Glass fiber reinforced composites of phenolic–urea–epoxy resin blends

The present work aims to modify conventional epoxy resin by blending with four different phenolic–urea oligomers. These oligomers are similar to phenolic–urea resin matrix and simultaneously function as amino curing agent for epoxy matrix. In this context, phenolic–urea oligomers were prepared respectively by polycondensation reaction of four phenols namely phenol, m-cresol, resorcinol and 1,5-dihydroxy naphthalene, respectively with formaldehyde and urea in presence of acid catalyst. The resulting oligomers were characterized by elemental analysis, spectral studies (IR & NMR), number average molecular weight $(\overline{M}n)$ estimated by non-aqueous conductometric titration and thermal stability by thermogravimetric analysis (TGA). Each of these oligomers was used in resin matrix as a blending component for the modification of commercial epoxy resin for fabricating glass fiber reinforced laminates. Finally these laminates were evaluated for their synergetic thermal stability, mechanical properties and chemical resistance to different reagents.     

Thermal behavior of BST//PVDF ceramic–polymer composites

In this paper, we report the results of a study of microstructure and thermal behavior of ceramic–polymer composites composed of barium strontium titanate Ba_0.6Sr_0.4TiO₃ (BST60/40) and polyvinylidene fluoride (PVDF). The Ba_0.6Sr_0.4TiO₃ ceramic powder was prepared by the sol–gel method. Thermal evolution of the dried gel as well as ceramic powder was studied by simultaneous thermal analysis. The composite BST60/40//PVDF was obtained by hot pressing method for volume fraction of BST60/40 ceramic powder c _v = 50 %. The morphology of BST60/40//PVDF composite powder was observed by transmission electron microscopy and the morphology of BST60/40//PVDF composite sample was observed by scanning electron microscopy. Temperature dependence of dielectric constant and dielectric loss factor of BST60/40//PVDF composites was measured in the frequency range of f = (10 × 10³–1 × 10⁶) Hz. Dynamic mechanical properties of BST60/40//PVDF composites were measured by dynamic mechanical thermal analysis DMTA.     

Coconut shell particles reinforced cardanol–formaldehyde resole resin biocomposites: Effect of treatment on thermal properties

The current work focuses on the thermal behavior of biocomposites based on cardanol formaldehyde resin (CFR) reinforced with untreated and treated coconut shell particles (CSP). CFR has been synthesized by condensing cardanol with formaldehyde in the presence of NH₄OH catalyst (ratio of 1:1.6:0.36). Fabricating biocomposites is performed by compression moulding technique. The CSP with particle size of 50?µm is used in various proportions: 30 and 40?wt%. The CSP is immersed in 5?wt% NaOH solution for 5?h. Fourier transform infrared spectroscopy is used to characterize chemical formation of the new biocomposites. Thermogravimetric analysis and differential thermal analysis are applied to measure the thermal stability of composites. The thermal stability exhibits a slight decrease with particles loading from 30 to 40?wt% against neat CFR. This work gives a path for the possibility of CSP usage in low-value products in composite manufacturing.     

Effect of fiber length and loading on the properties of Schumannianthus dichotomus (murta) fiber–reinforced epoxy composites

The present work was aimed at preparing composite materials using epoxy matrix and murta fibers of varying lengths and weight percentages. The composites were analyzed on the basis of density, thermal gravimetric analysis, infrared spectroscopy, scanning electron microscopy, tensile strength, flexural strength, Izod impact strength, and Rockwell hardness studies. Twenty-five weight percent of randomly oriented fibers of 25 mm length rendered the best mechanical properties to the composite. The tensile strength of the composite was analyzed using the Hirsch model. The characterization of the composite reveals that murta fiber is a good candidate for polymer reinforcement.     

