Formation Of Polar Groups Research Articles

UV exposure to PET microplastics increases their downward mobility in stormwater biofilters undergoing freeze-thaw cycles

Stormwater conveys microplastics and accumulates them in stormwater treatment systems such as biofilters, where they are exposed to sunlight and natural weather conditions such as drying, freezing, and wetting cycles....

Investigating the aging mechanism of asphaltene and its dependence on environmental factors through AIMD simulations and DFT calculations

To understand the complex aging mechanism of asphalt and its dependence on environmental factors, the chemical reactivity of asphaltene during aging under different environmental conditions was studied through first-principles molecular simulations and density functional theory calculations. The aging of asphaltene was demonstrated to involve a series of subreactions along different pathways on the asphaltene molecules, including hydrogen abstraction from carbon, formation of polar groups, aromatization of cycloalkanes, and homolysis of side chains. These subreactions occurred with different free-energy barriers and, therefore, had different kinetic rates. Asphaltene aging was found to be slightly accelerated in the presence of water owing to the improved electron transfer ability of the asphaltene molecule in an aqueous solvent. Under ultraviolet radiation, the asphaltene molecule transitioned to an excited state with an excitation energy of 348.7 kJ/mol, significantly increasing its aging rate. This work bridges the gap between electronic-scale modeling and diversified experimental observations related to asphalt aging and is expected to provide theoretical guidance for strategies to prevent or delay the aging-induced failure of asphalt pavements.

Surface Modification of Polypropylene by Atmospheric Pressure Plasma

In this investigation, we studied the influence of atmospheric pressure plasma treatment on the surface properties of polypropylene (PP). The PP samples were treated for various durations using a gliding arc plasma source with air as a working gas. The formation of polar groups (–OH and C = O) on the PP surface after plasma treatment was evaluated and analyzed using Raman spectroscopy and attenuated total reflection–Fourier transform infrared spectroscopy. The contact angle was measured using polar and non-polar liquids to obtain the polar and dispersive components as well as the surface free energy of the PP before and after treatment. A sevenfold increase after treatment was observed for the polar component, while hydrophobicity decreased 73% after treatment. Finally, changes in topography were observed using atomic force microscopy (AFM) analysis before and after plasma treatment. AFM images showed that under atmospheric treatment, the PP surface underwent etching, reducing the surface roughness. Microhardness measurements of the films also revealed significant changes in mechanical properties after plasma treatment.

Photochemical transformation of diketone dopants in polyester matrices: Effect of dopants concentration and polyester structure on changes in molecular characteristics and hydrolysis of the matrices

Photochemical transformations of photoactive diketone derivatives, 1,2-diphenylethane-1,2-dione (benzil, BZ) and 1,4-bis(benzoylcarbonyl)benzene (bisbenzil, BIS), and the effects of their transformations on changes in the molecular characteristics and hydrolytic properties of poly(ε-caprolactone) (PCL) and polylactide (PLA) matrices are reported. Studies were performed in a broad dopant concentration range of 0.2–7.5 wt%. Structural changes were observed by FTIR spectroscopy. FTIR spectroscopy proved the progressive transformation of BZ to benzoyl peroxides and, in the case of PCL, the formation of polar groups. Changes in molecular characteristics were observed in GPC traces. Irradiation of the doped polymer films at λ > 400 nm under an air atmosphere resulted mainly in the degradation of the polymer matrices. Additionally, high dopant concentrations in PCL led to partially crosslinked structures with gel contents up to 15%. The photochemical transformation of dopants had a large impact on the PCL matrices compared to that of the PLA matrices. A subsequent hydrolysis process was investigated by determining the extractable products as well as using GPC. Hydrolysis of irradiated PCL samples showed a significant acceleration of hydrolysis compared to that of nonirradiated samples. Furthermore, the hydrolysis rate gradually increased with increasing dopant concentration. The PCL crosslinking and degradation is adjustable by the type of dopant, concentration of dopant and intensity of light during irradiation of PCL. In contrast, a photochemical pretreatment had no observable effect on the hydrolysis of PLA under the investigated conditions.

