Fabrication of Degradable Bone-Like Substitutes Based on Poly-L-lactide and β-tricalcium Phosphate

Composite bone-like substitutes composed of poly-L-lactide (PLLA) and β-tricalcium phosphate (β-TCP) (average particle size: 4.43 μm) were fabricated and the properties were investigated. β-TCP was prepared by wet chemical precipitation, followed by calcining at 800°C. Composite films were obtained by completely mixing dissolved PLLA with granules of β-TCP; the agglomerated β-TCP powder granules were distributed homogeneously in the PLLA matrix. PLLA/β-TCP composite materials were obtained by cold and hot pressing the composite film at a pressure of 130 MPa and temperature of 185°C–195°C. With increase of the amount of β-TCP powder, the bending strength of the composites decreased while the bending modulus increased. The fracture mechanism of the composites was significantly influenced by the content of β-TCP powder, from ductile fracture to brittle fracture as the β-TCP powder content increased.     

The Preparation and Study on Ultrahigh Molecular Weight Polypropylene Gel‐spun Fibers

A novel polypropylene (PP) fiber was prepared by using gel spinning/crystallization from dilute solutions of ultrahigh molecular weight isotactic polypropylene (i‐UHMWPP), and subsequently drawing at various temperatures. The influence of drawing temperature on the properties of the resulted fibers was investigated. We found that the draw‐ability and mechanical as well as crystallization properties of the fibers obtained were dramatically improved with increasing drawing temperature. When the drawing temperature is below the α‐crystal relaxation temperature of PP, which was measured by wide‐angle X‐ray diffraction (WAXD) analysis as 100–120°C, the fibers are characterized by lower crystallinity and smaller crystals with less perfection, resulting in brittle fracture and subsequently poor mechanical durability. With drawing at temperatures above the α‐crystal relaxation temperature of PP, a novel UHMWPP fiber with Young's modulus of 27 GPa and tensile strength of 1.3 GPa was obtained. Higher crystallinity and larger crystals with better perfection and orientation were observed in this fiber.     

Development of continuous hydrothermal hot-pressing apparatus

Abstract

A process for continuous hydrothermal hot-pressing has been examined, with the resultant development of a new continuous hydrothermal hot-pressing apparatus. In this study, amorphous siliceous material, slaked lime and pulp fiber were mixed and solidified, at 200°C, to produce a board product. The duration of the hydrothermal hot pressing reaction process was 17 minutes. The bending strength of the board product was high; 11MPa.     

Preparation of Mg55Ni35Si10 Amorphous Powders by Mechanical Alloying and Consolidation by Vacuum Hot Pressing

Amorphous Mg55Ni35Si10 powders are fabricated by using a mechanical alloying technique. The amorphous powders are found to exhibit a relatively high crystallization temperature of 380℃. The as-milled amorphous Mg55Ni35Si10 powders are consolidated successfully into bulk body by vacuum hot pressing technique. Limited nanocrystallization is noticed. The Vickers microhardness range of the Mg55Ni35Si10 bulk sample is 7834 to 8048 MPa. Its bending strength and compressive strength are 529 MPa and 1466 MPa, respectively.     

AlON-TiN复相材料合成工艺参数的支持向量回归分析

根据在不同热压烧结工艺参数（包括TiN的含量、烧结温度和保温时间）下合成的AlON-TiN复相材料的抗弯强度实测数据集,应用基于粒子群算法寻优的支持向量回归（SVR）方法,建立了AlON-TiN复相材料在不同热压烧结工艺参数下抗弯强度的SVR预测模型,并与基于人工神经网络（ANN）模型的预测结果进行了比较.利用SVR预测模型并结合粒子群算法对AlON-TiN合成工艺参数进行了寻优和多因素分析.结果显示:对于相同的训练样本和检验样本,AlON-TiN复相材料抗弯强度的SVR模型比ANN模型具有更小的预测误差,表明SVR模型比ANN模型具有更强的预测能力.工艺参数寻优结果表明,当TiN质量分数为13.5%、烧结温度为1863.5 ℃和保温时间为5.8 h时, 可获得抗弯强度为555.452 MPa的AlON-TiN复相材料. 研究结果表明,该方法对于研发理想抗弯强度的AlON-TiN复相材料具有重要的理论指导意义和实用价值. 关键词： AlON-TiN 抗弯强度 支持向量回归 回归分析     

