Increase In Flexural Strength Research Articles

Oscillatory pressure-assisted plastic joining of zirconia ceramics with excellent flexural strength

Here, an oscillatory pressure is applied for the plastic joining of zirconia ceramics. The shear strain of all joined sample is as high as 0.82. After plastic joining, no large pores are observed in the joint layer, and the joint samples remain dense. The grain size of all joined samples is nearly 50 % higher than that of the sample OS (joint free). The fracture mode of the sample changes from the intergranular fracture of the sample OS to the transgranular fracture of the joined samples. The maximum flexural strength of the joined sample is as high as 1552±225 MPa, which is 110 % higher than that of the parent material. Such an increase in flexural strength may be due to the removal of large pores under a high shear strain, grain boundary strengthening, and the introduction of high-density dislocations.

Achieving property enhancements in dental resin composites via reduced concentrations of camphorquinone within a ternary initiator system

ObjectivesThe study aimed to assess the impact of diphenyliodonium hexafluorophosphate (DPI) on the physicochemical properties of experimental resin composites (ECRs) featuring reduced concentrations of camphorquinone (CQ)/amine. MethodsFive concentrations of CQ (0.125, 0.25, 0.5, 0.75, and 1 mol%) with dimethylaminoethyl amine benzoate (EDAB) in a 1:2 mol% ratio (CQ:EDAB) were incorporated into a 50:50 mass% monomer blend of bisphenol glycidyl methacrylate (BisGMA) and triethyleneglycol dimethacrylate (TEGDMA). An additional 5 groups with the same CQ:EDAB concentrations had 0.5 mol% DPI added. Each resin group contained 60 wt% of 0.7 µm barium-alumino-silicate glass. Light transmission (n = 3), real-time degree of polymerization (n = 3), temperature change during polymerization (n = 5), polymerization shrinkage strain (n = 3), flexural strength, and modulus (n = 12), as well as water sorption and solubility (n = 5), were evaluated. Data were analyzed using two-way ANOVA and Tukey's post-hoc test (α = 0.05). ResultsLight transmission was reduced in groups containing 0.125 and 0.25 mol% of CQ without DPI. DPI increased temperature, degree and rate of polymerization, despite the reduction in CQ/amine concentration. Additionally, there was an increase in polymerization shrinkage strain, flexural strength and modulus, and a reduction in water sorption and solubility in ECRs with DPI, even with lower concentrations of CQ/EDAB. SignificanceDPI improved the assessed properties of composites across various concentrations of CQ/EDAB, showing the benefit of reducing the quantity of CQ used without compromising the properties and curing of the resin composites.

Evaluation of physical and mechanical properties of graphene oxide reinforced epoxy/Kevlar hybrid composites

Graphene is a miracle material with low density, excellent mechanical strength, electrical conductivity, molecular barrier properties and many other remarkable properties. Hence, recent research has been more focused on delving into various application areas of graphene. In this study, the effects of graphene oxide (GO) on the mechanical properties of composites based on epoxy resin and Kevlar fibers were investigated. The composites were fabricated by incorporating varying concentrations (1 %, 3 %, 5 %, 10 %, and 16 %) of graphene oxide (GO) into an epoxy matrix. The matrix was reinforced by two different wt.% (12.5 % and 25 %) of Kevlar fibers (KF). The hybrid composites were manufactured by hand lay-up process in a silicon mold at room temperature. Mechanical characterizations such as flexural, impact and hardness test exhibited an enhancement of the mechanical properties of the composites. Moreover, the measured density showed a significant reduction in density with increasing wt.% of GO. As a result, it was possible to fabricate a composite with a significant increase of specific flexural strength and specific flexural modulus. A microstructural analysis of the composites was performed by Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDX). From the SEM images, it was revealed that the interphase bonding of the GO particles with Kevlar fibers and matrix was strong, thereby resulting in improved mechanical performance. It was observed that 5 wt% GO incorporation along with 25 wt% KF showed improved flexural strength, hardness and impact strength than that of sample fabricated only with Kevlar.

