Abstract:

Objective It is well known that natural starch exhibits insufficient adhesion to hydrophobic fibers and high-temperature thermal stability due to numerous hydroxyls and cyclic structure on its chains. As a result, monoester groups introduced onto starch chains by chemical esterification have the potential to improve the properties of starch. This study aims to strengthen interfacial adhesion of starch to polyester fibers using the new grafted starch (starch grafted two-block polyvinyl acetate, DES-g-(PVAc)₂) for promoting the sizing performance of starch, and providing a new grafted starch sizing agent (DES-g-(PVAc)₂) for warp sizing.

Method Starch was etherified to prepare dibromopropyl starch (DES). Subsequently, graft polymerization of the DES and vinyl acetate (VAc) monomer was conducted by atom transfer radical polymerization in the presence of the electron-transfer-activated regeneration catalyst, So as to synthesize the new grafted starch (DES-g-(PVAc)₂) samples with varying grafting ratios. Characterization was performed using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The influences of the grafting ratio on adhesion to polyester fibers, viscosity and viscosity thermal stability, surface tension, film properties, water contact angle of the film, and biodegradability were investigated. The adhesion was studied by measuring the bonding force of slightly sized roving. The measurement included three parts: (a) forming a starch sizing agent, (b) immersing the roving into the sizing agent and then air-drying, and (c) conducting tensile tests of sized roving. The tensile property of the film was estimated.

Results The FT-IR analysis revealed a new peak at 1 719 cm^-1 in the spectra of DES-g-(PVAc)₂ granules, which corresponded to the stretching vibration of ester carbonyl groups, revealing the successful introduction of grafted PVAc-b-PVAc branches onto the starch chains. The XRD analysis showed that the degree of crystallinity of the DES-g-(PVAc)₂ film was lower than that of ATS, meaning that introducing PVAc-b-PVAc branches containing ester carbonyl groups onto the starch chains decreased the degree of crystallinity of the starch film. When VAc monomer mass was 30 g, 45 g, and 60 g, respectively, the grafting ratios achieved for DES-g-(PVAc)₂ were 9.5%, 10.9%, and 12.5%, respectively. The introduction of PVAc-b-PVAc branches enhanced the viscosity the mal stability of the starch sizing agent, reduced its surface tension, significantly strengthened the interfacial adhesion of starch to polyester fibers, increased the elongation at break of the starch film, reduced the film strength, and increased the water contact angle of the film. As the grafting ratio increased, the adhesion force, film elongation at break, and water contact angle gradually increased, whereas surface tension and film strength gradually decreased. The grafting ratio exhibited a negative correlation with the viscosity and biodegradability of DES-g-(PVAc)₂, indicating a slight negative effect. However, even at the maximum grafting ratio of 12.5%, the 5-day biochemical oxygen demand (BOD₅)/chemical oxygen demand (COD) ratio remained above 0.3, confirming the biodegradability of DES-g-(PVAc)₂.

Conclusion The introduction of PVAc-b-PVAc branches strengthen interfacial adhesion of starch to polyester fibers, film property, and sizing agent stability, thereby improving its sizing properties. A new grafted starch (DES-g-(PVAc)₂) is provided for the sizing of polyester warp yarns, laying an important foundation for this application.

Key words: starch, sizing agent, grafting ratio, adhesion, film property, biodegradability