Molecular dynamics studies of polyurethane nanocomposite hydrogels

Polyurethane PEO-based hydrogels have a broad range of biomedical applicability. They are attractive for drug-controlled delivery systems, surgical implants and wound healing dressings. In this study, a PEO based polyurethane hydrogels containing Cloisite® 30B, an organically modified clay mineral, was synthesized. Structure of nanocomposite hydrogels was determined using XRD technique. Its molecular dynamics was studied by means of NMR spectroscopy, DMA and DSC analysis. The mechanical properties and thermal stability of the systems were improved by incorporation of clay and controlled by varying the clay content in polymeric matrix. Molecular dynamics of polymer chains depends on interaction of Cloisite® 30B nanoparticles with soft segments of polyurethanes. The characteristic nanosize effect is observed.     

Parametric Studies on the Grafting of Poly(Methyl Methacrylate) onto Organophilic Montmorillonite Using Silylated Clay Platelets

Poly(methyl methacrylate) (PMMA)/organophilic montmorillonite (Cloisite 30B) nanocomposites were synthesized by the chemical grafting of PMMA onto Cloisite 30B via solution polymerization of methyl methacrylate (MMA) with vinyl-modified organoclay. The effects of different parameters such as clay weight percent (CWP), solvent per monomer volume ratio, and dispersion time on the properties of the PMMA grafted Cloisite 30B were investigated using the Taguchi experimental design method. This method gives a much-reduced variance for the experiments with optimum setting of control parameters and provides a set of minimum experiments compared to the conventional methods. Qualitative evidence for the chemical grafting of the PMMA onto Cloisite 30B was confirmed by Fourier transform infrared spectroscopy (FT-IR). X-ray diffraction (XRD) was used to investigate interlayer changes of the clay in the grafted nanoplatelets. The exfoliated/intercalated morphology of the nanocomposites was confirmed by XRD. Furthermore, thermal properties were measured by thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA). Statistical analysis of results revealed that clay weight percent and solvent per monomer ratio had significant effects on the properties of final products. The percent of grafted PMMA and storage modulus of PMMA/30B nanocomposites decreased with increasing clay content due to better dispersion of the clay at lower loadings. On the other hand, because of a tendency to formation of homopolymer and oligomers at higher solvent loadings; the percent of grafted PMMA, storage modulus and glass transition temperature of PMMA/30B nanocomposites decreased with an increase in solvent per monomer volume ratio. However, the obtained PMMA/30B nanocomposites at the optimum conditions, was exhibited a higher glass transition temperature, higher storage modulus and better thermal stability than the pure PMMA.     

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.     

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.     

Preparation, characterization and properties of amino-functionalized montmorillonite and composite layer-by-layer assembly with inorganic nanosheets

An amino-functionalized montmorillonite (APTMS-MMT) was prepared by the grafting of 3-aminopropyltrimethoxysilane (APTMS) on the surface of MMT via the ultrasonic synthesis process and characterized by a variety of techniques: FT-IR, thermogravimetic analysis (TGA), particles size analysis and ζ-potential measurement. The results showed the size and size distribution of APTMS-MMT particles were decreased, and the ζ-potential of particles was increased obviously via the ultrasonic synthesis process. The particles of 30% APTMS-MMT_US (MMT modified with 30 wt% APTMS with ultrasonic synthesis process) had a z-average diameter of about 500 nm and a polydispersity index of 0.2. The resultant 30% APTMS-MMT_US was dispersed uniformly and stably in water. The poly(acrylic acid) (PAA)/APTMS-MMT multilayer films were grown through layer-by-layer (LBL) deposition of PAA and APTMS-MMT. SEM results indicated that the ultrasonic synthesis of APTMS-MMT increased dispersability of clay sheets at high loadings. The thermal stability and mechanical properties of PAA/APTMS-MMT composites were investigated by TGA and tensile test respectively. The results showed the ultrasonic synthesis of APTMS-MMT enhanced the thermal stability and mechanical properties of PAA/APTMS-MMT composites significantly. PAA/30% APTMS-MMT_US composite displayed 3 times higher strength and 6 times higher Young's modulus when compared with pure PAA polymer.     

