Composites from Brazilian natural fibers with polypropylene: mechanical and thermal properties

Brazil has a well established ethanol production program based on sugarcane. Sugarcane bagasse and straw are the main by-products that may be used as reinforcement in natural fiber composites. Current work evaluated the influence of fiber insertion within a polypropylene (PP) matrix by tensile, TGA and DSC measurements. Thus, the mechanical properties, weight loss, degradation, melting and crystallization temperatures, heat of melting and crystallization and percentage of crystallinity were attained. Fiber insertion in the matrix improved the tensile modulus and changed the thermal stability of composites (intermediary between neat fibers and PP). The incorporation of natural fibers in PP promoted also apparent T _c and ΔH _c increases. As a conclusion, the fibers added to polypropylene increased the nucleating ability, accelerating the crystallization process, improving the mechanical properties and consequently the fiber/matrix interaction.     

Study of microstructure and properties of HEC-g-AA/SiO2 organic-inorganic hybrid materials

HEC-g-AA/SiO₂ hybrid materials are prepared through a graft copolymerization reaction between acrylic acid (AA) monomer and hydroxyethyl cellulose (HEC), in the presence of a silica sol. The microstructure and properties of the hybrid materials are characterized by Fourier transform infrared spectra (FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively. The results show that a rigid inorganic phase SiO₂ is dispersed in flexible organic continuous phase uniformly. HEC-g-AA/SiO₂ hybrid material has no obvious phase separation in the presence of the crosslinking agent. The thermal performances of HEC-g-AA/SiO₂ are excellent, and the glass transition temperature (T _g) increases with the increased amount of the crosslinking agent.     

Thermal and mechanical properties and micro-mechanism of SiO2/epoxy nanodielectrics

In addition to electrical insulation properties, the thermal properties of nanodielectrics, such as glass transition temperature, thermal expansion coefficients, thermal conductivity, and mechanical properties, including Young's modulus, bulk modulus, and shear modulus, are also very important. This paper describes the molecular dynamics simulations of epoxy resin doped with SiO₂ nanoparticles and with SiO₂ nanoparticles that have been surface grafted with hexamethyldisilazane (HMDS) at 10% and 20% grafting rates. The results show that surface grafting can improve certain thermal and mechanical properties of the system. Our analysis indicates that the improved thermal performance occurs because the formation of thermal chains becomes easier after the surface grafting treatment. The improved mechanical properties originate from two causes. First, doping with SiO₂ nanoparticles inhibits the degree of movement of molecular chains in the system. Second, the surface grafting treatment weakens the molecular repulsion between SiO₂ and epoxy resin, and the van der Waals excluded region becomes thinner. Thus, the compatibility between SiO₂ nanoparticles and polymers is improved by the grafting treatment. The analysis method and conclusions in this paper provide guidance and reference for the future studies of the thermal and mechanical properties of nanodielectrics.     

Preparation, optical properties, magnetic properties and thermal stability of core-shell structure cobalt/zinc oxide nanocomposites

Cobalt nanoparticles coated with zinc oxide can form composite spheres with core-shell structure. This coating process was based on the use of silane coupling with agent 3-mercaptopropyltrimethoxysilane (HS-(CH₂)₃Si(OCH₃)₃, MPTS) as a primer to render the cobalt surface vitreophilic, thus it renders cobalt surface compatible with ZnO. X-ray photoelectron spectroscopy (XPS) was used to gain insight into the way in which the MPTS is bound to the surface of the cobalt nanoparticles. The morphological structure, chemical composition, optical properties and magnetic properties of the product were investigated by using transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), photoluminescence (PL) spectroscope and vibrating sample magnetometer (VSM). It was found that the Co/ZnO core-shell structure nanocomposites exhibited both of favorable magnetism and photoluminescence properties. Results of the thermogravimetric analysis (TGA) and differential thermal analysis (DTA) indicated that the thermal stability of cobalt/zinc oxide was better than that of pure cobalt nanoparticles.     