A novel bio-based water reducer for concrete application: Facile process and techno-economic analysis of xylonate bioproduction from lignocellulosic residues

The xylonate was bioproduced directly from lignocellulosic residues, and the application properties of crude xylonate powder were investigated with a promising potential as a bio-based concrete water reducer. The overall integrated process was evaluated on the view of mass balance and techno-economic analysis using Aspen Plus modeling. 56 g/L of calcium xylonate (XA-Ca) can be obtained within 8 h from acidic corncob hydrolysate (ACH) at a 100 % yield with the whole-cell catalysis of Gluconobacter oxydans. At the addition of 0.2 wt% in the dry concrete content, XA-Ca powder and sodium xylonate powder prepared from pure xylose and ACH could reduce water used in concrete by 15 %, 14 %, 13 %, and 13 %, respectively. XA-Ca from ACH led to a 33% increase in concrete compressive strength and a 24% increase in concrete flexural strength at day 7 compared to the blank group. The techno-economic analysis showed the minimum XA-Ca powder price to be $ 0.806/kg which can be economically feasible. This study provides a practical and economical process prototype for the industrial concrete water reducer application of novel bio-based xylonate produced from lignocellulosic residues.

Study on the characteristics of Napier grass fibre reinforced porcelain filler particulates poly lactic acid matrix biocomposite

This study investigates the complex properties of a novel biocomposite by a conventional process, which is composed of poly (lactic acid) (PLA) as the matrix, porcelain particles as fillers, and Napier grass fibre as reinforcement. The primary objective was to evaluate the mechanical, crystalline, water absorption, morphological, and antibacterial properties of the biocomposites in relation to the individual components and their synergistic impacts. When 25 g porcelain particles were added to PLA with Napier grass fibre, mechanical tests demonstrated a 25% increase in tensile strength (maximum tensile strength of 39.76 MPa) and a 30% increase in flexural strength (maximum flexural strength of 41.29 MPa). Scanning electron microscopy (SEM) revealed a strong interfacial bond between the fibre and matrix, with porcelain particles serving as bridges to facilitate stress transmission. The biocomposite exhibited reduced water absorption due to the inherent hydrophobic nature of porcelain, which enhances its resistance to bacterial growth. The study demonstrates that combining Napier grass fibre with porcelain filler particles synergistically enhances the properties of PLA, creating a viable biocomposite material suitable for use in packaging, automotive, and sustainable building industries.

Utilizing decommissioned windmill blades as reinforcement or filler for biocomposites

Decommissioned or damaged windmill blades and other wastes have limited applications and are generally disposed into landfills or incinerated. Increasing generation of wind energy will also lead to increase in blades available for disposal. It is estimated that more than 800,000 tons of blades will be available annually for disposal from 2050. Blades contain glass, carbon, resins and other valuable materials and hence it is prudent to develop methods to reuse or recycle the blades. In this study, we have used windmill blade waste (WBW) as reinforcement for polypropylene (PP) and also as filler/additive for coir-WBW-PP hybrid composites. Various proportions of the components were made into composites and studied for the changes in mechanical, acoustic, thermal and noise insulation properties. Tensile strength did not show major increase in properties whereas 70/30 WBW/PP composites had highest flexural strength and modulus. Addition of WBW considerably increased both the tensile and flexural properties of the hybrid composites with up to 180% increase in flexural strength and 173% increase in modulus. Similarly, hybrid composites had better thermal conductivity and the composites containing 80% WBW and 20% PP had the highest thermal conductivity. Coir improved the acoustic sorption due to the presence of pores and voids in the composites whereas WBW acts as filler and decreased the sound sorption. WBW can be effectively used as reinforcement or filler for PP based composites.

