Influence of accelerated ageing on the physico-mechanical properties of alkali-treated industrial hemp fibre reinforced poly(lactic acid) (PLA) composites

30 wt% aligned untreated long hemp fibre/PLA (AUL) and aligned alkali treated long hemp fibre/PLA (AAL) composites were produced by film stacking and subjected to accelerated ageing. Accelerated ageing was carried out using UV irradiation and water spray at 50 °C for four different time intervals (250, 500, 750 and 1000 h). After accelerated ageing, tensile strength (TS), flexural strength, Young's modulus (YM), flexural modulus and mode I fracture toughness (K_Ic) were found to decrease and impact strength (IS) was found to increase for both AUL and AAL composites. AUL composites had greatest overall reduction in mechanical properties than that for AAL composites upon exposure to accelerated ageing environment. FTIR analysis and crystallinity contents of the accelerated aged composites support the results of the deterioration of mechanical properties upon exposure to accelerated ageing environment.     

Modification of nano-hybrid silicon acrylic resin with anticorrosion and hydrophobic properties

Silicone-acrylic resin (SAR) was prepared from acrylic monomers and silicone prepolymer by the free radical solution polymerization, and then mixed TiO₂ and SiO₂ nanoparticles modified by KH570 were added to prepare nanocomposite coating. Thermogravimetric analysis and contact angle measurements showed that the acrylic resin modified by silicone prepolymer exhibited an improved thermostability and a better hydrophobicity compared with the unmodified sample. The adding of nanoparticles further increased the hydrophobicity. The contact angle of modified silicone-acrylic resin with mixed TiO₂ and SiO₂ nanoparticles of 3 wt% is the highest, 108.4°. The UV resistance and weather resistance of the modified silicone-acrylic resin are significantly improved. It was also found through electrochemical impedance spectroscopy that the corrosion resistance was significantly improved by the addition of mixed TiO₂ and SiO₂ nanoparticles. Modified silicone-acrylic resin with mixed TiO₂ and SiO₂ nanoparticles of 3 wt% and 5 wt% coating system maintains an excellent anticorrosion performance (coating resistance R_c of more than 10⁹ Ω cm²) even at 3.5% NaCl electrolyte medium till to 1800 h.     

Electro-Optical Characteristics of Polymer Dispersed Liquid Crystal Doped with MgO Nanoparticles

In this paper, inorganic oxide MgO nanoparticles-doped polymer dispersed liquid crystal (PDLC) films were made from a mixture of the prepolymer, SLC1717 liquid crystal, and MgO nanoparticles by the polymerization induced phase separation (PIPS) process. To observe the effect of MgO concentration, PDLC was dispersed with 0.2, 0.4, 0.6, and 0.8 wt.% MgO. Electro-optical properties of the films have been investigated using LCD parameter meter and Scanning Electron Microscope (SEM) at room temperature. It is established that MgO nanoparticles affect the microstructure of PDLC films significantly because of the formed agglomerates of MgO nanoparticles. Results show an improvement in the electro-optical properties and a decrease in the driving voltage for doped systems with MgO nanoparticles. When the doping amount of MgO is 0.8 wt.%, the threshold voltage (V_th) is reduced to about 7.5 V. Therefore, MgO-doped PDLC is expected to become an excellent choice in the field of energy-saving.     

Multifunctional nanocomposites based on tetraethylenepentamine-modified graphene oxide/epoxy

Composites based on epoxy/graphene were investigated for thermal-mechanical performance. Initially, few-layer graphene oxide (GO) was modified with tetraethylenepentamine (GO-TEPA) in a reaction assisted by microwave radiation. GO and GO-TEPA samples were characterized for their structure and morphology. Composites containing 0.1, 0.3 and 0.5 wt.% of GO and GO-TEPA were prepared, and the effect of fillers on the morphology of cryofractured regions of epoxy matrix was observed through electron microscopy images. Dynamic mechanical thermal analysis (DMA) tests revealed increases of approximately 20 °C in glass transition. Moreover, when compared to neat polymer, composites containing 0.5 wt.% of GO-TEPA gained up to 103% in thermal conductivity (obtained by flash laser). Finally, nanoindentation analyses showed increases of 72% in Young's modulus and 143% in hardness for the same sample. The system is characterized as multifunctional nanocomposites because of the simultaneous gains in thermal and mechanical properties. The best results of the multifunctional composites were strongly associated with the chemical modification of the GO by TEPA.     

