Short sisal fibre reinforced bacterial cellulose polylactide nanocomposites using hairy sisal fibres as reinforcement

“Hairy” bacterial cellulose coated sisal fibres were created using a simple slurry dipping process. Neat sisal fibres were coated with BC to create (i) a dense BC coating around the fibres or (ii) “hairy” fibres with BC oriented perpendicular to the fibre surface. These fibres were used to produce hierarchical sisal fibre reinforced BC polylactide (PLLA) nanocomposites. The specific surface area of the BC coated fibres increased when compared to neat sisal. Single fibre tensile tests revealed no significant difference in the tensile modulus and tensile strength of “hairy fibres”. However, when sisal fibres were coated with a dense BC layer, the mechanical fibre properties decreased. The tensile, flexural and visco-elastic properties of the hierarchical PLLA nanocomposites reinforced by both types of BC coated sisal fibres showed significant improvements over neat PLLA.     

Carbohydrate derived copoly(lactide) as the compatibilizer for bacterial cellulose reinforced polylactide nanocomposites

A novel, entirely bio-derived polylactide carbohydrate copolymer (RP1) is used as a compatibilizer, to produce bacterial cellulose (BC) poly(l-lactide) (PLLA) nanocomposites with improved mechanical properties. Contact angle measurements of RP1 droplets on single BC nanofibres proved that it has a higher affinity towards BC than PLLA. RP1 has a comparable Young’s modulus, but lower tensile strength, than PLLA. When RP1 was blended with PLLA at a concentration of 5 wt%, the tensile modulus and strength of the resulting polymer blend decreased from 4.08 GPa and 63.1, respectively, for PLLA to 3.75 GPa and 56.1 MPa. A composite of BC and PLLA (with 5 wt% RP1 and 5 wt% BC) has a higher Young’s modulus and tensile strength, compared to either pure PLLA or PLLA–BC nanocomposites.     

Interfacial properties and self-sensing of single carbon fiber reinforced CNT-phenolic nanocomposites using electro-micromechanical and wettability tests

Interfacial and other properties along with self-sensing were investigated for single carbon fiber/neat phenolic resins and carbon nanotube (CNT)-phenolic nanocomposites by electro-micromechanical and wettability tests. The apparent modulus was higher for samples with a single carbon fiber in CNT-phenolic nanocomposite than for samples with a single carbon fiber in neat phenolic resin, indicating better stress transfer. In water droplet contact angle measurements the contact angle increased form slightly less than 90° on neat phenolic resin to more than 90° on CNT-phenolic nanocomposites. This behavior was attributed to hydrophobic domains randomly distributed on the surface as a result of the heterogeneous microstructure of CNT. The work of adhesion between a single carbon fiber and CNT-phenolic nanocomposites was greater than for neat phenolic resin which is attributed to an increase in viscosity by adding CNT. Micro-failure patterns and interfacial adhesion between CNT-phenolic nanocomposites and single carbon fibers were consistent with these other results.     

Interfacial and hydrophobic evaluation of glass fiber/CNT–epoxy nanocomposites using electro-micromechanical technique and wettability test

Interfacial evaluation of glass fiber reinforced carbon nanotube (CNT)–epoxy nanocomposites and the hydrophobicity of CNT–epoxy nanocomposites were investigated by micromechanical and wettability tests. The contact resistance of the CNT–epoxy nanocomposites was measured using a gradient specimen, containing electrical contacts with gradually-increasing spacing. The contact resistance of CNT–epoxy nanocomposites could be better valuated by mainly the two-point method. Due to the presence of hydrophobic domains on the heterogeneous surface, the static contact angle of CNT–epoxy nanocomposites was about 120°, which was somewhat lower than that for super-hydrophobicity (>150°). For surface treated glass fiber, tensile strength decreased dramatically, whereas tensile modulus exhibited little change despite the presence of flaws on the etched fiber surface. The interfacial shear strength (IFSS) between the etched glass fiber and the CNT–epoxy nanocomposites increased due to enhanced surface energy and roughness. As thermodynamic work of energy, W_a increased, both the mechanical IFSS and the apparent modulus increased.     