Improvement of bagasse fiber–cement composites by addition of bacterial nanocellulose: an inverse gas chromatography study

The design of green fiber-reinforced nanocomposites with enhanced properties and durability has attracted attention from scientists. The present study aims to investigate the potential of bacterial nanocellulose (BNC) as a green additive for fiber–cement composites. Inverse gas chromatography (IGC) was used to evaluate the influence of incorporation of BNC as powder or gel, or coated onto the bagasse fibers, on the fiber–cement composite (FCC) surface. The results indicated that BNC incorporation made the FCC surface more reactive, increasing the dispersive component of the surface energy. The most relevant effects were found for BNC incorporation as gel or coated on the fibers. Incorporation of BNC as gel resulted in a predominantly organic FCC surface with substantial decreased surface basicity (K _a/K _b ratio from 2.88 to 5.75). IGC also showed that FCC with BNC incorporated as gel was more susceptible to hydration. However, BNC coated on fibers prevented fiber mineralization, increasing the inorganic materials at the surface, which caused an increase in the surface basicity (K _a/K _b ratio decrease to 2.00). These promising results could contribute to development of a new generation of green hybrid composites. The IGC technique enabled understanding of the physicochemical changes that occur on deliberate introduction of nanosized bacterial cellulose into fiber–cement composites.     

Thermal behavior of Mullite–Zirconia–Zircon composites. Influence of Zirconia phase transformation

Mullite–Zirconia–Zircon composites have proved to be suitable for high-temperature structural applications, with good mechanical and fracture properties and good thermal shock resistance. In this paper, the special dilatometric behavior of a series of Mullite–Zirconia–Zircon (3–40 vol.% ZrO₂) composites is evaluated and compared with that of a pure Zircon material and explained in terms of the high Zirconia linear thermal expansion coefficient (α) and Zirconia martensitic transformation. Linear thermal expansion (α) up to 1273 K is studied and correlated with the phase composition of the composites; a linear correlation was found with the m-ZrO₂ content evaluated with the Rietveld method. Zirconia (m-ZrO₂) dispersed grains containing ceramics material showed a hysteresis in a reversible dilatometric curve (DC). The martensitic transformation temperatures could be evaluated and then compared with the endothermic and exothermic peaks temperatures obtained from the differential thermal analysis (DTA). Furthermore, the hysteresis area was correlated with m-ZrO₂ content, where composites with less than 10 vol.% ZrO₂ did not show this behavior, and from this content up to 40 vol.% of ZrO₂ a linear increase of the hysteresis area was found.     

Effect of surface treatments on the dynamic mechanical behavior of piassava fiber–polyester matrix composites

The effect of several fiber surface treatments upon the dynamic mechanical behavior of piassava fiber-reinforced composites was evaluated. In the light of the experimental results obtained the critical volume fraction for the fibers to effectively perform as reinforcement was established. The results show that all treatments performed (mercerization, acetylation, and mercerization + acetylation) enhance the fiber/matrix adhesion, but some treatments also affect the fiber’s integrity. At the elastic region the storage modulus of the composites fabricated with treated fibers was higher than that of the untreated fiber-reinforced composite. However, only the composite manufactured with 10 wt% mercerized fibers showed a statistically significant increase of the storage modulus. Above T _g the storage modulus was primarily governed by the volume fraction of fibers. Therefore, raw and treated fiber composites had essentially the same behavior.     

Thermal conductivity behavior of SiC–Nylon 6,6 and hBN–Nylon 6,6 composites

A study was performed to determine the effect of the content and orientation of fillers on the thermal conductivity of a polymeric composite packed with hexagonal boron nitride (hBN) and silicon carbide (SiC) fillers. The thermal conductivity behavior of SiC–Nylon 6,6 and hBN–Nylon 6,6 composites was more dependent on the orientation and shape of the filler than on its thermal conductivity. The thermal conductivity of SiC–Nylon 6,6 composites with 59 % (v/v) isotropic SiC fillers increased from 0.25 to 3.83 W/m K. That of hBN–Nylon 6,6 composites with 62 % (v/v) anisotropic hBN fillers increased from 0.25 to 2.16 W/m K in the perpendicular direction whereas in the parallel direction it increased rapidly to 8.55 W/m K .     

