Interphase sizing temperature effect of LaRC PETI-5 on the dynamic mechanical thermal properties of carbon fiber/BMI composites

The dynamic mechanical thermal properties of carbon fiber-reinforced bismaleimide (BMI) composites processed using polyacrylonitrile(PAN)-based carbon fibers unsized and sized with LaRC PETI-5 amic acid oligomer as interphase material at 150°C, 250°C, and 350°C were investigated by means of dynamic mechanical thermal analysis. It was found that the storage modulus, loss modulus, tan δ and the peak temperature significantly depend on the sizing temperature as well as on the presence and absence of LaRC PETI-5 sizing interphase. The result showed that the carbon fiber/BMI composite sized at 150°C had the highest storage modulus at a measuring temperature of 250°C. The storage modulus decreased with increasing sizing temperature from 150°C to 350°C, being influenced by interdiffusion and co-reaction between the LaRC PETI-5 interphase and the BMI matrix resin. The present result is quite consistent with the interfacial result reported earlier in term of interfacial shear strength and interlaminar shear strength of carbon fiber/BMI composites. It is addressed that in the present composite system the sizing temperature of LaRC PETI-5 interphase critically influences not only the interfacial properties but also the dynamic mechanical thermal properties and its control is also important.     

Three-dimensional structure of a polymer/clay nanocomposite characterized by transmission electron microtomography

Three-dimensional (3D) morphology of a polymer/clay nanocomposite, an organophilic montmorillonite (MMT) dispersed in poly(ethylene-co-vinylacetate) (EVA), was examined by transmission electron microtomography (TEMT). Using this technique, individual clay layers dispersed in the EVA matrix were clearly visualized. A volume fraction of the clay layers evaluated from the 3D reconstructed image agreed well with that calculated from the weight of the MMT component in the MMT/EVA system. The individual clay layers were digitally extracted by a newly developed 3D particle algorithm. A size distribution of the clay layers was directly obtained from the 3D reconstruction. Anisotropy of each clay layer was characterized by the determination of three semi-axes of an approximating ellipsoid with the same volume. One of the representative semi-axis of the ellipsoid was used to estimate average orientation of the MMT layers in the ultra-thin section used in the TEMT experiment. Thus, the combination of quantitative TEMT and 3D structural analysis is shown to be a powerful tool to investigate a relationship between the MMT distribution and a variety of physical properties of the nanocomposites.     

Morphology and properties of poly(methyl methacrylate)/clay nanocomposites by in-situ solution polymerization

Poly(methyl metacrylate)/montmorillonite (PMMA)/(MMT) nanocomposites were prepared by in-situ solution polymerization of methyl methacrylate monomer in the presence of the organic modified MMT-clay. After the organic modification by ionic exchanging with amine salts, the organoclay becomes more hydrophobic and compatible then pristine clay with methyl methacrylate monomer. The modified clays are characterized by wide angle X-ray diffraction (WAXRD). The powdered X-ray diffraction and transmission electron microscopy (TEM) techniques were employed to study the morphology of the PMMA/clay nanocomposites which indicate that the modified clays are dispersed in PMMA matrix to form both exfoliated and intercalated PMMA/modified clay nanocomposites. The thermo-mechanical properties were measured by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC). Gas permeability analyzer (GPA) shows the excellent gas barrier property of the PMMA nanocomposites which is in good agreement with the morphology. The optical property was measured by UV-vis spectroscopy which shows that these materials have good optical clarity, and UV resistance.     

Experimental evidence for reduced chain segment mobility in poly(amide)-6/clay nanocomposites

Poly(amide)-6/clay nanocomposites are investigated by means of modulated temperature differential scanning calorimetry. The importance of polymer–filler interaction is explored by comparing nanocomposites based on untreated and organically modified clay. During quasi-isothermal crystallization experiments, an excess contribution is observed in the recorded heat capacity signal due to reversible melting and crystallization. The magnitude of this excess contribution depends on the nanocomposite investigated. We suggest that it is directly related to the segmental mobility of the polymer chains in the interphase region. As such, the magnitude of this excess contribution can be used to quantify the efficiency of the polymer–clay interaction. Depending on the clay type used, differences in interfacial interaction can be achieved, which is of great importance with respect to the improvement of material properties. Based on thermal analysis results, a simple interphase model is proposed that is able to account for both the thermal and mechanical properties of poly(amide)-6/clay nanocomposites.     

