Deterioration Valuation of Polymer Materials in UV-ozone Generator

using Microwave Plasma

NAOKI KUSUMOTO1, ATSUYA WATANABE2, SHIGEMI HIRAOKA3,

NORIMICH KAWASHIMA4, YOSHIKAZU TOKUOKA2, HITOSHI KIJIMA1

Gunma University of Health and Welfare,

191-1 Kawamagari-machi, Maebashi-shi. Gunma 371-0823,

JAPAN

JAPAN

University of the Pacific Rim,

4-17-1 Sakuragicho, Nishi-ku, Yokohama 220-0021,

JAPAN

Abstract: - Various materials are used to sterilize medical instruments. Rubber and other products deteriorate

use because of the lack of an efficient method for decomposing ozone and the corrosion of metals. If a medical

device is altered, it cannot be used as a sterilizing device. In this study, we exposed polymeric materials, which

are often used in medical instruments, to ozone and UV light to determine whether their properties changed.

Elution tests were conducted on polymeric medical materials from the viewpoints of their physical and

chemical properties, functional decline, and biological safety. This study investigates changes in mechanical

strength and surface chemical properties, representing the physical and chemical aspects.

Key-Words: - microwave, ozone, UV, sterilizer, mercury bulb, active oxygen, polymer material.

Received: January 19, 2023. Revised: November 21, 2023. Accepted: December 20, 2023. Published: March 6, 2024.

and UV exposure, [1]. If a medical device

undergoes alterations, it becomes unsuitable for use

as a sterilizing device. In this study, we exposed

polymeric materials, which are often used in

medical instruments, to ozone and UV light to

determine whether their properties changed.

Specifically, we exposed hard polymer

materials like polyethylene, polypropylene,

polyethylene terephthalate, and polyvinyl chloride,

as well as soft polymer materials such as natural

colostomies, infusion bags, packaging films, etc [2],

[3], [4], [5], [6]. Polyethylene terephthalate (PET) is

used as a relatively large-diameter artificial blood

vessel because it undergoes little tissue reaction and

is less susceptible to in vivo deterioration.

Polypropylene is stable to drugs, biochemically inert,

and is used as a material for rigid medical devices

term for synthetic rubbers prepared by the

polymerization or copolymerization of monomers

containing fluorine atoms, [7]. Although it has been

reported to deteriorate under alkaline and high-

temperature conditions, it is known as a rubber that

can be used even in harsh environments, [8] and is

used for endoscopes, scope tip covers, etc. Silicone

rubber is made into a rubber-like material by

adjusting the molecular weight of silicone and is

used for rubber tubes and external shunts for blood

chemical properties, functional decline, and

biological safety, [10], [11], [12]. In this study,

changes in mechanical strength and surface

chemical properties were investigated as physical

and chemical properties.

1.1 Ozone

Ozone is represented by the molecular formula O3

and has a molecular structure in which three oxygen

atoms are bonded in an isosceles triangular shape. It

based on wavelength: UVA (320–400 nm), UVB

(320–280 nm), and UVC (280–200 nm). UV lamps

are a technologically mature field, and many

products are already in use. DNA is damaged by

short-wavelength UV light (254 nm) emitted by

germicidal lamps, [12]. UV is used in a variety of

fields, and it must be used in a way that prevents it

from directly irradiating the human body, [13].

corresponds to the difference between the two

energy levels. The mercury atoms in this study were

excited by 2.45 GHz microwaves. The

electromagnetic waves emitted dominant

wavelengths of 184.957 nm and 253.652 nm, [13].

1.4 Principles of Ozone Generation and

In this study, ozone was generated via a

referred to as a UV-ozone-generating bulb. By

contrast, ozone decomposition requires a

wavelength of 253.7 nm. Ozone is excited by 253.7

nm UV and separates into atomic oxygen and

oxygen molecules. The two oxygen atoms react with

each other, resulting in oxygen molecules.

Fig. 1: Ozone generation and decomposition process

Figure 6, Figure 7, Figure 8 and Figure 9

display the stress-strain curves for polyethylene,

polyethylene terephthalate, polypropylene, and

polyvinyl chloride, respectively. Figure 10

illustrates the post-treatment elastic modulus,

normalized to 1 as the ratio, and Figure 11 depicts

the yield stress after treatment, also normalized to a

Fig. 8: Stress strain curve of polypropylene

Fig. 9: Stress strain curve of

Polyvinyl chloride

The results of the IR spectral analysis used to

investigate the surface conditions are shown in

Figure 12, Figure 13, Figure 14 and Figure 15. No

conditions of polyethylene, polypropylene, and

terephthalate, a peak believed to be derived from

hydroxyl or carboxy groups, [14] was confirmed at

Previous reports indicate that UV treatment induces

scission reactions in the molecular main chain of

studies have shown that the contact angle with

different liquids decreases, enhancing wettability,

Fig. 12: IR spectrum analysis of polyethylene

Fig. 14: IR spectrum analysis of

polypropylene

Fig. 15: IR spectrum analysis of

Polyvinyl chloride

modulus is the slope of the straight line in the elastic

region of the stress-strain curve (the region that

returns to its original state after being stretched).

