Performance Of Polymeric Materials Research Articles

Prediction of long-term creep response: accelerated characterization of industrial nylon6,6 and HMLS PET filaments

The performance of polymeric materials in dynamic loading conditions and their long-term reliability are the two main issues practitioners in the composite field face today. The purpose of this study was to construct master creep curves for industrial nylon6,6 and high modulus-low shrinkage polyethylene terephthalate (HMLS PET) filaments in order to predict their long-term performance. Here, the procedure to develop the master creep curves with short-term creep strain of industrial filaments was investigated under different isothermal conditions in the glass transition region. Nylon consistently exhibits a higher short-term creep strain than PET by around 5–10% based on its lower tensile modulus. Then, master creep curves were developed to foresee the creep of yarns for almost two decades (∼20 years) by the Time-Temperature Superposition principle shift factors. Based on the shift factors derived from master curves, PET and nylon have constant activation energies over the temperature range tested, implying that their creep mechanisms remain constant regardless of the temperature. Overall, rapid prediction of filament creep behavior and lifetime using this method is proposed.

Optimization of polymer materials performance on improving mechanical properties of fine-grained soils of forest

The present study aimed to determine the best performance of polymeric materials (RPP and CBR Plus) in various types of fine-grained soil, and the optimal percentage of polymeric materials and curing time such that the best performance in soil stabilisation can be achieved. To this end, the Taguchi and Taguchi-GRA methods were adopted to optimise swelling potential and uniaxial compressive strength (UCS) for each additive. The comparison of optimal states of two materials showed that the CBR Plus has a superior performance compared to RPP in increasing the UCS and reducing the swelling of soil. The best performance in increasing the UCS was obtained for CH specimen with 0.9% treatment with CBR Plus and curing time of 14 days. The best performance of CBR Plus in reducing soil swelling occurs when it is used on the ML soil modified with 0.07% CBR plus at the curing time of 8 days.

In‐line measurement and characterization in glass bead‐filled polypropylene extrusion based on machine vision

AbstractParticle filling is a typical method for reinforcing polymer matrix materials, and the properties of particle filler have a significant impact on the performance of polymeric materials. However, there is still a lack of effective in situ measurement and characterization methods of particulate‐filled polymer. In this paper, an in‐line measurement and characterization method for glass bead‐filled polypropylene (GB/PP) based on machine vision was proposed. A visual die was developed, and the polymer melt in the visual area was photographed by a high‐speed camera to obtain images for analysis. An improved YOLO target detection algorithm was applied to identify particles in images. The particle size distribution, dispersion, and component content of glass beads in the polypropylene were measured and characterized through statistical analysis, and then verified by other off‐line methods. These properties calculated by our method agree well with those measured by other off‐line methods. This method can achieve the in‐line measurement and characterization for GB/PP extrusion, which is promising for the in‐line property monitoring of particulate‐filled polymers in the industry.

Asymmetrical formation of isomorphism in the crystalline/crystalline blend of poly(butylene succinate) and poly(butylene fumarate)

Blending is a convenient method to regulate the crystallization behavior and thus the performance of polymer materials, but poor compatibility in crystalline phase for different components remarkably depresses the co-crystallization capability, which poses a great challenge to effective regulation of the properties for crystalline/crystalline blends. In this work, the co-crystallization between two kinds of polyester with similar chain structure, poly(butylene succinate) (PBS) and poly(butylene fumarate) (PBF) is investigated and found to be dependent on the blending ratio and crystallization condition. A new type of co-crystal is only discovered in the PBS-rich blends (i.e., PBS/PBF-6/4 and PBS/PBF-8/2), and, further, it is proved as the isomorphism between PBS and PBF by employing various characterizations of differential scanning calorimeter and Fourier transformation infrared spectrometer and X-ray diffractometer. Both the enhancing cooling rate and the increasing PBS content benefit the growth of isomorphic co-crystal, and, its fraction in the blend of PBS/PBF-8/2 can reach as high as ∼75% during a fast cooling rate of 40 °C/min. In addition, the changes of Gibbs free energy for including butylene fumarate unit into PBS-type crystal and including butylene succinate unit into PBF-type crystal are respectively calculated as −0.96 and 1.94 kJ/mol, revealing the intrinsic thermodynamic driving force for the forming of isomorphism and clarifying why isomorphism only occurs in the PBS-rich blends. Finally, a summary of the crystallization behavior of PBS/PBF blend is reasonably sketched, which will help design the crystalline/crystalline blends with desired structure and performance.

