Abstract
This study investigates the antibacterial activity of polyethylene nonwoven wipes treated with 13 types of commercially natural essential oils in Vietnam. The mechanical properties of 11 types of polyethylene nonwoven fabrics were examined to find a suitable material for antibacterial treatments. The findings of the inhibition zone on antibacterial treated samples against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria by the disk diffusion method indicated that essential oils from rosemary, clove, lilium, champak, Cinnamomum, melaleuca, and basil could completely inhibit both E. coli and S. aureus. The naturally treated products presented the highest antibacterial activities at 1%, 5%, and 7% of Cinnamomum, basil and clove essential oils, respectively. The antibacterial effects of Cinnamomum, basil, and clove on nonwoven fabrics increased with the liquid content, and the padding pressure should be adjusted to lower than 1.8 bar. Also, the survey results for skin allergy and fragrant feeling demonstrated that wipes treated with basil showed the most positive evaluations.
Introduction
Natural essential oils (EOs) are known as hydrophobic liquids with volatile properties and insolubility in organic solvents.1–4 They are mixtures of hydrocarbons, alcohols, aldehydes, acids, and esters but the most important compounds in EOs are terpenoid molecules with backbones of about 10, 15, 20, and 30 carbon atoms built from isoprene units. 5 Under ambient conditions, EOs are easily partially oxidized into terpenoids or isoprenoids that are diverse and important bioactive groups of natural compounds obtained from the bark, leaves, resin, flowers, roots, seeds, and woods of several higher plants. 6 The odor of EOs is dependent on ester, aldehyde, ketone, and other organic substances. Often EOs are extracted from plants for use in aromatherapy and medicine to support health with typical products including perfumes, cosmetics, flavoring agents in foods and drinks, scents of incense, and cleaning agents.7,8 Some EOs have been widely used for thousands of years in huge amounts such as orange, Mentha arvensis, peppermint, lemon, clove, eucalyptus, lavender, citronella, and so on.9,10 In 1901, a kind of EO (namely, valine) was first successfully isolated from the roots of valerian plants. Recently, some innovative extraction methods for EOs have been applied to achieve high yield as well as to reduce environmental impacts, which are much better than the conventional methods. 11
Although there has been a lot of research on the biological properties of EOs, yet the mysteries still remain. Turek and Stintzing 12 reviewed the stability of EOs through various paths of chemical degradation upon exposure, 12 while many authors have worked on their biological properties such as antibacterial and antioxidant activities.13,14 In terms of biological properties, terpenes and terpenoids are known to have some excellent effects against bacteria, yeasts, fungi, and viruses.15,16 Accordingly, the best antibacterial and antifungal properties of EOs from spices and herbs were determined through the agar diffusion method (paper disk and well) and dilution method (agar and liquid broth).17,18 Hulankova 19 also revealed the antibacterial activity of EOs using five different methods of disk diffusion, well diffusion, agar dilution, and broth dilution. 20 Therein, Cui et al. 21 clarified an antibacterial mechanism of oregano EO against Staphylococcus aureus. 21 Besides, antioxidant properties have been found in many kinds of natural EOs such as Nigella sativa, rosemary, clove, and onion owing to their ability to neutralize free radicals.22–25
In clothing, EOs from thyme have been studied to protect natural lignocellulosic textiles from attacks of bacteria and molds that could be observed through scanning electron microscope. 26 Wang and Chen 27 developed aromatherapy textiles from EOs using fragrances with β-cyclodextrin which were fixed in cotton by a binder. 27 Furthermore, a skin-health finishing agent for textiles obtained from EOs and the fragrance of citrus unshiu fruits was investigated by Fourier transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC-MS) techniques, while the extracts of lavender EOs were finished on fragrant and medical polyester textiles.28,29 However, few studies have been carried out on the antibacterial effects of textiles treated with EOs. In this work, the authors examine the bacterial inhibition of polyethylene (PE) nonwoven fabrics treated with commercially available EOs in Vietnam for producing wet wipes that are required not only in aromatherapy but also for their antibacterial abilities.