The influence of nanostructured UV‐blockers on mechanical properties of carbon fiber epoxy composites during accelerated weathering condition

In a 3‐stage experimental approach, it was attempted to enhance the weathering performance of carbon fiber reinforced epoxy composites (CFRC). For this purpose, 2 types of UV‐blocking nanoparticles titanium dioxide (TiO₂) and zinc oxide (ZnO) were employed to separately be introduced into the composite matrix. In the first stage, the optimum content of nanoparticles was found to be 0.5 wt.% for both nanoparticles. The second stage of experiments revealed that addition of nanoparticles into CFRC could increase the strength of the composite around 6% to 12% depending on the nanoparticles used. In the third stage (weathering), it was demonstrated that nanoparticles significantly enhanced the weathering stability of CFRC. Finally, it was concluded that while TiO₂ could reinforce the composite more efficiently, ZnO nanoparticles provided a higher level of protection (62% improvement in weathering stability compared with neat composite). The higher protection efficiency of ZnO compared with TiO₂ was explained by its lower photocatalytic activity during weathering.     

Failure analysis of plain woven glass/epoxy laminates: Comparison of off-axis and biaxial tension loadings

An experimental study was focused on investigation of the failure properties of plain woven glass/epoxy composites under off-axis and biaxial tension loading conditions. Four fibre orientations (0°, 15°, 30° and 45° with respect to the load direction) were considered for off-axis tests and two biaxial load ratios for biaxial tests to study failure characteristics and mechanism. Four classical polynomial failure criteria - Tsai-Hill, Hoffman, Tsai-Wu and Yeh-Stratton - were analysed comparatively to predict off-axis and biaxial failure strength of the composites. For failure prediction of the plain woven composites under multiaxial tension loads, the Tsai-Wu criterion was modified by introducing an interaction coefficient F₁₂ obtained from 45° off-axis or biaxial tension tests and the Yeh-Stratton criterion was modified with the interaction coefficient B₁₂ = 0 or obtained from the biaxial tension test. The former criterion was found to have higher accuracy. Finally, according to macroscopic and microscopic studies, the failed specimens showed mostly distinct failure with a specific fracture orientation, mainly exhibiting fibre or fabric tensile fracture mode and a combination of matrix cracking and delamination, both in off-axis and cruciform samples.     

Synthesis and characterization of poly1-hexene/silica nanocomposites

SiO₂ nano particles, with particle size of 12 nm, were first modified by substituting surface OH groups with O-hexyl moiety. Then, poly1-hexene/modified-SiO₂ composites with various nano-SiO₂ weight fractions were prepared by three different methods: in situ, solution, and melt methods and designated as PH-SiO₂/Insitu, PH-SiO₂/Sol and PH-SiO₂/Melt, respectively. PH-SiO₂/Insitu samples showed highly uniform particle dispersion up to 30 wt. % of silica while in PH-SiO₂/Sol and PH-SiO₂/Melt samples agglomeration of the silica nanoparticles occurred for filler contents ≥5 wt. % (i.e. 5, 10, 20 and 30 wt%). In the synthesized composites, the storage modulus significantly increased as high as 20.7 times when compared with neat poly1-hexene. Maximum decomposition temperature (T_max) and char yield at 600 °C increased with increasing silica level. Rheological results showed that G^ʹ> G^ʺ over the frequency range, illustrating the elastic behavior of the composite samples. In fact, samples showed the characteristic of a non-Newtonian fluid with a strong shear thinning effect in which η* increased with increasing filler weight fraction. From the results, it can be expected that modified silica could replace silica nanoparticles in polyolefin nanocomposite reinforcement.     