Non-woven shape-memory polymer blend actuators

The hierarchical design approach provides various opportunities to adjust the structural performance of polymer materials. Electrospinning processing techniques give access to molecular orientation as a design parameter, which we consider here in view of the shape-memory actuation performance. The aim of this work is to investigate how the reversible strain varepsilon^{prime}_{{{text{rev}}}} can be affected by a morphology change from a bulk material to an electrospun mesh. varepsilon^{prime}_{{{text{rev}}}} could be increased from 5.5 ± 0.5% to 15 ± 1.8% for a blend from a multiblock copolymer with poly(ε-caprolactone) (PCL) and poly(L-lactide) (PLLA) segments with oligo(D-lactide) (ODLA). This study demonstrates an effective design approach for enhancing soft actuator performance, which can be broadly applied in soft robotics and medicine.Graphic abstract

Investigation of the physical and mechanical properties of polymeric materials after blanks surface deformation

The results of an experimental study of the effect of surface deformation of polymeric materials, both as an individual operation and in combination with subsequent turning of workpieces, on some of operational characteristics of these materials are presented. It is experimentally proved that preliminary surface deformation does not reduce the performance of polymeric materials.

Preparation of Functional Long-Subchain Hyperbranched Polystyrenes via Post-polymerization Modification: Study on the Critical Role of Chemical Stability of Branching Linkage.

Post‐polymerization modification (PPM) is one of the most powerful strategy for preparing polymers with functional groups that cannot be synthesized by direct polymerization. So far, numerous experimental efforts have been devoted to the stability issue of monomer structures during the PPM process, but little attention was paid to chemical linkages. However, for hyperbranched polymers, a minor change of linkage unit could lead to a significant influence on the overall stability and performance of polymer materials. In this work, we investigated the chemical stability of long‐subchain hyperbranched polystyrenes with ester, aryl ether, and carbon‐carbon bonds as branching linkages under a few most popular PPM conditions, including NaOH hydrolysis reaction, TFA‐promoted hydrolysis reaction, BBr3‐catalyzed methoxy‐hydroxyl conversion reaction, and LiAlH4 carbonyl reduction reaction. Related results are summarized into a synthetic route map that can provide practical and intuitive guidance for preparing functional long‐subchain hyperbranched polystyrenes and other type of polymers by PPM for future applications.

Selective dynamics in polymeric materials: Insights from quasi-elastic neutron scattering spectroscopy

Polymeric materials exhibit a rich hierarchy of dynamics from fast sub-molecular motions to collective segmental relaxations and slow chain diffusion. Such dynamical hierarchy dictates that the performance of polymeric materials is tightly linked to fast molecular dynamics, necessitating a thorough understanding of the dynamic behavior of polymers on the nanoscale. Recent advances in the synthesis of polymer composites with nanoscale fillers further amplify the need to probe polymer dynamics over spatial and temporal nanoscales to achieve reliable engineering of materials with well-defined properties. This tutorial focuses on the efficacy of neutron spectroscopy techniques, combined with judicious hydrogen/deuterium labeling, in selectively probing local and collective dynamics that underlie macroscopic properties in polymeric materials with varying degrees of complexity.

Collapsibility of metastable sand by non-conventional oedometer tests

The stability of foundations soils could represent a clear and present threat for the conservation of even well preserved buildings, particularly for Architectural heritage conservation and land art heritage. A dramatic case is the presence of collapsible metastable sands as foundation soils, as it occurs in the sacral complex Valle dei Templi in Agrigento. This site listed by UNESCO, stands on a crest of a calcarenite cuesta, overlaying a layer of these sands. When the collapsible sand is dry, the structure is strong enough to bond the sand particles together. When the sand becomes wet, a de-structuration mechanism occurs and the soil’s strength is compromised. This paper has a twofold aim: (1) to gain a better understanding of the kind of bonding forces between the textural components of the collapsible metastable sand and (2) to identify a proper consolidant, that could combine the compatibility of inorganic systems and the performance of polymeric materials, paying attention to the environmental issues related to this site. Soaking tests have been performed by submerging sand samples in different solvents in order to verify the role of water menisci in mechanical stability of the sand highlighting a perfect stability using a non polar solvent. Sand samples have been consolidated by using poly ethylene glycol and nanosilica. Oedometer tests on consolidated and untreated samples have been used to verify the reduction of collapse potential induced by the treatment with the proposed mixtures.