Organo clay mineral-melted polyolefin nanocomposites Effect of surfactant/CEC ratio

Clay mineral-polymer nanocomposites are prepared by dispersing solid organo clay minerals in two different melted polyolefin matrices, namely polyethylene (PE) and ethylene vinyl acetate (EVA). The organo clay minerals are prepared by adding different amounts of surfactant corresponding to the CEC of the pristine clay mineral. The characteristics of the organo clay minerals are obtained by XRD, IR spectroscopy, TGA, and swelling volume measurements. The amount of added surfactant has a direct effect on the interlayer separation and organophilicity-hydrophilicity balance of the clay mineral, evidencing a particular behavior transition about OMt1.2 The intercalation of PE is found to be dependent on the interlayer distance of the organo clay minerals while EVA intercalates in the organo clay minerals whatever the amount of surfactant (> 0.5CEC), leading to the same interlayer spacing (4 nm). The polymer intercalation is more homogeneous in clay minerals having high surfactant loading corresponding to 1.5 and 2 CEC. Cone calorimeter results of the studied nanocomposites show a PHRR reduction of 32% for PE-OMt1.5 and of 47% for EVA-OMt1. For both polymers, the best compromise between mechanical and thermal properties, is obtained for organoclay filler obtained with an amount of added surfactant in a range 1-1.5 CEC.     

The effects of ultrasound on organoclay dispersion in the PP matrix

PP/MMT nanocomposites were prepared by solution intercalation using sonication and quiescent conditions, and the effects on the morphological, thermal and mechanical properties were evaluated by WAXD, TEM, DMA, TGA and DSC analyses. The present study aims to clarify the effects of ultrasound use on the organoclay surface with different amounts of organic modifiers and on the exfoliation processes. The sonication process decreased around of 200 nm the aspect ratio of C15A organoclay. Besides, the effectiveness of the ultrasound process was only achieved with the C15A system because there is a small energetic barrier between their layers (clay with larger d 001). The sonication process increased the exfoliation and distribution of the C15A platelets in the PP matrix, increasing by 5% its reinforcement capacity. However, for I44P system, the use of ultrasound did not show any significant effect on the morphology and consequently on the final properties of the PP matrix. The T(c) temperature and the thermal stability of the PP nanocomposites were increased, independent of the clay type or of the ultrasound use.     

Thermal,Mechanical, and Dielectric Properties of a Dielectric Elastomer for Actuator Applications

Dielectric elastomers (DE) are a new type of electro-active material, which is able to produce a large degree of deformation under electrical stimulation. The thermal, mechanical, and dielectric properties of the most widely used dielectric acrylic elastomer (VHB 4910), commercially available from the company 3M, were studied by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), and broadband dielectric spectroscopy (BDS) analyzer, respectively. DSC experiments on the VHB 4910 showed a glass transition at about ?40°C. VHB 4910 started to lose weight at about 250°C from the TGA study. The results of DMA indicated the storage modulus of VHB 4910 increased with frequency and had a strong temperature dependence of elasticity. The dielectric constant of VHB 4910 increased as a function of temperature up to 0°C, followed by a drop till 100°C. The mechanical and electrical efficiency of dielectric elastomer actuators (DEA) of VHB 4910 were analyzed. It was demonstrated that the actuation performance is dominated by the mechanical properties of the elastomer and is less influenced by the frequency and the temperature dependence of the dielectric properties; this may be used to guide the design of actuator configurations, as well as the choice of actuator materials.     

