Thermal and Flammability Properties of Polypropylene/Silica Aerogel Composites

Polypropylene (PP)/silica aerogel (SA) composites were prepared and their thermal and flammability properties were studied. The PP/SA composites with different weight percent were prepared via melt compounding method using an internal mixer. Their morphology, thermal conductivity, thermal stability and combustion behavior were characterized. The SEM images confirmed the homogenous mixing of the components. The measurement of the thermal conductivities of samples indicated that PP would be a better thermal barrier in the presence of SA. The thermal gravimetric analysis results showed that combining the silica aerogel particles into polypropylene increased the decomposition temperature. The resultant composites displayed improved flame retardancy with a significant reduction in the peak heat release rate and increase of limited oxygen index value. It can be concluded that the flame retardant mechanism of PP/SA composites is associated with two decisive factors: a coat-like char effect and a physical crosslinking effect.     

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.     

Investigation on Properties of Polypropylene/Multi-walled Carbon Nanotubes Nanocomposites Prepared by a Novel Eccentric Rotor Extruder Based on Elongational Rheology

The properties of polymer matrix composites are related not only to the chemical composition of the materials but also to the processing equipment used for their preparation which has a direct influence on the microstructure of the composites. In this paper polypropylene (PP)/multi-walled carbon nanotubes (MWCNTs) nanocomposites were prepared by melt blending through a self-developed, eccentric rotor extruder (ERE). The structure and elongational deformation mechanism of an ERE were described in detail. The morphological, rheological, thermal and mechanical properties of the resulting PP/MWCNTs nanocomposites were investigated. Scanning electron microscopy (SEM) and rheological analysis showed that the MWCNTs were well dispersed in the PP matrix. The thermal stability was investigated by thermogravimetric analysis (TGA) and indicated that the addition of MWCNTs could effectively improve the thermal stability of pure PP. The percentage of crystallinity and tensile strength of the composites were improved as a result of the heterogeneous nucleation effect of the MWCNTs in the PP matrix. The research results revealed that the enhancement of the properties of PP/MWCNTs composites could be attributed to a better dispersion of the MWCNTs in the matrix as compared to samples prepared by conventional extrusion.     

Preparation and Mechanical and Tribological Properties of High-Density Polyethylene/Hydroxyapatite Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with hydroxyapatite nanorods (nHA) were fabricated by means of extrusion and injection molding. The thermal, mechanical, and dry sliding wear properties of HDPE-based nanocomposites filled with nHA loadings up to 20 wt% were investigated. The results of mechanical property characterization showed that nHA additions improved the hardness, elastic modulus, and yield strength of HDPE at the expense of its tensile ductility and impact strength. Thermogravimetric analysis and heat deflection temperature measurements revealed that nHA fillers are very effective to enhance the thermal stability of HDPE. The wear behavior of HDPE/nHA nanocomposites was studied using a pin-on-disk tribometer. nHA fillers of a large aspect ratio improved the wear resistance of HDPE substantially because of their load-bearing effect and the formation of a continuous transfer film on the steel counterface.     

Mechanical and Thermal Properties Enhancement of Poly(Lactic Acid)/Halloysite Nanocomposites by Maleic-Anhydride Functionalized Rubber

Poly(lactic acid) (PLA)/halloysite composites were prepared using melt compounding followed by compression molding. Maleic anhydride grafted styrene-ethylene/butylene-styrene (SEBS-g-MAH) was used to toughen the PLA composites. The mechanical properties of the PLA composites were studied through tensile, flexural, and impact tests. The thermal properties were characterized by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The fracture surfaces of the composites were assessed by using field emission scanning electron microscopy (FESEM). The impact strength and thermal properties of the PLA/halloysite composites were increased by addition of SEBS-g-MAH.     

