# Investigation of the Effect of Operational Factors on Conveyor Belt Mechanical Properties
## 4 Comparison of Results and Discussion
### Specimens Exposed in the Climatic Chamber
A low temperature (above 0 \({}^{\circ}\)C) contributes to the fact that polymers behave like vitrified glass bodies with high stiffness, which have already been damaged by a slight deformation and exhibit resilience characteristics, and in particular the presence of reversible deformations, most often increasing proportionally to the increase in stress. The results of this study confirm that the Young's modulus of polymeric plastics is significantly higher at low temperatures compared to room temperature [24; 25; 26; 27]. As for yield strength (Figure 15), it can be observed that the reference samples (except one case, KKB-80-80) have a higher yield strength \(R_{p0,5}\). The lowest yield strength was obtained for exposure at a temperature of 10 \({}^{\circ}\)C (303 K) and a humidity of 80% (KKA-10-80). Therefore, it can be concluded that exposure under these conditions leads to decreased yield strength, thereby decreasing the plastic properties of the belt. In addition, it was observed that the parameter \(A_{gt}\), i.e., total elongation at the highest tensile force, has similar values for the tested variants of ageing. Most polymers have low humidity, but there are exceptions. Increased humidity causes the consumption of raw material during processing and exposes the producer to losses. Some polymeric materials absorb water or moisture from the air. An increase in the water content of the material increases the impact strength and elasticity but reduces the strength. However, it should be remembered that the absorption of water is also associated with increasing the volume of the material, and thus the dimensions of the elements, which may lead to incompatibility of construction dimensions, adversely affecting the work of the element. It can be seen (Figure 15) that an increase in humidity causes a decrease or increase in some mechanical parameters, but this is a more complex phenomenon, as it is also associated with the seasoning temperature. Comparing the results of tensile modulus and tensile strength of the samples exposed to the constant humidity of 80% and at different temperatures--10 \({}^{\circ}\)C (283 K), 30 \({}^{\circ}\)C (303 K), 80 \({}^{\circ}\)C (353 K) (Figure 16)--it can be observed that the highest tensile strength was obtained for exposure at a humidity of 80% and at a temperature of 30 \({}^{\circ}\)C (303 K). When both lower and higher temperatures are applied, the tensile strength significantly decreases by 15% and by 26%, respectively. Some statistical results (correlation coefficient) of the tensile modulus for the samples subjected to ageing in different climatic conditions and for reference samples are presented in Table 8. In the analysis, the Pearson correlation coefficient was used. Some information regarding the correlation coefficient was presented in [28]. Based on the correlation of the coefficient results presented in Table 8, the following observations can be made:  
* comparing the results of the tensile modulus for the samples subjected to ageing under different climatic conditions and for reference samples, in the majority of cases, a correlation between the value of tensile modulus and the ageing conditions (considering both temperature and humidity) could not be observed,
* in some cases, a correlation (both positive and negative) was observed, but the correlation is not strong. For example, the negative correlation of the tensile modulus for the samples KKB-10-80 and KKB-80-80 subjected to ageing at the same relative humidity (80%), but at different temperatures  
Figure 16: Tensile modulus and tensile strength of samples exposed to selected ageing variants. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Variable**  
(10 \({}^{\circ}\)C (283 K) and 80 \({}^{\circ}\)C (353 K)); the correlation coefficient here was \(-\)0.7128, indicating the negative influence of the higher temperature on the value of the tensile modulus. This means that an increase in the temperature leads to a decrease in the tensile modulus in the case of high humidity (80%).