PLA/algae composites: Morphology and mechanical properties

Bio-composites with poly(lactic) acid as matrix and various algae (red, brown and green) as filler were prepared via melt mixing. Algae initial size (below 50 μm and between 200 and 400 μm) and concentration (from 2 to 40 wt%) were varied. First, algae morphology, composition and surface properties are analysed for each algae type. Second, an example of algae particle size decrease during processing is given. Finally, tensile properties of composites are analysed. The surface of algae flakes was covered with inorganic salts affecting filler–matrix interactions. The Young’s modulus of composites increased at 40 wt% load of algae as compared with neat PLA although the strain at break and tensile strength decreased. In most cases the influence of algae type was minor. Larger flakes led to better mechanical properties compared to the smaller ones.     

Thermal and mechanical properties of phenolic-based composites reinforced by carbon fibres and multiwall carbon nanotubes

The thermal, mechanical and ablation properties of carbon fibre/phenolic composites filled with multiwall carbon nanotubes (MWCNTs) were investigated. Carbon fibre/phenolic/MWCNTs were prepared using different weight percentage of MWCNTs by compression moulding. The samples were characterized by scanning electron microscopy (SEM), flexural tests, thermal gravimetric analysis and oxyacetylene torch tests. The thermal stability and flexural properties of the nanocomposites increased by increasing MWCNTs content (wt% ⩽1), but they decreased when the content of MWCNTs was 2 wt%. The linear and mass ablation rates of the nanocomposites after modified with 1 wt% MWCNTs decreased by about 80% and 52%, respectively. To investigate the material post-test microstructure, a morphological characterization was carried out using SEM. It was shown that the presence of MWCNTs in the composite led to the formation of a strong network char layer without any cracks or opening.     

Effect of mechanical activation pretreatment on the properties of sugarcane bagasse/poly(vinyl chloride) composites

This current work is concerned with the pretreatment of sugarcane bagasse (SCB) by mechanical activation (MA) using a self-designed stirring ball mill and surface modification of SCB using aluminate coupling agent (ACA). The untreated and differently treated SCBs were used to produce composites with poly(vinyl chloride) (PVC) as polymer matrix. The activation grade (A_g) measurement and Fourier transform infrared (FTIR) analysis of SCB showed that MA enhanced the condensation reaction between ACA and hydroxyl groups of the SCB fibres, which obviously increased the hydrophobicity of SCB. It was found that the mechanical properties of both the PVC composites reinforced by SCB with and without ACA modification increased with increasing milling time (t_M). Scanning electron microscopy (SEM) analysis showed that MA pretreatment significantly improved the dispersion of SCB in the composites and interfacial adhesion between SCB and PVC matrix, resulting in better mechanical properties of the composites.     

Mechanical and thermal properties of chicken feather fiber/PLA green composites

Chicken feather fiber (CFF)/reinforced poly(lactic acid) (PLA) composites were processed using a twin-screw extruder and an injection molder. The tensile moduli of CFF/PLA composites with different CFF content (2, 5, 8 and 10 wt%) were found to be higher than that of pure PLA, and a maximum value of 4.2 GPa (16%↑) was attained with 5 wt% of CFF without causing any substantial weight increment. The morphology, evaluated by scanning electron microscopy (SEM), indicated that an uniform dispersion of CFF in the PLA matrix existed. The mechanical and thermal properties of pure PLA and CFF/PLA composites were compared using dynamic mechanical analysis (DMA), thermomechanical analysis (TMA) and thermogravimetric analysis (TGA). DMA results revealed that the storage modulus of the composites increased with respect to the pure polymer, whereas the mechanical loss factor (tan δ) decreased. The results of TGA experiments indicated that the addition of CFF enhanced the thermal stability of the composites as compared to pure PLA. The outcome obtained from this study is believed to assist the development of environmentally-friendly composites from biodegradable polymers, especially for converting agricultural waste – chicken feather into useful products.     