The fracture energy of concrete reinforced with double-helix macro basalt-fibre-reinforced polymer fibre

A novel type of fibre – double-helix macro basalt-fibre-reinforced polymer (DHM BFRP) fibre – is proposed to increase the cracking, tensile strength and ductility of concrete. The novel fibre is made from micro basalt fibres and resin, twisted together in a double helix. BFRP offers high tensile strength, good corrosion resistance and low cost, while the double-helix geometry provides excellent bond–slip performance between the fibre and the concrete matrix. Three-point bending (3PB) tests were conducted to measure the fracture energy of concrete reinforced with DHM BFRP fibres. The influences of fibre orientation (aligned and random) on cracking load, peak load, flexural strength and fracture energy were analysed. Compared with random DHM BFRP fibres, aligned fibres resulted in a 26.4% higher fracture energy and a 29.7% increase in flexural strength. Finite-element models of the 3PB tests were established using LS-Dyna. The Karagozian & Case concrete model was calibrated based on the fracture energy results to obtain a material model of fibre-reinforced concrete (FRC) considering fibre orientation. The errors between the simulated and tested maximum loads for 3PB tests of plain concrete, FRC and fibre-reinforced self-compacting concrete were 8.3%, 4.0% and 11.4%, respectively, indicating that the simulated and test results were in good agreement. This study provides a theoretical foundation and technical support for practical engineering applications of DHM BFRP fibres.

Influence of laser powder bed fusion parameters on microstructure and mechanical properties of Co–Cr dental alloy

This research investigates the impact of three process parameters of Laser Powder Bed Fusion (LPBF) - laser power, scanning speed, and base plate preheating temperature on the structure and mechanical properties of the EOS CoCr SP2 dental alloy. The LPBF process was used to fabricate dental Co–Cr alloy specimens for microstructural analysis and mechanical properties testing. Light and electron microscopy were used to determine microstructural parameters, including porosity, inclusions, and cracks. The material's chemical composition was analysed by EDS, while XRD and EBSD methods were used to determine the presence of microstructural phases and the crystallographic orientation of individual grains. The mechanical properties were evaluated through a static tensile test (Rp0.2, ε), a toughness test (KVa), and a three-point bending test to determine the flexural strength (Rms). In the microstructure, differences were observed that reflected statistically significant differences in mechanical properties (one-way analysis of variance (ANOVA) and Scheffé post hoc test (α = 0.05)) Using the base plate preheating temperature ϑp = 310 °C with a constant scanning speed v = 900 mm/s in combination with increasing laser power P from 160 W to 250 W the proportion of porosity decreased while the mechanical properties of toughness (KVa) and flexural strength (Rms) increase to maximum values.

Synthesis and characterization of chicken feather derived rachis fiber-bamboo particulate hybrid reinforced epoxy composites for sustainable structural applications

Purpose This paper aims to reduce waste management and generate wealth by investigating the novelty of combining chicken feather fiber and bamboo particles to produce hybrid biocomposites. This is part of responsible production and sustainability techniques for sustainable development goals. This study aims to broaden animal and plant fiber utilization in the sustainable production of epoxy resins for engineering applications. Design/methodology/approach This research used two reinforcing materials [chicken feather fiber (CFF) and bamboo particles (BP)] to reinforce epoxy resin. The BPs were kept constant at 6 Wt.%, while the CFF was varied within 3–15 Wt.% in the composites to make CFF-BP polymer-reinforced composite (CFF-BP PRC). The mechanical experiment showed a 21% reduction in densities, making the CFF-BP PRC an excellent choice for lightweight applications. Findings It was discovered that fabricated composites with 10 mm CFF length had improved properties compared with the 15 mm CFF length and pristine samples, which confirmed that short fibers are better at enhancing randomly dispersed fibers in the epoxy matrix. However, the ballistic properties of both samples matched. There is a 40% increase in tensile strength and a 54% increase in flexural strength of the CFF-BP PRC compared to the pristine sample. Originality/value According to the literature review, to the best of the authors’ knowledge, this is a novel study of chicken fiber and bamboo particles in reinforcing epoxy composite.

