good agreement with the calculated values.Reference 26, figures 5.

Progress in improving high-temperature properties of thermosetting resins: development of the microheterogeneous model for the formation of crosslinked rolivsan-epoxy blends

Thermochemical transformations in blends of rolivsans (ROLs, i.e., compositions of (di)vinylaromatic ethers and thermosensitive (di)methacrylates) with epoxy resins were used to obtain new glassy heat resistant highly crosslinked ROLs/epoxy blends (block copolymers) which differ in composition, crosslink density, chemical, topological and morphological structure. The influence of the ROLs/epoxy blocks ratio in the blends and temperature-time regimes of curing on heat resistant properties of the materials was estimated by studying temperature dependences of breaking strength at three-point flexural test, dynamical elastic modulus, mechanical loss tangents (in dynamic mechanical analysis, DMA) and thermooxidative aging processes. Unusually high values of high temperature strength of the epoxy-modified ROLs were reached when using a new method for enhancing heat resistance and thermal stability of microheterogeneous network polymers (cured resins) consisting of highly crosslinked microdomains. These microdomains are weakly bound to each other by defective polymer interlayers. This method is illustrated by the example of transformations in ROLs/epoxy blends; it suggests (macro)molecular design and curing development. The method involves functionalization of microdomains, target delivery of epoxies into interlayers and carrying out high temperature chemical reactions in these interlayers. These reactions lead to additional crosslinking of supramolecular formations (highly crosslinked ROL microdomains) by epoxy bridges. The results obtained in the studies of structural transformations in rolivsans modified with epoxy resins were used as a basis for the new approach to enhancing heat resistance and thermal stability of thermosetting resins.

Effects of heating humidity on the physical properties of hydrothermally treated spruce wood

To clarify the effects of humidity during heating on the physical properties of hydrothermally treated wood, Sitka spruce wood was heated in an autoclave at 120 °C and different heating humidity (HRH), and their equilibrium moisture content (EMC), specific dynamic Young’s modulus (E′/ρ), and mechanical loss tangent (tanδ) were measured at 25 °C and 60 % RH prior to and after the hydrothermal treatment. Higher values of HRH resulted in greater loss in weight (WL) because of the acceleration of thermal degradation in the presence of moisture. The time–humidity superposition was applicable to the changes in WL. The EMC was minimized by heating at intermediate HRH (60 %), but it recovered significantly after the wood was moistened at 100 % RH. This fact suggested that the reduction in hygroscopicity due to hydrothermal treatment included both reversible and irreversible effects. The reversible effect was not observed when the wood was heated at 92 % HRH or above. After the moistening, the EMC value of hydrothermally treated wood decreased monotonically with increasing HRH and WL. An irreversible chemical change such as decomposition of hemicelluloses was responsible for the irreversible effect, whereas the reversible effect may have resulted from the annealing of amorphous wood polymers. After hydrothermal treatment at 80 % HRH or lower, E′/ρ increased and tanδ decreased mainly because of the reduction in EMC. On the other hand, high-humidity heating (92 % HRH) resulted in significant decrease in E′/ρ and remarkable increase in tanδ probably because of the depolymerization of hemicelluloses. The color of wood was darkened by the hydrothermal treatment, and the CIELAB color parameters of hydrothermally treated wood were closely connected to the WL.

Bound rubber morphology and loss tangent properties of carbon-black-filled rubber compounds

The bound rubber phenomenon of carbon-black-filled rubber compounds, which is still an intensively discussed subject, is visualized in this research as a stable nanoscale interphase. Using the novel amplitude and phase-modified atomic force microscope technique, a viscoelastic mapping mode, it becomes possible to quantify mechanical loss tangent properties that are defined as the ratio of loss modulus G″ to storage modulus G′. Imaging loss tangent enables the observation of separated energy dissipation of single constituents within a blend system as well as bound rubber dimensions. Determined with the conventional quantification of insoluble rubber, the amount of bound rubber is correlated with values from the analytical evaluation of loss tangent images. Comparing the loss tangent images and histograms to dynamic mechanical analyses allows the characterization of each single component. On the base of the time-temperature superposition principle, bound rubber dimensions and mechanical properties of filled compounds can be optimized.

