Properties Of Polymeric Materials Research Articles

Synthesis of MWCNTs from xylenes for fabrication of highly electrically conductive and gas-sensitive polymer composites

For Multi-Walled Carbon Nanotubes (MWCNTs), high quality, purity, and low cost are very desirable. Therefore, in this reported research work, qualitative and pure MWCNTs were synthesized using a cheap and affordable carbon source-xylenes (a mixture of isomers) by the Aerosol Chemical Vapor Deposition Method (A-CVD). The high quality, purity, and homogeneity of the synthesized material have been verified by Raman spectroscopy, EDX, XRD, and SEM results. In the present study, Polystyrene/xMWCNT, Polyvinyl acetate/xMWCNT, and Polyvinyl alcohol/xMWCNT composites with different MWCNT contents of (x = 1, 2, 4, 8, and 16) wt% were prepared by an optimized technique for irreversible dispersion of MWCNTs inside polymers, which was developed by our research group. SEM analysis results revealed that the MWCNTs are well incorporated inside all three polymer matrices, and a highly dispersed distribution of MWCNTs has been obtained inside all three matrices due to this technique. Also, the electrical conductivity of the prepared composites was measured, and the prepared nanocomposites show high electrical conductivity for all concentrations of MWCNTs. Based on the maximum dispersion of MWCNTs inside the PS polymer matrix, the highest electrical conductivity is observed for this composite, which once more proves that the dispersion technique as well as the nature of the polymer play an important role in the preparation of highly electroconductive nanocomposites (1%-0.136 S/m; 2%-1.053 S/m; 4%-5.376 S/m; 8%-71.48 S/m; 16%-933.71 S/m). Comparison of electrical conductivity results of these composites with literature results demonstrates the advantages of this technique in substitution of the another dispersion methods. The nanocomposites prepared by our research group also show a sensor effect (change of resistivity) under different gases (methane, propane, carbon monoxide). It is interesting that, for analyzed gases, the resistivity of some nanocomposites increased, whereas for others it decreased. This effect can be explained by the different nature of the adsorption interaction between the analyzed gas and the polymer composite, and this depends on the chemical composition and properties of both gases and polymer matrices.

Physical Properties of Isotactic Polypropylene Blended with Less Crystalline Polypropylene

AbstractThe physical properties of polymeric materials, which are mixtures of various molecules, are determined by the sum of their contributions. Industrially important isotactic polypropylene (iPP), which is produced using heterogeneous Ziegler–Natta catalysts, shows broader distributions of molecular weight and stereoregularity because of the multisite nature, compared to molecular catalysts. However, systematic studies on the effects of these distributions on physical properties are lacking, especially for variations in stereoregularity. In this study, polypropylene (PP) additives with various molecular weights and stereoregularities (and their distributions) are added to an iPP matrix to clarify the effects of low‐concentration components on the overall physical properties. The results indicate the importance of incorporating the PP additives into the crystal structure of the iPP matrix.

Influence of Iron-Based Powder Additive on a Shape Accuracy of Injection Moulded Parts

Abstract This paper reviews the effects of iron-based powder on shape accuracy of injection moulded parts. Analysed specimens were produced on a micro injection moulding machine. At first, specimens of pure polypropylene (PP) were manufactured. Then specimens containing 1, 2 and 3 vol. % of iron powder additive were produced using the same process parameters. Subsequently, the samples were scanned using scanned using Zeiss METROTOM CT scanner. Results were analysed via CAE inspection tools. The main aim was to compare the shape and flatness of the scanned specimens to the nominal models. Results showed that iron-based additives of this vol.% had no significant effect on shape accuracy of produced parts. This paper is a partial result of the ongoing research focused on effect of iron and steel-based additives on material, magnetic and mechanical properties of polymers.

Self-Healable and Recyclable Dual-Shape Memory Liquid Metal-Elastomer Composites.

