Structural and thermal properties of HDPE/n-AlN polymer nanocomposites

High-density polyethylene (HDPE) containing various volume fractions (0–20 vol%) of aluminum nitride nanoparticles (n-AlN) is prepared by melt mixing. Structural and morphological characterizations of the prepared composites are carried out by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and atomic force microscopy (AFM). Thermal stability and degradation kinetics of HDPE/AlN (nano) composites are investigated by Thermogravimetric analysis (TG). HR-TEM micrographs confirm fairly uniform dispersion of AlN nanoparticles, as well as the existence of long interconnected chain-like aggregates. AFM images also confirm homogeneous dispersion of n-AlN in the polymer matrix. Roughness analysis from the AFM data indicates the presence of substantial undulation from the mean surface level. Thermogravimetric data indicate small improvement in the thermal stability of the composites. Kinetic parameters, viz., the activation energy (E _a), frequency factor (A), and reaction order (n) are estimated using the isoconversional methods of Kissinger, Flynn–Wall–Ozawa (FWO), KAS, and Friedman. Activation energies (E _a) calculated by the above four models display nearly similar features and are enhanced by the presence of AlN nanoparticles. Kinetics of degradation of HDPE-AlN (nano) composites follows a first-order reaction.     

Effect of natural weather on the structure and properties of polylactide/Cloisite 30B nanocomposites

The degradation of polylactide (PLA)/Cloisite 30B nanocomposites under natural weathering was investigated as a function of clay loadings (1, 3 and 5 wt.%) for up to 130 days using Fourier transform infrared (FT-IR) spectroscopy, size exclusion chromatography (SEC), nanoindentation measurements, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). For comparative purposes, the neat PLA was also considered. The FT-IR results showed that the photo-oxidation mechanism of PLA was not modified in the presence of Cloisite 30B, but only the degradation rates were accelerated. Moreover, the photo-oxidative degradation of PLA nanocomposite samples led to the formation of vinyl unsaturation, carbonyls, anhydrides and hydroperoxides groups as a result of the occurrence of several chemical mechanisms simultaneously. The decrease of the weight-average molecular weight, and the number-average molecular weight associated with an enhanced polydispersity of the nanocomposite samples indicated that chain scission was the most prominent phenomenon in natural weathering. The thermal degradation of the PLA was faster in the presence of clay. Modulus and hardness measured by nanoindentation increased slightly with exposure time for both neat PLA and PLA nanocomposite samples; the increase is also a function of the clay content. Finally, the weathering effect on the morphology of exposed samples observed by SEM revealed that the fractured surfaces exhibited many voids and cracks. These defects were much more pronounced for the PLA nanocomposites.     

Flammability and morphology of HDPE/clay nanocomposites

High-density polyethylene/modified bentonite clay/polar compatibilizer nanocomposites were prepared through the melt intercalation process. The clay was organophilizated using different percentages of quaternary ammonium salt 100, 125, and 150 % based cation exchange capacity of the clay. The nanocomposites were prepared in a counter-rotating twin-screw extruder and then specimens were injection molded. For the evaluation of flammability of the test system was used for burning in the horizontal position according to the norm (Underwriters Laboratories, UL94HB) and to the method of cone calorimeter. The thermal behavior of nanocomposites was evaluated by thermogravimetry and X-ray diffraction techniques, and transmission electron microscopy were used to characterize the morphology and analyze the degree of expansion of the clays prepared and the degree of exfoliation of nanocomposites. It was observed that the percentage of ammonium salt and the compatibilizer polar influence on the final properties of the systems and consequently improving the thermal stability and reducing the flammability of the matrix.     

