• Journal of Biosystems Engineering
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• v.37 no.1
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• pp.28-35
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• 2012

Purpose: This study performed the oscillatory test using the texture analyzer to characterize the viscoelastic behavior of apples such as the storage modulus (E'), the loss modulus (E"), the complex modulus (${\mid}E^*{\mid}$) and the energy dissipated per cycle ($W_{diss}$). Methods: The sinusoidal deformation with the frequency of 1-10 Hz and the maximum displacement of 0.1 mm were applied to the flesh tissues of Fuji, Golden Delicious and Red Delicious apples. The Lissajous figure was used to measure the phase angle(${\delta}$) between stress and strain curve. Results: Trigger force was critical to the measurement of the phase angle. E', E", ${\mid}E^*{\mid}$ and Wdiss were measured using the Lissajous figure and the phase angle. The complex modulus of Golden Delicious apple was significantly lower than those of Fuji apple and Red Delicious apple. Conclusions: Apple flesh was exhibiting more elasticity at low frequency, and more viscosity at high frequency. Dynamic compressive properties of Fuji apple were similar to those of Red Delicious apple but significantly different from those of Golden Delicious apple.

• Journal of the Korean Wood Science and Technology
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• v.34 no.2
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• pp.37-45
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• 2006

The viscoelastic properties of blends of melamine-formaldehyde (MF) resin and poly(vinyl acetate) (PVAc) for engineered flooring used on the Korean traditional ONDOL house floor heating system were investigated by dynamic mechanical thermal analysis (DMTA). Because MF resin is a thermosetting adhesive, the effect of MF rein was shown across all thermal behaviors. The addition of PVAc reduced the curing temperature. The DMTA thermogram of MF resin showed that the storage modulus (E') increased as the temperature was further increased as a result of the cross-linking induced by the curing reaction of the resin. The storage modulus (E') of MF resin increased both as a function of increasing temperature and with increasing heating rate. From isothermal DMTA results, peak $T_{tan{\delta}}$ values, maximum value of loss modulus (E") and the rigidities (${\Delta}E$) of MF/PVAc blends at room temperature as a function of open time, peak $T_{tan{\delta}}$ and maximum loss modulus (E") values were found to increase with blend MF content. Moreover, the rigidities of the 70:30 and 50:50 MF/PVAc blends were higher than those of the other blends, especially of 100% PVAc or MF. We concluded that blends the MF/PVAc blend ratios correlate during the adhesion process.

• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.2
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• pp.193-202
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• 2006

Objective To evaluate the influence of water storage on the mechanical properties of dental adhesives over 1 and 3 months. Materials and Methods Adhesive resin sheets were prepared by pouring either All-bond 2(AB), Clearfil SE Bond(SE) into a mold measuring $15{\times}15{\times}0.9mm$. After solvent in primer evaporation, the adhesives were light-cured and removed from the mold and divided in two pieces, trimmed to hourglass shape that were used to determine the micro-tensile strength(MTS). Another hourglass shaped metal mold measuring $2.0{\times}1.5mm$ in cross-section area was made to determine the Young's modulus(E). Adhesive specimens for Young's modulus(E) were prepared in the same method. Specimens were stored at $37^{\circ}C$ in distilled water and tested after 1 and 3 months. The data were analyzed by one-way ANOVA and Tukey's test. Results Water storage significantly decreased the micro-tensile strength(MTS) of AB and SE specimens after 1 and 3 months(P<0.05). The Young's modulus(E) were also decreased after water storage for 1 and 3 months, but statistically not significant in each group of AB and SE group respectively. Conclusions Long-term exposure of adhesive resin to water can cause reduction of mechanical properties. It may compromise resin/dentin bonds and affect longevity of restorations.

