Novel oxide fiber composites by freeze casting

A freeze casting process with gelatine as gelling agent is presented to manufacture novel oxide fiber composites. The growth of ice crystals causes an in situ densification of the green matrix when the composite is frozen after the lamination of 2D-fabrics. This freeze casting process leads to a porous matrix with a cellular morphology, showing no shrinkage during sintering. The porous structure is suitable for a subsequent infiltration with a precursor to densify the matrix. As the matrix is crack-free, the sintered composites have high mechanical properties. The processing is demonstrated by manufacturing laminated Nextel™610/YAG-ZrO₂ oxide fiber composites.     

Novel freeze-casting fabrication of aligned lamellar porous alumina with a centrosymmetric structure

A novel freeze-casting method is used to fabricate aligned lamellar porous alumina with a centrosymmetric structure from aqueous alumina slurries. Two cold fronts oriented perpendicularly to each other, originating from the bottom and side of the cylindrical copper mold, induce the growth of ice crystals in specific directions along the radius of the cylindrical mold. Lamellar channels of porous alumina are arranged centrosymmetrically along the radial axis. The pore distribution of the currently prepared porous ceramics is more regular when compared with that of porous ceramics prepared by conventional freeze casting. This affords porous ceramics with improved mechanical properties and stability. The current method addresses the issue of partial failure as induced by the randomly distributed channels in lamellar porous ceramics.     

三元乙丙橡胶/聚丙烯热塑性硫化胶细观力学数值模拟分析Ⅱ.三元乙丙橡胶结构对细观力学性能的影响

通过建立三元乙丙橡胶(EPDM)/聚丙烯(PP)热塑性硫化胶(TPV)的细观尺寸多颗粒随机分布的RVE模型,研究了分散相EPDM粒子形状及大小、间距对TPV应力和弹性模量的影响。结果表明,在分散相EPDM体积分数不变的条件下,EPDM粒子形状越接近圆形,TPV的应力值越低,EPDM粒径的减小可提高TPV的弹性模量;EPDM粒子间距增大,TPV的应力值下降,TPV中EPDM体积分数越高,其应力值受EPDM粒子间距的影响越显著。     

Morphology and crystallization behavior of nylon 6‐clay/neat nylon 6 bicomponent nanocomposite fibers

Nylon 6‐clay hybrid/neat nylon 6, sheath/core bicomponent nanocomposite fibers containing 4 wt % of clay in sheath section, were melt spun at different take‐up speeds. Their molecular orientation and crystalline structure were compared to those of neat nylon 6 fibers. Moreover, the morphology of the bicomponent fibers and dispersion of clay within the fibers were analyzed using scanning electron microscopy and transmission electron microscopy (TEM), respectively. Birefringence measurements showed that the orientation development in sheath part was reasonably high while core part showed negligibly low birefringence. Results of differential scanning calorimetry showed that crystallinity of bicomponent fibers was lower than that of neat nylon 6 fibers. The peaks of γ‐crystalline form were observed in the wide‐angle X‐ray diffraction of bicomponent and neat nylon 6 fibers in the whole take‐up speed, while α‐crystalline form started to appear at high speeds in bicomponent fibers. TEM micrographs revealed that the clay platelets were individually and evenly dispersed in the nylon 6 matrix. The neat nylon 6 fibers had a smooth surface while striped pattern was observed on the surface of bicomponent fibers containing clay. This was speculated to be due to thermal shrinkage of the core part after solidification of the sheath part in the spin‐line. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39996.     

Synthesis,characterization and biocompatibility evaluation of sol–gel derived bioactive glass scaffolds prepared by freeze casting method

In this study, a new class of bioactive glass scaffolds was prepared through freeze casting method for bone tissue engineering applications. After analyzing the structural characteristics of the scaffolds, in vitro biological evaluations were assessed through monitoring alkaline phosphatase (AP) activity of osteoblast cells and soaking in simulated body fluid (SBF) for different time intervals. It was shown that the scaffolds consisted of bioactive glass plates with interconnected pores between them, aligned along the ice growth direction. The ability of the scaffolds for supporting the growth of human fetal osteoblastic cells (hFOB 1.19) was approved. Moreover, inductively coupled plasma-atomic emission spectrometry (ICP-AES) showed meaningful compositional changes of calcium, phosphorus and silicon in SBF solution, indicating the apatite forming ability of the scaffolds. The present investigation revealed that freeze casting could be an effective method for the preparation of highly bioactive scaffolds. In addition, the scaffolds proved to be highly compatible for the proposed works in vivo.     