Thermal properties and microhardness of HDPE/clay nanocomposites compatibilized by different functionalized polyethylenes

The calorimetric characteristics, the flammability, the thermal stability and the microhardness of polyethylene high density/clay nanocomposites (HDPE/clay) have been studied by differential scanning calorimetry, thermogravimetry, determination of limiting oxygen index and microhardness tests. The nanocomposites have been compatibilized by ethylene–acrylic acid copolymer (EAA), acrylic acid grafted HDPE (HDAA) and maleic anhydride grafted HDPE (HDMA). The clay was montmorillonite Cloisite 15A. The influence of the presence and the type of the compatibilizers on the properties of the nanocomposites has been evaluated. The results have shown that the thermal stability, the reduction of the flammability and the microhardness of HDPE/clay nanocomposites, compatibilized by HDAA and HDMA are higher than those for nanocomposite compatibilized by EAA. Moreover, the presence and the type of compatibilizer have negligible effect on the characteristics of the HDPE phase transitions. These results have been interpreted by the better clay dispersion and higher level of clay exfoliation in the presence of compatibilizers HDAA and HDMA, than those in the presence of EAA compatibilizer.     

环境温度对紫外辐照HDPE结构与性能的影响研究

采用元素、XPS、GPC分析，凝胶和力学性能测定，研究了空气中不同环境温度下紫外辐照官能化HDPE的结构、粘着性以及紫外辐照官能化HDPE对HDPE/聚乙烯醇(PVA)体系的增容作用。实验结果表明，提高环境温度可显著提高引入C-O、C(=O)O和C=O等含氧基团的速度。在相同辐照时间下，随环境温度提高，辐照HDPE的分子量下降、分子量分布变宽以及剥离强度提高的幅度增大，并在70℃时产生凝胶。较高环境温度下辐照的HDPE对HDPE/PVA共混体系有较好增容作用，在HDPE/PVA(83/17)体系中加入10%(质量分数)的70℃环境温度下辐照24h的HDPE，共混物的拉伸屈服强度和缺口冲击强度分别从30.8MPa和110J/m提高到34.9MPa和142J/m。     

Effect of ethylene-acrylic acid copolymer on flame retardancy and properties of LLDPE/EAA/MH composites

Halogen-free flame retardant linear low density polyethylene (LLDPE)/ethylene-acrylic acid copolymer (EAA) blends were prepared in a melt process using magnesium hydroxide (MH) as flame retardant. The effect of EAA on flame retardancy and properties of LLDPE/EAA/MH composites was studied. The flammability of composites was investigated using Limiting Oxygen Index (LOI) and Cone calorimeter test. The results showed that the introduction of EAA into composites apparently increased LOI from 28% to 39%, meanwhile, reduced heat release rate (HRR) and smoke production rate (SPR) according to Cone calorimeter results, which was mainly due to the uniform dispersion of MH as a result of hydrogen bonding and acid-base reaction between MH and EAA. This improved interfacial adhesion was confirmed by Scanning Electronic Microscopy (SEM). Thermogravimetric analysis (TGA) showed that EAA could enhance the thermal oxidative stability of composites. It was attributed to the formation of a stable barrier to prevent the heat and mass transfer in fire, which was confirmed by the observation of fire performance with Cone calorimeter. The crystallization and rheological behaviour of composites were studied using Differential scanning calorimeter (DSC) and oscillatory rheological measurements. Mechanical test results indicated that the addition of EAA could increase the elongation at break and impact strength of composites.     

Effect of dendrimer modified montmorillonite on structure and properties of EPDM nanocomposites

The purpose of this work was to study the effect of dendrimer modified clay minerals on the structure and properties of ethylene-propylene-diene monomer (EPDM) nanocomposites.Flame-retardant and dendrimer modified organic montmorillonite (FR-DOMt) was successfully prepared by Na⁺-montmorillonite, tetrahydroxymethyl phosphonium chloride (THPC), N, N-dihydroxyl-3-aminomethyl propionate, and boric acid. This dendritic type of organoclay (OC) was used in preparation of EPDM/FR-DOMt nanocomposites. The properties of these nanocomposites were studied. The dispersion status of the layered silicates in EPDM was revealed by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD and TEM results showed that FR-DOMt was exfoliated in the EPDM matrix when 10 phr of FR-DOMt was incorporated. The mechanical behavior, thermal stability, and flame retardance of the samples were examined. The experimental data demonstrated that the EPDM hybrids owned an improved tensile strength and elongation at break. In addition, the nanocomposites exhibited higher thermal stability and flame retardance than that of unfilled EPDM matrix.     