PLASMA-ETCHING AND MODIFICATION OF POLYETHYLENE FOR IMPROVED SURFACE STRUCTURE, WETTABILITY AND OPTICAL BEHAVIOR

In the present paper, the surface modification of low-density polyethylene (LDPE) polymer is done by plasma-etching to tune its surface structure, wettability and optical behavior to make it useful for technical applications. For this purpose, two gasses (N[Formula: see text] and (O[Formula: see text] are used as the discharge precursors in a home-built plasma reactor. The plasma-treated LDPE surface etch-rate (control other surface properties) is high at the beginning and slows down as the treatment time increases due to surface restructuring. The etched surfaces are analyzed by scanning electron microscopy (SEM), which indicate greater surface changes due to O2plasma compared to that of N2. Also, the surface hardness is slightly low at the first treatment time and increases rapidly at higher exposure durations. Besides, the friction coefficient is significantly changed by plasma treatment, suggesting the formation of cohesive surface skin. The obtained X-ray diffraction (XRD) patterns show that the plasma-treated LDPE samples suffer disordering and structural changes which increase with raising the treatment duration. Surface restructuring is attributed to the combined effects of active species (from plasma) bombardments and surface oxidation. Also, the surface chemistry changes are evaluated using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy which reveals chain scission after N2plasma treatment. Whereas, the O2plasma-treated samples suffer surface oxidation and formation of polar groups which offer some surface oxidation coatings. Furthermore, the surface wettability has been determined by the sessile drop method and shows enhancement upon plasma treatment due to the combined influence of surface chemistry and morphology. Also, the surface free energy (SFE) and adhesion are found to increase with the plasma exposure time due to surface activation. The optical behavior of LDPE is studied using ultraviolet–visible (UV–Vis) spectrophotometer which indicates that the optical bandgap performance depends on the amorphous or crystalline nature of the polymer. Also, the conjugated carbon atoms were examined and correlated to the reduced bandgap. In conclusion, the studied home-built glow discharge plasma reactor could be utilized efficiently to tune polymer surface properties to be used in high technology applications.

Influence of atmospheric pressure plasma jet and diffuse coplanar surface barrier discharge treatments on wood surface properties: A comparative study

Beech and larch substrates were successfully treated by an atmospheric pressure plasma jet (APPJ) or a diffuse coplanar surface barrier discharge (DCSBD) system. Applying both technologies on wood, more hydrophilic properties were achieved, potentially by the degradation of hydrophobic extractives, the generation of polar functional groups and a modification of surface roughness. Comparing both plasma systems, the hydrophilization effect was stronger using the APPJ. The formation of polar groups on the surface was detected by X–Ray photoelectron spectroscopy. Investigated by scanning electron microscopy, APPJ further showed a more distinct impact on surface morphology compared to DCSBD. Following natural aging, plasma treatment effects such as hydrophilicity were partially reduced and the recovery was more pronounced for larch wood compared to beech.

Dielectric properties of UV-irradiated ultrathin polysulfone films revealed by surface plasmon resonance method

ABSTRACTThe surface plasmon resonance research of manufactured highly homogeneous ultrathin polysulfone films was performed, which were exposed to the short-wave (254 nm) UV irradiation of various durations. Surprisingly, the resonance incident angle and dielectric constant increase after short-term UV irradiation before the ordinary decrease caused by usual polymer degradation. The experimental results are ascribed to the formation of polar groups leading to orientation of chain fragments of intermediate length followed by their breaking and formation of mobile short fragments under longer times of irradiation.

RF plasma cleaning of silicon substrates with high-density polyethylene contamination

Upon contact with a polymeric material, microparticles from the polymer may adhere to a silicon (Si) substrate during device processing. The adhesion contaminates the surface and, in turn, leads to defects in the fabricated Si-based microelectronic devices. In this study, Si substrates with artificially induced high-density polyethylene (HDPE) contamination was exposed to 13.56 MHz radio frequency (RF) plasma utilizing argon and oxygen gas admixtures at a power density of 5.6 W/cm2 and a working pressure of 110 Pa for up to 6 min of treatment. Optical microscopy studies revealed the removal of up to 74% of the polymer contamination upon plasma exposure. Surface free energy (SFE) increased owing to the removal of contaminants as well as the formation of polar groups on the Si surface after plasma treatment. Atomic force microscopy scans showed a decrease in surface roughness from 12.25 nm for contaminated samples to 0.77 nm after plasma cleaning. The smoothening effect can be attributed to the removal of HDPE particles from the surface. In addition, scanning electron microscope images showed that there was a decrease in the amount of HDPE contaminants adhering onto the surface after plasma exposure.

