Abstract:

Objective The large number of hydroxyls in starch molecules and the rigid cyclic structure of starch molecules result in insufficient adhesion to fibers, especially polyester and other synthetic fibers, and it is difficult to meet the requirements of warp sizing well. The aim of this study was to prepare a new type of starch-g-poly(3-acrylamidopropyl trimethylammonium chloride/methyl acrylate) [S-g-P(ATC/MA)] used as sizing agent with excellent adhesion properties by introducing both quaternary ammonium cations and ester groups simultaneously into starch molecules through a graft copolymerization reaction, so as to improve the sizing quality.
Method With 3-acrylamidopropyl trimethylammonium chloride (ATC) and methyl acrylate (MA) as monomers and acid-thinned starch (ATS) as raw material, four types of S-g-P(ATC/MA) with different mole fractions of ATC units in the branches were prepared by adjusting the mole ratio of ATC to MA when the total mass of the monomers was 15% of that of ATS. The molecular structures of ATS and S-g-P(ATC/MA) were characterized using an IRPrestige-21 Fourier transformation infrared spectrometer. The nitrogen element and ester group content of S-g-P(ATC/MA) samples were tested by Kjeldahl method and a saponification reaction, respectively, and their grafting ratios were analyzed. The adhesion force of S-g-P(ATC/MA) was obtained by stretching the slightly sized roving using a universal materials testing machine. The Zeta potential and light transmittance of S-g-P (ATC/MA) paste were measured using a Zetasizer Nano-ZS90 analyzer and a UV9600 spectrophotometer, respectively.
Results Comparing the FT-IR spectra of S-g-P(ATC/MA) and ATS, three new sharp absorption peaks appeared in the spectra of S-g-P (ATC/MA). The sharp absorption peak of S-g-P(ATC/MA) at 1 641 cm^-1 was attributed to the C＝O double bond stretching vibration of amide carbonyl, and the sharp absorption peak at 1 481 cm^-1 was attributed to the stretching vibration of C—N. The sharp absorption peaks at these two locations confirmed that the grafted branches contained quaternary ammonium cations. In addition, the sharp absorption peak of S-g-P (ATC/MA) at 1 736 cm^-1 was attributed to the stretching vibration of ester carbonyl group. The sharp absorption peak here confirmed that the grafted branches contained ester groups. It was confirmed by FT-IR analysis that S-g-P(ATC/MA) was successfully prepared. When the total amount of monomers is constant, the influence of the mole ratio of ATC to MA on the grafting ratio is not obvious, and the grafting ratio of S-g-P(ATC/MA) prepared is basically the same, all about 7%. When the total amount of monomers is constant, with the increase of the mole fraction of ATC units in the branches, the Zeta potential and light transmittance of S-g-P (ATC/MA) paste increase gradually, and the water dispersibility of S-g-P(ATC/MA) paste gradually improves. When the total amount of monomers is constant, the adhesion force of S-g-P(ATC/MA) to cotton fibers and polyester fibers gradually increases with the increase of the mole fraction of ATC units in the branches. When the mole fraction of ATC units in the branches increases from 20.5% to 81.1%, the adhesion force of S-g-P(ATC/MA) to cotton fibers increases from 71.57 N to 76.92 N, and its adhesion force to polyester fibers increases from 118.35 N to 127.42 N.
Conclusion S-g-P(ATC/MA) increases the Zeta potential of its paste, improves the water dispersibility of its paste, reduces the internal stress and stress concentration within the starch adhensive layer and at the bonding interface by virtue of the hydrophilic quaternary ammonium cations contained in the grafted branches, and thus enhances the adhesion force to fibers. S-g-P(ATC/MA) can improve the adhesion properties to cotton fibers and polyester fibers more compared to S-g-PMA. The successful development of S-g-P(ATC/MA) used as sizing agent will promote the high-value application of starch.

Key words: cation, acrylate, grafted starch, sizing agent, adhesion property, grafting ratio