Effect of clay modification on the structure and mechanical properties of polyamide-6 nanocomposites

Polyamide-6 nanocomposites were prepared from a new phosphonium organoclay obtained at pilot scale in supercritical carbon dioxide (scCO₂) and a commercially available ammonium modified-silicate. The composites were homogenised by twin-screw extrusion, then specimens for testing were prepared by injection moulding. The clay content of the composites was varied from 0 to 7 vol.% in 7 steps. The clays were characterised in detail; they differed in their surface coverage and gallery structure, while their particle size was similar and their surface energy differed only slightly. X-ray diffraction, electronic microscopy and rheology were used for the characterisation of composite structure. Different gallery structure of the clays led to dissimilar extent of exfoliation. The phosphonium organoclay exfoliated better in PA than the silicate treated with the ammonium salt in spite of its smaller surface coverage. The nanocomposites showed the usual complex structure: besides individual platelets and intercalated stacks, large particles were also present and the development of a silicate network could be shown at large clay contents. Quantitative determination of the extent of reinforcement revealed two determining factors: contact surface and strength of interaction. The first increases with exfoliation, but the latter decreases as an effect of organophilisation. The extent of exfoliation was also estimated quantitatively, and the calculation confirmed the results of qualitative evaluation showing larger extent of exfoliation for the scCO₂-prepared phosphonium clay.     

Effect of polyol structure on the properties of the resultant magnetic polyurethane elastomer nanocomposites

In this study, two types of magnetic polyurethane (PU) elastomer nanocomposites using polycaprolactone (PCL) and polytetramethylene glycol (PTMG) as polyols were synthesized by incorporating thiodiglycolic acid surface modified Fe₃O₄ nanoparticles (TSM‐Fe₃O₄) into PU matrices through in situ polymerization method. TSM‐Fe₃O₄ nanoparticles were prepared using in situ coprecipitation method in alkali media and were characterized by X‐ray diffraction, Fourier Transform Infrared Spectrophotometer, Transmission Electron Microscopy, and Vibrating Sample Magnetometer. The effects of PCL and PTMG polyols on the properties of the resultant PUs were studied. The morphology and dispersion of the nanoparticles in the magnetic nanocomposites were studied by Scanning Electron Microscope. It was observed that dispersion of nanoparticles in PTMG‐based magnetic nanocomposite was better than PCL‐based magnetic nanocomposite. Furthermore, the effect of polyol structure on thermal and mechanical properties of nanocomposite was investigated by Thermogravimetric Analysis and Dynamic Mechanical Thermal Analysis. A decrease in the thermal stability of magnetic nanocomposites was found compared to pure PUs. Furthermore, DMTA results showed that increase in glass transition temperature of PTMG‐based magnetic nanocomposite is higher than PCL‐based magnetic nanocomposite, which is attributed to better dispersion of TSM‐Fe₃O₄ nanoparticles in PTMG‐based PU matrix. Additionally, magnetic nanocomposites exhibited a lower level of hydrophilicity compared to pure PUs. These observations were attributed to the hydrophobic behavior of TSM‐Fe₃O₄ nanoparticles. Moreover, study of fibroblast cells interaction with magnetic nanocomposites showed that the products can be a good candidate for biomedical application. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of compatibilizer on morphology and properties of HDPE/Nylon 6 blends

