A series of hydroxypropylated starch (HPS) that can be dissolved in water at 60-65℃ was obtained via two-step method in water system from corn starch. The structure and property of the HPS and its gelatinization temperature were characterized by Fourier transform infrared spectrometer (FTIR), nuclear magnetic resonance spectroscopy ( 1 H NMR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and transmission electron microscope (TEM). It was concluded that hydroxypropyl mainly bonded on the hydroxyl group at C2 position from anhydroglucose unit of starch in the form of C-O-C, and the substitution level at C6 position was slightly higher than that at C3 position; and the crystallinity of starch decreased from 52.41% to 29.4% due to the introduction of hydroxypropyl and was confirmed by XRD. At the same time, the grooves on the surface of starch granules were observed by SEM. The above-mentioned two synergism promoted the permeation and transmission of water molecules in the starch microstructure. Moreover, the gelatinization temperatures and enthalpy of synthetic HPS was lower than that of raw corn starch, as further confirmed by DSC. This caused the HPS with a molar substitution greater than 0.1 soluble in water at 65℃, and the dissolution state was similar to that of at 95℃ (transmittance above 55%), as well as exhibited high slurry stability. Interestingly, compared with the raw starch, the HPS film showed excellent mechanical property at the relative humidity of 65%, which could be attributed 2 to the hydrophilic ether bond and the flexible alkyl chain bonded on the structure of starch. This study will provide a new way for the preparation of high performance starch size for sizing yarn at medium low temperature.

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In this paper, size formulations for cotton yarns suitable for weaving fabrics in an environment of lower relative humidity (RHs) are investigated, which is desirable for both human comfort and the reduction of energy costs during fabric production. Moisture regain, tensile strength and abrasion resistance of cotton yarns sized with different size formulations were studied at 28℃ and various RHs. While the tensile strength of sized yarns with different size formulations was hardly affected by RH, both their abrasion resistance and weavability vary significantly with RH. Better abrasion resistance and weavability of cotton yarns sized with polyvinyl alcohol (PVA) and modified starch were achieved at 60% RH, and they were obtained at 70% RH for cotton yarns sized with PVA, modified starch and polyacrylic acid size. It was thus concluded that the selection of suitable size formulations could enable corresponding sized yarns to be weaved at lower RH. The suitable size formulation was composed of 60% oxidized starch, 30% PVA1799 and 10% polyacrylic acid size. It was noticed that better abrasion resistance of yarns sized with solely modified starches were obtained at 65% RH.

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