Effect of Pickering emulsion on the mechanical performances and fracture toughness of epoxy composites

The improvement of mechanical properties and toughness of nanoparticles for epoxy composites was mostly dependent on the disperse state of nanoparticles in epoxy matrices. When the content of nanoparticles was higher than a threshold value, it was easy to aggregate and then affect the improvement effect. Pickering emulsion was prepared using SiO₂ nanoparticles as emulsifier and functional monomer as oil phase. The influence of Pickering emulsion on the curing process was investigated. The effect of Pickering emulsion on the mechanical properties, toughness, and glass transition temperature (Tg) was studied. Impact and tensile fracture surface were observed by scanning electron microscopy (SEM). Results from differential scanning calorimeter (DSC), tensile, impact, and fracture toughness tests are provided. The results indicated that the introduction of Pickering emulsion can eliminate the residual stress and accelerate curing reaction. Epoxy composites were capable of increasing tensile strength by up to 29.9%, impact strength of three‐fold, fracture toughness of 35%, and Tg of 20.7°C in comparison with the reference sample. SEM images showed that SiO₂ nanoparticles exhibit a good dispersion in epoxy matrix. The increases in mechanical properties, toughness, and Tg of epoxy composites were attributed to the “Second Phase Toughness” mechanism.     

Novel antimicrobial polyethylene composites prepared by metallocenic in situ polymerization with TiO2‐based nanoparticles

Polyethylene (PE) composites with titanium oxide (TiO₂) nanoparticles were produced via in situ polymerization representing a novel route to obtain antimicrobial polymeric materials. The TiO₂ nanoparticles synthesized by the sol–gel method were used either as‐synthesized or modified organically with hexadecyltrimethoxysilane (Mod‐TiO₂). These particles were added, together with the catalytic system (formed by a metallocenic catalyst and methylaluminoxane as cocatalyst), directly to the reactor, yielding in situ PE composites with 2 and 8 wt % content of nanofiller. The catalytic polymerization activity presented a slight decrease with the incorporation of the TiO₂ and Mod‐TiO₂ nanoparticles compared to polymerization without filler. Regarding the properties of the composites, crystallinity increased slightly when the different nanofillers were added, and the elastic modulus increased around 15% compared to neat PE. PE/TiO₂ nanocomposites containing 8 wt % of TiO₂ exposed to UVA irradiations presented antimicrobial activity against Escherichia coli. The PE/Mod‐TiO₂ nanocomposite with 8 wt % filler killed 99.99% of E. coli, regardless of light and time irradiation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Novel DOPO-based flame retardants in high-performance carbon fibre epoxy composites for aviation

Two novel, halogen-free, phosphorus-based oligomeric flame retardants are investigated in the commercial epoxy resin RTM6 and ∼70 wt.% carbon fibre RTM6 composites (RTM6-CF) with respect to pyrolysis and fire behaviour. The flame retardants are based on 9,10-dihydro-9-oxy-10-phosphaphenanthrene-10-oxide (DOPO) units linked to the star-shaped aliphatic ground body tetra-[(acryloyloxy)ethyl] pentarythrit (DOPP), or heterocyclic tris-[(acryloyloxy)ethyl] isocyanurate (DOPI), respectively. The glass transition temperature is reduced by adding DOPP and DOPI, but the mechanical properties of the composites (e.g. interlaminar shear strength (ILSS) and G_c in mode I and II) remain unchanged. Decomposition models are proposed based on mass loss, evolved gas analysis (TG–FTIR) and condensed product analysis (hot stage cell within FTIR). The fire behaviour is investigated comprehensively (UL 94, limiting oxygen index (LOI) and cone calorimeter). Both flame retardants act in the gas phase through flame inhibition and in the condensed phase through charring. The UL 94 of RTM6 is improved from HB to V-1 and V-0; the LOI from 25% to 34–38%. Peak heat release rate (PHRR) and total heat evolved (THE) are lowered by 31-49% and 40–44%, respectively. Adding CF increases the residue, reduces the THE, but suppresses the charring due to RTM6 and flame retardants. Thus the THE of RTM6-CF is reduced by about 25% when DOPI and DOPP are added. However, UL 94: V-0 and LOI of 45% and 48% are achieved with ∼0.6 wt.% phosphorus.     

