The effect of molecular weight on the interfacial properties of GF/PP injection molded composites

It is well established that the molecular weight of recycled PP decreases significantly as compared to the virgin material. Hence this study involved 2 PP grades of different molecular weights in order to simulate the recycling process. The effect of weight–average molecular weight on interfacial adhesion between GF and PP was investigated. Tensile test was done and the fiber length distribution around the fracture zone in both composites was compared with the distributions from similar locations of unstressed composites. The effect of PP-grafted maleic anhydride coupling agent was also studied. It was found that a decrease in weight–average molecular weight of PP improved interfacial adhesive strength between GF/PP. The lower molecular weight matrix has a lower viscosity that enables its molecules to penetrate easily into the silane interphase. In that case, the interfacial area that is available for coupling is higher, leading to a more effective coupling. The higher interfacial shear strength between the glass fiber and the lower molecular weight matrix induced more breakage of the glass fiber during tensile test.     

A study of internal friction in polypropylene (PP) filled with nanometer-scale CaCO3 particles

The internal friction and relative elastic modulus of polypropylene (PP) filled with nanometer-scale calcium carbonate (nm-CaCO₃) particles in different contents (0, 4, 7, and 15 vol.%) are measured in the temperature range 150–400 K with a torsion pendulum. The peak associated with the glass transition and a small peak (′ peak) associated with the pre-melting process in crystalline parts of PP was observed around 290 and 370 K, respectively. At temperatures lower than 270 K, no peaks were observed. With increasing content of nm-CaCO₃ particles, the apparent activation energy of the peak decreases, and after passing a minimum of 4.7 eV at 4 vol.% of nm-CaCO₃, it increases. In contrary to this behavior, the peak temperature has a maximum of 289 K at the same filler fraction. Correspondingly, the highest tensile and flexural strength of PP were obtained around this content. These observations may be understood through the influences of fillers on the degree of crystallization of PP and on the mobility of molecules of PP.     

Thrust Force Analysis in Drilling Glass Fiber Reinforced/Polypropylene (GFR/PP) Composites

Glass fiber reinforced thermoplastic (GFRTP) composites are an important alternate to the conventional engineering materials owing to their good application-oriented properties. Drilling is unavoidable and an important operation used in automotive and aerospace industries in the assembly stage. The reduction of thrust force is required to minimize delamination. This paper examines the parameters that influence the thrust force on drilling glass fiber reinforced polypropylene (GFR/PP). The experiments are conducted using the Box–Behnken experimental design method. An empirical relation is established for determining the thrust induced in the drilling of GFRTP. The factors that affect the drilling process and their interaction are analyzed and presented in detail.     

国内开发与应用PP/EPDM-TPE的状况

以PP/EPDM(聚丙烯/三元乙丙橡胶)型TPE(热塑弹性体)为例,介绍了国内进行PP基TPE的研制与生产状况及其在汽车、电器和包装等领域的应用.     

纳米CaCO3／PP／PS复合材料的结晶与熔融行为

熔融方法制备了纳米CaCO3／PP／PS复合材料，DSC研究了PP／PS、增容PP／PS共混物及其纳米CaCO3填充共混物的结晶与熔融行为。研究结果表明加入PS对PP结晶行为影响不大，但导致PP熔点下降，熔融峰从单峰变为双峰。纳米CaCO3和增容剂对PP／PS共混物中PP结晶存在异相成核作用，提高PP结晶温度和熔点，PP—g—MA和PP—g—AA的异相成核作用比CaCO3的大。PP—g—MA增容的PP／PS共混物和CaCO3填充共混物有利于PP形成β晶，但CaCO3填充共混物、PP—g—AA的增容PP／PS共混物和CaCO3填充共混物无β晶形成。     

Interlaminar Fracture Toughness of CF/PEI and GF/PEI Composites at Elevated Temperatures

