Abstract
The use of polymers in all aspects of daily life is increasing considerably, so there is high demand for polymers with specific properties. Polymers with antibacterial properties are highly needed in the food and medical industries. Low-density polyethylene (LDPE) is widely used in various industries, especially in food packaging, because it has suitable mechanical and safety properties. Nevertheless, the hydrophobicity of its surface makes it vulnerable to microbial attack and culturing. To enhance antimicrobial activity, a progressive surface modification of LDPE using the antimicrobial agent grafting process was applied. LDPE was first exposed to nonthermal radio-frequency (RF) plasma treatment to activate its surface. This led to the creation of reactive species on the LDPE surface, resulting in the ability to graft antibacterial agents, such as ascorbic acid (ASA), commonly known as vitamin C. ASA is a well-known antioxidant that is used as a food preservative, is essential to biological systems, and is found to be reactive against a number of microorganisms and bacteria. The antimicrobial effect of grafted LDPE with ASA was tested against two strong kinds of bacteria, namely, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), with positive results. Surface analyses were performed thoroughly using contact angle measurements and peel tests to measure the wettability or surface free energy and adhesion properties after each modification step. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the surface morphology or topography changes of LDPE caused by plasma treatment and ASA grafting. Surface chemistry was studied by measuring the functional groups and elements introduced to the surface after plasma treatment and ASA grafting, using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). These results showed wettability, adhesion, and roughness changes in the LDPE surface after plasma treatment, as well as after ASA grafting. This is a positive indicator of the ability of ASA to be grafted onto polymeric materials using plasma pretreatment, resulting in enhanced antibacterial activity.
Highlights
Low-density polyethylene (LDPE) is the most common industrial polymer and is mainly used in food packaging because of its useful properties, such as its ease of shaping, handling, and recycling, and its high cost efficiency [1,2,3,4]
The pellets were melted at 160 ◦ C and compressed for 2 min using a force of 2 tons, while maintaining the set temperature to obtain a film with the desired smooth surface
Plasma treatment was used as an effective tool for generation of active species in the LDPE
Summary
Low-density polyethylene (LDPE) is the most common industrial polymer and is mainly used in food packaging because of its useful properties, such as its ease of shaping, handling, and recycling, and its high cost efficiency [1,2,3,4]. Many studies have enhanced the surface properties of LDPE using physical or chemical methods together with conventional methods such as flame treatment, chemical grafting, irradiation, free-radical mechanism, and corona and radio-frequency (RF) plasma treatments [7,8,9,10,11]. These plasma treatments have been found to be more effective techniques for the modification of the surface properties of polymers without any disruption of bulk polymer properties [12,13].
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