Strength and relaxation properties of synthetic shoe thread

Abstract

Modem shoe manufacture requires the use of high-quality materials, including shoe thread. Shoe thread is exposed to significant mechanical effects during manufacture and wear and for this reason improving its service properties is very pressing.The strength and deformation properties of shoe thread of two types are compared here: the polyester fibre Lavsan, widely used in the industry, and Lavsan fibre modified by adding the viscose fibre Siblon. In addition, our studies were directed toward investigating the residual component of strain of these threads as one of the most important properties appearing in stitched shoe uppers, the appearance of a dependence between residual stresses and the character of the stress--strain curve, and determination of the regions of deformation with different molecular mechanisms. We also wanted to quantitatively describe the family of stress relaxation curves and then predict this process for a long time.Lavsan shoe thread with a linear density of 70 tex and thread made from a blend of Lavsan (67%) and Siblon (33%) fibres were investigated. The threads were processed at the S. M. Kirov Spinning-Thread Combine in St. Petersburg.The strength and elastic relaxation properties of the threads were tested in different conditions. The experimental studies were conducted on an Instron-1122 tensile-testing machine. The stress--strain curves were recorded with a clamp speed of 100 mm/min and a sample base of 200 mm. The families of stress relaxation curves were obtained in a wide range of given strains, up to prebreaking strains. The duration of holding at a given deformation was 10 min. The samples were then unloaded and the residual strain in the thread was measured after 10 min of"rest."Since shoe thread is exposed to moisture during manufacture of shoes and finished articles, thread samples held in water for 24 h were also investigated. It follows from the stress--strain diagrams of the initial thread and the thread held in water (Fig. 1) that the breaking stress for these threads is almost the same (650-700 MPa), but the breaking strain is much higher for Lavsan--Siblon thread: e b = 19%, versus e b = 15% for Lavsan thread. Addition of Siblon fibres thus increases the elasticity of the thread.The insignificant effect of moisture on the properties of Lavsan fibre and the more pronounced changes in the stress--strain diagram of the starting Lavsan--Siblon thread and thread held in water should be noted: the strength decreased slightly and the elasticity of the "wet" thread increased. This result was not surprising, since poly(ethylene terephthalate) is a hydrophobic polymer, while hydrated cellulose (Siblon) is relatively sensitive to moisture.St. Petersburg State University of Technology and Design.

Effects of ozone exposure on the structural, mechanical and barrier properties of select plastic packaging films

“…It was reported that simultaneous degradation and rebuilding of macromolecules was the reason for the property changes in polymers after O 3 treat- ment. 14,22 In our study, O 3 concentration was also a signi®cant factor and had a negative effect on TS and EB for LLDPE (p < 0.05). Also, the RH of O 3 gas had only a slight reducing effect on TS (p < 0.1).…”

“…26 The observed increase in methyl content of O 3 -treated LLDPE in our study might indicate degradation of the polymer backbone. Other studies 13,14 also have reported chain scission for PE ®lms after O 3 treatment.…”