Physical and mechanical properties of silicon near the SiO2/Si interface

The influence of an oxide coating on the strength characteristics of single-crystal silicon surface layers is investigated by the microindentation method. It is shown experimentally that a strengthened layer with a thickness of 0.2–0.4 μm and a microhardness of 20–35 GPa, which is two or three times as much as the microhardness of bulk single-crystal silicon, is present near the SiO₂/Si interface. The thickness and microhardness of this layer depends on the growth conditions of the oxide. The formation of this layer is most probably caused by interstitial silicon atoms formed near the SiO₂/Si interface during silicon oxidation.     

Effect of clay silylation on curing and mechanical and thermal properties of unsaturated polyester/montmorillonite nanocomposites

This work focuses on the chemical modification of montmorillonite (MMT) (Cloisite® Na) with compatible silanes, vinyltriethoxysilane (CVTES) and γ-methacryloxypropyltrimethoxysilane (CMPS) in order to prevent agglomeration and to improve montmorillonite interaction with an unsaturated polyester resin matrix seeking to achieve a multifunctional composite. Clays were dispersed in the resin by mechanical stirring and sonication and the nanocomposites were prepared by resin transfer into a mold. The mechanical, morphological, thermal and flammability properties of the obtained composites were compared with those prepared using commercial Cloisite® 30B (C30B) and Cloisite® 15A (C15A) clays. Advantages of using silane-modified clays (CVTES and CMPS) as compared with organic-modified clays (C30B and C15A) can be summarized as similar flexural strength and linear burning rate but higher storage modulus and improved adhesion to the polyester resin with consequent higher thermal deflection temperature and reinforcement effectiveness at higher temperatures. However, organic modified clays showed better dispersion (tendency to exfoliate) and consequently delayed thermal volatilization due to the clay barrier effect.     

Glass transition temperature and thermal stability of ZnS/PMMA nanocomposites

In this article, ZnS nanoparticles were prepared by wet chemical precipitation method using zinc sulphate (ZnSO₄), sodium sulphide (Na₂S) and thio-glycerol. These nanoparticles were characterized through X-ray diffraction (XRD) and transmission electron microscope (TEM) measurements. The solution-based processing was used to prepare Poly methyl methacrylate (PMMA) nanocomposites with different weight percents (0, 2, 4, 6 and 8) of ZnS nanoparticles. The obtained ZnS/PMMA nanocomposites were characterized through XRD, scanning electron microscope and TEM measurements. The dynamic mechanical analyzer was used to obtain the storage modulus and glass transition temperature (T _g) of the nanocomposites. The apparent activation energy of the glass transition region was also determined using the Vogel–Fulcher–Tammann equation. The results indicated that the thermal stability of ZnS/PMMA nanocomposites was higher than PMMA and 6 wt. % of ZnS nanoparticles in PMMA matrix showed the maximum activation energy, which indicated that this nanocomposite had higher thermal stability than other composites.     

Physical and mechanical characterization of nanocomposites with carbon nanotubes functionalized with the matrix polymer

Single wall carbon nanotubes (SWNT) are functionalized with poly(vinyl alcohol) (PVA). The functionalized nanotubes are homogeneously dispersed in a PVA solution. Nanocomposite films with low SWNT content (0.1 to 1%) are produced by the wet-casting method. X-ray diffraction shows that the PVA crystallinity was not affected by the presence of the SWNT. The improvement in tensile modulus and strength at such low reinforcement loadings is indicative of good interfacial bonding between the functionalized nanotubes and the polymer matrix.     