Influence of TiO2 particles and APP on combustion behavior and mechanical properties of flame-retardant thermoplastic polyurethane

The experimental investigation on combustion behavior and mechanical properties of flame-retardant thermoplastic polyurethane were performed in the article. By the masterbatch-melt blending technique, the TiO₂ particles were well dispersed in TPU/APP composites. The microscopic morphology structure was observed by TEM and SEM. TEM images of TPU–TiO₂ masterbatch material showed that the grain sizes of TiO₂ particles were 200–400 nm. The SEM result indicated that the TiO₂ particles could enhance compatibility and dispersion of APP in TPU. The mechanical properties of TPU composites were characterized by dynamic mechanical analysis (DMA) and tensile tests, respectively. The DMA results indicated that TiO₂ particles could improve the viscoelastic property of the TPU/APP composites. The tensile strength achieved a significant improvement with addition of TiO₂ particles. APP/TiO₂-5 obtains a better value of 344% than APP-1 (277%). Also, the flame-retardant property and thermal stability of the TPU composites were characterized using cone calorimeter test (CCT) and thermogravimetric analysis (TGA), respectively. The CCT results revealed that TiO₂ particles could enhance the flame-retardant property of APP in TPU. The peak heat release rate of APP/TiO₂-4 containing 0.5% TiO₂ decreased to 157.27 kW m^?2 from 225.5 kW m^?2 of APP-1 sample without any TiO₂. The TiO₂ particles could promote the formation of carbon layers which restrict the diffusion of fuels into combustion zone and access of oxygen to the underlying materials. The TGA results indicated that TiO₂ can improve the thermal stability of TPU/APP composites.

     

Composites of poly(L‐lactide‐trimethylene carbonate‐glycolide) and surface modified SBA‐15 as bone repair material

This work aims to develop novel composites from a poly(L ‐lactide‐co‐trimethylene carbonate‐co‐glycolide) (PLTG) terpolymer and mesoporous silica (SBA‐15) nanofillers surface modified by post‐synthetic functionalization. SBA‐15 first reacts with a silane coupling agent, γ‐aminopropyl‐trimethoxysilane to introduce ammonium group. PLLA chains were then grafted on the surface of SBA‐15 through ammonium initiated ring‐opening polymerization of L ‐lactide. Composites were prepared via solution mixing of PLTG terpolymer and surface modified SBA‐15. The structures and properties of pure SBA‐15, γ‐aminopropyl‐trimethoxysilane modified SBA‐15 (H₂N‐SBA‐15), PLLA modified SBA‐15 (PLLA‐NH‐SBA‐15), and PLTG/PLLA‐NH‐SBA‐15 composites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, N₂ adsorption‐desorption, differential scanning calorimetry, contact angle measurement, and mechanical testing. The results demonstrated that PLLA chains were successfully grafted onto the surface of SBA‐15 with grafting amounts up to 16 wt.%. The PLTG/PLLA‐NH‐SBA‐15 composites exhibit good mechanical properties. The tensile strength, Young's modulus, and elongation at break of the composite containing 5 wt.% of PLLA‐NH‐SBA‐15 were 39.9 MPa, 1.3 GPa, and 273.6%, respectively, which were all higher than those of neat PLTG or of the composite containing 5 wt.% of pure SBA‐15. Cytocompatibility tests showed that the composites present very low cytotoxicity.     

