Plasma-treated Low-density Polyethylene Research Articles

Biodegradation of low-density polyethylene by plasma-activated Bacillus strain

Plastic biodegradation by microorganisms is an eco-friendly and sustainable method without any ramifications. Herein, we used a cultivation method and 16S rRNA sequencing to screen bacteria that can efficiently colonize and degrade low-density polyethylene (LDPE) from various plastic wastes. We identified Bacillus safensis BS-10L through whole-genome sequencing analysis and verified its LDPE-degradation ability. However, the decomposition mechanism of the isolated bacteria was unclear and the decomposition efficiency was insufficient, so low-temperature plasma was used to increase the decomposition efficiency of the bacteria. The population and viability of bacteria treated with cold plasma increased. Plasma-activated bacteria could induce cracks, holes, and roughness on the surface of LDPE films over 90 days, and over 30 days; the LDPE film lost 13.40 ± 0.013% and 27.78 ± 0.014% of its mass by BS-10L and plasma-treated BS-10L, respectively. Fourier-transform infrared spectroscopic analysis identified new peaks of the C=O and C-O groups in the plasma-treated LDPE film, exhibiting high transmittance in the LDPE film that was inoculated with bacteria. X-ray photoelectron spectroscopic analysis showed that C-O bonds were generated by BS-10L strain, and relatively strong C=O bonds were generated in the film inoculated with plasma-treated BS-10L strain. Plasma treatment increased the colonization of the BS-10L strain and changed the chemical bonding of the LDPE film, suggesting that plasma-activated BS-10L could accelerate decomposition by oxidation by increasing the carbonyl group of the PE film. Therefore, plasma technology may be effective for enhancing the plastic-degrading ability of microorganisms.

Plasma-treated LDPE film incorporated with onion and potato peel extract – A food packaging for shelf life extension on chicken thigh

This study aimed to develop a new antimicrobial food packaging from low-density polyethylene (LDPE) film containing the natural extract. In this regard, onion and potato peel extract were obtained using the ultrasound-assisted method. The polyethylene film surface was exposed to atmospheric plasma treatment to improve the wettability properties and subsequently increase the attachment of the extract on the film surface. Results showed significant changes in surface hydrophilicity; the contact angle reduced from 89° to 42° after 45 s treatment (350 W). The 10 % and 20 % concentrations of extracts were coated on the plasma-treated film’s surface, separately and in their combinations, by immersing the film into the extract solutions. The absorption and release rate of the film samples containing potato peel extract (PPE) was considerably higher than the other samples. However, the film containing onion peel extract (OPE) showed the highest phenolic content and antioxidant activity. The antibacterial activity of film samples demonstrated the significantly higher antibacterial activity of OPE than PPE. Results introduced the plasma-treated film containing 20 % OPE as the most effective antimicrobial film used for packaging chicken thighs. The chicken thigh samples packaged by antimicrobial film showed a lower value of thiobarbituric acid (0.09 mg MDA/kg sample), total volatile nitrogen (14.27 mg/100 g), and total viable count (4.05 log CFU/g) compared to the control sample (pristine film) during 6 days’ storage period. Our results suggest that plasma-treated film containing 20 % OPE has potential application as a functional food packaging film in food antimicrobial packaging.

Immobilization of glucose oxidase on plasma-treated polyethylene for non-invasive glucose detection

Glucose oxidase (GOx) has been covalently immobilized onto plasma-treated low-density polyethylene (PT-LDPE) deposited by solvent-casting onto a glassy carbon electrode. PT-LDPE acts as a very simple and cheap mediator between the enzyme and the conducting substrate, the resulting electrode (GOx/PT-LDPE/GC) being able to detect effectively glucose under conditions of pH and temperature that mimic those of sweat. Glucose has been successfully monitored using GOx/PT-LDPE/GC electrodes via both, chronoamperometric and voltammetric measurements. The lowest limit of detection (LOD) was obtained with electrodes prepared with a GOx concentration of 5 mg/mL. This represents a significant reduction in the amount of enzyme as compared to electrodes obtained by dropping GOx onto PT-LDPE/GC (non-covalent immobilization), in which the required enzyme concentration was 33 mg/mL. Furthermore, the LOD has been decreased two orders of magnitude, from 1.3 mM for sensors without covalent immobilization to less than 0.05 mM. It is worth noting that the latter value is fully compatible with glucose concentration in sweat, which ranges from 0.06 to 0.11 mM for healthy patients and from 0.01 to 1 mM in diabetic patients. Moreover, the developed sensor is able to promote the reduction of hydrogen peroxide produced during the oxidation of glucose to gluconolactone.