Liquid metal (LM)–polymer composites that combine the thermal and electrical conductivity of LMs with the shape-morphing capability of polymers are attracting a great deal of attention in the fields of reconfigurable electronics and soft robotics. However, investigation of the synergetic effect between the shape-changing properties of LMs and polymer matrices is lacking. Herein, a self-healable and recyclable dual-shape memory composite, comprising an LM (gallium) and a Diels–Alder (DA) crosslinked crystalline polyurethane (PU) elastomer, is reported. The composite exhibits a bilayer structure and achieves excellent shape programming abilities, due to the phase transitions of the LM and the crystalline PU elastomers. To demonstrate these shape-morphing abilities, a heat-triggered soft gripper, which can grasp and release objects according to the environmental temperature, is designed and built. Similarly, combining the electrical conductivity and the dual-shape memory effect of the composite, a light-controlled reconfigurable switch for a circuit is produced. In addition, due to the reversible nature of DA bonds, the composite is self-healable and recyclable. Both the LM and PU elastomer are recyclable, demonstrating the extremely high recycling efficiency (up to 96.7%) of the LM, as well as similar mechanical properties between the reprocessed elastomers and the pristine ones.

The Influence of Temperature on the Tensile Mechanical Properties of PPA

In the automotive industry and not only, more and more attempts are being made to replace parts made of metals with those made of plastics, due to their low weight and low manufacturing cost. Thus, a detailed knowledge of the mechanical properties of polymeric materials is a must. This paper presents a study of the influence of temperature on the tensile mechanical properties of semicrystalline polyphthalamide (PPA). Dog bone specimens were obtained by injection molding and, in order to eliminate the possible moisture absorbed in the place of storage of the specimens, they were subjected to a drying treatment in an airtight oven at a temperature of 80 degrees for 12 hours. The specimens were tested at 5 different temperatures (25, 40, 80, 120, and 160°C) with a loading speed of 5 mm/min. For each test temperature 3 specimens were used, according to the ISO 527-2 standard. With the data extracted from the experimental tests, the mechanical properties were calculated. Also, the force – displacement and stress – strain curves were plotted. After the experimental tests, it was concluded that the dry specimens are more resistant, and with increasing temperature, the PPA material changes from a brittle to a ductile behavior. Moreover, the main tensile properties decrease significantly with increasing temperature (the modulus of elasticity decreases by 66.8% from temperature of 25 °C to temperature of 160 °C).

A Cocatalyst Strategy to Enhance Ruthenium‐Mediated Metathesis Reactivity towards Electron‐Deficient Substrates

Ruthenium-mediated olefin metathesis has been widely applied for the synthesis of various organic molecules and polymers. Inspired by the cocatalyst strategy for olefin polymerization, here we demonstrate that the abstraction of a chloride ion from various commercially available ruthenium catalysts significantly enhances their reactivity towards electron-deficient internal olefins. This cocatalyst strategy can be implemented in ethenolysis and cross-metathesis reactions of FG-CH=CH-FG type substrates bearing electron-withdrawing groups and the synthesis of telechelic polymers that can be converted to polyethylene-like materials with closed-loop recycling properties. The copolymerization of cyclic substrate with cycloolefins followed by hydrogenation afforded polyolefin materials with in-chain break points. Interestingly, switchable catalysis was achieved in the absence and presence of a cocatalyst, which allowed the polymer microstructure and material properties to be fine-tuned.

A Cocatalyst Strategy to Enhance Ruthenium‐Mediated Metathesis Reactivity towards Electron‐Deficient Substrates

Ruthenium-mediated olefin metathesis has been widely applied for the synthesis of various organic molecules and polymers. Inspired by the cocatalyst strategy for olefin polymerization, here we demonstrate that the abstraction of a chloride ion from various commercially available ruthenium catalysts significantly enhances their reactivity towards electron-deficient internal olefins. This cocatalyst strategy can be implemented in ethenolysis and cross-metathesis reactions of FG-CH=CH-FG type substrates bearing electron-withdrawing groups and the synthesis of telechelic polymers that can be converted to polyethylene-like materials with closed-loop recycling properties. The copolymerization of cyclic substrate with cycloolefins followed by hydrogenation afforded polyolefin materials with in-chain break points. Interestingly, switchable catalysis was achieved in the absence and presence of a cocatalyst, which allowed the polymer microstructure and material properties to be fine-tuned.

