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.     

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.     

Preparation and properties of poly (p-phenylene sulfide)/multiwall carbon nanotube composites obtained by melt compounding

In this paper, electrical and mechanical properties of Poly (p-phenylene sulfide) (PPS)/multi-wall carbon nanotubes (MWNTs) nanocomposites were reported. The composites were obtained just by simply melt mixing PPS with raw MWNTs without any pre-treatment. The dispersion of MWNTs and interfacial interaction were investigated through SEM &TEM and Raman spectra. The rheological test and crystallization behavior were also investigated to study the effects of MWNTs concentration on the structure and chain mobility of the prepared composites. Though raw MWNTs without any pre-treatment were used, a good dispersion and interaction between PPS and MWNTs have been evidenced, resulting in a great improvement of electrical properties and mechanical properties of the composites. Raman spectra showed a remarkable decrease of G band intensity and a shift of D bond, demonstrating a strong filler–matrix interaction, which was considered as due to π–π stacking between PPS and MWNTs. The storage modulus (G′) versus frequency curve presented a plateau above the percolation threshold of about 2–3 wt% with the formation of an interconnected nanotube structure, indicative of ‘pseudo-solid-like’ behavior. Meanwhile, a conductive percolation threshold of 5 wt% was achieved and the conductivity of nanocomposites increased sharply by several orders of magnitude. The difference between electrical and rheological percolation threshold, and the effect of critical percolation on the chain mobility, especially on crystallization behavior of PPS, were discussed. In summary, our work provides a simple and fast way to prepare PPS/MWNTs nanocomposites with good dispersion and improved properties.     

Structure–property relationships in isotactic polypropylene/multi-walled carbon nanotubes nanocomposites

In this work, the influence of multi-walled carbon nanotubes (MWCNT) on electrical, thermal and mechanical properties of CNT reinforced isotactic polypropylene (iPP) nanocomposites is studied. The composites were obtained by diluting a masterbatch of 20 wt.% MWCNT with a low viscous iPP, using melt mixing. The morphology of the prepared samples was examined through SEM, Raman and XRD measurements. The effect of MWCNT addition on the thermal transitions of the iPP was investigated by differential scanning calorimetry (DSC) measurements. Significant changes are reported in the crystallization behavior of the matrix on addition of carbon nanotubes: increase of the degree of crystallinity, as well as appearance of a new crystallization peak (owing to trans-crystallinity). Dynamic mechanical analysis (DMA) studies revealed an enhancement of the storage modulus, in the glassy state, up to 86%. Furthermore, broadband dielectric relaxation spectroscopy (DRS) was employed to study the electrical and dielectric properties of the nanocomposites. The electrical percolation threshold was calculated 0.6–0.7 vol.% MWCNT from both dc conductivity and dielectric constant values. This value is lower than previous mentioned ones in literature in similar systems. In conclusion, this works provides a simple and quick way for the preparation of PP/MWCNT nanocomposites with low electrical percolation threshold and significantly enhanced mechanical properties.     

Structural characterization, thermal and mechanical properties of polyurethane/CoAl layered double hydroxide nanocomposites prepared via in situ polymerization

Dodecyl sulfate (DS), one kind of sulfate anion, was intercalated in the interlayer space between CoAl layered double hydroxide (CoAl-LDH) layers, and then polyurethane (PU) based nanocomposites were prepared by in situ intercalation polymerization with different amounts of the organo-modified CoAl-LDH. An exfoliated dispersion of CoAl-LDH layers in PU matrix was verified by the disappearance of the (0 0 3) reflection of the XRD results when the LDH loading was less than 2.0 wt%. Tensile testing indicated that excellent mechanical properties of PU/LDH nanocomposites were achieved. The weak alkaline catalysis of DS to polyurethane chains, combined with the dehydration and structural degradation of the LDH below 300 °C, accounted for the process of proceeded degradation as shown in TGA results. The real-time FTIR revealed that the as-prepared nanocomposites had a slower thermo-oxidative rate than neat PU from 160 °C to 340 °C, probably due to the barrier effect of LDH layers. These results suggested potential applications of CoAl-LDH as a promising flame retardant in PUs.     