Hydrothermal hot pressing for recycling of waste glass

Abstract

Recycling of waste glasses has been conducted by a hydrothermal hot-pressing method to produce high density compacts. Our research was focussed on the intluence of various reaction variables (temperature, time, water content and loading pressure) during compaction of several types of waste glasses. The compaction of all glasses starts around 120°C and proceeds rapidly with increasing temperature. Under hydrothermal hot pressing conditions, the compaction of the waste glass is most strongly controlled by temperature and water content, and affected to a lesser degree by reaction time and loading pressure. A maximum tensile strength of 65 MPa was obtained for ‘blue’ glass at 200°C, 10wt% water content, after applying 60 MPa loading pressure for 2 hours.     

Experimental study of pressure and density of saturated and superheated vapor of refrigerant R-236ea from 20 to 150 °C

The saturation pressure, pressure and density of superheated vapor of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea, R-236ea) were studied by an isochoric piezometer within the temperature range of 294–423 K up to the pressure of 4.0 MPa. The uncertainties of temperature, pressure, and density measurements were estimated as ±20 mK, ±1.5 kPa, ±(0.1–0.2) %, and ±(0.1–0.2) %, correspondingly. The purity of studied samples was 99.68 mass %. The obtained experimental data are shown as tables and analytical equations. Coefficients of the virial state equation were calculated for R-236ea on the basis of these data. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 04-02-16355).     

Void content and interfacial properties of composite laminates under different autoclave cure pressure

With an identical temperature profile, various cure pressures were applied to determine the effect of cure pressure on void distribution and interlaminar shear strength (ILSS) of [0]₁₀ T800/X850 composite laminate. Void shape, distribution, and void content within the composite laminates were characterized using optical microscope. The ILSS was evaluated using short-beam three-point bending tests and their interface debonding failure and fracture surfaces were determined using scanning electron microscope. The experimental results indicated that long strips voids are generated in the low-pressure curing stage. The voids mainly exist in the two forms of rod-like shape and spherical shape, and their number and size decrease as the cure pressure increases. The influence of cure pressure on the void content and ILSS shows a different trend in two stages: when the cure pressure is lower than 0.4 MPa, the ILSS decrease by 5.21% with 1% increase in void content, and their relationship is inversely linear. However, when the cure pressure is higher than 0.4 MPa, the void content is less than 1% and ILSS increase slightly by 1.69% when the cure pressure goes from 0.4 to 0.6 MPa, the influence of cure pressure on void content and ILSS is clearly presented.     

Development of Stereocomplex Crystal of Polylactide in High-Speed Melt Spinning and Subsequent Drawing and Annealing Processes

High-speed melt spinning of racemate polylactide (r-PLA), which is a blend of equal amounts of poly(l-lactide) and poly(d-lactide) molecules, was performed up to the take-up velocity of 7.5 km/min. In the fiber structure analysis, particular attention was paid to the formation of stereocomplex crystals, because this crystal form has a melting temperature about 60° higher than the homocrystals. It was found that highly oriented and highly crystallized fibers containing the α-form and stereocomplex crystals were obtained when the take-up velocity exceeded about 4 km/min. The amount of stereocomplex crystal was higher under the spinning conditions of higher take-up velocity, lower throughput rate, and lower extrusion temperature. Under these conditions, higher tensile stress can be applied to the spinning line, and therefore, the orientation-induced crystallization is promoted. Annealing of the fibers obtained at high-take-up velocities, such as 6 km/min, which already have the crystalline structure with a certain amount of stereocomplex crystal, at a temperature between the melting temperatures of α-form and stereocomplex crystals, yielded the fiber structure mainly consisting of highly oriented stereocomplex crystal. The annealed fibers showed fairly high mechanical properties and good thermal stability.     

