Curved thermoplastic polymeric

The curve of the apparent viscosity data versus temperature for PP/PU/APP is reported in the Figure 10.9. In the first step (200°C-240°C), the viscosity of the material decreases when the temperature increases following the behavior of a thermoplastic material. Even though we observe in this step a carbonization of the material surface, the polymeric matrix has been preserved under the surface. In the 240°C-300°C temperature range, the viscosity value slightly decreases and its value remains close to the low apparent viscosity of the material molten at 240°C. The sample appears as completely carbonized and liquid. The plateau may then be explained by the chemical transformation of the material (formation of phosphoric acid esters and aromatic species).33... 

The synthesis of ABA blocks from a glassy thermoplastic A and an elastomeric B produces other elastoplastics with attractive properties. Polyester chains can be extended with di-isoeyanate, which is then treated with cumene hydroperoxide to leave a peroxide group at both ends of the chain. By heating this in the presence of styrene, a vinyl polymerization is initiated and an ABA block created. The modulus-temperature curves show how the mechanical properties can be modified in this way (Figure 15.7). These block copolymers are known as thermoplastic elastomers. 

Eceiza et al investigated a series of thermoplastic PUs synthesized in bulk by two-step polymerization, obtained with the isocyanate-chain extender couple MDI-BG and various SS macrodiols. The chemical structure, the SS molecular weight and the HS content were varied. The effects on the thermal and mechanical properties were investigated [77]. The changes in the macrodiols in the case of PUs based on MDl-BG, resulted in a modulus curve that showed a plateau indicating the existence of physical crosslinks because of the increase in the size and inter-connectivity... 

Schematic recovery curves for constant strain and stress-free conditions for thermoplastics and polymeric networks are shown in Fig. 9. Recovery of a thermoplastic SMP under constant strain initially leads to an increase of cr until is reached. At higher temperatures a drop in stress can be observed, where the softening of the polymer dominates, which is caused by an increase in mobility of the chain segments. In SMP networks the stress remains constant above and is only reduced after cooling the sample again.

RIC Riccardi, C.C., Borrajo, J., Meynie, L., Fenouillot, F., and Pascault, J.-P., Thermodynamic analysis of the phase separation during the polymerization of a thermoset system into a thermoplastic matrix. I. Effect of the composition on the cloud-point curves, J. Polym. Sci. PartB Polym. Phys., 42, 1351, 2004. 

In practice polymeric materials are often subjected to mechanical loads. Therefore, it is essential to know how polymers respond to the mechanical load. Figure 1.3 presents the common behavior of thermoplastic polymers under uniaxial deformation. On the stress(a)-strain(e) curve four regions [7] can be distinguished in region I the material shows an elastic behavior. In this region the material is characterized by its Young s modulus of elasticity. In region II the material yields. The slope of... 

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