Preparation and properties of UV-cured acrylated silane intercalated polymer/LDH nanocomposite

A novel UV-cured polymer/layered double hydroxide (LDH) nanocomposite was prepared by modifying the LDH with sodium dodecyl sulfate (SDS) and [3-(methyl-acroloxy)propyl]trimethoxysilane (KH570) followed by UV irradiation after blended into a acrylate system. From the XRD analyses, the SDS-modified LDH-DS presented the basal spacing of 2.67 nm, whereas the further KH570-intercalated LDH-KH showed a slight decrease to 2.41 nm. After UV irradiated the exfoliated microstructure was formed, and observed by TEM and HR-TEM, showing the fine dispersion and random orientation of LDH in the polymer matrix. The storage modulus and glass transition temperature of the nanocomposite containing 5% LDH-KH increased to 47.5 MPa and 67.8 °C, respectively, from 39.7 MPa and 66 °C of the pure polymer from DMTA measurements. The tensile strength and Persoz hardness were enhanced to 10.6 MPa and 111 s, respectively, from 7.7 MPa and 85 s of the pure polymer.     

Structural characterization and thermal and mechanical properties of poly(propylene carbonate)/MgAl-LDH exfoliation nanocomposite via solution intercalation

Poly(propylene carbonate)/MgAl layered double hydroxide (PPC/MgAl-LDH) exfoliated nanocomposites were synthesized by solution intercalation of PPC into the galleries of organic modified MgAl-LDH (OMgAl-LDH) in cyclohexanone. The crystal morphological structures, thermal degradation behavior, and mechanical properties have been studied by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, and thermogravimetric analysis (TGA). The nanoscale dispersion of OMgAl-LDH layers in the PPC matrix has been verified by the disappearance of d_0 0 1 XRD diffraction peak of OMgAl-LDH and the observation of TEM image. The TGA data give evince that the thermal degradation temperature of the exfoliated PPC/MgAl-LDH nanocomposites with 1% OMgAl-LDH is 10 °C higher than that of pure PPC resin when 20% weight loss was selected as a point of comparison. The data from the mechanical test show that the tensile strength of the PPC/MgAl-LDH nanocomposites with 5% LDH is 36.9 MPa, which is 72% and 30% higher than those of pure PPC resin and simple mixed sample with the same content of LDH, and its Young’s modulus is 1303 MPa, which is 57% and 21% higher than those of the same two samples, respectively.     

Elevated temperature tensile properties and thermal expansion of CNT/2009Al composites

1.5 vol.% and 4.5 vol.% carbon nanotubes reinforced 2009Al (CNT/2009Al) composites with homogeneously dispersed CNTs and refined matrix grains, were fabricated using powder metallurgy (PM) followed by 4-pass friction stir processing (FSP). Tensile properties of the composites between 293 and 573 K and the coefficient of thermal expansion (CTE) from 293 to 473 K were tested. It was indicated that load transfer mechanism still takes effect at temperatures elevated up to 573 K, thus the yield strength of the 1.5 vol.% CNT/2009Al composite at 423–573 K, was enhanced compared with the 2009Al matrix. However, for the 4.5 vol.% CNT/2009Al composite, the yield strength at 573 K was even lower than that for the matrix, due to the quicker softening of ultrafine-grained matrix. Compared with the 2009Al matrix, the CTEs of the composites were greatly reduced for the zero thermal expansion and high modulus of the CNTs and could be well predicted by the Schapery’s model.     