Synthesis and characterization of biodegradable poly(l-lactide)/layered double hydroxide nanocomposites

This study reports the preparation and physical properties of biodegradable nanocomposites fabricated using poly(l-lactide) (PLLA) and magnesium/aluminum layered double hydroxide (MgAl-LDH). The MgAl-LDH with molar ratio of Mg/Al = 2 were synthesized by the co-precipitation method. In order to improve the chemical compatibility between PLLA and LDH, the surface of LDH was organically-modified by polylactide with carboxyl end group (PLA–COOH) using ion-exchange process. Then, the PLLA/LDH nanocomposites were prepared by solution intercalation of PLLA into the galleries of PLA–COOH modified LDH (P-LDH) in tetrahydrofuran solution. Both X-ray diffraction data and Transmission electron microscopy images of PLLA/P-LDH nanocomposites indicate that the P-LDHs are randomly dispersed and exfoliated into the PLLA matrix. Mechanical properties of the fabricated 1.2 wt.% PLLA/P-LDH nanocomposites show significant enhancements in the storage modulus when compared to that of neat PLLA. Adding more P-LDH into PLLA matrix induced a decrease in the storage modulus of PLLA/P-LDH nanocomposites, probably due to the excessive content of PLA–COOH moleculars with low mechanical properties. The thermal stability and degradation activation energies of the PLLA and PLLA/P-LDH nanocomposites can also be discussed.     

Effect of phenoxy-based coating resin for reinforcing pitch carbon fibers on the interlaminar shear strength of PA6 composites

Carbon fiber-reinforced thermoplastic composites have not been considered as constituent materials for structural parts due to the poor interfacial adhesion between the fiber and the thermoplastic matrix. In this work, polyamide 6 (PA6) composites with pitch carbon fibers (pCF) were fabricated by alternatively stacking PA6 films and pCF fabrics followed by being pressed. In order to improve the interfacial adhesion, phenoxy resin-based materials were coated on the surface of the fiber. The surface analyses of the fiber were carried out by XPS, TGA and dynamic contact angle method. Interlaminar shear strength (ILSS) of the composites was measured to evaluate the effect of the coating materials. The results showed that the composites with the coated pCF had higher ILSS than that with neat pCF by more than 20%. This indicated that a proper coating material can improve mechanical properties of the PA6 composites, which can be applied to the structural parts.     

Effect of multi-walled carbon nanotubes on the crystallization and hydrolytic degradation of biodegradable poly(l-lactide)

Biodegradable poly(l-lactide) (PLLA)/carboxyl-functionalized multi-walled carbon nanotubes (f-MWNTs) nanocomposites were prepared via solution blending. Scanning electron microscopy observations reveal a fine dispersion of f-MWNTs in the PLLA matrix. The presence of f-MWNTs enhances the crystallization of PLLA in the nanocomposites compared with that of neat PLLA; moreover, the overall crystallization rate of PLLA increases with increasing the f-MWNTs content in the PLLA matrix. The incorporation of f-MWNTs improves the storage modulus of the PLLA/f-MWNTs nanocomposites, with this effect being more pronounced at lower f-MWNTs content. The exciting aspect of this research is the enhanced hydrolytic degradation of PLLA after nanocomposites preparation with f-MWNTs, which may be of great interest for its wide practical application.     

Influence of fiber surface-treatment on interfacial property of poly(l-lactic acid)/ramie fabric biocomposites under UV-irradiation hydrothermal aging

The present study is devoted to the effect of fiber surface-treatment on the interfacial property of biocomposites based on poly(l-lactic acid) (PLLA) and ramie fabric. Ramie fiber is used as reinforced material because it's lowest water absorption among sisal, jute, kenaf and ramie fiber. Fiber surface-treatment can increase the water absorption of natural fibers. SEM images show that PLLA biocomposites with treated ramie fabric exhibit better interfacial adhesion character. DMA results show that the storage modulus of PLLA biocomposites with treated ramie increase compared to neat PLLA and PLLA biocomposites with untreated ramie. Unexpectedly, fiber surface-treatment can cause an accelerated decline in mechanical properties of PLLA biocomposites after UV-irradiation hydrothermal aging. Finally, GPC results show that there is no obvious decline in the molecular weight of PLLA. The main reason for this decline is the interfacial destructive effect induced by the water absorption of ramie fiber.     

Preparation and properties of biodegradable poly(L-lactide)/octamethyl-polyhedral oligomeric silsesquioxanes nanocomposites with enhanced crystallization rate via simple melt compounding