Polypropylene/clay nanocomposites prepared with masterbatches of polypropylene ionomer and organoclay

Polypropylene (PP) ionomers were obtained by the neutralization of maleic anhydride groups in a maleated PP of which maleic anhydride content was 1 wt%; these were studied as vehicle resins for the masterbatches of an organoclay for PP nanocomposites. PP/clay nanocomposites were prepared by melt mixing of PP with the masterbatches employing a twin screw extruder. Intercalation and/or exfoliation of the organoclay in the PP nanocomposites were observed. It was found that the PP nanocomposite prepared with the masterbatch of an organoclay and the PP ionomer obtained by 75% neutralization of maleic anhydride groups in the maleated PP showed the largest improvement in dispersion of organoclay. Very large increase of Young's modulus was observed in the nanocomposites with the PP ionomer obtained by 75% neutralization of maleic anhydride groups in the maleated PP. The improvements in the dispersion and mechanical properties were attributed to strong interactions between ionic groups of the PP ionomer and ionic surfactants of the organoclay.     

Predicting the self-assembled morphology and mechanical properties of mixtures of diblocks and rod-like nanoparticles

We couple a morphological study of a mixture of diblock copolymers and rod-like, solid nanoparticles with a micromechanical simulation to determine how the spatial distribution and aspect ratio of the particles affects the mechanical behavior of the composite. The morphological studies are conducted through the SCF/DFT technique, which couples the self-consist field theory (SCFT) for the diblocks and a density functional theory (DFT) for parallelepiped particles. Through the SCF/DFT calculations, we obtain the equilibrium morphology of the diblock/particle mixtures. We find that the distribution of particles within the polymers is dependent not only on the relative interaction energies between the particles and the different blocks, but also on the aspect ratio of the rod-like solids. The output of the SCF/DFT model serves as the input to the Lattice Spring Model (LSM), which consists of a three-dimensional network of springs. In particular, the location of the different phases is mapped onto the LSM lattice and the appropriate force constants are assigned to the LSM bonds. A stress is applied to the LSM lattice, and we calculate the local stress and strain fields and overall elastic response of the material. We find that high aspect ratio rods can dramatically increase the Young's modulus of the material. By integrating the morphological and mechanical models, we can isolate how modifications in physical characteristics of the particles and diblocks affect both the structure of the mixture and the macroscopic behavior of the composite. Thus, we can establish how choices made in the components affect the ultimate performance of the material.     

Effect of chemical treatment on dynamic mechanical properties of sisal fiber-reinforced polyester composites fabricated by resin transfer molding

The dynamic mechanical properties of treated sisal fiber-reinforced polyester composites fabricated by resin transfer molding (RTM) have been studied with reference to fiber surface modifications, frequency and temperature. The sisal fibers have been subjected to various chemical and physical treatments like mercerization, heating at 100°C, permanganate, benzoylation and vinyl tris(2-ethoxymethoxy) silane to improve the interfacial bonding with isophthalic polyester resin. Results indicated that treatment changed the storage modulus (E′), loss modulus (E″) and damping factor (tan δ) drastically at a wide range of temperature. The E′ value increased for every treatment, and is maximum for the composites fabricated by benzoylated-treated fibers. The T _g value obtained from the E″value showed an increase as compared to untreated fiber-reinforced composites. The alkali-treated fiber-reinforced composites showed lower tan δ value. Using Arrhenius' equation the activation energy was calculated and found maximum for the composites fabricated by alkali-treated fiber, which shows good fiber/matrix interactions.     

