Dispersion and characteristics of surfactant modified cellulose whiskers nanocomposites

Biodegradable nanocomposites based on 5 wt% cellulose nanowhiskers (CNW) and polylactic acid (PLA) were prepared using an extrusion process. An anionic surfactant (5, 10 and 20 wt%) was used to improve the dispersion of the CNW in the PLA matrix. The results showed that increased surfactant content resulted in improved dispersion but at the same time degraded the PLA matrix. The results from mechanical testing showed a maximum modulus for the composite with 5 wt% surfactant and as the surfactant content increased, the CNW dispersion improved and the tensile strength and elongation at break was improved compared to its unreinforced counterpart.     

Effect of Carbon Nanotubes on the Mechanical Properties of Polypropylene/Wood Flour Composites: Reinforcement Mechanism

Maleic anhydride grafted polypropylene (PP-g-MA) was employed as the compatibilizer and carbon nanotubes (CNTs) or hydroxylated CNTs as reinforcements for polypropylene/wood flour composites. The results showed that when the PP-g-MA loading level was 10 wt%, the bending strength, tensile strength, Izod notched impact strength, and elongation at break of PP-wood composites were enhanced by 85% (66.3 MPa), 93% (33.7 MPa), 5.8% (2.01 kJ/m²), and 64% (23%), respectively, relative to the uncompatibilized composites. The introduction of pristine CNTs only improved slightly the overall mechanical properties of the compatibilized composites due to poor interfacial compatibility. Unlike CNTs, incorporating hydroxylated CNTs (CNT-OH) could significantly improve all of the mechanical properties; for instance, at 0.5 wt% CNT-OH loading, the flexural strength and tensile strength reached 68.5 MPa, and 40.4 MPa about 6.6% higher than that for the composites with the same CNT loading. Furthermore, CNT-OH also remarkably enhanced the storage modulus. Contact angle and morphology observations indicated that the increases in mechanical properties could be attributed to the improvements of interfacial interactions and adhesions of CNTs with the matrix and fillers.     

Carbon nanotubes as reinforcement of styrene-butadiene rubber

This study reports an easy technique to produce cured styrene-butadiene rubber (SBR)/multi-walled carbon nanotubes (MWCNT) composites with a sulphur/accelerator system at 150 °C. Significant improvement in Young's modulus and tensile strength were achieved by incorporating 0.66 wt% of filler without sacrificing SBR elastomer high elongation at break. A comparison with carbon black filled SBR was also made. Field emission scanning electron microscopy was used to investigate dispersion and fracture surfaces. Results indicated that the homogeneous dispersion of MWCNT throughout SBR matrix and strong interfacial adhesion between oxidized MWCNT and the matrix are responsible for the considerable enhancement of mechanical properties of the composite.     

Thermal and Mechanical Properties of Poly(lactic acid)/Modified Carbon Black Composite

Poly(ethylene glycol) (PEG) was added as a plasticizer to the composite of poly(lactic acid) (PLA) and a modified carbon black (MCB). Among the three different molecular weight (M_n = 1000, 2000, 6000) PEGs used, PEG2000 promoted crystallization of PLA and enhanced the nucleation activity of MCB more efficiently than the other two. The crystallization rate of PLA/PEG2000/3 wt% MCB composite was three times that of PLA. Although a small decrease in tensile strength and modulus of elasticity of the composite was found as the PEG content increased, the elongation at break of the PLA/PEG/MCB composites significantly improved. When the PEG2000 content was 15 wt%, the elongation at break of the blend was 90%, 4.5 times that of the neat PLA.     

Design and tensile properties of aluminum borate whiskers reinforced aluminum composite with low whisker volume fraction

ZnO was firstly coated on the surface of aluminum borate whiskers (ABOw) by sol–gel. Then, ZnO-coated ABOw was added into soybean slurry to make a preform with low volume fraction and the preform was sintered at high temperatures to obtain a sufficient strength. ABOw reinforced aluminum composite (ABOw/Al) was fabricated by squeeze casting. Interfacial microstructures, tensile properties, and fracture mechanisms of the ABOw/Al composite were investigated. The results show that the coating of ABOw and the addition of soybean sacrificial filler can effectively decrease the volume fraction of whiskers in the composite. The ultimate tensile strength of composite has not changed much with the decrease of whiskers volume fraction in the composite. However, the elongation to fracture of the composite evidently increases and it can reach 11.1% at room temperature.     