Molecular dynamics simulation of gas diffusion behavior in polyethylene terephthalate/aluminium/polyethylene interface

Molecular dynamics (MD) simulations were performed to estimate the diffusion coefficients of O2 and H2O molecules in polyethylene terephthalate/aluminum/polyethylene interface at the temperature of 298 K. It came out that the diffusion coefficient of gasses in the interface is smaller than that of a single polymer, and the diffusion coefficients compare well with experimental data as well as previously published work. Furthermore, the diffusion coefficients of H2O molecules in the interface are preferable to that of O2 molecules. Interestingly, the largest diffusion coefficient was detected in the polyethylene terephthalate/aluminum(1 0 0)/polyethylene interface, while the smallest value of the diffusion coefficients was found in the polyethylene terephthalate/aluminum(1 1 1)/polyethylene interface. Calculation and analysis of the interaction between aluminum and polymers indicated that the interaction of polymer/aluminum(1 1 0) has the most interface strength, and crystal density of the metal surface has a definite effect on the planar interface energy. What’s more, the figure of gas molecule concentration is further resulted that the interface make contribution to adsorption of gas molecules. Moreover, the diffusion is belonging to the Einstein diffusion in the multilayer materials, and this work provides some key clues to improve the performance of polymer materials.

Detection and analysis of micro cracks in low modulus materials with thermal loading using laser speckle interferometry

Micro-defect detection is an essential field of failure analysis for the assessment and reliability of engineering materials under various loading conditions. This paper illustrates the effect of thermal loading on micro crack formation in certain low modulus materials used for aerospace applications and further analysis. The demands of increased performance of polymeric materials have created a need for new experimental techniques for accurate measurements of their structural defects through non-destructive ways. The present work employs one such optical non-destructive technique such as Laser Speckle Interferometry (LSI) to study the micro crack formation in the low modulus material used as an insulator in solid rocket motors. The low modulus material used is a nitrile based rubber compound which, when thermally loaded to a differential temperature in the range of 20°C to 28°C generates an optimum fringe pattern for the analysis of defects. Extremely small defects in the micrometer scale can be detected by analyzing the anomalies in the generated fringe pattern.

Hydrogen bonding in stereoregular poly(methyl methacrylate)/poly(vinyl chloride) blends as studied by molecular dynamics simulations

In this work, two technically important polymer blends composed of isotactic poly (methyl methacrylate) (iPMMA) or syndiotactic poly (methyl methacrylate) (sPMMA) and isotactic poly (vinyl chloride) (iPVC) have been extensively investigated by molecular dynamics simulations. It is confirmed that sPMMA exhibits stronger interactions with iPVC than does iPMMA, and the non-conventional hydrogen bonds (HBs) occur between the two distinct components. Furthermore, the HBs in sPMMA/iPVC are more than those in iPMMA/iPVC, and the structural relaxation of HBs is closely associated with the backbone chain dynamics, which well explain the experimental trends in miscibility of the two systems and in glass transition temperature of single components. It should be noted that these results cannot be directly obtained by the experiments and single simulations, and the multiscale schemes used to prepare the initial all-atomistic configurations can play an important role. This work provides some key clues to improve the performance of polymer materials.