Biodegradable poly(l-lactide) (PLLA)/octamethyl-polyhedral oligomeric silsesquioxanes (ome-POSS) nanocomposites were prepared via simple melt compounding at various ome-POSS loadings in this work. Scanning and transmission electron microscopy observations indicate that ome-POSS were homogeneously dispersed in the PLLA matrix. Effect of ome-POSS on the nonisothermal crystallization behavior, isothermal melt crystallization kinetics, spherulitic morphology, crystal structure, dynamic mechanical properties, and thermal stability of PLLA in the nanocomposites was investigated in detail. It is found that the presence of ome-POSS enhances both nonisothermal cold and melt crystallization of PLLA in the nanocomposites relative to neat PLLA. The overall isothermal melt crystallization rates are faster in the PLLA/ome-POSS nanocomposites than in neat PLLA and increase with increasing the ome-POSS loading; however, the crystallization mechanism of PLLA remains unchanged. The nucleation density of PLLA spherulites is enhanced, while the crystal structure of PLLA is not modified in the PLLA/ome-POSS nanocomposites. The storage modulus has been apparently improved in the PLLA/ome-POSS nanocomposites with respect to neat PLLA, whereas the glass-transition temperatures vary slightly between neat PLLA and the PLLA/ome-POSS nanocomposites. The thermal stability of PLLA matrix is reduced slightly in the PLLA/ome-POSS nanocomposites.     

Carbon fibre reinforced poly(vinylidene fluoride): Impact of matrix modification on fibre/polymer adhesion

The quality of interfacial interaction is dictated by the surface chemistry of the carbon fibres and the composition of the matrix. The composition of poly(vinylidene fluoride) (PVDF) was modified by the addition of maleic anhydride grafted PVDF. The surface properties of the various matrix formulations were characterised by contact angle and electrokinetic measurements. Carbon fibres were modified by industrial electrochemical oxidation and oxidation in nitric acid, or the use of a traditional epoxy-sizing of industrially oxidised fibres. The surface composition, morphology and wetting behaviour of the carbon fibres was characterised. The interaction between modified PVDF and the carbon fibres was studied by direct contact angle measurements between PVDF melt on single carbon fibres and by single fibre pull-out tests. The best wetting and adhesion behaviour was achieved between PVDF containing 5 ppm grafted maleic anhydride (MAH) and epoxy-sized carbon fibres. The addition of MAH-grafted PVDF to the unmodified PVDF caused the apparent interfacial shear strength to increase by 184%. The apparent interfacial shear strength of this fibre–matrix combination allowed for the utilisation of 100% of the yield tensile strength of PVDF.     

Study on interfacial adhesion strength of single glass fibre/polypropylene model composites by altering the nature of the surface of sized glass fibres

Polypropylene (PP) compatibly sized glass fibres (GFs) were treated with boiling water and toluene, respectively, to reveal the interactions of water and toluene with different components in the sizing of sized GF and their influences on the interfacial adhesion strength of GF/PP model composites. Compared to control GF/PP model composites, about 30% increase of interfacial adhesion strength was achieved for composites with water-treated GF, whereas a small decrease of interfacial adhesion strength was revealed for composites with toluene-treated GF. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Zeta-potential measurement, and water contact angle measurement demonstrated that the boiling water-treated GFs posses a more polar and hydrophilic surface with homogeneously distributed derivatives of 3-aminopropyltriethoxysilane, which is related to a higher interfacial adhesion strength for water-treated GF/PP model composites. In contrast, hot toluene-treated GFs led to a more hydrophobic surface with low molar mass PP and surfactants enriching on the outermost surface.     

Poly(ε-caprolactone)-based nanocomposites: Influence of compatibilization on properties of poly(ε-caprolactone)–silica nanocomposites

In the present paper, results about preparation and characterization of poly(ε-caprolactone) (PCL) based nanocomposites filled with silica nanoparticles are reported. In order to promote polymer/inorganic nanofiller compatibility and to increase the interfacial adhesion between the two components, silica nanoparticles surface has been functionalised by grafting a M_w = 10,000 Da PCL onto it. Successively, PCL based nanocomposites have been prepared by extrusion process. The relationships among size, amount of the nanofiller, organic coating and the final properties have been investigated. The morphological analysis has revealed that the silica functionalization can provide a useful method of preparation of the nanocomposites with the achievement of a fine, a good dispersion and a strong adhesion level. Thermal characterization has shown an improved thermal stability due to the presence of the silica nanoparticles, especially in the case of modified nanofillers. Finally mechanical tests revealed an increase of the Young’s modulus in the PCL based nanocomposites.     