Interfacial structure and mechanical properties of MgLi matrix composites

The study on interfacial structure and tensile properties of MgLi matrix composites. The results showed that there was a clear interface between the MgLi matrix and SiC whiskers. Calculation of thermodynamics confirmed that the clear interface between the matrix and SiC whiskers may contribute to the low reactionary potential or the low reactionary dynamics. However, some SiC whiskers were attacked. As a result, SiC whiskers connected with matrix in {111} and formed 70.5° or 109.5° stages on the whiskers surface in {111} face. The reason was the lower interfacial energy of {111} face. Tensile test confirmed that the SiC_w /MgLiAl composites showed higher tensile strength and higher modulus compared with MgLi matrix. Moreover, the specific strength and specific modulus were also increased obviously.     

The Mechanical and Tribological Properties of Aramid (Twaron) Fabric/Polytetrafluoroethylene Composites

A series of composites with Twaron fabric as reinforcement and polytetrafluoroethylene (PTFE) as matrix were fabricated with various contents of PTFE, viz. 30, 40, 50, 60, and 70 vol%. The Rockwell hardness and tensile strength of the composites were tested according to the corresponding standards. The composites were also evaluated for their tribological behaviors on an MPX-2000A friction and wear tester. The worn surface and wear debris of the composites were observed by scanning electron microscopy (SEM) and the mechanism is discussed. The PTFE content in the composites had a great influence on both the mechanical and tribological properties. The composite with 40 vol% PTFE provided the proper wetting of the fibers and the best load transfer efficiency and, hence, showed the best mechanical properties and tribological behaviors.     

Effect of Polyethylene Functionalization on Mechanical Properties and Morphology of PE/SiO2 Composites

In this study composites of high density polyethylene (HDPE) with various SiO₂ content were prepared by melt compounding using maleic anhydride grafted polyethylene (PE-g-MAH) as a compatibilizer. The composites containing 2, 4 and 6% by weight of SiO₂ particles were melt-blended in a co-rotating twin screw extruder. In all composites, polyethylene-graft-maleic anhydride copolymer (PE-g-MAH, with 0.85% maleic anhydride content) was added as a compatibilizer in the amount of 2% by weight. Morphology of inorganic silica filler precipitated from emulsion media was investigated. Mechanical properties and composite microstructure were determined by tensile tests and scanning electron microscopy technique (SEM). Tensile strength, yield stress, Young's modulus and elongation at break of PE/SiO₂ composites were mainly discussed against the properties of PE/PE-g-MAH/SiO₂ composites. The most pronounced increase in mechanical parameters was observed in Young's modulus for composites with polyethylene grafted with maleic anhydride. The increase in the E-modulus of PE/PE-g-MAH/SiO₂composites was associated with the compatibility and improvement of interfacial adhesion between the polyethylene matrix and the nanoparticles, leading to an increased degree of particle dispersion. This finding was verified on the basis of SEM micrographs for composites of PE/PE-g-MAH/4% by weight of SiO₂. The micrographs clearly documented that addition of only 2 wt% of the compatibilizer changed the composite morphology by reducing filler aggregates size as well as their number. Increased adhesion between the PE matrix and SiO₂ particles was interpreted to be a result of interactions taking place between the polar groups of maleic anhydride and silanol groups on the silica surface. These interactions are responsible for reduction of the size of silica aggregates, leading to improved mechanical properties.     

Influence of material processing and interface on the fiber fragmentation process in titanium matrix composites

The objective of this work is to study the effect of composite processing conditions on the nature of the fiber–matrix interface in titanium matrix composites and the resulting fragmentation behavior of the fiber. Titanium matrix, single fiber composites (SFCs) were fabricated by diffusion bonding and tensile tested along the fiber axis to determine their interfacial load transfer characteristics and the resulting fiber fragmentation behavior. Two different titanium alloys, Ti-6Al-4V (wt%) and Ti-14Al-21Nb (wt%), were used as matrix material with SiC (SCS-6) fibers as reinforcement. The tensile tests were conducted at ambient temperature and were continuously monitored by acoustic emission. It was observed that the Ti-6Al-4V/SCS-6 composite system exhibited a greater degree of fiber–matrix interfacial reaction, as well as a rougher interface, compared to Ti-14Al-21Nb/SCS-6 composites. Acoustic emissions during tensile testing showed that most of the fiber fractures in Ti-6Al-4V/SCS-6 occurred at strains below ～5% and the fragmentation ceased at ～10% strain corresponding to specimen necking. In contrast, the Ti-14Al-21Nb/SCS-6 composite deformed without necking and fiber fractures occurred throughout the plastic range until final fracture of the specimen at about 12% strain. The markedly different fragmentation characteristics of these two composites were attributed to differences in the fiber–matrix interfacial regions and matrix deformation behavior.     