Enhanced sound insulation and mechanical properties of LDPE/mica composites through multilayered distribution and orientation of the mica

In this work, the composites with multilayered distribution of the mica were fabricated by a multilayer coextrusion technique. The influence of layer number on sound insulation and mechanical properties of multilayered composites was investigated. The distribution, dispersion and orientation of mica particulates in composites were characterized by PLM and SEM. The sound insulation property of composites was measured by four microphone impedance tube. PLM and SEM images showed that the mica was distributed as the multilayered structure along the thickness direction of the composites. With the increase of layer number, more mica aggregates delaminated into thin flakes and aligned parallel to the flow direction. Compared to the conventional composites, the multilayered composites showed the enhanced sound insulation efficiency and mechanical properties. The discontinuity of sound impedance and the improved stiffness were considered to play a crucial role in the improvement of sound transmission loss.     

Influence of acid precursors on physicochemical properties of nanosized titania synthesized by thermal-hydrolysis method

The influence of nature and concentration of acid species on surface morphology and physicochemical properties of titania particles synthesized by direct thermal hydrolysis of titanium tetrachloride was investigated. The acids used were hydrochloric acid, nitric acid, sulfuric acid, and perchloric acid with a concentration of 3 M. Thermal hydrolysis of titanium tetrachloride in hydrochloric acid and perchloric acid with molar ratios of [H⁺]/[Ti⁴⁺] = 0.5, 1.0, 1.5, and 2.0, respectively, was used to study the effect of acid concentration. The synthesized materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, and thermogravimetric analysis. Characterization of the samples by X-ray diffraction studies revealed the influence of acid species on the phase transformation of titania. Samples prepared by hydrochloric acid, nitric acid, and perchloric acid formed rutile phase with rhombus primary particles, while sulfuric acid resulted in anatase phase with flake-shaped primary particles. Transmission electron microscopy and dynamic light scattering results confirmed the nanosized titania particles and the agglomeration of primary particles to form secondary particles in spherical shape. The particle size of titania prepared using perchloric acid was smaller than those prepared with other acid sources. A direct correlation between [H⁺]/[Ti⁴⁺] ratio and particle size of titania was observed.     

Development and characterization of the composites based on mesoporous MCM-41 and polyethylene glycol and their properties

Novel MCM-41/polyethylene glycol composites have been synthesized using different ratios of MCM-41. The structure of the different composites was confirmed by using various characterization tools, including: thermal analyses (TGA and DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FE-SEM). The XRD and FT-IR results indicated that PEG interacts with MCM-41 via the formation of hydrogen bonds where no new phase was detected. The TGA analysis results demonstrated that the presence of MCM-41 practically affects the temperature of the main step of degradation. The DTA analysis demonstrated that an increase in the MCM-41 content up to 30 wt.% is accompanied by a continuous decrease in the melting point of PEG.     

Grafting of nano-TiO2 onto flax fibers and the enhancement of the mechanical properties of the flax fiber and flax fiber/epoxy composite

In this article, a flax fiber yarn was grafted with nanometer sized TiO₂, and the effects on the tensile and bonding properties of the single fibers and unidirectional fiber reinforced epoxy plates were studied. The flax fiber yarn was grafted with nanometer sized TiO₂ through immersion in nano-TiO₂/KH560 suspensions under sonification. The measured grafting content of the nano-TiO₂ ranged from 0.89 wt.% to 7.14 wt.%, dependent on the suspension concentration. With the optimized nano-TiO₂ grafting content (∼2.34 wt.%), the tensile strength of the flax fibers and the interfacial shear strength to an epoxy resin were enhanced by 23.1% and 40.5%, respectively. The formation of Si–O–Ti and C–O–Si bonds and the presence of the nano-TiO₂ particles on the fiber surfaces contributed to the property enhancements. Unidirectional flax fiber reinforced epoxy composite (V_f = 35.4%) plates prepared manually showed significantly enhanced flexural properties with the grafting of nano-TiO₂.     

Characterization and catalytic properties of some perovskites

The perovskite oxides are promising catalysts for VOCs combustion. The purpose of this work is to comparatively evaluate catalytic activity of some simple perovskites with various cationic compositions in combustion reactions of acetone, benzene, propane and Pb free gasoline. Nanometer particles of nominal composition: GdAlO₃, SrMnO₃, SrCoO₃ and MnFeO₃ were prepared by the sol–gel self-combustion method followed by heat treatment at 1000 °C in air. The samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and nitrogen adsorption/desorption isotherms. All samples have perovskite type structure and the crystallite size is in the range of 40–89 nm. Catalytic testing evidenced that the degree of the catalytic activity varied considerably with the perovskite composition. Among the four perovskites, SrMnO₃ is generally the most active catalyst at low temperatures. MnFeO₃ and SrCoO_3−x catalysts proved high catalytic activity in acetone conversion only. The change in the catalytic activity as a result of the modification of the perovskite composition may be explained either by the different reactivity of the active oxygen species involved in the catalytic oxidation, or by the variation in the number of active sites on the perovskite surface determined by the specific structural properties of each perovskite.     

