Pressureless densification,microstructure tailoring and properties of Ta0.8Hf0.2C-based composites

Ta_0.8Hf_0.2C (TH) ceramics are desirable for applications in ultra-high temperature environments, but they are difficult to be sintered pressurelessly. TH ceramics were densified up to 98.8% from commercial powders via pressureless sintering (PLS) at 2473 K. SiC was introduced as secondary phase to tailor microstructures and improve properties of TH. The influence of SiC volume fraction on the densification, microstructure evolution and room-temperature properties of TH-based ceramics were examined. Average grain size of TH was refined from 13.6 down to 2.0 μm. 10 vol% SiC addition contributed to densification of Ta_0.8Hf_0.2C-SiC (THS) composites with a relative density of 99.6%. The mechanical properties of THS were fairly good, and thermal properties of sintered THS displayed a remarkable improvement compared with TH: the coefficient of thermal expansion (CTE) showed a reduction of 8.6% while the thermal conductivity increased from 18.6 to 41.5 W/m K.     

Friction and wear behavior of C-based composites in situ reinforced with W2B5

The C-W₂B₅ composites with W₂B₅ content of 30 vol.% and 40 vol.% were fabricated by reaction hot pressing sintering. The mechanical properties and friction and wear behavior of the composites were investigated. For comparison, the friction and wear behavior of graphite was also studied. It was found that the presence of W₂B₅ grain resulted in notable improvements in mechanical properties and wear resistance of the composites compared to graphite in spite of a little higher friction coefficient. A graphite-rich mechanically mixed layer (MML) was formed on the worn surface of the composites, which facilitated the low friction coefficient. Fracture and removal of the MML depending on the fracture toughness of the composites and Hertzian stress levels were considered to be the main wear mechanism.     

PPR/甘蔗渣复合材料的力学性能

利用硅烷处理的甘蔗渣纤维填充无规共聚聚丙烯制备了复合材料,研究其力学性能与相态结构。结果表明:在甘蔗渣用量为10～15份时,用硅烷KH570处理的甘蔗渣制备的复合材料较直接填充物的拉伸强度与冲击强度各提高30％以上;试样结晶更完善,纤维在树脂中分布更均匀。     

Crystallization kinetics and morphological behavior of reactively processed PBT/epoxy blends

Polybutylene terephthalate (PBT), a versatile engineering thermoplastic, has been processed using epoxy resin as a reactive solvent. Following processing of this blend, the epoxy was cured using a bi-functional amine curing agent, resulting in phase separation and phase inversion thus producing a different morphology. Change in crystallization kinetics of PBT in the presence of the epoxy monomer and cured epoxy resin has been studied using differential scanning calorimetry. Half time of crystallization (t_1/2) of PBT decreased in the presence of epoxy monomer while it remained constant in the presence of cured epoxy resin. The value of Avrami exponent varied between 1 and 2 in pure PBT as well as for uncured and cured blends, indicating mixed type of spherulitic growth. Morphology of the uncured and cured blends was studied using small angle light scattering (SALS) and polarizing microscopy for samples crystallized at different temperatures at all levels of the epoxy resin. Scattering pattern in H_v and V_v mode of SALS provided information about the type of spherulites as well as volume filling nature of the spherulites. In general, typical unusual type of spherulitic pattern for PBT, in which scattering lobes lie along the polar axis, changed to usual type of pattern for PBT/epoxy blends, in which scattering lobes lie at 45° to the polar axis.     

Mechanical properties of biorenewable fiber/plastic composites

Plastic fiber composites, consisting of polypropylene (PP) or polyethylene (PE), and pinewood, big blue stem (BBS), soybean hulls, or distillers dried grain and solubles (DDGS), were prepared by extrusion. Young's modulus, tensile and flexural strengths, melt flow, shrinkage, and impact energy, with respect to the type, amount, and size of fiber on composites, were evaluated. Young's moduli under tensile load of wood, BBS, and soybean‐hull fiber composites, compared with those of pure plastic controls, were either comparable or higher. Tensile strength significantly decreased for all the PP/fiber composites when compared with that of the control. Strength of BBS fiber composites was higher than or comparable to that of wood. When natural fibers were added there was a significant decrease in the melt flow index for both plastic/fiber composites. There was no significant difference in the shrinkage of all fiber/plastic composites compared to that of controls. BBS/PE plastic composites resulted in higher notched impact strength than that of wood or soybean‐hull fiber composites. There was significant reduction in the unnotched impact strength compared to that of controls. BBS has the potential to be used as reinforcing materials for low‐cost composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2484–2493, 2004     