Plasma-treated polyethylene coated with polysaccharide and protein containing cinnamaldehyde for active packaging films and applications on tilapia (Orechromis niloticus) fillet preservation

This study aimed to develop an antimicrobial active packaging using carboxymethyl cellulose (CMC) or collagen (COL) as carriers of cinnamaldehyde (CNMA) coating on plasma-treated low density polyethylene (LDPE) for application on tilapia fillet packaging. COL carriers exhibited stronger antimicrobial and antioxidant activities than no carrier and CMC. The films also showed good physical and mechanical properties after coating. The results on tilapia preservation analysis showed that the COL with 6% CNMA slowed the total plate count and growth of Vibrio parahaemolyticus by about 1.82 log colony-forming units (CFU)/g and 1.76 log CFU/g compared to the control at day 14. All active films were better than Control in delaying the production of volatile basic nitrogen and thiobarbituric acid during storage whilst simultaneously maintaining organoleptic properties. Based on results, the antimicrobial active films significantly prolonged the shelf life of tilapia fillets to 3 days compared with the Control group. The COL with 6% CNMA may potentially play an effective role in maintaining and preserving the microbial qualities of tilapia fillets.

The Separation of Emulsified Water/Oil Mixtures through Adsorption on Plasma-Treated Polyethylene Powder.

This paper addresses the preparation and characterization of efficient adsorbents for tertiary treatment (oil content below 100 ppm) of oil/water emulsions. Powdered low-density polyethylene (LDPE) was modified by radio-frequency plasma discharge and then used as a medium for the treatment of emulsified diesel oil/water mixtures in the concentration range from 75 ppm to 200 ppm. Plasma treatment significantly increased the wettability of the LDPE powder, which resulted in enhanced sorption capability of the oil component from emulsions in comparison to untreated powder. Emulsions formed from distilled water and commercial diesel oil (DO) with concentrations below 200 ppm were used as a model of oily polluted water. The emulsions were prepared using ultrasonication without surfactant. The droplet size was directly proportional to sonication time and ranged from 135 nm to 185 nm. A sonication time of 20 min was found to be sufficient to prepare stable emulsions with an average droplet size of approximately 150 nm. The sorption tests were realized in a batch system. The effect of contact time and initial oil concentrations were studied under standard atmospheric conditions at a stirring speed of 340 rpm with an adsorbent particle size of 500 microns. The efficiency of the plasma-treated LDPE powder in oil removal was found to be dependent on the initial oil concentration. It decreased from 96.7% to 79.5% as the initial oil concentration increased from 75 ppm to 200 ppm. The amount of adsorbed oil increased with increasing contact time. The fastest adsorption was observed during the first 30 min of treatment. The adsorption kinetics for emulsified oils onto sorbent followed a pseudo-second-order kinetic model.

Eco-friendly foam biocomposites based on cellulose extracted from date palm leaves and low-density polyethylene

The design of composite materials using environmentally compatible materials and adopting sustainable preparation techniques is very necessary for a better environment. The present study is a step towards developing an environmentally friendly alternative to foam-based composites. The aim of the study is to understand the effect of natural fibers from date palms on the property of foam biocomposites. We adopted an environmentally friendly method of compatibilization between the polymer and the fibers for better reinforcement. The compatibility was done by environmentally friendly physical modification using plasma treatment. Plasma treatment provides surface modification and is an economical solution for further processing. In fact, three types of interfaces have been created: (1) by the addition of maleic anhydride, (2) by the use of plasma-treated low-density polyethylene, (3) by the combination of maleic anhydride and plasma. The overall performance was best in the use of plasma treatment alone. The effect was carefully analyzed based on morphological, mechanical and thermal studies. Finally, a morphology–property correlation was established.

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.

Modification of Polyethylene by RF Plasma in Different/Mixture Gases

Herein, low-density polyethylene (LDPE) films were treated using radio-frequency plasma discharge in the presence of air, nitrogen, oxygen, argon, and their mixtures to introduce new chemical functionalities. The surface properties of treated LDPE were qualitatively and quantitatively characterized using various analytical and microscopic techniques. It was found that the optimum plasma treatment for LDPE occurs in the presence of air plasma at an exposure time of 120 s and 80 W of nominal power. The plasma formed layer had tendency to increasing thickness with increasing treatment time up to 60 s using air and oxygen and even more with inert gases. An aging study of plasma-treated LDPE samples stored in ambient air or water medium revealed the partial hydrophobic recovery.