Generation of Hydrogen through the Reaction between Plasma‐Modified Aluminum and Water

AbstractOne of the main challenges related to hydrogen energy technologies is hydrogen storage in a safe and economically reasonable way. A promising solution could be related to the use of aluminum or its alloys to reduce water to form hydrogen when needed. The aluminum–water reaction is thermodynamically favorable, but does not proceed due to the passivation of the aluminum surface by the protective aluminum oxide layer, which prevents water molecules from coming into direct contact with metal particles. Herein, the surface of aluminum particles was modified by using a low‐temperature plasma‐activation approach. Such a modification induces a hydrophilicity effect and the modified aluminum powder sinks instantly in water, whereas unmodified powder floats on the top of the water. The plasma‐based activation technology is also discussed in detail. The structure and morphology of the samples were characterized by using SEM, energy‐dispersive X‐ray spectroscopy, and XRD. BET surface area analyses were also performed. The elemental composition on the nanoscale level and formation of polar groups were experimentally investigated by using X‐ray photoelectron spectroscopy. Amounts of oxygen/hydrogen were measured by using the inert‐gas fusion method. Tests show that hydrogen production starts after 1 min of aluminum powder immersion into slightly alkaline water and continues for up to 20 min. The reaction by‐product is environmentally friendly and could be used for the production of aluminum oxide.

Functionalization of polyolefins via the reaction of ozone with double bonds

Polar groups are introduced into polyolefin chains via the postpolymerization polymer-analogous transformations using the ozonolysis of side ethylidene groups of ethylene (propylene) copolymers with the cyclic comonomer 5-ethylidene-2-norbornene. The copolymers are synthesized using ansa-zirconocene catalysts Me2Si[Ind]2ZrCl2/MAO, Et[Ind]2ZrCl2/MAO and Et[IndH4]2ZrCl2/MAO, which provide insersion of the cyclic monomer into the polymer chain without ring opening. The study of number-average molecular mass and compositions of homo- and copolymers of ethylene and propylene with 5-ethylidene-2-norbornene confirms a high selectivity of the ozonolysis of unsaturated double bonds of polyolefins. The formation of polar groups in the ozonized ethylene and propylene copolymers with 5-ethylidene-2-norbornene is proved by IR and Raman spectroscopy. The thermophysical characteristics of the initial and ozonized copolymers are compared.

Photochemically promoted degradation of poly(ɛ-caprolactone) film

Poly(ɛ-caprolactone) (PCL) films were doped with photoactive 1,2-diphenylethane-1,2-dione (benzil, BZ), and the effect of the photochemical transformation of benzil on the molecular characteristics of the PCL films and the rate of PCL hydrolysis was studied. Both crosslinking and degradation of the PCL film were observed during irradiation of the PCL/BZ films. Irradiation of a PCL/BZ film at λ > 400 nm under an air atmosphere resulted in a decrease of the average molecular weight (Mn) of PCL to approximately one half, while formation of polar groups and an increase in the hydrophilicity of the PCL film were observed. Moreover, a subsequent hydrolytic test showed a significant increase in the hydrolytic degradation rate of the PCL/BZ film in comparison with non-irradiated or irradiated PCL films without doped benzil. Using benzil as a dopant in the PCL matrix can allow adjusting the degradation rate of PCL, what can be very important from both environmental and biomedical perspectives.

Low Pressure DC Glow Discharge Air Plasma Surface Treatment of Polyethylene (PE) Film for Improvement of Adhesive Properties

The present work deals with the change in surface properties of polyethylene (PE) film using DC low pressure glow discharge air plasma and makes it useful for technical applications. The change in hydrophilicity of the modified PE film surface was investigated by measuring contact angle and surface energy as a function of exposure time. Changes in the morphological and chemical composition of PE films were analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The improvement in adhesion was studied by measuring T-peel and lap-shear strength. The results show that the wettability and surface energy of the PE film has been improved due to the introduction of oxygen-containing polar groups and an increase in surface roughness. The XPS result clearly shows the increase in concentration of oxygen content and the formation of polar groups on the polymer surface. The AFM observation on PE film shows that the roughness of the surface increased due to plasma treatment. The above morphological and chemical changes enhanced the adhesive properties of the PE film surfaces, which was confirmed by T-peel and lap-shear tests.

Controlling in-line the energy level applied during the corona treatment

A method to corona treat a polymeric surface with a fixed and pre-set treatment energy level is proposed. In order to reduce the effect of humidity, the Corona Discharge Energy – CDE value was controlled during the corona treatment by an in-line monitoring apparatus, which indicates when the energy level is attained. The method was tested applying a negative corona treatment discharge on a polypropylene copolymer film. Chemical and morphological surface changes were examined by IR spectra, contact angle and morphology. Treated samples show the presence of carbonyl, hydroxyl and unsaturations, the first being less concentrated. The formation of polar groups on the film surface led to a reduction of the contact angle and an increase in the surface tension. Film surface morphology was also modified, showing a second phase granular structure which grows with the increase of the CDE level.