淀粉/天然橡胶复合材料的力学性能研究

采用不同偶联剂对淀粉活化改性,通过直接共混法制备淀粉/天然橡胶复合材料。研究了淀粉种类、添加量及偶联剂对复合材料的拉伸性能、硬度、耐磨性的变化规律。结果表明:改性后淀粉/天然橡胶复合材料的拉伸性能、硬度、耐磨性明显增加,而改性后木薯淀粉/天然橡胶复合材料的力学性能最佳;采用质量分数为3%的有机硼偶联剂对橡胶材料的改性效果最好。     

Mechanical properties of LDPE/granular starch composites

The mechanical properties of composites of granular starch and low density polyethylene (PE) have been studied as functions of starch volume fraction ?, granule size, and presence of compatibilizer. Property–volume fraction relationships were interpreted using various theories of composite properties. The dependence of elongation (? ～ ?^1/3) and tensile strength (σ ～ ?^2/3) agree with theoretical predictions, although the proportionality constants are less negative than theoretical values. The addition of compatibilzer (ethylene-co-acrylic acid copolymer, EAA) did not significantly affect the elongation or tensile strength, but significantly increased the composite tensile modulus. The cornstarch/PE moduli could be described by the Kerner or Halpin-Tsai equations. Analysis of the composite moduli data using the Halpin-Tsai equation allowed the estimation of the modulus of granular starch. The value obtained, 15 GPa, is considerably greater than most unfilled synthetic polymers of commercial importance, but significantly lower than the modulus of cellulose. It is also greater than a previously reported value of 2.7 GPa. © 1994 John Wiley & Sons, Inc.     

Mechanical properties of HDPE/bark flour composites

Tensile and impact properties of Neem bark flour (BF) containing high density polyethylene (HDPE) composites were studied at 0–0.26 volume fraction of filler. Tensile modulus and strength and breaking elongation decreased with increase in BF concentration. The decrease in tensile modulus and strength was attributed to the decrease in crystallinity of the polymer compared to the imposed mechanical restraint by the BF. Analysis of tensile strength data indicated formation of stress concentration in the interphase. Because of this stress concentration and the mechanical restraint, the elongation‐at‐break and Izod impact strength decreased. Use of a coupling agent, HDPE‐g‐MAH, brings about enhanced phase adhesion, increasing the tensile modulus and strength. Enhanced adhesion marginally lowers composite ductility at higher filler contents and aids stress transfer increasing the Izod impact strength inappreciably. Scanning electron microscopic studies indicated better dispersion of BF particles and enhanced interphase adhesion in presence of the coupling agent. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Mechanical properties of natural fibers/polyamides composites

The aim of this investigation has been to use high performance thermoplastic matrices such as polyamides instead of the commonly used polyolefins to develop natural fiber composites for substituting glass fibers without renouncing to their mechanical properties. For this purpose, different natural fibers such as flax, jute, pure cellulose, and wood pulps have been melt compounded with different polyamides to analyze the effect of fiber content on mechanical properties. Fibers have not been treated as polyamides are less hydrophobic than polyolefins. Thermal behavior of the different fibers was determined by thermogravimetry to know the boundary for processing at high temperatures, since the melting points of the polyamides are much higher than those of polyolefins and this could lead to a higher degradation of the natural fibers. Rheological parameters were deduced by measuring torque values during the mixing process. Flexural and tensile modulus and strength of composites were analyzed, finding an increase in the mechanical properties compared with the unreinforced matrix that turns natural fibers into a considerable reinforcement offering a wealth of possibilities for industrial applications. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Mechanical properties of HAp–ZrO2 composites

Hydroxyapatite is a well-known and valuable implant material with bioactive properties. Full utilisation of the unique properties of hydroxyapatite ceramics is, however, possible only after its proper reinforcement, i.e., by preparation of composites. In the present work zirconia reinforced hydroxyapatite composites were obtained by hot pressing method. The reinforcing phase in the form of ZrO₂ particles was selected due to the satisfactory biocompatibility of ZrO₂ and also because of its exceptional mechanical properties.Our investigations were aimed at assessing the influence of varying ZrO₂ on the phase composition and mechanical properties of HAp–ZrO₂ composites. In order to produce dense sinters, we used three types of initial zirconia powders which differed in morphology and contents of the tetragonal and monoclinic phases. We studied the influence of these oxides on thermal stability of hydroxyapatite matrix as well as on the phase composition and mechanical properties of the composite materials produced.     

