On the Use of Atmospheric Pressure Plasma for the Bio-Decontamination of Polymers and Its Impact on Their Chemical and Morphological Surface Properties

Low temperature atmospheric pressure plasma processes can be applied to inactivate micro-organisms on products and devices made from synthetic and natural polymers. This study shows that even a short-time exposure to Ar or Ar/O₂ plasma of an atmospheric pressure plasma jet leads to an inactivation of Bacillus atrophaeus spores with a maximum reduction of 4 orders of magnitude. However, changes in the surface properties of the plasma exposed material have to be considered, too. Therefore, polyethylene and polystyrene are used as exemplary substrate materials to investigate the effect of plasma treatment in more detail. The influence of process parameters, such as type of operating gas or jet-nozzle to substrate distance, is examined. The results show that short-time plasma treatment with Ar and Ar/O₂ affects the surface wettability due to the introduction of polar groups as proofed by X-ray photoelectron spectroscopy. Furthermore, atomic force microscopy images reveal changes in the surface topography. Thus, nanostructures of different heights are observed on the polymeric surface depending on the treatment time and type of process gas.     

Quality Assessments of Recycled Plastics by Spectroscopy and Chromatography

Quality assessments will be important for improved use of recycled polymeric materials. Ongoing preparation of new standards in the area of recycled polymers needs an overview of which properties and thus which polymer characterisation methods that will be important for that purpose. We suggest three polymeric properties as important for this work; these are degree of mixing (composition), degree of degradation and number and amount of low molecular weight compounds (e.g. degradation products, additives, flavour compounds). DSC showed increased degradation as multi modality for LDPE materials obtained from three different sites in a recycling plant. IR demonstrated that the carbonyl index increased during the various steps going from collected material to new product. GC chromatograms obtained for collected film flakes, processed granules and ready-made bags were quite complex with a series of hydrocarbons among other compounds. The recycling process seems, however, to remove some of the low molecular weight compounds found in the incoming dirty material.     

Re-Emerging Field of Lignocellulosic Fiber – Polymer Composites and Ionizing Radiation Technology in their Formulation

Natural cellulose-based fibers offer low cost, low density composite reinforcement with good strength and stiffness. Because of their annual renewability and biodegradability, natural fibers have materialized as environmentally-friendly alternatives to synthetic fibers in the last two decades. They are replacing synthetic materials in some traditional composites in industrial manufacturing sectors such as automotive, construction, furniture, and other consumer goods. In this work, the use of lignocellulosic fibers in green materials engineering, particularly their application as polymeric composite reinforcement and surface treatment via ionizing radiation are reviewed. Because these cellulose-based materials are intrinsically hydrophilic, they require surface modification to improve their affinity for hydrophobic polymeric matrices, which enhances the strength, durability, and service lifetime of the resulting lignocellulosic fiber-polymer composites. In spite of a long history of using chemical methods in the modification of material surfaces, including the surface of lignocellulosic fibers, recent research leans instead towards application of ionizing radiation. Ionizing radiation methods are considered superior to chemical methods, as they are viewed as clean, energy saving, and environmentally friendly. Recent applications of controlled ionizing radiation doses in the formulation of natural fiber –reinforced polymeric composites resulted in products with enhanced fiber-polymer interfacial bonding without affecting the inner structure of lignocellulosic fibers. These applications are critically reviewed in this contribution.     

Some Factors Governing the Coating of Organic Polymers by Sol-Gel Derived Hybrid Materials

Organic-inorganic hybrid materials can exhibit some properties of organic polymers, such as toughness and elasticity, and/or that of ceramics, such as chemical stability and hardness. In this review, we discuss the main factors that should be considered when coating a polymeric substrate with a sol-gel derived organic-inorganic hybrid material. The effects of the solution characteristics, the polymer substrate chemistry and preparation, the application process and materials characteristics are considered. Examples of commercial and published systems are discussed. We find that due to the wide diversity of the systems investigated, it is difficult to be specific in recommending guidelines applicable to all systems. However, some general considerations can be made that should be useful in the design of functional hybrid coatings aimed at improving the characteristics of polymeric surfaces.     

Pyrolysis of flame retardants and fire protected polymers

The simultaneously working combination of thermal analysis and mass spectrometry (TA/MS) is a very useful method for studying the degradation process of polymeric materials during thermal treatment [1–7]. Beside the thermal effects, as recorded from thermogravimetry (TG) or differential thermal analysis (DTA) the evolved degradation products can be determined and identified by the on - line coupled mass spectrometer. Additional their temperature depending abundance can be registrated. Combustion of polymers in horizontal (BIS) or vertical (VCI) furnaces and subsequent off line high resolution GC/MS analysis of pyrolysis products is suitable for the simulation of burning processes     

Automatic control systems for technological processes of curing products made of polymeric composites

The system of classification of the main types of automatic control systems for curing regimes of the products made of polymeric composite materials has been examined. The methods of formation of control signals have been determined. The means of controlling and taking into account exothermic effects arising in the curing process on the accuracy of controlling the temperature-time regimes of the technological processes have been studied. Hybrid composite materials based on epoxy binder with carbon and organic fibrous fillers used in rocket and space production have been considered as objects of study.     