The role of interface modification on the mechanical properties of injection-moulded composites from commingled polypropylene/banana granules

Commingled polypropylene (PP)/banana granules were fabricated from slivers by mixing PP fibers and banana fibers by textile equipment. By twisting the sliver, the reinforcing fibers were compacted and bonded with the molten matrix material. PP/banana composites were prepared from commingled PP/banana granules by injection moulding method with special reference to the effect of maleic anhydride modified polypropylene (MAH-PP) concentration. The mechanical properties of the composites were found to depend on the concentration of MAH-PP. The tensile and flexural properties of the composites increased with the addition of MAH-PP up to 2 wt%. After 2 wt% addition of MAH-PP, these properties tend to be stabilized. On the other hand the unmodified composites showed the maximum impact strength. Fourier transform infrared spectroscopic (FTIR) analysis of the MAH-PP modified composites showed evidence of a chemical bridge between the hydroxyl group of the banana fiber and maleic anhydride of the MAH-PP through an esterification reaction. The feature peak of the esterification occurred in the range ～ 1743 cm^?1. In order to confirm the esterfication reaction further, FTIR spectra of the banana microfibrils and MAH-PP modified PP/banana microfibril composites were taken and compared. The tensile fracture surfaces of the unmodified and MAH-PP modified PP/banana composites were studied by scanning electron microscopy (SEM). An improvement in adhesion between the fiber and the matrix was observed in the case of MAH-PP modified composites. Two different processing methods, both injection and compression mouldings were performed to prepare the PP/banana composites. Tensile properties of the composites prepared by these two methods were compared. The enhancement of tensile properties for injection-moulded composites compared to the compression-moulded composites is owing to the occurrence of orientation, better mixing and interaction between the fiber and the matrix during injection moulding. Finally, experimental results of the tensile properties of the injection-moulded composites have been compared with theoretical predictions.     

Influence of Carbon Nanotubes on the Crystallization and Directional Tensile Behavior of High-Density Polyethylene Prepared by Dynamic-Packing Injection Molding

The influence of multi-walled carbon nanotubes (MWCNTs) on the crystallization and directional tensile properties of high-density polyethylene (HDPE) was studied for samples prepared by dynamic-packing injection molding (DPIM). Oscillatory shear was imposed on the gradually cooled melt during the packing solidification stage of DPIM. For the oriented composites containing 1.8 wt% MWCNTs, the tensile fracture behavior showed typical brittle features along the flow direction (FD) and perpendicular direction (PD), which were almost the same as those that occurred in oriented pure HDPE. The elongation at break along both directions decreased due to the incorporation of MWNCTs in the oriented composites compared with the oriented pure HDPE. However, the tensile strength of the oriented HDPE/MWCNT composites was greatly improved along the FD due to the presence of carbon nanotubes; meanwhile, it was not weakened along the PD. In scanning electron microscopy observations, it was found that there were some oriented hybrid shish-kebab structures in a nanometre scale in the oriented HDPE/MWCNT composites, but not in its isotropic composites. This suggests that MWCNTs were involved in the shear-induced crystallization of HDPE. Differential scanning calorimetry measurements confirmed that the crystallinity of oriented HDPE composites with 1.8 wt% MWCNTs was higher than those of isotropic HDPE and isotropic composites, but was not obviously higher than that of oriented pure HDPE. These findings demonstrate that MWCNTs indeed affected the formation of crystalline structures, but did not greatly influence the crystallinity of HDPE under shear flow. The transition of crystalline morphology might be the reason for change in tensile behavior for the oriented HDPE/MWCNT composites compared with the oriented pure HDPE.     