Tribological and mechanical properties of the composites made of carbon fabrics modified with various methods

Carbon fabric (CF) was modified with strong HNO₃ etching, plasma bombardment, and anodic oxidation, respectively. The modified carbon fabric was then used to prepare carbon fabric composites (CFC) by dip-coating in a phenolic resin and the relative mass content of carbon fabric in the carbon fabric composites is 65%. The friction and wear behaviors of the carbon fabric composites were evaluated with a Xuanwu-III high temperature friction and wear tester, and their mechanical properties were evaluated on a Shimadzu™ universal materials testing machine, respectively. The changes in the chemical compositions of the unmodified and modified carbon fabrics were analyzed by means of X-ray photoelectron spectroscopy. The morphologies of the worn surfaces of the unmodified and modified carbon fabric composites were analyzed by means of scanning electron microscopy. It was found that the friction-reduction and anti-wear properties of the carbon fabric composites were improved by anodic oxidation, plasma bombardment, and strong HNO₃ etching, so were the mechanical properties and load-carrying capacity. The composite made of the carbon fabric modified with anodic oxidation showed the best tribological and mechanical properties, and the one made of the carbon fabric etched with HNO₃ had the poorest tribological and mechanical properties among the three kinds of the tested composites. The active groups were produced during the oxidation process, which contributed to strengthen the bonding strength between the carbon fabric and the adhesive and hence to improve the tribological and mechanical properties of the composites made of the modified carbon fabric. The friction and wear properties of the carbon fabric composites were closely dependent on the environmental temperature. Namely, the wear rates of the composites at elevated temperature above 180 °C were much larger than that below 180 °C, which was attributed to the degradation and decomposition of the adhesive resin at excessively elevated temperature. Moreover, the composite made of the carbon fabric modified with anodic oxidation had better thermal stability than the one made of the unmodified carbon fabrics.     

Processing and mechanical properties of carbon nanotube-alumina hybrid reinforced high density polyethylene composites

Carbon nanotube-alumina hybrid reinforced high density polyethylene (HDPE) matrix composites were prepared by melt processing technique. Microstructure studies verified that the nanotubes consisting of well-crystallized graphite formed a network structure with Al₂O₃ in the hybrid, which was homogeneously dispersed in the HDPE matrix composites. Mechanical measurements revealed that 5% addition of nanotube-alumina hybrid results in 100.8% and 65.7% simultaneous increases in Young's modulus and tensile strength, respectively. Fracture surface showed homogenous dispersion of nanotubes and Al₂O₃ in the HDPE matrix and presence of interlocking like phenomena between hybrid and HDPE matrix, which might contribute to the effective reinforcement of the HDPE composites.     

Bioactivity and mechanical properties of CaSiO3/high-density polyethylene (HDPE) composites prepared by a new surface loading method of CaSiO3 powder

CaSiO₃/high-density polyethylene (HDPE) composites with flexibility and biocompatibility were prepared by a new surface loading method. CaSiO₃ powder was synthesized by coprecipitation method with heating at 1300 °C for 2 h. The obtained α-CaSiO₃ powder was sieved to 45-75 μm (sample M) and 75-150 μm (sample C). Fine powder sample (sample F) was prepared by grinding the powder being the average particle size of 2.9 μm. These powders were sprinkled on the melted HDPE sheets heated at 160, 180 and 200 °C. The amounts of sprinkled powder were only <0.1 vol.% but the ratios of surface coverage area were >50% in all the samples. Apatite formation in simulated body fluid (SBF) was observed by soaking for 5 days in sample F while within 1 day in samples M and C. The sample M retained flexible properties of HDPE together with excellent biocompatible properties.     