Effect of Low-Temperature Plasma Treatment on Surface Properties of LDPE Film

Low-density polyethylene (LDPE) film was treated by low-temperature plasma. Scanning electronic microscope, electronic universal testing machine, contact angle/interfacial tension measuring instrument were used to analyze the surface morphology, surface contact angle, bonding strength and performance of LDPE film before and after they were treated by low-temperature plasma. The results show that air ambience is more appropriate than N2, CO2 for treatment. Specifically, plasma treatment in air ambience, under conditions of 44 W (power), 30 s (duration) and 60 Pa (vacuum degree), can decline static contact angle of LDPE film from 101° to 13.5°. The transiency of plasma-treated LDPE film is so obvious that storage time of longer than one hour will result in a contact angle up to 74° and loss of plasma treatment effect (timeliness). Therefore, the reversible plasma-treated LDPE film should be processed immediately.

Nanoscale mechanical and tribological properties of fluorocarbon films grafted onto plasma-treated low-density polyethylene surfaces

Fluorocarbon (FC) films were grafted onto Ar plasma-treated low-density polyethylene (LDPE) surfaces by plasma polymerization and deposition. The evolution of the surface morphology of the grafted FC films was investigated at different scales with an atomic force microscope. Nanoscale sliding experiments performed with a surface force microscope provided insight into the nanotribological properties of Ar plasma-treated LDPE, with and without grafted FC films, in terms of applied normal load and number of sliding cycles. The observed trends are explained in the context of microstructure models accounting for morphological and structure changes at the LDPE surface due to the effects of plasma treatment (e.g., selective etching of amorphous phase, chain crosslinking and FC film grafting) and surface sliding (e.g., crystalline lamellae alignment along the sliding direction). Nanoindentation experiments elucidated the effect of plasma treatment on surface viscoelasticity and global contact stiffness. The results of this study demonstrate that plasma-assisted grafting of FC films is an effective surface modification method for tuning the nanomechanical/tribological properties of polymers.

Investigating the effect of power/time in the wettability of Ar and O 2 gas plasma-treated low-density polyethylene

Low-pressure glow discharges of Ar or O 2 gas plasmas were used to increase the wettability of low-density polyethylene (LDPE) films in order to improve their adhesion properties hence making them useful in technical applications. Surface free energies of such films were estimated by the aid of contact angle measurements at different exposure power/time combinations for a series of test liquids. Additionally, plasma-treated samples were subjected to several aging processes to determine the durability of different plasma treatments. Characterization of the surface changes due to plasma treatments were carried out by means of attenuated total reflectance, Fourier transform infrared spectroscopy (FTIR-ATR) to determine the presence of polar species such as hydroxyl, carbonyl, carboxyl, etc. groups. Furthermore, atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to evaluate changes in surface morphology and roughness. Considering the semi-crystalline nature of the LDPE film, XRD studies were also carried out to determine changes in the percentage of crystalinity. The results showed that all low-pressure Ar or O 2 gas plasmas improve the wettability properties of LDPE films. Contact angles decreased significantly depending on the discharge powers and exposure times. Surface morphology was also found to vary with plasma discharge powers, exposure times, and the type of gas being used. Ar gas plasmas comparatively produced superior results.

Dependence of nanomechanical modification of polymers on plasma-induced cross-linking

The nanomechanical properties of low-density polyethylene (LDPE) modified by inductively coupled, radio-frequency Ar plasma were investigated by surface force microscopy. The polymer surface was modified under plasma conditions of different ion energy fluences and radiation intensities obtained by varying the sample distance from the plasma power source. Nanoindentation results of the surface stiffness versus maximum penetration depth did not reveal discernible differences between untreated and plasma-treated LDPE, presumably due to the small thickness of the modified surface layer that resulted in a substrate effect. On the contrary, nanoscratching experiments demonstrated a significant increase in the surface shear resistance of plasma-modified LDPE due to chain cross-linking. These experiments revealed an enhancement of cross-linking with increasing ion energy fluence and radiation intensity, and a tip size effect on the friction force and dominant friction mechanisms (adhesion, plowing, and microcutting). In addition, LDPE samples with a LiF crystal shield were exposed to identical plasma conditions to determine the role of vacuum ultraviolet (VUV) and ultraviolet (UV) radiation in the cross-linking process. The cross-linked layer of plasma-treated LDPE exhibited much higher shear strength than that of VUV/UV-treated LDPE. Plasma-induced surface modification of the nanomechanical properties of LDPE is interpreted in the context of molecular models of the untreated and cross-linked polymer surfaces derived from experimental findings.