Physical properties of a high molecular weight hydroxyl-terminated polydimethylsiloxane modified castor oil based polyurethane/epoxy interpenetrating polymer network composites

A series of polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites modified by a high molecular weight hydroxyl-terminated polydimethylsiloxane (HTPDMS) were prepared. The effects of HTPDMS content on the phase structure, damping properties and the glass transition temperature (Tg) of the HTPDMS-modified PU/EP IPN composites were studied by scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). Thermogravimetric analysis (TGA) showed that the thermal decomposition temperature of the composites increased with the increase of HTPDMS content. The tensile strength and impact strength of the IPN composites were also significantly improved, especially when the HTPDMS content was 10%. The modified IPN composites were expected to be used as structural damping materials in the future.     

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.     

PVDF-Based Nanocomposite Solid Polymer Electrolytes; the Effect of Affinity Between PVDF and Filler on Ionic Conductivity

Nanocomposite solid polymer electrolytes (NSPEs) based on poly(vinylidene fluoride) (PVDF) were prepared by dispersing two kinds of organoclay (Cloisite^® 30B, Cloisite^® 15A) consisting of silicate layers in the polymer matrix. The effect of affinity between PVDF and organoclay as the filler on ionic conductivity was investigated in relation to its content, dispersed condition of organoclay, and structural changes of nanocomposites. The characterizations of PVDF-based nanocomposites with various organoclay contents were carried out by XRD, TEM, DSC, and DMA. In order to confirm the ion conduction properties of NSPEs with LiCF₃SO₃ at room temperature, ac impedance analyzer and FT-IR spectrometer were used. As a result, a higher ionic conductivity appeared in the case of NSPE with C15A than that with C30B and the maximum conductivity was 1.04 × 10^–3 S/cm for the NSPE containing 5 wt% of C15A and 40 wt% of LiCF₃SO₃.     

Melt intercalation and exfoliation of maleated polypropylene modified polypropylene nanocomposites

Melt blending of maleic anhydride-grafted polypropylene (PPgMA) and organically modified clay nanocomposites were first prepared in a plasticorder. PPgMAs, including PB3150, PB3200, PB3000, and E43, with a wide range of MA content and molecular weight were used. The structure was investigated with X-Ray diffraction (XRD) and transmission electron microscopy (TEM). PPgMA compatiblizers gave rise to similar degree of dispersion beyond the weight ratio of 3 to 1 with the exception of E43, which had the highest MA content and the lowest molecular weight. It was found that thermal instability and high melt index were responsible for ineffective modification by E43. Furthermore, PPgMA with lower molecular weight and higher melt index had to be compounded at lower mixing temperature in order to achieve a reasonable level of torque for clay dispersion. We then modified polypropylene/organoclay nanocomposites with different levels of PPgMA compatibilizers on a twin-screw extruder. The PP/E43/clay system, as shown through XRD patterns and TEM observation, yielded the poorest clay dispersion among the compatibilizers under investigation. The relative complex viscosity curves also revealed a systematic trend with the extent of exfoliation and showed promise for quantifying the hybrid structure of the nanocomposites. Mechanical properties and thermal stability were determined by dynamical mechanical analysis (DMA) and thermogravimeric analysis (TGA), respectively. Though PPgMA with lower molecular weight would lead to better clay dispersion in the polypropylene nanocomposites, it caused deterioration in both mechanical and thermal properties of the hybrid systems.     

Preparation and properties of polyurethane/MMT nanocomposite actuators

This study dealt with the electrostrictive response of a polyurethane (PU)/clay nanocomposite film, which was a promising candidate for a material to be used in polymer actuators. The nanocomposites were produced by using three types of montmorillonites (MMTs) such as natural MMT (Cloisite^®Na⁺), hydrophobic MMT (Cloisite^® 20A), and hydrophilic MMT (Cloisite^® 30B). The nanometer-scale silicate layers of organo-clay were completely exfoliated in PU for the cases of 1, 3 and 5 wt% PU/MMT nanocomposites as confirmed by wide X-ray diffraction (WAXD) profiles. Actuation tests indicated that the displacement of PU/MMT nanocomposite actuator was larger than pure PU actuator, caused by an increase in dielectric constant. Especially, PU/MMT nanocomposite actuator with Cloisite^® 30B had the largest displacement and it became possible to operate at low voltage.     