Studies on the oxygen barrier and mechanical properties of low density polyethylene/organoclay nanocomposite films in the presence of ethylene vinyl acetate copolymer as a new type of compatibilizer

Nanocomposite films based on low density polyethylene (LDPE), containing of 2, 3, and 4 wt.% organoclay (OC) and ethylene vinyl acetate (EVA) copolymer as a new compatibilizer were prepared and characterized using rheological tests, X-ray diffraction, differential scanning calorimetry, oxygen permeation measurements, and tensile tests. There was no exfoliation or intercalation of the clay layers in the absence of EVA, while an obvious increase in d-spacing was observed when the samples were prepared with EVA present. This issue was reflected in the properties of nanocomposites. The oxygen barrier properties of the LDPE/EVA/OC film were significantly better than those of the LDPE/OC film. The average aspect ratio of clay platelets in nanocomposites was determined from permeability measurements and using Lape–Cussler model. In addition to barrier properties, the LDPE/EVA/OC film also had better elastic modulus than their counterparts without EVA. The modulus reinforcement of nanocomposites was studied using Halpin–Tsai equations, which are universally used for composites reinforced by flake-like or rod-like fillers.     

Morphology,thermal and mechanical properties of PVC/MMT nanocomposites prepared by solution blending and solution blending + melt compounding

Two types of montmorillonite (MMT), natural sodium montmorillonite (Na-MMT) and organically modified montmorillonite (OMMT), in different amounts of 1, 2, 5, 10 and 25 phr (parts per hundred resin), were dispersed in rigid poly (vinyl chloride) by two different methods: solution blending and solution blending + melt compounding. The effects on morphology, thermal and mechanical properties of the PVC/MMT nanocomposites were studied by varying the amount of Na-MMT and OMMT in both methods. SEM and XRD analysis revealed that possible intercalated and exfoliated structures were obtained in all of the PVC/MMT nanocomposites. Thermogravimetric analysis revealed that PVC/Na-MMT nanocomposites have better thermal stability than PVC/OMMT nanocomposites and PVC. In general, PVC/MMT nanocomposites prepared by solution blending + melt compounding revealed improved thermal properties compared to PVC/MMT nanocomposites prepared by solution blending. Vicat tests revealed a significant decrease in Vicat softening temperature of PVC/MMT nanocomposites prepared by solution blending + melt compounding compared to unfilled PVC.     

Strain rate dependency of mechanical properties of TCP/PLLA composites after immersion in simulated body environments

In order to clarify strain rate dependency of mechanical properties of β-tricalcium phosphate (TCP)/poly(l-lactic acid) (PLLA) composites after immersion in simulated body environment, tensile tests at various loading rate were conducted on the TCP/PLLA specimens with and without immersion. TCP contents in the composite were 5, 10 and 15 wt%. Phosphate buffered solution was selected as simulated body environment and immersion periods were 8, 16 and 24 weeks. Young’s modulus and tensile strength increased with increasing strain rates. However, the strain rate dependencies decreased with immersion. Swelling and cracks around TCP agglomerations were observed in the cross-section of 15 wt% specimen after 24 weeks immersion. From the fracture surface observation, voids existed only in the ductile fracture surface of the specimen without immersion, whereas they existed in both ductile and brittle surface of the specimen with immersion. These results indicated that diffused water through the interfaces between TCP and PLLA hydrolyzed and weakened the interfaces and/or matrix near the interfaces.     

Preparation of polybenzoxazine-functionalized Fe3O4 nanoparticles through in situ Diels–Alder polymerization for high performance magnetic polybenzoxazine/Fe3O4 nanocomposites

Hybrids and nanocomposites of polymer and magnetic Fe₃O₄ nanoparticles have been utilized as magnetically-responsive materials and magnetically-directed nanoparticles. In this work, we prepare polymer-functionalized Fe₃O₄ nanoparticles through in situ Diels–Alder polymerization using maleimide-functionalized Fe₃O₄ nanoparticle as a precursor. Polybenzoxazine-functionalized Fe₃O₄ nanoparticles (MNP-PBz) have been obtained and characterized with Fourier Transform Infrared, X ray photoelectron, and Raman spectroscopies. The high saturation magnetization value of 51.9 emu g⁻¹ of the MNP-PBz nanoparticles demonstrates its superparamagnetism. Moreover, MNP-FBz has been utilized as a nanofiller for preparation of cured PBz/MNP-PBz nanocomposites, which contain various MNP-PBz contents of 67, 50, 33, and 17 wt.%. The sample of PBz/MNP-PBz-67 shows a storage modulus of 8.0 GPa, a saturation magnetization value of 37.6 emu g⁻¹, and a glass transition temperature above 380 °C. As a result, the PBz/MNP-PBz nanocomposites could be classified as magnetically-responsive high performance materials.     