Influence of Degradation of Poly-L-lactide on Mass Loss,Mechanical Properties,and Crystallinity in Phosphate-Buffered Solution

A bulk degradation of poly-L-lactide (PLLA) rectangular bars was studied by incubating them in phosphate-buffered solution at 37°C for different periods. The characteristics of the mass, water uptake, mechanical properties, thermal behavior, and crystallinity of the PLLA samples were investigated. The results indicate that mass loss and water uptake of PLLA increase with increasing time; however, pH value and mechanical strength decrease. The melting temperature, melting enthalpy, and crystallinity of PLLA firstly increase and then decrease with increasing degradation time. There is no new diffraction peak formed with increasing degradation time, which indicates that the degradation could occur in the amorphous regions firstly and then in the crystalline regions.     

Comparison of the properties of Nextel 720/SiC composites at room temperature and 1300°C

Continuous Nextel 720 fibers reinforced SiC composites with PyC interface are fabricated by LPCVI at 1000°C for 200 h using SiCH₃Cl₃ as precursor. The mechanical properties at RT and 1300°C are measured by three-point bending. The microstructures of the interface are characterized by TEM. The results indicate the composites have the metal-like behavior of fracture, whether they are at RT or high temperature. The RT and 1300°C strengths are 310 MPa and 140 MPa, respectively. The RT and 1300°C strains are 0.32% and 0.12%, respectively. The loss of flexural strength and strain of the Nextel 720/SiC composites at high temperature result from stronger residual thermal stress caused by the mismatch of CTE between fibers and matrix. A gap appears between fibers and PyC interface after the 1300°C test, which could be resulted from 7.7% compressive strain of PyC interface caused by the residual thermal stress and 0.1% sintering shrinkage of Nextel 720 fiber.     

新型高准确度光纤光栅压力传感系统

提出一种使用光纤双布喇格光栅测定压力的测量方法.在外界压力作用下,传感光纤布喇格光栅反射波长的漂移,被转变成在交变力策动下,发生弯曲的等强度悬臂梁调制扫描光栅反射光脉冲间隔的变化.实验结果表明,光纤布喇格光栅反射波长漂移的测量范围为0～3 nm,波长测量的不确定度为1 pm;压力传感器的量程为0～6 MPa时,压力的测量不确定度为0.005 Mpa.     

Co-precipitation of asiatic acid and poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) using rapid expansion of subcritical solutions into liquid solvents

Poly(l-lactide) (PLLA) nanoparticles loaded with asiatic acid (AA) were successfully produced by rapid expansion of a subcritical solution into an aqueous receiving solution containing a dispersing agent. A mixture of carbon dioxide (CO₂) and ethanol (EtOH) with a weight ratio of 1:1 was used as the solvent for AA and PLLA. Two surfactants, Pluronic F127 and sodium dodecyl sulfate were employed. The former was found to be more effective for stabilizing AA-loaded PLLA nanoparticles, as a rapid expansion into a 0.1 wt% Pluronic F127 solution produced a stable nanosuspension consisting mainly of well-dispersed, individual nanoparticles. The effects of rapid expansion-processing conditions—AA to PLLA weight ratio and pre-expansion temperature (T_pre)—on the size and morphology of composite nanoparticles, and the loading capacity and entrapment efficiency of AA in PLLA nanoparticles, were systematically investigated. It was found that AA-loaded PLLA nanoparticles with a size range of 30–100 nm were consistently fabricated by rapid expansion at T_pre of 70–100 °C and AA to PLLA weight ratios of 1:2 and 1:4, and with a constant pre-expansion pressure of 330 bar. The T_pre and AA to PLLA weight ratio had no significant effects on the size of the nanoparticles. The AA to PLLA weight ratio is a controlling parameter for both the loading capacity and the entrapment efficiency of AA in PLLA nanoparticles. The loading capacity and entrapment efficiency increased from 8–11 to 16–21 wt%, and 38–57 to 50–62 wt%, respectively, when the AA to PLLA weight ratio changed from 1:4 to 1:2. However, increasing the T_pre from 70 to 100 °C decreased both the loading capacity and entrapment efficiency of AA in PLLA nanoparticles by ~20–30%.     