Comparison of extraction methods for sampling of low molecular compounds in polymers degraded during recycling

The demand for mechanical recycling of plastic waste results in an increasing amount of recycled polymeric materials available for development of new products. In order for recycled materials to find their way into the material market, high quality is demanded. Thereby, a complete and closed loop of polymeric materials can be achieved successfully. The concept of high quality for recycled plastics imply that besides a pure fraction of e.g. polyethylene (PE) or polypropylene (PP), containing only minor trace amount of foreign plastics, knowledge is required about the type and amount of low molecular weight (LMW) compounds. During long-term use (service-life), products made of polymeric materials will undergo an often very slow degradation where a series of degradation products are formed, in parallel, additives incorporated in the matrix may also degrade. These compounds migrate at various rates to the surrounding environment. The release rate of LMW products from plastics depends on the initiation time of degradation and the degradation mechanisms. For polymers the formation of degradation products may be initiated already during processing, and subsequent use will add products coming from the surrounding environment, e.g. fragrance and aroma compounds from packaging. During recycling of plastics, emissions which contain a series of different LMW compounds may reach the environment leading to unwanted exposure to additives and their degradation residues as well as degradation products of polymers.Several extraction techniques are available for sampling of LMW compounds in polymers before chromatographic analysis. This paper reviews and compares polymer dissolution, accelerated solvent extraction (ASE), microwave assisted extraction (MAE), ultrasound assisted extraction (UAE), super critical fluid extraction (SFE), soxhlet extraction, head-space extraction (HS), head-space solid phase micro extraction (HS-SPME), and head-space stir bar sorptive extraction (HSSE) as appropriate sampling methods for LMW compounds in recycled polymers. Appropriate internal standards useful for these kinds of matrices were selected, which improved the possibility for later quantification. Based on the review of extraction methods, the most promising techniques were tested with industrially recycled samples of HDPE and PP and virgin HDPE and PP for method comparison.     

Effect of processing on the environmental stress cracking resistance of high-impact polystyrene

Processing conditions have a strong effect on the final mechanical properties of products made of polymeric materials. Relevant phenomena most commonly include thermal stresses, physical ageing, frozen-in strains and molecular orientation. In this work, two different high-impact polystyrenes, processed by thermoforming, were considered: a “standard” one and a grade specifically resistant to Environmental Stress Cracking (ESC). The main effect induced by thermoforming was molecular orientation. The local degree of orientation was measured on a thermoformed product and its effect on the material ESC behavior in sunflower oil was studied. A Fracture Mechanics approach was applied to evaluate the fracture resistance of the two materials. Results show that a higher degree of orientation increases the fracture resistance in air but has no effect on the (expectedly lower) resistance in the active oil environment.     

Mechanisms of structural bearing capacity exhaustion of large-sized pressure shells made of polymeric composite materials

In this paper, the mechanisms of structural bearing capacity exhaustion of large-sized pressure shells made of polymeric composite materials are considered. These mechanisms include strength reduction of layers within one or more elements of the pressure shell, general buckling of the pressure shell, local buckling, and specific fracture mechanisms of a composite material that take place in particular cases depending on material reinforcement.     

Modified split column technique for the experimental determination of thermal conductivity of polymers

The continuous increase in the utilization of polymeric materials in many specific applications has demanded detailed knowledge of their physical properties, both during their processing as raw material, as well as in the overall range of the working temperature of the final polymer product. Nowadays, mathematical modeling has become an established tool for improving process control and product quality in polymer processing. As models become more sophisticated, there is an increasing need for reliable thermo-physical properties data. In this work, a very simple and low cost arrangement, a variation of the well-known split column method, is employed in the experimental determination of the thermal conductivity of some selected polymers. Rectangular parallelepiped shaped samples, (200 × 100 × 20) mm were prepared by cutting such pieces from long commercial plates or through an extrusion process starting from the powder or pellets of the solid polymer. Experimental results show a solid consistence when they are checked against results obtained by other techniques.     

Preheat Compression Molding for Polyetherketoneketone: Effect of Molecular Mobility

Polyetherketoneketone(PEKK)is a new evolving polymeric material,and is considered as another important member of the polyaryletherketone(PAEK)family in addition to polyetheretherketone(PEEK).Hot compression molding can be used to compact and consolidate the PEKK products,where the temperature and pressure play key roles to affect the molecular mobility,entanglement and crystallization,and thus the mechanical properties of PEKKs.In this study,a preheating treatment was introduced in the compression molding,and it is found that such preheating is very essential to avoid the formation of crystal FormⅡ,based on the increased chain entanglement.Molecular dynamics simulations revealed that the molecular mobility is always suppressed when a compression is applied.Therefore,by increasing the entanglement via the preheating and maintaining such entanglement in the consequent compression molding,strong and tough PEKK materials were obtained,with a negligible fraction of crystal FormⅡ.     

Improvement of Fibre-Matrix-Adhesion of Natural Fibres by Chemical Treatment

Plastics, also called synthetic polymers, are playing an important role in daily living. To raise more applications it is necessary to modify known polymeric systems to reach improved materials/material systems. A possibility to create new optimised materials out of neat polymers is offered by compounding them with different filling material. Besides chemical modification of polymers, mixing, combining or use of different fillers, one possibility is given by the composite technique, whereas the combination of the polymeric matrix and the embedded reinforcement (e.g. fibre) are yielding in optimised materials adjusted to the required properties. Concerning the polymeric matrix, either thermoplastic or thermoset material can be used. In case of the reinforcement, either synthetic (carbon-, glass- or polymeric fibres) or natural fibres are introduced to composites. To obtain an appropriate adhesion of the matrix to the reinforcement system, synthetic fibres are equipped with an avivage. For natural fibres, there are no such materials available and the hydrophilic property of this system surface prevents an adhesion to hydrophobic polymers, as well as to sizings. In this paper, ways are shown to modify the natural fibres via chemical treatment to yield higher physical properties at better adhesion. Also we will explain activities on the use of natural fibres as reaction systems and processing tools as well as the attempt to isolate the different compounds of the neat fibre via selective work-up.     

Ageing Monitoring of Plastics Used in Nuclear Power Plants by DSC

Degradation of polymeric materials used in nuclear power plants (NPP), especially polymeric cable insulation materials, in the course of their service can be monitored by measuring their properties by DSC, mainly oxidative induction time — OIT. The studied materials were in-laboratory aged by applying main stressors that act in NPP — ionising radiation and temperature. The dependence of OIT on radiation and thermal degradation of polymeric material was determined. The OIT values have been compared to elongation at break as a property that directly reflects the functionality of the studied material. The comparison of monitored OIT of real cable samples taken from NPP with dependencies on how the OIT values change with the elongation at break, makes possible to establish the extent of cable degradation. This method can be considered as a suitable and effective technique for lifetime assessment not only of cable insulations but also of many other plastics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Progress in the chemistry of functional aramids properties

High-performance polymers based on amide aromatic rings are known as wholly aromatic polyamides or aramids. The arrangement and admirable properties of aramids are built on the basis of amide linkage and rigid aromaticity. Aramids are attractive because of their extraordinary bond strengths and very high stiffness. Synthetic aromatic polymeric chains provide increased mechanical resistance and thermal softening compared to aliphatic aramids. In addition, aramids exhibit high thermal stability, low creep, and good optical activity with fluorescence. Hence, aramids are found in advanced arenas for engineering thermoplastics such as transport applications, electroactive materials, films, bullet-proof body armor, smart materials, protective clothing, fibers, in nanocomposites as asbestos alternatives, cutting edge complexes in arming, high-temperature lining material, in space engineering, and more. The objective of this review is to make the field of aramids functionality more accessible to the materials science community, that is, scientists, academicians, and engineers.     

Polymeric composite systems modified with allotropic forms of carbon (review)

Most widely occurring classes of carbon nanoparticles used to create polymeric composite systems are considered. The possibility is demonstrated of using “polymer-carbon nanoparticles” composites for raising the level of mechanical properties of polymeric materials, creating friction units with improved tribological characteristics, developing new electrochemical, microelectronic, and optical devices, and modifying barrier properties of polymeric membranes. Methods for treatment of nanoparticles to provide their compatibility with polymeric matrices and preclude their aggregation are discussed.     

Achievements and Research Tasks for Poly(vinyl chloride) Ageing and Stabilization

Perspectives of PVC manufacture, not containing of labile groups in a backbone are considered. It will provide drastic increase of an intrinsic stability of polymeric products, possibility of PVC processing with the minimal contents or in total absence of stabilizers and other chemicals - additives and opportunity of creation of materials and products on a PVC basis with the essentially increased service life-time. Presented data allow to create rigid, semi-rigid and flexible (plasticized) materials and products with the minimal contents of chemicals - additives and increased life-time of their service at exploitation in natural and special conditions.     

High damping and mechanical properties of hydrogen-bonded polyethylene materials with variable contents of hydroxyls: Effect of hydrogen bonding density

Hydrogen bonding is considered to have significant effect on the interaction between polymeric chains and on the viscoelasticity of the polymeric materials. In this paper, we attempt to discuss the relationship between hydrogen bonding density and damping behavior and mechanical properties of polyethylene-based polymeric materials. For this reason, a series of pendant chain hydrogen bonding polymers(PCHBP) with different hydrogen bonding density(HBD) were prepared by quantitatively changing the content of pendent hydroxyl groups on the main chain of polyethylene. It was found that PCHBP with low HBD showed similar properties to polyethylene, indicating that the property of the materials was dependent mainly on the structure of the main chain. However, PCHBP with high HBD exhibited two tanδ peaks and a platform of loss modulus as well as a high storage modulus(about 400 MPa) at the second tanδ peak temperature, demonstrating that a polymeric material with high strength and damping properties was obtained. More importantly, the maximum of loss modulus showed a linear increase with the HBD, indicating that a higher HBD greatly improved the damping properties of the polymeric materials.     

Nanocarbon-Based Flame Retardant Polymer Nanocomposites

In recent years, nanocarbon materials have attracted the interest of researchers due to their excellent properties. Nanocarbon-based flame retardant polymer composites have enhanced thermal stability and mechanical properties compared with traditional flame retardant composites. In this article, the unique structural features of nanocarbon-based materials and their use in flame retardant polymeric materials are initially introduced. Afterwards, the flame retardant mechanism of nanocarbon materials is described. The main discussions include material components such as graphene, carbon nanotubes, fullerene (in preparing resins), elastomers, plastics, foams, fabrics, and film–matrix materials. Furthermore, the flame retardant properties of carbon nanomaterials and their modified products are summarized. Carbon nanomaterials not only play the role of a flame retardant in composites, but also play an important role in many aspects such as mechanical reinforcement. Finally, the opportunities and challenges for future development of carbon nanomaterials in flame-retardant polymeric materials are briefly discussed.     

Growth mechanism of soap-free polymerization of styrene investigated by AFM

To clarify the growth mechanism of polystyrene (PSL) particles in the soap-free polymerization, characteristics of not only particles but also polymeric materials floating in the bulk were investigated on the molecular scale by using atomic force microscope (AFM), where a cationic initiator V-50 is used to make the formed polymeric materials transfer on the mica plate in sampling. Our main attention here is to know the reason why the particle size increases with increasing initiator concentration in the production of PSL particles. The following are found. (1) As far as the initiators and monomers remain in the bulk solution, the polymeric materials are born in the bulk continuously, because of the slow decomposition rate of initiators. (2) The growth of particles at the early stage of t(r) > or = 0.75 h is considered to be attributable mainly to the particle swelling by absorbing monomers from the bulk. The rapid growth at the intermediate stage is due to the deposition of polymeric materials in the bulk on the particle surface and their simultaneous swelling by monomers in the bulk. (3) The reason why the particle size increases with increasing concentration of initiator is that the growth process is controlled by the deposition rate of polymeric materials in the bulk whose amount increases with the initiator concentration. (4) The particle size and the smoothness of particle surface depend on the relative concentration of initiators and monomers remained.     

Degradation issues of polymer materials used in railway field

Polymer materials used in railway field are degraded by environmental factors such as thermal, oxidative, photolytic, hydrolytic, and mechanical. The expected service life of the polymer materials used in railway field is approximately 20 years that is relatively long period for the polymer material; therefore, respective degradation factors should be well considered. Some of the degradation conditions indicate similar mechanism. The oxidative reaction was seen in every degradation conditions under air atmosphere. The hydrolytic reaction was mainly observed in chemical and biological degradations. The degradation behavior of the polymer material was analyzed by various methods. FTIR, thermal analysis (TG, DSC), and molecular weight determination were mainly applied for its purpose. However, the degradation mechanism of practical products made of polymer material was insufficiently studied and the exchange criteria of the products depended on the visual inspection without the suitable degradation analysis not only in the railway field but also in other commercial and industrial fields. In addition, most of the methods to analyze degradation of polymer material are performed on the standard specimen forms. For the installed product, some kinds of damage are generated through the sample collection process; therefore, the damaged products have to be exchanged for brand new ones or repaired totally to be used for more period. Moreover, it is hard to suspend the railway service for the degradation analysis of polymer products. From these backgrounds, the prospect of degradation analysis related to polymer materials used in railway field was proposed.