Fabrication and property characterization of biocomposite based on polyamide 11 and AP1 green ramie fiber modified with epoxy

AbstractIn this article, Vietnam ramie fiber from Moc Chau, Son La province was chosen as a reinforcement for polyamide 11 (PA11) to prepare full–biocomposites. To enhance the compatibility and adhesion with the matrix, the original ramie fiber (oRF) was treated with Ca(OH)2 solution (tRF) and then modified by epoxy (mRF). Properties and structure of these fibers were characterized by tensile test, chemical composition, Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The obtained results showed the removal of hemicellulose and lignin after treatment improved the morphology and mechanical properties of the fiber. Rheology in melting state indicated the increase in the torque of PA11 matrix by adding tRF and mRF. The improvement in mechanical properties was observed for both PA11/tRF and PA11/mRF composites. After modification, epoxy on the fiber surface enhanced the adhesion and compatibility with the matrix. This led to a strong increase in Young's modulus, tensile strength and flexural strength of about 37%, 57%, and 33%, respectively. tRF and mRF also improved thermal stability of the composite as shown in TGA and DSC analysis. Finally, mRF showed a better compatibility with PA11 than tRF by observation of SEM images.

Strengthening sandwich composites by laminating ultra-thin oriented carbon nanotube sheets at the skin/core interface

Strong, tough, and lightweight composites are increasingly needed for diverse applications, from wind turbines to cars and aircraft. These composites typically contain sheets of strong and high-modulus fibers in a matrix that are joined with other materials to resist fracture. Coupling these dissimilar materials together is challenging to enhance delamination properties at their interface. We herein investigate using a trace amount of carbon nanotube sheets to improve the coupling between composite skins and core in a composite sandwich. Ultra-thin (∼100 nm) forest-drawn multi-walled carbon nanotube (MWNT) sheets are interleaved within the skin/core interphase, with MWNTs aligned in the longitudinal direction. The mechanical behavior is characterized by end-notched flexural testing (ENF). With two MWNT sheets placed in the skin/core interphase, the following performance enhancements are achieved: 36.8 % increase in flexural strength; 127.3 % and 125.7 % increases in mode I & II fracture toughness values, respectively; and 152.8 % increase in interfacial shear strength (IFSS). These are achieved with negligible weight gain of the composite sandwich (0.084 wt% increase over the baseline sandwich without MWNT sheets). The finite element simulation results show that MWNT sheets enhance the skin/core coupling by reducing stress concentration, enabling the transition from catastrophic brittle failure to a stable ductile failure mode. The MWNT sheets interleaved sandwich composites are thus demonstrated to be stronger and tougher while providing electrical conductivity (4.3 × 104S/m) at the skin/core interface for potential de-icing, electromagnetic interference shielding, and structural health monitoring.

Biomimetic versatile wood hybrids with gradient structure towards lightweight, high strength, fire-retardant, and deterioration-resistant materials

The development of versatile wood-based biomaterials with integrated low density, high surface hardness, high strength, fire-resistance, anti-decay, and termite-resistance is highly desirable, yet challenging to skillfully fabricate. Inspired by the ubiquity of gradient biostructures in nature, we achieve biomimetic gradient densification structures by controlling the distribution of thermal-moisture fields within the wood, and combine this with in-situ curing of polyacrylic acid/borate supramolecular resins within the wood cells to transform bulk natural wood into lightweight, high strength, and multifunctional materials. The optimally gradient-densified hybrid wood, with a slight increase in density, demonstrates markedly improved mechanical properties (≈2.4 × increase in surface hardness, ≈52 % increase in flexural strength), excellent dimensional stability, and leaching resistance. In addition, the collaboration of the gradient-densified structure and the in-situ cured acrylic resin/borate supramolecular network provides the biomimetic wood hybrids with excellent fire resistance (V-0 rating in fire retardant grade, 74 % reduction in total smoke release, ≈2.5 × increase in fire performance index), decay and mildew resistance (mass loss of less than 10 %), as well as termite resistance (100 % protection efficiency and termite kill rate) properties. It is the first report to combine gradient densification with in-situ curing of supramolecular resins in the structural design and functionalization of wood-based composites. This new design principle provides guidance for fabricating advanced all-in-one wood materials with applications in lightweight, strong, fire-resistant, deterioration-resistant, and scalable building and furniture materials.