An experimental study has been conducted to assess temperature effects on mode-I and mode-II interlaminar fracture toughness of carbon fibre/polyetherimide (CF/PEI) and glass fibre/polyetherimide (GF/PEI) thermoplastic composites. Mode-I double cantilever beam (DCB) and mode-II end notched flexure (ENF) tests were carried out in a temperature range from 25 to 130°C. For both composite systems, the initiation toughness, G _IC,ini and G _IIC,ini, of mode-I and mode-II interlaminar fracture decreased with an increase in temperature, while the propagation toughness, G _IC,prop and G _IIC,prop, displayed a reverse trend. Three main mechanisms were identified to contribute to the interlaminar fracture toughness, namely matrix deformation, fibre/matrix interfacial failure and fibre bridging during the delamination process. At delamination initiation, the weakened fibre/matrix interface at elevated temperatures plays an overriding role with the delamination growth initiating at the fibre/matrix interface, rather than from a blunt crack tip introduced by the insert film, leading to low values of G _IC,ini and G _IIC,ini. On the other hand, during delamination propagation, enhanced matrix deformation at elevated temperatures and fibre bridging promoted by weakened fibre/matrix interface result in greater G _IC,prop values. Meanwhile enhanced matrix toughness and ductility at elevated temperatures also increase the stability of mode-II crack growth.     

Short Fibre Reinforced PP/PANI-Complex Blends and their Mechanical and Electrical Properties

This study deals with the mechanical and electrical properties of polypropylene (PP)/ polyaniline (PANI)-complex blends and their short glass fibre (GF) composites. In particular, the surface resistivity, the electrical conductivity and its profile were characterized. Tensile modulus, tensile strength and impact resistance of the materials were also measured as a function of GF- and PANI-complex content. The miscibility and microstructure of the blends could be studied by using light optical and scanning electron microscopy. While a steady increase in tensile modulus with increasing GF content was observed in all material combinations, an improvement in the tensile strength could only be achieved in case of the glass fibre reinforced unmodified PP-matrix composites. The conductivity of the materials increased with increasing PANI-complex content. The low percolation threshold for conductivity could be explained by the formation of a PANI-complex network near the surface of the samples.     

Modeling and testing strain rate-dependent compressive strength of carbon/epoxy composites

A technique for testing high modulus fiber-reinforced composites in compression at different strain rates is investigated. The rate-dependent compressive behavior of unidirectional AS4/3501-6 carbon/epoxy composite is characterized by using off-axis specimens. It is found that, in the compression test, a titanium coating applied at the contact ends of the off-axis specimen can greatly reduce contact frictions, allowing a fully developed extension–shear coupling so that a state of uniform stress in the specimen can be achieved. A rate-dependent nonlinear constitutive model and a dynamic compressive strength model (fiber microbuckling model) for the unidirectional AS4/3501-6 composite are established based on the low strain rate off-axis test data. Model predictions and experimental data including high strain rate data are in very good agreement indicating that the constitutive model and compressive strength model obtained with low strain rate data are valid for high strain rates as well. A technique is also developed to extract the longitudinal compressive strength of the composite from those of the off-axis specimens.     

Morphology, dynamic mechanical and thermal studies on poly(styrene-co-acrylonitrile) modified epoxy resin/glass fibre composites

Poly(styrene-co-acrylonitrile) (SAN) was used to modify diglycidyl ether of bisphenol-A (DGEBA) type epoxy resin cured with diamino diphenyl sulfone (DDS) and the modified epoxy resin was used as the matrix for fibre reinforced composites (FRPs) in order to get improved mechanical and thermal properties. E-glass fibre was used as the fibre reinforcement. The morphology, dynamic mechanical and thermal characteristics of the systems were analyzed. Morphological analysis revealed heterogeneous dispersed morphology. There was good adhesion between the matrix polymer and the glass fibre. The dynamic moduli, mechanical loss and damping behaviour as a function of temperature of the systems were studied using dynamic mechanical analysis (DMA). DMA studies showed that DDS cured epoxy resin/SAN/glass fibre composite systems have two T_gs corresponding to epoxy rich and SAN rich phases. The effect of thermoplastic modification and fibre loading on the dynamic mechanical properties of the composites were also analyzed. Thermogravimetric analysis (TGA) revealed the superior thermal stability of composite system.     

