Structure and properties of syndiotactic polystyrene fibers prepared in high-speed melt spinning process

High-speed melt spinning of syndiotactic polystyrene was carried out using high and low molecular weight polymers, HMs-PS and LMs-PS, at the throughput rates of 3 and 6 g/min. The effect of take-up velocity on the structure and properties of as-spun fibers was investigated. Wide angle X-ray diffraction (WAXD) patterns of the as-spun fibers revealed that the orientation-induced crystallization started to occur at the take-up velocities of 2–3 km/min. The crystal modification wasα-form. Birefringence of as-spun fibers showed negative value, and the absolute value of birefringence increased with an increase in the take-up velocity. The cold crystallization temperature analyzed through the differential scanning calorimetry (DSC) decreased with an increase in the take-up velocity in the low speed region, whereas as the melting temperature increased after the on-set of orientation-induced crystallization. It was found that the fiber structure development proceeded from lower take-up velocities when the spinning conditions of higher molecular weight and lower throughput rate were adopted. The highest tensile modulus of 6.5 GPa was obtained for the fibers prepared at the spinning conditions of LMs-PS, 6 g/min and 5 km/min, whereas the highest tensile strength of 160 MPa was obtained for the HMs-PS fibers at the take-up velocity of 2 km/min. Elongation at break of as-spun fibers showed an abrupt increase, which was regarded as the brittle-ductile transition, in the low speed region, and subsequently decreased with an increase in the take-up velocity. There was a universal relation between the thermal and mechanical properties of as-spun fibers and the birefringence of as-spun fibers when the fibers were still amorphous. The orientation-induced crystallization was found to start when the birefringence reached — 0.02. After the starting of the orientation-induced crystallization, thermal and mechanical properties of as-spun fibers with similar level of birefringence varied significantly depending on the processing conditions.     

Comparision of the properties of UV-cured polyurethane acrylates containing different diisocyanates and low molecular weight diols

UV-curable polyurethane acrylate prepolymers were prepared from diisocyanates [isophorone diisocyanate (IPDI), 2,4-toluene diisocyanate (TDI), or 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI)], diols [ethylene glycol (EG), 1,4-butane diol (BD), or 1,6-hexane diol (HD)], polypropylene glycol as a polyol. UV-curable mixtures were formulated from the prepolymer (90 wt%), reactive diluent monomer trimethylol propane triacrylate (10 wt%), and photoinitiator 1-hydroxycyclohexyl ketone (3 wt% based on prepolymer/diluent). The effects of different diisocyanates/low molecular weigh diol on the dynamic mechanical thermal properties and elastic recovery of UV-cured polyurethane acrylate films were examined. The tensile storage modulus increased a little in the order of EG>BD>HD at the same diisocyanate. Two loss modulus peaks for all samples are observed owing to the glass transition of soft segments (T _gs ) and the glass transition temperature of hard segments (T _gh ). For the same diisocyanate,T _gs decreased, however,T _gh increased, in the order of HD>BD>EG. The elastic recovery also increased in the order of HD>BD>EG at the same diisocyanate. In case of same diols,T _gh increased in the order of H₁₂MDI>TDI>IPDI significantly. The ultimate elongation and elastic recovery increased in the order of TDI>IPDI>H₁₂MDI at the same diol.     

Dyeing and fastness properties of a reactive disperse dye on PET, nylon, silk and N/P fabrics

Dyeing and color fastness properties of a reactive disperse dye containing an acetoxyethylsulphone group on PET, Nylon, silk and N/P fabrics were examined. The reactive disperse dye exhibited almost the same dyeing properties on PET fabric as a conventional disperse dye except the level of dye uptake. The most appropriate pH and dyeing temperature for the dyeing of Nylon fabric were 7 and 100°C respectively. The build-up on Nylon fabric was good and various color fastnesses were good to excellent due to the formation of the covalent bond. Application of the reactive disperse dye on silk fabric at pH 9 and 80°C yielded optimum color strength. The rate of dyeing on Nylon fabric was faster than that on PET fabric when both fabrics were dyed simultaneously in a dye bath, accordingly color strength of the dyed Nylon was higher. The reactive disperse dye can be applied for one-step and one-bath dyeing of N/P mixture fabric with good color fastness.     

中国常规稻主栽品种的遗传结构及籼粳组分变化

 采用SSR标记分析了304份我国20世纪50-90年代生产上广泛应用的常规稻主栽品种的遗传结构及不同时期籼粳组分的变化。结果显示,我国常规稻主栽品种可明显分为籼、粳两类,籼稻的亚遗传结构比粳稻更为复杂,但晚籼和早粳类型的遗传背景略为单一。早、中、晚各季节类型与遗传结构的分型结果符合度较低。利用12个籼粳分化特异的SSR位点分析各品种的籼粳组分,发现20世纪90年代晚籼类型的粳型组分明显增加,而其他类型不同时期间籼粳组分的差异较小。研究结果对了解我国常规稻品种的遗传结构以及籼粳交育种具有一定的意义。