Terms Of Dynamic Mechanical Properties Research Articles

Comparison of two compounding techniques for carbon nanotubes filled natural rubbers through microscopic and dynamic mechanical characterizations

Natural rubber used in wave energy converters requires higher fatigue life and better energy harvesting efficiency to make it inexpensive compared to other renewable energy resources. Carbon nanotubes (CNTs) were extensively used to enhance the mechanical properties of natural rubber, however, its performance in a double-bonded shear condition was rarely investigated. In addition, the state of CNT dispersion was a critical factor for better energy harvesting efficiency and fatigue life. Therefore, this study was aimed to compare two different dispersion approaches in CNT synthesis so that better dynamic mechanical properties and lower hysteresis loss were achieved. One approach was done in the liquid state whereas the other one was carried out in dry condition. Although the former manifested a better CNT dispersion, no significant differences in terms of dynamic mechanical properties and dissipation losses compared to the latter compounding were obtained.

A dieugenol-based epoxy monomer with high bio-based content, low viscosity and low flammability

A renewable eugenol-based biphenyl bifunctional epoxy monomer (DEUEP) is synthesized via a facile method. Eugenol is coupled into 5,5′-dieugenol and then glycidized to yield DEUEP with a potentially 100% biobased content in a high purity (96%). DEUEP displays a lower viscosity (9.2 vs. 20.6 Pa·s at 25 ℃) and a flow activation energy (60.4 ± 0.4 vs. 81.1 ± 0.4 kJ/mol) than a commodity bisphenol A-based epoxy prepolymer (E54) does. With a 3,3′-diaminodiphenylsulfone (33DDS) hardener, DEUEP/33DDS is found to express the reactivity identical to E54/33DDS with a similar activation energy (~62 kJ/mol). The cured DEUEP/33DDS thermoset is systematically examined and compared with E54/33DDS in terms of dynamic mechanical properties, thermal stability, flammability, flexural, impact and shear properties, fracture behaviors, water resistance, and wettability. DEUEP/33DDS has a lower flammability as indicated by the increased limited oxygen index (26.4% vs. 22.1%), the decreased heat release rate (HRR), total heat release (THR) and heat capacity (HR) by 46%, 33% and 46%, respectively. DEUEP/33DDS has Tg of 120.9 ℃, a storage modulus of 2.57 GPa (25 ℃), a higher char yield of 32.2% (750 ℃ in N2), and a higher water-contact angle of 110.6°.

Characterizing the Frequency Response of Compliant Materials by Laser Döppler Vibrometry Coupled Acoustic Excitation

Low-stiffness or compliant materials are inherently difficult to characterize in terms of dynamic mechanical properties. Their free-vibration behavior is not frequently analyzed, given that performing classic vibration testing in these type of materials may imply the tampering of the results by external sources, either by changes in the geometry of the sample, by gravity-induced buckling, or the instrumentation itself (e.g., the mass of accelerometers). This study proposes an approach to determine the frequency response of these types of materials, using a noncontact methodology based on acoustic excitation and displacement measurement by Laser Döppler Vibrometry. The detailed method may be optimized by changing the sample design into a half-cane configuration to increase sample stiffness. This approach significantly increases the sample eigenmodes, facilitating their excitation by the acoustic pressure source. Numerical analysis using the values of the dynamic Young’s modulus from the experimental approaches validates the overall procedure. It is shown that the combination of numerical analysis and the proposed experimental method is a possible route for the determination of the dynamic Young’s modulus of these types of materials by inverse engineering.

Bio-Based Packaging Materials Containing Substances Derived from Coffee and Tea Plants.