Effect of surface modification of bamboo cellulose fibers on mechanical properties of cellulose/epoxy composites

Bamboo cellulose fibers were treated with NaOH aqueous solution and silane coupling agent, respectively, before they were applied into epoxy composites. The effect of surface modification on mechanical properties was evaluated by tensile and impact tests under controlled conditions. Compared with the untreated cellulose filled epoxy composites, the NaOH solution treatment increased the tensile strength by 34% and elongation at break by 31%. While silane coupling agent treatment produced 71% enhancement in tensile strength and 53% increase in elongation at break. The scanning electron microscopy (SEM) was used to observe the surface feature of the cellulose fibers and the tensile fractures as well as cryo-fractures of the composites. The Fourier transform infrared (FTIR) was employed to analyze the chemical structure of the cellulose fibers before and after modifications. The results indicated different mechanisms for the two modifications of cellulose. The NaOH solution partly dissolved the lignin and amorphous cellulose, which resulting in splitting the fibers into smaller size. This led to easier permeating into the gaps of the fibers for epoxy resin (EP) oligmer and forming effective interfacial adhesion. Based on the emergence of Si–O–C and Si–O–Si on the cellulose surface, it was concluded that the enhancement of mechanical properties after coupling agent modification could be ascribed to the formation of chemical bonds between the cellulose and the epoxy coupled with the coupling agent.     

Cellulosic fibers from rice straw and bamboo used as reinforcement of cement-based composites for remarkably improving mechanical properties

The cement-based composites reinforced with cellulosic fibers isolated from rice straw were fabricated by a slurry vacuum de-watering technique. The physical structures and mechanical properties of the composites with fiber contents ranging from 2% to 16% by weight (wt.%) were investigated. Moreover, the composites reinforced with bamboo cellulosic fibers and the control cement paste, sample without cellulosic fibers, were also fabricated as reference materials. As a result, the cement-based composites reinforced by cellulosic fibers showed a remarkable improvement in the mechanical properties. The measurements of the flexural strength and the fracture toughness of the optimal sample were found to be increased by 24.3% and 45 times, respectively. The bulk density of the composites was decreased by 12.4–37.3% as a result of the introduction of cellulosic fibers. Additionally, the field emission scanning electron microscope (FSEM) observations and energy dispersive spectroscopy (EDS) analyses revealed that the hydration products of Portland cement migrated to the fiber lumens, resulting in mineralizing the cellulosic fibers and decreasing the fracture toughness of the composites.     

Ductility of polylactide composites reinforced with poly(butylene succinate) nanofibers

Sustainable “green nanocomposites” of polylactide (PLA) and poly(1,4-butylene succinate) (PBS) were obtained by slit die extrusion at low temperature. Dispersed PBS inclusions were sheared and longitudinally deformed with simultaneous cooling in a slot capillary and PBS nanofibers were formed. Shearing of PBS increases nonisothermal crystallization temperature by 30 °C. Tensile deformation was investigated by in-situ experiments in SEM chamber. Dominant deformation mechanism of PLA is crazing, however, there are dormant shear bands formed during slit die extrusion. Pre-existing shear bands are inactive in tensile deformation but contribute to ductility by blocking, initiating and diffusing typical craze growth. PBS nanofibers are spanning PLA craze surfaces and bridging craze gaps when PLA nanofibrils broke at large strain. Straight crazes become undulated because either dormant or new shear bands become activated between crazes. Due to interaction of crazes and shear bands the ductility increases while high strength and stiffness are retained.     

Machinable Al2O3/BN composite ceramics with strong mechanical properties

Al₂O₃/BN composite ceramics with nano-sized BN dispersions ranging from 0 to 30 vol.% were successfully fabricated by hot-pressing α-Al₂O₃ powders with turbostratic BN (t-BN) coating, which was prepared through chemical processes using boric acid and urea. SEM observations revealed that the nano-sized hexagonal BN (h-BN) particulates were homogeneously dispersed within Al₂O₃ grains as well as at grain boundaries. Vickers hardness of materials decreased with an increase in BN content. The fracture toughness was improved but the fracture strength had a small decrease, in comparison to Al₂O₃ monolithic ceramics. The nanocomposite ceramics with BN content more than 20 vol.% exhibited excellent machinability, which could be drilled using conventional hard metal alloy drills. Drilling rates and normal forces demonstrate the ease of machining of these materials. The preliminary information on the relationship between microstructures and properties are provided. The mechanism of material removal is also discussed.     