Effect of interfacial interaction on the structure and rheological properties of polyamide-6/clay nanocomposites

A series of polyamide-6 (PA6)/layered silicate (clay) nanocomposites were prepared via direct melt compounding using a conventional single screw extruder, and then the effect of interfacial interaction on the characteristic internal structure and rheological properties of PA6/clay nanocomposites was investigated. XRD diffractograms indicated a large extent of exfoliation of the layered silicate entering into a strong interaction with PA6. The formation of such morphology was further supported by TEM images. In addition, various rheological properties were interpreted in conjunction with morphological characteristics depending on interfacial interaction between PA6 and the layered silicate.     

Morphology and thermal properties of clay/PMMA nanocomposites obtained by miniemulsion polymerization

Miniemulsion polymerization was used as the synthetic method to produce clay/poly(methyl methacrylate) nanocomposites. Two kinds of interfacial interactions clay–polymer particle were observed by electron microscopy, one where the polymer particles are adhered on the surface of the larger fragments of clay, and another where nanometric fragments of clay are encapsulated by polymer particles. Variations in the glass transition temperature (T_g) and thermomechanical properties of the matrix, as function of clay content, were observed. In particular, at the highest clay loading (1.0 wt%) depression of T_g and thermomechanical properties were observed. The increased clay–polymer matrix interfacial area appears to be the conditioning factor that determines such behavior.     

Enhancement of thermal and mechanical properties of poly(MMA-co-BA)/Cloisite 30B nanocomposites by ultrasound-assisted in-situ emulsion polymerization

This study reports synthesis and characterization of poly(MMA-co-BA)/Cloisite 30B (organo-modified montmorillonite clay) nanocomposites by ultrasound-assisted in-situ emulsion polymerization. Copolymers have been synthesized with MMA:BA monomer ratio of 4:1, and varying clay loading (1–5 wt% monomer). The poly(MMA-co-BA)/Cloisite 30B nanocomposites have been characterized for their thermal and mechanical properties. Ultrasonically synthesized nanocomposites have been revealed to possess higher thermal degradation resistance and mechanical strength than the nanocomposites synthesized using conventional techniques. These properties, however, show an optimum (or maxima) with clay loading. The maximum values of thermal and mechanical properties of the nanocomposites with optimum clay loading are as follows. Thermal degradation temperatures: T_10% = 320 °C (4 wt%), T₅₀ = 373 °C (4 wt%), maximum degradation temperature = 384 °C (4 wt%); glass transition temperature = 64.8 °C (4 wt%); tensile strength = 20 MPa (2 wt%), Young’s modulus = 1.31 GPa (2 wt%), Percentage elongation = 17.5% (1 wt%). Enhanced properties of poly(MMA-co-BA)/Cloisite 30B nanocomposites are attributed to effective exfoliation and dispersion of clay nanoparticles in copolymer matrix due to intense micro-convection induced by ultrasound and cavitation. Clay platelets help in effective heat absorption with maximum surface interaction/adhesion that results in increased thermal resistivity of nanocomposites. Hindered motion of the copolymer chains due to clay platelets results in enhancement of tensile strength and Young’s modulus of nanocomposite. Rheological (liquid) study of the nanocomposites reveals that nanocomposites have higher yield stress and infinite shear viscosity than neat copolymer. Nonetheless, nanocomposites still display shear thinning behavior – which is typical of the neat copolymer.     

The effects of organoclay on the morphology and mechanical properties of PAI/clay nanocomposites coatings prepared by the ultrasonication assisted process

In this research, solvent based polyamide – imide (PAI)/clay nanocomposites were prepared successfully using the solution dispersion technique. With the assistance of the ultrasonic wave, the effect of the ultrasonic wave time on the microstructure of 3 wt% PAI/C20A nanocomposite (NC) was investigated. Then, the best ultrasonic parameters were selected and the effects of the concentration of Cloisite 20A (C20A) (1, 3 and 5 wt% C20A) on the microstructure and mechanical properties (adhesion, hardness, flexibility, wear and impact) of NCs were investigated. The PAI, C20A and nanocomposites (NC)s were characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDX), and Wide-angle X-ray diffraction (WAXD). The results showed that the sample with 1 and 3 wt% C20A had better mechanical properties, as compared to the pure PAI and the 5 wt% NC.     