Correlation of proliferation, morphology and biological responses of fibroblasts on LDPE with different surface wettability

In order to find a correlation between cell adhesion, growth and biological response with different wettability, NIH/3T3 fibroblast cells were cultured on plasma-treated low-density polyethylene (LDPE) film generated with radio frequency. Different surface wettabilities (water contact angle 90–40°) were created by varying the duration of plasma treatment between 0 and 15 s, respectively. Growth and proliferation rate of cells on LDPE surfaces was evaluated by MTT assay, and cell morphology, by means of spreading and adhesion, was characterized by scanning electron microscopy (SEM). The expression of particular genes in cells contacted on films with different wettability was analyzed by RT-PCR. Using the MTT assay, we confirmed that the amount of cell adhesion was higher on surface of film with a water contact angle of 60° than with other water contact angle. Also, the proliferation rate of cells was highest with a water contact angle of 60°. It was confirmed by SEM that the morphology of cells adhered with a water contact angle of 50–60° was more flattened and activated than on other surfaces. Furthermore, c-fos mRNA in cells showed maximum expression on the film with contact angle range of 50–60° and c-myc mRNA expressed highly on the film with a contact angle of 50°. Finally, p53 gene expression increased as wettability increase. These results indicate that a water contact angle of the polymer surfaces of 50–60° was suitable for cell adhesion and growth, as well as biological responses, and the surface properties play an important role for the morphology of adhesion, growth and differentiation of cells.

Effect of ion energy fluence on the topography and wettability of low-density polyethylene exposed to inductively coupled argon plasma

The topography and wettability of low-density polyethylene (LDPE) were modified by an inductively coupled Ar plasma. The extent and mechanisms of surface modification were correlated with the ion energy fluence, determined from the ion density measured with a Langmuir probe. The ion energy fluence was varied in the range of (0.3–6.3) × 105 J m−2 by changing the sample distance from the plasma power source. Physical and chemical changes of the plasma-treated LDPE surfaces were evaluated with an atomic force microscope, goniometer and x-ray photoelectron spectrometer. Images of plasma-treated and chemically etched LDPE surfaces provided insight into the mechanisms responsible for the topography changes observed at different length scales in terms of the sample distance (ion energy fluence). A significant effect of the nanoscale roughness on the contact angle of LDPE was observed for high ion energy fluence. The results demonstrate a strong effect of the ion energy fluence on the modification of the surface morphology and wettability of plasma-treated polymer surfaces.

The effect of maleic anhydride grafting on the flame retardation of plasma pretreated polyethylene

A rotating cylindrical-type argon plasma treatment system was used for pretreating low-density polyethylene (LDPE) to graft polar vinyl monomers. Maleic anhydride (MA) was used to graft onto plasma-treated LDPE (PLDPE) using UV-induced polymerization. The MA-grafted PLDPE (MA-g-PLDPE) was characterized by FT-IR spectra, SEM, TGA and ESCA measurement. The modified PLDPE was blended with a commercial flame-retardant additive (FR 44-94S), a coupling agent, lubricant and antioxidant to improve the flammability. The flammability of these blends increases with increasing amounts of FR 44-94S. However, the tensile strength and impact strength were decreased as the amount of FR 44-94S increased. From the results of notched Izod impact strength vs flame-retardant content, this flame-retardant seemingly exhibited plasticizer characteristics. As MA-g-PLDPE and FR 44-94S were blends, the mechanical strength, such as the tensile strength, impact strength, Young's modulus and LOI increased because the grafted MA can enhance the affinity between matrix and additives.

Improvement of wettability and reduction of aging effect by plasma treatment of low-density polyethylene with argon and oxygen mixtures

To improve the hydrophilicity and reduce the aging effect, argon and oxygen mixtures were employed in the plasma treatment of low-density polyethylene (LDPE). Argon resulted in producing more oxygen ions and radicals in the plasma than only oxygen and forming cross-linked layers on the LDPE surface. Therefore, the water contact angle on plasma-treated LDPE decreased and the oxygen content measured by X-ray photoelectron spectroscopy (XPS) increased with the increase of argon content. The aging effect was also much reduced with the increase of argon content since argon induced cross-linking.