• Journal of Adhesion and Interface
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• v.3 no.4
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• pp.1-9
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• 2002

The main goal of this study was to analyze the effect of process additives, i.e. maleated polypropylene (MAPP), and nucleating agent on the viscoelastic properties of different types of extruded polypropylene-wood plastic composites manufactured from either PP homopolymer, high crystallinity PP or PP impact copolymer using dynamic mechanical thermal analysis. And also, the esterification reaction between wood flour and maleated polypropylene, and its role in determining the mechanical properties of wood flour-polypropylene composites was investigated. The wood plastic composites were manufactured using 60% pine wood flour and 40% polypropylene on a Davis-Standard $Woodtruder^{TM}$. Dynamic mechanical thermal properties, polymer damping peaks(than ${\delta}$), storage modulus (E') and loss modulus (E") were measured using a dynamic mechanical thermal analyzer. XPS (X-ray Photoelectron Spectroscopy), also known as ESCA (Electron Spectroscopy for Chemical Analysis) study of wood flour treated with MAPP was performed to obtain information on the chemical nature of wood fiber before and after treatment. To analyze the effect of frequency on the dynamic mechanical properties of the various composites, DMA tests were performed over a temperature range of -20 to $100^{\circ}C$, at four different frequencies (1, 5, 10 and 25 Hz), and at a heating rate of $5^{\circ}C/min$. From these results, the activation energy of the various composite was measured using an Arrhenius relationship to investigate the effect of maleated PP and nucleating agent on the measurement of the interphase between the wood and plastic of the extruded polypropylene wood plastic composites.

• Journal of the Korean Wood Science and Technology
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• v.32 no.5
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• pp.29-38
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• 2004

In this study, we investigated the thermal properties of corn-starch filled polybutylene succinate-adipate (PBS-AD) bio-composites. Thermal analysis (TA) is used to describe the analytical method for measuring the chemical property and weight loss of composite materials as a function of temperature. The thermal stability of corn-starch was lower than that of pure PBS-AD. As corn-starch loading increased, the thermal stability and degradation temperature of the bio-composites decreased and the ash content increased. It can be seen that the degree of compatibility and interfacial adhesion of the bio-composites decreased because of the increasing mixing ratio of the corn-starch. As the content of corn-starch increased, there was no significant change in the glass transition temperature (T_g) and the melting temperature (T_m) for the bio-composites. The storage modulus (E') and loss modulus (E") of the corn-starch flour filled PBS-AD bio-composites were higher than those of PBS-AD, because of the incorporation of corn-starch increased the stiffness of the bio-composites. At higher temperatures, the decreased storage modulus (E') of bio-composites was due to the increased polymer chain mobility of the matrix polymer. From these results, we can expect that corn-starch has potential as a reinforcing filler for bio-composites. Furthermore, we recommend using a coupling agent to improve the interfacial adhesion between corn-starch and biodegradable polymer.

• The Korean Journal of Rheology
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• v.10 no.4
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• pp.227-233
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• 1998

The effects of 1 mol% N-benzylpyrazinium hexafluoroantimonate(BPH) as a thermal latent initiator and blend compositions composed of cycloaliphatic and DGEBA epoxies were investigated in the rheological properties and cure kinetics. Latent properties were performed by measurement of the conversion as a function of reaction time using isothermal DSC at $150^{\circ}C$ and $50^{\circ}C$ Rheological properties of the blend systems were investigated in terms of isothermal experiments using a rheometer. The gelation time was obtained from the evaluation of storage modulus (G'), loss modulus (G") and damping factor (tan$\delta$)). Cross-linking activation energy ($E_c$) was also determined from the Arrhenius equation based on gel time and curing temperature. As a result, the gel time and cross-linking activation energy increased with increasing DGEBA composition. The cure activation energies ($E_a$) were obtained by Kissinger method using dynamic DSC thermograms. In this work, the cure activation energy decreased with increasing CAE concentration, which might be resulted from the short repeat units, simple side-groups and viscosity of reaction media.edia.

• Applied Chemistry for Engineering
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• v.5 no.6
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• pp.981-989
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• 1994

For the development of new material used bentonite in ceramic/organic material composite, ABS(acrylonitrile-butadiene-styrene) material was used as a matrix polymer and a series of bentonite was blended together. This bentonite, filler like talc or mica for plastic material, was used since natural bentonite(Ca type) is easily obtainable in Korea, Na-bentonite changed from natural bentonite by $Na_2CO_3$ based on the specified compositions, changes in the static and dynamic mechanical properties. It was discovered that the increased content of natural and Na- bentonite results in higher modulus with reduced impact strength. And Rockwell hardness was constant. And Na- bentonite filled polymer showed improvement in impact strength and lower in modulus as the natural bentonite filled polymer. The storage modulus(E') of Na- bentonite filled ABS resin was higher than that of Ca- bentonite filled ABS resin, while higher temperature, storage modulus(E') decreased. At higher frequency, tan ${\delta}$ peak was shifted at high temperature.