Chemical vapor deposition and characterization of nitrogen doped TiO2 thin films on glass substrates

Photocatalytically active, N-doped TiO₂ thin films were prepared by low pressure metalorganic chemical vapor deposition (MOCVD) using titanium tetra-iso-propoxide (TTIP) as a precursor and NH₃ as a reactive doping gas. We present the influence of the growth parameters (temperature, reactive gas phase composition) on the microstructural and physico-chemical characteristics of the films, as deduced from X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and ultra-violet and visible (UV/Vis) spectroscopy analysis. The N-doping level was controlled by the partial pressure ratio R = [NH₃]/[TTIP] at the entrance of the reactor and by the substrate temperature. For R = 2200, the N-doped TiO₂ layers are transparent and exhibit significant visible light photocatalytic activity (PA) in a narrow growth temperature range (375-400 °C). The optimum N-doping level is approximately 0.8 at.%. However, the PA activity of these N-doped films, under UV light radiation, is lower than that of undoped TiO₂ films of comparable thickness.     

Preparation, characterisation and processing of carbon fibre/polyamide-12 composites for selective laser sintering

Aiming at developing carbon fibre/polyamide-12 (CF/PA) composite powders for manufacturing high-performance components by selective laser sintering (SLS), the preparation, characteristics and sintering process of the composite powders and mechanical properties of sintered components were studied. Surfaces of the carbon fibres were treated by the oxidation modification and coated with polyamide-12 through the dissolution-precipitation process to provide good interfacial adhesion and homogenous dispersion within the polyamide-12 matrix. The particle size and micro-morphology analyses show that the CF/PA composite powders with 30 wt%, 40 wt% and 50 wt% carbon fibres present the suitable powder sizes and format for SLS. The incorporation of carbon fibres into the polyamide-12 matrix decreases the initial melting temperature and consequently lowers the SLS part bed temperatures, implying lower energy requirement and less thermal degradation in the sintering process. The CF/PA composites also represent higher thermal stability than the pure polyamide-12. The CF/PA sintered components with 30 wt%, 40 wt% and 50 wt% carbon fibres exhibit the greatly enhanced flexural strengths by 44.5%, 83.3%, 114%, and the flexural modulus by 93.4%, 129.4%, 243.4%, respectively, as compared with the pure polyamide-12 sintered parts. Fractured surface analysis shows that the carbon fibres are encapsulated and bonded well with the polyamide matrix. The complex SLS parts with the thinnest wall of 0.6 mm, the density of 1.09 ± 0.02 g/cm³ and the relatively density of 94.13 ± 1.72% were manufactured using the CF/PA composite powder with 30 wt% carbon fibres. This study demonstrates that the CF/PA composite powders prepared by the surface treatment and dissolution-precipitation method represent suitable interfacial adhesion, filler dispersion, particle sizes and sintering behaviours for SLS and enable the manufacture of complex components with high performance.     

炮弹、汽车雨刮器等中小工件阴极电泳涂装生产线设计

详细论述了炮弹、汽车雨刮器等中小工件阴极电泳涂装生产线的工艺设计,阐述了生产线的基本型式、设备组成和设计原则,介绍了一种新型的针对中小工件阴极电泳涂装的步进直线式T型行车输送涂装生产线.     

Novel processing and characterization of Cu/CNF nanocomposite for high thermal conductivity applications

Enhancing the thermal conductivity and reducing the thermal expansion for electronic packaging applications can be achieved by compositing carbon nanofibers in copper-matrices. Though achieving these optimal thermal properties is theoretically possible, such composites are currently not available due to many unresolved practical problems. Conventional compositing processes are incapable of obtaining the desired fiber distribution while controlling the fiber–matrix interfaces for effective heat and load transfers. In this paper, three different powder metallurgy based processes are presented; two based on conventional techniques and the third a relatively new method. The first method is basically the conventional powder metallurgy process. The second and the third methods are also powder metallurgy processes with different ways of modifying the surface of the fibers using either electroless coating or the novel salt decomposition method. It is shown that the salt decomposition method is capable of achieving the desired high thermal conductivity values while the thermal expansion values remain the same in all the three processes.     