ОСОБЕННОСТИ ОБРАБОТКИ ДЕТАЛЕЙ ИЗ ПОЛИМЕРНЫХ МАТЕРИАЛОВ ЛЕЗВИЙНЫМИ ИНСТРУМЕНТАМИ

The study objective is to select the tool cutting part materials and to assign the operating parameters taking into account the properties of polymer materials that characterize their machinability. The problems to which the paper is devoted are experimental studies of ways to expand the technological capabilities of cutting polymer materials. Research methods: experimental studies are conducted on the basis of the main provisions of the engineering technology, the theory of elasticity and plasticity. Experimental studies are carried out according to standard methods in production and laboratory conditions with the use of certified control and measuring equipment. The obtained data are processed using computational techniques and presented in the form of empirical dependencies convenient for practical application. The novelty of the work consists in conducting experimental studies of choosing materials for the tool cutting parts and their design features and geometric parameters, as well as in obtaining the operating parameters of machining parts made of polymer materials.
 Conclusions: On the basis of experimental studies, the ways of expanding the technological capabilities of cutting polymer materials are chosen.

Nonlinear Elongation Flows in Associating Polymer Melts: From Homogeneous to Heterogeneous Flow

Numerical simulations explore how material properties of polymers are altered as clusters of strongly interacting groups along the chain break apart and reform under flow, an insight that can help control complex fluids.

Unexpected Role of Short Chains in Entangled Polymer Networks.

The knowledge of chain entanglement is key to our understanding of the relation between the viscoelastic properties of polymeric material and their microscopic structure and dynamics. This work conducted a detailed study on the role of short chains in the entangled polymer network. A series of poly(ethylene oxide) (PEO) mixtures with bimodal molecular weight distribution were selected for this study. 1H double-quantum (DQ) NMR combined with the rheology measurement was used to investigate the entangled polymer network. We found that short-chain polymers have the potential to significantly alter the entangled polymer network formed by long-chain polymers. Additionally, both the amount of chain ends and the size of the short-chain polymer were found to have clear disentanglement influences on the entangled polymer network. Moreover, adding low molecular weight PEO to the entangle framework formed by the high molecular weight PEO, resulted in the formation of inhomogeneous entangled polymer networks. The effect of low molecular weight polymers on the entangled polymer networks in PEO melts provides a perspective on the molecular level effect of molecular weight distribution (MWD) on entanglement polymer networks.

Thermal buckling of thin injection-molded FRP plates with fiber orientation varying over the thickness

The different thermo-elastic properties of glass fibers and polymer matrices can generate residual thermal stresses in injection-molded fiber-reinforced plastic (FRP) objects. During cooling from mold to room temperature, these stresses can be relaxed by large deformations resulting from an instability of the unwarped configuration (i.e., buckling). This article investigates the thermal buckling of thin FRP disks via an analytical formulation based on the Föppl-von Kármán theory. A novel extension of our previous work is the assumption of cylindrical orthotropy with material parameters varying over the disk thickness in order to account for thickness dependency of the glass fiber orientation distribution. A disk parameter generalizing the thermal anisotropy ratio for homogeneous orthotropic disks is introduced and its relation with the occurrence and periodicity of buckling is discussed. This is done for a skin-core-skin model, for which the core-to-total thickness ratio is defined. For fiber orientation distributions typical of injection-molded disks, it is found that there exists a value of the thickness ratio for which no buckling occurs. It is also demonstrated that the periodicity of the first buckling mode is described by the generalized thermal anisotropy ratio, thus extending the results obtained for a homogeneous fiber orientation distribution. Improvements in the accuracy of the predictions for experimental data available in the literature when using the skin-core-skin model are shown. Finally, we study the relation between buckling temperature and disk thickness and propose an expression for the dependence of the normalized buckling temperature on the thermal anisotropy ratio. Results of FEM simulations are used to validate the proposed expression, proving its applicability and accuracy.

Evaluation of Changes in Polymer Material Properties Due to Aging in Different Environments.

