PLA/ATBC增塑改性体系结晶热性能及耐老化性能的研究

采用熔融共混法,以乙酰柠檬酸三正丁酯(ATBC)作为增塑剂,对聚乳酸(PLA)进行增塑改性,讨论了增塑剂用量对改性PLA结晶热性能及耐老化性能的影响.研究发现:当增塑剂ATBC含量增加时,改性PLA中存在β晶型向α晶型的转变,增塑剂的加入可以使改性PLA的熔点(Tm)、玻璃化转变温度(Tg)降低,结晶度增加;起始热分解温度(Te)和最大热分解温度(Ti)增加,热稳定性变好;增塑剂ATBC的加入可以很好的改善PLA的柔韧性,且当w(ATBC)为20份时,改性PLA的拉伸屈服强度、直角撕裂强度分别为30.16MPa和119.29 kN/m,断裂伸长率增加至380.65%,增塑改性效果最好,即使是在自然条件下老化一年后,其综合力学性能仍可以满足一般产品的要求.

基于水浴静电纺的芳纶/PA6纳米纤维包芯纱制备与表征

针对单一纳米纤维纱力学性能较差、进一步后加工困难、应用受限等问题,本文采用静电纺丝法在水浴表面收集纳米纤维,制备以芳纶1414(PPTA)长丝为芯层、聚酰胺6(PA6)纳米纤维为皮层的PPTA/PA6纳米纤维包芯纱,并分析了纳米纤维包芯纱和外层纳米纤维包覆层的结构与性能。结果表明:纳米纤维均匀地包覆在芯纱外层,纳米纤维的直径范围主要分布在90~110 nm,平均直径为98.81 nm;纳米纤维包覆层的熔点为223.16℃,结晶度为18.55%,与常规PA6纤维接近;纳米纤维包芯纱的力学性能与芯纱接近,且纳米纤维包覆层也具备一定的力学性能,平均强度为0.57 cN/dtex,平均伸长率为33.30%;纳米纤维包覆层具有一定的耐摩性,经棉织物摩擦600次后其形态结构基本未发生变化。

Microstructure and mechanical properties of as-cast and extruded biomedical Mg-Zn-Y-Zr-Ca alloy at different temperatures

A type of biomedical magnesium alloy Mg-3Zn-1Y-0.6Zr-0.5Ca was cast and extruded at three extrusion temperatures of 270, 300 and 330 °C. The microstructure and mechanical properties of the cast and extruded alloys, tailored at different extrusion parameters, were investigated using tensile tests, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, transmission electron microscopy and electron backscattered diffraction. Optimum comprehensive mechanical properties are achieved in the alloy extruded at 270 °C, the ultimate tensile strength and the elongation reach 315 MPa and 26%, respectively, which is deemed to be associated with the grain refinement, weak basal texture and second phases strengthening. After hot extrusion, extensive dynamic recrystallization is found in the Mg-3Zn-1Y-0.6Zr-0.5Ca alloy. Continuous Mg3YZn6 phase bands are gradually broken into discontinuous chain-like or dot-like structures, and the grains distribute more uniformly. The as-extruded Mg-3Zn-1Y-0.6Zr-0.5Ca alloy exhibits a weak texture with (0001) basal planes parallel to the extrusion direction.

Transformation of β to α phase of isotactic polypropylene nucleated with nano styrene butadiene rubber-based β-nucleating agent under microwave irradiation

This paper investigates the effect of microwave irradiation on theβtoαphase transformation of theβ-nucleated isotactic polypropylene(iPP).Ten microwave irradiation cycles was applied to the iPP and iPP modified with 0.3 wt%and 0.5 wt%β-NA,and the data at 2nd,4th,6th,8th and 10th irradiation were reported.As expected,the sample temperature was found to increase with the irradiation time,by more than 130°C,due to high frequency of microwave processing.This was the major factor that induced theβ-phase transformation and structural change.Both the differential scanning calorimetry(DSC)and X-ray diffraction(XRD)results indicated thatβ-phase was mainly transformed toα-phase and partially converted to the amorphous section.It was reflected as 1)the reduction of the enthalpy ofβ-crystal melting(ΔHmβ),2)the increased enthalpy ofα-crystal melting(ΔHmα),3)the decreasedβ-crystalline phase fraction(Kβ)and 4)the decrease of the overall degree of crystallinity(Xall).Under impact force,neat iPP showed a slight increase in the impact strength with the irradiation time,due to the increase of amorphous region.For theβ-iPP,it decreased due to the reduction of theβ-phase content.