Nano clay treated jute fiber reinforced epoxy composites: Thermo‐kinetic, morphological and mechanical analysis

AbstractCurrent scientific research prioritizes sustainable and cost‐effective materials due to the depletion of traditional non‐renewable sources. Natural fiber reinforced composite materials emerge as promising solutions. However natural fibers being hydrophilic in nature are less compatible with hydrophobic epoxy matrix, to address this issue nano clay treatment of jute fibers have been done and epoxy composites were formed with their reinforcement. Through FT‐IR, thermal, mechanical, and morphological analyses, both treated and untreated composites are evaluated. The treated composites exhibit a notable 19% increase in activation energy (FWO and KAS methods) compared to untreated ones (217.5–259 KJ/mol), indicating improved thermal stability. Moreover, the treated composite demonstrates a significant 38% boost in tensile strength (30–41.4 MPa) and a 28% enhancement in flexural strength (50–64 MPa), highlighting the impact of alkali‐nano clay treatment in reinforcing structural integrity. These enhancements suggest the potential applicability of composites manufactured with alkali‐nano clay treated jute fibers (A/NC/J fiber) across various industries. This innovative approach not only bridges the gap in sustainable material development but also offers cost‐effective solutions for commercial utilization.Highlights Analyzed alkali‐nano clay treatment effects on jute fiber in epoxy composites. Studied activation energy (FWO, KAS) for untreated and treated composites. Treated composites show a 19% increase in activation energy: Thermal stability Significant improvements: 38% rise in tensile, 28% increase in flexural strength.

Enhancing Mechanical and Thermal Properties of 3D-Printed Samples Using Mica-Epoxy Acrylate Resin Composites-Via Digital Light Processing (DLP).

Digital light processing (DLP) techniques are widely employed in various engineering and design fields, particularly additive manufacturing. Acrylate resins utilized in DLP processes are well known for their versatility, which enables the production of defect-free 3D-printed products with excellent mechanical properties. This study aims to improve the mechanical and thermal properties of 3D-printed samples by incorporating mica as an inorganic filler at different concentrations (5%, 10%, and 15%) and optimizing the dispersion by adding a KH570 silane coupling agent. In this study, mica was introduced as a filler and combined with epoxy acrylate resin to fabricate a 3D-printed sample. Varying concentrations of mica (5%, 10%, and 15% w/w) were mixed with the epoxy acrylate resin at a concentration of 10%, demonstrating a tensile strength increase of 85% and a flexural strength increase of 132%. Additionally, thermal characteristics were analyzed using thermogravimetric analysis (TGA), and successful morphological investigations were conducted using scanning electron microscopy (SEM). Digital light-processing technology was selected for its printing accuracy and cost-effectiveness. The results encompass comprehensive studies of the mechanical, thermal, and morphological aspects that contribute to the advancement of additive manufacturing technology.

In-situ hybridization of an epoxy resin using polyurethane and MXene nanoplatelets for thermally stable nanocomposites with improved strength and toughness

A novel ternary composite system has been developed by combining MXene nanoplatelets with pre-polyurethane (PU) and an epoxy (EP) resin through in-situ polymerization and solution blending. Our approach aims to enhance the strength and toughness of the EP matrix while maintaining its thermal stability. The strong compatibility between isocyanate-terminated PU and hydroxyl-terminated MXene with the resin was demonstrated through chemical grafting and hydrogen bonding processes. In this ternary composite, significant improvements were observed, including a 32 % increase in tensile strength, a 46.4 % increase in flexural strength, and a 13.4 % increase in fracture toughness, even at very low filler contents of 0.05 wt% for MXene and 1 wt% for PU. A thorough examination of the fractured surfaces revealed the underlying mechanisms responsible for the improved strength and toughness. These mechanisms involve a transition from a brittle to a ductile fracture mode, which can be attributed to the combined effects of thermoplastic toughness, strong chemical bonding between PU and EP, and crack-anchoring and bridging effects facilitated by MXene nanoplatelets. The results presented herein are relevant to a wide range of applications in aerospace, automotive, electronics and various other industries where durability and thermomechanical performance of materials are critical.

