Electrical insulation properties of silicone rubber under accelerated corona and thermal aging

A contactless method based on energy shift of high-energy cut-off of the x-ray bremsstrahlung, the so-called Duane Hunt Limit and a conventional low voltage electrical technique (three-probes technique) is applied on thermal and corona aged silicone rubber (SiR) to measure, respectively, the surface potential, V_s, and the surface resistivity, ρ_s. The effect of aging on these quantities, representing the dielectric properties, is studied. The results are highly reproducible and highlight a good correlation between V_s and ρ_s. It was observed that thermal aging combined with electrical aging deteriorates more the electrical properties of the polymer than thermal aging alone. Explanations for electrical characteristics (V_s, ρ_s) change with aging are supported by attenuated total reflection Fourier transform infrared spectroscopy spectra analysis and a chemical mechanism of aging in three steps (i.e., oxidation-polycondensation, degradation, and thermal cracking). The surface degradation of the polymer is revealed by images of surface morphology obtained by using scanning electron microscopy (SEM). Roughness is greater for combined thermal and corona aging mode compared to thermal aging alone. In addition, the surface degradation of SiR polymer is confirmed by the loss of its hydrophobicity.     

Tracking the hydrophobicity recovery of PDMS compounds using the adhesive force determined by AFM force distance measurements

Polydimethylsiloxane (PDMS) materials show the unique phenomenon that when exposed to electrical discharge, such as corona discharge, their hydrophobic surface becomes hydrophilic. However, after a certain relaxation time they gradually regain their hydrophobicity. In this study the adhesive force obtained by AFM force distance measurements using a hydrophilic Si₃N₄ probe is used to track the recovery of the hydrophobicity. The time constant of the recovery can be determined by measuring the adhesive force as a function of the recovery time after corona exposure. It is shown how these time constants can be used to monitor the recovery rate as a function of corona treatment time for both filled and unfilled PDMS compounds.     

Kinetic analysis and modelling of thermal degradation of perspex (PMMA) and perspex blend plastic waste

The thermal decomposition of pure perspex and a mixture of 50% perspex and 50% poly(ethylene terephthalate; PET) was carried out between 295 and 325°C using a thermogravimetric analyser (TGA) in air and nitrogen (N₂) atmosphere. The weight losses of decomposition products were measured during these experiments. The thermal degradation process is slower in inert atmosphere than air, where oxidation reaction expedites the decomposition process. Kinetic rate constants (k), pre‐exponential factor (A) and activation energy (E) for both pure prespex and a blend of perspex/PET were calculated for both air and N₂ conditions. The thermal degradation process followed a third‐order reaction in air and second‐order in N₂. A second‐order (n = 2) model for the pyrolytic process based on simultaneous reactions was developed using experimental data for pure and blend. The pyrolytic products are gases, liquids, waxes, aromatics and char, which can be ultimately used as raw material and fuel in various applications. It is important to note that the addition of PET to perspex was found to suppress/inhibit the decomposition of perspex compared with pure perspex. Pre‐exponential factor (A) and activation energy (E) values support such an observation. © 2012 Canadian Society for Chemical Engineering     

Use of different size grids to control the surface chemistry of plasma‐polymerized acrylic acid films in a hybrid discharge

The surface chemistry of plasma‐polymerized acrylic acid (ppAc) films were controlled in a two‐stage (primary and processing) hybrid radio frequency (RF) discharge by changing the grid wire spacing (d_s). Two regions were defined in terms of d_s with respect to Debye length (λ_d) in the primary chamber at the grid to control the electron temperature (T_e) and surface chemistry of the ppAc films deposited in the processing chamber. A higher T_e (>3 eV) in the processing plasma was possible for d_s > λ_d, whereas decreasing d_s relative to λ_d reduced T_e. X‐ray photoelectron spectroscopy was used to characterize the ppAc films deposited on a glass substrate. The ppAc films surface characterization showed the maximum proportion of carbon atoms as carboxylic/ester [C(?O)OX] functionalities in C1s at the surface of films for the grid with d_s ≈ λ_d. The proportion of carbon atoms as ? [C(?O)OX] and COX in C1s at the surface decreased when d_s decreased relative to λ_d. The proportion of carbon atoms as carbonyl (C?O) at the film surface showed very good stability for all of the d_s values explored in this study. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2219–2224, 2007     

Surface energy of corona treated PP,PE and PET films,its alteration as function of storage time and the effect of various corona dosages on their bond strength after lamination