Clay dispersion and physical properties of melt-blended PP/organoclay nanocomposites: effect of interfacial interaction

Melt blending of maleic anhydride-grafted polypropylene (PPgMA) and organically modified clay nanocomposites was first carried out in a plasticorder. The structure was investigated with x-ray diffraction (XRD) and transmission electron microscopy (TEM). The interfacial interaction between PB3150 compatibilizer and I30 clay surface was altered with the addition of different loadings of PB3150. It was found at the PB3150 compatiblizer gave rise to a high degree of clay dispersion beyond the PB3150/I30 weight ratio of 3. We then also modified polypropylene/organoclay nanocomposites with different loadings of PB3150 on a twin-screw extruder. When the PB3150 loading exceeded 15 wt%, extensive exfoliation of clay was observed. The relative complex viscosity curves also revealed a systematic trend with the extent of exfoliation and showed promise for quantifying the hybrid structure of the nanocomposites. Mechanical properties and thermal stability were determined by tensile and impact tests and thermogravimeric analysis (TGA), respectively. Although high loading of PB3150 leads to better clay dispersion in the polypropylene nanocomposites, it causes deterioration in both mechanical and thermal properties of the hybrid systems.     

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.     

Nanoclay and Cu Nanoparticles Loaded Polyethylene Nanocomposites for Natural Gas Transfer Applications

High density polyethylene nanocomposites loaded with a reinforcing filler (Cloisite 20A as a modified nanoclay) and an electrically conductive filler (Cu nanoparticles) were prepared by a melt blending method. The morphological, mechanical, thermal, and electrical properties of the prepared nanocomposites were investigated to evaluate their performances as appropriate materials for production of reinforced conductive polymeric pipes to be used in natural gas distribution and transportation pipelines. A random and uniform dispersion of both nanoparticles in the polyethylene matrix, with a nanoclay intercalated morphology, was observed by scanning electron microscopy and X-ray diffraction techniques. The results revealed ca. 117, 13 and 21% increases in the Young’s modulus, tensile strength and yield stress of the polyethylene matrix by adding 3 wt.% of Cloisite 20A into it. For the similar conditions, however, more than a 71% decrease was observed for the elongation at break. Thermal analysis demonstrated that the melting points of the nanocomposites were increased by incorporating both fillers and the crystallinity of polyethylene chains was decreased by incorporating Cloisite 20A and then slightly increased by adding Cu nanoparticles. Moreover, the results revealed the creation of conductivity inside the non-conductive polyethylene matrix due to the presence of the conductive Cu nanoparticles.     

Structure and Properties of Polypropylene/Polyolefin Elastomer/Organic Montmorillonite Nanocomposites

The crystallinity, mechanical properties, and thermal stability of polypropylene (PP)/organic montmorillonite (OMMT) and PP/polyolefin elastomer (POE)/OMMT composites, with polypropylene-g-maleic anhydride/styrene (PPMS) as a compatibilizer for both, were compared. The results showed that the strong interaction between the clay platelets and compatibilizer, which were generated by the maleic anhydride (MAH), improved the compatibility of the polymer matrices with the OMMT. A unique lamellar, flocculated structure of OMMT was formed after introduction of the POE. The highly dispersed clay layers could act as nucleating agents, resulting in smaller spherulites and higher crystallization temperatures. Compared with pure PP, the PP/OMMT nanocomposite showed enhanced mechanical properties and thermal stability; however, the PP/POE/OMMT had the best impact toughness.     