With the increase in awareness of the importance of engagement in physical activities, high requirements have been placed on polymers intended for use in sports. A number of authors investigated the influence of aging factors on the performance of the polymer. Still, there is a lack of aging protocols that would be product-centered, especially when high performance is imperative. This paper presents a new approach to polymer aging and examines the change of the identified set of properties due to aging under different conditions, and the duration of each (topography, thickness, moisture management, elongation, and bursting force). The results of the testing revealed the increase in thickness due to exposure, especially to the sun-exposed materials. The ability of materials to elongate until the moment of rupture decreases due to exposure to the sun (strong relationship to the time of exposure; R2 reaches 0.99) and the bursting force (up to 6.8%). Furthermore, results indicate the significantly impaired capacity of the polymer material to absorb moisture. The results of measurements indicated (derived) by spectroscopic studies, based on the ATR-FTIR (attenuated total reflectance) method, showed that there was no detectable influence of aging in the sun or shade on the chemical structure of polyester samples.

Novel design of MOFs-based hierarchical nanoarchitecture: Towards reducing fire hazards of epoxy resin

The inherent inflammability of epoxy resin (EP) has seriously limited its further application. The structural design of flame retardants has huge potential for boosting the fire safety properties of polymer materials. Herein, a novel MOFs-based hierarchical nanoarchitecture (ZIF-8@PA@SiO2) was constructed, composed of ZIF-8 nanoparticles, as well as in-situ grown phytic acid (PA) and silica. The results indicated that not only was ZIF-8@PA@SiO2 uniformly dispersed in the EP matrix, but it also formed a good interface bond, which was beneficial to boosting the thermal and fire safety properties of EP composites. The incorporation of ZIF-8@PA@SiO2 markedly decreased the maximum weight loss rate (MLRmax) and increased char residues. Compared with neat EP, the limiting oxygen index (LOI) value of EP/5% ZIF-8@PA@SiO2 increased from 23.4% to 28.8%. Furthermore, the peak heat release rate (PHRR), fire growth index (FGI), peak smoke production rate (PSPR), peak CO production rate (PCOPR) and smoke factor (SF) were decreased by 38.3%, 41.6%, 45.5%, 42.9% and 69.3%, respectively. The TG-FTIR results provided strong evidence for suppressed emissions of CO, aromatic, hydrocarbons and carbonyl, further corroborating the impeded heat release and the hindered fire toxicity, which were primarily ascribed to the barrier effect, free-radical scavenging and dilution effect of the multi-integrated P/N/Si-containing MOFs-based hierarchical nanoarchitecture.

In Situ Testing of Polymers Immersed in Aging Fluids at Elevated Temperature and Pressure.

A novel elevated-temperature and high-pressure in situ punch-shear-test cell was developed to qualify materials for reliable service in harsh environments representative of those typically encountered in oil and gas operations. The proposed modular and compact test device is an extension of the ASTM D 732 punch-shear method. Conventionally, materials are first exposed to harsh environments, then removed from the aging environment for mechanical testing. This practice can lead to the generation of unrealistic (often optimistic) mechanical properties. This is especially true in the case of materials for which fluid ingress is reversible. The present contribution elaborates on the developed in situ punch-shear device that has been successfully used to realistically assess the tensile yield strength and modulus properties of in-service polymer materials based on experimentally established correlations between shear and tensile tests.

Impact of Film Thickness on the Spectroscopic Evolution of Polyimides in a Simulated GEO Environment

Space domain awareness (SDA) is becoming more important with a constantly increasing number of artificial objects in space. Astronomical reflectance spectroscopy (ARS) is a promising technique employed for remote characterization of space objects. In geosynchronous earth orbit (GEO), the chemical characteristics of a material change continuously, as it is exposed to the harsh radiation environment of several damaging species (with electrons being the primary damaging species in terms of energy deposition). These chemical modifications alter the light absorbed by and reflected from the object at certain wavelengths, resulting in a concomitant change of the measured object’s brightness and color index. By understanding the evolution of the color index of a material as a function of time on orbit, ARS can become a powerful tool for remote characterization of space objects as well as anomaly characterization and resolution. In this study, we investigate the effect of a space-simulated environment represented by high-energy (100 keV) electrons on the evolution of optical properties of several spacecraft-relevant polymer materials.

