Effects of Rice Husk Derived Amorphous Silica on the Thermal-Mechanical Properties of Unsaturated Polyester Composites

Rice husk is rich in amorphous silica which has found various applications as a filler in rubbers and plastics. In the research described here silica was extracted from rice husk ash in the form of sodium silicate which was used to produced amorphous precipitated silica (PS) and silica aerogel (SA) using a sol – gel process and supercritical drying. These materials were then physically mixed with unsaturated polyester (UP) resin and cured at room temperature to form polymer composites. The experimental results showed that the UP composites with 30% (volume percent) of SA filler had lower density and better thermal insulation than the composites with the same amount of PS. Thermogravimetric analysis (TGA) results showed that the T_onset of the PS and SA composites were slightly delayed by 15 and 10°C, respectively. The tensile stress-strain curves showed that addition of the fillers reduced the tensile strength, but increased the elastic moduli of the UP matrix. PS filled UP composites exhibit higher moduli (higher stiffness) than that of SA filled UP composites. This was due to agglomeration and poor adhesion of the SA particles to the UP matrix while better dispersion was observed for the PS filled composite.     

Influence of binder viscosity on the control of infrared emissivity in low emissivity coating

Low emissivity is the complex system and polymer binder is one of the most important factors that affect optical and mechanical properties of the coating. Low infrared emissivity coatings were prepared by using flake aluminum particles and three types of polymer resins as fillers and binders, respectively. The influence of polymer binder viscosity on pigment particles distribution, surface morphology and infrared emissivity of the coating was systematically investigated. The results indicate that infrared emissivity of the coating can be strongly affected by the resin viscosity at the same preparation condition, which induces different aluminum particles distribution and surface morphology of the coating. Low resin viscosity is helpful for aggregating pigments and reducing the top polymer layer thickness near the surface, thus the infrared emissivity is reduced. If the resin viscosity value is decreased by two orders of magnitude, the infrared emissivity values would be reduced as much as 0.2. Additionally, a theoretical model is proposed to account for this mechanism, which indicates that sedimentation, evaporation and diffusion play important roles in forming different aluminum particles distribution during the drying process of the coating.     

Crystallization,Flame Retardancy and Mechanical Properties of Poly(Butylene Terephthalate)/Brominated Epoxy/Nano-Sb2O3 Composites Dispersed By High Energy Ball Milling

Nano-Sb2O3 particles and brominated epoxy resin (BEO) powders were dispersed in poly (butylene terephthalate) (PBT) by high energy ball milling (HEBM). Then the nanocomposites were prepared by a twin screw extruder. The influence of the nano-Sb2O3 particles on the crystallization, thermal stability, flame retardancy and mechanical properties of the PBT/BEO/nano-Sb2O3 composites were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 tests and scanning electron microscopy (SEM). The results showed that the nano-Sb2O3 particles improved the crystallizability, thermal stability and flame retardancy properties of the PBT/BEO/nano-Sb2O3 composites. When the content of nano-Sb2O3 particles was 2.0?wt%, the LOI of nano-Sb2O3/BEO/PBT composites increased from 22.0 to 27.8 and the tensile strength reached its maximum value (62.44?MPa), which indicated that the optimum value of flame retardancy and mechanical properties of PBT/BEO/nano-Sb2O3 composites were obtained.     

Mechanical and Flame Retardant Properties and Microstructure of Expandable Graphite/Silicone Rubber Composites

Flame-retardant expandable graphite (EG)/silicone rubber (SR) composites were prepared using nano-CaCO₃ particles as reinforcement filler. In addition to mechanical measurements, limited oxygen index (LOI), UL-94 and cone calorimeter tests (CCT), the thermal properties were tested by thermogravimetric analysis (TGA). The results showed that the content and particle size of the EG both had large effects on the flammability and mechanical properties of the EG/SR blends. The composites that contained 25 phr EG (50–80 mu) had excellent LOI values, 47–48, and achieved the UL-94 V-0 level while the pure SR sample had the LOI value of 25 and achieved the UL-94 V-2 level. The data obtained from the CCT indicated that the addition of EG decreased remarkably the heat release rate, smoke emission, and mass loss rate of the composites. SEM microphotographs of the EG/SR composites before and after combustion demonstrated that EG underwent a large volume expansion, and the multiporous char structure blocked heat transfer and protected the substrate from fire.     