The compatibilization effect of linear low‐density polyethylene‐grafted maleic anhydride (LLDPEgMA) and high‐density polyethylene‐grafted maleic anhydride (HDPEgMA) on high‐density polyethylene (HDPE)/polyamide 6 (Nylon 6) blend system is investigated. The morphology of 45 wt %/55 wt % polyethylene/Nylon 6 blends with three compatibilizer compositions (5 wt %, 10 wt %, and 15 wt %) are characterized by atomic force microscopic (AFM) phase imaging. The blend with 5 wt % LLDPEgMA demonstrates a Nylon 6 continuous, HDPE dispersed morphology. Increased amount of LLDPEgMA leads to sharp transition in morphology to HDPE continuous, Nylon 6 dispersed morphology. Whereas, increasing HDPEgMA concentration in the same blends results in gradual morphology transition from Nylon 6 continuous to co‐continuous morphology. The mechanical properties, oxygen permeability, and water vapor permeability are measured on the blends which confirm the morphology and indicate that HDPEgMA is a better compatibilizer than LLDPEgMA for the HDPE/Nylon 6 blend system. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 281–290     

Flammability, structure and mechanical properties of PP/OMMT nanocomposites

Polypropylene/organoclay (PP/OMMT) nanocomposites were prepared in a twin-screw corotating extruder using two methods. The first method was the dilution of commercial (PP/50% Nanofil SE3000) masterbatch in PP (or PP with commercial flame retardant). The second method consists of two stages was the extrusion of maleic anhydride grafted polypropylene (PP-g-MAH) with commercially available organobentonite masterbatch in first stage and dilution of the masterbatch in PP (or PP with commercial flame retardant) in second stage. XRD results showed no intercalation in composites obtained from commercial masterbatch without compatibilizer and semi - delamination for compatibilized systems. Tensile tests revealed that nanocomposites with 5% of organoclay have a slightly higher tensile modulus and tensile strength than pristine PP, however addition of the commercial flame retardant (FR) reduces mechanical parameters to roughly the level of those for neat PP. PP/OMMT composites have approx. 25% higher oxygen index than pristine PP, and this changes slightly after the addition of FR. The cone calorimeter tests showed a decrease of a heat release rate (HRR) and a mass loss rate (MLR) after the addition of FR.     

Internal structure and linear viscoelastic properties of EVA/asphalt nanocomposites

The effect of the addition of two different organoclays as a third component in polymer-modified asphalts has been investigated. Ternary mixtures were prepared by adding clay and poly(ethylene-co-vinyl acetate) to the asphalt, either separately, or in the form of a premixed master batch. The performed characterizations allowed the determination of how the two methods of mixing influence the interactions between asphalt and polymer and therefore the final rheological properties. In particular, it was shown that the clay had a compatibilizing effect on asphalt and polymer and that a high compatibility between clay and polymer led to a better dispersion of the polymer in the asphalt, thus influencing the final rheological properties of the studied systems.     

Copolyester/layered silicate nanocomposites: The effect of the molecular size and molecular structure of the intercalant on the structure and viscoelastic properties of the nanocomposites

The preparation of poly(ethylene glycol‐co‐cyclohexane‐1,4‐dimethanol terephthalate)/layered silicate nanocomposites via a melt‐intercalation technique is reported. Layered silicates modified with different alkyl ammonium intercalants have been used for this purpose. A comparison is made between carefully chosen pairs of the nanocomposites, the choice depending on the cation‐exchange capacity or the intercalant concentration of the organically modified montmorillonite, to study the effects of the molecular size and molecular structure of the intercalant. The structure of the nanocomposites is characterized with wide‐angle X‐ray diffraction. The presence of well‐defined diffraction peaks and an observed increase in the interlayer spacing in the nanocomposites imply the formation of an intercalated hybrid. To investigate the viscoelastic behavior, these nanocomposites are also subjected to dynamic mechanical analysis. The dynamic mechanical properties show an increase in the storage modulus of the nanocomposites over the entire temperature range studied (except in the transition region from 68 to 78 °C) in comparison with that of the pristine polymer. The size of the intercalant molecule and the presence of functional groups capable of forming favorable interactions with the polymer govern the amount of polymer infiltrating the clay gallery space and control the increase in the modulus of the nanocomposite. The tan δ peak signifying the glass‐transition temperature shifts to lower temperatures in the nanocomposites. Interestingly, the nanocomposites show less damping than the pristine polymer. This behavior is understood in terms of the confinement of the polymer chains in the clay interlayer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3102–3113, 2003     