Thermal and Mechanical Properties of Epoxy/Carbon Fiber Composites Reinforced with Multi-walled Carbon Nanotubes

Multi-scale hybrid composite laminates of epoxy/carbon fiber (CF) reinforced with multi-walled carbon nanotubes (MWCNTs) were fabricated in an autoclave. For laminate fabrication, 0.5 wt% of pristine MWCNTs or silane-functionalized MWNCTs (f-MWCNTs) were dispersed into a diglycidyl ether of bisphenol-A epoxy system and applied on the woven carbon fabric. The neat epoxy/CF composite and the MWCNTs-reinforced epoxy/CF hybrid composites were characterized by thermogravimetric analysis (TGA), thermomechanical analysis (TMA), tensile testing, and field emission scanning electron microscopy (FE-SEM). A significant improvement in initial decomposition temperature and glass transition temperature of epoxy/CF composite was observed when reinforced with 0.5 wt% of f-MWCNTs. The coefficient of thermal expansion (CTE), measured by TMA, diminished by 22% compared to the epoxy/CF composite, indicating an improvement in dimensional stability of the hybrid composite. No significant improvement in tensile properties of either MWCNTs/epoxy/CF composites was observed compared to those of the neat epoxy/CF composite.     

Upgrading poly(butylene succinate)/wood fiber composites by esterified lignin

Aliphatic chains were introduced into the macromolecule of kraft lignin using aliphatic chlorides as esterification reagents. The hydrophobicity of esterified lignin (EL) was enhanced as compared to the original lignin. EL was further used as a macromolecular coupling agent in poly(butylene succinate)/chemi-thermomechanical pulp fiber composites. As a result, the composites with enhanced mechanical performance were obtained, and the tensile strength, impact strength, and bending strength were increased by 25.1, 22.4, and 19.3%, respectively, under 2 wt% EL-treatment (synthesized by palmitoyl chloride, –COCl/–OH = 1.5:1) in comparison with those of the specimen without any coupling agent treatment. Furthermore, the composite prepared with EL-treated fibers shows significant lower water absorption ratio than that of untreated one. A significant increase in storage modulus (E′) was observed upon the incorporation of treated fibers. Furthermore, the improved interfacial bonding between treated fibers and matrix was verified by SEM images. The shear viscosity of composite was increased by the incorporation of EL, but in general, the rheological behaviors of composites are not significantly changed.     

Synthesis and Properties of Polyphenylsilsesquioxane Modified Phenolic Resin by in-situ Polymerization from Phenyltriethoxysilane Precursor

A series of phenolic resin-polyphenylsilsesquioxane (PR-PPSQ) composites were prepared by in situ formation from phenyltriethoxysilane (PTES) precursor during polymerization of the PR. The precursor was firstly hydrolyzed in a solution, and then the sol was added to the PR polymerization system. The structures of the composites were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and solid-state ²⁹Si nuclear magnetic resonance (Si-NMR). The PPSQs were spherical particles with a diameter of about 3 µm and nearly uniformly dispersed in the matrix, as revealed by scanning electron microscopy (SEM). The influence of PTES content on the thermal behavior of the PR was characterized by thermogravimetric analysis (TGA) in nitrogen and air atmospheres. The results showed that the onset temperature and residual weight of the composite containing 20 wt% PTES content were improved by 47°C and 8.4%, respectively, compared to the pure PR. The thermal oxidative stability was also greatly increased; the 50 wt% weight loss temperature rose from 567°C for PR to 601°C. The flexural strength of the composites was improved; in particular, the value of the composite containing 15 wt% PTES content was elevated by 32% (from 41.66 to 55.33 MPa).     

Improving the performance of conventional glass fiber epoxy matrix composites by incorporating nanodiamonds

Multiscale glass fiber epoxy matrix composites containing nanodiamonds were fabricated using vacuum bagging technique. Three different loadings of nanodiamonds were incorporated in epoxy resin after their functionalization through ozone-treatment, i.e., 0.1, 0.3 and 0.5 wt%. The functionalization of nanodiamonds was confirmed by infrared spectroscopy, which improved the dispersion of nanodiamond in epoxy resin thus improving the mechanical properties. Tensile, compression, flexural and interlaminar shear properties of the composites were improved. The tensile, compression and flexural strengths improved up to 36, 56 and 30% by the addition of 0.5 wt% nanodiamonds while the corresponding moduli increased to 30, 125 and 46%, respectively. An improvement of 38% in interlaminar shear strength was observed. The microscopy of the composites was performed using optical and electron microscopy and proper impregnation of glass fibers and the absence of the agglomerates of nanodiamonds were ensured. The homogeneous dispersion of nanodiamonds and their adhering role at fiber/matrix interface improved the mechanical properties of the composites. The developed composites are ideal candidate materials for engineering applications demanding high specific mechanical properties.     

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.     