The aim of this study was to analyze how corona dosages above recommended levels affect film surface energy and hydrophobic recovery of such treated film surfaces as well as laminate bond strength of laminates made of these films. The adhesive for lamination was a polyurethane‐adhesive with a dry film thickness of ～5 µm. Polar and dispersive parts of the surface energy were measured frequently according to DIN 55660‐2 (Owens–Wendt–Rabel‐and‐Kaelble method) for up to 140 days after corona treatment. The corona dosage had a value of up to 280 W min/m². Laminate bond strength was measured according to DIN 55543‐5. The effect of corona treatment was highest for low‐density polyethylene (PE‐LD) films, mean for biaxial‐oriented polypropylene (PP‐BO) films, and lowest for biaxial‐oriented poly(ethylene terephthalate) (PET‐BO) films. With increasing storage time, surface energy decreased, as expected. The higher the effect of corona treatment, the faster the polar part of surface energy decreased. At PE‐LD, laminate bond strength increased with a higher corona dosage from 0.05 to 8.87 mN/15 mm, whereas at PET‐BO and PP‐BO laminate bond strength was so high that samples teared before delamination during bond strength testing. By our results is shown that corona dosages above recommended levels resulted in higher laminate bond strength. Only at PP‐BO a reduction of laminate bond strength due to “overtreatment” was be observed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45842.     

Chitosan and N‐carboxymethylchitosan: I. The role of N‐carboxymethylation of chitosan in the thermal stability and dynamic mechanical properties of its films

Chitosan (degree of deacetylation of 90.2%) and N‐carboxymethylchitosan (N‐CMCh) (degree of substitution of 18.5%) were analyzed using thermogravimetric analysis in order to determine their thermal stability. Also, their films were evaluated using scanning electron microscopy (SEM) and mechanical and dynamic mechanical analysis (DMA). Both polymers showed a thermal degradation peak at T_m ～ 250 °C, with T_onset and weight loss of 175 °C and 62% and 190 °C and 35% for chitosan and N‐CMCh, respectively. N‐CMCh showed a second thermal degradation peak at T_m = 600 °C, with an additional weight loss of 25%. Kinetic thermal analysis showed a slower process of degradation at 100 °C for N‐CMCh compared with chitosan, and an activation energy 13 times higher for the former, confirming the higher stability of N‐CMCh. Analysis of chitosan and N‐CMCh films showed that the latter support a high tension, with lower elasticity, and, as revealed by DMA, N‐CMCh has a more compact film structure, with a crossing arrangement of N‐CMCh fibers, as compared with the chitosan films which were determined from SEM analysis to have fibers in one direction only. Copyright © 2006 Society of Chemical Industry     

Synthesis and Performance Evaluation of CO2/N2 Switchable Tertiary Amine Gemini Surfactant

A type of switchable tertiary amine Gemini surfactant, N,N′‐di(N,N‐dimethyl propylamine)‐N,N′‐didodecyl ethylenediamine, was synthesized by two substitution reactions with 3‐chloro‐1‐(N,N‐dimethyl) propylamine, bromododecane and ethylene diamine as main raw materials. The structure of the product was characterized by FTIR and ¹H‐NMR. We also investigated the surface tension when CO₂ was bubbled in different concentrations of surfactant solution and the influence of different CO₂ volumes on surface tension under a constant surfactant concentration. Finally the surface tension curve and the related parameters were acquired by surface tension measurements. The experimental results showed that the structure of the synthesized compounds were in conformity with the expected structure of the surfactant, and displayed a better surface activity after bubbling CO₂. The critical micelle concentration (CMC) surface tension at CMC (γ_cmc) pC₂₀ (negative logarithm of the surfactant's molar concentration C₂₀, required to reduce the surface tension by 20 mN/m) surface excess (Γ_max) at air/solution interface and the minimum area per surfactant molecule at the air/solution interface (A_min) were determined. Results indicate that the target product had good surface activity after bubbling CO₂.     

Corona treatment of isotactic polypropylene in nitrogen and carbondioxide

Corona discharge treatment of isotactic polypropylene surfaces in N₂ and CO₂ was investigated by contact angle measurements and ESCA. The electrical characteristics of the discharges as well as the influence of indirect parameters (moment of air contact and ageing time) and direct parameters (applied charge, electrical field strength and film temperature) on the surface modification were determined. These investigations showed that electrons, emitted by photo effect are the dominant charge carriers and the main cause of surface activation. The active species in the surfaces (presumably radicals) can either perform crosslinking and H-abstraction or react with the discharge gas. In the N₂-discharge the polymer radicals can only react with atomic or excited nitrogen whereas in CO₂ they also react with ground state molecules. If the samples are brought into air contact after discharge leftover radicals are oxidized by atmospheric oxygen. In addition a UV-radiation causing activation in a surface layer was found. The bulk of the polymer is not influenced by corona discharge.     