Preparation and characterization of TiO2/Pebax/(PSf‐PES) thin film nanocomposite membrane for humic acid removal from water

New thin film composite (TFC) membrane was prepared via coating of Pebax on PSf‐PES blend membrane as support, and its application in wastewater treatment was investigated. To modify this membrane, hydrophilic TiO₂ nanoparticles were coated on its surface at different loadings via dip coating technique. The as‐prepared membrane was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), field emission SEM, and contact angle analysis. The Fourier transform infrared spectroscopy analysis and surface SEM images indicated that TiO₂ was successfully coated on the membrane surface. In addition, the results stated that the hydrophilicity and roughness of membrane surface increased by addition of TiO₂ nanoparticles. Performance of TFC and modified TFC membranes was evaluated through humic acid removal from aqueous solution. Maximum permeate flux and humic acid rejection were obtained at 0.03 and 0.01 wt% TiO₂ loadings, respectively. Rejection was enhanced from 96.38% to 98.92% by the increase of feed concentration from 10 to 30 ppm. Additionally, membrane antifouling parameters at different pressures and feed concentration were determined. The results indicated that surface modification of membranes could be an effective method for improvement of membrane antifouling property.     

Development of multifunctional polydimethylsiloxane (PDMS)‐epoxy‐zinc oxide nanocomposite coatings for marine applications

Multifunctional epoxy‐polydimethylsiloxane nanocomposite coatings with antifouling and anticorrosion characteristics have been developed via in situ polymerization method at different loading (1, 3, and 6.5 wt.%) of ZnO nanoparticles to cater marine applications. A detailed comparative analysis has been carried out between epoxy‐polydimethylsiloxane control (EPC) and ZnO‐reinforced coatings to determine the influence of ZnO loading on various properties. The incorporation of ZnO in EPC led to increase in root mean square (RMS) roughness to 126.75 nm and improved hydrophobicity showing maximum contact angle of 123.5° with low surface energy of 19.75 mN/m of nanocomposite coating as compared with control coating. The differential scanning calorimetry (DSC) result indicated improved glass transition temperature of nanocomposite coatings with highest T_g obtained at 83.69°C in case of 1 wt.% loading of ZnO. The increase in hydrophobicity of the system was accompanied by upgraded anticorrosion performance exhibiting 98.8% corrosion inhibition efficiency (CIE) as compared with control coating and lower corrosion rate of 0.12 × 10^?3 mm/year. The Taber abrasion resistance and pull‐off adhesion strength results indicated an increment of 34.7% and 150.7%, respectively, in case of nanocomposite coating as compared with the control coating. The hardness of nanocomposite coatings was also improved, and maximum hardness was found to be 65.75 MPa for nanocomposite coating with 1 wt.% of ZnO. Our study showed that the nanocomposite coating was efficient in inhibiting accumulation of marine bacteria and preventing biofouling for more than 8 months. The developed environment‐friendly and efficient nanocomposite material has a promising future as a high‐performance anticorrosive and antifouling coating for marine applications.     

Preparation of an asymmetric perovskite-type membrane and its oxygen permeability

A crack-free asymmetric membrane of perovskite-type oxide (La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ) was successfully prepared by coating a slurry containing La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ powders directly on the surface of a green support of the same composition, followed by sintering. It was found that crack-free asymmetric membranes could be obtained by controlling the powder concentration of the slurry in the range of 15–25 wt.%. After sintering, the crystal phase of the top layer of asymmetric membranes prepared was the same as that of powders, which were of the cubic perovskite phase. The nitrogen permeability and SEM photograph of the support showed that the support was porous, and the gas-tight test and SEM demonstrated that the top layer of asymmetric membrane was dense and crack-free. The asymmetric membrane prepared, whose dense top layer was 200 μm thick, exhibited about three to four times as high an oxygen flux as a 2 mm dense sintered disc.     

Synergistic effect of polyfunctional silane coupling agent and styrene acrylonitrile copolymer on the water‐resistant and mechanical performances of glass fiber–reinforced polyamide 6

