Stretching processes

Thermal-Phase-Inversion Process. Still another approach to forming porous membranes out of polymers not soluble at room temperature is to elevate the temperature until they dissolve in a selected solvent. The resulting solution is then cooled in a controlled way until the polymer precipitates around the solvent which serves as the pore-former at room temperature. The process is called thermal-phase-inversion.  

---

We begin by remembering the mechanical definition of work and apply that definition to the stretching process of Fig. 3.1. Using the notation of Fig. 3.1, we can write the increment of elastic work we associated with an increment in elongation dL as... 

A great many liquids have entropies of vaporization at the normal boiling point in the vicinity of this value (see benzene above), a generalization known as Trouton s rule. Our interest is clearly not in evaporation, but in the elongation of elastomers. In the next section we shall apply Eq. (3.21) to the stretching process for a statistical—and therefore molecular—picture of elasticity. 

Recently, Nitto Denko has patented a single-layer separator made from a PE/PP blend by the dry stretch process [24], According to the patent, the separator has microporous regions of PE and PP. On heating in an oven, the impedance of the separator increases near the melting point of PE and the impedance remains high until beyond the melting point of PP. However, battery performance data have not been presented. 

Film stretching process, 19 546 Film sulfonating-sulfating systems, Chemithon, 23 544-547 Film theory, 1 37, 46 21 642 model, 21 643... 

C. What is the entropy change for the universe (spring plus surrounding thermostat) for the total process, stretching plus return collapse to initial Lq d. How much work was performed on the spring in the stretching process ... 

The first term (dE/d/) in Equation 9.43 is important in the initial low modulus stretching process, and the second term [T (dG/d/)] predominates in the second high modulus stretching process. For an ideal rubber, only the second term is involved. 

Nearly all polymeric objects have some orientation during the forming (shaping) of the specimen the molecules are oriented by viscous flow and part of this orientation is frozen in as the object cools down. But this kind of orientation is negligible compared with the stress-imposed orientation applied in drawing or stretching processes. 

Although some operations in the plastics industry, such as calendering, could be described as stretching processes, the most important application of stretching is usually called drawing (of fibres and films). 

Like the snap back process, billow forming is a sheet pre-stretch process used with a male mold. The sheet is clamped across a pressure chamber and is billow pre-stretched by applying a low magnitude positive air pressure to the chamber. The male mold is then moved into the stretched sheet until the clamp seals on the mold periphery. Contact between the mold and controlling the rate at which the pressure chamber is vented to compensate for the advancing mold can regulate the sheet. 

Figure 1.4. Stretching process of a triple walled carbon nanotube. Reproduced from reference 24 with permission from Elsevier.

---