Suspension stability and sintering influence on yttria-stabilized zirconia fabricated by colloidal processing

The stability of nano-zirconia 3YSZ powder in suspension was extensively studied by the colloidal method, and the optimum sintering temperature of the green sample fabricated through slip casting was determined. Zirconia suspensions with 10 vol% powder loading were prepared with distilled water, and HNO₃ was used to adjust the pH of the suspension to pH 1–6. All of the suspensions were subjected to sedimentation test, and the results showed that the suspensions adjusted to pH 2 had the lowest sediment volume. This finding indicates that a suspension with pH 2 produces higher packing density. Viscosity test was carried out for the suspensions added with dispersant ranging from 0.3 wt% to 0.7 wt% polyethyleneimine (PEI) with and without pH adjustment. The suspension containing 0.5 wt% PEI with pH 2 adjustment produced the lowest viscosity because of interparticle bond breakage in the aggregates, thus forming colloidally stable suspensions. The zirconia suspension containing 0.5 wt% PEI and whose pH was adjusted to pH 2 was chosen to be slip casted into cylindrical shape. Green samples were sintered at various sintering temperatures that ranged from 1100 °C to 1500 °C through a two-step sintering method. The sample sintered at 1500 °C was found to be porosite-free, and its highest relative density was 99.6% of the theoretical density. Morphological studies detected pores in the microstructure of the samples sintered at low sintering temperatures (1100 and 1200 °C). By contrast, the samples sintered at 1400 and 1500 °C were fully densified. However, the grain size of the sample sintered at 1500 °C was 230 nm, which indicated excessive grain growth. The Vickers hardness of the sample sintered at 1400 °C was found to be highest (12.9 GPa) and comparable to results found in the literature.     

双恶唑啉及环氧类扩链剂对PA6的改性效果比较

通过熔融挤出的方法分别用环氧类扩链剂和双恶唑啉类扩链剂对尼龙(PA)6进行扩链增黏,并对扩链产物的特性黏度,力学性能和加工性能等进行了测试,对比了两类扩链剂对PA6的改性效果。结果表明,当这两类扩链剂的质量分数均为0.9%时,PA6的各项性能最佳;双恶唑啉类扩链剂对PA6的改性效果比环氧类扩链剂要好。相对于纯PA6,添加质量分数为0.9%的双恶唑啉类扩链剂,可使扩链PA6的特性黏度由0.86 d L/g增加到1.57 d L/g,熔体流动速率由14.3 g/10 min降到5 g/10 min,缺口冲击强度由5.5 k J/m2增加到7.3 k J/m2,拉伸强度由54 MPa增加到65.85 MPa,断裂伸长率由130%增加到450.9%,弯曲强度由53.16 MPa增加到72.66 MPa,平衡扭矩由2.1 N·m升高到5.3 N·m。     

无卤阻燃增强高流动性尼龙6的研究

采用高流动性尼龙(PA)6为原料,制备了一系列玻璃纤维(GF)增强无卤阻燃PA6材料。考察了材料配方和挤出工艺对改性材料阻燃性能、力学性能、热性能及熔体流动速率(MFR)的影响,并对其原因进行了分析。结果表明,与普通PA6相比,高流动性PA6由于熔体黏度低、MFR高,有利于无卤阻燃剂和GF在基体材料内的混合和分散,因此在同样配方和工艺条件下,显示出更好的阻燃效果与更优的力学性能。     

医用尼龙血液过滤网材料的差热分析

医用尼龙血液过滤网材料的标准鉴别方法为差热分析(DSC),但尼龙材料的多重熔融以及加工历史、测试条件等给熔点测试带来许多不确定因素。文章通过改变DSC测试条件,测试某定型尼龙血液过滤网材料,分析其材料种类和加工热历史等信息,并进一步确定应用差热分析技术定性鉴别常见医用尼龙血液过滤网材料品种的合理程序。     

马来酸单聚乙二醇单甲醚酯的合成及应用

采用无溶剂法合成了马来酸单聚乙二醇单甲醚酯,并对其合成工艺进行了探讨。实验以原料醇酸物质的量比、催化剂用量、阻聚剂用量、反应温度和反应时间为5因素,设计成5因素4水平的正交实验,由实验确定出组分质量分数和最佳酯化反应条件：醇酸物质的量比1.0∶1、催化剂质量分数5%、阻聚剂质量分数3%、反应温度120℃,反应时间为5 h,最佳酯化条件下酯化率达到95.25%。进一步由大单体与丙烯酸、丙烯酸丁酯、烯丙基苯磺酸钠共聚制备出水煤浆分散剂,由大同煤制浆,在分散剂质量分数为1.0%,干粉煤质量分数为65%时,水煤浆粘度为1550mPa·s-1,静置90min后,粘度为2100mPa·s-1。