The effect of polymer spatial configuration on the microwave absorbing properties of non-covalent modified MWNTs

The polar polymer of linear and star polymethyl methacrylate (PMMA) was used to modify the surface of multi-walled carbon nanotubes (MWNTs). Raman and TGA were used to characterize structure of the functionalized MWNTs. The effect of polymer spatial configuration on the MWNTs dispersion, morphology and interfacial interaction was investigated by scanning electron microscopy and transmission electron microscopy. The aim of the work is to investigate the effect of polymer spatial configuration on the microwave absorbing properties. The results showed that the maximum reflection loss of linear PMMA/MWNTs hybrids was −37 dB in the frequency of 8.8 GHz, and the bandwidth below −10 dB was more than 2.1 GHz. While the maximum reflection loss of the S-PMMA/MWNTs hybrids reached −50 dB in the frequency of 8.4 GHz, and the bandwidth below −10 dB was 2.3 GHz. The results indicated that the microwave absorbing properties of star PMMA polymers modified MWNTs were superior to that of linear PMMA polymers.     

Influence of the process parameters on the mechanical properties of engineering biocomposites using a twin-screw extruder

The utilization of bio-based engineering polymers as a matrix material for cellulosic fiber reinforced composites has become an important focus in materials research. This is due to a rising demand for sustainable materials from renewable resources. In addition to this aspect, the bio-based materials provide an advantage for lightweight applications with their lower density. In this investigation, the completely bio-based polyamide 10.10, with a melting point above 200 °C, was used as a polymer matrix. Chopped man-made cellulose fibers (Cordenka CR-Type) were investigated as reinforcement for use in injection molded applications. A co-rotating twin-screw extruder with a screw-diameter of 18 mm was used for compounding. It was verified that reinforcing polyamide 10.10 with 20 wt% and 30 wt% cellulosic fibers is possible, resulting in an increase of impact and tensile properties. Furthermore, it was shown that the temperatures and screw-configurations of the twin-screw extruder only result in different fiber length distributions but in minor differences of the morphological structure and mechanical properties of PA 10.10 with 20 wt% fibers. Compounds with 30 wt% cellulose fibers show significant higher impact properties that those with 30 wt% glass fibers.     

Comparison of the thermal,dynamic mechanical and morphological properties of PLA-Lignin & PLA-Tannin particulate green composites

The study of Lignin and Tannin as filler materials in PLA-based polymeric systems has been uncommon in literature. Composites of PLA-Lignin with 5, 10, 15 wt% Lignin and PLA-Tannin with 5, 10, 15 wt% Tannin were fabricated using injection moulding. SEM morphology reveals Lignin forms droplet like dispersions within the PLA matrix in contrast to Tannin. The particle size of Lignin within the matrix is also 10–150 times smaller than Tannin. Isothermal frequency sweeps on the composites show that storage modulus of PLA-Tannin composites starts to degrade at 15 wt% filler concentration and damping rises. PLA-Lignin composites do not show such degradation in storage modulus. The tensile strength of both PLA-Lignin and PLA-Tannin composites falls with increase in filler content. Lignin has a more inhibitory effect on PLA crystallization than Tannin. The onset of thermal degradation of PLA-Lignin and PLA-Tannin composites occurs at slightly lower temperatures than pure PLA.     

Synthesis and anomalous magnetic properties of hexagonal CoO nanoparticles

CoO nanoparticles in the 38-93 nm range have been prepared by thermal decomposition. The particles were characterized to be pyramid shape with a hexagonal close-packed structure. Their anomalous magnetic behavior includes: (i) vanishing of antiferromagnetic transition around 300 K; (ii) creation of hysteresis below a blocking temperature of 6-11 K; (iii) presence of relatively large moments and coercivities accompany with specific loop shifts at 5 K; and (iv) appearance of an additional small peak located in low field in the electron spin resonance spectrum. Further, the present results provide evidence for the existence of uncompensated surface spins. The coercivity and exchange bias decrease with increasing particle size, indicating a distinct size effect. These observations can be explained by the multisublattice model, in which the reduced coordination of surface spins causes a fundamental change in the magnetic order throughout the total CoO particle.