Self-Reinforced High-Density Polyethylene Prepared by Low-Frequency,Vibration-Assisted Injection Molding. 1. Processing Conditions and Physical Properties

Using a low-frequency, vibration-assisted injection molding (VAIM) device, the effects of vibration variables (frequency and amplitude) on mechanical properties and thermal softening temperature of high-density polyethylene (HDPE) injection moldings were investigated. For VAIM-processed samples, the mechanical properties can be improved by changing vibration frequency and vibration pressure amplitude. Injected at a constant vibration pressure amplitude, a low range of frequency (below 0.7 Hz) was favorable for increasing yield strength; in the high range of frequency (0.7 Hz < f < 2.33 Hz) the yield strength remained at a plateau. Injected at a constant frequency (0.7 Hz) the yield strength increased sharply with decreased elongation when applying large vibration pressure amplitude. The maximal yield strength and Young's modulus were 60.6 MPa and 2.1 GPa for a VAIM sample compared with 39.8 MPa and 1.0 GPa for a conventional injection-molded (CIM) sample, respectively; there was also a 10°C increase in Vicat softening point temperature.     

Beneficial effects of an ultra-fine α-SiC incorporation on the sinterability and mechanical properties of ZrB2

A fully dense ZrB₂ ceramic containing 10 vol. % ultra-fine α-SiC particulate was successfully hot pressed at 1900 °C for 20 min and 40–50 MPa of applied pressure. Faceted ZrB₂ grains (average size ≈3 μm) and SiC particles dispersed regularly characterized the base material. No extra secondary phases were found. The introduction of the ultra-fine α-SiC particulate was recognized as the key factor that enabled both the control of the diboride grain growth and the achievement of full density. The mechanical properties offered an interesting combination of data: 4.8±0.2 MPafracture toughness, 507±4 GPa Young’s modulus, 0.12 Poisson’sratio, and 835±35 MPa flexural strength at room temperature. The flexural strength measured at 1500 °C (in air) provided values of 300±35 MPa. The incorporated ultra-fine α-SiC particulate was fundamental, sinterability apart, to enhancing the strength and oxidation resistance of ZrB₂. The latter property was tested at 1450 °C for 20 h in flowing dry air. In such oxidizing conditions, the formation of a thin external borosilicate glassy coating supplied partial protection for the faces of the material exposed to the hot environment. The oxidation attack penetrated into the material’s bulk and created a 200-μm-thick zirconia scale. The SiC particulate included in the oxide scale, lost by active oxidation, left carbon-based inclusions in the formerly occupied sites. PACS 81.05.Je; 81.20.Ev; 81.70.Bt     

Electric strength of rocks at a pulsed voltage under high pressures at high temperatures

The electric strength of rocks (granite, limestone, and sandstone) for the first time has been measured under the simultaneous effect of the pressure up to 35 MPa and temperature up to 120°C in the system of rod-rod electrodes arranged on one sample surface and point-plane electrodes in the liquid medium of a drilling agent. With the simultaneous increase in pressure and temperature, the electric strength of rocks for point-plane electrodes continuously increases (especially rapidly in the pressure range of 10–24 MPa and temperature range of 35–85°C), while for rod-rod electrodes arranged on the same sample surface, the electric strength varies with a maximum at pressures of 5–12 MPa and temperatures 20–35°C.     