The role of interfacial interactions on the glass-transition and viscoelastic properties of silica/polystyrene nanocomposite

Filler surface properties and polymer-filler interactions have dominate influence on viscoelastic behavior of polymeric matrix composites. When the filler-filler spacing is on the order of the polymeric matrix molecular size, fillers may agglomerate through direct short-range interactions, also by overlapping of interfacial layers of neighboring fillers. In this work the effect of interfacial layer on the viscoelastic properties of silica/polystyrene composite was investigated.The Si/Ps nanocomposites were prepared by solution mixing method, and dynamic rheometry was employed to determine the viscoelastic behavior in the melt state. Experimental results show that, addition of silica nanoparticles to polystyrene matrix would increase the glass-transition temperature of polymer. This increasing will be accelerated by presence of nanoparticles with more filler-polymer adhesion energy, because of more interfacial layer volume fraction. It is helpful in evaluating the volume fraction and equivalent thickness of interfacial layer in polymer nanocomposites. Likewise it is shown that, the dynamic moduli of nanocomposite is enhanced associated with the increase in the glass-transition temperature. This study implies that the main source of increment in both dynamic modulus and glass-transition temperature of polymer nanocomposites is the presence of the immobilized interfacial layer and the secondary filler network.     

Improvement on the properties of polylactic acid (PLA) using bamboo charcoal particles

Bamboo charcoal (BC) derived from bamboo plants is one kind of well recognized multi-functional materials which has been used in various applications such as medical, cosmetic, food processing and health-related products. In this paper, BC particle is used as reinforcement for polylactic acid (PLA) to enhance its mechanical, thermal and optical properties. The comparison on tensile, flexural and impact properties of BC particle reinforced PLA composites (BC/PLA composites) with the content ranging from 2.5 to 10 wt.% is conducted. Experimental results indicated that the maximum tensile strength, flexural strength and ductility index (DI) of BC/PLA composites increased by 43%, 99% and 52%, respectively as compared with those of neat PLA. This phenomenon was attributed to the uniform distribution of high aspect ratio and surface area of BC particles. Further increasing the BC content to 7.5 wt.% would decrease the glass transition temperature of BC/PLA composites. The mechanical properties of BC/PLA composites were reduced as compared with a neat PLA sample when they were exposed to compost degradation. However, less reduction in these properties was found when they were subject to UV irradiation. UV–Vis spectrometer analysis supported the results of UV irradiation. Fracture surfaces of tensile test samples with and without compost degradation or UV irradiation were analysed by using scanning electron microscopy (SEM). SEM images revealed that there was a good BC particle dispersion in the composites through extrusion and injection moulding processes if the particle content was below 7.5 wt.%.     

Enhanced thermal conductivity of poly(L-lactide) composites with synergistic effect of aluminum nitride and modified multi-walled carbon nanotubes

Poly (ethylene glycol)-grafted multi-walled carbon nanotubes (PEG-MWNTs) were prepared and added into poly(L-lactide) (PLLA)/aluminum nitride (AlN) composites to obtain PLLA/AlN/PEG-MWNTs nanocomposites. Microstructure and thermal conductivity of the composites were investigated on the basis of the influence of PEG-MWNTs incorporated. The results showed that PEG-MWNTs were well-dispersed in the PLLA matrix and had strong interfacial adhesion with the matrix. The addition of PEG-MWNTs improved the thermal conductivity of PLLA/AlN composites. When 3 wt.% of PEG-MWNTs and 50 wt.% of AlN were both added into the PLLA matrix, the thermal conductivity reached 0.7734 W/mK with enhancement almost by 400% as compared to a neat PLLA. However, the thermal conductivity is 0.3401 W/mK for the PLLA composite with 3 wt.% of PEG-MWNTs and 0.4286 W/mK for the one with 50 wt.% of AlN. The synergistic effect of aggregated AlN particles and well-dispersed MWNTs could form efficient thermal conductive paths for improving the thermal conductivity of PLLA composites greatly.     

Relationship between microstructure and fracture behavior of bioabsorbable HA/PLLA composites

Hydroxyapatite particles of four different shapes, that is, micro, nano, spherical and plate, were used to fabricate hydroxyapatite filled poly(l-lactic acid) (HA/PLLA) composites. Effects of HA particle shape on the fracture behavior of HA/PLLA were investigated by mode I fracture testing, fracture surface measurement and scanning electron microscopy. It was found that the micro-HA/PLLA has the highest critical energy release rate, G_IC, with the largest surface roughness, while G_IC of the nano-HA/PLLA was lowest corresponding to the smallest surface roughness. The micro-HA/PLLA composites exhibited interfacial debonding and local ductile deformation of the PLLA matrix, indicating higher fracture energy and therefore, the highest G_IC. On the other hand, the nano-HA/PLLA composites showed brittle fracture surface due to nano-scale interaction between PLLA fibrils and primary HA particles, corresponding to lower fracture energy and hence the lowest G_IC.     