Physical Properties of Micro Hollow Glass Bead Filled Castor Oil-Based Polyurethane/Epoxy Resin IPN Composites

A series of micro hollow glass beads (HGB) filled castor oil-based polyurethane/epoxy resin graft interpenetrating polymer network (IPN) composites were prepared. The tensile and impact strengths, impact fractured surfaces, damping properties and thermal stability of the IPN composites were studied systematically in terms of composition. Results revealed that the addition of HGB into polyurethane/epoxy IPN can significantly improve not only the tensile strength but also the impact strength. The tensile strength was increased by 61% and at the same time the impact strength was increased by 25% when the HGB content was 1.5%. The damping properties were better than the composition of 0.5% or 2% HGB content when the HGB content was 1% or 1.5%. The thermal decomposition temperature was also slightly improved by the incorporation of HGB. It is suggested that the HGB reinforced polyurethane/epoxy resin IPN composites could be used as structural damping materials.     

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.     

Study on the Tribological Properties of Carbon Fabric Reinforced Phenolic Composites Filled with Nano-Al2O3

Carbon fabric reinforced phenolic (CFRP) composites filled with nano-Al₂O₃ were prepared by a dip-coating and heat molding process and the tribological properties of the resulting composites under different sliding conditions were investigated systematically on a block-on-ring test rig. The worn surfaces were observed in a scanning electron microscope (SEM) to understand the mechanism. Nano-Al₂O₃ particles, as the filler, were effective in reducing the friction coefficient and wear rate of the CFRP composites. The steady state friction coefficient of the CFRP composites filled with 4 wt.% nano-Al₂O₃ particles was about 65.5% of that of unfilled CFRP composites, and the wear rate, in this case, was about 74.7% of that of unfilled CFRP composites. Tribological tests under different sliding conditions revealed that the filled CFRP composites seemed to be more suitable than unfilled CFRP composites for tribological applications under higher sliding speed and load. Moreover, the wear resistances of the unfilled and filled CFRP composites were found to be related to the stability of the transfer film on the counterface.     

Preparation and Properties of Nano‐SiO2/Epoxy Composites Cured by Mannich Amine

Nano‐SiO₂/epoxy composites cured by Mannich Amine (type T‐31) were prepared and studied and the results are reported in this paper. The nano‐SiO₂ was pretreated by a silane coupling agent (type KH‐550) and mixed with epoxy resin (type E‐51) using an ultrasonic processor. Amounts of filler loading ranged from 1% to 5% of the weight of the epoxy resin. Some properties of the resulting composites were characterized by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results of tensile tests and impact tests showed that the composite with 3% nano‐SiO₂ loading presented the best mechanical performances. The tribological performance and thermal stability of the materials were also improved with the addition of nano‐SiO₂.     

Physical properties of a high molecular weight hydroxyl-terminated polydimethylsiloxane modified castor oil based polyurethane/epoxy interpenetrating polymer network composites

A series of polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites modified by a high molecular weight hydroxyl-terminated polydimethylsiloxane (HTPDMS) were prepared. The effects of HTPDMS content on the phase structure, damping properties and the glass transition temperature (Tg) of the HTPDMS-modified PU/EP IPN composites were studied by scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). Thermogravimetric analysis (TGA) showed that the thermal decomposition temperature of the composites increased with the increase of HTPDMS content. The tensile strength and impact strength of the IPN composites were also significantly improved, especially when the HTPDMS content was 10%. The modified IPN composites were expected to be used as structural damping materials in the future.     

Effect of Abrasives on Three-Body Abrasive Wear Behaviour of Particulate-Filled Polyamide66/Polypropylene Nanocomposites

Polyamide66/polypropylene (PA66/PP) blend, graphite (Gr)-filled PA66/PP composite and nanoclay (NC)-filled PA66/PP nanocomposites were prepared by twin screw extrusion and injection molding. Three-body abrasive wear behaviour of the injection moulded composites was carried out using a rubber wheel abrasion wear tester. In this study, angular silica sand and quartz particles of size ranging from 200 to 250 μm were used as dry and loose abrasives. The tests were carried out for 150, 300, 450 and 600 m abrading distances at a constant load of 36 N. It was observed that inclusion of particulate fillers in PA66/PP have significant influence on wear under varied abrading distances for different abrasive particles. Further, it was found that NC-filled PA66/PP nanocomposite exhibited lower wear rate compared to Gr filled ones for different abrasive particles. In addition, the worn surfaces of the samples were examined by scanning electron microscopy (SEM) and the morphology was also discussed.     