Nanoparticle Synthesis in a Plasma Downstream Reactor – From Plasma Parameters to Nanoparticle Properties

In the presented study a tubular plasma reactor is investigated, which is normally used for the continuous plasma surface modification of fine-grained powders. The plasma reactor basically consists of a 1.5 m long glass tube with a gas and precursor feed unit at its top and a particle-gas separation unit at the lower end. The power is coupled inductively into the plasma via a coil which is wrapped around the reactor tube. Substrate powders normally pass the discharge tube with high velocity and are functionalized on their way through the plasma in approximately 0.1 s. Possible plasma surface functionalization processes for powders are illustrated in Figure 1.1. The wettability of powders is increased by the formation of polar groups on the surface. Films are deposited on particle surfaces to protect the substrate from harsh environments or for catalytic applications. In recent years, also a new plasma process, which increases the flowability of fine-grained powders, gained increasing attention. Nanostructured SiOx is formed in the plasma and directly deposited on the substrate particle surface. These nanoparticle structures increase the surface roughness of the substrate particles. Thus, the interparticle van der Waals forces are reduced, which leads to a major improvement of the powder flowability. This process shows promise for companies dealing with cohesive granular materials. The feasibility of this process was shown in the past, but at the same time the need for fundamental research in this field was recognized. Which ion density is required to yield in an effective surface modification? What is the thermal load of a substrate particle during the treatment? Which precursor should be used for a maximum improvement of the flowability? In order to answer such questions, we measured axial profiles of plasma parameters in this continuous reactor and studied the nanoparticle synthesis in detail. No substrate powder was fed during these investigations to facilitate probe measurements and to focus on the produced nanoparticles.Silica-like nanoparticles were produced from the four organosilicon monomers hexamethyldisiloxane (HMDSO), tetramethyldisiloxane (TMDSO), tetraethyl orthosilicate (TEOS), and tetramethyl orthosilicate (TMOS) in argon-oxygen gas mixtures. The chemical composition and morphology of the emerging particles and its production rate were studied as a function of process pressure (100 – 400 Pa), plasma power (200 – 350 W), gas velocity (5 – 16 m/s) and gas composition. Langmuir double probe and calorimetric probe measurements allowed determining the axial profiles of electron temperature, positive ion density, and energy influx along the vertical axis of this tubular reactor.

Mechanical and Surface Properties of E-beam Irradiated Polytetrafluoroethylene-Silicone Rubber Composites

Compounding electron beam irradiated polytetrafluoroethylene (PTFE or Teflon) powder with silicone rubber produced silicone rubber/PTFE composites with desired physical properties. PTFE powder was exposed to electron beam irradiation at various doses and characterized by FTIR, DSC and contact angle measurements. Irradiation of PTFE with high energy electron beam induced chain scission reactions. Irradiated PTFE showed higher degree of crystallization and lower melting point with increasing absorbed dose. Number average molecular weight of irradiated PTFE was reduced significantly at higher absorbed doses. Formation of polar groups on the surface of irradiated PTFE powder was detected by FTIR spectroscopy. The latter was also verified by measurements of water-drop contact angle, which decreased with increasing absorbed dose. Mechanical and surface properties of the composites of silicone rubber and PTFE were characterized by tensile strength, abrasion resistance and water drop contact angle measurements. All the composites containing 5–15 phr PTFE showed higher tensile strength compared to the silicone rubber. Irradiation of PTFE powder had a significant effect on improving the abrasion resistance of the silicone rubber upon addition of only 5 phr irradiated PTFE. Similar abrasion resistance was obtained with the addition of higher amounts of non-irradiated PTFE (15 phr). Water drop contact angle of the composites decreased slightly with increasing the absorbed dose of PTFE.

Effects of operating parameters on DC glow discharge plasma induced PET film surface

A DC glow discharge plasma surface modification techniques are used to modify surface properties of polymeric materials such as adhesivity, hydrophobicity, hydrophilicity and biocompatibility. The plasma interaction with the surface produces modifications of its chemical structure and morphology. The objective of this study is to examine the effect of operating parameters such as discharge potential, pressure and exposure time on surface properties of polyethylene terephthalate (PET) film. The changes in hydrophilic properties of PET films were studied in detail using contact angle and surface energy measurements. The surface morphology and chemical composition of plasma modified film surfaces were studied by atomic force microscopy (AFM) and X-ray photo electron spectroscopy (XPS). It was found that the efficiency of the surface treatment increases with increasing discharge potential, pressure and exposure time. The AFM and XPS analysis showed changes in surface topography and formation of polar groups on the plasma modified PET surfaces.