Role of curing conditions and silanization of glass fibers on carbon nanotubes (CNTs) reinforced glass fiber epoxy composites

Curing behavior of amino-functionalized carbon nanotubes (ACNT) used as reinforcing agent in epoxy resin has been examined by thermal analysis. Experiments performed as per supplier’s curing conditions showed that modification of the curing schedule influences the thermo-mechanical properties of the nanocomposites. Specifically, the glass transition temperature (T_g) of ACNT-reinforced composites increased likely due to the immobility of polymer molecules, held strongly by amino carbon nanotubes. Further, a set of composites were prepared by implementing the experimentally determined optimal curing schedule to examine its effect on the mechanical properties of different GFRP compositions, while focusing primarily on reinforced ACNT and pristine nanotube (PCNT) matrix with silane-treated glass fibers. From the silane treatment of glass fibers in ACNT matrix composition it has been observed that amino silane is much better amongst all the mechanical (tensile and flexural) properties studied. This is because of strong interface between amino silane-treated glass fibers and modified epoxy resin containing uniformly dispersed amino-CNTs. On the other hand, PCNT GFRP composites with epoxy silanes demonstrated enhanced results for the mechanical properties under investigation which may be attributed to the presence of strong covalent bonding between epoxy silane of glass fiber and epoxy–amine matrix.     

Fracture of composites based on polyethylene and elastic particles

The composites based on low-density polyethylene with elastomer filling particles are studied. A fracture mechanism induced by the fracture of filler particles or their separation from the matrix polymer is revealed. The fracture of the composites is caused by the growth of formed rhombic pores. The natural relative elongation in a neck is shown to be an important characteristic of a polymer. If the relative elongation in a neck is lower than the strain of appearance of rhombic pores, they form at the stage of uniform tension after necking, and the composite remains plastic. If the relative elongation in a neck is higher than the strain of formation of rhombic pores, they nucleate during necking, and the material undergoes quasi-brittle fracture. Good adhesion between the matrix polymer and elastic particles hinders the appearance of rhombic pores in a neck and, thus, retains high deformation properties of the composites.     

高压下制备的累托石/酚醛树脂复合材料微结构和热性能研究

 采用物理方法在高压下制备了酚醛树脂（PF）/累托石（REC）纳米复合材料,用X射线衍射（XRD）、透射电子显微镜（TEM）及热分析（DSC/TGA）等方法,研究了复合材料的物相、显微结构以及热学性能。结果表明,不通过层间高分子聚合反应,不预先对累托石进行有机化处理,在高压下,由聚合物分子插入粘土层间,可以形成剥离型树脂/粘土纳米复合材料,并且其热学性能发生了较大的改变。     

Fast magic-angle spinning proton NMR studies of polymers at surfaces and interfaces

Solid-state proton NMR with fast magic-angle sample spinning has been used to study the structure and dynamics of polymers and the water interface in porous glass composites. The composites were prepared by photopolymerization of poly(ethyl acrylate) and other acrylate formulations in a high surface-area rigid glass matrix with 40-A interconnected pores. High resolution solid-state proton spectra were obtained for polymer films and composites with 15 kHz magic-angle sample spinning at temperatures above the polymer glass transition temperature. The solid-state proton spectra can be detected with high sensitivity and used to determine the composition of polymer and water filling the pores. These results and spin diffusion studies using 1H-29Si 2D heteronuclear correlation and wideline separation NMR show that the polymer fills the central 30 A of the pore, and that the remaining volume is filled with surface hydroxyl groups and water.     