Mechanical properties of graphene nanoplatelet/epoxy composites

Because of their high‐specific stiffness, carbon‐filled epoxy composites can be used in structural components in fixed‐wing aircraft. Graphene nanoplatelets (GNPs) are short stacks of individual layers of graphite that are a newly developed, lower cost material that often increases the composite tensile modulus. In this work, researchers fabricated neat epoxy (EPON 862 with Curing Agent W) and 1–6 wt % GNP in epoxy composites. The cure cycle used for this aerospace epoxy resin was 2 h at 121°C followed by 2 h at 177°C. These materials were tested for tensile properties using typical macroscopic measurements. Nanoindentation was also used to determine modulus and creep compliance. These macroscopic results showed that the tensile modulus increased from 2.72 GPa for the neat epoxy to 3.36 GPa for 6 wt % (3.7 vol %) GNP in epoxy composite. The modulus results from nanoindentation followed this same trend. For loadings from 10 to 45 mN, the creep compliance for the neat epoxy and GNP/epoxy composites was similar. The GNP aspect ratio in the composite samples was confirmed to be similar to that of the as‐received material by using the percolation threshold measured from electrical resistivity measurements. Using this GNP aspect ratio, the two‐dimensional randomly oriented filler Halpin–Tsai model adjusted for platelet filler shape predicts the tensile modulus well for the GNP/epoxy composites. Per the authors' knowledge, mechanical properties and modeling for this GNP/epoxy system have never been reported in the open literature. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical properties of corona-modified cellulose/polyethylene composites

The effect of corona treating the surfaces of components on tensile properties of wood fiber linear low-density polyethylene composites has been investigated. Corona treatment results in a significant increase in strength properties of the composites. Yield stress increases after treatment of one or both of the composite components. Pronounced improvement in ductility has been observed for composites containing 15 to 30% of the corona modified fiber. Relevant mechanisms involved are discussed.     

Mechanical properties of i-PP/CaCO3 composites

Tensile and impact behavior of CaCO₃-filled polypropylene was studied in the composition range 0–60 wt % filler. Tensile modulus increased while tensile strength and breaking elongation decreased with increase in CaCO₃ content. The modulus increase and elongation decrease were attributed to increased filler–polymer interaction resulting in reduction in molecular mobility, while increased amorphization and obstruction to stress transfer accounted for the tensile strength decrease. Analysis of tensile strength data showed introduction of stress concentration in the composites. Izod impact strength at first increased up to a critical CaCO₃ content, beyond which the value decreased. Surface treatment of CaCO₃ with a titanate coupling agent LICA 12 enhances the adhesion of the filler and polymer, which further modifies the strength properties. Scanning electron microscopic studies indicated better dispersion of CaCO₃ particles upon surface treatment, which effected the changes in the strength properties of the composites.     

Mechanical properties of surface-functionalized SWCNT/epoxy composites

Well-dispersed epoxy/single-walled carbon nanotube (epoxy/SWCNT) composites were prepared by oxidization and functionalization of the SWCNT surfaces using polyamidoamine generation-0 (PAMAM-0) dendrimer. For comparison purposes, neat epoxy, epoxy/PAMAM-0 and epoxy/pristine-SWCNTs were also prepared. The morphology and mechanical properties of the above composite systems were investigated and correlated with the surface characteristics of SWCNTs. It is found that surface functionalization can effectively improve the dispersion and adhesion of SWCNTs in epoxy. This leads to enhancement in mechanical properties of epoxy, but the improvement is not as significant as expected. It is also found that surface functionalization agent will have an undesirable effect on the physical and mechanical properties of epoxy/SWCNT composites. Issues regarding optimization of mechanical properties of epoxy/SWCNT composites are discussed.     

PP/PP-g-DBM/CaCO3复合材料的力学性能

以马来酸二丁酯接枝聚丙烯(PP-g-DBM)作界面改性剂,制备了聚丙烯(PP)/PP-g-DBM/CaCO_3复合材料。PP-g-DBM提高了复合材料的抗冲击性能和弹性模量。当w(CaCO_3)为30%时效果最佳,悬臂梁缺口冲击强度达到6 kJ/m~2,相对PP提高了20%;界面改性剂较大程度地改善了分散相(CaCO_3)在连续相(PP)中的分散状态。     

Mechanical properties of NR/BR/cellulose II composites

Summary Blends of natural rubber (NR) and butadiene rubber (BR) with cellulose filler have been investigated. The coprecipitation of the rubber latex-cellulose xanthate mixtures by acidulation lead to elastomer-cellulose II composites in granular form. In these blends, the NR/BR ratio has been varied from 75/25 to 25/75, and the cellulose content has been increased from 0 to 25 phr. Mechanical tests have been applied to the composite samples, and the results showed that cellulose II may be considered as a reinforcing agent. Those results gave also an insight into the role of NR and BR on the properties of the composite samples.     