Effect of chlorine dioxide gas on physical, thermal, mechanical, and barrier properties of polymeric packaging materials

AbstractThe effects of gaseous chlorine dioxide (ClO2) on properties and performance of 10 selected polymeric packaging materials, including polyethylene (PE), biaxially oriented poly(propylene), polystyrene, poly(vinyl chloride), poly(ethylene terephthalate) (PET), poly(lactic acid), nylon, and a multilayer structure of ethylene vinyl acetate (EVA)/ethylene vinyl alcohol (EVOH), were evaluated. Physical, mechanical, barrier, and color properties as well as infrared (IR) spectra were assessed before and after polymer samples were exposed to 3600 ppmV ClO2 gas at 23°C for 24, 168, and 336 h. The IR spectra of the ClO2‐treated samples revealed many changes in their chemical characteristics, such as the formation of polar groups in the polyolefin, changes in functional groups, main chain scission degradation, and possible chlorination of several materials. The ClO2‐treated PE samples showed a decrease in tensile properties compared with the untreated (control) films. Decreases in moisture, oxygen, and/or carbon dioxide barrier properties were observed in the treated PE, PET, and multilayer EVA/EVOH/EVA samples. A significant increase (P < 0.05) in the barrier to O2 was observed in the ClO2‐treated nylon, possibly the result of molecular reordering, which was found through an increase in the crystallinity of the material. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Robust and hydrophilic polymeric films with honeycomb pattern and their cell scaffold applications

Starting from a commercially available block copolymer, polystyrene-b-polybutadiene-b-polystyrene (SBS), micro-patterned polymer films were successfully prepared by evaporating SBS/carbon disulfide solutions with different concentrations under high humidity. The influence of solution concentration on the pore size and array was investigated in detail. With the increase of solution concentration, regular pore arrays turned into random because of weakened convention. Once the concentration was more than 60 mg mL−1, a bimodal size distribution appeared. Photo-chemical cross-linking was achieved by exposing the polymer films in deep UV light (wavelength = 254 nm), monitored by attenuated total reflective Fourier transform infrared and X-ray photoelectron spectroscopy. After 1 h cross-linking, either solvent resistance or thermal stability or surface wettability of the films was significantly improved. The cross-linked honeycomb structured films became resistant to a wide range of organic solvents and thermally stable up to 350 °C, an increase of more than 250 K as compared to the un-crosslinked films. Another beneficial effect of the photo-chemical process was the formation of polar groups on the film surface, changing surface wettability from hydrophobicity to hydrophilicity, enhanced by the micro-patterned surface. The resultant films were non-cytotoxic and hence suitable as cell scaffolds. It was found that hydrophilic, micro-patterned polymer films with a uniform pore size of 3 µm facilitated cell attachment and proliferation.

Adhesive properties of polypropylene (PP) and polyethylene terephthalate (PET) film surfaces treated by DC glow discharge plasma

In this study, the adhesive properties of the plasma modified polypropylene (PP) and polyethylene terephthalate (PET) film surfaces have been investigated. Hydrophilicity of these polymer film surfaces was studied by contact angle measurements. The surface energy of the polymer films was calculated from contact angle data using Fowkes method. The chemical composition of the polymer films was analyzed by X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) was used to study the changes in surface feature of the polymer surfaces due to plasma treatment. The adhesion strength of the plasma modified film was studied by T-peel strength test. The results showed a considerable improvement in surface wettability even for short exposure times. The AFM and XPS analyses showed changes in surface topography and formation of polar groups on the plasma modified PP and PET surfaces. These changes enhanced the adhesive properties of polymer film surfaces.

Effect of Surface Treatment of Polyethylene on Metal–Polyethylene Bond Strength Using an Epoxy Based Adhesive

Polyethylene (PE) was treated with chromic acid for improvement of adhesion. The treated PE samples were characterized by Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy. Adhesive bond studies were carried out on stainless steel–PE joints using a toughened epoxy based adhesive developed in our laboratory. The improvement of bond strength has been correlated with the formation of polar groups on PE estimated by FT-IR spectroscopy. No change in surface topography was observed by optical and scanning electron microscopy studies. The bulk mechanical properties of PE film were investigated as a function of time of treatment. No significant change in mechanical properties was observed up to the time of treatment of about 1 h.