The disorderly exfoliated LDHs/PMMA nanocomposites synthesized by in situ bulk polymerization: The effects of LDH-U on thermal and mechanical properties

The disorderly exfoliated layered double hydroxides/poly(methyl methacrylate) (LDHs/PMMA) nanocomposites were obtained in a two-stage process by the in situ bulk polymerization of methyl methacrylate (MMA) in the presence of 10-undecenoate intercalated LDH (LDH-U). The dispersed behavior of the LDH-U in the PMMA matrix was identified by using X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV/visible transmission spectroscopy. All these nanocomposites showed significantly enhancement of glass transition temperature (T_g) and the decomposition temperatures compared to pristine PMMA, as identified in differential scanning calorimetry (DSC) and thermogravimetric (TGA) analysis. The tensile modulus of these nanocomposites was also enhanced by incorporating the LDH-U into the PMMA matrix and increased as the amount of LDH-U increased. According to the analytical method of Ozawa-Flynn, the degradation activation energies of these nanocomposites are higher than that of pristine PMMA.     

Effects of cellulose nanofibrils on the structure and properties on PVA nanocomposites

A green method—joint mechanical grinding and high pressure homogenization—was used to defibrillate paper pulp into nanofibrils. The prepared cellulose nanofibrils (CNF) were then blended with PVA in an aqueous system to prepare transparent composite film. The size and morphology of the nanofibrils and their composites were observed, and the structure and properties were characterized. The results showed that CNFs are beneficial to improve the crystallinity, mechanical strength, Young’s modulus, T _g and thermal stability of the PVA matrix because of their high aspect ratio, crystallinity and good compatibility. Therefore, nano cellulosic fibrils were proven to be an effective reinforcing filler for the hydrophilic polymer matrix. Moreover, the green fabrication approaches will be helpful to build up biodegradable nanocomposites with wide applications in functional environmentally friendly materials.     

Films on amorphous polyamide nanocomposites: structure and properties

The ability of a nanoclay to improve the transport and mechanical properties of amorphous polyamide (aPA)‐based films was studied as a function of the draw ratio (DR) and the nanoclay content. The presence of nanoclay did not hinder the drawing ability as the maximum DR of the nanocomposites (NCs) and of the aPA were almost the same (51 for the aPA and from 51 to 55 for the NCs). The high degree of exfoliation and orientation along the drawing direction led to a 30% reduction in the water diffusion coefficient compared with the aPA. Moreover, the already low permeability of the aPA to oxygen was halved. The modulus of elasticity presented unusual increases both in the machine and transverse directions. Both increases of properties were attributed to the planar geometry of the oriented nanoclay sheets. The effects of the presence of nanoclay on the modulus of elasticity in the draw direction in addition to the effects caused by drawing lead to a combined modulus increase of 65% in the highly drawn 6%NC films. The nanoclay also reduced the modulus anisotropy of the films. An increase in either the nanoclay content or the DR causes a decrease in ductility due to both the stress concentrations created by the nanoclay and to the increasing number of chain segments located parallel to the drawing direction. The dimensional stability of the films greatly increased as the addition of 6% nanoclay led to a 70% decrease in creep deformation after 120 h. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of the type of alkylammonium ion clay modifier on the structure and thermal/mechanical properties of glassy and rubbery epoxy-clay nanocomposites

