Abstract:

Objective Knitted sports shoe materials have the advantages of structural integration, light weight, comfort and low cost, which attractes wide attention from the industry and consumers in recent years. However, with the increasingly prominent environmental pollution caused by conventional aqueous dyeing, how to achieve the eco-friendly dyeing of sports shoe materials has become the key development direction.

Method In order to solve the problems of serious dyeing pollution and high energy consumption in the conventional dyeing, waterless dyeing of polyester knitted shoe materials was conducted with Disperse Yellow 54 using supercritical CO₂ as medium. Influences of dyeing temperature, pressure, time and CO₂ flow on the K/S values and levelling property were analyzed. The mechanical properties of polyester knitted shoe materials before and after dyeing were investigated, including bending, shrinkage, friction, tensile and durable properties.

Results The results showed that supercritical CO₂ displayed obvious influence on the dyeing properties of polyester knitted shoe materials. In supercritical CO₂ dyeing system, the K/S values of the dyed polyester knitted shoe materials increased significantly with the rising of dyeing pressure, temperature and time. This is mainly because the increasing CO₂ temperature and pressure present more and more plasticizing effect on polyester fiber. The dissolved dye molecules were more likely to approach the fiber interface, and would complete the adsorption through self-diffusion. Compared with aqueous dyeing, the dyeing process of polyester knitted shoe materials was able to completed with in 60 min in supercritical CO₂ and the change of CO₂ flow rate showed no significant influence on the K/S values. The deviation values of K/S data fluctuated around 0.1 at pressure ranging from 18 MPa to 26 MPa, temperature ranging from 105 ℃ to 125 ℃, time ranging from 20 min to 100 min as well as a CO₂ flow from 380 kg/h to 460 kg/h, which represents good levelness. After supercritical CO₂ dyeing, color fastness to rubbing and soaping of polyester shoe materials reached level 4 or above(Tab.1). The influence of CO₂ temperature and pressure on the mechanical properties of shoe materials was different, and temperature had more significant influence on mechanical properties than pressure. When the CO₂ temperature rose from 105 ℃ to 125 ℃, the bending rigidity increased from 9.90 mN·cm to 15.30 mN·cm(Fig.8), the maximum bending strength increased from 75.29 cN to 126.30 cN(Fig.8), the longitudinal shrinkage rate increased from 6.72% to 11.21%(Fig.9), the transverse shrinkage rate increased from 3.80% to 6.58%(Fig.9), the breaking strength increased from 1 048.23 N to 1 281.17 N(Fig.11), the elongation at break decreased from 42.05% to 36.6%(Fig.11), and the bursting strength increased from 2 235 N to 2 390 N(Fig.13). However, the test results revealed that the temperature and pressure played no remarkable influence on the tribological properties(Tab.2), and the static friction coefficient and dynamic friction coefficient of the polyester samples were almost constant.

Conclusion By using supercritical CO₂ instead of water as the medium, waterless dyeing of polyester knitted shoe materials can be achieved, and the deviation of K/S values is stable at 0.1±0.05. The optimal dyeing procedure was determined by balancing the dyeing effect and resource consumption. The dyed polyester knitted shoe materials with superior properties after supercritical CO₂ dyeing indicate a favorable foreground. The above investigation provides an impurtant support for the clean industrial production of supercritical CO₂ dyeing.

Key words: supercritical CO₂, knitted shoe material, polyester, dyeing property, mechanical property