Crystallization Features of Normal Alkanes in Confined Geometry

How polymers crystallize can greatly affect their thermal and mechanical properties, which influence the practical applications of these materials. Polymeric materials, such as block copolymers, graft polymers, and polymer blends, have complex molecular structures. Due to the multiple hierarchical structures and different size domains in polymer systems, confined hard environments for polymer crystallization exist widely in these materials. The confined geometry is closely related to both the phase metastability and lifetime of polymer. This affects the phase miscibility, microphase separation, and crystallization behaviors and determines both the performance of polymer materials and how easily these materials can be processed. Furthermore, the size effect of metastable states needs to be clarified in polymers. However, scientists find it difficult to propose a quantitative formula to describe the transition dynamics of metastable states in these complex systems. Normal alkanes [CnH2n+2, n-alkanes], especially linear saturated hydrocarbons, can provide a well-defined model system for studying the complex crystallization behaviors of polymer materials, surfactants, and lipids. Therefore, a deeper investigation of normal alkane phase behavior in confinement will help scientists to understand the crystalline phase transition and ultimate properties of many polymeric materials, especially polyolefins. In this Account, we provide an in-depth look at the research concerning the confined crystallization behavior of n-alkanes and binary mixtures in microcapsules by our laboratory and others. Since 2006, our group has developed a technique for synthesizing nearly monodispersed n-alkane containing microcapsules with controllable size and surface porous morphology. We applied an in situ polymerization method, using melamine-formaldehyde resin as shell material and nonionic surfactants as emulsifiers. The solid shell of microcapsules can provide a stable three-dimensional (3-D) confining environment. We have studied multiple parameters of these microencapsulated n-alkanes, including surface freezing, metastability of the rotator phase, and the phase separation behaviors of n-alkane mixtures using differential scanning calorimetry (DSC), temperature-dependent X-ray diffraction (XRD), and variable-temperature solid-state nuclear magnetic resonance (NMR). Our investigations revealed new direct evidence for the existence of surface freezing in microencapsulated n-alkanes. By examining the differences among chain packing and nucleation kinetics between bulk alkane solid solutions and their microencapsulated counterparts, we also discovered a mechanism responsible for the formation of a new metastable bulk phase. In addition, we found that confinement suppresses lamellar ordering and longitudinal diffusion, which play an important role in stabilizing the binary n-alkane solid solution in microcapsules. Our work also provided new insights into the phase separation of other mixed system, such as waxes, lipids, and polymer blends in confined geometry. These works provide a profound understanding of the relationship between molecular structure and material properties in the context of crystallization and therefore advance our ability to improve applications incorporating polymeric and molecular materials.

Studies in Finishing Effects of Clay Mineral in Polymers and Synthetic Fibers

The use of clay mineral in modifying the properties of polymeric material is improved in application. The current interest in modifying the polymeric materials, particularly polyethylene, polypropylene, polystyrene, and nylon using clay mineral for improved flame retardancy, thermal stability, peak heat release rate, fracture, and strength properties generated significant research literature. This paper aims to review some of the important recent modification achieved in the performance of polymeric materials using organoclay mineral. Degradation of clay mineral-polymer (nm) composite is discussed with appropriate known examples. Clay mineral (nm) loading of 5 wt.% to 7 wt.% that was significantly smaller than the percent loading of conventional fillers in polymeric materials introduced significant improvement in terms of thermal and physical stability. An attempt is made to emphasize flammability and thermal stability and to indicate the areas that are relatively little explored in modification of fiber-forming polymers to enhance further research interest.

FLAME RETARDATION PERFORMANCES OF HALOGEN-FREE FLAME RETARDANT WHEN APPLIED TO UNSATURATED POLYESTER

In order to improve fire performance of polymeric materials, phosphorus flame retardants (FRs) were studied in an attempt to obtain UL-94 ratings for materials based on unsaturated polyester. The fire behaviors and thermal stability properties were evaluated using UL-94 vertical test and thermogravimetric analysis (TGA). The UL-94 test results show that V-1 rating is achieved. TGA and UL-94 results concluded that phosphorus FRs employed in this study works on both vapor phase and condensed phase, but the vapour phase is dominant mode of action. These suggested that the addition of FRs probably does affect on the char layer formed during combustion behavior and increase the flame retardant properties in the case of condensed phase mode of action. The efficiency of flame retardant of phosphorus also highly depends upon the phosphorus moieties generated during the decomposition which further converted to radical capturing species, and consequently quenching the flame in the case of gas phase mode of action. These FRs can be promising candidates that replace the halogen-based.

Study of Material Parameters’ Effect on Polymer Scratch Using SOM Method

Due to its inherited complexity, the polymer material parameters’ effect on the scratch resistance is difficult to detect. Using the scratch experimental results of a set of polypropylene (PP), the Self-Organizing Map (SOM) method, an artificial neural network algorithm, was adopted to study the effect of various material parameters on polymer scratch. Especially suitable for the analysis of high-dimensional data with nonlinear statistical relationships, SOM method helps to find out the influence of different material parameters on scratch behavior. This information can be used to estimate the possible performance of polymeric materials to certain extent without extra scratch experimental work. It also helps researchers to decide which group of properties should be paid more attention when studying the coupling effect of material parameters on polymer scratch resistance.

