The filler effect: The influence of filler content and type on the hydration rate of tricalcium silicate

The partial replacement of ordinary portland cement (OPC) by fine mineral fillers accelerates the rate of hydration reactions. This acceleration, known as the filler effect, has been attributed to enhanced heterogeneous nucleation of C‐S‐H on the extra surface provided by fillers. This study isolates the cause of the filler effect by examining how the composition and replacement levels of two filler agents influence the hydration of tricalcium silicate (T1‐Ca₃SiO₅; C₃S), a polymorph of the major phase in ordinary portland cement (OPC). For a unit increase in surface area of the filler, C₃S reaction rates increase far less than expected. This is because the agglomeration of fine filler particles can render up to 65% of their surface area unavailable for C‐S‐H nucleation. By analysis of mixtures with equal surface areas, it is hypothesized that limestone is a superior filler as compared to quartz due to the sorption of its aqueous CO₃^2? ions by the C‐S‐H—which in turn releases OH^? species to increase the driving force for C‐S‐H growth. This hypothesis is supported by kinetic data of C₃S hydration occurring in the presence of CO₃^2? and SO₄^2? ions provisioned by readily soluble salts. Contrary to prior investigations, these results suggest that differences in heterogeneous nucleation of the C‐S‐H on filler particle surfaces, caused due to differences in their interfacial properties, have little if any effect on C₃S hydration kinetics.     

The effect of filler content and size on the mechanical properties of polypropylene/oil palm wood flour composites

The effect of filler content and size on the mechanical properties of a new type of wood-based filler, oil palm wood flour (OPWF), in polypropylene (PP) was investigated. Four sizes of OPWF filler at different filler loadings were compounded using a twin screw compounder. All sizes of filler showed a similar trend of declining mechanical properties with increasing filler content. In terms of size, the composites filled with larger-sized filler showed higher modulus, tensile and impact strengths, particularly at high filler loadings. The OPWF used in this study was not treated with any coupling agent.     

Effect of carbon fabric type on the mechanical performance of 2D carbon/carbon composites

A stabilized PAN fabric was carbonized and graphitized from 800°C to 2500°C. Two-dimensional (2D) carbon/carbon composites were made using the stabilized PAN fabric, carbonized fabrics, and a resol-type phenol-formaldehyde resin. These composites were heat-treated from 600°C to 2500°C. The influence of different heat-treated fabrics and heat treatment on the fracture and flexural strength of these composites was also studied. The composite reinforced with higher heat-treated fabrics showed a lower weight loss than that with lower heat-treated fabrics. When the composites were graphitized at 2500°C, the loss was 49.7 wt% for the composite made with stabilized PAN fabric and 26 wt% for that with carbonized fabric at 2500°C. Those composites also have a higher density than composites produced by other methods. Composites made with stabilized PAN fabric exhibited a strong bonding in the fiber/matrix during pyrolysis. This composite showed catastrophic fracture and a smooth fracture surface with no fiber pullout. Composites made with higher carbonized fabrics exhibited a weak interface bonding. These composites showed a pseudo-plastic fracture pattern with fiber pullout during pyrolysis. Composites made with carbonized fabrics at 2000°C and 2500°C showed the highest flexural strength at the prolysis temperature of 1000°C. Composites made with carbonized fabric at 1300°C showed the highest flexural strength above 1500°C to 2500°C. The composite made with stabilized PAN fabric exhibited the lowest flexural strength during pyrolysis.     

碳填料/聚四氟乙烯复合材料的研究进展

综述了近几年来国内外对碳填料/PTFE(聚四氟乙烯)复合材料的研究进展。对碳填料的种类及特性进行了阐述,并归纳分析了改性后复合材料的力学、摩擦磨损等性能。重点分析了石墨和石墨烯对复合材料综合性能的影响,为碳填料/PTFE复合材料的研究提供了参考。     

The effects of filler content on cure and mechanical properties of dichlorocarbene modified styrene butadiene rubber/carbon black composites

A study has been carried out on the curing characteristics and mechanical properties of carbon black filled dichlorocarbene modified styrene butadiene rubber (DCSBR). Processing characteristics such as optimum cure time and maximum torque increases with increasing of the concentration of carbon black in DCSBR whereas scorch time decreases. The mechanical properties and resistance of the vulcanizate towards thermal, flame and oil resistance have been carried out. Variation of bound rubber content of carbon black filled DCSBR and the influence of the extracting temperature on the bound rubber content was investigated and its activation energy was calculated from the Arrhenius plot. The reinforcing nature of the filler was assessed from stress strain and swelling data. The enhancement in mechanical properties was supported by data on the increased content of crosslink density in these samples obtained from swelling and stress strain analysis. The results of the studies indicate that carbon black can be used as a good reinforcing filler for DCSBR.     