Two-nozzle electrospinning of (MWNT/PU)/PU nanofibrous composite mat with improved mechanical and thermal properties

Composite nanofibrous mat composed of neat polyurethane (PU) and multiwalled carbon nanotubes/polyurethane (MWNT/PU) nanofibers have been fabricated by one-step angled two-nozzle electrospinning. The morphological, thermal, and mechanical properties of the electrospun nanofibers were evaluated. The diameters of electrospun neat PU and composite nanofibers ranged from 239 to 1058 nm. The two-nozzle electrospun (MWNT/PU)/PU composite nanofibers showed curly, and randomly-oriented fibers with interfiber bonding, and were generally bigger in size than single-nozzle electrospun nanofibers. The tensile strength of the neat PU composite nanofiber mat obtained from two-nozzle electrospinning was 25% higher than that obtained from neat PU single-nozzle electrospinning. The incorporation of MWNTs in the composite nanofiber increased the tensile strength by as much as 64% without reducing elongation, made the composite nanofiber more thermally stable, and improved the melting zone. The present results showed that side-by-side angled two-nozzle electrospinning can improve the quality of the electrospun nanofibers that could have potential application in different fields such as filtration, protective clothing and tissue engineering.     

Interphase sizing temperature effect of LaRC PETI-5 on the dynamic mechanical thermal properties of carbon fiber/BMI composites

The dynamic mechanical thermal properties of carbon fiber-reinforced bismaleimide (BMI) composites processed using polyacrylonitrile(PAN)-based carbon fibers unsized and sized with LaRC PETI-5 amic acid oligomer as interphase material at 150°C, 250°C, and 350°C were investigated by means of dynamic mechanical thermal analysis. It was found that the storage modulus, loss modulus, tan δ and the peak temperature significantly depend on the sizing temperature as well as on the presence and absence of LaRC PETI-5 sizing interphase. The result showed that the carbon fiber/BMI composite sized at 150°C had the highest storage modulus at a measuring temperature of 250°C. The storage modulus decreased with increasing sizing temperature from 150°C to 350°C, being influenced by interdiffusion and co-reaction between the LaRC PETI-5 interphase and the BMI matrix resin. The present result is quite consistent with the interfacial result reported earlier in term of interfacial shear strength and interlaminar shear strength of carbon fiber/BMI composites. It is addressed that in the present composite system the sizing temperature of LaRC PETI-5 interphase critically influences not only the interfacial properties but also the dynamic mechanical thermal properties and its control is also important.     

Physical properties,thermal stability,and glass transition temperature of multi-walled carbon nanotube/polypyrrole nanocomposites

Polypyrrole (PPy) was synthesized and doped with 1, 2, 4, and 8?wt.% of functionalized multi-wall carbon nanotubes (MWCNTs) by in situ polymerization. TGA/DTA analysis of nanocomposites revealed an increase in thermal stability by increasing the CNTs wt.%. Measurement of electrical resistivity showed a reduction in the resistivity of the composites at all temperatures. The glass transition temperature (T_g) of the samples was measured using electrical resistivity measurements and showed that by increasing the amount of functionalized MWCNTs in PPy, its T_g was increased. Temperature dependence of resistivity of pressed pure PPy showed that by increasing the pelletization pressure, the T_g increased. Also the hardness of nanocomposites was increased by increasing the MWCNTs wt.%.     

Evaluation of thermal and flame properties of HDPE-MWCNT-SiO2 nanocomposites

High-density polyethylene (HDPE) composites reinforced with multiwalled carbon nanotubes (MWCNTs) and nano-silicon dioxide (SiO₂) fillers were evaluated for flame retardancy and thermal properties for cable and wire applications. In this study, the filler percentages of MWCNT and nano-SiO₂ have varied from 0 to 5 wt% in HDPE composite with polyethylene-grafted glycidyl methacrylate compatibilizer and 3-aminopropyl triethoxy silane coupling agent. Addition of MWCNT’s and nano-SiO₂ to the HDPE composite is observed to enhance the limiting oxygen index and char formation. Cone calorimeter results also show a 53% reduction in the peak heat release rate of the HDPE composite with 5 wt% of MWCNT. The existence of synergism between the uniformly dispersed MWCNT and nano-SiO₂ has been verified using Finite Element Method (FEM)-based thermal simulations.     