Effect of Si and Ti on dynamic recrystallization of high-performance Cu-15Ni-8Sn alloy during hot deformation

Effect of Si and Ti on dynamic recrystallization(DRX)of Cu-15Ni-8 Sn alloy was studied using hot compression tests over deformation temperature range of 750-950℃and strain rate range of 0.001-10 s^-1.The results show that the dynamic recrystallization behavior during hot deformation is significantly affected by the trace elements of Si and Ti.The addition of Si and Ti promotes the formation of Ni16Si7Ti6 particles during hot deformation,which promotes the nucleation of dynamic recrystallization by accelerating the transition from low-angle boundaries(LABs)to high-angle boundaries(HABs).Ni16Si7Ti6 particles further inhibit the growth of recrystallized grains through the pinning effect.Based on the dynamic recrystallization behavior,a processing map of the alloy is built up to obtain the optimal processing parameters.Guided by the processing map,a hot-extruded Cu-15 Ni-8Sn alloy with a fine-grained microstructure is obtained,which shows excellent elongation of 30%and ultimate tensile strength of 910 MPa.

Study on structural,mechanical and thermodynamic properties of TiAl alloy under high pressure based on first-principles

The effect of pressure on structural, mechanical properties as well as the temperature dependence of thermodynamic properties of TiAl alloy are investigated by implementing first-principles calculations. The results show that the volume decrea-ses with the pressure increasing. We calculated the CtJ at various pressures and all the results satisfy mechanical stability crite-ria, thus the TiAl alloy is mechanically stable. The elastic constants？ bulk modulus and shear modulus calculated are well in a-greement with the calculated values at zero the pressure. The bulk modulus and shear modulus increase with the pressure in-creasing, which reflects the deformation resistance, and accordingly, deformation resistance can be strengthened with the in-crease of pressure. The brittle nature of TiAl alloy turns to ductile nature in 10 - 20 GPa . The Debye temperature, linear ther-mal expansion and heat capacity are calculated using the quasi-harmonic Debye model under the pressure ranging from 0 to 50 GPa and the temperature ranging from 0 to 1 000 K, which are useful to investigate the effect of temperature and pressure on thermodynamic parameters. Finally, electronic structure is calculated at various pressures,and it can be found that the peak intensity decreases with increasing pressure and the the strength of d-d orbital of Ti is weakened but the ductility is enhanced.

Hot workability of cast and wrought Ni-42Cu alloy through hot tensile and compression tests

In order to analyze the flow behavior and workability of Ni-42Cu in cast and wrought conditions, hot deformation tests were performed at temperatures and strain rates within the ranges of 900-1150 ℃ and 0.001-1 s^-1, respectively. Tensile tests showed a “hot ductility trough” at 950 ℃ for both alloys. The drop in hot ductility was more considerable in the cast alloy because of the sluggish dynamic recrystallization. The hot ductility drop and grain boundary cracking, particularly in the cast alloy, were attributed to the segregation of detrimental atoms to the boundaries. It was shown that the hot ductility of the wrought alloy could be improved with increasing strain rate. It was associated with increasing the fraction of dynamic recrystallization at higher strain rates. This finding corroborated the change in the mechanism of dynamic recrystallization with strain rate. The strain rate sensitivity and instability parameters calculated for the wrought alloy showed that the material is prone to strain localization at low temperatures, i.e., 950-1050 ℃, and high strain rates of 0.1 and 1 s-1. Based on the tensile and compression tests, the best temperature range for a desirable hot workability was introduced as 1050-1150 ℃.

Impact of Zn(Ⅱ)Ions on Crystallization and Thermal Properties of Poly(lactic acid)

The issues of low crystallinity and slow crystallization rate of poly(lactic acid)(PLA)have been widely addressed.In this work,we find that doping PLA with Zn(Ⅱ)ions can speed up the process of crystallization of PLA.Three kinds of Zn(Ⅱ)salts(ZnCl2,ZnSt and ZnOAc)were tested in comparison with some other ions such as Mg(Ⅱ)and Ca(Ⅱ).The increased crystallinity and crystallization rate of PLA doping with Zn(Ⅱ)are reflected in FT-IR and variable temperature Raman spectroscopy.The crystallinity is further confirmed or measured with differential scanning calorimetry and X-ray diffraction.The crystallinity rate of the PLA/ZnSt-0.4 wt%material can reach 22.46% and the crystallinity rate of the PLA/ZnOAc-0.4 wt%material can reach 24.83%,as measured with differential scanning calorimetry.

Fabrication and Properties of Microencapsulated n-octadecane and Paraffin

Microencapsulated n-alkanes as energy- storage materials have promising application prospects. The ndcrocapsules containing 100 - 50 wt% of n - octadecane, 0 -20 wt% of paraffin and 0 - 30 wt% of cyclohexane were synthesized by in-situ polymerization using melamine- formaldehyde polymer as shell. Cyclohexane was removed after heat-treated the microcapsules at 100℃. The morphologies, cell parameters, phase change properties, thermal stable temperatures of these microcapsules were examined. The diameters of these microcapsules are lower than 5 μm. The effect of paraffin in the microcapsules on the cell parameters of n-octadecane is negligible. The paraff＇m is effectively used as a nucleating agent to decrease the degree of supercooling. The melting enthalpy is decreased from 132 J/g to 111 J/g due to the increase of the cyclohexane contents. The thermal stable temperature is enhanced 6 - 16℃ after heat-treated the microcapsules at 160℃ for 30 min.