Temperature sensing with fluorescence intensity ratio technique in epoxy-based nanocomposite filled with Er-doped 7YSZ

Luminescent nanocomposite of epoxy filled with Er³⁺-doped yttria-stabilized zirconia (7YSZ) is prepared with their luminescence spectra measured in the temperature range 123–423 K. Fluorescence intensity ratio (FIR) of the two Er³⁺ emissions is also obtained in the same temperature range. Er–7YSZ/epoxy nanocomposites exhibited higher sensitivity of 0.18%/K as compared with the bare Er–7YSZ particles. Luminescence thermometry is demonstrated by using the nanocomposites as temperature sensitive paint (TSP) with a resolution of 1 K. The advantage of FIR technique combined with the excellent thermal stability of epoxy matrix makes the Er–7YSZ/epoxy nanocomposites viable as temperature sensitive paint for aerodynamic applications.     

Dielectric properties of montmorillonite clay filled poly(vinyl alcohol)/poly(ethylene oxide) blend nanocomposites

Organic–inorganic nanocomposites of poly(vinyl alcohol) (PVA)–poly(ethylene oxide) (PEO) blend filled with montmorillonite (MMT) nanoclay up to 10 wt.% concentration were synthesized by aqueous solution-cast technique. The complex dielectric function, electrical conductivity, electric modulus and impedance spectra of the nanocomposites were measured in the frequency range 20 Hz–1 MHz at ambient temperature. A direct correlation was observed between the real part of dielectric function and the mean relaxation time of the polymer chain segmental dynamics, with the exfoliated and intercalated MMT clay structures, and the extent of miscibility between PVA and PEO due to hydrogen bonded bridging through exfoliated MMT clay nanosheets. The large increase of dielectric relaxation time revealed that the dispersed exfoliated nanoscale MMT clay in the polymers blend matrix produces a large hindrance to the polymer chain dynamics. Results confirm that the real part of dielectric function of the nanocomposites can be tailored by varying amount of MMT clay filler for their use as nanodielectric materials in the microelectronic technology.     

Sulfonated polyoxadiazole composites containing carbon nanotubes prepared via in situ polymerization

In the present work, in situ polymerizations of sulfonated polyoxadiazole through a polycondensation reaction of A–A (hydrazine sulphate) and B–B (aromatic dicarboxylic acid) monomers with carbon nanotubes in poly(phosphoric acid) were performed. The structures of composites were characterized by elemental analysis, Raman and FTIR spectroscopy. The sulfonated polyoxadiazole composites with high molecular weight (in the order of magnitude of 10⁵ g/mol) are soluble in organic solvents and can be cast as dense films. They exhibit good mechanical properties (storage modulus up to around 4 GPa at 300 °C) and an electrical conductivity in the order of 10⁻⁵ S m⁻¹. The composites can be used at temperatures as high as 470 °C.     

Mechanical properties of cellulose nanofiber (CNF) reinforced polylactic acid (PLA) prepared by twin screw extrusion

The aim of this study was to develop cellulose nanofiber (CNF) reinforced polylactic acid (PLA) by twin screw extrusion. Nanocomposites were prepared by premixing a master batch with high concentration of CNFs in PLA and diluting to final concentrations (1, 3, 5 wt.%) during the extrusion. Morphology, mechanical and dynamic mechanical properties (DMA) were studied theoretically and experimentally to see how different CNF concentrations affected the composites’ properties. The tensile modulus and strength increased from 2.9 GPa to 3.6 GPa and from 58 MPa to 71 MPa, respectively, for nanocomposites with 5 wt.% CNF. The DMA results were also positive; the storage modulus increased for all nanocomposites compared to PLA; being more significant in the high temperature region (70 °C). The addition of nanofibers shifted the tan delta peak towards higher temperatures. The tan delta peak of the PLA shifted from 70 °C to 76 °C for composites with 5 wt.% CNF.     