Investigation of the Morphological and Mechanical Properties of Polyethylene Terephthalate (PET)/Ethylene Propylene Diene Rubber (EPDM) Blends in the Presence of Multi-Walled Carbon Nanotubes

In this study the blends of polyethylene terephthalate (PET)/ethylene propylene diene rubber (EPDM) in the presence of multi-walled carbon nanotubes (MWCNT) (1 and 3?wt %) were prepared by melt compounding in an internal mixer. Mechanical and morphological properties of the nanocomposites were investigated. The thermal behaviors of the PET/EPDM nanocomposites were also investigated, by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results of the mechanical tests showed that the tensile strength, elastic modulus and the hardness of the blends were increased with increasing CNT, while the impact strength and elongation at break decreased. The DSC and TGA results showed an increase of melting temperature (T_m) and degradation temperature of the nanocomposites with the addition of the carbon nanotubes, because the carbon nanotubes serve both as nucleating agents to increase T_m and prevent the composite from degradation to increase the thermal stability. The microstructure of the composites was evaluated through field emission scanning electron microscopy (FESEM) and the results showed a good distribution of the MWCNT within the polymer blend.     

Dielectric characteristics of CaCu3Ti4O12/P(VDF-TrFE) nanocomposites

Composite thin film is highly desirable for the dielectric applications. In order to develop composite thin film, a nanocomposite, in which nanosized CaCu₃Ti₄O₁₂ (CCTO) particles are used as filler and P(VDF?CTrFE) 55/45 mol% copolymer is used as polymer matrix, is investigated. The contents of CCTO in the nanocomposites range from 0% to 50?vol%. The dielectric property of these nanocomposites was characterized at frequencies ranging from 100 Hz to 1 MHz and at temperatures ranging from 200 K to 370 K. A dielectric constant of 62 with a loss of 0.05 was obtained in nanocomposite with 50?vol% CCTO at room temperature at 1 kHz. At the phase transition temperature (??340?K) of the copolymer, a dielectric constant of 150 with a loss less than 0.1 was obtained in this nanocomposite. It is found that the dielectric loss of the nanocomposites is dominated by the polymer which has a relaxation process. Comparing to composites made using microsized CCTO, the nanocomposites exhibit a much lower dielectric loss and a lower dielectric constant. This indicates that the nanosized CCTO particles have a lower dielectric constant than the microsized CCTO particles.     

Preparation and Thermal Properties of Boron-Containing o-Cresol-Formaldehyde Resin/Octa(aminophenyl)-POSS Nanocomposites

The boron-containing o-cresol-formaldehyde resin (BoCFR) and octa(aminophenyl) polyhedral oligomeric silsesquioxane (OAP-POSS) were synthesized, and the BoCFR/OAP-POSS nanocomposite prepared via an in-situ method. The curing process of the resin was characterized by Fourier transform infrared (FTIR). The thermal properties and dynamic mechanical properties of the nanocomposites were investigated. The results show that the maximal mechanical loss temperature (T_p) increased with increasing OAP-POSS content. When the content of OAP-POSS was 10 wt% the T_p was over 200°C, 27°C higher than the pure BoCFR. The BoCFR/OAP-POSS nanocomposite had better thermal stablitity than the pure BoCFR. The residual weight of the o-cresol-formaldehyde resin was only 6.13 wt% at 600°C. But the residual weight of the pure BoCFR was 55.73 wt% at 600°C, and the residual weights of the BoCFR nanocomposites were all higher than pure BoCFR. The residual weight of the BoCFR nanocomposite was 63.2 wt% at 600°C and 21.83 wt% at 900°C when the OAP-POSS content was 10 wt%. The weight loss of BoCFR/OAP-POSS nanocomposite can be divided primarily into two temperature stages, from 430°C to 550°C and from 550°C to 900°C. The main thermal degradation reaction follows first order kinetics.     

Structure and Properties of Poly(Oxypropylene) Diamine Intercalated Montmorillonite/Epoxy Composites

Abstract

A type of micro-multilayer particles with a structure similar to that of nacre was prepared by poly(oxypropylene) diamine (POPD) intercalating organic montmorillonite (OMMT). The prepared particles were then blended with epoxy resin (EP) to obtain high performance EP composites. The Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and contact angle analysis of the OMMT showed that the (POPD) had been successfully intercalated into the OMMT and the micro-multilayer particles were obtained as expected. Transmission electron microscope observation of the cured composites further confirmed that the micro-multilayer particles were well maintained in the EP network. The tensile and bending strength and glass transition temperature of the OMMT/EP composites were all increased compared with those of the EP. All these showed that the addition of the OMMT was an effective way to obtain high performance EP composites.     