Physical and mechanical properties of meta-halloysite-based geopolymer mortars

Geopolymers are amorphous materials produced by the polymerisation reaction between an aluminosilicate precursor and an alkaline reagent or by activation with phosphoric acid. The aluminosilicate raw material used in the manufacture of geopolymers an be industrial waste, such as fly ash or volcanic ash, blastfurnace slag, or it can be obtained from natural raw materials, such as metakaolin and meta-halloysite. The work aimed to select the composition of an activator for the production of meta-halloysite geopolymers with optimum physico-mechanical properties such as specific and bulk density, porosity, weight, and bulk absorption, as well as flexural and compressive strength. A two-factor experimental design was employed to determine the composition of the alkaline activator for geopolymer mortars, with sodium hydroxide solution molar concentration and sodium silicate to NaOH ratio as variables. Research has shown that increasing the amount of sodium silicate relative to the mass of a 12M NaOH solution in the activator solution improves the compressive strength of geopolymers by 36.8%, while an increase in flexural strength of 14.2% was achieved. As the molar concentration of caustic soda in the activator solution increases from 19.0 to 24.5%, the porosity of geopolymer mortars decreases. The reduction in the ratio of water glass to sodium hydroxide and the reduction in the molar concentration of NaOH increases the mass and volume water absorption of the mortar. Further studies is necessary to determine the optimal mixture of metahalloysite geopolymer, taking into account its functional properties and durability.

Studying the influence of additives of cationic latex and basalt fiber on the calculated characteristics of stone-sand mixtures made of iron tailings reinforced with cement

Problem. As a major industrial solid waste, iron tailings not only occupy a lot of agricultural land, but also pollute the environment. It is necessary to study the effect of adding different concentrations of aqueous cationic latex and different lengths of basalt fibers to the composition of crushed stone-sand mixtures of iron tailings and cement on the parameters of flexural ultimate tensile strength and the characteristics of the modulus of elasticity calculation. Goal. The effect of additives of aqueous cationic latexes of different concentrations and basalt fiber of different lengths in the composition of crushed stone-sand mixtures of iron tailings with cement on the flexural tensile strength and the elastic modulus as design characteristics was investigated. Methodology. The first stage of the study was to determine the effect of the content of two cationic latexes on the values of the tensile strength in flexion and the elastic modulus of the material from CSM-40 made of iron tailings reinforced with cement. The content of Butonal NS 198 and Butonal 5126 latexes in the composition of CSM-40 was 0, 3, 5, and 10 % by weight of the optimal amount of water at the maximum density of the mixture with cement. At the second stage, the influence of the length of basalt fibers at their content of 0.05 % by weight of the crushed stone and sand mixture on the values of the flexural tensile strength and the elastic modulus of the material from the cement-reinforced iron tailings CSM-40 was studied. It has been established that the addition of cationic latexes of the Butonal series to the composition of crushed stone-sand mixtures of iron tailings with cement causes a moderate increase in the values of the flexural tensile strength and the elastic modulus, compared to the material without the addition of latexes. Experimentally, a more significant increase in the values of the flexural tensile strength and elastic modulus of fiber-reinforced materials made of crushed stone-sand mixtures of iron tailings with cement was found compared to materials modified with cationic latexes. Conclusions:1.When the latex content is 5% (equivalent to the critical concentration of micelle formation in aqueous solution), the flexural tensile strength can be increased by a maximum of 14-15%. Under similar conditions, the elastic modulus value increases by 12-18%. 2.The addition of 0.05% (by weight) basalt fiber to the crushed stone and sand mixture of rust-colored quartzite reinforced with cement improves the bending strength and elastic modulus values compared to the non-fiber material. The largest increases in flexural tensile strength (18.5%) and elastic modulus (27.1%) are for materials with basalt fiber lengths of 18 mm.