Properties of hydrophobically-modified graphene oxide (HG)/butyl rubber (IIR) nanocomposites prepared by shear mixing process

Abstract

Butyl rubber (IIR)/hydrophobically modified graphene oxide (GO) (HG) nanocomposites were prepared via shear-induced compounding. Hydrophilic GO was synthesized through the chemical oxidation of graphite (GP) and modified hydrophobically by octadecylamine which has a hydrophobic long alkyl chain. The obtained HG was characterized by Fourier transform infrared and wide-angle X-ray diffraction (WAXD) patterns. It was well dispersed in toluene for more than 30 days under stationary condition. The IIR/HG nanocomposites were prepared by the shear mixing process and followed by thermal vulcanization process through compression molding. Their properties were studied using oscillating disk rheometer, universal testing machine, differential scanning calorimetry, thermogravimetric analysis, WAXD patterns, and scanning electron microscope analysis. The hydrophobic HG was dispersed at the nanoscale within IIR matrix, and the resulting nanocomposites had significantly reduced curing time. The overall tensile properties were enhanced.     

Effects of enhanced hydrogen bonding on the mechanical properties of poly (vinyl alcohol)/carbon nanotubes nanocomposites

In this study, poly (vinyl alcohol) (PVA) composites reinforced by multiwall carbon nanotubes (MWCNTs) functionalized with either phenolic hydroxyl groups (MWCNTs-f-OH) or PVP molecule (PVP@MWCNTs) were fabricated. The objective was to elucidate the effect of different MWCNTs surface functionalization on the mechanical properties of the nanocomposites. It was found that both of PVP@MWCNTs and MWCNTs-f-OH had a good dispersion in PVA matrix. However, the MWCNTs-f-OH had stronger effective interfacial interaction with PVA matrix than PVP@MWCNTs, owe to the formation of hydrogen bonds between MWCNTs-f-OH and PVA. The stress-strain measurements showed that the Young’s modulus and tensile strength of MWCNTs-f-OH/PVA with only 1.0 wt.% contents increased by 200 and 100% compare with that of PVA, respectively. The findings of this experimental study emphasized the critical role of MWCNTs surface morphology in determining the mechanical properties of nanocomposites, and shed new light on understanding and advancing the properties of carbon nanotube based composites.     

Synthesis of poly(butylene succinate) nanocomposites via in-situ interlayer polymerization: thermo-mechanical properties and morphology of the hybrid fibers

A series of poly(butylene succinate) (PBS) nanocomposites with the organoclay C₁₂PPh-Mica were synthesized by using the in-situ interlayer polycondensation of 1,4-butanediol with succinic acid. The PBS nanocomposites were melt-spun to produce monofilaments with various organoclay contents and draw ratios (DRs). The thermo-mechanical properties and morphologies of the PBS nanocomposites were determined using differential scanning calorimetry, thermogravimetric analysis, wide angle X-ray diffraction, transmission electron microscopy, and a universal tensile machine. Some of the clay particles were found to be well dispersed in the PBS matrix, with some agglomerated at a size level greater than approximately 20 nm. The thermal degradation properties of undrawn PBS hybrid fibers were found to improve with increasing clay content. The ultimate tensile strengths and initial moduli of the hybrid fibers increased with increasing clay content at DR = 1. However, the ultimate strengths were found to decrease markedly with increases in DR from 1 to 6. In contrast to the trend for the tensile strengths, the initial moduli of the hybrid fibers increased only slightly with increases in DR up to 6.     