A COMPARISON OF THE HOT-COMPACTION BEHAVIOR OF ORIENTED,HIGH-MODULUS,POLYETHYLENE FIBERS AND TAPES*

The purpose of this article is twofold. First, there is an account of the hot-compaction behavior of a new, highly oriented, high-modulus polyethylene (PE) tape with the trade name of Tensylon® (manufactured by Synthetic Industries, USA). This tape, produced by a melt spinning route, has mechanical properties comparable to those of commercially available gel-spun fibers. Unidirectional samples were produced for a range of compaction temperatures to determine the optimum compaction conditions to obtain the best mechanical properties of the resulting compacted sheets. Second, the mechanical properties of the best Tensylon sample, manufactured at a compaction temperature of 153°C, was compared with three other hot-compacted, highly oriented PE materials, based on Certran®, Dyneema®, and Spectra® commercial PE fibers. The results showed that the optimum compaction temperature was in most cases about 1°C below the point at which substantial crystalline melting occurred. At this optimum temperature, differential scanning calorimetry (DSC) melting studies showed that approximately 30% of the original oriented phase had been lost to bond the structure together. In the case of Dyneema, the properties of the fiber were not translated into the properties of a compacted sheet, and morphological studies showed that this was because melting did not occur on the fiber surfaces, but rather in the interior of the fiber due to a skin structure. The properties of the compacted Tensylon tapes were found to be exceptional, combining very high modulus and strength with interlayer bonding and good creep resistance. Moreover, the optimum temperature appeared to be about 2°C below the point at which complete melting occurred, giving a wider processing window for this material.

     

Powder metallurgy technology of NiTi shape memory alloy

Powder metallurgy technology was elaborated for consolidation of shape memory NiTi powders. The shape memory alloy was compacted from the prealloyed powder delivered by Memry SA. The powder shows M_s = 10°C and A_s = -34°C as results from DSC measurements. The samples were hot pressed in the as delivered spherical particle's state. The hot compaction was performed in a specially constructed vacuum press, at temperature of 680°C and pressure of 400 MPa. The alloy powder was encapsulated in copper capsules prior to hot pressing to avoid oxidation or carbides formation. The alloy after hot vacuum compaction at 680°C (i.e. within the B2 NiTi stability range) has shown similar transformation range as the powder. The porosity of samples compacted in the as delivered state was only 1%. The samples tested in compression up to ε = 0.06 have shown partial superelastic effect due to martensitic reversible transform- ation which started at the stress above 300 MPa and returned back to ε = 0.015 after unloading. They have shown also a high ultimate compression strength of 1600 MPa. Measurements of the samples temperature changes during the process allowed to detect the temperature increase above 12°C for the strain rate 10^-2 s^-1 accompanied the exothermic martensite transformation during loading and the temperature decrease related to the reverse endothermic transformation during unloading.     

复合材料弹侵彻混凝土靶的研究

 利用碳纤维复合材料壳体和金属弹头组成的复合弹体,对混凝土靶进行了高速侵彻实验,弹体分别以336、447和517 m/s的速度对强度为30 MPa、厚度为200 mm的混凝土靶进行正侵彻和30°斜侵彻。实验结果表明：碳纤维复合材料壳体具有较高的强度,在高速侵彻靶体的过程中弹体结构能够保持完整,复合材料壳体没有纤维分层和断裂产生。相对于同样结构尺寸的金属弹体（将复合材料壳体替换为密度7.8 g/cm³的金属材料）,复合材料弹填充物的质量分数（18.5%）约为金属弹体的两倍,因此采用轻质高强复合材料替代高密度金属弹身,不仅可以提高弹体装填比、增加比毁伤威力,而且还具有较高的侵彻能力。     

The Effect of Poly(Ethylene Succinate) on Mechanical Properties of PLLA/PES Blend Prepared by Melt-Blending

Fully biodegradable poly(L-lactide) and poly(ethylene succinate) (PLLA/PES) blends were prepared via melt-blending using PLLA and PES as reactants in a stainless steel chamber. The prepared PLLA/PES blend, as well as neat PLLA and PES, was characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) to confirm the structure and the crystallization of PLLA in the blend. The mechanical properties of PLLA/PES blends were determined by bending and tensile tests and the effects of PES content on the mechanical properties of PLLA/PES blends were investigated. It was found that blending some amount of PES could significantly improve the elongation at break while still keeping considerably high strength and modulus. With increasing PES content, both strength and modulus gradually decreased; however the elongation at break significantly increased. SEM was used to examine the morphology of fracture surfaces of PLLA/PES blends.