Vulcanization and Thermal Properties of Silicone Rubber/Fluorine Rubber Blends

With the rapid development of automobile, aviation, aerospace, machinery and other fields, rubber products used in these fields required to meet higher requirements. Fluorine rubber (FKM) and silicone rubber (MVQ) have excellent performance in some areas. However, the FKM is poor in low-temperature resistance and processing performance, limiting its applicability. Although the MVQ has a wide range of temperature and excellent processing performance, but its mechanical properties and oil resistance are not good. In this work, the MVQ/FKM blends were prepared by two different mechanical blending methods. The effects of the mixing process, mass ratio, curing system and conditions of the blends were studied. The chemical compositions of the blends were analyzed by infrared spectroscopy (IR). The compatibility and the thermal properties of the blends were investigated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), respectively. The results showed that the mechanical properties, compatibility and thermal stability of the blends were the best when they were prepared by kneading the FKM and MVQ individually in a two-rool mill roll, then mixing them together homegeneously with an MVQ/FKM mass ratio of 10/90, curing system of (4 phr, 1/9) dicumyl peroxide (DCP)/N, N-Dicinnamylidene-1, 6-hexanediamine (3^# Vulcanizer), first curing conditions at 170?°C under 10?MPa for 30?min and post curing conditions at 200?°C for 6?hours at 1 atmospheric pressure.     

Studies of Luminescence Performance on Carbazole Donor and Quinoline Acceptor Based Conjugated Polymer

We report on the synthesis of conjugated polymer (CV-QP) containing carbazole (donor) and quinoline (acceptor) using Wittig methodology. The structural, optical and thermal properties of the polymer were investigated by FT-IR, NMR, GPC, UV, PL, cyclic voltammetry, atomic force microscopy (AFM) and thermogravimetric analysis (TGA). The polymer exhibits thermal stability upto 200 °C and shows good solubility in common organic solvents. The polymer has optical absorption band in a thin film at 360 nm and emission band formed at 473 nm. The optical energy band gap was found to be 2.69 eV as calculated from the onset absorption edge. Fluorescence quenching of the polymer CV-QP was found by using DMA (electron donor) and DMTP (electron acceptor). AFM image indicated that triangular shaped particles were observed and the particle size was found as 1.1 μm. The electrochemical studies of CV-QP reveal that, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the CV-QP are 6.35 and 3.70 eV, which indicated that the polymers are expected to provide charge transporting properties for the development of polymer light-emitting diodes (PLEDs).     

Preparation and Characterization of Para-Aramid Fibers with the Main Chain Containing Heterocyclic Units

Abstract

A para-aramid fiber whose main chain contained heterocyclic units was prepared by low temperature copolycondensation, wet-spinning, and high temperature thermal treatment. The prepared fibers (named F-368) and two commercial aramid fibers, K49 (Kevlar 49, Dupont de Nemours Co., USA) and APMOC (Kamenskvolokno and Tver’khimvolokno, Russia), were characterized and analyzed in detail. Infrared spectroscopy (IR) and wide-angle X-ray diffraction (WAXD) were employed to characterize their chemical and aggregation structures, respectively. The results showed the introduction of heterocyclic units into the wholly para-aromatic polyamide backbone of K49 in the F-368 and APMOC reduced the crystallinity significantly. The tenacity of F-368 and APMOC were 32.2 and 30.5cN/dtex, which were about 68% and 59% higher than that of K49, respectively. Thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) were used to investigate their thermal properties; the results indicated that these aramid fibers showed exceptional thermal properties with glass transition temperatures of 240–260?°C, and decomposition temperatures at 510–560?°C, both in nitrogen and air. The TGA results also showed the decomposition mechanism of K49 and the heterocyclic aramid fibers in nitrogen and air were different. The decomposition temperature of K49 was higher than that of the heterocyclic copolyaramid fibers both in nitrogen and air. On the contrary, the char yields of the heterocyclic copolyaramid fibers at 800?°C were higher than that of K49 in both nitrogen and air.