Nonlinear rheological models and their application to describe the mechanical behavior of highly oriented polymer materials

The nonlinear viscoelasticity of uniaxial oriented polymer materials is considered. To explain the deformation mechanisms of oriented polymers and the possibility of predicting their mechanical behavior in various operating modes, new nonlinear rheological models have been proposed. The application of the simplest rheological model of a real viscoelastic solid to the description and explanation of the recovery process in polymer materials is studied. From the standpoint of rheology, a model of an ideal viscoelastic solid is introduced. Using the balance equation for the number of transitions through energy barriers, a method for calculating the new nonlinear rheological model has been proposed. To eliminate the shortcomings of the ideal viscoelastic solid model associated with the impossibility of predicting creep and stress relaxation modes for long times, a generalized rheological model of a real viscoelastic solid was obtained. In the corrected model, the simplest elements are connected in parallel, which means the presence of not one, but several energy barriers in the materials, the transmission through which have their own relaxation times. To describe the recovery processes in polymer materials, the model of an ideal viscoelastic solid is supplemented by a parallel connected elastic spring. An additional Hooke spring replaces the interfibrillar interaction between the individual elements of the structure and is responsible for possible obstacles during jump-like transitions through the energy barrier. Using the method of rheological models and describing interfibrillar bonds within the framework of the theory of elasticity, a constitutive equation was obtained for the case of recovery processes. Based on the constitutive equation of viscoelasticity for uniaxial oriented polymer materials, a new nonlinear highly elastic element is introduced, which replaces the Maxwell’s element in the theory of linear viscoelasticity. A new rheological model of parallel connection of elastic elements is shown. An explanation of the retardation of the recovery process in polymers is given. The simplest rheological model of a real viscoelastic solid is proposed, in which an elastic spring is responsible for interfibrillar bonds. A constitutive equation is obtained that describes the recovery process in polymers. This equation can be integrated by quadratures and gives a solution that is an analogue of the Newton-Leibniz formula for the proposed model. It is shown that the deformation recovery process in polymer does not depend on the level of initial deformation and the loading method. The obtained result is confirmed by experimental data for polyamide and polyethylene film yarns. When specifying a certain initial level of deformation, generalized recovery curves of these materials are obtained. The proposed simplest rheological model of a real viscoelastic solid makes it possible to predict the reducing properties of polymer materials. And also makes it possible to determine the height of the energy barrier and the magnitude of the elastic modulus in the model. Based on the new rheological models, it is planned in the future to consider the issues of modeling and forecasting different modes of deformation.

Network structural hardening of polypropylene matrix using hybrid of 0D, 1D and 2D carbon-ceramic nanoparticles with enhanced mechanical and thermomechanical properties

Abstract Various dimensional structured inorganic nanoparticles have different ways of improving mechanical properties of polymeric materials. However, there are limited studies on hybridization of different nanoparticles with different dimensional structures for optimal enhancement of mechanical properties of polymer matrix. Therefore, this study combined nanoparticles with 0D (barium titanate [BT]), 1D (carbon nanotubes [C]), and 2D (graphene [G] and boron nitride [BN]) to significantly promote the hardness, elastic modulus, tensile strength/modulus, heat deflection and Vicat softening temperature of polypropylene (PP) nanocomposites. The nanoparticles were surface functionalized to take care of good interfacial interaction with the PP matrix. The nanocomposites were fabricated via melt compounding techniques. Although all the developed nanocomposites showed enhanced mechanical and thermomechanical properties, the ones containing hybrid of carbon and ceramic nanoparticles with different dimensional structures showed superior responses. For instance, optimal hardness, elastic modulus, heat deflection and Vicat softening temperature of about 269.5 MPa, 2.9 GPa, 100.7 °C, and 160 °C were measured for the hybrid PP/3 wt%BNG/3 wt%BTC nanocomposite, which are about 239.4%, 77.7%, 19 °C, and 11 °C higher than that of the pure PP, respectively. The significant enhancement in the measured properties is attributed to effective mechanical interlocking and network structural hardening of the PP matrix.

