## 4 Discussion
### Difference in Mechanical Properties between Longitudinal and Transverse Specim  
TMA measures the deformation (one-dimensional dimension) of specimens with temperature under the constant action (non-alternating load), which can heat specimen at a constant rate, so that the specimen deforms with increasing temperature under a constant smaller load, and the temperature-deformation relationship and the contraction and expansion coefficients of the membranes were obtained. In this paper, 5 mm \(\times\) 10 mm (width \(\times\) length) longitudinal and transverse specimens were selected for thermodynamic tests, and the results are shown in Figure 10. It is evident that the deformation temperature curves of longitudinal specimen follow different patterns to that of transverse specimen: the deformation of longitudinal specimen is positive and slightly increased at temperatures less than 60 \({}^{\circ}\)C; however, it is negative and decreases constantly at a temperature ranging from 60 \({}^{\circ}\)C to 150 \({}^{\circ}\)C, while that of the transverse specimen is positive and increases with the temperature. The results show that when the ambient temperature exceeds a certain value, the deformation of longitudinal specimen is negative, i.e., heat-absorbing contraction macroscopically, while that of the transverse specimen increases gradually with the increasing temperature and exhibits heat-absorbing expansion.  
The heat absorption and contraction of the longitudinal specimen is related to the material production process, where the raw material is in the flow state after being fused and mixed and is extruded and condensed at the outlet. The rapid condensed GEM is  
Figure 10: Relationship between deformation and temperature: (**a**) longitudinal specimen; (**b**) transverse specimen.  
Figure 9: Thermodynamic analysis curve by DSC.  
pulled to the roller and coiled; molecular orientation appears in the molecular chain by the traction force in condensation molding process. The accumulated deformation by molecular orientation is \"frozen\" in the internal molecule, and there is no traction effect in the transverse direction [36]. When the temperature activates the polymer motion, the \"frozen\" deformation begins to return, which is manifested as contraction. The \"frozen\" deformation is in a tensile stress state, and when the energy produced by temperature is higher than the molecular activation energy, the axial tensile stress needs to offset the stress to be activated before the same displacement increment occurs, resulting in increased tensile stress. As in Table 1, the Young's modulus of the longitudinal specimen at above 0 \({}^{\circ}\)C is slightly higher than that of the transverse specimen.  
The difference in mechanical properties between longitudinal and transverse specimen is mainly attributed to the production process of GEM. The accumulated deformation of the longitudinal molecular orientation is \"frozen\" in the molecular structure during the condensation process at the extrusion outlet. The polymer chain is in a tensile stress state. When the energy generated by the temperature action can activate the \"frozen\" state, the released stress increases the axial force under the condition of displacement-controlled tensile rate, which explains the higher the temperature and the greater difference in Young's modulus between longitudinal and transverse specimen. The difference in the internal stress state accounts for the difference in the mechanical properties of longitudinal and transverse specimen.