Enhanced mechanical properties of multiscale carbon fiber/epoxy composites by fiber surface treatment with graphene oxide/polyhedral oligomeric silsesquioxane

Graphene oxide (GO) and polyhedral oligomeric silsesquioxane (POSS) grafted carbon fiber (CF) was demonstrated to reinforce the mechanical properties of fiber composites. Such a fiber composite was prepared by grafting POSS onto the CF surface using GO as the linkage. The presence of GO linkage and POSS could significantly enhance both the area and wettability of fiber surface, leading to an increase in the interfacial strength between fibers and resin. Compared with the desized CF composites, the grafted CF composites fabricated by compression molding method exhibited 53.05% enhancement in the interlaminar shear strength. The changed surface morphology, surface composition and surface energy were supposed to be related with the interfacial performance of unidirectional composites, as revealed by scanning electron microscopy, atomic force microscope, dynamic contact angle test and X-ray photoelectron microscopy charaterizations.     

Wrapping of polyrhodanine onto tubular clay and its prominent effects on the reinforcement of the clay for rubber

Polyrhodanine (PRd) was wrapped onto the surface of halloysite nanotubes (HNTs) through the oxidative polymerization of rhodanine on Fe³⁺-impregnated-HNTs. The wrapping mechanisms were disclosed. The PRd-HNTs exhibited a prominent reinforcing effect for rubber. With the incorporation of 30 phr of PRd-HNTs, the tensile strength was increased by almost 8-fold, and the modulus (at 300% strain) was increased by 257% compared to neat SBR. More strikingly, with only 2.9 wt.% of PRd (relative to HNTs), the tensile strength and modulus of the composite were enhanced by 117% and 87%, respectively, suggesting the high efficiency of the modification. Such profound changes in the reinforcement were attributed to the formation of covalent linkages between PRd-HNTs and rubber through the participation of PRd-HNTs in curing process. In view of the versatility of PRd-wrapping procedure, this method offers significant insight into the interfacial design of rubber nanocomposites consisting of nonpolar matrices and inorganic reinforcements.     

Effects of organic chain length of layered zirconium phosphonate on the structure and properties of castor oil-based polyurethane nanocomposites

Three novel organic–inorganic hybrid molecules, layered zirconium phosphates or phosphonates, were synthesized. To study the effects of organic chain length of them on the structure and properties of polymer nanocomposites, the polyurethane/α-zirconium phosphate (PU/ZrP), polyurethane/zirconium 2-aminoethylphosphonate (PU/ZrAEP) and polyurethane/zirconium 2-(2-(2-(2-aminoethylamino)ethylamino)ethylamino) ethylphosphonate (PU/Zr(AE)₄P) nanocomposites were prepared, and characterized by Fourier Transform Infrared (FT-IR) spectroscopy, wide-angle X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing. It was revealed that morphological, mechanical, and thermal properties of these nanocomposites were strongly dependent on the organic chain length of the layered zirconium phosphonates. The results showed that the fillers with longer chain length exhibited better dispersion in the PU matrix. As expected, the mechanical properties and water resistance were improved with the increasing of organic chain length of fillers, which attributed to better interfacial adhesion between fillers and PU matrix.     

Effects of gamma-irradiation on UHMWPE/MWNT nanocomposites

Ultra high molecular weight polyethylene (UHMWPE) is a polymer that is widely used in industrial and orthopaedic applications. In this work, pristine multiwalled carbon nanotubes (MWCNTs) were incorporated into UHMWPE in different concentrations (1, 3 and 5 wt.%) using a ball milling process. UHMWPE/MWCNT nanocomposites were gamma irradiated at 90 kGy to improve the interaction between MWCNTs and the polymer matrix. Structural, thermal and mechanical characterizations were conducted by means of transmission electron microscopy (TEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and uniaxial tensile techniques. Gamma irradiation produced an increase in the melting temperature, crystallinity and temperature of maximum decomposition rate. The irradiation produced a 38% decrease in the toughness of neat UHMWPE. The incorporation of MWCNTs did not significantly affect the melting point of the neat UHMWPE but decreased the degree of crystallinity of the raw UHMWPE, which was related to a reduction in the UHMWPE lamellar density. An increase in thermal stability was also observed for the nanocomposites compared to neat UHMWPE. The tensile tests showed a 38% increase in the Young’s modulus in the reinforced nanocomposites and a small decrease in toughness (5%). Gamma irradiation of the nanocomposites increased crystallinity, which was related to an increased lamellar thickness, and also improved their thermal stability. The Young’s modulus increased by up to 71% for irradiated nanocomposites and their toughness showed no significant changes in comparison with the non-irradiated nanocomposites. The incorporation of MWCNTs reduced the negative effects of irradiation and compensated for the reduction in toughness. This fact might be attributed to the radical scavenger behaviour of the MWNT as was proved by Electron Spin Resonance (ESR) detection of the radiation-induced radicals.