ENGINEERING ORIENTATION IN BLOCK COPOLYMERS FOR APPLICATION TO PROSTHETIC HEART VALVES

This study demonstrates how the mechanical performance of polymeric material can be enhanced by morphology and phase orientation of block copolymers to achieve desired anisotropic mechanical properties. The material used was a new Kraton block copolymer consisting of styrene-isoprene-butadiene-styrene blocks having cylindrical morphology. We report a method of achieving long range uniaxial as well as biaxial orientation of block copolymer. Each microstructural organization results in a specific mechanical performance, which depends on the direction of the applied deformation. The method of tailoring mechanical properties by engineering microstructure may be successfully utilized to applications requiring anisotropic mechanical response, such as prosthetic heart valves.

Determination of Interphase Thickness and Mechanical Properties of Effective Nanofillers in Polymer Nanocomposites by Molecular Dynamic Simulation

The properties of interphase in polymer composites are often different from those of bulk polymer matrix, which may include chemical, physical, microstructural, and mechanical properties. The nature of interphase is critical to the overall properties and performance of polymer materials, in particular in nanofiller reinforced composites. Experimental efforts have been made to determine the effective interphase thickness and its properties, for example, by nanoindentation and nanoscratch techniques. Yet, it is very difficult to quantify the interphase and its properties because of its nanoscale nature and the unclear boundary. In this regard, computer simulation, e.g., molecular dynamics, provides an effective tool to characterize such interphase and the properties. In this work, molecular dynamics simulations are applied to quantify the interphase thickness in clay-based polymer nanocomposites. Then, the mechanical properties of the so-called effective nanofiller (i.e., the physical size of nanofiller plus the thickness of interphase) will be determined by a series of simulations.

Online Monitoring of Molecular Weight and Other Characteristics during Semibatch Emulsion Polymerization under Monomer Starved and Flooded Conditions

Reaction kinetics in semibatch emulsion polymerization of methyl methacrylate, were monitored by automatic continuous online monitoring of polymerization reactions (ACOMP). Semibatch reagent feed to the reactor at different flow rates allowed the transition between the monomer starved and flooded regimes and the approach to and maintenance of near steady state conditions to be monitored and quantified, and yielded relationships between flow regimes and monomer conversion kinetics, polymer weight-average molecular weight Mw, and intrinsic viscosity (η)w. Polymer molecular weight distributions togetherwithlatexparticlesizeandnumberplayanimportantroleindefiningthemacroscopiccharacteristics and performance of polymeric materials. The change in the monomer feed rates during reaction allowed simultaneous influence on and verification of the evolution of these parameters during synthesis. When flow rate changes to the reactor were made it was verified that the characteristic rate of achieving the new pseudosteady state was close to the first order reaction rate. Multidetector size exclusion chromatography was used to cross-check results and measure full distributions of endproducts. Latex polymer size was measuredwithdynamiclightscattering.AnimportantadvanceforthisfieldisthatpolymerMwisdetermined continuously during the reaction and in an absolute fashion, based on multiangle light scattering detection available.

Predictive control and verification of conversion kinetics and polymer molecular weight in semi-batch free radical homopolymer reactions

Polymer molar mass distributions critically affect macroscopic characteristics and performance of polymeric materials. While multi-detector methods coupled to size exclusion chromatography (SEC) are widely used to measure endproduct mass distributions, less progress has been made in simultaneously controlling and verifying the evolution of these distributions during synthesis. This work focuses on quantitative predictions and online verification of conversion kinetics and of molecular weight during free radical homopolymerization of acrylamide, where reagents were fed into the reactor during the reaction. The central task is to establish and experimentally test a formalism combining free radical polymerization kinetics with time dependent processes related to flows of material into and out of the reactor. Monomer feed experiments were performed that alternately hold molecular weight constant and ramp the weight up, in contrast to batch reactions, where molecular weight decreases. Three types of initiator feed ‘tapers’ were also used to produce predictable conversion kinetics and mass distributions: (i) constant initiator feed, (ii) linearly stepped feed to produce Gaussian conversion kinetics, and (iii) booster shots to produce multi-modal masses. Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP) was used to follow the conversion and evolution of the average mass distribution, and multi-detector SEC was used to cross-check results and measure full distributions of endproducts. In general, there was good agreement between the predictions and results. In future work this approach can be used as an Ansatz for reaction trajectory prediction, and the online monitoring signals exploited to make feedback controlled corrections to the reagent flows and other reaction conditions.