Thermal stability and glass transition behavior of PANI/γ-Al2O3 composites

Polyaniline/γ-Al₂O₃ (PANI/γ-Al₂O₃) composites were synthesized by in-situ polymerization at the presence of HCl as dopant by adding γ-Al₂O₃ nanoparticles into aniline solution. The composites were characterized by FTIR and XRD. The thermogravimetry (TG) and modulated differential scanning calorimetry (MDSC) were used to study the thermal stability and glass transition temperature (T _g) of the composites, respectively. The results of FTIR showed that γ-Al₂O₃ nanoparticles connected with the PANI chains and affected the absorption characteristics of the composite through the interaction between PANI and nano-sized γ-Al₂O₃. And the results of XRD indicated that the peaks intensity of the PANI/γ-Al₂O₃ composite were weaker than that of the pure PANI. From TG and derivative thermogravimetry (DTG) curves, it was found that the pure PANI and the PANI/γ-Al₂O₃ composites were all one step degradation. And the PANI/γ-Al₂O₃ composites were more thermal stable than the pure PANI. The MDSC curves showed that the nano-sized γ-Al₂O₃ heightened the glass transition temperature (T _g) of PANI.     

Characterization of the physical–mechanical properties of dental resin composites reinforced with novel micro-nano hybrid silica particles: An optimization study

Abstract

In the study, dental composites of color A2 using Bis-GMA/UDMA/TEGDMA resins (ratios 70/10/20), and silica filler (70%wt, 75%wt, and 80%wt) which is a hybrid of two silica types in nano and micro dimensions were made using two different photoinitiators namely BAPO and camphorquinone. The optimum photoinitiator was selected based on the mechanical tests results after which the composites were subjected to the following tests: FTIR to evaluate polymerization degree, microhardness test, UTM, and SEM micrographs were taken to analyze the surface fracture of samples. The results of photoinitiator selection (flexural strength test) is 36.54?MPa, 37.62?MPa, and 75.08?MPa for BAPO?+?camphorquinone, camphorquinone, and BAPO respectively. The results show that the BAPO photoinitiator exhibits better results over camphorquinone and also BAPO/camphorquinone initiator systems. Then after choosing the photoinitiator system composites with different filler contents show higher mechanical strength than existing dental composites. The results of the mechanical tests for the composites with different filler contents synthesized after initiator system selection were significantly higher than the values specified in ISO 4049:2009 (102?MPa over 80?MPa). FTIR results indicate that the degree of conversion in these composite is 25.41%, 37.68, and 40.94% for composites with different filler amounts.     

Thermal behavior of modified urea–formaldehyde resins

The thermal stability of pure urea–formaldehyde resin (PR) and modified urea–formaldehyde (UF) resins with hexamethylenetetramine-HMTA (Resin 1), melamine-M (Resin 2), and ethylene urea (EU, Resin 3) including nano-SiO₂ was investigated by non-isothermal thermo-gravimetric analysis (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA) supported by data from IR spectroscopy. Possibility of combining inorganic filler in a form of silicon dioxide with UF resins was found investigated and percentage of free formaldehyde was determined. The shift of DTG peaks to a high temperature indicates the increase of thermal stability of modified UF resin with EU (Resin 3) which is confirmed by data obtained from the FTIR study. The minimum percentage (6%) of free formaldehyde was obtained in Resin 3.     

Thermal properties and combustibility of elastomer–protein composites

The article describes the measurements results of the influence of waste keratin on the properties of cross-linked styrene-butadiene rubber especially taking its thermal properties and flammability into consideration. The biopolymer used was thoroughly examined by means of derivatography, elementary analysis, FTIR spectroscopy, Zetasizer nano S90, and Zetasizer 2000. It has been found that the presence of protein facilitates the cross-linking of the elastomer investigated and the elastomeric-protein materials are characterized by good thermal and mechanical properties as well as a considerably increased resistance to thermooxidative aging. Under the influence of keratin, the flammability of the composites obtained is decreased.     

Thermal behavior of the Cu–22.55 at.%Al alloy with small Ag additions

In this study the effect of Ag additions on the thermal behavior of the Cu–22.55 at.%Al alloy was studied using electrical resistivity measurements, in situ X-ray diffractometry, differential scanning calorimetry, and optical microscopy. The results indicated that Ag additions do not change the phase transformations sequence in the studied alloys, but modify its critical temperatures due to a change on entropy of system. It was verified that at the cooling rate of 10 K/min the decomposition of β phase into (α + γ₁) is incomplete, but for lower cooling rates than 1.0 K/min this reaction is completed.     