Glassy and rubbery epoxy-clay nanocomposites were synthesized by using various montmorillonite organoclays in order to investigate and compare the effect of the type of alkylammonium ion clay modifier on the structure and properties of the nanocomposites. The organoclays studied were the Nanomer I.28E and I.30E and the Cloisite C10A, C15A and C20A. The functionality (acidity), size and shape of backbone chain, hydrophobicity and polarity were the varying parameters of the organic modifiers that were correlated to the ability of the organoclays to form highly intercalated or exfoliated nanocomposites and to the changes observed in the mechanical (tensile measurements), thermo-mechanical (DMA) and thermal (TGA) properties of the epoxy nanocomposites. The primary alkylammonium ion modifiers with reactive/acidic hydrogen atoms, compared to the quaternary octadecyl, dihydrogenated tallow and benzyl-substituted hydrogenated tallow ammonium ions, were the most effective for the formation of exfoliated clay glassy and rubbery epoxy nanocomposites which exhibited improved properties compared to the pristine epoxy polymers.     

Influence of processing technique on morphology and mechanical properties of PVC nanocomposites

This study aims to compare the influence of processing techniques and procedures on the morphology and mechanical properties of polyvinyl chloride (PVC) nanocomposites. PVC nanocomposites with 5 phr montmorillonite (MMT) clay were prepared on a two-roll mill or in a microcompounder, both were either processed once or via a masterbatch containing 20 phr MMT. The MMT was treated with non-ionic surfactants and analysed by thermo gravimetric analysis and X-ray diffraction prior to being added. The final composites were analysed and tested using X-ray diffraction, scanning and transmission electron microscopy (SEM/TEM), tensile test, and Charpy impact test. The dispersion was found to be best in the roll milled samples prepared via the masterbatch and the elongation at break and impact strength was also better for the roll milled samples. E-modulus and tensile strength, on the other hand, were significantly better for the microcompounded samples despite the larger particle size. This can be explained by a higher degree of orientation in these samples. Finally, it must be stated that the change in properties are not satisfactory. Although we see an increase in E-modulus, the decreased impact properties are not acceptable. The main reason for this is the lack of compatibility between the clay particles as observed by high resolution SEM.     

Effects of reprocessing on the structure and properties of polyamide 6 nanocomposites

PA6 based nanocomposites (NCs) were reprocessed by repeated injection moulding to find out whether reprocessing is possible in these materials by means of the observation of the changes in the structure and mechanical properties. The studied variables were (a) the number of cycles (1-5), (b) the origin of the NC: either laboratory mixed or commercial and (c) the processing temperature (230 °C and 270 °C). Neat PA6 was also reprocessed as a reference material. In spite of the colour change, the Young's modulus, the solid state characteristics and the dispersion level were preserved upon reprocessing. The lack of change of chemical nature observed by FTIR, and the observed decreases in viscosity indicated that the main effect of reprocessing was a decrease in the molecular weight. At 230 °C the decreases in viscosity were smaller after reprocessing, and almost no change was seen in the structural parameters and properties. The decrease in the molecular weight after reprocessing at 270 °C leads to lower ductility and mainly to a decrease in the ability of the nPA6 matrix to cold draw. However, no change of the interphase conditions or agglomeration of the OMMT was detected and the NCs remained clearly ductile; thus, revealing a lack of deterioration of the interface and the ability of the NCs for recycling.     

Effect of thermal annealing on the crystalline structure of PVDF/PMMA-modified graphene nanocomposites

Abstract

Poly(vinylidene fluoride)-based nanocomposite films with different loadings of PMMA-modified graphene sheets were prepared by a solution-mixing and solvent casting method. The prepared films were annealed at three different temperatures and the crystalline structures of the samples were investigated. X-ray diffraction data confirmed the PMMA-modified graphene nanosheets enhanced the preferential β-crystalline structure when increasing the annealing temperature to 90?°C, while increasing the annealing temperature to 120?°C led to a β → γ phase conversion. The tendency of the graphene sheets to restack by increasing the annealing temperature was confirmed by XRD. The PMMA-modified graphene sheets, however, didn’t showa nucleating effect on the PVDF crystallizationduring DSC cooling scans.