Pattern recognition for the analysis of polymeric materials

A new method of polymer classification is described involving dynamic mechanical analysis of polymer properties as temperature is changed. The method is based on the chemometric analysis of the damping factor (tan delta) as a function of temperature. In this study four polymer groups, namely, polypropylene, low density polyethylene, polystyrene and acrylonitrile-butadiene-styrene, each characterised by different grades, were studied. The aim is to distinguish polymer groups from each other. The polymers were studied over a temperature range of -50 degrees C until the minimum stiffness was reached, tan delta values were recorded approximately every 1.5 degrees . Principal components analysis was performed to visualise groupings and also for feature reduction prior to classification and clustering. Several clustering and classification methods were compared including k-means clustering, hierarchical cluster analysis, linear discriminant analysis, k-nearest neighbours, and class distances using both Euclidean and Mahalanobis measures. It is demonstrated that thermal analysis together with chemometrics provides excellent discrimination, representing a new approach for characterisation of polymers.     

Multifunctional polymeric materials for biomedical applications

The work performed by our research group during the last few years in the area of bioerodible-biodegradable polymers as designed to the formulation of systems for the controlled delivery of drugs and as specific sorbents of uraemic toxins is broadly reviewed. In particular, attention has been focused on the strategies adopted in the preparation of functional polymers containing hydroxyl or carboxyl groups, suitable to establish specific bonding and non-bonding interactions with conventional and proteic drugs.     

Macroporous polymeric materials for bioanalytical microchips

Macroporous copolymers derived from 2-cyanoethyl methacrylate were prepared using low-molecular-weight and polymeric porogens. The influence of the polymerization conditions on the pore characteristics and surface morphology of the macroporous materials was examined. The possibility of efficiently using the synthesized polymeric matrices for protein assay was evaluated with a model biocomplementary couple as example.     

Carbonyl polymeric electrode materials for metal-ion batteries

This review presents the recent progress in carbonyl polymeric electrode materials for lithium-ion batteries, sodium-ion batteries and magnesiumion batteries. This comprehensive review is expected to be helpful for arousing more interest of organic materials for metal-ion batteries and designing novel battery materials with high performance.     

Stimuli-responsive supramolecular polymeric materials

Supramolecular materials, dynamic materials by nature, are defined as materials whose components are bridged via reversible connections and undergo spontaneous and continuous assembly/disassembly processes under specific conditions. On account of the dynamic and reversible nature of noncovalent interactions, supramolecular polymers have the ability to adapt to their environment and possess a wide range of intriguing properties, such as degradability, shape-memory, and self-healing, making them unique candidates for supramolecular materials. In this critical review, we address recent developments in supramolecular polymeric materials, which can respond to appropriate external stimuli at the fundamental level due to the existence of noncovalent interactions of the building blocks.     

Preparation of polymeric nanostructured materials

A procedure for forming nanostructured materials by impregnation filling of pores of poly(ethylene terephthalate) track membranes with polymeric compounds was examined. The relationships of formation of these materials were elucidated, and the structural and surface properties of these materials were studied.     

Raman microspectroscopy of polymeric materials

Vibrational spectroscopy is an important tool to characterize polymeric materials. Confocal Raman Microspectroscopy allows to analyze micrometric areas and yields information about the chemical and physical parameters of polymers. The interpretation of the Raman spectra is usually related to the properties and processing. Thus, this non‐destructive technique is appropriated to investigate the skin/core morphology of injection‐molded semicrystalline polymers, blends, interface of composites, etc.     

Polytetrafluoroethylene-based polymeric composite materials intended for triboengineering applications

The influence of ultradispersed ceramics particles on formation and wear of polytetrafluoroethylene-based polymer composites was elucidated. Factors improving the performance characteristics of the composites were identified.     

Application and limitations of the flexural creep test for polymeric materials

Application and limitations of the flexural creep test are described. For this purpose six different thermoplastic materials are tested under low and moderate stress and temperature conditions. The log-log method and a nonlinear creep compliance is used to analyze and compare the data. In order to assess the applicability range of elementary small deflection theory in calculation of strain values, a large deflection analysis is performed. This analysis indicates the presence of an instability condition. Design curves are drawn to reveal the percentage difference between the deflection values obtained on the basis of small and large deflection theories.     

Molecular engineering of mechanophore activity for stress-responsive polymeric materials

Force reactive functional groups, or mechanophores, have emerged as the basis of a potential strategy for sensing and countering stress-induced material failure. The general utility of this strategy is limited, however, because the levels of mechanophore activation in the bulk are typically low and observed only under large, typically irreversible strains. Strategies that enhance activation are therefore quite useful. Molecular-level design principles by which to engineer enhanced mechanophore activity are reviewed, with an emphasis on quantitative structure–activity studies determined for a family of gem-dihalocyclopropane mechanophores.     

