Abstract:

Objective In order to explore the influence of polyvinyl alcohol (PVA) polymerization and alcoholysis degrees on sizing performance, the performance of cotton yarn sized with 10 different polymerization and alcoholysis degrees of PVA was investigated. The most suitable PVA for cotton yarn was selected by fuzzy comprehensive evaluation method, minimizing the amount of PVA to ensure sizing performance.

Method The sealing performance of the size box of the single yarn sizing machine was improved to keep the size concentration and hence the size pick-up stable. Cotton yarns of 14.6 tex were sized using PVA sizing agents with different degrees of polymerization (500, 800, 1 200, 1 400, 1 700) and alcoholysis (partial, 88%; full, 99%) respectively, and the size pick-up was controlled within the range of (8.2±0.1)% by finely adjusting the size concentration. The size pick-up percentage of sized yarn was obtained using the constant-length gravimetric method. The performance of the sized yarn was tested for breaking strength and elongation at break, wear resistance, and hairiness, which was evaluated using fuzzy comprehensive evaluation taking tested parameters as the indexes for selecting the most suitable PVA polymerization and alcoholysis degrees for cotton yarn sizing.

Results The results showed that the breaking strength of the sized yarns increased and then decreased with increased polymerization degrees of partially and fully alcoholyzed PVA under the same size pick-up, and finally stabilized. The breaking strength of yarns sized with partially alcoholyzed PVA peaked at 800 degree of polymerization, while the breaking strength of yarns sized with fully alcoholyzed PVA reached a maximum 1 200 degree of polymerization. The elongation at break of partially and fully alcoholyzed PVA sized yarns was very similar. However, the elongation at break of sized yarns decreased with increased PVA polymerization degree and ranged from 5.57% to 3.94%. The strength resistance of yarns sized with partially and fully alcoholyzed PVA increased and then reduced with increased degree of polymerization. The strength resistance of yarns sized with partially alcoholyzed PVA reached its maximum at 800 degrees of polymerization. The strength resistance of yarns sized with fully alcoholyzed PVA increased significantly at 1 200 and 1 400 degrees of polymerization. The effect of PVA polymerization degree on the hairiness number of sized yarns was less at the same alcoholysis degree. When the degree of polymerization ranged between 500 and 1 700, the hairiness number of yarns sized with partially alcoholyzed PVA was 18-19, while those sized with fully alcoholyzed PVA showed significantly lower values (9-12). The results of the fuzzy comprehensive evaluation demonstrated that the fully alcoholyzed PVA sizing agent showed superior performance compared to the partially alcoholyzed PVA. Among the fully alcoholyzed PVA, PVA-1299 had the best performance, while among the partially alcoholyzed PVA, PVA-0888 presented the optimal performance.

Conclusion The single yarn sizing experiment method was improved to study the influence of PVA with different degrees of polymerization and alcoholysis on sized yarn properties. It was found that the optimal interval of sizing performance for both partially and fully alcoholyzed PVA was located in the intermediate polymerization degree under the same size pick-up percentage. In addition, the results of fuzzy comprehensive evaluation revealed that for cotton sized yarns, the sizing performance of fully alcoholyzed PVA was usually better than that of partially alcoholyzed PVA, with PVA-1299 showing the finest sizing performance, followed by PVA-1499. This study provides theoretical guidance for size producers to develop intermediate polymerization degree fully alcoholyzed PVA sizing agent, and thus reduce the use of PVA-1799 to further improve the sizing effectiveness.

Key words: polyvinyl alcohol, polymerization degree, alcoholysis degree, cotton yarn, single yarn sizing machine, sizing performance