Mechanical properties of siliceous earth/natural rubber composites

Siliceous earth (SE), which has a special morphology and structure, was selected as filler of natural rubber (NR) and mechanical properties of compounds were analyzed. Two processes were employed to prepare SE/NR compounds described as mechanical mixing method and latex method, respectively. Cure characteristics, mechanical properties of the vulcanizates prepared from the masterbatches were compared with those prepared by mechanical mixing method. X‐ray diffraction results of NR/SE vulcanizations indicated that mechanical mixing above the latex process facilitated the intercalation of NR into the galleries of SE. The results of mechanical properties show that SE has good reinforcing properties on NR both by latex or mechanical mixing process. By comparison, H samples show slightly higher crosslink density, tensile strength, 300% modulus, and lower elongation at break than M sample in same loading. But in the aspect of dynamic properties there exist obviously difference between latex and mechanical mixing process. Rubber processing analyzer (RPA) results showed that uncured M samples showed obviously higher storage modulus than that of H samples. The heat build‐up of M30 is much lower than that of H30. These behaviors indicated better dynamitic properties when the masterbatches prepared by the predispersing method was utilized. POLYM. ENG. SCI., 58:1043–1052, 2018. © 2017 Society of Plastics Engineers     

PP/针形纳米CaCO3复合材料的力学性能

用硬脂酸皂化改性针形纳米CaCO3表面后,将其与聚丙烯(PP)共混、挤出和注塑,制成PP／CaCO3纳米复合材料。与纯PP相比,填充针形纳米CaCO3的体积分数为4.21％时,PP体系的冲击强度和断裂伸长率分别提高了49％,339％,拉伸强度下降2．7％。改性后的纳米CaCO3与PP之间的界面作用与改性前相比有所减弱,冲击断面扫描电子显微镜照片显示,针形纳米CaCO3均匀地分散在PP基体中。偏光显微照片显示,针形纳米CaCO3对PP有明显的异相成核作用。     

Mechanical properties of wood-fiber/toughened isotactic polypropylene composites

This study investigates the mechanical properties of wood-fiber/toughened PP composite modified by physical blending with an EPDM rubber to improve impact toughness. Wood-fiber thermoplastic composites were prepared with a modified PP matrix resin, employing high shear thermokinetic compounding aided with maleated PP for the fiber dispersion. The addition of EPDM improved the impact toughness, while it reduced stiffness and strength properties. To compensate the non-plane strain fracture toughness, the specimen strength ratio (R_sb) was adopted as a comparative measure of fracture toughness. The strength ratio increased with the addition of EPDM, while it decreased with increasing wood-fiber concentration. The work of fracture increased with EPDM level except at large wood-fiber concentration. The effectiveness of the impact modification was assessed with the balance between tensile modulus and unnotched impact energy as a function of wood-fiber concentration. EPDM rubber modification was moderately effective for wood-fiber PP composites. The examination of fracture surfaces showed twisted fibers, fiber breakage, and fiber pull-out from the matrix resin.     

Mechanical properties of woodflour/linseed oil resin composites

The purpose of this project was to obtain new composites using filler and resin obtained from renewable resources, combining low cost and good mechanical properties. The matrix consisted of a polyester resin synthesized from linseed oil and further crosslinked with styrene in a peroxide‐initiated reaction. Composite materials made from the unsaturated polyester/styrene thermoset and containing various percentages of woodflour were prepared and tested. The relationships between the filler content, porosity fraction, and mechanical properties of the materials were evaluated. The bending modulus and strength of the composites were significantly higher than that of the matrix. Simple models were successfully applied in the analysis of the mechanical properties of the materials. The porosity effect was also considered in the model predictions. The results of the mechanical and dynamic mechanical tests, the scanning electron micrographs of surface fractures, and the adhesion parameter calculated from the strength models all indicated that there was a strong interfacial interaction between matrix and filler. Copyright © 2005 Society of Chemical Industry