Adverse effects of a high‐water absorption rate on properties of a glass fiber–reinforced polyamide 6 (GF‐PA6) composite significantly reduce performance and limit application in humid environments. In this paper, a polyfunctional silane (PFS) coupling agent with amino (–NH₂) and imino (–NH) groups and styrene acrylonitrile copolymer (SAN) were added to a composite, GF‐PA6, to prepare GF‐PA6/SAN/PFS composites via melt blending in a twin‐screw extruder. The effects of SAN and PFS content on the static and dynamic mechanical properties of the composites before and after water absorption were investigated in detail. The microstructure of the fracture surface was analyzed by a scanning electron microscope (SEM). The results show that the addition of SAN and PFS could effectively inhibit water absorption of the GF‐PA6 composites. The alkoxyl groups on PFS reacted chemically with the nitrile groups of SAN, which enriched SAN on the interface between the fiber and matrix during the extrusion and mixing process to improve the effect of water prevention. Therefore, the mechanical properties of the wet state were notably improved while preventing water from permeating the interface by only the addition of a small amount of SAN and PFS. Dynamic mechanical analysis (DMA) results showed that the addition of PFS improved the compatibility of PA6 with SAN and enhanced the interface adhesion between fiber and PA6. In terms of test result of the comprehensive performance, 10 phr SAN with 0.6 phr PFS was the best dosage.     

Effect of wet spinning parameters on the properties of novel cellulosic fibres

Novel cellulose fibres (Biocelsol) were spun by traditional wet spinning technique from the alkaline solution prepared by dissolving enzyme treated pulp directly into aqueous sodium zincate (ZnO/NaOH). The spinning dope contained 6 wt.% of cellulose, 7.8 wt.% of sodium hydroxide (NaOH) and 0.84 wt.% of zinc oxide (ZnO). The fibres were spun into 5% and 15% sulphuric acid (H₂SO₄) baths containing 10% sodium sulphate (Na₂SO₄). The highest fibre tenacity obtained was 1.8 cNdtex⁻¹ with elongation of 15% and titre of 1.4 dtex. Average molecular weights and shape of molecular weight distribution curves of the celluloses from the novel wet spun cellulosic fibre and from the commercial viscose fibre were close to each other.     

Interlaminar Fracture Toughness of Carbon Fiber/Epoxy Composites using Short Kevlar Fiber and/or Nylon-6 Powder Reinforcement

Mode I (G_IC) and Mode II (G_IIC) interlaminar fracture toughness of carbon-fiber/epoxy composites have been investigated as a function of the amount of short Kevlar-29 fiber (SKF) and/or Nylon-6 powder (N6P) between continuous fiber layers. G_IIC increased with increasing crack length as a consequence of the presence of SKFs bridging in the wake of propagating crack. G_IIC of SKF alone could reach the maximum at an intermediate amount of SKF. G_IIC of SKF and N6P was lower than that of SKF alone because N6P prevented the orientation of SKF to out-of-plane. The extent of SKF's bridging phenomenon may be influenced by the amount and orientation of SKF. G_IC showed no significant effect with SKF and uniform irrespective of crack length. Scanning electron microscopy after G_IIC test showed that new surfaces were created by extensive fiber bridging, pull-out and fracture of SKF in random direction without any fixed pattern. © 1997 John Wiley & Sons, Ltd.     

New (PP/EPR)/nano‐CaCO3 based formulations in the perspective of polymer recycling. Effect of nanoparticles properties and compatibilizers

Phase structure of composite polypropylene (PP)/ethylene–propylene–rubber (EPR)/coated nano‐CaCO₃ composites, used in the manufacture of bumpers, with and without compatibilizers has been investigated using scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) mechanical tests, and differential scanning calorimetry (DSC). Blends of various compositions were prepared using a corotating twin‐screw extruder. The experimental results indicated that the dispersion of nanoparticles in (PP/EPR) depends on their surface (stearic acid and fatty acid coatings). In both cases, the final morphology is the core–shell structure in which EPR acts as the shell part encapsulating coated nano‐CaCO₃. In this case, EPR‐g‐MAH copolymer does not improve the interface between (PP/EPR) and nanoparticles but PEP propylene ethylene copolymer should be preferentially localized at the interface of PP and (EPR/nano‐CaCO₃) phases generating an improved adherence, which will ensure a better cohesion of the whole material. According to the nature of the compatibilizers and surface treatment, it is believed that the synergistic effect of both the EPR elastomer and CaCO₃ nanoparticles should account for the balanced performance of the ternary composites. Copyright © 2009 John Wiley & Sons, Ltd.