Abstract:

Objective As is well known, natural starch presents an inadequate adhesion to fibers, due to numerous hydroxyls and cyclic structure on the starch chains. The adhesion has the main function of enhancing yarn strength by bonding the fibers in the warp yarns and lessening warp surface hairs by more than 80% by bonding the hairs onto warp body. Therefore, this study aims to improve the adhesion of starch to cotton and polyester fibers by using a new starch derivative, propionylated-tertiary aminated starch (PTAS), for promoting sizing quality of the warp yarns with the new starch derivative sizing agent (PTAS).

Method A series of PTAS samples with different total degrees of substitution were prepared by propionylation-tertiary amination of acid-hydrolyzed starch (AHS) with propionic anhydride (PA) as esterifying agent and 2-dimethylaminoethyl chloride hydrochloride (DMC-HCl) as etherifying agent, and with the method of fixing the amount of PA as well as altering the amount of DMC-HCl, under weak alkaline and low temperature conditions, in an aqueous medium. In order to reveal the successful preparation of PTAS, the chemical structure of PTAS was characterized by Fourier transform infrared (FT-IR) spectroscopy, while its elemental analysis was carried out by a X-ray energy spectrometer. The surface morphology of PTAS particles was observed and analyzed by a scanning electron microscope, and the effect of modification on the surface morphology of PTAS granules was clarified. The modification levels of propionylation and tertiary amination were determined by titration analysis and Kjeldahl method, respectively. The effects of modification on the adhesion between starch and polyester, polyester/cotton and cotton roving, and the surface tension of starch paste, were also investigated, and the adhesion was investigated by a Chinese standard method (FZ/T 15001-2008) via measuring the bonding strength of slightly sized roving. The measurement mainly includes three processes: (a) forming a starch, (b) immersing the roving and then air-drying, and (c) conducting tensile test of sized roving.

Results FT-IR analysis found that a new peak was present in the wavenumber of 1730 cm^-1, which corresponded to the stretching vibration of ester carbonyl group, revealing the successful introduction of propionate substituents in the starch molecules. The element analysis proved that in addition to C and O elements, there were N and Cl elements in the starch sample. The results from the two analyses demonstrated the successful preparation of PTAS. SEM technique revealed that PTAS sample was still in particle state, but some partide surfaces were damaged, which was mainly attributed to the facts that the modifications were occurred under alkaline condition and at the free hydroxyls on the particle surfaces. By using the previous preparation method, PTAS samples with propionylation level of 0.030 and tertiary amination level range of 0.010-0.035 could be prepared, by fixing the 4.63% in the mass ratio of PA to AHS and altering the amounts of DMC-HCl in the range of 10-40 g. The adhesion of PTAS to polyester, polyester/cotton and cotton roving was obviously higher than that of AHS, but the surface tension was significantly lower than that of the latter. The introduction of propionate and 2-dimethylammonium chloride ethyl substituents on the starch chains not only significantly reduced the surface tension and heterogeneous state of the starch paste, improved wetting and spreading of the paste on the fiber surface, but also played an internal plasticization on the starch adhesive layers, which is conducive to reducing the internal stresses within the adhesive layer and at the interface between the adhesive layer and fibers, hence promoting the bonding forces to three roving. With the increase in the total degrees of substitution, the surface tension was gradually decreased, and the bonding force was gradually increased. In addition, the bonding of PTAS to cotton roving was better than that to polyester roving. One main reason is that the positively charged 2-dimethylammonium chloride ethyl substituents can induce the electrostatic attraction between PTAS and cotton fiber, thereby promoting the adhesion of starch to cotton fiber.

Conclusion The propionylation-tertiary amination could improve the adhesion of starch, and this in turn promotes its sizing quality to warp yarns. This study proposed a new starch derivative (PTAS) for the warp sizing of polyester, polyester/cotton and cotton yarns and laid an important foundation for this application.

Key words: starch, sizing agent, propionylation-tertiary amination, degree of substitution, adhesion