Multifunctional properties of polyester fabrics modified by corona discharge/air RF plasma and colloidal TiO2 nanoparticles

In this study the possibility of tailoring the textile nanocomposite materials based on the polyester fabric and TiO₂ nanoparticles that can simultaneously provide desirable level of antibacterial activity, UV protection, and self‐cleaning effects with long‐term durability was investigated. To enhance the binding efficiency of colloidal TiO₂ nanoparticles, the surface of polyester fabrics was activated by low‐pressure RF air plasma, and corona discharge at atmospheric pressure. Obtained functionalized textile materials provided maximum antibacterial efficiency against gram‐negative bacterium E. coli. High values of UV protection factor (UPF) indicate the maximum UV blocking efficiency (50+) of these fabrics. The results of self‐cleaning test with blueberry juice stains and photodegradation of methylene blue in aqueous solution confirmed excellent photocatalytic activity of TiO₂ nanoparticles deposited on the fiber surface. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Balance of mechanical and electrical performance in polyimide/nano titanium dioxide prepared by an in‐sol method

Hybrid polyimide (PI)/titanium dioxide (TiO₂) films were prepared by in situ polymerization and sol–gel and in‐sol methods (where in‐sol method indicates that in situ polymerization and the sol–gel method were used in the same samples). The mechanical and electrical properties were found to be sensitive to the processing methods and the dispersion of nano titanium dioxide (nano‐TiO₂) in the PI matrix. For the PI/TiO₂ films prepared by the in situ polymerization method, their tensile strength increased with increasing TiO_{2‐in situ} (“TiO_{2‐in situ}” is “the TiO₂ nano‐particles prepared by in situ polymerization method”) concentration. However, the optimal corona lifetime of the PI/TiO₂ films was 15 min at 20 kHz and 2 kV because of poor dispersion. For the PI/TiO₂ films prepared by the sol–gel method, the corona lifetime reached 113 min because of superior dispersion and a tensile strength of about 19.63 MPa. A balance of mechanical and electrical performances was achieved with the in‐sol method. The corona‐resistant life of the PI/TiO₂ films was 43 min, which was about six times longer than that of the neat PI. Their tensile strength was 83.5 MPa; these films showed no decrease in this value compared with the pure PI films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44666.     

Surface graft copolymerization of 2‐hydroxyethyl methacrylate onto low‐density polyethylene film through corona discharge in air

The corona discharge technique was explored as a means of forming chemically active sites on a low‐density polyethylene (LDPE) film surface. The active species thus prepared at atmospheric pressure in air was exploited to subsequently induce copolymerization of 2‐hydroxyethyl methacrylate (HEMA) onto LDPE film in aqueous solution. The results showed that with the corona discharge voltage, reaction temperature, and inhibitor concentration in the reaction solution the grafting degree increased to a maximum and then decreased. As the corona discharge time, reaction time, and HEMA concentration in the reaction solution increased, the grafting degree increased. With reaction conditions of a 5 vol % HEMA concentration, 50°C copolymerization temperature, and a 2.0‐h reaction time, the degree of grafting of the LDPE film reached a high value of 158.0 μg/cm² after treatment for 72 s with a 15‐kV voltage at 50 Hz. Some characteristic peaks of the grafted LDPE came into view at 1719 cm^?1 on attenuated total reflectance IR spectra (C?O in ester groups) and at 531 eV on electron spectroscopy for chemical analysis (ESCA) spectra (O_1s). The C_1s core level ESCA spectrum of HEMA‐grafted LDPE showed two strong peaks at ～286.6 eV (? C ? O? from hydroxyl groups and ester groups) and ～289.1 eV (O?C ? O? from ester groups), and the C atom ratio in the ? C? O? groups and O?C? O groups was 2:1. The hydrophilicity of the grafted LDPE film was remarkably improved compared to that of the ungrafted LDPE film. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2881–2887, 2001     

Preparation of transparent PMMA/Fe(IO3)3 nanocomposite films from microemulsion polymerization

Polymethyl methacrylate (PMMA)/Fe(IO₃)₃ nanocomposite thin films are obtained by in situ particle generation in microemulsions and subsequent photopolymerization of a mixture containing methyl methacrylate, trimethylolpropane triacrylate, and crystallized iron iodate (Fe(IO₃)₃) nanorods. Hyper‐Rayleigh scattering measurements combined with X‐ray diffraction, transmission electron microscopy, and dynamic light scattering are first used to probe in situ the crystallization kinetics of iron iodate nanorods in water‐in‐oil microemulsions prepared with methyl methacrylate as the oil phase and marlophen NP12 as a surfactant. Trimethylolpropane triacrylate is then added as a crosslinker before spin‐coating. Films are deposited on glass substrates for the nonlinear optical characterizations and on silicon wafers for the piezoelectric and mechanical measurements. Nanocomposite films treated by corona discharge are finally characterized through optical microscopy, laser Doppler vibrometry, and Brillouin spectroscopy. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1203‐1211, 2013     

Plasma surface treatments of melt‐extruded sheets of poly(L‐lactic acid)

Poly(L‐lactic acid) sheets, prepared by melt extrusion, were treated with O₂?, He?, and N₂?plasmas generated in radio frequency (RF) at 13.56 MHz. Atmospheric pressure discharge at 20 kHz in helium was also applied to the modification of the sheets. The surface of the PLLA sheets was etched to form the characteristic morphology, and the patterns were different depending on the type of plasma. Polar groups composed of –COOH and –OH were incorporated by plasma treatment, and the surface became wettable. Surface modification became effective after a short treatment period, e.g., 30 seconds. Receding contact angles (θ_r) changed remarkably, and the surface properties were closely related to the increase in the surface energy of the polar contribution (γ_s^p). Biodegradation of the poly(L‐lactic acid) sheets was not enhanced practically, even though the surface became hydrophilic after plasma treatment.     

Preparation and characterization of the copolymer containing N‐pyridyl bi(methacryl)imide unit

The copolymer of methacrylic acid anhydride and N‐2‐pyridyl bi(methacryl)imide was prepared based on the reaction of polymethacrylic acid with 2‐pyridylamine. The molecular structure was characterized by ¹H‐NMR, FTIR, UV–Vis, and circular dichroism techniques. The physical properties of polymethacrylic acid change significantly after an introduction of 6 mol % N‐2‐pyridyl bi(methacryl)imide unit. In particular, the thermal degradation of the polymer was systematically studied in flowing nitrogen and air from room temperature to 800°C by thermogravimetry at a constant heating rate of 10°C/min. In both atmospheres, a four‐stage degradation process of the copolymer of methacrylic acid anhydride and N‐2‐pyridyl bi(methacryl)imide was revealed. The initial thermal degradation temperature T_d, and the first, second, and third temperatures at the maximum weight‐loss rate T_dm1, T_dm2, and T_dm3 all decrease with decreasing sample size or changing testing atmosphere from nitrogen to air, but the fourth temperature at the maximum weight‐loss rate T_dm4 increases. The maximum weight‐loss rate, char yield at elevated temperature, four‐stage decomposition process, and three kinetic parameters of the thermal degradation were discussed in detail. It is suggested that the copolymer of methacrylic acid anhydride and N‐2‐pyridyl bi(methacryl)imide exhibits low thermal stability and multistage degradation characteristics. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1673–1678, 2002     

Studies of the moisture‐sensitive shape memory effect of pyridine‐containing polyurethanes

Shape memory polymers have been much researched in recent years. In the work reported, moisture‐sensitive shape memory effects (SMEs) of novel pyridine‐containing shape memory polyurethanes (Py‐SMPUs) were investigated systematically. The results show that the strain recovery start immersion time (t_s), strain recovery immersion time (t_r) and final strain recovery immersion time (t_e) are prolonged with a decrease of relative humidity as well as a decrease of temperature. The final strain recovery decreases with a decrease of relative humidity as well as an increase of temperature. The key component affecting the moisture‐sensitive SME is the N,N‐bis(2‐hydroxyethyl)isonicotinamide (BINA) unit. The lower limit of BINA content for Py‐SMPUs to exhibit a good moisture‐sensitive SME is 30 wt%. The addition of diphenylmethane diisocyanate (MDI) and 1,4‐butanediol (BDO) enhances the moisture‐sensitive shape recovery. The final shape recovery decreases with a decrease of BINA content or an increase of MDI–BDO content. In addition, t_s, t_r and t_e become shorter in the Py‐SMPUs with higher BINA content or with lower MDI‐BDO content. Copyright © 2011 Society of Chemical Industry     

Sensitivity analysis pertaining to effective parameters on electrohydrodynamic drying of porous shrinkable materials