Microstructure,interfacial interaction,and properties of polyimide/poly(vinylsilsesquioxane)/titania ternary hybrid nanocomposites

Ternary hybrid nanocomposites of polyimide (PI), poly(vinylsilsesquioxane) (PVSSQ), and titania (PI/PVSSQ/Ti) were prepared by thermal imidization from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA)-4,4'-oxydianiline (ODA) polyamic acid (BPDA–ODA PAA) and a sol-gel process from vinyltriethoxysilane(VSSQ) and titanium isopropoxide(Ti(OPr)₄). The microstructure, interfacial interaction, and optical and thermo-mechanical properties of the hybrid films have been investigated. The phase morphology and the properties are influenced by the composition of PVSSQ and titania. For the PI/VSSQ/titania ternary hybrid systems, the particle size is significantly decreased and the inorganic particles are extremely finely distributed in the nanometer scale, suggesting that the interaction between the particles and the matrix increases. It is concluded that the addition of titania plays a compatibilizing role for the PI/PVSSQ binary hybrids, resulting in the enhancement of optical transparencies and thermo-mechanical properties of the binary hybrids.     

Preparation of MPS (mercaptopropyltrimethoxysilane)-coated SiO2 nanoparticle and its effect on mechanical properties of surface treated SiO2/EVA nanocomposite

SiO₂ nanoparticles were synthesized from different three precursors, namely, TEOS (tetraethyl orthosilicate), sodium metasilicate and sodium silicate. First, SiO₂ nanoparticles were prepared by a controlled hydrolysis of TEOS. In another method, SiO₂nanoparticles were prepared by precipitation in an emulsion medium from sodium metasilicate and hydrochloric acid solution. Finally, SiO₂ nanoparticles were also synthesized from sodium silicate by an emulsion method. In this study, we concentrated on dispersion and compatibility between nanosized SiO₂ particles and EVA (ethylene vinyl acetate). Therefore, surface modification of synthesized SiO₂ nanoparticles was accomplished with MPS (3-mercaptopropyl trimethoxysilane) to enhance homogeneous dispersion and compatibility between the obtained SiO₂ nanoparticles and EVA. Finally, nanocomposites of surface treated SiO₂ nanoparticles and EVA were prepared. By inserting the MPS-coated SiO₂ nanoparticles into EVA, abrasion resistance and hardness were increased remarkably. On the other hand, insertion of SiO₂ nanoparticles barely decreased original tensile strength and elongation of EVA. Consequently, MPS-coated SiO₂/EVA nanocomposite can have an improved abrasion resistance and hardness compared with raw EVA, without decrease tensile strength and elongation. The characterization of synthesized SiO₂ nanoparticles and their nanocomposite with EVA was conducted by TEM, SEM, FTIR photography and mechanical property tests such as abrasion, hardness, tensile strength and elongation.     

Effect of clay silylation on curing and mechanical and thermal properties of unsaturated polyester/montmorillonite nanocomposites

This work focuses on the chemical modification of montmorillonite (MMT) (Cloisite® Na) with compatible silanes, vinyltriethoxysilane (CVTES) and γ-methacryloxypropyltrimethoxysilane (CMPS) in order to prevent agglomeration and to improve montmorillonite interaction with an unsaturated polyester resin matrix seeking to achieve a multifunctional composite. Clays were dispersed in the resin by mechanical stirring and sonication and the nanocomposites were prepared by resin transfer into a mold. The mechanical, morphological, thermal and flammability properties of the obtained composites were compared with those prepared using commercial Cloisite® 30B (C30B) and Cloisite® 15A (C15A) clays. Advantages of using silane-modified clays (CVTES and CMPS) as compared with organic-modified clays (C30B and C15A) can be summarized as similar flexural strength and linear burning rate but higher storage modulus and improved adhesion to the polyester resin with consequent higher thermal deflection temperature and reinforcement effectiveness at higher temperatures. However, organic modified clays showed better dispersion (tendency to exfoliate) and consequently delayed thermal volatilization due to the clay barrier effect.     