The harder the material, the larger the elastic

modulus, and the closer it becomes vertical. Tensile

strength is the limiting strength of a material, and

Fig. 16: Stress strain curve in tension

Figure 17 shows the stress–strain curve of the

fluorororubber, and Figure 18 shows the results of

the IR spectrum analysis used to investigate the

surface conditions. It seems that the elastic modulus

ratio of the fluororubber gradually decreases as the

ozone exposure time increases, but if the fluorubber

becomes softer (elastic modulus decreases) by

exposure to UV ozone, then it increases with

exposure time. The elastic modulus should decrease

with increased exposure time. However, the increase

This is because the carbon-fluorine bond in the main

chain is extremely stable even in ozone water.

Another factor contributing to its stability is that it is

shielded from ozone and OH radicals by the highly

electronegative F atoms, [14]. However, the alkyl

moiety that forms the crosslinking point is oxidized

and decomposed in ozone water, [14]. A similar

reaction generating ozone at high humidity is

thought to occur in this device. Therefore, the

reaction of fluororubber is likely influenced by the

specific device used. However, the ozonated water

exposure time was 60 h, and in this experiment, the

exposure was for 300 min. Considering that it was

in the gas phase, it was necessary to expose it for a

longer time to understand the changes in more detail.

Fig. 17: Stress-strain curve of fluororubber

The stress–strain curve of the silicone rubber is

shown in Figure 19, and the IR spectrum analysis

results are shown in Figure 20. The elastic modulus

increased as the UV ozone exposure time increased

but decreased again after 300 min of exposure. This

implies that the material was hardened and softened

by the device. However, no change in the surface

discharge, was evaluated using X-ray photoelectron

spectroscopy and Fourier-transform infrared (FT-

IR) spectroscopy, [16]. Silicone rubber surfaces

undergo specific structural changes in the polymer

backbone, [17]. Therefore, even in ozone water,

silicone rubber may exhibit a different deterioration

behavior than other general-purpose rubber

materials. This is thought to apply in this

experiment, in which ozone was generated at high

humidity. It should be noted that ozone water

Fig. 20: IR spectrum analysis of

silicon rubber

The stress–strain curve of natural rubber is

shown in Figure 21, and the IR spectrum analysis

results are shown in Figure 22. The elastic moduli

and tensile strengths decreased after 15 min of

exposure. The decrease in the elastic modulus

occurs because the UV ozone exposure leads to

Ozone forms a bond called ozonide, [1], in the

carbon-carbon double bond of the isoprene unit,

[18] of natural rubber, as shown in Figure 23. This

is reflected in the absorption wavelength of 1500

that the peak that existed without exposure

decreased after 60 minutes of exposure (arrow in the

figure). It is considered that the elastic modulus

decreases because of this change. As shown in

Figure 24, the elastic modulus ratio with an

Fig. 22: IR spectrum analysis of natural rubbe

Fig. 23: molecular structure of

natural rubber

Fig. 24: Elastic modulus ratio of

soft polymer material

medical devices, we found that polyethylene,

polypropylene, and polyvinyl chloride have

excellent mechanical strength, and no change in the

surface condition was observed.

(2) However, changes in the surface conditions of

term exposure to ozonated water have been reported.

It was found that natural rubber should not be

sterilized using this device because, in addition to

the change in the surface conditions, the mechanical

(4) Given that the sterilization process is repeated

frequently, the absence of changes in mechanical

strength or surface conditions after 300 min does not

preclude alterations occurring over several tens of

hours. Consequently, further testing with extended

exposure times and increased concentrations is

necessary.

(5) However, it is a useful new sterilization option

in the field of medical engineering.

(6) We are planning to confirm whether UV ozone

(7) Additionally, we will consider the possibility of

deploying UV ozone sterilizers to general

households to prevent pandemics such as the new

coronavirus infection.

(8) Furthermore, using actual medical instruments,

we will compare the degree of material deterioration

with other sterilization methods and UV ozone

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