The aim of the research was to obtain intelligent and eco-friendly packaging materials by incorporating innovative additives of plant origin. For this purpose, natural substances, including green tea extract (polyphenon 60) and caffeic acid, were added to two types of biodegradable thermoplastics (Ingeo™ Biopolymer PLA 4043D and Bioplast GS 2189). The main techniques used to assess the impact of phytocompounds on materials’ thermal properties were differential scanning calorimetry (DSC) and thermogravimetry (TGA), which confirmed the improved resistance to thermo-oxidation. Moreover, in order to assess the activity of applied antioxidants, the samples were aged using a UV aging chamber and a weathering device, then retested in terms of dynamic mechanical properties (DMA), colour changing, Vicat softening temperature, and chemical structure, as studied using FT-IR spectra analysis. The results revealed that different types of aging did not cause significant differences in thermo-mechanical properties and chemical structure of the samples with natural antioxidants but induced colour changing. The obtained results indicate that polylactide (PLA) and Bioplast GS 2189, the plasticizer free thermoplastic biomaterial containing polylactide and starch (referred to as sPLA in the present article), both with added caffeic acid and green tea extract, can be applied as smart and eco-friendly packaging materials. The composites reveal better thermo-oxidative stability with reference to pure materials and are able to change colour as a result of the oxidation process, especially after UV exposure, providing information about the degree of material degradation.

Static and dynamic mechanical properties of PLA bio-composite with hybrid reinforcement of flax and jute

Natural fibers are used as a reinforcement material in polymer composite. High specific strength, corrosion-resistance and biodegradability are some important properties that makes natural fibers comparable to some of the synthetic fibers. The main objective of this study is the fabrication and mechanical characterization of a hybrid composite of jute/flax/PLA. Hybrid composites achieved higher flexural strength and modulus, whereas flax/PLA have higher tensile strength. For impact strength hybrid composite has achieved higher value. At the same time, flax/PLA composite was found to be superior than other developed composites in terms of dynamic mechanical properties.

Dynamic mechanical behavior of nano-ZnO reinforced dental composite

Abstract In the present work, Bisphenol-A Glycidyl Methacrylate / Triethylene Glycol Dimethylacrylate based dental composites filled with 0-30 wt.% silane treated nano-ZnO were fabricated and tested for their dynamic mechanical properties. Samples were kept in each of three different mediums such as cold drink, distilled water and saliva for 7 days. The dynamic mechanical properties such as storage modulus, loss modulus and Tan delta were evaluated and compared for each composite under different conditions. The finding of results indicated that on adding 30 wt.% nano-ZnO, the storage modulus was increased by 109% in case of post cured, 120% in case of cold drink, 125% in case of artificial saliva but decreased by 70% in case of distilled water. The loss modulus was increased by 175% in case of post cured, 30% in case of cold drink, 50% in case of artificial saliva but decreased by 50% in case of distilled water. Further, minimum value of storage modulus was reported in case of distilled water medium followed by cold drink and then artificial saliva. Also, cold drink seems to be better medium than distilled water in terms of dynamic mechanical properties of dental composite. Graphical abstract Variation of storage modulus of sample kept in artificial saliva for 7 days Addition of 30 wt.% nano-ZnO increased the storage modulus by 109% in case of post cured, 120% in case of cold drink, 125% in case of artificial saliva but decreased by 70% in case of distilled water. Addition of 30 wt.% nano-ZnO increased the loss modulus by 175% in case of post cured, 30% in case of cold drink, 50% in case of artificial saliva but decreased by 50% in case of distilled water. Immersion of sample in each medium led to decrease in storage modulus but increase in Tan delta. Further, minimum value of storage modulus was reported in case of distilled water medium followed by cold drink and then artificial saliva. Cold drink seems to be better medium than distilled water in terms of dynamic mechanical properties of dental composite.

The effect of surface modification of microfibrillated cellulose (MFC) by acid chlorides on the structural and thermomechanical properties of biopolyamide 4.10 nanocomposites

Microfibrillated cellulose (MFC) has recently been identified as an innovative product of wood and agriculture industry with potential applications as reinforcement and carrier for functional properties of polymer composite materials, such as improved barrier and optical properties. The widespread commercial application of MFC in polymer technology still requires the development of new methods of MFC surface modifications in order to provide stong interfacial adhesion and good dispersibility of additive in polymer matrix. In this work microfibrillated cellulose was modified by acid chlorides arranged in a homologous series that showed high efficiency in changing the surface properties of the material. The modified MFC displayed hydrophobic character combined with preserved fibrillar morphology and high crystallinity. Chemical modification of MFC was assessed by Fourier transformed infrared spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses. Despite the fact that the reactivity of acid chloride slightly decreased with increasing chain length the total effect on MFC wetting with water was most pronounced for the modifier with the longest alkyl chain. Completely bio-based engineering nanocomposites of biopolyamide 4.10 (PA4.10) and surface modified MFC were prepared by melt blending. Structural, morphological and thermomechanical analysis by scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic mechanical analysis (DMA) methods evidenced clear dependence of composite performance on the length of alkyl chain attached to the MFC surface. The modification of MFC by hexanoyl chloride produced nanofiller with good dispersibility in PA4.10 matrix and was favorable in terms of dynamic mechanical properties of composites. While PA4.10 composites containing MFC functionalized by longer alkyl chains (more than 10 carbon atoms) showed a decrease of storage modulus due to insufficient interfacial interactions or plasticization effect.