The effect of TIO2 filler content on the mechanical,thermal, and tribological properties of TiO2/PPS composites

In an attempt to overcome existing limited studies about the residual flexural properties of solid particle eroded particle reinforced thermoplastic composites, this study is aimed to determine particularly titanium dioxide (TiO₂) particle concentrations (0, 5, 10, 15, 20, and 25 wt %) effects on the flexural and solid particle erosive wear properties of TiO₂ particle reinforced polyphenylenesulphide (PPS) composites. In addition, thermal and viscoelastic properties of PPS composites were also studied by using Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA) methods. TiO₂ reinforced PPS composite samples were prepared by using a twin screw extruder and injection molding machines. Subsequently, composite samples were eroded under various impingement angles in specially designed erosion test rig by using silica particles and then flexural tests were performed. It was found that increase of particle concentrations in PPS improves composite's stiffness. Besides, maximum flexural and residual flexural strength were obtained at 10 wt % particle concentrations for both uneroded and eroded composites. The erosion rate of composite was increased with augmentation in TiO₂ concentration. Moreover, TGA analysis indicated that remarkable results on thermal stability were obtained. The effects of TiO₂ reinforcement on the results of DMA were also discussed. POLYM. COMPOS., 34:1591–1599, 2013. © 2013 Society of Plastics Engineers     

The effect of carbon fiber content on the friction and wear properties of carbon fiber reinforced polyimide composites

The current study examines the tribological performance of polyimide and carbon fiber reinforced polyimide (CF/PI) under dry sliding condition. Different contents of carbon fibers were employed as reinforcement. All filled and unfilled polyimide composites were tested against CGr15 ball and representative testing was performed. The effects of carbon fiber content on tribological properties of the composites were investigated. The worn surface morphologies of neat PI and its composites were examined by scanning electron microscopy and the wear mechanisms were discussed. Moreover, all filled polyimides have superior tribological characteristics to unfilled polyimides. The optimum wear reduction was obtained when the content of carbon fiber is 20 vol %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetics of filler wetting and dispersion in carbon nanotube/rubber composites

The effects of the surface modification of multi-walled carbon nanotubes (MWCNTs) by an ionic liquid, 1-butyl 3-methyl imidazolium bis(trifluoromethyl-sulphonyl)imide (BMI) on the kinetics of filler wetting and dispersion as well as resulting electrical conductivity of polychloroprene (CR) composites were studied. Two different MWCNTs were used, Baytubes and Nanocyl, which differ in their structure, purity and compatibility to CR and BMI. The results showed that BMI can significantly improve the macrodispersion of Baytubes, and increases the electrical conductivity of the uncured BMI–Baytube/CR composites up to five orders of magnitude. In contrast, the use of BMI slows the dispersion process and the development of conductivity of BMI–Nanocyl/CR composites. Our wetting concept was further developed for the quantification of the bound polymer on the CNT surface. We found that the bonded BMI on the CNT surface is replaced by the CR molecules during mixing as a result of the concentration compensation effect. The de- and re-agglomeration processes of CNTs taking place during the subsequent curing process can increase or decrease the electrical conductivity significantly. The extent of the conductivity changes is strongly determined by the composition of the bound polymer and the curing technique used.     

The effect of fibre surface treatment,resin type and fabrication process on the interlaminar shear strength of carbon fibre composites

Some data related to the preparation of carbon fibre composites is summarised. A limited investigation concerned with presenting markedly different fibre surfaces to the resin by coating with metals and stearic acid is also described. There are carbon fibre surface treatments which lead to improved shear strength, but it is not clear how they are affecting the fibre surface. It also seems likely that some facets of the processing technique can have a large effect on composite quality as indicated by shear strength measurements. The difficulties in interpreting results and identifying sources of variability points to the advisability of statistically planned experiments to assess the significance of changes when investigating possible materials and processing improvements.     