反应溅射VN/SiO2纳米多层膜的微结构与力学性能

采用 V 和 SiO2 靶通过反应溅射方法制备了一系列具有不同 SiO2 和 VN 调制层厚的 VN/SiO2 纳米多层膜.利用X射线衍射、X射线能量色散谱、高分辨电子显微镜和微力学探针表征了多层膜的微结构和力学性能.结果表明:在Ar,N2混和气体中,射频反应溅射的SiO2薄膜不会渗氮.单层膜时以非晶态存在的SiO2,当其厚度小于1 nm时,在多层膜中因VN晶体层的模板效应被强制晶化,并与VN层形成共格外延生长.相应地,多层膜的硬度得到明显提高,最高硬度达34 GPa.随SiO2层厚度的进一步增加,SiO2层逐渐转变为非晶态,破坏了与VN层的共格外延生长结构,多层膜硬度也随之降低.VN调制层的改变对多层膜的生长结构和力学性能也有影响,但并不明显.     

Dependence of structural and magnetic properties of CoFe2O4/SiO2 nanocomposites on annealing temperature and component ratio

Cobalt ferrite (CoFe₂O₄) nanoparticles embedded in amorphous silica can be synthesized by using tetraethylorthosilicate (TEOS) and metallic nitrates as precursors. A well-established silica matrix network provides nucleation locations for CoFe₂O₄ nanoparticles, thus confining their growth and aggregation. The structural and magnetic properties show strong dependence on the variation of particle size caused by annealing temperature and CoFe₂O₄ ratio, resulting in higher crystallization, saturation magnetization M_s and remanent magnetization M_r as the annealing temperature and CoFe₂O₄ ratio increase. But the variation of coercivity H_c is not in accordance with that of M_s and M_r, indicating that H_c is not determined by the size of CoFe₂O₄ nanoparticles only. The realization of the adjustable particle sizes and the controllable magnetic properties makes the applicability of CoFe₂O₄ even more versatile.     

Swelling and mechanical properties of radiation crosslinked Au/PVA hydrogel nanocomposites

Hydrogel nanocomposites of polyvinyl alcohol (PVA) filled with gold nanoparticles (Au NPs) were synthesised using gamma irradiation technique. Structural, optical, and morphological characterisation was performed using powder XRD, UV-vis, FESEM, and TEM techniques. Inclusion of Au NPs at the time of crosslinking may have reduced the binding sites of PVA matrix, which resulted in high-swelling capacity of Au/PVA hydrogel nanocomposites. The increase in mechanical stability of the Au/PVA hydrogel nanocomposites has been observed and it may be due to increase in the crystallinity percentage with increased Au NPs in PVA matrix. These nanocomposites may fulfil the increasing demand for multifunctional hydrogel with enhanced swelling and mechanical properties.     

Study of thermal and optical properties of SiO2/GaN opals by photothermal deflection technique

In this paper the thermal and optical properties of the SiO₂/GaN synthetic opals are studied by photothermal deflection technique. This technique, used in different configurations, allows to determine the effective thermal diffusivity and the absorption spectra.     

Improvement of the mechanical and rheological properties of HDPE/PET/MWCNT nanocomposites

High density polyethylene (HDPE)/poly (ethylene terephthalate) (PET) (90/10 wt.%) blends and HDPE/PET/multi-walled carbon nanotubes (MWCNTs) nanocomposites were prepared by melt mixing process, and the influence of MWCNTs on the mechanical and rheological properties of the nanocomposites was investigated. MWCNTs were added up to 5 wt.% in the HDPE/PET matrix. Transmission electron microscopy images reveal that the MWCNTs were homogeneously dispersed in the HDPE/PET matrix. Improvement of mechanical properties was observed by the addition of MWCNTs compared with HDPE/PET blends. Prominent increases in the complex viscosity and storage modulus of the nanocomposites were found with increasing MWCNT content.     