高压高产含硫气井测试技术及应用

川东北海相气藏埋藏深、温度压力高、普遍含硫、平面及纵向产量变化大,测试工艺复杂,面临井下工具受限、井下事故复杂、井控及环境污染风险大等难题。在川东北高含硫气井测试实践与经验基础上,形成了高压高产含硫气井测试技术。形成了三类六套APR射孔—酸压—测试联作短期测试管柱;管柱力学分析、多级压力控制、国产抗硫及复合地面流程等测试配套工艺满足各类测试要求;以压井、防喷、防漏为主的测试应急方案及措施确保了作业安全。该技术在YB1-侧1,YB12,HB1-1D等井中成功应用,为该类气田勘探开发的顺利进行提供了技术支撑。     

工艺参数对直流溅射沉积CrAlN涂层结构和性能的影响

采用直流反应磁控溅射的方式,用AlCr合金靶,在高速钢(M2)上沉积CrAlN涂层。采用扫描电镜、X射线衍射、能谱和纳米压痕仪等分析和测量手段,系统研究了Ar/N2气流比、气压和基片温度等工艺参数对CrAlN涂层结构和性能的影响。研究表明,Ar/N2气流比、气压和基片温度对涂层均有较大的影响,当Ar/N2气流比为1、总气压为0.2 Pa、基片温度为300℃时所得涂层性能最好,最高硬度和弹性模量分别为34.8,434.3 GPa。     

Formation mechanism of in situ Al3Ti in Al matrix during hot pressing and subsequent friction stir processing

In situ Al₃Ti/Al composites were fabricated by a combination of vacuum hot pressing (VHP) and friction stir processing (FSP). The formation mechanism of the Al₃Ti and the effect of VHP and FSP parameters on the resultant microstructure and mechanical properties were investigated. The Al₃Ti formed due to the reactive diffusion between Al and Ti during VHP, and the number of Al₃Ti particles increased with increasing the temperature and holding time of the VHP. FSP not only induced the Al–Ti reaction, but also resulted in significant refining of the Al₃Ti, thereby creating a homogeneous distribution of Al₃Ti particles in the Al matrix. These microstructural changes led to significant improvement in the tensile properties of the in situ Al₃Ti/Al composite. However, the change trends of the tensile properties of the FSP samples were dependent on the extent of the Al–Ti reaction during VHP.     

Glass transition kinetics and optical band gap in Se85−xSb15Snx (x = 10, 11, 12.5, and 13) chalcogenide glasses

Se_85−xSb₁₅Sn_x (10 ≤ x ≤ 13) chalcogenide glasses were prepared by melt quenching technique. The glass transition temperature T_g of the samples was recorded at different heating rates using differential scanning calorimeter DSC. From the heating rate dependence of T_g, the activation energy for thermal relaxation E_t was calculated using Moynihan model and Kissinger equation. It is found that T_g increases with Sn content due to enhancement of both the degree of cross-linking parameter D_cl and the mean bond energy of the average cross-linking per atom 〈E_cl〉. The observed increase in D_cl and 〈E_cl〉 is attributed to the formation of SnSe_4/2 structural units of energies higher than that of Se–Se and Se–Sb bond energies. The decreasing trend of E_t with the addition of Sn is an indication of improving thermal stability as it is also evident from the values of the temperature difference T_c − T_g. Correlation of T_g values with the physical parameters of the studied glasses (for instance, the average coordination number 〈Z〉, the average heat of atomization (H_s), the overall mean bond energy 〈E〉, and the optical band gap (E_g)) reveals that T_g increases linearly with 〈Z〉, H_s, and 〈E〉 but the behavior with E_g is opposite.     

Synthesis, characterization and magnetic properties of CoFe2O4 nanorods

In this work, we demonstrated a new precursor route to synthesize CoFe₂O₄ one-dimensional (1D) nanorods. CoFe₂O₄ nanorods were prepared via the thermal decomposition of CoFe₂(C₂O₄)₃ nanorod precursor, which was prepared by solvothermal method without the assistance of template or surfactant. The microstructure and magnetic property of the obtained products were characterized by x-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), thermogravimetric (TG) and differential thermal analysis (DTA) and vibrating sample magnetometer (VSM). The results showed that the as-prepared CoFe₂O₄ nanorods were built by magnetic nanoparticles after calcining the precursor nanorods at different temperatures, and the size variation of magnetic nanoparticles with calcination temperatures leaded to variable magnetic properties.