Organic Nano-Montmorillonite for Simultaneously Improving the Flame Retardancy,Thermal Stability,and Mechanical Properties of Intumescent Flame-Retardant Silicone Rubber Composites

The flammability of room temperature vulcanized silicone rubber (RTVSR) composites filled with melamine phosphate (MP) as intumescent flame-retardant additives was characterized by limiting oxygen index (LOI), UL-94 test, and cone calorimeter. In addition, the thermal degradation of the composites was studied using thermogravimetric analysis (TGA). Furthermore, in order to relate to actual application requirements, the comprehensive performance of the RTVSR/MP composites was optimized by adding organic nano-montmorillonite (OMMT) as a partial substitute for the MP. The as-prepared intumescent flame-retardant RTVSR/MP/OMMT nanocomposites were characterized by LOI, UL-94 test, TGA, cone calorimetry, scanning electron microscopy (SEM), and mechanical tests. The residue morphology formed after the burning of the nanocomposites was analyzed by its SEM and digital photographs. The results showed that the flame-retardant nanocomposites filled with 10 phr OMMT and 35 phr MP displayed the best comprehensive performance in terms of the flame retardancy, mechanical properties, and heat stability at low cost. It is expected that the intumescent flame-retardant silicone rubber composites with simultaneously improved flame retardancy, thermal stability, and mechanical properties will meet more requirements of the increasingly complex applications.     

Mechanical and tribological enhancement of polyoxymethylene-based composites with long basalt fiber through melt pultrusion

Abstract

The polyoxymethylene (POM)/basalt fiber composites were prepared by use of long fiber-reinforced thermoplastic technology through melt pultrusion. The mechanical and tribological properties, morphology, and thermal stability of the resulting composites were investigated. The composites exhibit significant improvements in tensile, flexural, and notched impact strength. These mechanical strength and toughness are dependent on the fiber content over the full range of the study. The residual fiber length and distribution in the injection-molded specimens were characterized. The prominent reinforcement effect of basalt fiber on POM is derived from the supercritical fiber length, which is much longer than that of the short fiber-reinforced ones and thus makes the composites take full advantage of the strength of the reinforcing fibers. The Kelly–Tyson model was used to predict the ultimate tensile strength of POM composites using the measured values of residual fiber length in the matrix, but the deviations were observed at the high contents of basalt fiber. The morphologic investigation indicates that the fiber pullout and fiber breakage both contribute energy dissipation to the tensile fracture of the composites. The tribological characterization indicates that the friction coefficients and specific wear rates of POM composites also decrease remarkably. Such an improvement of tribological performance is due to the presence of the high wear-resistant basalt fibers on the top of the worn surface bearing the dynamic loadings under sliding. Moreover, the dynamic mechanical analysis reveals that the storage moduli of the composites increase with increasing the fiber content, whereas the loss factors present an opposite trend.     

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.     

Evaluation of thermomechanical properties of epoxy–basalt fibre composites modified with zeolite and silsesquioxane

The aim of this study was to verify the influence of zeolite and silsesquioxane (POSS) addition on thermo-mechanical properties of basalt fiber reinforced epoxy composites. The dynamic mechanical thermal analysis was conducted with different frequencies at bending mode. The mechanical properties were determined at static tensile test and Charpy impact strength method. The structure of composites was determined by scanning electron microscopy. The thermal stability was characterized by thermogravimetric analyses in inert and oxidizing atmospheres. The impact strength and thermal stability of the composites with zeolite and silseqioxane were higher than the reference sample. Thus, these composites can be used as thermally stable materials with high stiffness.     