Preparation of MPS (mercaptopropyltrimethoxysilane)-coated SiO2 nanoparticle and its effect on mechanical properties of surface treated SiO2/EVA nanocomposite

SiO₂ nanoparticles were synthesized from different three precursors, namely, TEOS (tetraethyl orthosilicate), sodium metasilicate and sodium silicate. First, SiO₂ nanoparticles were prepared by a controlled hydrolysis of TEOS. In another method, SiO₂nanoparticles were prepared by precipitation in an emulsion medium from sodium metasilicate and hydrochloric acid solution. Finally, SiO₂ nanoparticles were also synthesized from sodium silicate by an emulsion method. In this study, we concentrated on dispersion and compatibility between nanosized SiO₂ particles and EVA (ethylene vinyl acetate). Therefore, surface modification of synthesized SiO₂ nanoparticles was accomplished with MPS (3-mercaptopropyl trimethoxysilane) to enhance homogeneous dispersion and compatibility between the obtained SiO₂ nanoparticles and EVA. Finally, nanocomposites of surface treated SiO₂ nanoparticles and EVA were prepared. By inserting the MPS-coated SiO₂ nanoparticles into EVA, abrasion resistance and hardness were increased remarkably. On the other hand, insertion of SiO₂ nanoparticles barely decreased original tensile strength and elongation of EVA. Consequently, MPS-coated SiO₂/EVA nanocomposite can have an improved abrasion resistance and hardness compared with raw EVA, without decrease tensile strength and elongation. The characterization of synthesized SiO₂ nanoparticles and their nanocomposite with EVA was conducted by TEM, SEM, FTIR photography and mechanical property tests such as abrasion, hardness, tensile strength and elongation.     

Effect of monomer-treated inorganic fillers on mechanical,rheological, and thermal properties of LLDPE nanocomposites

This article discusses the role of nanoscale calcium carbonate (nCC) surface treatment in affecting the mechanical, rheological, and thermal properties of linear low-density polyethylene (LLDPE). The mechanical tests indicated that nCC could simultaneously reinforce and toughen LLDPE. In addition, the composite sample with methacrylic acid (MA)-treated nanoparticles shows further increased mechanical properties as compared to unmodified nanoparticles. In the presence of dicumyl peroxide (DCP), a small amount of MA could increase markedly the mechanical properties of LLDPE/nCC composites. The results of rheological property analysis indicated that the viscosity increased with increasing amount of the filler, especially at low shear rates, but showed a substantial reduction with increasing concentration of the reactive monomer. The thermal behavior of these materials is evaluated by differential scanning calorimetry and thermogravimetric analysis. The addition of a small amount of MA and DCP enhances the stabilization of the blends.     

Microstructure and interfacial interaction of polyimide/silica hybrid nanocomposites prepared with 3-aminopropyltriethoxysilane

A series of polyimide (PI)-silica hybrid nanocomposites are prepared from 3,3′,4,4′biphenyltetracarboxylic dianhydride (BPDA)-4,4′-oxydianiline (ODA) polyamic acid (PAA) and tetraethoxysilane (TEOS) or tetramethoxysilane (TMOS) by the sol-gel process. 3-Aminopropyltriethoxysilane (3-APS) is used to enhance the interfacial interaction between polyimide and silica. The morphology, interfacial interaction, and properties of the hybrids are investigated using scanning electron microscope (SEM), UV-vis spectroscopy, atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). SEM and AFM images indicate that silica particles of ca. 45-55 nm size are uniformly distributed in polyimide matrices and that the interfacial interaction between PI and TEOS is better than that between PI and TMOS. The optical transparencies of the PI/TEOS hybrids are better than that of the PI/TMOS hybrids. FTIR spectra confirm the Si O Si bond as well as the conversion of PAA to polyimide and PI/silica hybrid films. The thermal stability is increased after incorporation of the silicas in the polyimide matrix.