Thermo-mechanical characterizations and erosion wear studies of fumed silica-reinforced jute/epoxy composites

This study investigates the influence of nano-fumed silica content on thermo-mechanical properties of jute/epoxy composites. The results reveal that jute composites without filler (JJJJ-0) exhibited highest tensile strength (33.01 MPa) and percentage elongation (1.9522%), while composites with 1.5% and 2.5% filler demonstrated the highest tensile modulus (1967 MPa) and flexural modulus (2432.9 MPa), respectively. The observation demonstrates that as the filler content increases in jute composites, tensile strength decreases but flexural strength increases. However, an exception is noted for sample containing excess filler (3.5%), which exhibited the lowest flexural strength (44.36 MPa). The composite with 2.5% filler exhibited the highest flexural strength (53.5 MPa). Thermal analysis indicated that the addition of nanofiller enhanced both the activation energy (Ea) and thermal stability of the jute composites. A four-layer carbon composite without filler (CCCC-0) was also fabricated in order to compare wear and thermal stability performance with jute composites. The wear study was performed at different temperatures and found that JJJJ-3.5 composite exhibited superior wear resistance at ambient temperature, while CCCC-0 composite had better wear resistance at high temperatures. Also, the surface morphology of the eroded surface was examined using a scanning electron microscope (SEM) to study the failure mechanism of composites.

In English

Natural fibre reinforced polymer composites nowadays are considered to be attractive cheap, safe and eco-friendly materials. The main problem of such composites related to the hydrophilicity of plant fibres may be successfully solved by chemical modification of their surface. However, some characteristics of the materials may be suppressed after this procedure. Therefore, the aim of the research is to find out the impact of chemical modification of filler on thermooxidative stability, tensile and flexural strength, as well as on biodegradability of polymer composites. The novelty of this work is in the examining new materials on the basis of Si-containing epoxyurethanes and chemically treated hemp woody core (HWC). Woody core that is the side product of hemp industry requiring its apropriate utilization was exposed to mercerization with sodium hydroxide solution and to further functionalization with epoxidized soybean oil (ESO) or 3-aminopropyltriethoxysilane (APS). Raw and surface treated HWC was used as reinforcement for two types of organic-inorganic epoxyurethane matrices made from sodium silicate, polyurethane prepolymer based on polyisocyanate and castor oil, and either diglycidyl ether of bisphenol-A (DGEBA) or ESO as epoxy component. Functionalization of HWC led to better mechanical properties of composites. Compared to the corresponding materials including untreated filler, maximum increase in flexural strength (26 %) was observed for the samples with ESO-containing epoxyurethane and silanized HWC, while maximum increase in tensile strength (53 %) was revealed for the ones with DGEBA-containing epoxyurethane and oil treated HWC. Thermooxidative stability was also higher for composites reinforced with functionalized HWC. The specimens with APS-treated HWC performed the best at thermal decomposition. The values of their T50% were up to 68 °C more than those for composites with unmodified filler. At the same time, the samples based on APS- or ESO-treated HWC were the most resistant to biodegradation, which may be concluded from their smallest weight loss during soil burial test.

Effects of polymer-derived ZiC interlayer on mechanical properties and ablation performance of C/C-ZiC-ZrC-SiC composites prepared by RMI

C/C-ZiC-ZrC-SiC composites were prepared by a combination of PIP (polymer infiltration & pyrolysis) and RMI (reactive melt infiltration) processes on porous C/C composites. The PIP is used for preparing a ZrC-SiC interlayer (denoted as ZiC) between the C/C composites and ZrC-SiC matrix prepared by RMI. Mechanical properties and microstructure of the composites with and without ZiC were characterized. The results show that, the increase of both flexural and tensile strength of the composites after RMI can be optimized by adjusting the ZiC and achieves 50.54% and 56.76%, respectively. The mechanisms can be attributed to the facts that the ZiC effectively protects carbon fibers and PyC from serious erosion by high-temperature melt and weakens the interfacial bond between ceramic matrix and carbon fibers, ensuring a series of stress release under external load. Interestingly, the composites with ZiC also exhibit enhanced ablation performance at ca. 2200 °C due to the improved ZrC content.