Temperature-modulated thermomechanical analysis as a potential technique for irreversible stress relaxation measurement in various cables

Abstract

Temperature-modulated thermomechanical analysis (TMA) is a technique which allows for separation of the temperature-dependent thermal expansion from the time and temperature-dependent creep or stress relaxation behavior. Extrusion during the cable production process may orient and stretch polymer chains which are rapidly cooled in water. Such frozen-in stresses might relax over a longer time period, or when the sample is heated up, the polymer chains are able to move back to their initial state. Using this method allows for measurement of both effects-irreversible stress relaxation and reversible thermal expansion-at the same time. Additionally, a reversible signal might be used for the determination of the coefficient of thermal expansion for different materials. This work compares polyethylene samples with and without frozen-in stresses measured on standard and temperature-modulated TMA.

Evaluation of the Fusion Quality of Bead Foams Made from Polybutylene Terephthalate (E‐PBT) Depending on the Processing Temperature

“…In addition, polymers with frozen‐in stresses show irreversible stress relaxation when the sample is heated up. [ 41 ] During the bead foam process, the internal CO 2 gas pressure of the foam cells causes an equibiaxial expansion of the surrounding melt. Through the underwater pelletizing process the oriented and stretched polymer chains are frozen in that state by rapidly cooling in water.…”

Influence of Molecular Weight on the Bead Foaming and Bead Fusion Behavior of Poly(butylene terephthalate) (PBT)

“…At 80 °C, the chain mobility is too low that the internal stresses cannot be reduced. In general, such materials having frozen-in stresses exhibit relaxation processes when the chain mobility is increased by heating . With the help of TMA measurements, these relaxation process phenomena, which are evident in a shrinkage of the sample, can be detected (Figure ).…”

“…In general, such materials having frozen-in stresses exhibit relaxation processes when the chain mobility is increased by heating. 49 With the help of TMA measurements, these relaxation process phenomena, which are evident in a shrinkage of the sample, can be detected (Figure 12). A temperature increase in the range below the glass transition temperature causes only a slightly pronounced volume expansion due to limited chain mobility.…”