Preparation and Characterization of Composites Based on Poly (Butylene Succinate) and Poly (Lactic Acid) Grafted Tetracalcium Phosphate

Tetracalcium phosphate (TTCP, Ca₄(PO₄)₂O) was functionalized by poly (l-lactic acid) (PLLA) in order to improve the dispersion of TTCP particles in poly (butylene succinate) (PBS) matrices, and then a series of the PLLA grafted TTCP/PBS (g-TTCP/PBS) composites were prepared via melt processing. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), tensile analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (DTG/TGA) and melt rheological analysis were used to investigate the structure and properties of the g-TTCP/PBS composites. The results revealed that l-lactide could be grafted onto the surface of TTCP, and the g-TTCP/PBS composites showed the best mechanical properties when the content of g-TTCP was 10 wt%. The crystallization temperature of g-TTCP/PBS composites tended to increase with the increase of g-TTCP contents. The functionalized particles played an important role in augmenting the thermal degradation rate and the complex viscosity of the composites due to their unique structure and the reasonable interfacial interaction between the particles and PBS matrix.     

Magnetostrictive properties of titanate coupling agent treated Terfenol-D composites

As a kind of composites, the bond strength between the polymer matrix and the Terfenol-D particles affects the performance of magnetostrictive composites. By observing the fracture morphologies, the bond strength of the magnetostrictive composites prepared with untreated Terfenol-D was proved weak. Titanate coupling agent was used for particles to improve the bond strength. Contact angle analysis indicates the work of adhesion of the epoxy resin to the treated Terfenol-D is larger than that to the untreated Terfenol-D. Different magnetostrictive composites with 20%, 35% and 50% particle volume fractions were prepared with treated and untreated Terfenol-D particles. Their static and dynamic magnetostriction was tested without pre-stress at room temperature. The results indicate titanate coupling agent treating increases the magnetostrictive properties of magnetostrictive composites, that is probably because the bond strength improves due to the particle treating.     

Dispersion of Nano TiO2 in Ethylene Glycol and Poly(ethylene terephthalate)

Nano TiO₂ was dispersed in ethylene glycol (EG) by the replacement of dispersion medium from water sol. EG/TiO₂ suspension was well stabilized by the electrostatic repulsive force when pH value of suspension was less than 4.3. In situ polymerization starting from bis(2-hydroxyethyl) terephthalate (BHET) and EG/TiO₂ suspension was carried out to prepare a series of poly(ethylene terephthalate) (PET)/TiO₂ nanocomposites. Under highly acidic conditions, 97% particles dispersed in PET matrix had the size less than 100 nm. With the increase of pH value, aggregation occurred and larger size particles appeared. A tensile test showed that Young's modulus of PET was increased by the addition of nano TiO₂     

Pithecellobium Clypearia Benth Fiber/Recycled Acrylonitrile-Butadiene-Styrene (ABS) Composites Prepared in a Vane Extruder: Analysis of Mechanical Properties and Morphology

The effect of compatibilizer types and concentrations on the mechanical properties and morphology of Pithecellobium Clypearia Benth Fiber (PCBF)/recycled ABS composites prepared by a vane extruder were characterized. In addition, the percentage of compatibilizer was fixed at 8%, and the effect of lubricant concentrations on the mechanical properties and torque behaviors of the composites was also studied. Maleic anhydride grafted ABS (ABS-g-MAH) and maleic anhydride grafted PS (PS-g-MAH) were used as compatibilizers; the lubricant used was Struktol TPW 604 (blend of aliphatic carboxylic acid salts and mono diamides). The composite with 8% ABS-g-MAH showed superior mechanical properties compared to the composite without compatibilizer and the 8% PS-g-MAH compatibilized composites. Compared with PS-g-MAH, ABS-g-MAH was more effective for the composites to improve the interfacial interaction and mechanical properties. The comprehensive mechanical properties of PCBF/recycled ABS composite filled with 4% lubricant were better than the composites without lubricant and the composites with any other content of TPW 604. Moreover, the torque of the composites in an internal mixer decreased with an increasing lubricant content.     