Thermal analysis kinetics of thermal decomposition of nickel–viscose composite fiber

In this study, the thermal decompositions of nickel composite fibers (NCF) under different atmospheres of flowing nitrogen and air were investigated by XRD, SEM–EDS, and TG–DTG techniques. Non-isothermal studies indicated that only one mass loss stage occurred over the temperature regions of 298–1,073 K in nitrogen. The mass loss was from the decomposition. But after this decomposition, nickel was oxidized in air, when the temperature was high enough. In nitrogen media, the model-free kinetic analysis method was applied to calculate the apparent activation energy (E _a) and pre-exponential factor (A). The method combining Satava–?esták equation with one TG curve was used to select the suitable mechanism functions from 30 typical kinetic models. Furthermore, the Coats–Redfern method was used to study the NCF decomposition kinetics. The study results showed that the decomposition of NCF in nitrogen media was controlled by three-dimension diffusion; mechanism function was the anti-Jander equation, the apparent activation energy (E _a) and the pre-exponential factor (A) were 172.3 kJ mol^?1 and 2.16 × 10⁹ s^?1, respectively. The kinetic equation could be expressed as following: $$ \frac{{{\text{d}}\alpha }}{{{\text{d}}T}} = \frac{{ 2. 1 6\times 1 0^{ 9} }}{\beta }{ \exp }\left( {\frac{ - 2 0 7 2 4. 1}{T}} \right)\left\{ {\frac{ 3}{ 2}(1 + \alpha )^{2/3} [(1 + \alpha )^{1/3} - 1]^{ - 1} } \right\}. $$      

Optimization of short Indian Areca fruit husk fiber (Areca catechu L.)–reinforced polymer composites for maximizing mechanical properties

Natural fibers are being used as reinforcing materials for polymer composites due to their eco-friendly properties. Areca fruit husk fiber (AFHF) is one such fiber; it is currently discarded waste from the tobacco industry, but has huge potential. It is light in weight with a perforated surface that enables good bonding with a polymer matrix. In this study, comprehensive characterization of physical, chemical, thermal, mechanical, and microstructural properties was carried out on the fiber and the composite made with that fiber to optimize the fiber content. The optimum fiber content is found to be 40 wt.%, whereas beyond that, fiber pull-out and debonding reduces the load-bearing capacity of the composite. The specific properties of AFHF polymer composite are even higher than that of the popular E-glass fiber composite, which positions AFHF composite as an alternative structural material.     

Thermal and quality evaluation of vegetable oils used in ruminant feed

Dairies add fat supplements to the diets of small ruminants to increase energy production and consequently the production and quality nutritional and sensorial of the milk. This study investigated the thermal and oxidative stability of babassu, castor, faveleira, and sesame oils by TG/DTA and PDSC. The profile of the fatty oils studied was determined by GC–MS as well as physicochemical characteristics. The thermogravimetric profile of the oils indicated that mass loss was caused by the decomposition or volatility of the triacylglycerides. Faveleira and sesame oils showed a high percentage of polyunsaturated fatty acids, especially C18:2. From a nutritional standpoint, unsaturated oils are more suitable supplements for animals because they promote biochemical changes beneficial to human health.     

Sintering behavior and thermal expansion of zirconia–titanium composites

The dilatometric and thermogravimetric methods were used to investigate the sintering conditions of 3Y–ZrO₂ and 3Y–ZrO₂–Ti composites. For the materials preparation, the nanometric zirconia stabilized by 3 mol% Y₂O₃ powder and micrometric titanium powder (3 and 10 vol%) were used. The green body samples were formed by slip casting method. The morphology of samples microstructures was determined by SEM observations. The stereological analysis of zirconia and zirconia–titanium composites was carried out using computer program. The density was measured using the Archimedes method. The hardness of sinters was also investigated. Addition of Ti into ZrO₂ influenced the sintering behavior and thermal expansion of obtained composites. The analysis of the sintering process and characteristic temperatures confirmed the increase of onset and final temperature of shrinkage with the increase in Ti content. The changes of the thermal expansion curves for the pure zirconia and 3Y–ZrO₂–Ti composites were the result of the αTi → βTi transformation and the transition temperature of the zirconia m → t transformation. The zirconia and composite samples were characterized by relative density about 98%, close to theoretical density. The slight growth of zirconia grains was observed.     

