ABSTRACT:The values of the percentage crystallinity, melting temperature, birefringence, and cross-sectional area of ultrahigh molecular weight polyethylene (UHMWPE)/ low MWPE (LMWPE) as-prepared fiber specimens are reduced consistently as the formation temperatures decreased from 60 to 0°C. Much more sparse structures with significantly larger voids are found on the fractured surfaces of those as-prepared fibers that were prepared at higher formation temperatures than those prepared at lower formation temperatures. The cross sections of the as-prepared fiber specimens gradually change from an oblate to a nearly circular to an uneven circular shape as the formation temperatures are reduced from 60 to 10 to 0°C, respectively. It is worth noting that the achievable draw ratios (D ra ) of the as-prepared fibers reach maximum when they are prepared at an optimum formation temperature of 10°C. Moreover, the D ra values of the as-prepared fiber (UL 10 ) specimens can be further improved by using a two-stage drawing process, wherein the temperature used in the second drawing stage (T sec ) is higher than 95°C. In fact, the optimum T sec of the two-stage drawn UL 10 fiber specimens increases significantly from 105 to 115°C as the first-stage draw ratio (D lr ) values increase from 20 to 40, respectively. The birefringence values, tensile strengths, and moduli of one-and two-stage drawn UL 10 fiber specimens increase consistently with increasing draw ratios, although the increasing rate of these values is gradually reduced as the draw ratios are greater than certain values. In contrast, at a constant draw ratio, the two-stage drawn UL 10 fiber specimens drawn at a higher T sec always exhibit higher values of birefringence, tensile strengths, and moduli than those with the same D lr but drawn at a lower T sec . Moreover, at a constant draw ratio, the birefringence values, tensile strengths, and moduli of the fiber specimens drawn at a fixed optimum T sec reach the maximum when they are first drawn up to an optimum D lr of about 50. In fact, by using the proper optimum T sec and D lr , the tensile strengths and moduli of the two-stage drawn UL 10 fiber specimens can reach more than 11 and 155 GPa, respectively. The possible mechanisms accounting for these interesting properties are proposed in this study.

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Efficacy of added nano-CaCO3 (NC) on engineering performances, including fluidity, initial setting time, bleeding rate and yield stress of cement grouts was investigated in this study. Results showed that the fluidity and bleeding rate for NC-cement (NCC) composite grout first decreased with increased NC content (i.e., ratio of NC mass to cement mass) and then slightly recovered as the NC content exceeded 2%. The initial setting time was always reduced while the yield stress increased with increased NC content. The microstructure of NCC was analyzed by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the NC can promote the cement hydration, but an excess amount of NC will inhibit the cement hydration and affect the engineering performances of cement grouts. The optimum NC content for modification of cement grouts was thus 2%.

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