Rheological,thermal, and mechanical properties of poly(ethylene naphthalate)/poly(ethylene terephthalate) blends

Structural, Theological, thermal, and mechanical properties of blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) obtained by melt blending were investigated using capillary rheometry, differential scanning calorimetry (DSC), scanning electron microscopic (SEM) observation, tensile testing. X-ray diffraction, and ¹H nuclear magnetic resonance (NMR) measurements. The melt Theological behavior of the PEN/PET blends was very similar to that of the two parent polymers. The melt viscosity of the blends was between that of PEN and that of PET. Thermal properties and NMR measurement of the blends revealed that PEN is partially miscible with PET in the as molded blends, indicating that an interchange reaction occurs to some extent on melt processing. The blend of 50/50 PEN/PET was more difficult to crystallize compared with blends of other PEN/PET ratios. The blends, once melted during DSC measurements, almost never showed cold crystallization and subsequent melting and definitely exhibited a single glass transition temperature between those of PEN and PET during a reheating run. Improvement of the miscibility between PEN and PET with melting is mostly due to an increase in transesterification. The tensile modulus of the PEN/PET blend strands had a low value, reflecting amorphous structures of the blends, while tensile strength at the yield point increased linearly with increasing PEN content.     

Evaluation of an alternative modification route for layered silicates and synthesis of poly(styrene) layered silicate nanocomposites by in-situ suspension polymerisation

The organically modified montmorillonites (o-MMT) used in this study were prepared in a semi-solid state in molten long chain alkyl (hydrogenated tallow (HT) or stearyl) dimethyl/aryl ammonium chloride intercalant (quat), within a Brabender Plasticorder W50E chamber. The effect of quat level and structure was investigated using WAXS, FTIR (DRIFTS) and solvent swelling/dispersion viscosity studies. It was found that mono-stearyl (or HT) quats were the most suitable intercalants for the in-situ polymerised PS matrix nanocomposites produced. The distearyl (or HT) quats generally led to reduced interfacial effects in the composites and reduced toluene dispersion viscosity due to the close proximity of long alkyl tails within the molecules facilitating their self-assembly into ordered arrays, which were difficult for toluene to penetrate (toluene was used as a probe to gauge compatibility with styrene). Substitution of a benzyl group (for a methyl) led to increased compatibility with styrene/toluene, though the detrimental effect of two long alkyl groups was not overcome. PS matrix nanocomposites have been formed via in-situ free radical suspension polymerisation of styrene/organo-montmorillonite (o-MMT) dispersions. These composites displayed evidence of large interfacial area relative to the volume fraction of montorillonite added; this was manifested as a reduction in melt flow rate, broadening of the molar mass distribution (increase in M _w) and an increase in thermal stability, relative to the unfilled matrix. However, wide angle X-ray scattering (WAXS) patterns of the composites revealed a strong (001) reflection (d = 3.3–3.4 nm) together with clear (002) and (003) reflections. Therefore a mixed intercalated/flocculated morphology, with no significant exfoliation into single platelets, was indicated.     

Dynamic rheological and dynamic thermomechanical properties of poly(trimethylene terephthalate)/short carbon fibre composites

The dynamic rheology and thermomechanical properties of poly(trimethylene terephthalate) (PTT)/short carbon fibre (CF) composites at different mechanical states were investigated by a rotational rheometer and a dynamic mechanical analyzer (DMA). At molten state, the composite melts were pseudo-plastic fluids, and the complex viscosity of the composite melts decreased much with increasing CF content because of the poor adhesion at the fiber/matrix interface. The viscous behavior was predominant rather than elastic behavior in the composites melt and viscous behavior was increased with increasing CF at low shearing frequency. An apparent slope change in storage modulus and loss modulus plot suggested that a structure change occurred in the melt that was dependent on shearing frequency. At glassy state, the storage modulus increased with increasing CF content, suggesting that CFs had good reinforcing effect on PTT. At glass transition region, the increasing loss modulus indicated a better toughness of the composites, and the elastic behavior was predominant rather than viscous behavior. Moreover, the glass-transition temperatures of the composites increased with 10% CF content. The composites have larger cold-crystallization rate than pure PTT.