Dynamic Mechanical Analysis of Composite Materials Based on Polyvinyl Chloride and Thermal Power Station Waste

Investigations have been conducted in which the temperature dependences of the viscoelastic properties of highly filled polymer–mineral composites based on polyvinyl chloride were measured and the loss modulus, dynamic modulus, and mechanical loss tangent were determined using dynamically changing loads.

Badania wlasciwosci termomechanicznych i morfologii rur z polietylenu poddanych procesowi starzenia za pomoca promieniowania UV

This paper presents the results of an assessment of structure and thermomechanical properties of polyethylene before and after the aging by UV irradiation. The test specimens were cut from the pipes manufactured by extrusion. They were analyzed using dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC) and microscopic examination at 400× magnification. The hardness, colour and gloss of the specimens were also investigated. It was shown that UV radiation induces irreversible changes in polyethylene leading to deterioration of polymer mechanical properties i.e. a decrease of storage modulus and mechanical loss tangent values. Polyethylene samples exhibit a lower degree of crystallization, reduced hardness and tensile strength as well as changed gloss and colour tone after UV aging. Also, a slight reduction in the size of spherulites was observed in microscopy investigations.

Synthesis and physical properties of poly(l‐lactic acid)‐poly(dimethyl siloxane) multiblock copolymers prepared by direct polycondensation

ABSTRACTMultiblock copolymers consisting of poly(l‐lactic acid) and poly(dimethyl siloxane) were prepared by the polycondensation of oligo(l‐lactic acid) (OLLA) with dihydroxyl‐terminated oligo(dimethyl siloxane) and dicarboxyl‐terminated oligo(dimethyl siloxane). Copolymers with number‐average molecular weights of 18,000−33,000 Da and various content ratios of oligo(dimethyl siloxane) (ODMS) unit were obtained by changing the feed ratio of these oligomers. A film prepared from the copolymer with an ODMS content ratio of 0.37 exhibited two independent peaks at −107°C and 37°C in the mechanical loss tangent for temperature dependence, suggesting the formation of microphase separation between the OLLA and ODMS segments. The film had a tensile strength of 3.2 MPa and a high elongation of 132%. The film also exhibited a high strain recovery even after repeated straining. The incorporation of dimethyl siloxane units as multiblock segments was confirmed to improve the flexibility of poly(l‐lactic acid). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40211.

Study on Lead Zirconate-Titanate/Interpenetrating Polymer Network Composites

In order to improve damping properties of polyurethane/vinyl ester resin interpenetrating polymer network (PU/VER IPN), a series of Lead Zirconate-Titanate/IPN (PZT/IPN) composites were prepared by adding PZT into PU/VER IPN by in-situ polymerization process and were polarized. The optimal polarization process is obtained. The influence of PZT contents on microstructure, damping performances, mechanical performances, relative dielectric constant and piezoelectric constant (d¬33) was studied. The results show that PZT particles disperse in composites uniformly. The optimal polarization parameters of PZT/IPN composites are as follows: polarization temperature 100°C, polarization field strength 6kV/mm and polarization time 40min. Mechanical loss tangent (tanδ) values of the optimal PZT/IPN composites with 75 wt.% PZT are higher than 0.3 from –31°C to higher than 120°C, which meets the requirement of damping materials with excellent performances.

The influence of gas-assisted injection molding parameters on the structure and thermomechanical properties of hollow parts

The purpose of the work was to estimate an influence of gas-assisted injection conditions (the temperature of plastic material, switch time-delay time, gas injection time) of shape, position and dimension of gas channel, and structure of injection molded parts. The change in the value of the dynamic Young modulus and the mechanical loss tangent in function of temperature and oscillation frequency by the dynamic mechanical thermal analysis (DMTA) method was determined. It was found that injection molding parameters: injection molding temperature, switching time and gas injection time influenced significantly mass, wall thickness, and thermomechanical properties of parts. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers