Influence of plasma pre-treatment of polytetrafluoroethylene (PTFE) micropowders on the mechanical and tribological performance of polyethersulfone (PESU)-PTFE and impact modified polyamide (PA66)-PTFE compounds

Polytetrafluoroethylene (PTFE), (CF2-CF2)n exhibits a low coefficient of friction (CoF, 0.07 - 0.15) and is therefore widely used as an additive in polymer compounds to improve their friction and wear properties. However, its applications in polymer compounds are limited due to the PTFE’s inherent poor chemical reactivity, low wettability and poor adhesion with other polymers preventing the establishment of good interfacial bonding. To overcome this, the work introduces plasma treatment of PTFE micropowders in a low-pressure 2.45 GHz microwave plasma reactor, using NH3 and H2 as process gasses to chemically modify their surface by introducing surface nitrogen and oxygen polar groups leading to more hydrophilic surfaces. The presence of these functional groups enhances the surface energy of the plasma treated PTFE and enhances the compatibility with thermoplastic polymers. It must be emphasised that nearly all the literature existing on the surface functionalisation of PTFE focuses on the PTFE films only. The first publication from this research work, in the group of three, reports on the effects of the H2, NH3 plasma processing time (2.5, 10 h), resulting defluorination (1.13 for NH3/10h, 1.30 for H2/10h as compared to 1.86 for pristine PTFE) and measurement of changes in wettability and crystallinity of the PTFE micropowders. The resulting plasma modified PTFE micropowders were further used as dry lubricants to enhance the tribological and mechanical properties of amorphous polyethersulfone (PESU) and semi-crystalline α-olefin-copolymer impact-modified polyamide 66 (PA66i) polymer compounds resulting in the next two publications. At the same loading levels (10wt%) of PTFE, prepared using twin-screw compounding, the pinon- disc tribological measurements of the PESU-PTFE compounds revealed a lowCoF from 0.55 for pristine PESU to 0.20 along with corresponding reduction in the wear rates from 5.75 x 10-06 mm3/Nm (pristine PTFE) to 4.70 x 10-06 mm3/Nm (for H2 treated PTFE) to 3.42 x 10-06 mm3/Nm (for NH3 treated PTFE). In the PA66i matrix, the wear rates of the pristine and plasma treated PTFE were observed to be similar for the sliding speeds up to 2 m/s. However, at the higher sliding speeds, the benefits of plasma treatment became more apparent. At the sliding speed of 3 m/s, the wear rate of pristine PTFE-PA66i compound was 1.1 x 10-06 (± 0.2) mm3/Nm whereas the wear rate of H2 treated PTFE was 0.7 x 10-06 (± 0.1) mm3/Nm and the wear rate of NH3 treated PTFE was 0.6 x 10-06 (± 0.1) mm3/Nm. These improvements in the tribological and mechanical properties have been ascribed to the enhanced dispersion of PTFE in the host matrix with the plasma processing introduced functional polar groups providing enhanced intermolecular bonding (as confirmed using Fourier transform infrared spectroscopy, differential scanning calorimetry and dynamic mechanical-thermal analysis) between the components. Therefore, the incorporation of functional groups into PTFE micro-powders by plasma treatment is an effective and efficient route for enhancing the mechanical and tribological properties of engineering polymer compounds such as PESU-PTFE and PA66i- PTFE offering significant cost and environmental benefits over the existing e- beam and wet chemical technologies

Pretreatments of fluoropolymers to enhance adhesion

The aim of the project was to gain a better understanding of the factors that affect adhesion of fluoropolymers. This was achieved by employing various analytical techniques to the treated and untreated polymers. The effects of novel pretreatments, and established treatments, on Polytetrafluoroethylene, PTFE, Poly (vinyl fluoride), PVF, and poly (vinylidene fluoride) PVdF, were characterised using: adhesion tests, X-ray photoelectron spectroscopy (XPS), including derivatisation reactions, Fourier Transform Infrared (FTIR), contact angles and scanning electron microscopy (SEM) For untreated PVF and PTFE it was found that a certain degree of adhesion improvement was achievable without any chemical modification of the surfaces. This was observed when the substrates were repeatedly bonded. It is proposed that weakly cohesive material was present in the polymers and these acted as weak boundary layers when bonded. Removal of weak boundary layers alone was found to be insufficient to obtain high adhesion with PTFE. Surface functionality, increased wettabiIity and favourable topography all contributed to the high bond strengths observed with 'Tetra-Etch' treated PTFE. 'Tetra-Etch' treatment is used commercially on PTFE but prior to this programme was unreported on PVF and PVdF. The treatment was effective at promoting adhesion for PVF though at a· much slower rate than for PTFE. Additional mechanisms to that for PTFE (Le. electron transfer) are proposed for the action of 'Tetra-Etch' on PVF. These are dehydrohalogenation through electron transfer and an elimination reaction. The same mechanisms are proposed for PV dF. Flame and Iow pressure plasma treatments·,w7re carried out on PVF and PTFE. Flame was found to be ineffective for PTFE but with PVF chemical modification (oxidation) occurred at the carbon/hydrogen sites. No defluorination was observed; this was in contrast to the mechanism of oxidation via plasmas on PVF, where defluorination, oxidation, ablation, and crosslinking may have all contributed to the high bond strength obtained. Certain plasma treatments were effective at improving the adhesion of PTFE but were slower and caused less modification. Removal of weak boundary layers was proposed as the major factor since oxidation was often slight. Reaction with solutions of potassium hydroxide (KOH), sodium hydroxide (NaOH) and lithium hydroxide (LiOH) were effective as adhesion pretreatments for PVF and PVdF but not for PTFE. For PVF and PVdF rates of reaction and chemical modification varied with time, temperature, molarity of solution and the nature of the solution i.e. aqueous or alcoholic. The greatest improvement in rate and effectiveness of the treatment for adhesion improvement was on the addition of a phase transfer catalyst to the aqueous solution. It was found for PVF that substantial surface oxidation could be achieved without improving the adhesion. It was suggested that oxidation occurred at sites present in a weakly cohesive layer. Mechanisms of the reactions were considered in terms of neucloephilic substitution and elimination; for PVF and PV dF both are likely. The mechanism of the phase transfer catalyst was investigated and found to be complex. It was found not to be simply a wetting agent but had inherent reactivity on its own. A combination of mechanisms was proposed

Nonthermal Plasma Technology as a Versatile Strategy for Polymeric Biomaterials Surface Modification: A Review

In modern technology, there is a constant need to solve very complex problems and to fine-tune existing solutions. This is definitely the case in modern medicine with emerging fields such as regenerative medicine and tissue engineering. The problems, which are studied in these fields, set very high demands on the applied materials. In most cases, it is impossible to find a single material that meets all demands such as biocompatibility, mechanical strength, biodegradability (if required), and promotion of cell-adhesion, proliferation, and differentiation. A common strategy to circumvent this problem is the application of composite materials, which combine the properties of the different constituents. Another possible strategy is to selectively modify the surface of a material using different modification techniques. In the past decade, the use of nonthermal plasmas for selective surface modification has been a rapidly growing research field. This will be the highlight of this review. In a first part of this paper, a general introduction in the field of surface engineering will be given. Thereafter, we will focus on plasma-based strategies for surface modification. The purpose of the present review is twofold. First, we wish to provide a tutorial-type review that allows a fast introduction for researchers into the field. Second, we aim to give a comprehensive overview of recent work on surface modification of polymeric biomaterials, with a focus on plasma-based strategies. Some recent trends will be exemplified. On the basis of this literature study, we will conclude with some future trends for research

Advances in Plasma Processes for Polymers

Polymerized nanoparticles and nanofibers can be prepared using various processes, such as chemical synthesis, the electrochemical method, electrospinning, ultrasonic irradiation, hard and soft templates, seeding polymerization, interfacial polymerization, and plasma polymerization. Among these processes, plasma polymerization and aerosol-through-plasma (A-T-P) processes have versatile advantages, especially due to them being “dry", for the deposition of plasma polymer films and carbon-based materials with functional properties suitable for a wide range of applications, such as electronic and optical devices, protective coatings, and biomedical materials. Furthermore, it is well known that plasma polymers are highly cross-linked, pinhole free, branched, insoluble, and adhere well to most substrates. In order to synthesize the polymer films using the plasma processes, therefore, it is very important to increase the density and electron temperature of plasma during plasma polymerization

High performance fibre reinforced fluoropolymers

Imperial Users onl

Friction Behavior of Engineering Polymers Treated by Atmospheric DBD Plasma

The frictional behavior of (PA6 E and PETP) engineering polymers commonly used in the industry were investigated implying 3D surface topography due to Dielectric Barrier Discharge (DBD) source, atmospheric cold plasma surface treatment and compared to the pristine surface results under the same test conditions. The 3D surface topography shows a decrease in the surface roughness after treatment and keeps good topographical stability with the function of time. The friction coefficient of treated samples were lower than the pristine one under “run-out” lubrication conditions in line with surface characterization results

White paper on the future of plasma science and technology in plastics and textiles

This is the peer reviewed version of the following article: “Uros, C., Walsh, J., Cernák, M., Labay, C., Canal, J.M., Canal, C. (2019) White paper on the future of plasma science and technology in plastics and textiles. Plasma processes and polymers, 16 1 which has been published in final form at [doi: 10.1002/ppap.201700228]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."This white paper considers the future of plasma science and technology related to the manufacturing and modifications of plastics and textiles, summarizing existing efforts and the current state‐of‐art for major topics related to plasma processing techniques. It draws on the frontier of plasma technologies in order to see beyond and identify the grand challenges which we face in the following 5–10 years. To progress and move the frontier forward, the paper highlights the major enabling technologies and topics related to the design of surfaces, coatings and materials with non‐equilibrium plasmas. The aim is to progress the field of plastics and textile production using advanced plasma processing as the key enabling technology which is environmentally friendly, cost efficient, and offers high‐speed processingPeer ReviewedPostprint (author's final draft

Polymer Processing and Surfaces

This book focuses on fundamental and applied research on polymer processing and its effect on the final surface as the optimization of polymer surface properties results in the unique applicability of these over other materials. The development and testing of the next generation of polymeric and composite materials is of particular interest. Special attention is given to polymer surface modification, external stimuli-responsive surfaces, coatings, adhesion, polymer and composites fatigue analysis, evaluation of the surface quality and microhardness, processing parameter optimization, characterization techniques, among others

Wettability and Other Surface Properties of Modified Polymers

Surface wettability is one of the crucial characteristics for determining of a material’s use in specific application. Determination of wettability is based on the measurement of the material surface contact angle. Contact angle is the main parameter that characterizes the drop shape on the solid surface and is also one of the directly measurable properties of the phase interface. In this chapter, the wettability and its related properties of pristine and modified polymer foils will be described. The wettability depends on surface roughness and chemical composition. Changes of these parameters can adjust the values of contact angle and, therefore, wettability. In the case of pristine polymer materials, their wettability is unsuitable for a wide range of applications (such as tissue engineering, printing, and coating). Polymer surfaces can easily be modified by, e.g., plasma discharge, whereas the bulk properties remain unchanged. This modification leads to oxidation of the treated layer and creation of new chemical groups that mainly contain oxygen. Immediately after plasma treatment, the values of the contact angles of the modified polymer significantly decrease. In the case of a specific polymer, the strongly hydrophilic surface is created and leads to total spreading of the water drop. Wettability is strongly dependent on time from modification

Carbon Fibre Reinforced Poly(vinylidene Fluoride)

The demand for oil in the world is expected to rise by 1.7% in the fourth quarter of 2012 compared to fourth quarter of 2011. In order to cater for this increasing demand, the oil and gas industry continues to explore and develop deep-sea oilfields where oil and gas risers and pipelines encounter extreme conditions. The combination of high pressure and temperature with aggressive media which contains of hydrocarbon, alkanes, acids, sour gas (H2S), and CO2, etc., requires superior material performance and durability. Conventional engineering materials, such as steel are heavy and require corrosion protection, which are currently used as risers, flowlines and choke and kill lines have reached their limits. This is because of the poor chemical resistance and damage tolerance and the high costs involved in supporting their own weight. This has motivated the industry to explore non-corroding and lighter alternative materials if deeper sea reservoirs are to be explored. One such material that has the potential to overcome such limitations thus enabling new design strategies for cost effective, weight and energy saving materials is fibre reinforced composites. The remarkable properties and the tailorability of fibre reinforcement along load paths to achieve excellent performance of the composites is an attribute not found in any other material. The aim of this research was to manufacture novel carbon fibre reinforced polyvinylidene fluoride (PVDF) composites by incorporating atmospheric plasma fluorination of the carbon fibres. Powder impregnation method was adapted for the manufacturing of continuous unidirectional (UD) carbon fibre reinforced PVDF composite prepregs. The resulting composite laminates were characterised through various macro-mechanical tests. The impact of atmospheric plasma fluorination of the carbon fibre on the tensile, flexural, short beam shear and tearing properties of the UD composites were investigated to determine whether the improvements observed in the single fibre model composite can be translated to macro-level composite laminates. Apart from this, the impact of combining both fibre and matrix modifications on the composite were studied and the preliminary results on micro-mechanical scale are presented. Finally, composite pipe structures, made by filament winding technique using unidirectional carbon fibre reinforced PVDF composite prepregs onto a pure PVDF liner were fabricated, and characterised with respect to its mechanical properties