• Restorative Dentistry and Endodontics
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• v.29 no.6
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• pp.489-497
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• 2004

Objective: The purpose of this study was to investigate the viscoelastic properties related to handling characteristics of composite resins, Methods: A custom designed vertical oscillation rheometer (VOR) was used for rheological measurements of composites. The VOR consists of three parts: (1) a measuring unit, (2) a deformation induction unit and (3) a force detecting unit, Two medium viscous composites, Z100 and Z250 and two packable composites, P60 and SureFil were tested. The viscoelastic material function, including complex modulus $E^{*}$ and phase angle ${\delta}$, were measured. A dynamic oscillatory test was used to evaluate the storage modulus (E'), loss modulus (E") and loss tangent ($tan{\delta}$) of the composites as a function of frequency ($\omega$) from 0.1 to 20 Hz at $23^{\circ}C$. Results: The E' and E" increased with increasing frequency and showed differences in magnitude between brands. The $E^{*}s$ of composites at ${\omega}{\;}={\;}2{\;}Hz$, normalized to that of Z100, were 2.16 (Z250), 4,80 (P60) and 25.21 (SureFil). The magnitudes and patterns of the change of $tan{\delta}$ of composites with increasing frequency were significantly different between brands. The relationships between the complex modulus $E^{*}$, the phase angle ${\delta}$ and the frequency \omega were represented by frequency domain phasor form, $E^{*}{\;}(\omega){\;}={\;}E^{*}e^{i{\delta}}{\;}={\;}E^{*}{\angle}{\delta}$. Conclusions: The viscoelasticity of composites that influences handling characteristics is significant different between brands, The VOR is a relatively simple device for dynamic, mechanical analysis of high viscous dental composites. The locus of frequency domain phasor plots in a complex plane is a valuable method of representing the viscoelastic properties of composites.

• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.3
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• pp.262-272
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• 2023

A polymer-based mechanical low-pass filter(m-LPF) for high-g accelerometers makes it possible to remove high-frequency transient noises from acceleration signals, thus ensuring repeatable and reliable measurement on high-g acceleration. We establish a prediction model for performance of m-LPF by combining a fundamental vibration model with the fractional derivative standard linear solid(FD SLS) model describing the storage modulus and loss modulus of polymers. Here, the FD SLS model is modified to consider the effect of m-LPF shape factor (i.e., thickness) on storage modulus and loss modulus. The prediction accuracy is verified by comparing the displacement transmissibility(or cut-off frequency) estimated using our model with that measured from 3 kinds of polymers(polysulfide rubber(PSR), silicone rubber(SR), and polydimethylsiloxane(PDMS)). Our findings will contribute a significant growth of m-LPF for high-g accelerometers.

• Carbon letters
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• v.10 no.4
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• pp.314-319
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• 2009

The surface treatment effects of reinforcement filler were investigated based on the dynamic mechanical properties of mutiwalled carbon nanotubes (MWCNTs)/epoxy composites. The as-received MWCNTs(R-MWCNTs) were chemically modified by direct oxyfluorination method to improve the dispersibility and adhesiveness with epoxy resins in composite system. In order to investigate the induced functional groups on MWCNTs during oxyfluorination, X-ray photoelectron spectroscopy was used. The thermo-mechanical property of MWCNTs/epoxy composite was also measured based on effects of oxyfluorination treatment of MWCNTs. The storage modulus of MWCNTs/epoxy composite was enhanced about 1.27 times through oxyfluorination of MWCNTs fillers at $25^{\circ}C$. The storage modulus of oxyfluorinated MWCNTs (OF73-MWCNTs) reinforced epoxy composite was much higher than that of R-MWCNTs/epoxy composite. It revealed that oxygen content led to the efficient carbon-fluorine covalent bonding during oxyfluorination. These functional groups on surface modified MWCNTs induced by oxyfluorination strikingly made an important role for the reinforced epoxy composite.