Structure-Property Relationship in Terms of Dynamic Mechanical Properties of High Energy Radiation Treated Industrially Important Thermoplastic Elastomer Blend

A series of low-density polyethylene (LDPE)/ethylene propylene diene terpolymer (EPDM) blends with various compositions have been prepared by melt mixing followed by injection molding. These specimens are irradiated at 40, 80, 120 and 160 kGy electron beam radiation. The gel content increases with increase in EPDM and as well as EB dose. Storage modulus (E’) and loss modulus (E”) are decreased with increase in EPDM content. Storage modulus continues to increase and loss modulus keeps on decreasing with radiation dose. Interestingly, damping property is found to be more for EPDM rich blends, which again decreases upon irradiation. Morphology of fractured surface of LDPE/EPDM shows that with increase in EPDM content, the size and depth of the cavity becomes larger and deeper indicating higher ductility. But, EB crosslinking makes the surface smoother and the smoothness keeps on increasing with increase in dose rendering stiffness to the samples.

Reactive acrylic liquid rubber with terminal and pendant carboxyl groups as a modifier for epoxy resin

AbstractReactive acrylate rubbers with the terminal and pendent carboxyl groups have been investigated as a modifier for a room temperature curing epoxy resin. The liquid rubbers with varying molecular weights and carboxyl‐functionality were synthesized by bulk polymerization of 2‐ethyl hexyl acrylate using acrylic acid as a comonomer. The liquid rubbers were characterized by FTIR, 13C NMR spectroscopic analysis, nonaqueous titration, vapor pressure osmometry, and solubility characteristics. The liquid rubbers were incorporated into the epoxy resin by the prereact method and the effect of functionality on impact properties of the modified networks were investigated. The results were explained in terms of dynamic mechanical properties and morphology analyzed by scanning electron microscope (SEM). Polym. Eng. Sci. 47:26–33, 2007. © 2006 Society of Plastics Engineers.

Shape memory polyurethanes having crosslinks in soft and hard segments

Two types of shape memory polyurethanes (PUs) with various hard segment contents (hsc)were designed and synthesized based on the position of crosslinks, either in the softsegment or in the hard segment, and were tested for tensile cyclic loading behavior aswell as mechanical and dynamic mechanical properties. It was found that hardsegment crosslinks gave much smaller shape fixability and much higher shaperecoverability as compared with soft segment crosslinks at the same hsc. For soft segmentcrosslinks, shape recovery increased as the hsc decreased, and these results couldpossibly be interpreted in terms of dynamic mechanical properties of the PUs,which possibly were interpreted in terms of microphase separation and crosslinkdensity.

Polyurethane ionomers having shape memory effects

Polyurethane (PU) ionomers and non-ionomers with various soft segment contents (SSC) and lengths have been synthesized from polycaprolactone diols (PCL), 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BD) and dimethylolpropionic acid (DMPA), and tested for shape memory behaviour as well as for mechanical and dynamic mechanical properties. It was found that ionomers gave higher hardness, modulus and strength as compared with non-ionomers, and the effects were more pronounced with increasing hard segment contents (HSC) and at room temperature, since the increased HSC makes use of more Coulombic forces which are stronger at room temperature than at high temperature. Regarding the tensile cyclic behaviour, ionomers gave higher recovery strain and lower residual strain, and these were interpreted in terms of dynamic mechanical properties, i.e. the higher the rubbery modulus, the higher the recovery strain results.