The hierarchical structure and properties of multifunctional carbon nanotube fibre composites

The axial mechanical, electrical and thermal properties of carbon nanotubes (CNTs) can be exploited macroscopically by assembling them parallel to each other into a fibre during their synthesis by chemical vapour deposition. Multifunctional composites with high volume fraction of CNT fibres are then made by direct polymer infiltration of an array of aligned fibres. The fibres have a very high surface area, causing the polymer to infiltrate them and resulting in a hierarchical composite structure. The electrical and thermal conductivities of CNT/epoxy composites are shown to be superior to those of equivalent specimens with T300 carbon fibre (CF) which is widely used in industry. From measurements of longitudinal coefficient of thermal expansion (CTE) of the composites we show that the CTE of CNT fibres is approximately ?1.6 × 10^?6 K^?1, similar to in-plane graphite. The combination of electrical, thermal and mechanical properties of CNT fibre composites demonstrates their potential for multifunctionality.     

Effect of filler dispersion on the electrical conductivity and mechanical properties of carbon/polypropylene composites

Conducting carbon/polypropylene composites containing a mixed filler of crystalline natural graphite powder, carbon black, and multiwalled carbon nanotubes have been prepared. The effect of the filler dispersion on the electrical conductivity and mechanical properties has been studied. Keeping the graphite content constant and increasing the ratio of carbon black to nanotubes, the conductivity and the flexural modulus increased linearly at different graphite contents. Graphite aggregates on the cross sections were analyzed by optical microscopy to characterize the dispersion of graphite. The results of the optical microscopy studies showed that the dispersion of graphite is affected by the composition and amount of the nanofiller system. Based on the observations simplified morphological models were set up, that allowed to explain the change in the electrical and mechanical properties of the composites of different compositions. POLYM. COMPOS., 34:1195–1203, 2013. © 2013 Society of Plastics Engineers     

添加剂对炭/石墨复合材料性能的影响

以酚醛树脂为黏结剂,石油焦、石墨为原料,分别添加磷酸氢二钠、硼酸、碳化硅,在1 100℃下热处理,制备出炭/石墨复合材料,并考察了其机械性能、微观结构和热性能。研究表明:经过焙烧后,炭/石墨复合材料中的添加剂起到增强颗粒间键合能力,提高炭/石墨复合材料机械强度的作用。同时,硼酸、碳化硅可以在炭/石墨复合材料表面形成抗氧化物质,使其具有更好的抗氧化能力,起始氧化温度提高180℃,终了氧化温度提高了200℃。     

Polycarbonate composites: Effect of filler type and melt‐blending process on the light diffusion properties

Transmittance and haze are key properties of light diffusion materials. Hybrid light diffusion agents (LDAs) and melt‐blending process are introduced to study optical performance and mechanical properties of polycarbonate (PC) light diffusion materials. Optical properties of PC composites prepared by two‐step melt‐blending process has better repeatability compared to one‐step method due to the better dispersion state of hybrid fillers in PC matrix. The hybrid fillers silicate microspheres (SMS)/nano titania particles (nTiO₂) are more suitable for PC matrix compared to cross‐linked poly(methyl methacrylate) microspheres (PMMA)/nTiO₂, for the reason that the PC/SMS/nTiO₂ composites exhibit favorable optical performance and almost no deterioration of mechanical properties. The good balance between high transmittance and substantial haze can be achieved when the SMS/nTiO₂ content is 1.2 wt% (the transmittance and haze are 60.97% and 88.73%, respectively). POLYM. ENG. SCI., 57:374–380, 2017. © 2016 Society of Plastics Engineers     

Effect of filler addition and weathering conditions on the performance of PVC/CaCO3 composites

This study deals with the effects of calcium carbonate (CaCO₃) fillers and hygrothermal aging on the performance of polyvinylchloride (PVC). The properties of the PVC/CaCO₃ composite were studied before and after aging in water up to 3 months at 24°C ± 3°C, 70°C, and 90°C. In terms of fillers effect, it was found that the incorporation of fillers in PVC induces an increase in both T_g value and storage modulus; however, it had no significant effect on the water absorption. However, the addition of fillers has resulted in an improvement in the elastic modulus, whereas it has shown harmful effect on the tensile strength and elongation at break. Concerning flexural properties, an important filler percentage, that is, 35 wt%, is proved to be the optimum content to achieve maximum strength and modulus as well as wear properties. In terms of aging impact, it was found that shift in color on aging occurs noticeably. Elastic modulus, tensile strength, flexural strength, and flexural modulus increase with increasing temperature from ambient to 70°C, whereas they decrease at 90°C. Dynamic mechanical thermal analysis confirmed that at high temperature, the absorbed water affects the PVC matrix during aging. As a result, a loss in strength and stiffness but a gain of ductility was observed. The great quantity of absorbed water acts as a barrier layer and, thus, minimizes the wear. POLYM. COMPOS., 37:2171–2183, 2016. © 2015 Society of Plastics Engineers     