Finite element analysis of the mechanical performance of a two-layer polymer composite stent structure

Bioresorbable stents (BRS) are an alternative to existing bare-metal stents (BMS) and drug-eluting stents (DES), aiming to reduce the short- and long-term complications in cardiovascular interventions. A combination of biodegradable polymers in a composite scaffold is a promising solution to improve BRS flexibility and strength, which is currently limited by the material properties of polymers. In this study, a mechanical performance of a composite BRS comprised of two layers with four different combinations of polylactic acid (PLA) and polycaprolactone (PCL) was examined with finite element analysis (FEA). Stent crimping and expansion with the balloon inside an atherosclerotic artery was simulated, and stent performance parameters were evaluated and compared between different composite layer configurations. The single-material PCL stent showed the highest recoil and failed to provide support to the artery, while the stiffer single-material PLA stent experienced significantly lower recoil, but also the highest dogboning during expansion, which could increase arterial wall damage. Nearly identical performance was observed for both mixed-material configurations, with recoil and foreshortening closer to single-material PLA stent and dogboning during expansion between both single-material stents. They showed the highest dogboning after balloon deflation due to a combination of permanent deformation at the ends of the stent and lower stiffness at the middle, which allowed for higher recoil at the middle but not at both ends of the stent. The combination of biodegradable polymers into composite BRS shows potential for targeted stent designs with performance tailored to specific needs.

Tailoring Fibre Structure Enabled by X-ray Analytics for Targeted Biomedical Applications

The rising interest in designing fibres via spinning techniques combining the properties of various polymeric materials into advanced functionalised materials is directed towards targeted biomedical applications such as drug delivery, wearable sensors or tissue engineering. Understanding how these functional polymers exhibit multiscale structures ranging from the molecular level to nano-, micro-and millimetre scale is a key prerequisite for their challenging applications that can be addressed by a non-destructive X-ray based analytical approach. X-ray multimodalities combining X-ray imaging, scattering and diffraction allow the study of morphology, molecular structure, and the analysis of nano-domain size and shape, crystallinity and preferential orientation in 3D arrangements. The incorporation of X-ray analytics in the design process of polymeric fibers via their nanostructure under non-ambient conditions (i.e. temperature, mechanical load, humidity…) allows for efficient optimization of the fabrication process as well as quality control along the product lifetime under operating environmental conditions. Here, we demonstrate the successful collaboration between the laboratory of Biomimetic Textiles and Membranes and the Center of X-ray Analytics at Empa for the design, characterisation and optimisation of advanced functionalised polymeric fibrous material systems.

Predicting Young's Modulus of Linear Polyurethane and Polyurethane-Polyurea Elastomers: Bridging Length Scales with Physicochemical Modeling and Machine Learning.

Predicting the properties of complex polymeric materials based on monomer chemistry requires modeling physical interactions that bridge molecular, interchain, microstructure, and bulk length scales. For polyurethanes, a polymer class with global commercial and industrial significance, these multiscale challenges are intrinsic due to the thermodynamic incompatibility of the urethane and polyol-rich domains, resulting in heterogeneities from molecular to microstructural length scales. Machine learning can model patterns in data to establish a relationship between the monomer chemistry and bulk material properties, but this is made difficult by small data sets and a diverse set of monomers. Using a data set of 63 industrially relevant and complex elastomers, we demonstrate that accurate machine learning predictions are possible when monomer chemistry is used to estimate interactions at interchain length scales. Here, these features were used to accurately (r2 = 0.91) predict the Young's modulus of polyurethane and polyurethane-urea elastomers. Furthermore, by a query of the trained model for compositions that yield a target modulus within the range of accessible values, the capabilities of using this methodology as a design tool are demonstrated. The presented methodology could become increasingly useful in building models for materials with small data sets and may guide the interpretation of the underlying physicochemical forces.