Leathery-to-rubbery transition

If temperature continuously increases, the polymer molecular stracture further changes and a transition from the leathery to mbbery state occurs. In this transition, the E-modulus of the material maintains stable, while the loss modulus 

---

According to Chapter 2, because the T-modulus of the leathery and rubbery states are almost the same, the leathery and rubbery states are not discernible based solely on the change in F-modulus. Therefore, the leathery-to-rubbery transition can be neglected and this results in only glass transition and decomposition. The... 

Considering that the E-modulus of the leathery (Ej) and rubbery (Ej.) states are almost the same (see Chapter 2, the leathery and rubbery states are not discernible based solely on the change in E-modulus), the leathery-to-rubbery transition can be neglected. Therefore, within a unit volume of initial material at a specified temperature, the volume of the material at the different states (glassy, leathery or rubbery, and decomposed) was derived in Eq. (3.3), Eq. (3.4), and Eq. (3.5). Furthermore, after decomposition, the decomposed material no longer has significant structural stiffness. Its modulus, E, can be taken as zero. The following equation can thus be obtained to describe the effective E-modulus ... 

Since dynamic mechanical tests measure the response of a material to an applied stress at different temperature and frequency, they measure the transition of the material from glassy to leathery to rubbery state. If the frequency is kept constant and low (about one cycle/sec), the results are related to measurements of transition by other techniques. Thus, some cross-checking is possible. 

Although the transition from a solid to a liquid state at the Tm is relatively precise and occurs over a short temperature range, the transition from a glassy solid to a leathery state occurs over somewhat broader temperature ranges around Tr The modulus, or stiffness, of the polymer decreases as the temperature is increased above the Tg, and the polymer changes from a leathery to a rubbery state. 

Blends of LDPE with ethylene styrene interpolymers (ESI, see Section 3.2) also have a complex microstructure. The semi-crystalline LDPE is immiscible with the amorphous ESI, which has a glass transition temperature (Tg) just above room temperature. Consequently there are rigid crystalline regions and rubbery amorphous LDPE, mixed on a 0.1 pm scale, together with regions of leathery ESI on a 5 to 10 pm scale (71). 

An amorphous material such a polystyrene does not solidify sharply. It goes from a viscous liquid to a rubbery solid, then to a leathery solid. Finally, it becomes a glassy solid. This last change is a sharper one and the temperature at which it occurs is called the glass transition temperature, Tg. Or upon heating a polymer, it is the temperature at which the polymer loses... 

Substantially crystalline plastics in the range between Tg and T are referred to as leathery, because they are made up of a combination of rubbery noncrystalline regions and stiff crystalline areas. The result is that such plastics as PE and PP are still useful at room temperature and nylon is useful to moderately elevated temperatures even though those temperatures may be above their respective glass-transition temperatures. 

Polymers come in many forms, inclndmg plastics, rubber, and fibers. Plastics are strffer than rubber yet have reduced low-temperature properties. Generally, a plastic differs from a rubbery material due to the location of its glass transition temperatnre (Tg), which is the temperature at which the polymer behavior changes from glassy to leathery. A plastic has a Tg above room temperatnre, whereas a rnbber has a Tg below room temperature. Tg is most clearly defined by evalnating the classic relationship of elastic modnlns to temperature for polymers as presented in Fig. 1.5. 

---