Improving the performance of carbon/graphite composites through the synergistic effect of electrostatic self-assembled carbon nanotubes and nano carbon black

Superior performance fillers are considered as an effective means to enhance the performance of carbon/graphite composites. However, poor interfacial properties and incomplete filler networks limit the performance enhancement of the composites. In this study, a new method was proposed to weaken this impact through the synergistic effect of the electrostatic self-assembly of nano carbon black (NCB) onto carbon nanotubes (CNTs). The results showed that the synergistic effect between NCB and the CNTs significantly improved the mechanical and electrical properties of the composites. NCB reduces the porosity of the composites and increases the interaction between the CNTs and matrix. The compressive strength of the composite was 143.2 Mpa, and the flexural strength was 46.3 MPa, which is 210% higher than that of the pristine carbon/graphite composites. Moreover, NCB and CNTs form a globally connected synergistic network in the carbon skeleton. Composites filled with CNTs/NCB exhibited the lowest resistivity and highest thermal conductivity, with a resistance that was 42% lower than that of pristine carbon/graphite composites at 44.8 μΩ m. All of these results suggest that the synergistic effect of CNTs/NCB show great potential to improve the performance of carbon/graphite composites.     

The effect of carbon nanotubes on the damage development in carbon fiber/epoxy composites

The aim of this study is to investigate the effect of carbon nanotubes (CNTs) on the initiation and development of damage in a woven carbon fiber/epoxy composite under quasi-static tensile loading. The composite is produced using resin transfer moulding and contains 0.25 wt.% of CNTs in the matrix. The results in the fiber direction report no improvement of the Young’s modulus and a slight improvement of the strength and strain-to-failure. The most important result of the study is a notion that CNTs have a hindering effect on the formation of transverse cracks. The conclusion is drawn from a combined analysis of the acoustic emission measurements (reporting a pronounced shift of all damage development thresholds towards higher strains by more than 30%) and X-ray/SEM observations (revealing a lower crack density in the CNT modified composite). The same analysis also indicates that the mechanism of energy dissipation through transverse microcracking is partially replaced by another mechanism that promotes (distributed) damage through fiber debonding.     

The effect of nanotube alignment on stress graphitization of carbon/carbon nanotube composites

Carbon nanotubes, when used as filler in a glass-like carbon matrix, has been reported to induce stress graphitization in the matrix. The effects on stress graphitization of the amount of carbon nanotube loading and nanotube orientation in the composite were investigated through microscopy and X-ray diffraction analyses. Results showed that an increase in nanotube content and nanotube alignment could increase the extent of formation of anisotropic regions, thereby hastening stress graphitization. It was shown that the distance between nanotubes could affect the formation of the anisotropic structures, such that they could develop in a circumferential manner around the nanotubes when the nanotubes are situated far from each other or develop continuous regions between nanotubes when they are closer together. The development of these microstructures and its relationship to the residual stresses that accumulate in the material during heat treatment is discussed here.     

The preparation and performance of short carbon fiber reinforced adhesive for bonding carbon/carbon composites

A short carbon fiber reinforced adhesive for bonding carbon/carbon composites was developed. We found that when the thickness of the bonding layer was 80 μm, the concentration of short carbon fiber was 0.2 wt.%, and the heat-treatment temperature was 1000 °C, the adhesive could operate below 1700 °C and endure 20 times of thermal shock circles at 1500 °C. Finite element and micrograph analysis indicated that the bonding strength was larger than the interlaminar shear strength of carbon/carbon substrate, so that the fracture did not occur in the bonding layer but the carbon/carbon substrate. Weibull distribution analysis results showed that the Weibull modulus was 21.56 and the bonding strength was 11.43 MPa. We investigated that short carbon fiber could advance the tensile strength and thermal shock resistance of the adhesive, release residual stress and inhibit extension of micro-crack in the bonding layer.