Processing of ultra-high molecular weight polyethylene/graphite composites by ultrasonic injection moulding: Taguchi optimization

Ultrasonic injection moulding was confirmed as an efficient processing technique for manufacturing ultra-high molecular weight polyethylene (UHMWPE)/graphite composites. Graphite contents of 1 wt%, 5 wt%, and 7 wt% were mechanically pre-mixed with UHMWPE powder, and each mixture was pressed at 135 °C. A precise quantity of the pre-composites mixtures cut into irregularly shaped small pieces were subjected to ultrasonic injection moulding to fabricate small tensile specimens. The Taguchi method was applied to achieve the optimal level of ultrasonic moulding parameters and to maximize the tensile strength of the composites; the results showed that mould temperature was the most significant parameter, followed by the graphite content and the plunger profile. The observed improvement in tensile strength in the specimen with 1 wt% graphite was of 8.8% and all composites showed an increase in the tensile modulus. Even though the presence of graphite produced a decrease in the crystallinity of all the samples, their thermal stability was considerably higher than that of pure UHMWPE. X-ray diffraction and scanning electron microscopy confirmed the exfoliation and dispersion of the graphite as a function of the ultrasonic processing. Fourier transform infrared spectra showed that the addition of graphite did not influence the molecular structure of the polymer matrix. Further, the ultrasonic energy led oxidative degradation and chain scission in the polymer.     

Fabrication and characterization of jute fabrics reinforced polypropylene-based composites: effects of ionizing radiation and disaccharide (sucrose)

Composites were prepared successfully by compression molding technique using jute fabrics (reinforcing agent) and polypropylene (matrix). Jute fabrics were treated with disaccharide (sucrose) solution and composites were fabricated with the treated fabric and polypropylene. The fiber content of the prepared composites was 40% by weight. It was found that the sucrose (2% solution) decreased the tensile strength (TS) and elongation at break about 6% and 37%, respectively, but tensile modulus and impact strength improved about 27% and 32%, respectively. When gamma radiation was applied through the untreated and treated composites the mechanical properties were improved much higher in non-treated Jute/PP-based composites than that of sucrose treated composites. For 5.0?kGy gamma dose the highest mechanical properties were observed for non-treated composites. At 5.0?kGy gamma dose the improvement of TS was 14% and 2% for non-treated and sucrose treated composites, respectively. The water uptake property of the sucrose treated composites was performed up to 10 days and composites absorbed 18% water. The functional groups of the both composites were analyzed by Fourier transform infrared spectroscopy machine. The scanning electron microscopic images of the both composites were taken for the surface and fiber adhesion analysis.     

Mechanical and Thermal Properties of Polypropylene/Silica Aerogel Composites

Polypropylene (PP) composites including various amounts of silica aerogel (SA) microparticles were prepared by melt mixing in an internal mixer. The morphology and microstructure of the prepared composites were investigated by scanning electron microscopy (SEM). Mechanical properties of the samples, including elastic modulus, tensile stress, elongation and stress at break, were measured by tensile tests. In addition, the other mechanical features, including Izod impact strength, hardness and wear resistance, were evaluated and then related to the structure of the PP/SA composites. Furthermore, the thermal characteristics of the composites, such as heat deflection temperature and thermal stability, were studied by thermal gravimetric analysis (TGA). The SEM photographs indicated the satisfactory SA particles dispersion for the compositions of 1% and 3% but agglomeration of the aerogels at higher SA contents. Since the composites became stiffer, the impact and tensile strength decreased. The addition of the SA to the PP matrix yielded harder samples with lower weight loss and coefficients of friction in wear tests. The TGA evaluations confirmed that the presence of SA promoted and upgraded the thermal stability and heat deflection temperature of PP. The thermal results proved the superior potential of PP as an insulator when the SA particles were added.     

Mechanical Properties and Morphology of Polylactide Composites with Acrylic Impact Modifier

Polylactide (PLA) composites with acrylic impact modifier BPM, i.e., PLA/BPM composites, were produced by the melt blending method. The effects of BPM on the thermal properties, melting behaviors, and dynamic mechanical properties of the PLA/BPMs were investigated by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. Tensile strength, flexural strength, and modulus of the injection molded specimens were measured by an Instron tensile machine. The influence of BPM on the impact strength of injection molded PLA/BPM composites was examined using an impact tester. The morphology of cryofractured surfaces and fracture surfaces of the composites after the tensile and impact testing was also investigated using scanning electron microscope. The test results show that the composites with BPM possess better flexibility when compared with neat PLA. However, the notched Izod impact strength showed improvement only when the BPM content was higher than 15 wt%.