Abstract

A phenomenological computational fluid dynamics model was developed to simulate drying process of a porous body using electric field corona discharge. The set of coupled nonlinear partial differential equations were solved simultaneously and compared with the experimental findings in the literature. The relative error of the corona wind velocity compared to the experiments was less than 1%. The main gradients of the EHD volume force and corona wind were close to the discharge electrode. Moreover, for no inlet air, the corona wind velocity and field distribution indicated the existence of vortices as the main factor for enhancing mass transfer during the drying process. At a constant air velocity, increase in the voltage caused increasing the corona velocity. In addition, by increasing the air velocity to some extent, the corona velocity first increased and then started to drop. As a result, for any voltage and electrode distance from the surface, an optimum air velocity could be determined. Due to the sweep impact of the primary air flow and moving the ionized molecules to the outside, the drying rates at air velocity of 1?m s^?1 were higher than those for air velocity of 1.5?m s^?1. Applying an intake air flow also altered the optimal electrode velocity from the surface due to the occurred change in the corona discharge. Therefore, is concluded that the severity of mass humidity changes is affected by the applied voltage, electrode distances from the surface, temperature, and the intake air velocity.     

Surface tailoring of an ethylene propylene diene elastomeric terpolymer via plasma‐polymerized coating of tetramethyldisiloxane

In the research presented here, we explore the use of a low‐energy plasma to deposit thin silicone polymer films using tetramethyldisiloxane (TMDSO) (H(CH₃)₂? Si? O? Si? (CH₃)₂H) on the surface of an ethylene propylene diene elastomeric terpolymer (EPDM) in order to enhance the surface hydrophobicity, lower the surface energy and improve the degradation/wear characteristics. The processing conditions were varied over a wide range of treatment times and discharge powers to control the physical characteristics, thickness, morphology and chemical structure of the plasma polymer films. Scanning electron microscopy (SEM) shows that pore‐free homogeneous plasma polymer thin films of granular microstructure composed of small grains are formed and that the morphology of the granular structure depends on the plasma processing conditions, such as plasma power and time of deposition. The thicknesses of the coatings were determined using SEM, which confirmed that the thicknesses of the deposited plasma‐polymer films could be precisely controlled by the plasma parameters. The kinetics of plasma‐polymer film deposition were also evaluated. Contact angle measurements of different solvent droplets on the coatings were used to calculate the surface energies of the coatings. These coatings appeared to be hydrophobic and had low surface energies. X‐ray photoelectron spectroscopy (XPS) and photoacoustic Fourier‐transform infrared (PA‐FT‐IR) spectroscopy were used to investigate the detailed chemical structures of the deposited films. The optimum plasma processing conditions to achieve the desired thin plasma polymer coatings are discussed in the light of the chemistry that takes place at the interfaces. Copyright © 2004 Society of Chemical Industry     

Structural estimation of particle arrays at air–water interface based on silica particles with well‐defined and highly grafted poly(methyl methacrylate)

Silica nanoparticles with well‐defined, highly grafted dense poly(methyl methacrylate) (MMA) were prepared by surface‐initiated activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) of methyl methacrylate with an initiator‐fixed silica particle in the presence of air. Two different polymerizations of MMA were carried out under the same conditions using tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) and N,N,N′,N′,N″‐pentamethyldiethylene‐triamine (PMDETA) as the ligand, respectively. In the CuCl₂/PMDETA system, polymerization appeared to be more controlled with a lower polydisperisty compared with the CuCl₂/Me₆TREN system. The monolayer of these particles was formed at the air–water interface using Langmuir‐Blodgett (LB) technique. Multilayers of the particles were fabricated by repetition of LB depositing. A surface pressure–area (π–A) measurement and SEM observation were used to characterize the particle arrays. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

A study on thermal behavior of a poly(VDF‐CTFE) copolymers binder for high energy materials

This article describes a study on thermal behavior of poly(vinylidene fluoride‐chlorotrifluoroetheylene) [poly(VDF‐CTFE)] copolymers as polymeric binders of specific interest for high energy materials (HEMs) composites by thermal analytical techniques. The non‐isothermal thermogravimetry (TG) for poly (VDF‐CTFE) copolymers was recorded in air and N₂ atmospheres. The results of TG thermograms show that poly(VDF‐CTFE) copolymers get degrade at lower temperature when in air than in N₂ atmosphere. In the derivative curve, there was single maximum degradation peak (T_max) indicating one‐stage degradation of poly(VDF‐CTFE) copolymers for all the samples. The other thermal properties such as glass transition temperature (T_g) and degradation temperature (T_d) for poly(VDF‐CTFE) copolymers were measured by employing differential scanning calorimeter (DSC) technique. The kinetic parameters related to thermal degradation of poly(VDF‐CTFE) copolymers were investigated through non‐isothermal Kissinger kinetic method using DSC method. The activation energies for thermal degradation of poly(VDF‐CTFE) copolymers were found in a range of 218–278 kJ/mol. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013