Adhesion enhancement of polymer surfaces by atmospheric plasmatreatment

An atmospheric pressure non-equilibrium plasma (APNEP) developedin the UK by EA Technology Ltd is currently being investigated incollaboration with the University of Surrey. Of the many applications ofsurface modification that can be induced using plasmas, adhesionenhancement is one of the most commercially important. In this paper, weillustrate the use of an atmospheric plasma to enhance the adhesioncharacteristics of low-density polyethylene (LDPE) and poly(ethyleneterephthalate) (PET). The polymers were treated in the remote afterglowregion of an atmospheric pressure plasma to avoid the thermal effects thatcan cause degradation for thermally sensitive materials when placed indirect contact with the plasma. Reactive (oxygen containing) and inert(oxygen free) atmospheric plasmas rapidly impart adhesion enhancement by afactor of two to ten as measured by 180° peel tests. However,extended exposure to the atmospheric plasma does not impart additionaladhesion enhancement as the surface is ablated revealing the underlyingpolymer with poor adhesive characteristics. In contrast, vacuum plasmatreated LDPE and PET show increased adhesion with extended plasmatreatment. An adhesion enhancement in excess of two to three orders ofmagnitude was found to be achievable for vacuum plasma treatment timesgreater than 10 min.

Retardation of the surface rearrangement of O2 plasma-treated LDPE by a two-step temperature control

The effects of the specimen temperature of low-density polyethylene (LDPE) in O2 plasma treatment were studied to enhance the amount of hydrophilic functional groups introduced and to reduce the aging effect. The specimen temperature was varied from 25°C to 100°C. The smallest water contact angle was obtained with the 45°C specimen and the largest amount of hydrophilic functional groups was introduced with the 100°C specimen, as determined by X-ray photoelectron spectroscopy (XPS). Therefore, a two-step plasma treatment with two different specimen temperatures, i.e. 100°C followed by 45°C, decreased the water contact angle and reduced the aging effect. It appears that the hydrophilic functional groups introduced were located at the specimen surface (about 0.5 nm) at low temperature and that the aging effect was reduced due to the hydrophilic functional groups formed inside (0.5-8 nm) at high specimen temperature. The aging rate and the diffusion coefficient were also estimated, depending on the specimen temperature, using the experimental aging data.

The aging effects of repeated oxygen plasma treatment on the surface rearrangement and adhesion of LDPE to aluminum

The effects of aging temperature and time on the adhesion properties of oxygen plasmatreated low-density polyethylene (LDPE) were investigated. As the aging temperature and time increased, surface rearrangement and the migration of molecules containing polar functional groups into the bulk were accelerated to the surface to form a hydrophobic surface. The adhesion strength of oxygen plasma-treated LDPE/aluminum joints was measured using a 90° peel test by varying the plasma treatment time and aging temperature. The adhesion strength was constant, regardless of the plasma treatment time. As the aging temperature increased, the adhesion strength of the LDPE/aluminum joints decreased and the locus of failure changed from cohesive to interfacial failure. It was also found that the polar functional groups buried in the bulk could be reoriented to the surface in a polar environment. This study also investigated whether repeated oxygen plasma treatment would increase the concentration of polar functional groups at the surface and reduce the surface rearrangement and the migration of molecules containing polar functional groups during aging. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) showed that repeated oxygen plasma treatments increased the concentration of polar functional groups at the surface. However, the aging time between plasma treatments had a negligible effect on the concentration of polar functional groups at the surface.

Mechanical properties and surface energies of low density polyethylene-poly(vinyl chloride) blends

A series of blends of poly(vinyl chloride) (PVC) and low density polyethylene (LDPE) are prepared and examined. Plasma treatment is applied to one of the components (LDPE) in order to affect the degree of compatibility. For this purpose, different monomers, such as carbon tetrachloride and vinyl chloride, are used. Tensile test results for all the blend samples, with and without plasma-treated LDPE, are compared. The surface energy results of blends prepared from untreated and treated LDPE-PVC showed considerable differences, with appreciable increases for the latter, indicating an increase in the work of adhesion as a result of the plasma surface modifications applied. The tensile test results and the measured surface energies are found to show a similar parallel behaviour.