Experiments
All types of EOs including eucalyptus (EU), rosemary (RO), orange (OR), clove (CL), Cupressus (CU), lilium (LI), champak (CH), Cymbopogon (CY), Cinnamomum (CI), Leptospermum (LE), Melaleuca (ME), basil (BA), and lavender (LA), which have been successfully commercialized, were provided by the Vietnam Academy of Science and Technology (VAST). Types of PE nonwoven fabrics with specific weights of 13, 18, 23, 25, 27, 40, 45, 50, 65, 75, and 97 were collected and abbreviated as NW13, NW18, NW23, NW25, NW27, NW40, NW45, NW50, NW67, NW75, and NW79, respectively.
The strength and elongation of the treated samples with EOs were measured by a tensile testing machine (Testometric M350-5) with a maximum loading capacity of 5 kN, according to ISO 9073-3:1989. To evaluate the bacterial inhibition of the treated samples with EOs, it is necessary to determine an inhibition zone where there is no bacterial growth, as illustrated in Figure 1. Through such measurements, the inhibition zone (W, mm) is calculated as the following equation:
where D (mm) is the width of the specimen and T (mm) is the width of the inhibition zone.

Illustration of bacterial inhibition zone through agar disk diffusion method on antibacterial treated specimen according to AATCC 147.
All prepared nonwoven samples (50 mm ×25 mm) were sterilized by an upright autoclave (HVA-110 Hirayama) at 120°C for 4 h and then conditioned at 23°C and 65% RH for 24 h in an air cabinet (Type M250-RH). A stirrer (Vortex) was used to shake the oil solutions well prior to application on fabrics. All nonwoven wipes were padded with EOs and pure water (the reverse osmosis purification process) at various concentrations (on fabric weight) and a specific wet pick-up value (a given pressure) through a padding mangle (Roaches). The treated samples with different EOs were packed in plastic bags to prevent evaporation. Moreover, diethyl phthalate was used as a fixative agent (flavoring agent) and glyceryl caprylate was used as a wetting agent for all treated samples with EOs. Determination of the bacteriostatic activity of treated fabrics with two kinds of bacteria (S. aureus and Escherichia coli) was carried out according to the AATCC-147 test method (i.e. the parallel streak).
Nonwoven specimens with the original mass (MO) were immersed in distilled water to determine the saturated mass (MS). The water content (%) in the sample was determined according to the following equation:
Finally, three types of optimized nonwoven wipes were examined for skin allergy and fragrant feeling on 100 students from the University of Economic and Technical Industries.
Results and Discussion
Water Absorption and Breaking Strength of PE Nonwoven Fabrics
Since PE is a hydrophobic material, if its ability for liquid absorption is improved, the antibacterial ability of the treated fabrics with EOs will be significantly enhanced. Accordingly, all samples of the collected nonwoven fabrics were investigated for water absorption in a saturated condition to select the appropriate material for antibacterial treatments with EOs.
In Figure 2, the obtained results show that the nonwoven samples with the highest and lowest water absorption capacities were NW27 (1521.65%) and NW97 (149.78%), respectively. In general, all samples possessed very high water absorption that meets the quality requirements for wet wipes. It can be found that the water content in nonwoven fabrics is not much affected by the specific weight because of many other physical effects such as binders and web forming techniques. Obviously, adhesive agents as well as bonding methods play an important role in absorbing liquid into the structure of nonwoven fabrics.

Water absorption of polyethylene nonwoven fabrics with various specific weights in saturated condition.
Similarly, the tensile strength and tensile elongation at break were assessed (according to ISO 9073-3:1989) to ensure the best longevity of antibacterial nonwoven fabrics treated with EOs. It appears that most tensile strengths and breaking elongations increased with the specific weight of nonwoven fabrics, as shown in Figure 3. However, the difference in fiber orientation caused changes in the tensile strength and breaking elongation of nonwoven fabrics. Through the images obtained from an optical microscope, the surface changes of three different nonwoven samples can be clearly observed, as shown in Figure 4.

(a) Tensile strength and (b) tensile elongation at break of PE nonwoven fabrics with various specific weights.

Surface photos of polyethylene nonwoven fabrics: (a) NW50, (b) NW65, and (c) NW75 with different fiber orientations observed by an optical microscope.