Fluorinated organic materials for electronic and optoelectronic applications: the role of the fluorine atom

In this article we highlight, by means of selected examples drawn from work performed in our or other laboratories, the features of some classes of fluorinated conjugated materials and their use in electronic devices such as electroluminescent diodes or field effect transistors. A variety of fluorinated conjugated systems, either molecular or polymeric, such as poly(phenylenevinylene)s, poly(phenyleneethynylene)s, polythiophenes, polyphenylenes, are dealt with. Attention is also focused on a different class of electroluminescent compounds, represented by the cyclometalated iridium complexes with various forms (mer and fac). In particular, fluorine atoms lower both the HOMO and LUMO energy levels. Consequently, the electron injection is made easier, the materials display a greater resistance against the degradative oxidation processes and organic n-type or ambipolar semiconducting materials may result. Moreover, the C-H...F interactions play an important role in the solid state supramolecular organization, originating a typical pi-stack arrangement which enhances the charge carrier mobility.     

Humidity-sensitive and water-resistive polymeric materials

Four types of polymers with pyridinium groups were prepared and their electrical properties as humidity sensors were studied. The polymers are quaternized vinylpyridine and styrene copolymers, partially quaternized polyvinylpyridine, polytetrafluoroethylene grafted with quaternized polyvinylpyridine and polyvinylpyridine crosslinked with dibromobutane. The latter two polymers showed excellent water resistivity as well as a sensitivity to humidity.     

Approaches to polymeric mechanochromic materials

Mechanochromic materials respond to mechanical stimuli with a change of their optical properties. Such materials are of interest for many technological applications and support fundamental research as they help improving the understanding of stress transfer in polymeric objects and aid in the identification of the processes that lead to mechanical failure. In this highlight, different approaches are discussed that permit the design of polymeric materials, which signal mechanical stresses through a chromic response. This highlight emphasizes materials that exhibit mechanically induced changes of their intrinsic absorption or emission properties. These responses almost exclusively originate from changes of molecular structure, conformational rearrangements, or disruption of intermolecular interactions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 640–652     

Reversible shape-shifting in polymeric materials

In recent years, significant progress has been made in polymeric materials, which alter shape upon external stimuli, suggesting potential applications in robotics, biomedical engineering, and optical devices. These stimuli-responsive materials may be categorized into two classes: (i) shape-changing materials in which a specific type of shape-shifting is encoded in the original material structure and (ii) shape-memory materials, which do not possess any predetermined shape-shifting as prepared, yet allow programming of complex shape transformations on demand. While shape alterations in shape-changing materials are intrinsically reversible, shape memory is usually a one-way transformation from a metastable (programmed) to an equilibrium (original) state. Recently, different principles for both one-way reversible and two-way reversible shape memory have been developed. These offer a powerful combination of reversibility and programmability, which significantly expands the range of potential applications. The goal of this review is to highlight recent developments in reversible shape-shifting by introducing novel mechanisms, materials, and applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1365–1380     

Factors affecting the combustion toxicity of polymeric materials

Fire gas toxicity is an essential component of any fire hazard analysis. However, fire toxicity, like flammability, is both scenario and material dependent. A number of different methods exist to assess the fire toxicity, but many of them fail to relate this to a particular fire scenario. Sample thickness alone, in a closed box test such as the NBS Smoke Chamber, is shown to change the fire scenario from well-ventilated to under-ventilated. Data from two flow-through tests, the static tube furnace (NF X 70-100) and the steady state tube furnace (the Purser furnace, BS 7990 and ISO TS 19700) show that there are different patterns of behaviour for different polymers (LDPE, polystyrene, rigid PVC and Nylon 6.6). The predicted toxicities show variation of up to two orders of magnitude with change in fire scenario. They also show change of at least one order of magnitude for different materials in the same fire scenario. Finally, they show that in many cases CO, which is often assumed to be the most, or even the only toxicologically significant fire gas, is of less importance than either HCl, or HCN, when present, and in some cases less important than organo-irritants. Nylon 6.6 shows the highest predicted toxicity, the greatest scenario dependence, and the least sensitivity to different apparatuses, while polystyrene shows the highest sensitivity to the different apparatuses, but the lowest to different fire scenarios. PVC shows high toxicity, mostly due to HCl in the fire effluent, under all fire conditions, and LDPE shows a more progressive increase in toxicity from well-ventilated flaming to both smouldering and under-ventilated flaming.     

Determination of antioxidants in polymeric materials

A review of methods proposed for the analysis of antioxidants in polymeric materials, cast in the form of a step-by-step examination of the problems involved in any scheme of analysis, with a critical appraisal of the published procedures designed to overcome them.     

Uniaxial compression testing of polymeric materials

Two methods for uniaxial compression testing were investigated and compared using polypropylene as a model material. An overview of various parameters affecting compression test results is provided with particular emphasis on friction between the specimen and the compression plate. A procedure for the determination of the compressive modulus is introduced and results are shown. To enable the detection of instability associated with friction and barreling and to calculate true stress-true strain curves, the measurement of transverse expansion of the specimen at large strains is necessary. Nominal and true Poisson's ratio values in the pre- and post-yield regime are presented and the resulting true stress-true strain curves are compared and discussed. While in the post-yield regime nominal stress values misleadingly result in strain hardening, significant strain softening was observed using true stress values representing the intrinsic material behavior.     

Autoignition limits of some polymeric materials

This paper is concerned with the autoignition limits of some well known polymeric materials (polyethylene, polypropylene and polystyrene) in still air, obtained by the spontaneous autoignition method. Results have been obtained over a wide range of conditions; they show the existence of a two-stage autoignition resulting from a cool combustion for polyethylene and polypropylene. These results confirm and extend previous studies.