Dynamic Mechanical Tensile Analysis

As noted in Subsection 24.1.2, viscoelasticity of polymers represents a combination of elastic and viscous flow material responses. Dynamic mechanical analysis (DMA, also called dynamic mechanical thermal analysis, DMTA) enables simultaneous study of both elastic (symbol ) and viscous flow (symbol ") types of behavior. One determines the response of a specimen to periodic deformations or stresses. Normally, the specimen is loaded in a sinusoidal fashion in shear, tension, flexion, or torsion. If, say, the experiment is performed in tension, one determines the elastic tensile modulus E called storage modulus and the corresponding viscous flow quantity E" called the loss modulus. 

Mechanical properties of biodegradable polyesters are important for applications such as materials for sutures and bioresorbable screws. The characterization of mechanical properties is carried out by means of tensile test, rheology, and dynamic mechanical temperature analysis. ... 

Details are given of the physicochemical properties and in vitro resistance to encrustation of films of polycaprolactone or blends of polycaprolactone with a polyvinylpyrrolidone-iodine mixture. Films were characterised in terms of tensile properties, dynamic mechanical thermal analysis, dynamic contact angle, and SEM. 29 refs. 

Natural rubber based-blends and IPNs have been developed to improve the physical and chemical properties of conventional natural rubber for applications in many industrial products. They can provide different materials that express various improved properties by blending with several types of polymer such as thermoplastics, thermosets, synthetic rubbers, and biopolymers, and may also adding some compatibilizers. However, the level of these blends also directly affects their mechanical and viscoelastic properties. The mechanical properties of these polymer blended materials can be determined by several mechanical instruments such as tensile machine and Shore durometer. In addition, the viscoelastic properties can mostly be determined by some thermal analyser such as dynamic mechanical thermal analysis and dynamic mechanical analysis to provide the glass transition temperature values of polymer blends. For most of these natural rubber blends and IPNs, increasing the level of polymer and compatibilizer blends resulted in an increase of the mechanical properties until reached an optimum level, and then their values decreased. On the other hand, the viscoelastic behaviours mainly depended on the intermolecular forces of each material blend that can be used to investigate the miscibility of them. Therefore, the natural rubber blends and IPNs with different components should be specifically investigated in their mechanical and viscoelastic properties to obtain the optimum blended materials for use in several applications. 

Modifications in order to improve starch matrix-starch nanoparticles nanocomposites were also proposed. For example, Ma et al. (2008c), proposed the fabrication and characterization of citric acid-modified starch nanoparticles/plasti-cized pea starch composites. In dynamic mechanical thermal analysis, the introduction of CA-S-NP could improve the storage modulus and the glass transition temperature of pea starch/CA-S-NP composites. The tensile yield strength and Young s modulus increased Irom 3.94 to 8.12 MPa and from 49.8 to 125.1 MPa, respectively, when the CA-S-NP contents varied fiom 0 to 4 wt%. 

Viscoelastic properties are often determined with steady state oscillation or vibratory tests using small tensile (compressive) bars, thin cylinders or flat strips in torsion, beams in bending, etc. The approach is usually referred to as dynamic mechanical analysis (DMA) testing or sometimes dynamic mechanical thermal analysis (DMTA). The latter term is more appropriate as properties are often determined and expressed in terms of temperature... 

The study of the thermo-mechanical behaviour was performed by dynamic-mechanical thermal analysis (DMTA), using a Gabo Eplexor 500 N equipment. Rectangular specimens, 50 mm long, 5 mm wide, and 2 mm thick, were prepared for the measurements. The tests were performed in tensile mode at a fiequency of 10 Hz with a static strain of 0.6% and a dynamic strain of 0.1%. The samples were measured between -120 °C and 150 °C at a heating rate of 3 °C/min. 

Different mechanical properties have been analyzed in the literature, that is, storage modulus analyzed in dynamic mechanical thermal analysis, tensile strength. Young s modulus, and toughness obtained in tensile tests. These mechanical characterizations were conducted on freestanding coatings stirred mixtures of sols and fillers were cast on glass or polypropylene plates previously surface treated with a common fabric softener and subsequently spread with a bar coater with a 500 pm gap. 

The authors have characterized the graft polymer by solvent extraction, transmission electron microscopy, dynamic mechanical analysis, mechanical testing (including measurement of tensile, tear, and impact strength), and morphology by SEM. The reaction scheme is given in Figure 11.25. 

An appropriate cure cycle was established based on the results obtained from the thermal analysis and cure rheology studies of the resin and cured BCB bar and dogbone shaped samples were fabricated for testing. Bar shaped specimens had the dimensions of 3.5 x 0.5 X 0.125 and were used to stake compact tension specimens for fracture toughness studies and for dynamic mechanical analysis of a torsion bar. Dogbone shaped specimens for tensile tests had a gauge area of 1 x 0.15 and were approximately 0.040 thick. 

The physical properties of barrier dressings were evaluated using the Seiko Model DMS 210 Dynamic Mechanical Analyzer Instrument (see Fig. 2.45). Referring to Fig. 2.46, dynamic mechanical analysis consists of oscillating (1 Hz) tensile force of a material in an environmentally (37°C) controlled chamber (see Fig. 2.47) to measure loss modulus (E") and stored modulus (E ). Many materials including polymers and tissue are viscoelastic, meaning that they deform (stretch or pull) with applied force and return to their original shape with time. The effect is a function of the viscous property (E") within the material that resists deformation and the elastic property (E )... 

---