Mechanical behaviour and essential work of fracture of halloysite nanotubes filled polyamide 6 nanocomposites

Polyamide 6 (PA 6)/halloysite nanotubes (HNT) nanocomposites were prepared by melt-extrusion compounding via masterbatch dilution process. A homogeneous dispersion of HNTs in PA 6 matrix was achieved. Differential scanning calorimetric measurements showed that addition of HNTs into PA 6 matrix enhanced the crystallization temperature and degree of crystallinity, thus indicating an effective nucleation induced by the addition of HNTs. Upon halloysite addition, glass transition temperature, storage modulus, Young modulus, tensile strength and notched Charpy impact strength increased without loss of ductility. For the first time, the essential work of fracture (EWF) concept was used to analyse the toughening and fracture behaviour of PA 6/HNT systems. Significant increase (+38%) of the essential work of fracture of PA 6/HNT nanocomposites was noticed at HNTs contents as low as 4 wt.%.     

Creep of Nextel™720/alumina–mullite ceramic composite at 1200 °C in air,argon, and steam

The tensile creep behavior of an oxide–oxide continuous fiber ceramic composite was investigated at 1200 °C in laboratory air, in steam and in argon. The composite consists of a porous alumina–mullite matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The tensile stress–strain behavior was investigated and the tensile properties measured at 1200 °C. The elastic modulus was 74.5 GPa and the ultimate tensile strength was 153 MPa. Tensile creep behavior was examined for creep stresses in the 70–140 MPa range. Primary and secondary creep regimes were observed in all tests. Creep run-out (set to 100 h) was achieved in laboratory air for creep stress levels ?91 MPa. The presence of either steam or argon accelerated creep rates and reduced creep lifetimes. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Tropical wood polymer nanocomposite (WPNC): The impact of nanoclay on dynamic mechanical thermal properties

In this study, wood polymer nanocomposites (WPNCS) were manufactured from five Malaysian tropical wood species by vacuum-impregnation attended by in situ polymerization using phenol–formaldehyde resin and montmorillomite nanoclay. Percentage weight gain and density of wood polymer nanocomposites depended on wood species. Thermo-mechanical properties of wood samples were investigated by the dynamic mechanical thermal analysis (DMTA) over the temperature range of −100 °C to 200 °C. The intrinsic properties of the components, morphology of the system and the nature of interface between the phases were also determined through DMTA test. Storage modulus (E′) of WPNC samples exhibited significant improvement over the temperature range, in both glassy region and rubbery plateau in relation to their corresponding raw wood samples and wood polymer composites (WPCs). Furthermore, damping (loss tan δ) peaks of all wood species were lowered by PF-Nanoclay system treatment, an indication of improved surface interphase of wood. Dynamic Young’s modulus (E_d) of wood was also calculated using free–free vibration testing. A significant increment was obtained for the PF-Nanoclay impregnated WPNC samples.     

Solidification behavior of PLLA/nHA nanocomposites

As part of a broader effort to establish processing-structure–property relationships in PLLA/nHA, which is currently under consideration for bioresorbable scaffolds for bone repair, hot stage optical microscopy and differential scanning calorimetry have been used to investigate the solidification behavior of a series of medical grade PLLA/nHA nanocomposites. The presence of the nHA resulted in an increase in the number of spherulites per unit volume during isothermal crystallization, but there was a substantial decrease in the spherulite growth rate with increasing nHA content in the temperature range 100–130 °C, argued to be associated with a significant increase in the melt viscosity in the presence of the nHA. The consequences for the global solidification rates and the phase structure of the PLLA/nHA nanocomposites are discussed.