Thermal study of phenol–formaldehyde resin modified with cashew nut shell liquid

In this study, an experimental phenol–formaldehyde resin with 20% phenol replacement by cashew nut shell liquid (CNSL) was studied and compared with a conventional phenol–formaldehyde resin synthesized totally from petrochemical raw materials. The resins were characterized with standard lab analysis for their physicochemical specifications, while their thermal properties were studied with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). For comparison reasons pure CNSL and wood were also included in the TGA study. A DSC study conducted both for the neat resins and the system wood–resin as to examine the effect of wood on the curing performance of the resins in the real time conditions of their usage at the wood-based panels industry.The adhesion strength of these resins was investigated by their application in plywood production. The plywood panels were tested for their shear strength and wood failure performance while their free formaldehyde emissions were determined with the desiccator method. It was proved that although the neat CNSL modified PF resin (PCF) cures at longer time and higher temperature than a conventional PF resin, wood affects it more significantly, resulting in the evening of their curing performance. This is a novel finding that manifests the possibility of replacing a convention PF resin by a CNSL modified one in the plywood production, without changing any of their production conditions and with improvement to their overall properties.     

Tensile property of cord reinforced rubber composites laminate double lap jointEI北大核心CSCD

According to the structural connection form of cord reinforced rubber composite，structural test samples with different lapping process parameters were designed and prepared. The dynamic and static tensile properties were studied by using two-dimensional digital image technology. The test results were as follows：The stiffness and tensile strength of double lap composites joints increased as the strain rate increasing，while the elongation at break unchanged. Compared with the no-lap samples，the tensile strength of the double lap composites sample was reduced by nearly 50%，and with the increase of the lap width，the elongation at break gradually decreased. The samples with lap width of 65 mm decreased by 24% compared with the no-lap ones. Compared with the elastic modulus of stage II，the elastic modulus of stage III increased significantly，that of the no-lap samples increased by 3 times，that of the lap samples were doubled，and the amplification of elastic modulus decreased with the increase of strain rate. © 2023, Youke Publishing Co.,Ltd. All rights reserved.     

Influence of the zirconia transformation on the thermal behavior of zircon–zirconia composites

During a heating?Ccooling cycle, zirconia (ZrO₂) undergoes a martensitic transformation from monoclinic to tetragonal structure phases, which presents special hysteresis loop in the dilatometry curve at temperatures between 800 and 1100?°C. Monoclinic zirconia (m-ZrO₂) particles reinforced ceramic matrix composites not always present this behavior. In order to elucidate this fact a series of zircon?Czirconia (ZrSiO₄?CZrO₂) ceramic composites have been obtained by slip casting and characterized. The final properties were also correlated with the zirconia content (0?C30?vol.%). The influence of the martensitic transformation (m?Ct) in well-dispersed zirconia grains ceramic composite on the thermal behavior was analyzed. Thermal behavior evaluation was carried out; the correlation between the thermal expansion coefficients with the zirconia content showed a deviation from the mixing rule applied. A hysteresis loop was observed in the reversible dilatometric curve of composites with enough zirconia grains (??10?vol.%). Over this threshold the zirconia content is correlated with the loop area. The transformation temperatures were evaluated and correlated with the zirconia addition. When detected the m?Ct temperature transformation is slightly influenced by the zirconia content (due to the previously evaluated decrease in the material stiffness) and similar to the temperature reported in literature. The reverse (cooling) transformation temperature is strongly decreased by the ceramic matrix. The DTA results are consistent with the dilatometric analysis, but this technique showed more reliable results. Particularly the endothermic m?Ct transformation temperature showed to be easily detected even when the only m-ZrO₂ present was the product of the slight thermal dissociation of the zircon during the processing of the pure zircon material.