The Thermogravimetric,Microscopic and Mechanical Analyses of PBT and PET yarns(6)

3.3 Mechanical Analyses
The mechanical properties of the samples are shown in Table 3. Since the yarn numbers were different, it could be considered that this fact could lead to uneven mechanical property comparison. However, it was determined that the flame retardant yarn had the lowest tensile strength, although it was the thickest one. So, it was understood that the difference between the yarn numbers did not affect the mechanical strength significantly. The fact that flame retardant yarn had the lowest tensile strength could be attributed to the weak O=P–O bond and phosphorus content in the yarn. In the related studies, it had been stated that the presence of higher phosphorus content caused lower crystallinity, melting temperature, decomposition temperature and tensile strength but higher residual char after thermal degradation (17, 18). As seen from the Table 3, the second yarn with low tensile strength was found to be PBT. Depending on the different nature, PBT is known to have slightly poorer mechanical properties than PET (4). But the mechanical properties of PBT can be enhanced by hybridization with other fibres (19). When the UV protective and antibacterial PET yarns were considered it could be said that there was no significant difference with regular PET.

4. CONCLUSION
Five polyester yarns were used to assess the effects of different modifications and components on microscopic, thermogravimetric and mechanical features. Experimental results indicated that the flame retardancy modification had more significant effect on thermogravimetric and mechanical features than that of other samples. Microscopic analyses demonstrated that polyester fibre had a smooth surface. Both the modification processes and difference in chemical composition caused differences like some particles attached on the fiber surface and increased roughness. From the light microscopy photos, cross section of regular and UV additive polyester fibres was found to be circular whereas antibacterial and flame retardant polyester fibres and PBT was pentalobal in terms of cross section. From the thermogravimetric analyses, it was determined that after flame retardancy process Tdi (initial degradation temperature) decreased due to the O=P–O bond and PBT had similar thermal behaviors than PET. The findings obtained from mechanical analyses indicated that the physical features of polyester yarns were affected distinctively by applied processes.

5. ACKNOWLEDGEMENTS
The authors would like to thank KORTEKS (polyester yarn producer) for the samples and TUBITAK (Turkish Scientific and Technological Research Institution) for financial support with the project Eureka E! 3272.

Writen by Buket ARIK1, Ebru BOZACI1, Asli DEMIR2, Esen ÖZDOGAN1