Dynamic Mechanical Analysis, crystallinity

Hsieh et al [62] found that for a range of thermotropic liquid crystalline polymers, the greater the free volume measured by PAL the greater the chain mobility at Tg and the higher the value of tan S (damping strength) measured by dynamic mechanical analysis. 

Dynamic mechanical analysis coupled with polarised step-scan FTIR transmission and two-dimensional correlation analysis was used to monitor the submolecular orientational responses of the components of a semicrystalline 50/50 blend of LDPE with perdeuterated HDPE to a small amplitude uniaxial 23.47 Hz sinusoidal mechanical strain. Perdeuteration of the HDPE component allowed the distinction of its response from that of the LDPE in the blend samples. Experiments were carried out at room temp. Analysis of the data indicated that the crystalline parts of the two components reorient at different rates, with the functional groups of the high density portion reorienting faster, in general, than those of the LDPE in response to the mechanical strain. 29 refs. USA... 

Crystallinity of PLA has a strong impact on its mechanical properties. Suryanegara et al. have prepared PLA/MFC nanocomposites in both fully amorphous and crystallized states. The tensile modulus and strength of pristine PLA were improved with an increase of MFC content in both amorphous and crystallized states. Dynamic mechanical analysis (DMA) has been used to study the effect of MFC reinforcement on the thermomechanical properties of PLA in both states and the results are shown in Figure 9.5. In the amorphous state, the storage modulus of pristine PLA below Tg is almost constant at around 3 GPa. Above Tg, the modulus drops to 4 MPa at 80 °C, and then increases to 200 MPa at 100 °C owing to the cold... 

Glass-transition data determined by DSC were similar to but slightly different from dynamic mechanical data. As-cast samples at high SAN contents and with no PCL crystallinity showed very similar single, composition-dependent TgS by both techniques. At higher PCL contents (30-70%, approximately), as-cast samples showed a constant Tg ( 50 °C) by dynamic mechanical analysis these data describe blends with combinations of different proportions of crystalline PCL... 

Fig. 25a,b. Variations in glass-transition temperatures in PCL/SAN blends a for quenched samples (O) without PCL crystallinity and ( ) with PCL crystallinity determined by dynamic mechanical analysis at 110 Hz b determined by DSC with solid line calculated from the Gordon Taylor equation with k=0,576 and TgS for PCL and SAN 190 K and 384 K respectively data taken from [19]... 

However, the overall crystallinity and melting temperature decreased with increasing filler content. Tensile and dynamic mechanical analysis measurements indicated that expanded graphite was a better hller than untreated graphite. The overall improvement in mechanical properties was not great, but the mechanical strength and stiffness of high-density polyethylene were improved by the addition of the fillers. 

Using a nanoindentation technique, Shen et al. [150] studied the effects of clay concentrations on the mechanical properties (hardness, elastic modulus, and creep behavior) of exfoliated polyamide 6,6-clay nanocomposites. The results were discussed in conjnnction with those obtained by dynamic mechanical analysis and optical microscopy, and also conjunction with changes in morphology, crystallinity, and x-ray diffraction. 

Picciochi Ricardo, Wang Yarning, Alves M. Natalia, and Mano E. Joao. Glass transition of semi-crystalline PLEA with different morphologies as stndied by dynamic mechanical analysis. Coll. Polym. Sci. 285 no. 5 (2007) 575-580. 

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