In the case of NW50 and NW65, the fibers were dominantly arranged crosswise; therefore, their tensile strength lengthwise was much higher than that in crosswise. Meanwhile, the fibers of NW75 were quite randomly arranged, so the tensile strength and breaking elongation both lengthwise and crosswise were not very different. From the above analyzed results, this research selected NW65 for the antibacterial treatments on PE nonwoven wipes with natural EOs.
Evaluation of Antibacterial Activity of EOs Against E. coli and S. aureus
All samples (NW65) treated with 13 types of EOs in Vietnam, which were denoted as EU, RO, OR, CL, CU, LI, CH, CY, CI, LE, ME, BA, and LA, were contacted with two species of bacteria, being E. coli (Gram-negative) and S. aureus (Gram-positive), to determine the antibacterial effects in vitro according to the disk diffusion method or parallel streak method (AATCC TM147), with a relatively quick and easy qualitative evaluation. The results of bacterial inhibition on the untreated and treated nonwoven samples with different EOs are reported in Table 1 and evidenced in Figure 5.
Evaluation results on bacterial inhibition of the treated sample with 13 essential oils against Escherichia coli (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria), where N represents no bacterial colonies and A represents completely killed bacteria.

Images of antibacterial effects of nonwoven fabrics treated with 13 various essential oils against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria.
There were no colonies on the surface of the control (CT) sample (i.e. treated with distilled water), but colonies strongly developed around the specimen. Most of the samples treated with EOs could inhibit S. aureus, in which CU and LE samples exhibited the worst values of W of about 12.35 and 14.5 mm, respectively. RO, CL, LI, CH, ME, and BA (highlighted in bold in Table 1) completely inhibited E. coli but the CU and CY samples could not prevent colonies like the control sample. Meanwhile, the EU, OR, LE, and LA samples could inhibit E. coli quite poorly, being 10.0, 7.5, 6.25, and 10.0 mm, respectively. Consequently, the RO, CL, LI, CH, CI, ME, and BA samples were able to inhibit completely both S. aureus and E. coli. Many previous researches have demonstrated that the antibacterial effects of natural EOs are due to the presence of bioactive chemical compositions such as aldehydes, phenolics, and terpenes. The functional groups of these compounds can react with the bacterial cells thanks to their antioxidant properties. Therefore, it can be concluded that there was a significant content of natural antibacterial agents on the RO, CL, LI, CH, CI, ME, and BA samples.
To clarify further the effects of the EO contents on the antibacterial ability of PE nonwoven fabrics, the samples including RO, CL, LI, CH, CI, ME, and BA, which exhibited the above antibacterial effects, were treated with various concentrations of EOs (1%, 3%, 5%, 7%, and 10%). Table 2 indicates that the CL, CI, and BA samples can completely inhibit both E. coli bacteria and S. aureus bacteria at concentrations of 7%, 1%, and 5%, respectively. Other samples including RO, LI, CH, and ME inhibited E. coli bacteria (i.e. 81.7%, 48.8. 73.3%, and 73.3% at 10% of EOs) quite poorly, but they inhibited S. aureus bacteria better (i.e. 100% at 7%, 1%, and 5% of EOs, respectively). Based on such investigations, the authors used three kinds of EOs possessing the best antibacterial effects against both E. coli and S. aureus bacteria, CL, CI, and BA, to optimize the antibacterial treatment for wet wipes that will be described in the following sections.
Bacterial inhibition ability (%) of treated samples with 1%, 3%, 5%, 7%, and 10% of RO, CL, LI, CH, CI, ME, and BA essential oils against E. coli and S. aureus.
Impact of Flavoring Agent and Wetting Agent on Antibacterial Ability of Treated Nonwoven Fabrics With EOs
As investigated above, the nonwoven samples treated with CI, BA, and CL presented the highest inhibitions of E. coli and S. aureus bacteria, in which the optimized EO concentrations were determined as 1.0%, 5.0%, and 7.0% (owf), respectively. The additives including 0.1% flavoring agent (diethyl phthalate) and 0.5% wetting agent (glyceryl caprylate) were inserted into the treated samples with EOs. As presented in Table 3, it can be seen that the flavoring agent and wetting agent did not cause a negative effect on the antibacterial activity of the CI and BA samples at all concentrations. In particular, the CI, BA, and CL samples exhibited perfect antibacterial ability (i.e. bacterial inhibition was 100%), except for the CL sample (7%). A slight change in bacterial inhibition was found by inserting flavoring and wetting agents to antibacterial treated nonwoven fabrics with 7% of CL EOs.