Structure and properties of thin-film metal-poly(p-xylylene) hybrid nanocomposites

Thin-film hybrid metal-poly(p-xylylene) composites synthesized by vacuum co-condensation were examined. It was demonstrated that the structure of the composites consists of a matrix comprised of polymer globules and inorganic filler nanoparticles. The shape, structure, and size of the polymer globules depend on the film thickness and the nature of the filler nanoparticles. Studying the conductivity of these materials demonstrated that it is determined by hopping conduction via surface states of the matrix. At high frequencies of the voltage applied (above 500 Hz), the electric conduction characteristics depend appreciably on the processes of recharging of the surface states of the matrix and of the nanoparticle-matrix interfaces. Tests of lithium battery anodes prepared from nanocomposites showed that these materials are promising for manufacturing chemical current sources.     

A Review of the Recent Advances in Cyclic Butylene Terephthalate Technology and its Composites

Cyclic butylene terephthalate (CBT®) oligomers are a relatively new class of material and are capable of polymerizing in an entropically driven ring-opening polymerization into high-molecular-weight polymerized CBT (pCBT) in very short times, i.e., within minutes. The most important feature of CBT is its very low, water-like melt viscosity prior to polymerization which gives rise to an excellent impregnation of fibrous reinforcements in contrast to conventional, high viscous thermoplastic resins. This opens up new possibilities in the thermoplastic composite production since thermoplastic-based composites show some advantages over thermoset-based ones. Specifically, they have a higher toughness and impact strength and they can be welded, postformed, and recycled due to their thermoplastic nature. CBT has the potential to substitute thermoset matrices in fiber-reinforced composites and may solve some of the today´s recycling issues associated with thermoset-based composites. Moreover, the low melt viscosity of CBT enhances the dispersion of nano- or conductive particles and can yield superior nano- and conductive composites. This article reviews the recent advances in processing–structure–property relationship, physical and chemical modification of pCBT, as well as the preparation of fiber-reinforced pCBT composites, pCBT nanocomposites, and conductive pCBT composites.     

Diffusion-filtration model of methane escape from a coal seam

Methane desorption from a coal seam is theoretically investigated using a model including both the diffusion of methane in coal lumps and its filtration through net-shaped pores and cracks. The methane density distribution along the seam at an arbitrary time instant is found. Explicit dependences of the amount of the methane escaped from the seam on the lump size, open and closed porosity, viscosity and solubility of methane, and pressure and temperature in the seam are determined. An effective diffusion coefficient in lumps containing methane-filled closed pores is found. In the case of hindered diffusion, the methane can be subdivided into the “fast” and “slow” fractions.     

Effect of the degree of crosslinking on the interfacial layer structure of poly(vinyl chloride) dispersed with crosslinked poly(n-butyl methacrylate) particles

The interfacial layer structure of a model incompatible polymer blend system was analyzed using ¹H pulse nuclear magnetic resonance (pulse NMR) spectroscopy. Non-crosslinked and crosslinked poly(n-butyl methacrylate) particles with a mean size of ca. 0.9 μm were prepared by seeded emulsion polymerization, and the degree of crosslinking was varied. The particles were powdered using a freeze-dry method and dispersed in poly(vinyl chloride) by melt blending. Dynamic mechanical analysis indicated that the non-crosslinked particles were completely compatible. In contrast, mutual diffusion of the polymer chains in the crosslinked particles was restricted within the particle/matrix interfacial layer. As a result, an incompatible phase structure in which the crosslinked particles were dispersed in the continuous phase was formed. Pulse NMR analysis indicated that the interfacial layer thickness was in the range of 17–98 nm. The thickness decreased with an increase in the degree of crosslinking in the particles. The interfacial layer thickness in the particles was approximately 10 times larger than that for the incompatible polymer pair. Tensile test results indicated that the elongation at break was dependent on the thickness of the interfacial layer. The yield stress was developed for the particles with high hardness that was independent of the interfacial thickness.