Preparation, characterization and properties of amino-functionalized montmorillonite and composite layer-by-layer assembly with inorganic nanosheets

An amino-functionalized montmorillonite (APTMS-MMT) was prepared by the grafting of 3-aminopropyltrimethoxysilane (APTMS) on the surface of MMT via the ultrasonic synthesis process and characterized by a variety of techniques: FT-IR, thermogravimetic analysis (TGA), particles size analysis and ζ-potential measurement. The results showed the size and size distribution of APTMS-MMT particles were decreased, and the ζ-potential of particles was increased obviously via the ultrasonic synthesis process. The particles of 30% APTMS-MMT_US (MMT modified with 30 wt% APTMS with ultrasonic synthesis process) had a z-average diameter of about 500 nm and a polydispersity index of 0.2. The resultant 30% APTMS-MMT_US was dispersed uniformly and stably in water. The poly(acrylic acid) (PAA)/APTMS-MMT multilayer films were grown through layer-by-layer (LBL) deposition of PAA and APTMS-MMT. SEM results indicated that the ultrasonic synthesis of APTMS-MMT increased dispersability of clay sheets at high loadings. The thermal stability and mechanical properties of PAA/APTMS-MMT composites were investigated by TGA and tensile test respectively. The results showed the ultrasonic synthesis of APTMS-MMT enhanced the thermal stability and mechanical properties of PAA/APTMS-MMT composites significantly. PAA/30% APTMS-MMT_US composite displayed 3 times higher strength and 6 times higher Young's modulus when compared with pure PAA polymer.     

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.     

改性高岭土填充聚丙烯的光谱分析

采用湿法对高岭土进行表面改性,熔融共混法制备了PP/高岭土/PP-g-MAH复合材料.利用傅里叶变换(FTIR)红外光谱仪、热重分析(TGA)、X射线衍射(XRD)和扫描电子显微镜(SEM)手段表征和力学、热学性能测试.结果表明:改性剂很好地与高岭土反应,并且与PP-g-MAH产生良好的协同作用.复合材料的拉伸强度提高...     

Preparation and physical properties of polypropylene nanocomposites with dodecylated graphene nanoplatelets

The most important practical application of graphene nanoplatelets (GNPs) would be as nanofillers for polymer nanocomposites. However, the modification of GNPs is needed to improve the interfacial adhesion between GNPs and a polymer matrix. Therefore, in this study, the alkylation of GNPs by dodecylamine was carried out via chemical reactions between the amine groups of the alkyl amine and the carboxyl and epoxy groups of the oxidized GNPs’ surfaces. The dodecylation of the GNPs was confirmed by FTIR and TGA. The TGA data showed that the dodecyl-GNPs comprised alkyl groups 2.4%. Polypropylene nanocomposites with the dodecyl-GNPs were prepared in a platy shape by melt-blending followed by compression molding. The mechanical and thermal properties of the nanocomposites were measured by UTM, izod impact tester, DSC and DMA. Compared to the neat PP sample, the flexural modulus, flexural strength and impact strength of the PP nanocomposite with the dodecyl-GNPs 0.5 phr were increased by 38, 4 and 34% respectively. The fracture surfaces’ images of the nanocomposites taken by SEM showed that the dodecylation of the GNPs improved the interfacial adhesion between the GNPs and the PP matrix.     

Effects on the evolution of microstructure and properties of low-silicon cast aluminum alloys in service

ABSTRACT

The microstructure evolution and property change of four kinds of low silicon cast aluminum alloy exposed to heat for 0–50?h at 200°C were studied by means of Brinell hardness test, tensile property test, friction and wear property test and XRD analysis. The results show that with increasing thermal exposure time, the tensile strength of each group of samples decreased and the amount of wear increased. The tensile strength of samples with more Si content decreased slowly. When the time increased to 50?h, the increase of wear loss was the largest. The hardness of samples after thermal exposure increases compared with that before thermal exposure. The residual stress of (311) diffraction crystal surface of AlSi3.5Mg0.66 under different thermal exposure time was measured. The type of residual stress changed from residual tensile stress to residual compressive stress after thermal exposure. There is an abnormal phenomenon that the hardness of the sample increased and the amount of wear increased, and it is evident that the distribution of residual stress was inhomogeneous after thermal exposure. It is found that with increasing thermal exposure time to 50?h, the average lattice distortion ε of the low-index crystal plane and the high-index crystal plane in the aluminum alloys gradually increased.