Bacterial inhibition of antibacterial treated nonwoven fabrics with CI, BA, and CL essential oils against E. coli and S. aureus bacteria by adding flavoring and wetting agents.
Water Content of PE Nonwoven Wipes Treated With EOs
Determination of the results of the water contents obtained from six various samples at pressures of 0.0, 0.2, 0.5, 1.0, 1.8, and 2.0 bar is shown in Table 3 and Figure 6. Certainly, the liquid content of the treated samples with CI, BA, and CL EOs decreased with pressure. In general, the treated samples with BA at higher pressures generated the lowest liquid content as compared with the treated samples with CI and CL. For example, the water contents of CI, BA, and CL samples were determined to be 354.0%, 214.4%, and 262.2% at 1.0 bar, and 271.0%, 148.3%, and 191.0% at 2.0 bar, respectively.

Liquid content of antibacterial treated samples with 1% CI, 5% BA, and 7% CL at pressures of 0.0, 0.2, 0.5, 1.0, 1.8, and 2.0 bar.
To evaluate the antibacterial activity of the treated samples with EOs against E. coli and S. aureus bacteria at various pressures, bacterial inhibition zones (W) on the treated samples with 1% CI, 5% BA, and 7% CL were examined and are reported in Table 4. Obviously, the antibacterial effects of the treated samples against E. coli and S. aureus bacteria decreased with increasing pressure. At high pressures, the inhibition of S. aureus was much better than that of E. coli, in which a decrease of inhibition zone was detected at a pressure higher than 1.8 bar, being 91.67% for the BA sample and 88.83% for the CL sample. However, a quite rapid reduction in bacterial inhibition occurred with the antibacterial samples (especially the CL sample) when exposed to E. coli bacteria.
Liquid content of antibacterial treated samples with CI, BA, and CL at various pressures.
Consequently, among the 13 species of commercial EOs in Vietnam processed on PE nonwoven fabrics under optimized conditions, the highest antibacterial effects or bacterial inhibition were attributed to the CI sample (i.e. Cinnamomum oil).
Evaluation on Skin Allergy of Treated Samples With EOs
To evaluate the effect of wipes treated with EOs on humans, skin allergy tests were carried out. Accordingly, the allergic reaction and the fragrant feeling of wipes treated with EOs were examined. As reported in Table 5, the survey results on 100 people exposed directly to three kinds of wipes (CI, BA, and CL) after 30 min indicated that there were no skin allergies or non-irritation. However, evaluations of the fragrant feeling of the CI, BA, and CL samples were 74%, 83%, and 13%, respectively. On the contrary, nonwoven wipes treated with BA and CL received the most positive and negative evaluations of fragrant feelings, respectively (Table 6). In combination with the above analysis, it can be concluded that PE wipes are the most suitable for commercial use.
Bacterial inhibition of antibacterial treated nonwoven fabrics with 1% CI, 5% BA, and 7% CL at pressures of 0.0, 0.2, 0.5, 1.0, 1.8, and 2.0 bar.
Evaluation results of skin allergy and fragrant feelings on optimized treated nonwoven samples with CI, BA, and CL.
Conclusion
Often, wet wipes are made from PE nonwoven fabrics that require not only aromatherapy properties but also antibacterial properties. This research investigated the bacterial inhibition of antibacterial treated nonwoven fabrics with EOs against Gram-negative and Gram-positive bacteria according to agar disk diffusion method. The results indicate that EOs from RO, CL, LI, CH, CI, ME, and BA completely inhibited E. coli and S. aureus bacteria. Among them, CI, BA, and CL exhibited the highest antibacterial effects. The pressure of the padding mangle should be established at lower than 1.8 bar to optimize the antibacterial activity of PE nonwoven fabrics. It can be affirmed that nonwoven wipes treated with CI were most applicable in terms of antibacterial activity, skin allergy, and fragrant feelings.
Footnotes
Acknowledgements
The authors thank Hanoi University of Industry, University of Economic and Technical Industries, Hanoi University of Science and Technology, and Ho Chi Minh City University of Technology and Education for their supports.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
